use std::{
    collections::{BTreeMap, VecDeque},
    io::{self, Stdout},
    time::{Duration, Instant},
};

use crossterm::{
    cursor::Show,
    execute,
    terminal::{disable_raw_mode, enable_raw_mode, EnterAlternateScreen, LeaveAlternateScreen},
};
use irtt_client::managed::{ManagedTargetEndReason, ManagedTargetOutcome, TargetInstance};
use irtt_client::{ClientEvent, NegotiationResult, SignedDuration};
use irtt_stats::{Snapshot, StatsCollector, TimeStats};
use ratatui::{
    backend::CrosstermBackend,
    layout::{Constraint, Direction, Layout, Rect},
    style::{Color, Modifier, Style},
    symbols,
    text::{Line, Span},
    widgets::{Axis, Block, Borders, Chart, Dataset, GraphType, Paragraph, Wrap},
    Frame, Terminal,
};

use crate::{
    cmd::{
        format::{
            format_count, format_duration, format_ns_f64, format_optional_count,
            format_optional_ns_i128, format_percent, format_percent_ratio, ABSENT,
        },
        tui::args::TuiArgs,
    },
    shared::client::{expected_probe_count, GroupPacingArg, ManagedRunSetup},
};

const HISTORY_LIMIT: usize = 100_000;
const RECENT_EVENT_LIMIT: usize = 80;
const MIN_WIDTH: u16 = 56;
const MIN_HEIGHT: u16 = 18;
const DEFAULT_GRAPH_WINDOW: Duration = Duration::from_secs(60);
const MIN_GRAPH_WINDOW: Duration = Duration::from_secs(5);
const MAX_GRAPH_WINDOW: Duration = Duration::from_secs(60 * 60);
const PAN_STEP_NUMERATOR: u32 = 1;
const PAN_STEP_DENOMINATOR: u32 = 4;

pub(super) struct TuiTerminal {
    terminal: Terminal<CrosstermBackend<Stdout>>,
}

impl TuiTerminal {
    pub(super) fn enter() -> io::Result<Self> {
        enable_raw_mode()?;
        let mut stdout = io::stdout();
        if let Err(err) = execute!(stdout, EnterAlternateScreen) {
            let _ = disable_raw_mode();
            return Err(err);
        }

        let backend = CrosstermBackend::new(stdout);
        match Terminal::new(backend) {
            Ok(mut terminal) => {
                if let Err(err) = terminal.clear() {
                    let _ = disable_raw_mode();
                    let _ = execute!(terminal.backend_mut(), LeaveAlternateScreen, Show);
                    let _ = terminal.show_cursor();
                    return Err(err);
                }
                Ok(Self { terminal })
            }
            Err(err) => {
                let _ = disable_raw_mode();
                let mut stdout = io::stdout();
                let _ = execute!(stdout, LeaveAlternateScreen, Show);
                Err(err)
            }
        }
    }

    pub(super) fn draw(&mut self, state: &TuiState) -> io::Result<()> {
        self.terminal
            .draw(|frame| draw_dashboard(frame, state))
            .map(|_| ())
    }
}

impl Drop for TuiTerminal {
    fn drop(&mut self) {
        let _ = disable_raw_mode();
        let _ = execute!(self.terminal.backend_mut(), LeaveAlternateScreen, Show);
        let _ = self.terminal.show_cursor();
    }
}

#[derive(Debug)]
pub(super) struct TuiState {
    status: TuiStatus,
    started_at: Instant,
    config: TuiConfig,
    target_index: BTreeMap<String, usize>,
    targets: Vec<TuiTargetState>,
    recent_events: VecDeque<String>,
    last_warning: Option<String>,
    dropped_events: u64,
    graph_metric: GraphMetric,
    graph_viewport: GraphViewport,
    view: TuiView,
    pub(super) paused: bool,
    pub(super) quit_requested: bool,
}

impl TuiState {
    pub(super) fn new(config: TuiConfig) -> Self {
        Self::with_target_labels(config, ["target".to_owned()])
    }

    pub(super) fn with_target_labels(
        config: TuiConfig,
        labels: impl IntoIterator<Item = String>,
    ) -> Self {
        let stats_config = stats_config(config.duration.is_none());
        let targets = labels
            .into_iter()
            .map(|label| TuiTargetState::new(label, stats_config))
            .collect::<Vec<_>>();
        let target_index = targets
            .iter()
            .enumerate()
            .map(|(idx, target)| (target.label.clone(), idx))
            .collect();
        Self {
            status: TuiStatus::Opening,
            started_at: Instant::now(),
            config,
            target_index,
            targets,
            recent_events: VecDeque::with_capacity(RECENT_EVENT_LIMIT),
            last_warning: None,
            dropped_events: 0,
            graph_metric: GraphMetric::EffectiveRtt,
            graph_viewport: GraphViewport::default(),
            view: TuiView::Graph,
            paused: false,
            quit_requested: false,
        }
    }

    pub(super) fn process_target_event(&mut self, target: &TargetInstance, event: &ClientEvent) {
        let label = target.id.as_str();
        let idx = if let Some(idx) = self.target_index.get(label).copied() {
            idx
        } else {
            let idx = self.targets.len();
            let mut target = TuiTargetState::new(
                label.to_owned(),
                stats_config(self.config.duration.is_none()),
            );
            target.status = TargetStatus::Unknown;
            self.targets.push(target);
            self.target_index.insert(label.to_owned(), idx);
            idx
        };
        self.process_event_for_target(idx, event);
    }

    pub(super) fn process_target_outcome(&mut self, outcome: &ManagedTargetOutcome) {
        let label = outcome.target.id.as_str();
        let idx = if let Some(idx) = self.target_index.get(label).copied() {
            idx
        } else {
            let idx = self.targets.len();
            self.targets.push(TuiTargetState::new(
                label.to_owned(),
                stats_config(self.config.duration.is_none()),
            ));
            self.target_index.insert(label.to_owned(), idx);
            idx
        };

        let (status, recent, primary_warning) = match &outcome.end_reason {
            ManagedTargetEndReason::TestComplete => {
                (TargetStatus::Closed, "test completed".to_owned(), None)
            }
            ManagedTargetEndReason::PeerClosed => (
                TargetStatus::Closed,
                "session closed by peer".to_owned(),
                None,
            ),
            ManagedTargetEndReason::NoTestComplete => (
                TargetStatus::NoTest,
                "no-test negotiation completed".to_owned(),
                None,
            ),
            ManagedTargetEndReason::Stopped => {
                (TargetStatus::Stopped, "target stopped".to_owned(), None)
            }
            ManagedTargetEndReason::Removed => {
                (TargetStatus::Removed, "target removed".to_owned(), None)
            }
            ManagedTargetEndReason::Replaced => {
                (TargetStatus::Replaced, "target replaced".to_owned(), None)
            }
            ManagedTargetEndReason::Failed(failure) => {
                let message = format!("{}: {}", failure.kind, failure.message);
                (
                    TargetStatus::Failed,
                    format!("target failed: {message}"),
                    Some(message),
                )
            }
        };

        let cleanup_warning = outcome.cleanup_failure.as_ref().map(|failure| {
            format!(
                "cleanup failed ({} {}): {}",
                failure.phase, failure.kind, failure.message
            )
        });
        let warning = match (primary_warning, cleanup_warning.as_ref()) {
            (Some(primary), Some(cleanup)) => Some(format!("{primary}; {cleanup}")),
            (Some(primary), None) => Some(primary),
            (None, Some(cleanup)) => Some(cleanup.clone()),
            (None, None) => None,
        };

