use crate::{varint, ProtoError, Result, PROTOCOL_VERSION};

#[derive(Debug, Clone, PartialEq, Eq, Default)]
pub struct Params {
    pub protocol_version: i64,
    pub duration_ns: i64,
    pub interval_ns: i64,
    pub length: i64,
    pub received_stats: ReceivedStats,
    pub stamp_at: StampAt,
    pub clock: Clock,
    pub dscp: i64,
    pub server_fill: Option<ServerFill>,
}

impl Params {
    pub fn with_protocol_defaults() -> Self {
        Self {
            protocol_version: PROTOCOL_VERSION,
            ..Self::default()
        }
    }

    pub fn encode(&self) -> Vec<u8> {
        let mut out = Vec::new();
        push_int(1, self.protocol_version, &mut out);
        push_int(2, self.duration_ns, &mut out);
        push_int(3, self.interval_ns, &mut out);
        push_int(4, self.length, &mut out);
        push_int(5, self.received_stats as i64, &mut out);
        push_int(6, self.stamp_at as i64, &mut out);
        push_int(7, self.clock as i64, &mut out);
        push_int(8, self.dscp, &mut out);
        if let Some(fill) = &self.server_fill {
            varint::encode_uvarint(9, &mut out);
            varint::encode_uvarint(fill.value.len() as u64, &mut out);
            out.extend_from_slice(fill.value.as_bytes());
        }
        out
    }

    pub fn decode(input: &[u8]) -> Result<Self> {
        let mut params = Self::default();
        let mut pos = 0;
        while pos < input.len() {
            let (tag, used) = varint::decode_uvarint(&input[pos..])?;
            pos += used;
            match tag {
                1 => params.protocol_version = read_int(input, &mut pos)?,
                2 => params.duration_ns = read_int(input, &mut pos)?,
                3 => params.interval_ns = read_int(input, &mut pos)?,
                4 => params.length = read_int(input, &mut pos)?,
                5 => params.received_stats = ReceivedStats::try_from(read_int(input, &mut pos)?)?,
                6 => params.stamp_at = StampAt::try_from(read_int(input, &mut pos)?)?,
                7 => params.clock = Clock::try_from(read_int(input, &mut pos)?)?,
                8 => params.dscp = read_int(input, &mut pos)?,
                9 => {
                    let (len, used) = varint::decode_uvarint(&input[pos..])?;
                    pos += used;
                    let len = len as usize;
                    if input.len().saturating_sub(pos) < len {
                        return Err(ProtoError::MalformedParams);
                    }
                    let value = std::str::from_utf8(&input[pos..pos + len])
                        .map_err(|_| ProtoError::InvalidUtf8)?
                        .to_owned();
                    pos += len;
                    params.server_fill = Some(ServerFill { value });
                }
                _ => {
                    let (_, used) = varint::decode_uvarint(&input[pos..])?;
                    pos += used;
                }
            }
        }
        Ok(params)
    }
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct ServerFill {
    pub value: String,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
#[repr(i64)]
pub enum ReceivedStats {
    #[default]
    None = 0,
    Count = 1,
    Window = 2,
    Both = 3,
}

impl ReceivedStats {
    pub fn has_count(self) -> bool {
        matches!(self, Self::Count | Self::Both)
    }

    pub fn has_window(self) -> bool {
        matches!(self, Self::Window | Self::Both)
    }
}

impl TryFrom<i64> for ReceivedStats {
    type Error = ProtoError;

    fn try_from(value: i64) -> Result<Self> {
        match value {
            0 => Ok(Self::None),
            1 => Ok(Self::Count),
            2 => Ok(Self::Window),
            3 => Ok(Self::Both),
            _ => Err(ProtoError::InvalidEnum {
                name: "ReceivedStats",
                value,
            }),
        }
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
#[repr(i64)]
pub enum StampAt {
    #[default]
    None = 0,
    Send = 1,
    Receive = 2,
    Both = 3,
    Midpoint = 4,
}

impl TryFrom<i64> for StampAt {
    type Error = ProtoError;

    fn try_from(value: i64) -> Result<Self> {
        match value {
            0 => Ok(Self::None),
            1 => Ok(Self::Send),
            2 => Ok(Self::Receive),
            3 => Ok(Self::Both),
            4 => Ok(Self::Midpoint),
            _ => Err(ProtoError::InvalidEnum {
                name: "StampAt",
                value,
            }),
        }
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
#[repr(i64)]
pub enum Clock {
    Wall = 1,
    Monotonic = 2,
    #[default]
    Both = 3,
}

impl Clock {
    pub fn has_wall(self) -> bool {
        matches!(self, Self::Wall | Self::Both)
    }

    pub fn has_mono(self) -> bool {
        matches!(self, Self::Monotonic | Self::Both)
    }
}

impl TryFrom<i64> for Clock {
    type Error = ProtoError;

    fn try_from(value: i64) -> Result<Self> {
        match value {
            1 => Ok(Self::Wall),
            2 => Ok(Self::Monotonic),
            3 => Ok(Self::Both),
            _ => Err(ProtoError::InvalidEnum {
                name: "Clock",
                value,
            }),
        }
    }
}

fn push_int(tag: u64, value: i64, out: &mut Vec<u8>) {
    if value == 0 {
        return;
    }
    varint::encode_uvarint(tag, out);
    varint::encode_varint(value, out);
}

fn read_int(input: &[u8], pos: &mut usize) -> Result<i64> {
    let (value, used) = varint::decode_varint(&input[*pos..])?;
    *pos += used;
    Ok(value)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn params_round_trip() {
        let params = Params {
            protocol_version: 1,
            duration_ns: 3_000_000_000,
            interval_ns: 1_000_000_000,
            length: 1472,
            received_stats: ReceivedStats::Both,
            stamp_at: StampAt::Both,
            clock: Clock::Both,
            dscp: 184,
            server_fill: Some(ServerFill {
                value: "pattern:abc".to_owned(),
            }),
        };
        assert_eq!(Params::decode(&params.encode()), Ok(params));
    }

    #[test]
    fn unknown_tags_are_ignored() {
        let mut encoded = Vec::new();
        varint::encode_uvarint(99, &mut encoded);
        varint::encode_varint(123, &mut encoded);
        varint::encode_uvarint(1, &mut encoded);
        varint::encode_varint(1, &mut encoded);

        let params = Params::decode(&encoded).unwrap();
        assert_eq!(params.protocol_version, 1);
    }

    #[test]
    fn explicit_clock_zero_is_rejected() {
        let mut encoded = Vec::new();
        varint::encode_uvarint(7, &mut encoded);
        varint::encode_varint(0, &mut encoded);

        assert_eq!(
            Params::decode(&encoded),
            Err(ProtoError::InvalidEnum {
                name: "Clock",
                value: 0,
            })
        );
    }
}