#![forbid(unsafe_code)]

use std::sync::atomic::{AtomicU64, Ordering};
use std::sync::{Arc, Mutex};
use std::time::Duration;
use tokio::sync::{OwnedSemaphorePermit, Semaphore};
use tokio::time::Instant;
use tracing::info;

/// Logical upstream media kinds that share one live-call session timeline.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum UpstreamMediaKind {
    /// Webcam uplink frames destined for the UVC/HDMI sink path.
    Camera,
    /// Microphone uplink packets destined for the UAC sink path.
    Microphone,
}

/// Lease returned when one upstream media stream becomes the active owner.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct UpstreamStreamLease {
    /// Shared session id for the current upstream live-call window.
    pub session_id: u64,
    /// Per-kind generation used to supersede older streams of the same kind.
    pub generation: u64,
}

/// One rebased upstream packet plus its planned server playout time.
#[derive(Clone, Copy, Debug)]
pub struct PlannedUpstreamPacket {
    /// Session-local packet timestamp after rebase onto the shared server clock.
    pub local_pts_us: u64,
    /// Wall-clock deadline when the server should present this packet.
    pub due_at: Instant,
    /// How late the packet already is when planned, if any.
    pub late_by: Duration,
}

#[derive(Debug, Default)]
struct UpstreamClockState {
    session_id: u64,
    active_camera_generation: Option<u64>,
    active_microphone_generation: Option<u64>,
    camera_base_remote_pts_us: Option<u64>,
    microphone_base_remote_pts_us: Option<u64>,
    last_video_local_pts_us: Option<u64>,
    last_audio_local_pts_us: Option<u64>,
    camera_packet_count: u64,
    microphone_packet_count: u64,
    startup_anchor_logged: bool,
    playout_epoch: Option<Instant>,
}

fn upstream_timing_trace_enabled() -> bool {
    std::env::var("LESAVKA_UPSTREAM_TIMING_TRACE")
        .ok()
        .map(|value| {
            let trimmed = value.trim();
            !(trimmed.eq_ignore_ascii_case("0")
                || trimmed.eq_ignore_ascii_case("false")
                || trimmed.eq_ignore_ascii_case("no")
                || trimmed.eq_ignore_ascii_case("off"))
        })
        .unwrap_or(false)
}

fn upstream_playout_delay() -> Duration {
    let delay_ms = std::env::var("LESAVKA_UPSTREAM_PLAYOUT_DELAY_MS")
        .ok()
        .and_then(|value| value.trim().parse::<u64>().ok())
        .unwrap_or(1_000);
    Duration::from_millis(delay_ms)
}

fn upstream_playout_offset_us(kind: UpstreamMediaKind) -> i64 {
    let name = match kind {
        UpstreamMediaKind::Camera => "LESAVKA_UPSTREAM_VIDEO_PLAYOUT_OFFSET_US",
        UpstreamMediaKind::Microphone => "LESAVKA_UPSTREAM_AUDIO_PLAYOUT_OFFSET_US",
    };
    std::env::var(name)
        .ok()
        .and_then(|value| value.trim().parse::<i64>().ok())
        .unwrap_or(0)
}

fn apply_playout_offset(base: Instant, offset_us: i64) -> Instant {
    if offset_us >= 0 {
        base + Duration::from_micros(offset_us as u64)
    } else {
        base.checked_sub(Duration::from_micros(offset_us.unsigned_abs()))
            .unwrap_or(base)
    }
}

/// Coordinate upstream stream ownership and keep audio/video on one timeline.
///
/// Inputs: stream-open/close events plus remote packet timestamps.
/// Outputs: active-stream leases and rebased local PTS values.
/// Why: live calls need one current webcam owner, one current microphone owner,
/// and one shared media clock so reconnects do not leave old sinks alive or let
/// audio/video drift onto separate timing islands.
#[derive(Debug)]
pub struct UpstreamMediaRuntime {
    next_session_id: AtomicU64,
    next_camera_generation: AtomicU64,
    next_microphone_generation: AtomicU64,
    microphone_sink_gate: Arc<Semaphore>,
    state: Mutex<UpstreamClockState>,
}

impl UpstreamMediaRuntime {
    /// Build an empty upstream runtime.
    #[must_use]
    pub fn new() -> Self {
        Self {
            next_session_id: AtomicU64::new(0),
            next_camera_generation: AtomicU64::new(0),
            next_microphone_generation: AtomicU64::new(0),
            microphone_sink_gate: Arc::new(Semaphore::new(1)),
            state: Mutex::new(UpstreamClockState::default()),
        }
    }