        if let Some(target) = self.targets.get_mut(idx) {
            target.remote = outcome.remote.map(|remote| remote.to_string());
            target.status = status;
            if let Some(warning) = &warning {
                target.last_warning = Some(warning.clone());
            }
        }
        if let Some(warning) = warning {
            self.last_warning = Some(warning);
        }
        self.push_event(format!("{label}: {recent}"));
        if let Some(cleanup_warning) = cleanup_warning {
            self.push_event(format!("{label}: {cleanup_warning}"));
        }

        if self
            .targets
            .iter()
            .all(|target| target.status.is_terminal())
        {
            self.status = if self.targets.iter().any(|target| target.status.is_success()) {
                TuiStatus::Complete
            } else if self
                .targets
                .iter()
                .any(|target| target.status == TargetStatus::Failed)
            {
                TuiStatus::Error
            } else {
                TuiStatus::Complete
            };
        }
    }

    fn process_event_for_target(&mut self, target_idx: usize, event: &ClientEvent) {
        let recent;
        let mut global_status = None;
        let mut global_warning = None;
        let label = {
            let Some(target) = self.targets.get_mut(target_idx) else {
                return;
            };
            target.stats.process(event);
            match event {
                ClientEvent::SessionStarted(irtt_client::SessionStarted {
                    remote,
                    token,
                    negotiation: negotiated,
                    ..
                }) => {
                    target.remote = Some(remote.to_string());
                    target.session = Some(format!("{token:#x}"));
                    target.negotiated = Some(negotiated.clone());
                    target.status = TargetStatus::Active;
                    global_status = Some(TuiStatus::Running);
                    recent = Some(format!("session started token={token:#x}"));
                }
                ClientEvent::NoTestCompleted(irtt_client::NoTestCompleted {
                    remote,
                    negotiation: negotiated,
                    ..
                }) => {
                    target.remote = Some(remote.to_string());
                    target.negotiated = Some(negotiated.clone());
                    target.status = TargetStatus::NoTest;
                    global_status = Some(TuiStatus::Complete);
                    recent = Some("no-test negotiation completed".to_owned());
                }
                ClientEvent::SessionClosed { token, .. } => {
                    target.session = Some(format!("{token:#x}"));
                    target.status = TargetStatus::Closed;
                    global_status = Some(TuiStatus::Complete);
                    recent = Some(format!("session closed token={token:#x}"));
                }
                ClientEvent::EchoSent { seq, bytes, .. } => {
                    recent = Some(format!("sent seq={} bytes={bytes}", format_seq(*seq)));
                }
                ClientEvent::EchoReply {
                    seq,
                    received_at,
                    rtt,
                    one_way,
                    server_timing,
                    ..
                } => {
                    let client_to_server_ns = one_way
                        .and_then(|sample| sample.client_to_server)
                        .map(SignedDuration::as_nanos);
                    let server_to_client_ns = one_way
                        .and_then(|sample| sample.server_to_client)
                        .map(SignedDuration::as_nanos);
                    let server_processing_ns = server_timing
                        .and_then(|timing| timing.processing)
                        .map(duration_ns);
                    target.push_graph_sample(GraphSample {
                        timestamp: received_at.mono,
                        seq: *seq,
                        effective_ns: rtt.effective.as_nanos(),
                        raw_ns: duration_ns(rtt.raw),
                        adjusted_ns: rtt.adjusted.map(SignedDuration::as_nanos),
                        client_to_server_ns,
                        server_to_client_ns,
                        server_processing_ns,
                    });
                    target.last_sample = Some(LastSample {
                        seq: *seq,
                        raw_ns: duration_ns(rtt.raw),
                        adjusted_ns: rtt.adjusted.map(SignedDuration::as_nanos),
                        effective_ns: rtt.effective.as_nanos(),
                        client_to_server_ns,
                        server_to_client_ns,
                        server_processing_ns,
                    });
                    recent = Some(format!(
                        "reply seq={} effective={}",
                        format_seq(*seq),
                        format_optional_ns_i128(Some(rtt.effective.as_nanos()))
                    ));
                }
                ClientEvent::EchoLoss { seq, .. } => {
                    recent = Some(format!("loss seq={}", format_seq(*seq)));
                }
                ClientEvent::DuplicateReply { seq, remote, .. } => {
                    recent = Some(format!("duplicate seq={} from {remote}", format_seq(*seq)));
                }
                ClientEvent::LateReply {
                    seq,
                    highest_seen,
                    rtt,
                    ..
                } => {
                    let timing = rtt
                        .map(|sample| {
                            format!(
                                " effective={}",
                                format_optional_ns_i128(Some(sample.effective.as_nanos()))
                            )
                        })
                        .unwrap_or_default();
                    recent = Some(format!(
                        "late seq={} highest_seen={}{}",
                        format_seq(*seq),
                        format_seq(*highest_seen),
                        timing
                    ));
                }
                ClientEvent::Warning { kind, message, .. } => {
                    let warning = format!("{kind:?}: {message}");
                    target.last_warning = Some(warning.clone());
                    global_warning = Some(warning.clone());
                    recent = Some(format!("warning {warning}"));
                }
            }
            target.label.clone()
        };
        if let Some(status) = global_status {
            self.status = if status == TuiStatus::Complete
                && self.is_multi_target()
                && !self
                    .targets
                    .iter()
                    .all(|target| target.status.is_terminal())
            {
                TuiStatus::Running
            } else {
                status
            };
        }
        if let Some(warning) = global_warning {
            self.last_warning = Some(warning);
        }
        if let Some(recent) = recent {
            self.push_event(format!("{label}: {recent}"));
        }
    }

    pub(super) fn set_status(&mut self, status: TuiStatus) {
        self.status = status;
    }

    pub(super) fn mark_dropped_managed_events(&mut self, dropped_events: u64) {
        self.mark_dropped_events(dropped_events, "managed run");
    }

    fn mark_dropped_events(&mut self, dropped_events: u64, source: &str) {
        if dropped_events == 0 {
            return;
        }
        self.dropped_events = dropped_events;
        let event_word = if dropped_events == 1 {
            "event"
        } else {
            "events"
        };
        let warning =
            format!("dropped {dropped_events} {source} {event_word}; statistics may be incomplete");
        self.last_warning = Some(warning.clone());
        self.push_event(format!("warning {warning}"));
    }

    pub(super) fn set_error(&mut self, message: String) {
        self.status = TuiStatus::Error;
        self.last_warning = Some(message.clone());
        if let Some(target) = self.targets.first_mut() {
            target.status = TargetStatus::Failed;
            target.last_warning = Some(message.clone());
        }
        self.push_event(format!("error {message}"));
    }

    pub(super) fn set_run_error(&mut self, message: String) {
        self.status = TuiStatus::Error;
        self.last_warning = Some(message.clone());
        self.push_event(format!("error {message}"));
    }

    pub(super) fn clear_visible_history(&mut self) {
        for target in &mut self.targets {
            target.graph_history.clear();
        }
        self.graph_viewport.follow_live();
        self.push_event("visible graph history reset".to_owned());
    }

    pub(super) fn toggle_pause(&mut self) {
        self.paused = !self.paused;
    }

    pub(super) fn cycle_graph_metric(&mut self) {
        self.graph_metric = self.graph_metric.next();
    }

    pub(super) fn toggle_view(&mut self) {
        self.view = self.view.next();
    }

    pub(super) fn pan_graph_left(&mut self) {
        let oldest = self.oldest_graph_sample_time();
        let newest = self.newest_graph_sample_time();
        self.graph_viewport.pan_backward(oldest, newest);
    }

    pub(super) fn pan_graph_right(&mut self) {
        let newest = self.newest_graph_sample_time();
        self.graph_viewport.pan_forward(newest);
    }