    /// Activate a camera stream as the current owner for the session.
    #[must_use]
    pub fn activate_camera(&self) -> UpstreamStreamLease {
        self.activate(UpstreamMediaKind::Camera)
    }

    /// Activate a microphone stream as the current owner for the session.
    #[must_use]
    pub fn activate_microphone(&self) -> UpstreamStreamLease {
        self.activate(UpstreamMediaKind::Microphone)
    }

    /// Reserve the single live microphone sink slot for one generation.
    ///
    /// Inputs: the microphone lease generation that wants to own the UAC sink.
    /// Outputs: an owned semaphore permit while that generation still owns the
    /// microphone slot, or `None` if a newer stream superseded it before the
    /// previous sink fully stood down.
    /// Why: ALSA only allows one live owner of the UAC playback device, so a
    /// replacement stream must wait for the old owner to release the sink
    /// before opening a new playback pipeline.
    pub async fn reserve_microphone_sink(&self, generation: u64) -> Option<OwnedSemaphorePermit> {
        let permit = self
            .microphone_sink_gate
            .clone()
            .acquire_owned()
            .await
            .ok()?;
        self.is_microphone_active(generation).then_some(permit)
    }

    fn activate(&self, kind: UpstreamMediaKind) -> UpstreamStreamLease {
        let generation = match kind {
            UpstreamMediaKind::Camera => {
                self.next_camera_generation.fetch_add(1, Ordering::SeqCst) + 1
            }
            UpstreamMediaKind::Microphone => {
                self.next_microphone_generation
                    .fetch_add(1, Ordering::SeqCst)
                    + 1
            }
        };

        let mut state = self
            .state
            .lock()
            .expect("upstream media state mutex poisoned");
        if state.active_camera_generation.is_none() && state.active_microphone_generation.is_none()
        {
            state.session_id = self.next_session_id.fetch_add(1, Ordering::SeqCst) + 1;
            state.camera_base_remote_pts_us = None;
            state.microphone_base_remote_pts_us = None;
            state.last_video_local_pts_us = None;
            state.last_audio_local_pts_us = None;
            state.camera_packet_count = 0;
            state.microphone_packet_count = 0;
            state.startup_anchor_logged = false;
            state.playout_epoch = None;
        }
        match kind {
            UpstreamMediaKind::Camera => state.active_camera_generation = Some(generation),
            UpstreamMediaKind::Microphone => state.active_microphone_generation = Some(generation),
        }
        UpstreamStreamLease {
            session_id: state.session_id,
            generation,
        }
    }

    /// Return whether the supplied camera lease is still the active owner.
    #[must_use]
    pub fn is_camera_active(&self, generation: u64) -> bool {
        self.is_active(UpstreamMediaKind::Camera, generation)
    }

    /// Return whether the supplied microphone lease is still the active owner.
    #[must_use]
    pub fn is_microphone_active(&self, generation: u64) -> bool {
        self.is_active(UpstreamMediaKind::Microphone, generation)
    }

    fn is_active(&self, kind: UpstreamMediaKind, generation: u64) -> bool {
        let state = self
            .state
            .lock()
            .expect("upstream media state mutex poisoned");
        match kind {
            UpstreamMediaKind::Camera => state.active_camera_generation == Some(generation),
            UpstreamMediaKind::Microphone => state.active_microphone_generation == Some(generation),
        }
    }

    /// Mark a camera stream as closed if it still owns the camera slot.
    pub fn close_camera(&self, generation: u64) {
        self.close(UpstreamMediaKind::Camera, generation);
    }

    /// Mark a microphone stream as closed if it still owns the microphone slot.
    pub fn close_microphone(&self, generation: u64) {
        self.close(UpstreamMediaKind::Microphone, generation);
    }

    fn close(&self, kind: UpstreamMediaKind, generation: u64) {
        let mut state = self
            .state
            .lock()
            .expect("upstream media state mutex poisoned");
        match kind {
            UpstreamMediaKind::Camera if state.active_camera_generation == Some(generation) => {
                state.active_camera_generation = None;
            }
            UpstreamMediaKind::Microphone
                if state.active_microphone_generation == Some(generation) =>
            {
                state.active_microphone_generation = None;
            }
            _ => return,
        }
        if state.active_camera_generation.is_none() && state.active_microphone_generation.is_none()
        {
            state.camera_base_remote_pts_us = None;
            state.microphone_base_remote_pts_us = None;
            state.last_video_local_pts_us = None;
            state.last_audio_local_pts_us = None;
            state.camera_packet_count = 0;
            state.microphone_packet_count = 0;
            state.startup_anchor_logged = false;
            state.playout_epoch = None;
        }
    }

    /// Rebase one upstream video packet timestamp onto the shared session clock.
    #[must_use]
    pub fn map_video_pts(&self, remote_pts_us: u64, frame_step_us: u64) -> u64 {
        self.plan_video_pts(remote_pts_us, frame_step_us.max(1))
            .local_pts_us
    }

    /// Rebase one upstream audio packet timestamp onto the shared session clock.
    #[must_use]
    pub fn map_audio_pts(&self, remote_pts_us: u64) -> u64 {
        self.plan_audio_pts(remote_pts_us).local_pts_us
    }

    /// Rebase and schedule one upstream video packet on the shared playout epoch.
    #[must_use]
    pub fn plan_video_pts(&self, remote_pts_us: u64, frame_step_us: u64) -> PlannedUpstreamPacket {
        self.plan_pts(
            UpstreamMediaKind::Camera,
            remote_pts_us,
            frame_step_us.max(1),
        )
    }

    /// Rebase and schedule one upstream audio packet on the shared playout epoch.
    #[must_use]
    pub fn plan_audio_pts(&self, remote_pts_us: u64) -> PlannedUpstreamPacket {
        self.plan_pts(UpstreamMediaKind::Microphone, remote_pts_us, 1)
    }

    fn plan_pts(
        &self,
        kind: UpstreamMediaKind,
        remote_pts_us: u64,
        min_step_us: u64,
    ) -> PlannedUpstreamPacket {
        let mut state = self
            .state
            .lock()
            .expect("upstream media state mutex poisoned");
        let session_id = state.session_id;
        let packet_count = match kind {
            UpstreamMediaKind::Camera => {
                state.camera_packet_count = state.camera_packet_count.saturating_add(1);
                state.camera_packet_count
            }
            UpstreamMediaKind::Microphone => {
                state.microphone_packet_count = state.microphone_packet_count.saturating_add(1);
                state.microphone_packet_count
            }
        };
        let base_slot = match kind {
            UpstreamMediaKind::Camera => &mut state.camera_base_remote_pts_us,
            UpstreamMediaKind::Microphone => &mut state.microphone_base_remote_pts_us,
        };
        let first_remote_for_kind = *base_slot.get_or_insert(remote_pts_us);
        if !state.startup_anchor_logged
            && state.camera_base_remote_pts_us.is_some()
            && state.microphone_base_remote_pts_us.is_some()
        {
            let camera_base_remote_pts_us = state.camera_base_remote_pts_us.unwrap_or_default();
            let microphone_base_remote_pts_us =
                state.microphone_base_remote_pts_us.unwrap_or_default();
            let startup_delta_us =
                camera_base_remote_pts_us as i128 - microphone_base_remote_pts_us as i128;
            info!(
                session_id,
                camera_base_remote_pts_us,
                microphone_base_remote_pts_us,
                startup_delta_us,
                "upstream media session anchors observed"
            );
            state.startup_anchor_logged = true;
        }
        let mut local_pts_us = remote_pts_us.saturating_sub(first_remote_for_kind);
        let last_slot = match kind {
            UpstreamMediaKind::Camera => &mut state.last_video_local_pts_us,
            UpstreamMediaKind::Microphone => &mut state.last_audio_local_pts_us,
        };
        if let Some(last_pts_us) = *last_slot
            && local_pts_us <= last_pts_us
        {
            local_pts_us = last_pts_us.saturating_add(min_step_us.max(1));
        }
        *last_slot = Some(local_pts_us);
        let now = Instant::now();
        let epoch = *state
            .playout_epoch
            .get_or_insert_with(|| now + upstream_playout_delay());
        let sink_offset_us = upstream_playout_offset_us(kind);
        let due_at =
            apply_playout_offset(epoch + Duration::from_micros(local_pts_us), sink_offset_us);
        let late_by = now.checked_duration_since(due_at).unwrap_or_default();
        if upstream_timing_trace_enabled()
            && (packet_count <= 10 || packet_count.is_multiple_of(300))
        {
            let remote_elapsed_us = remote_pts_us.saturating_sub(first_remote_for_kind);
            let playout_delay_us = epoch.saturating_duration_since(now).as_micros();
            let late_by_us = late_by.as_micros();
            info!(
                session_id,
                ?kind,
                packet_count,
                remote_pts_us,
                first_remote_for_kind,
                remote_elapsed_us,
                local_pts_us,
                playout_delay_us,
                sink_offset_us,
                late_by_us,
                "upstream media rebase sample"
            );
        }
        PlannedUpstreamPacket {
            local_pts_us,
            due_at,
            late_by,
        }
    }
}

#[cfg(test)]
mod tests;