    pub(super) fn pan_graph_page_left(&mut self) {
        let oldest = self.oldest_graph_sample_time();
        let newest = self.newest_graph_sample_time();
        self.graph_viewport.page_backward(oldest, newest);
    }

    pub(super) fn pan_graph_page_right(&mut self) {
        let newest = self.newest_graph_sample_time();
        self.graph_viewport.page_forward(newest);
    }

    pub(super) fn jump_graph_oldest(&mut self) {
        let oldest = self.oldest_graph_sample_time();
        let newest = self.newest_graph_sample_time();
        self.graph_viewport.jump_oldest(oldest, newest);
    }

    pub(super) fn jump_graph_live(&mut self) {
        self.graph_viewport.follow_live();
    }

    pub(super) fn zoom_graph_in(&mut self) {
        self.graph_viewport.zoom_in(self.newest_graph_sample_time());
    }

    pub(super) fn zoom_graph_out(&mut self) {
        self.graph_viewport
            .zoom_out(self.newest_graph_sample_time());
    }

    pub(super) fn reset_graph_window(&mut self) {
        self.graph_viewport
            .reset_window(self.newest_graph_sample_time());
    }

    fn push_event(&mut self, event: String) {
        push_bounded(&mut self.recent_events, event, RECENT_EVENT_LIMIT);
    }

    fn selected_target(&self) -> Option<&TuiTargetState> {
        self.targets.first()
    }

    fn selected_snapshot(&self) -> Snapshot {
        self.selected_target()
            .map(|target| target.stats.snapshot())
            .unwrap_or_else(|| StatsCollector::new(stats_config(true)).snapshot())
    }

    fn is_multi_target(&self) -> bool {
        self.targets.len() > 1
    }

    fn oldest_graph_sample_time(&self) -> Option<Instant> {
        self.targets
            .iter()
            .filter_map(|target| target.graph_history.front().map(|sample| sample.timestamp))
            .min()
    }

    fn newest_graph_sample_time(&self) -> Option<Instant> {
        self.targets
            .iter()
            .filter_map(|target| target.graph_history.back().map(|sample| sample.timestamp))
            .max()
    }
}

#[derive(Debug)]
pub(super) struct TuiTargetState {
    label: String,
    remote: Option<String>,
    session: Option<String>,
    status: TargetStatus,
    negotiated: Option<NegotiationResult>,
    graph_history: VecDeque<GraphSample>,
    last_sample: Option<LastSample>,
    last_warning: Option<String>,
    stats: StatsCollector,
}

impl TuiTargetState {
    fn new(label: String, stats_config: irtt_stats::StatsConfig) -> Self {
        Self {
            label,
            remote: None,
            session: None,
            status: TargetStatus::Opening,
            negotiated: None,
            graph_history: VecDeque::new(),
            last_sample: None,
            last_warning: None,
            stats: StatsCollector::new(stats_config),
        }
    }

    fn push_graph_sample(&mut self, sample: GraphSample) {
        push_bounded(&mut self.graph_history, sample, HISTORY_LIMIT);
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(super) enum TargetStatus {
    Opening,
    Active,
    Closed,
    Failed,
    NoTest,
    Stopped,
    Removed,
    Replaced,
    Unknown,
}

impl TargetStatus {
    fn label(self) -> &'static str {
        match self {
            Self::Opening => "opening",
            Self::Active => "active",
            Self::Closed => "closed",
            Self::Failed => "failed",
            Self::NoTest => "no-test",
            Self::Stopped => "stopped",
            Self::Removed => "removed",
            Self::Replaced => "replaced",
            Self::Unknown => "unknown",
        }
    }

    fn is_terminal(self) -> bool {
        matches!(
            self,
            Self::Closed
                | Self::Failed
                | Self::NoTest
                | Self::Stopped
                | Self::Removed
                | Self::Replaced
        )
    }

    fn is_success(self) -> bool {
        matches!(self, Self::Closed | Self::NoTest)
    }
}

impl GroupPacingArg {
    fn label(self) -> &'static str {
        match self {
            Self::Staggered => "staggered",
            Self::Burst => "burst",
        }
    }
}

/// Statistics policy for the TUI.
///
/// The TUI treats late replies as diagnostics, so it counts a matched late
/// reply without letting it contribute timing samples. That is an explicit
/// statistics policy rather than something the TUI expresses by degrading the
/// event it forwards.
fn stats_config(continuous: bool) -> irtt_stats::StatsConfig {
    let base = if continuous {
        irtt_stats::StatsConfig::continuous()
    } else {
        irtt_stats::StatsConfig::finite()
    };
    irtt_stats::StatsConfig {
        late_replies: irtt_stats::LateReplyMode::CountOnly,
        ..base
    }
}

impl Default for TuiState {
    fn default() -> Self {
        Self::new(TuiConfig::default())
    }
}

#[derive(Debug, Clone)]
pub(super) struct TuiConfig {
    interval: Duration,
    duration: Option<Duration>,
    timeout: Duration,
    target_probes: Option<u64>,
    pacing: GroupPacingArg,
}

impl TuiConfig {
    pub(super) fn from_args(args: &TuiArgs, setup: &ManagedRunSetup) -> Self {
        Self {
            interval: args.interval,
            duration: (!args.is_continuous()).then_some(args.duration),
            timeout: setup.client.probe_timeout,
            target_probes: (!args.is_continuous())
                .then(|| expected_probe_count(args.duration, args.interval)),
            pacing: args.pacing,
        }
    }
}

impl Default for TuiConfig {
    fn default() -> Self {
        Self {
            interval: Duration::from_secs(1),
            duration: Some(Duration::from_secs(10)),
            timeout: Duration::from_secs(2),
            target_probes: Some(10),
            pacing: GroupPacingArg::Staggered,
        }
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(super) enum TuiStatus {
    Opening,
    Running,
    Interrupted,
    Closing,
    Complete,
    Error,
}

impl TuiStatus {
    fn label(self) -> &'static str {
        match self {
            Self::Opening => "opening",
            Self::Running => "running",
            Self::Interrupted => "interrupted",
            Self::Closing => "closing",
            Self::Complete => "complete",
            Self::Error => "error",
        }
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum TuiView {
    Graph,
    Dashboard,
}

impl TuiView {
    fn next(self) -> Self {
        match self {
            Self::Graph => Self::Dashboard,
            Self::Dashboard => Self::Graph,
        }
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
struct GraphViewport {
    mode: GraphViewportMode,
    window: Duration,
}

impl Default for GraphViewport {
    fn default() -> Self {
        Self {
            mode: GraphViewportMode::Follow,
            window: DEFAULT_GRAPH_WINDOW,
        }
    }
}

impl GraphViewport {
    fn range(self, now: Instant, newest_sample: Option<Instant>) -> GraphViewportRange {
        let end = match self.mode {
            GraphViewportMode::Follow => newest_sample.unwrap_or(now).max(now),
            GraphViewportMode::Historical { end } => end,
        };
        GraphViewportRange {
            start: end.checked_sub(self.window).unwrap_or(end),
            end,
            window: self.window,
            is_live: matches!(self.mode, GraphViewportMode::Follow),
        }
    }

    fn follow_live(&mut self) {
        self.mode = GraphViewportMode::Follow;
    }

    fn pan_backward(&mut self, oldest: Option<Instant>, newest: Option<Instant>) {
        self.pan_by(
            -duration_fraction(self.window, PAN_STEP_NUMERATOR, PAN_STEP_DENOMINATOR),
            oldest,
            newest,
        );
    }

    fn pan_forward(&mut self, newest: Option<Instant>) {
        self.pan_by(
            duration_fraction(self.window, PAN_STEP_NUMERATOR, PAN_STEP_DENOMINATOR),
            None,
            newest,
        );
    }

    fn page_backward(&mut self, oldest: Option<Instant>, newest: Option<Instant>) {
        self.pan_by(-signed_duration(self.window), oldest, newest);
    }

    fn page_forward(&mut self, newest: Option<Instant>) {
        self.pan_by(signed_duration(self.window), None, newest);
    }

    fn jump_oldest(&mut self, oldest: Option<Instant>, newest: Option<Instant>) {
        let Some(oldest) = oldest else {
            return;
        };
        let live_end = newest.unwrap_or(oldest);
        self.mode = GraphViewportMode::Historical {
            end: (oldest + self.window).min(live_end),
        };
    }

    fn zoom_in(&mut self, newest: Option<Instant>) {
        self.set_window(duration_fraction(self.window, 2, 3).duration, newest);
    }

    fn zoom_out(&mut self, newest: Option<Instant>) {
        self.set_window(duration_fraction(self.window, 3, 2).duration, newest);
    }

    fn reset_window(&mut self, newest: Option<Instant>) {
        self.set_window(DEFAULT_GRAPH_WINDOW, newest);
    }

    fn set_window(&mut self, window: Duration, newest: Option<Instant>) {
        self.window = window.clamp(MIN_GRAPH_WINDOW, MAX_GRAPH_WINDOW);
        if let GraphViewportMode::Historical { end } = &mut self.mode {
            if let Some(newest) = newest {
                *end = (*end).min(newest);
            }
        }
    }

    fn pan_by(
        &mut self,
        delta: SignedViewportDuration,
        oldest: Option<Instant>,
        newest: Option<Instant>,
    ) {
        let Some(newest) = newest else {
            return;
        };
        let current_end = match self.mode {
            GraphViewportMode::Follow => newest,
            GraphViewportMode::Historical { end } => end,
        };
        let mut end = delta.apply(current_end);
        if let Some(oldest) = oldest {
            end = end.max(oldest + self.window);
        }
        end = end.min(newest);
        self.mode = GraphViewportMode::Historical { end };
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum GraphViewportMode {
    Follow,
    Historical { end: Instant },
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
struct GraphViewportRange {
    start: Instant,
    end: Instant,
    window: Duration,
    is_live: bool,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
struct SignedViewportDuration {
    duration: Duration,
    negative: bool,
}

impl SignedViewportDuration {
    fn apply(self, instant: Instant) -> Instant {
        if self.negative {
            instant.checked_sub(self.duration).unwrap_or(instant)
        } else {
            instant + self.duration
        }
    }
}

impl std::ops::Neg for SignedViewportDuration {
    type Output = Self;

    fn neg(self) -> Self::Output {
        Self {
            duration: self.duration,
            negative: !self.negative,
        }
    }
}

fn signed_duration(duration: Duration) -> SignedViewportDuration {
    SignedViewportDuration {
        duration,
        negative: false,
    }
}

fn duration_fraction(
    duration: Duration,
    numerator: u32,
    denominator: u32,
) -> SignedViewportDuration {
    let nanos =
        duration.as_nanos().saturating_mul(u128::from(numerator)) / u128::from(denominator.max(1));
    let nanos = nanos.max(1).min(u128::from(u64::MAX));
    SignedViewportDuration {
        duration: Duration::from_nanos(nanos as u64),
        negative: false,
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum GraphMetric {
    EffectiveRtt,
    RawRtt,
    AdjustedRtt,
    ClientToServer,
    ServerToClient,
    ServerProcessing,
}

impl GraphMetric {
    fn next(self) -> Self {
        match self {
            Self::EffectiveRtt => Self::RawRtt,
            Self::RawRtt => Self::AdjustedRtt,
            Self::AdjustedRtt => Self::ClientToServer,
            Self::ClientToServer => Self::ServerToClient,
            Self::ServerToClient => Self::ServerProcessing,
            Self::ServerProcessing => Self::EffectiveRtt,
        }
    }

    fn label(self) -> &'static str {
        match self {
            Self::EffectiveRtt => "effective RTT",
            Self::RawRtt => "raw RTT",
            Self::AdjustedRtt => "adjusted RTT",
            Self::ClientToServer => "client to server",
            Self::ServerToClient => "server to client",
            Self::ServerProcessing => "server processing",
        }
    }

    fn title(self) -> &'static str {
        match self {
            Self::EffectiveRtt => "effective RTT",
            Self::RawRtt => "raw RTT",
            Self::AdjustedRtt => "adjusted RTT",
            Self::ClientToServer => "client to server delay",
            Self::ServerToClient => "server to client delay",
            Self::ServerProcessing => "server processing",
        }
    }

    fn empty_message(self) -> &'static str {
        match self {
            Self::EffectiveRtt | Self::RawRtt => "waiting for primary replies",
            Self::AdjustedRtt => "waiting for adjusted RTT samples",
            Self::ClientToServer | Self::ServerToClient => "waiting for one-way delay samples",
            Self::ServerProcessing => "waiting for server processing samples",
        }
    }

    fn value_ns(self, sample: &GraphSample) -> Option<i128> {
        match self {
            Self::EffectiveRtt => Some(sample.effective_ns),
            Self::RawRtt => Some(sample.raw_ns),
            Self::AdjustedRtt => sample.adjusted_ns,
            Self::ClientToServer => sample.client_to_server_ns,
            Self::ServerToClient => sample.server_to_client_ns,
            Self::ServerProcessing => sample.server_processing_ns,
        }
    }

    fn axis_kind(self) -> ChartAxisKind {
        match self {
            Self::EffectiveRtt | Self::RawRtt | Self::ServerProcessing => {
                ChartAxisKind::NonNegative
            }
            Self::AdjustedRtt | Self::ClientToServer | Self::ServerToClient => {
                ChartAxisKind::Signed
            }
        }
    }

    fn style(self) -> Style {
        match self {
            Self::EffectiveRtt | Self::RawRtt | Self::AdjustedRtt => {
                target_style(0).add_modifier(Modifier::BOLD)
            }
            Self::ClientToServer => Style::default().fg(Color::Magenta),
            Self::ServerToClient => Style::default().fg(Color::LightBlue),
            Self::ServerProcessing => Style::default().fg(Color::Green),
        }
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(super) struct GraphSample {
    timestamp: Instant,
    seq: u32,
    effective_ns: i128,
    raw_ns: i128,
    adjusted_ns: Option<i128>,
    client_to_server_ns: Option<i128>,
    server_to_client_ns: Option<i128>,
    server_processing_ns: Option<i128>,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(super) struct LastSample {
    seq: u32,
    raw_ns: i128,
    adjusted_ns: Option<i128>,
    effective_ns: i128,
    client_to_server_ns: Option<i128>,
    server_to_client_ns: Option<i128>,
    server_processing_ns: Option<i128>,
}

fn push_bounded<T>(items: &mut VecDeque<T>, item: T, limit: usize) {
    if items.len() == limit {
        items.pop_front();
    } else if items.len() == items.capacity() && items.capacity() >= limit / 2 {
        // Growth is naturally exponential; once we're within reach of `limit`,
        // reserve exactly up to it instead of letting the next doubling step
        // overshoot it for long-running, heavily populated buffers.
        items.reserve_exact(limit - items.len());
    }
    items.push_back(item);
}

pub(super) fn draw_dashboard(frame: &mut Frame<'_>, state: &TuiState) {
    let area = frame.area();
    if area.width < MIN_WIDTH || area.height < MIN_HEIGHT {
        frame.render_widget(too_small(), area);
        return;
    }

    let snapshot = state.selected_snapshot();
    match state.view {
        TuiView::Graph => draw_graph_view(frame, area, state, &snapshot),
        TuiView::Dashboard => draw_dashboard_view(frame, area, state, &snapshot),
    }
}

pub(super) fn should_render(now: Instant, next_render: Instant, paused: bool, force: bool) -> bool {
    force || (!paused && now >= next_render)
}

fn draw_graph_view(frame: &mut Frame<'_>, area: Rect, state: &TuiState, snapshot: &Snapshot) {
    let header_height = if state.is_multi_target() { 7 } else { 3 };
    let rows = Layout::default()
        .direction(Direction::Vertical)
        .constraints([
            Constraint::Length(header_height),
            Constraint::Min(10),
            Constraint::Length(3),
        ])
        .split(area);

    if state.is_multi_target() {
        frame.render_widget(target_table_panel(state, rows[0].height), rows[0]);
    } else {
        frame.render_widget(graph_summary_panel(state, snapshot), rows[0]);
    }
    render_graph_area(frame, rows[1], state);
    frame.render_widget(status_line(state), rows[2]);
}

fn draw_dashboard_view(frame: &mut Frame<'_>, area: Rect, state: &TuiState, snapshot: &Snapshot) {
    if area.width >= 110 && area.height >= 32 {
        draw_large(frame, area, state, snapshot);
    } else {
        draw_compact(frame, area, state, snapshot);
    }
}

fn draw_large(frame: &mut Frame<'_>, area: Rect, state: &TuiState, snapshot: &Snapshot) {
    let rows = Layout::default()
        .direction(Direction::Vertical)
        .constraints([
            Constraint::Length(8),
            Constraint::Min(12),
            Constraint::Length(9),
            Constraint::Length(3),
        ])
        .split(area);
    let top = Layout::default()
        .direction(Direction::Horizontal)
        .constraints([Constraint::Percentage(40), Constraint::Percentage(60)])
        .split(rows[0]);
    let middle = Layout::default()
        .direction(Direction::Horizontal)
        .constraints([Constraint::Percentage(36), Constraint::Percentage(64)])
        .split(rows[1]);
    let bottom = Layout::default()
        .direction(Direction::Horizontal)
        .constraints([Constraint::Percentage(55), Constraint::Percentage(45)])
        .split(rows[2]);

    frame.render_widget(header(state, HeaderDensity::Large), top[0]);
    frame.render_widget(packet_panel(state, snapshot, top[1].height), top[1]);
    frame.render_widget(timing_panel(state, snapshot), middle[0]);
    render_graph_area(frame, middle[1], state);
    frame.render_widget(recent_events_panel(state, bottom[0].height), bottom[0]);
    frame.render_widget(sample_panel(state, snapshot), bottom[1]);
    frame.render_widget(status_line(state), rows[3]);
}

fn draw_compact(frame: &mut Frame<'_>, area: Rect, state: &TuiState, snapshot: &Snapshot) {
    let rows = Layout::default()
        .direction(Direction::Vertical)
        .constraints([
            Constraint::Length(6),
            Constraint::Length(7),
            Constraint::Min(7),
            Constraint::Length(3),
        ])
        .split(area);

    frame.render_widget(header(state, HeaderDensity::Compact), rows[0]);
    frame.render_widget(packet_panel(state, snapshot, rows[1].height), rows[1]);
    render_graph_area(frame, rows[2], state);
    frame.render_widget(status_line(state), rows[3]);
}

fn too_small() -> Paragraph<'static> {
    Paragraph::new(vec![
        Line::from("terminal too small"),
        Line::from("resize, or press q / Ctrl-C to quit gracefully"),
    ])
    .block(Block::default().title("irtt-rs").borders(Borders::ALL))
    .wrap(Wrap { trim: true })
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum HeaderDensity {
    Large,
    Compact,
}

fn header(state: &TuiState, density: HeaderDensity) -> Paragraph<'_> {
    let selected = state.selected_target();
    let selected_label = selected
        .map(|target| target.label.as_str())
        .unwrap_or("target");
    let remote = selected
        .and_then(|target| target.remote.as_deref())
        .unwrap_or("-");
    let session = selected
        .and_then(|target| target.session.as_deref())
        .unwrap_or("-");
    let elapsed = format_span(state.started_at.elapsed());
    let duration = format_optional_span(state.config.duration);
    let mode = if state.config.duration.is_some() {
        "finite"
    } else {
        "continuous"
    };
    let negotiated = selected
        .and_then(|target| target.negotiated.as_ref())
        .map(|params| format!("negotiated: {}", format_negotiated(params)))
        .unwrap_or_else(|| "negotiated: -".to_owned());
    let target_count = state.targets.len();
    let pacing = state.config.pacing.label();

    let mut lines = vec![
        Line::from(vec![
            Span::styled("irtt-rs", Style::default().add_modifier(Modifier::BOLD)),
            Span::raw(format!(
                "  status: {}  targets: {target_count}  pacing: {pacing}",
                state.status.label()
            )),
        ]),
        Line::from(if state.is_multi_target() {
            format!("first target: {selected_label}  remote: {remote}")
        } else {
            format!("remote: {remote}")
        }),
    ];
    match density {
        HeaderDensity::Large => {
            lines.extend([
                Line::from(format!("session: {session}")),
                Line::from(format!(
                    "mode: {mode}  elapsed: {elapsed}  duration: {duration}"
                )),
                Line::from(format!(
                    "interval: {}  timeout: {}",
                    format_span(state.config.interval),
                    format_span(state.config.timeout)
                )),
                Line::from(negotiated),
            ]);
        }
        HeaderDensity::Compact => {
            lines.extend([
                Line::from(format!("session: {session}")),
                Line::from(format!(
                    "{mode}  elapsed: {elapsed}  interval: {}",
                    format_span(state.config.interval)
                )),
            ]);
        }
    }

    Paragraph::new(lines)
        .block(Block::default().title("session").borders(Borders::ALL))
        .wrap(Wrap { trim: true })
}

fn graph_summary_panel(state: &TuiState, snapshot: &Snapshot) -> Paragraph<'static> {
    let selected = state.selected_target();
    let selected_label = selected
        .map(|target| target.label.as_str())
        .unwrap_or("target");
    let remote = selected
        .and_then(|target| target.remote.as_deref())
        .unwrap_or("-");
    let elapsed = format_span(state.started_at.elapsed());
    let packets = snapshot.packets;
    let last = state
        .selected_target()
        .and_then(|target| target.last_sample)
        .map(|sample| format_optional_ns_i128(Some(sample.effective_ns)))
        .unwrap_or_else(|| "-".to_owned());

    let target_context = if state.is_multi_target() {
        format!("first target {selected_label} remote {remote}")
    } else {
        format!("remote {remote}")
    };

    Paragraph::new(Line::from(format!(
        "irtt-rs  {}  {target_context}  elapsed {elapsed}  sent {}  replies {}  last {last}",
        state.status.label(),
        format_count(packets.packets_sent),
        format_count(packets.unique_replies)
    )))
    .block(
        Block::default()
            .title(if state.is_multi_target() {
                "session - first target"
            } else {
                "session"
            })
            .borders(Borders::ALL),
    )
}

fn packet_panel(state: &TuiState, snapshot: &Snapshot, panel_height: u16) -> Paragraph<'static> {
    if state.is_multi_target() {
        return target_table_panel(state, panel_height);
    }

    let packets = snapshot.packets;
    let loss = snapshot.loss;
    let progress = state
        .config
        .target_probes
        .map(|target| {
            format!(
                "{}/{} ({})",
                packets.packets_sent,
                target,
                format_percent_ratio(packets.packets_sent, target)
            )
        })
        .unwrap_or_else(|| "-".to_owned());
    let elapsed = state.started_at.elapsed();
    let recv_rate = format_rate(packets.unique_replies, elapsed);

    Paragraph::new(vec![
        Line::from(format!(
            "sent {:>8}   received {:>8}   unique {:>8}",
            format_count(packets.packets_sent),
            format_count(packets.packets_received),
            format_count(packets.unique_replies)
        )),
        Line::from(format!(
            "lost {:>8}   duplicates {:>6}   late {:>10}   warnings {:>6}",
            format_count(loss.lost_packets),
            format_count(packets.duplicates),
            format_count(packets.late_packets),
            format_count(snapshot.events.warning_events)
        )),
        Line::from(format!(
            "loss {:>8}   reply rate {:>10}   progress {progress}",
            format_percent(loss.packet_loss_percent),
            recv_rate
        )),
        Line::from(format!(
            "bytes sent {}   received {}",
            format_count(packets.bytes_sent),
            format_count(packets.bytes_received)
        )),
        Line::from(format!(
            "server received {}   window {}",
            format_optional_count(packets.server_packets_received),
            format_optional_hex(packets.server_received_window)
        )),
    ])
    .block(Block::default().title("packets").borders(Borders::ALL))
    .wrap(Wrap { trim: true })
}

fn target_table_panel(state: &TuiState, panel_height: u16) -> Paragraph<'static> {
    let visible = usize::from(panel_height.saturating_sub(3));
    let mut lines = vec![Line::from(format!(
        "{:<16} {:<8} {:>9} {:>5} {:>4} {:>4} {:>4}",
        "target", "status", "last", "loss", "dup", "late", "warn"
    ))];

    for (idx, target) in state.targets.iter().enumerate().take(visible) {
        let snapshot = target.stats.snapshot();
        let last = target
            .last_sample
            .map(|sample| format_optional_ns_i128(Some(sample.effective_ns)))
            .unwrap_or_else(|| "-".to_owned());
        lines.push(Line::from(vec![
            target_label_span(&target.label, idx, 16),
            Span::raw(format!(
                " {:<8} {:>9} {:>5} {:>4} {:>4} {:>4}",
                target.status.label(),
                last,
                format_count(snapshot.loss.lost_packets),
                format_count(snapshot.packets.duplicates),
                format_count(snapshot.packets.late_packets),
                format_count(snapshot.events.warning_events)
            )),
        ]));
    }

    Paragraph::new(lines)
        .block(Block::default().title("targets").borders(Borders::ALL))
        .wrap(Wrap { trim: false })
}

fn target_label_span(label: &str, target_idx: usize, width: usize) -> Span<'static> {
    Span::styled(
        format!("{:<width$}", truncate(label, width), width = width),
        target_style(target_idx).add_modifier(Modifier::BOLD),
    )
}

fn timing_panel(state: &TuiState, snapshot: &Snapshot) -> Paragraph<'static> {
    let mut lines = vec![Line::from(format!(
        "{:<18} {:>5} {:>9} {:>9} {:>9} {:>9}",
        "metric", "n", "min", "mean", "max", "stddev"
    ))];
    push_time_line(&mut lines, "effective RTT", &snapshot.rtt.primary);
    push_time_line(&mut lines, "raw RTT", &snapshot.rtt.raw);
    push_time_line(&mut lines, "adjusted RTT", &snapshot.rtt.adjusted);
    push_time_line(&mut lines, "IPDV/jitter", &snapshot.ipdv.round_trip);
    push_time_line(&mut lines, "send IPDV", &snapshot.ipdv.send);
    push_time_line(&mut lines, "receive IPDV", &snapshot.ipdv.receive);
    push_time_line(&mut lines, "send delay", &snapshot.one_way_delay.send_delay);
    push_time_line(
        &mut lines,
        "receive delay",
        &snapshot.one_way_delay.receive_delay,
    );
    push_time_line(
        &mut lines,
        "server process",
        &snapshot.server_processing.processing,
    );
    push_time_line(&mut lines, "send call", &snapshot.send_call);
    push_time_line(&mut lines, "timer error", &snapshot.timer_error);

    Paragraph::new(lines)
        .block(
            Block::default()
                .title(if state.is_multi_target() {
                    "timing - first target"
                } else {
                    "timing"
                })
                .borders(Borders::ALL),
        )
        .wrap(Wrap { trim: false })
}

fn render_graph_area(frame: &mut Frame<'_>, area: Rect, state: &TuiState) {
    let viewport = state
        .graph_viewport
        .range(Instant::now(), state.newest_graph_sample_time());
    if state.is_multi_target() {
        render_multi_target_graph(frame, area, state, viewport);
        return;
    }

    let history = state
        .selected_target()
        .map(|target| &target.graph_history)
        .expect("TuiState always has at least one target");
    let visible = visible_history_window(history, viewport);
    let series = graph_series(state.graph_metric, &visible, viewport);

    render_chart(
        frame,
        area,
        &visible,
        &series,
        ChartRenderConfig {
            metric: state.graph_metric,
            context: graph_context(state, viewport),
            viewport,
        },
    );
}

fn render_multi_target_graph(
    frame: &mut Frame<'_>,
    area: Rect,
    state: &TuiState,
    viewport: GraphViewportRange,
) {
    let metric = state.graph_metric;
    let series = state
        .targets
        .iter()
        .enumerate()
        .filter_map(|(idx, target)| target_metric_series(target, idx, viewport, metric))
        .collect::<Vec<_>>();
    if series.is_empty() {
        frame.render_widget(
            Paragraph::new(metric.empty_message())
                .block(
                    Block::default()
                        .title(graph_chart_title(metric, &graph_context(state, viewport)))
                        .borders(Borders::ALL),
                )
                .wrap(Wrap { trim: true }),
            area,
        );
        return;
    }

    let (min_y, max_y) = chart_y_bounds(&series, metric.axis_kind());
    let datasets = chart_datasets(&series);
    let chart = Chart::new(datasets)
        .block(
            Block::default()
                .title(graph_chart_title(metric, &graph_context(state, viewport)))
                .borders(Borders::ALL),
        )
        .x_axis(
            Axis::default()
                .bounds(viewport_x_bounds(viewport))
                .labels(viewport_x_axis_labels(viewport))
                .style(Style::default().fg(Color::Gray)),
        )
        .y_axis(
            Axis::default()
                .bounds([min_y, max_y])
                .labels(y_axis_labels(min_y, max_y, y_axis_label_count(area.height)))
                .style(Style::default().fg(Color::Gray)),
        );
    frame.render_widget(chart, area);
}

fn render_chart(
    frame: &mut Frame<'_>,
    area: Rect,
    _visible: &[&GraphSample],
    series: &[ChartSeries],
    config: ChartRenderConfig,
) {
    if series.is_empty() {
        frame.render_widget(
            Paragraph::new(config.metric.empty_message())
                .block(
                    Block::default()
                        .title(graph_chart_title(config.metric, &config.context))
                        .borders(Borders::ALL),
                )
                .wrap(Wrap { trim: true }),
            area,
        );
        return;
    }

    let (min_y, max_y) = chart_y_bounds(series, config.metric.axis_kind());
    let datasets = chart_datasets(series);
    let chart = Chart::new(datasets)
        .block(
            Block::default()
                .title(graph_chart_title(config.metric, &config.context))
                .borders(Borders::ALL),
        )
        .x_axis(
            Axis::default()
                .bounds(viewport_x_bounds(config.viewport))
                .labels(viewport_x_axis_labels(config.viewport))
                .style(Style::default().fg(Color::Gray)),
        )
        .y_axis(
            Axis::default()
                .bounds([min_y, max_y])
                .labels(y_axis_labels(min_y, max_y, y_axis_label_count(area.height)))
                .style(Style::default().fg(Color::Gray)),
        );
    frame.render_widget(chart, area);
}

#[derive(Debug, Clone)]
struct ChartRenderConfig {
    metric: GraphMetric,
    context: String,
    viewport: GraphViewportRange,
}

#[derive(Debug, Clone, PartialEq)]
struct ChartSeries {
    name: String,
    style: Style,
    data: Vec<(f64, f64)>,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum ChartAxisKind {
    NonNegative,
    Signed,
}

fn visible_history_window(
    history: &VecDeque<GraphSample>,
    viewport: GraphViewportRange,
) -> Vec<&GraphSample> {
    history
        .iter()
        .filter(|sample| sample.timestamp >= viewport.start && sample.timestamp <= viewport.end)
        .collect()
}

fn graph_series(
    metric: GraphMetric,
    visible: &[&GraphSample],
    viewport: GraphViewportRange,
) -> Vec<ChartSeries> {
    chart_series(metric, visible, viewport)
        .into_iter()
        .collect()
}

fn chart_series(
    metric: GraphMetric,
    visible: &[&GraphSample],
    viewport: GraphViewportRange,
) -> Option<ChartSeries> {
    let data: Vec<(f64, f64)> = visible
        .iter()
        .filter_map(|sample| {
            metric
                .value_ns(sample)
                .map(|ns| (sample_x(sample, viewport), ns as f64 / 1_000_000.0))
        })
        .collect();

    (!data.is_empty()).then_some(ChartSeries {
        name: metric.label().to_owned(),
        style: metric.style(),
        data,
    })
}

fn target_metric_series(
    target: &TuiTargetState,
    target_idx: usize,
    viewport: GraphViewportRange,
    metric: GraphMetric,
) -> Option<ChartSeries> {
    let data = target
        .graph_history
        .iter()
        .filter(|sample| sample.timestamp >= viewport.start && sample.timestamp <= viewport.end)
        .filter_map(|sample| {
            metric
                .value_ns(sample)
                .map(|ns| (sample_x(sample, viewport), ns as f64 / 1_000_000.0))
        })
        .collect::<Vec<_>>();

    (!data.is_empty()).then_some(ChartSeries {
        name: target.label.clone(),
        style: target_style(target_idx),
        data,
    })
}

fn sample_x(sample: &GraphSample, viewport: GraphViewportRange) -> f64 {
    sample
        .timestamp
        .saturating_duration_since(viewport.start)
        .as_secs_f64()
}

fn chart_datasets(series: &[ChartSeries]) -> Vec<Dataset<'_>> {
    series
        .iter()
        .map(|series| {
            Dataset::default()
                .name(series.name.as_str())
                .marker(symbols::Marker::Braille)
                .graph_type(GraphType::Line)
                .style(series.style)
                .data(&series.data)
        })
        .collect()
}

fn target_style(idx: usize) -> Style {
    const COLORS: [Color; 8] = [
        Color::Cyan,
        Color::Yellow,
        Color::Green,
        Color::Magenta,
        Color::LightBlue,
        Color::LightRed,
        Color::LightGreen,
        Color::White,
    ];
    Style::default().fg(COLORS[idx % COLORS.len()])
}

fn chart_y_bounds(series: &[ChartSeries], axis_kind: ChartAxisKind) -> (f64, f64) {
    let mut values = series.iter().flat_map(|series| {
        series
            .data
            .iter()
            .map(|(_, value)| match axis_kind {
                ChartAxisKind::NonNegative => (*value).max(0.0),
                ChartAxisKind::Signed => *value,
            })
            .filter(|value| value.is_finite())
    });
    let Some(first) = values.next() else {
        return default_y_bounds(axis_kind);
    };

    let (mut min_y, mut max_y) = (first, first);
    for value in values {
        min_y = min_y.min(value);
        max_y = max_y.max(value);
    }

    match axis_kind {
        ChartAxisKind::NonNegative => padded_non_negative_chart_y_bounds(min_y, max_y),
        ChartAxisKind::Signed => padded_signed_chart_y_bounds(min_y, max_y),
    }
}

fn default_y_bounds(axis_kind: ChartAxisKind) -> (f64, f64) {
    match axis_kind {
        ChartAxisKind::NonNegative => (0.0, 10.0),
        ChartAxisKind::Signed => (-1.0, 1.0),
    }
}

fn padded_non_negative_chart_y_bounds(min_y: f64, max_y: f64) -> (f64, f64) {
    let pad = chart_y_padding(min_y, max_y);
    let lower = (min_y - pad).max(0.0);
    let upper = max_y + pad;
    if lower < upper {
        (lower, upper)
    } else {
        (0.0, pad.max(1.0))
    }
}

fn padded_signed_chart_y_bounds(mut min_y: f64, mut max_y: f64) -> (f64, f64) {
    let pad = chart_y_padding(min_y, max_y);
    min_y -= pad;
    max_y += pad;
    if min_y >= max_y {
        (min_y - pad, max_y + pad)
    } else {
        (min_y, max_y)
    }
}

fn chart_y_padding(min_y: f64, max_y: f64) -> f64 {
    const MIN_PADDING_MS: f64 = 0.1;
    let span = max_y - min_y;
    if span <= f64::EPSILON {
        (max_y.abs() * 0.1).max(MIN_PADDING_MS)
    } else {
        (span * 0.1).max(MIN_PADDING_MS)
    }
}

fn viewport_x_bounds(viewport: GraphViewportRange) -> [f64; 2] {
    [0.0, viewport.window.as_secs_f64().max(1.0)]
}

fn viewport_x_axis_labels(viewport: GraphViewportRange) -> Vec<Span<'static>> {
    vec![
        Span::raw(format!("-{}", format_span(viewport.window))),
        Span::raw(if viewport.is_live { "live" } else { "end" }),
    ]
}

fn graph_context(state: &TuiState, viewport: GraphViewportRange) -> String {
    format!(
        "{} | window {}",
        graph_viewport_status(state),
        format_span(viewport.window)
    )
}

fn graph_chart_title(metric: GraphMetric, context: &str) -> String {
    format!("{} | {context}", metric.title())
}

fn y_axis_label_count(height: u16) -> usize {
    let inner = height.saturating_sub(2);
    if inner >= 14 {
        7
    } else if inner >= 9 {
        5
    } else if inner >= 5 {
        3
    } else {
        2
    }
}

fn y_axis_labels(min_y: f64, max_y: f64, label_count: usize) -> Vec<Span<'static>> {
    let label_count = label_count.max(2);
    let step = (max_y - min_y) / (label_count - 1) as f64;
    (0..label_count)
        .map(|idx| Span::raw(format_axis_time_ms(min_y + step * idx as f64)))
        .collect()
}

fn format_axis_time_ms(value_ms: f64) -> String {
    let value_ms = if value_ms.abs() < 0.000_5 {
        0.0
    } else {
        value_ms
    };
    let sign = if value_ms < 0.0 { "-" } else { "" };
    let abs_ms = value_ms.abs();
    if abs_ms < 1.0 {
        let us = abs_ms * 1_000.0;
        if us < 10.0 {
            format!("{sign}{us:.1}µs")
        } else {
            format!("{sign}{us:.0}µs")
        }
    } else if abs_ms < 1_000.0 {
        if abs_ms < 10.0 {
            format!("{sign}{abs_ms:.2}ms")
        } else if abs_ms < 100.0 {
            format!("{sign}{abs_ms:.1}ms")
        } else {
            format!("{sign}{abs_ms:.0}ms")
        }
    } else {
        let secs = abs_ms / 1_000.0;
        if secs < 10.0 {
            format!("{sign}{secs:.2}s")
        } else if secs < 100.0 {
            format!("{sign}{secs:.1}s")
        } else {
            format!("{sign}{secs:.0}s")
        }
    }
}

fn recent_events_panel(state: &TuiState, panel_height: u16) -> Paragraph<'_> {
    let lines: Vec<Line<'_>> = state
        .recent_events
        .iter()
        .rev()
        .take(recent_events_visible_count(panel_height))
        .map(|event| Line::from(event.as_str()))
        .collect();
    Paragraph::new(lines)
        .block(
            Block::default()
                .title("recent events")
                .borders(Borders::ALL),
        )
        .wrap(Wrap { trim: true })
}

fn recent_events_visible_count(panel_height: u16) -> usize {
    usize::from(panel_height.saturating_sub(2))
}

fn sample_panel(state: &TuiState, snapshot: &Snapshot) -> Paragraph<'static> {
    let selected = state.selected_target();
    let last = selected.and_then(|target| target.last_sample);
    let warning = selected
        .and_then(|target| target.last_warning.clone())
        .or_else(|| state.last_warning.clone())
        .unwrap_or_else(|| "-".to_owned());
    Paragraph::new(vec![
        Line::from(format!(
            "last seq: {}",
            last.map(|sample| format_seq(sample.seq))
                .unwrap_or_else(|| "-".to_owned())
        )),
        Line::from(format!(
            "raw / adjusted / effective: {} / {} / {}",
            last.map(|sample| format_optional_ns_i128(Some(sample.raw_ns)))
                .unwrap_or_else(|| "-".to_owned()),
            last.map(|sample| format_optional_ns_i128(sample.adjusted_ns))
                .unwrap_or_else(|| "-".to_owned()),
            last.map(|sample| format_optional_ns_i128(Some(sample.effective_ns)))
                .unwrap_or_else(|| "-".to_owned())
        )),
        Line::from(format!(
            "one-way c2s / s2c: {} / {}",
            last.map(|sample| format_optional_ns_i128(sample.client_to_server_ns))
                .unwrap_or_else(|| "-".to_owned()),
            last.map(|sample| format_optional_ns_i128(sample.server_to_client_ns))
                .unwrap_or_else(|| "-".to_owned())
        )),
        Line::from(format!(
            "server processing: {}",
            last.map(|sample| format_optional_ns_i128(sample.server_processing_ns))
                .unwrap_or_else(|| "-".to_owned())
        )),
        Line::from(format!(
            "events sent={} replies={} losses={} warnings={}",
            format_count(snapshot.events.sent_events),
            format_count(snapshot.events.echo_replies),
            format_count(snapshot.events.loss_events),
            format_count(snapshot.events.warning_events)
        )),
        Line::from(format!("last warning: {warning}")),
    ])
    .block(
        Block::default()
            .title(if state.is_multi_target() {
                "sample - first target"
            } else {
                "sample"
            })
            .borders(Borders::ALL),
    )
    .wrap(Wrap { trim: true })
}

fn status_line(state: &TuiState) -> Paragraph<'_> {
    let paused = if state.paused { " display paused" } else { "" };
    let quitting = if state.quit_requested {
        " quit requested"
    } else {
        ""
    };
    let view_hint = match state.view {
        TuiView::Graph => "g dashboard",
        TuiView::Dashboard => "g graph",
    };
    let incomplete = if state.dropped_events > 0 {
        format!(" incomplete:dropped={}", state.dropped_events)
    } else {
        String::new()
    };
    let controls = if state.graph_viewport.mode == GraphViewportMode::Follow {
        format!(
            "q quit | r reset | p pause | {view_hint} | m metric | arrows pan | +/- zoom | 0 reset window"
        )
    } else {
        format!(
            "q quit | End live | {view_hint} | m metric | arrows pan | PgUp/PgDn page | +/- zoom | 0 reset window"
        )
    };
    let lines = vec![Line::from(format!(
        "{}{}{}{} | {}",
        state.status.label(),
        paused,
        quitting,
        incomplete,
        controls
    ))];
    Paragraph::new(lines).block(Block::default().borders(Borders::ALL))
}

fn graph_viewport_status(state: &TuiState) -> String {
    match state.graph_viewport.mode {
        GraphViewportMode::Follow => "live".to_owned(),
        GraphViewportMode::Historical { end } => {
            let now = Instant::now();
            let live_end = state.newest_graph_sample_time().unwrap_or(now).max(now);
            format!(
                "history -{}",
                format_span(live_end.saturating_duration_since(end))
            )
        }
    }
}

fn push_time_line(lines: &mut Vec<Line<'_>>, label: &str, stats: &TimeStats) {
    if stats.count == 0 {
        lines.push(Line::from(format!(
            "{label:<18} {:>5} {:>9} {:>9} {:>9} {:>9}",
            0, "-", "-", "-", "-"
        )));
        return;
    }

    lines.push(Line::from(format!(
        "{label:<18} {:>5} {:>9} {:>9} {:>9} {:>9}",
        format_count(stats.count),
        format_optional_ns_i128(stats.min_ns),
        format_ns_f64(stats.mean_ns),
        format_optional_ns_i128(stats.max_ns),
        format_ns_f64(stats.stddev_ns())
    )));
}

fn format_negotiated(negotiated: &NegotiationResult) -> String {
    let params = &negotiated.accepted;
    let duration = params.duration.map_or_else(
        || "-".to_owned(),
        |duration| format_optional_ns_i128(Some(duration.as_nanos() as i128)),
    );
    let changes = if negotiated.changes.is_empty() {
        "none".to_owned()
    } else {
        negotiated.changes.len().to_string()
    };
    format!(
        "duration={} interval={} length={} clock={:?} timestamps={:?} stats={:?} changes={}",
        duration,
        format_optional_ns_i128(Some(params.interval.as_nanos() as i128)),
        params.length,
        params.clock,
        params.stamp_at,
        params.received_stats,
        changes
    )
}

fn format_optional_span(value: Option<Duration>) -> String {
    value.map(format_span).unwrap_or_else(|| ABSENT.to_owned())
}

/// Format a wall-clock span shown in the TUI's headers, config lines, and
/// graph window labels.
///
/// Spans are read at a glance rather than compared numerically, so they are
/// deliberately coarser than the shared scalar policy: a zero span is `0s`,
/// whole seconds carry one decimal, and a span of a minute or more is written
/// as minutes and seconds. Below one second there is nothing to gain from a
/// second spelling, so the shared scalar vocabulary is used directly.
fn format_span(value: Duration) -> String {
    if value.is_zero() {
        return "0s".to_owned();
    }
    let nanos = value.as_nanos();
    if nanos < 1_000_000_000 {
        return format_duration(value);
    }
    let secs = value.as_secs();
    if nanos < 60_000_000_000 {
        format!("{:.1}s", nanos as f64 / 1_000_000_000.0)
    } else {
        format!("{}m{:02}s", secs / 60, secs % 60)
    }
}

fn format_rate(count: u64, elapsed: Duration) -> String {
    let secs = elapsed.as_secs_f64();
    if secs <= f64::EPSILON {
        ABSENT.to_owned()
    } else {
        format!("{:.2}/s", count as f64 / secs)
    }
}

fn truncate(value: &str, max_chars: usize) -> String {
    if value.chars().count() <= max_chars {
        return value.to_owned();
    }
    value
        .chars()
        .take(max_chars.saturating_sub(1))
        .chain(std::iter::once('~'))
        .collect()
}

fn format_seq(value: u32) -> String {
    value.to_string()
}

fn format_optional_hex(value: Option<u64>) -> String {
    value
        .map(|value| format!("0x{value:x}"))
        .unwrap_or_else(|| ABSENT.to_owned())
}

fn duration_ns(value: Duration) -> i128 {
    i128::try_from(value.as_nanos()).unwrap_or(i128::MAX)
}