use std::sync::Arc;
use std::time::Duration;

use crate::calibration::CalibrationStore;
use crate::upstream_media_runtime::{UpstreamMediaRuntime, UpstreamPlannerSnapshot};

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
enum BlindHealTarget {
    Video,
    Audio,
}

#[derive(Clone, Copy, Debug)]
struct BlindHealConfig {
    enabled: bool,
    target: BlindHealTarget,
    min_samples: u64,
    deadband_ms: f64,
    max_handoff_abs_p95_ms: f64,
    max_client_send_abs_p95_ms: f64,
    max_server_receive_abs_p95_ms: f64,
    max_queue_age_p95_ms: f64,
    max_sink_late_p95_ms: f64,
    gain: f64,
    max_step_us: i64,
    interval: Duration,
    cooldown: Duration,
}

#[derive(Clone, Debug, PartialEq)]
struct BlindHealAction {
    audio_delta_us: i64,
    video_delta_us: i64,
    observed_sink_handoff_skew_ms: f64,
    observed_client_send_abs_p95_ms: f64,
    note: String,
}

#[cfg(not(coverage))]
pub fn spawn_blind_healer(runtime: Arc<UpstreamMediaRuntime>, calibration: Arc<CalibrationStore>) {
    let config = BlindHealConfig::from_env();
    if !config.enabled {
        tracing::info!("upstream blind healer disabled");
        return;
    }

    tokio::spawn(async move {
        let mut last_adjusted_session_id = 0;
        let mut last_adjusted_at: Option<tokio::time::Instant> = None;
        loop {
            tokio::time::sleep(config.interval).await;
            let snapshot = runtime.snapshot();
            if snapshot.session_id != last_adjusted_session_id {
                last_adjusted_session_id = snapshot.session_id;
                last_adjusted_at = None;
            }
            if last_adjusted_at.is_some_and(|last| last.elapsed() < config.cooldown) {
                continue;
            }
            let action = match evaluate_blind_heal_snapshot(&snapshot, config) {
                BlindHealDecision::Apply(action) => action,
                BlindHealDecision::Wait(reason) => {
                    tracing::trace!(reason, "upstream blind healer waiting");
                    continue;
                }
            };
            let state = calibration.apply_transient_blind_estimate(
                action.audio_delta_us,
                action.video_delta_us,
                action.observed_sink_handoff_skew_ms as f32,
                action.observed_client_send_abs_p95_ms as f32,
                action.note.clone(),
            );
            last_adjusted_at = Some(tokio::time::Instant::now());
            tracing::info!(
                session_id = snapshot.session_id,
                audio_delta_us = action.audio_delta_us,
                video_delta_us = action.video_delta_us,
                sink_handoff_skew_ms = action.observed_sink_handoff_skew_ms,
                client_send_abs_p95_ms = action.observed_client_send_abs_p95_ms,
                active_audio_offset_us = state.active_audio_offset_us,
                active_video_offset_us = state.active_video_offset_us,
                "upstream blind healer applied transient calibration nudge"
            );
        }
    });
}

#[derive(Clone, Debug, PartialEq)]
enum BlindHealDecision {
    Apply(BlindHealAction),
    Wait(&'static str),
}

fn evaluate_blind_heal_snapshot(
    snapshot: &UpstreamPlannerSnapshot,
    config: BlindHealConfig,
) -> BlindHealDecision {
    if !config.enabled {
        return BlindHealDecision::Wait("disabled");
    }
    if !matches!(snapshot.phase, "live" | "healing") {
        return BlindHealDecision::Wait("not-live");
    }
    if snapshot.client_timing_window_samples < config.min_samples {
        return BlindHealDecision::Wait("not-enough-client-samples");
    }
    if snapshot.sink_handoff_window_samples < config.min_samples {
        return BlindHealDecision::Wait("not-enough-sink-samples");
    }
    let Some(skew_ms) = snapshot.sink_handoff_skew_ms else {
        return BlindHealDecision::Wait("missing-sink-skew");
    };
    if skew_ms.abs() < config.deadband_ms {
        return BlindHealDecision::Wait("inside-deadband");
    }
    if exceeds(
        snapshot.sink_handoff_abs_skew_p95_ms,
        config.max_handoff_abs_p95_ms,
    ) {
        return BlindHealDecision::Wait("sink-handoff-p95-unstable");
    }
    if exceeds(
        snapshot.client_send_abs_skew_p95_ms,
        config.max_client_send_abs_p95_ms,
    ) {
        return BlindHealDecision::Wait("client-send-p95-unstable");
    }
    if exceeds(
        snapshot.server_receive_abs_skew_p95_ms,
        config.max_server_receive_abs_p95_ms,
    ) {
        return BlindHealDecision::Wait("server-receive-p95-unstable");
    }
    if exceeds(
        snapshot.camera_client_queue_age_p95_ms,
        config.max_queue_age_p95_ms,
    ) || exceeds(
        snapshot.microphone_client_queue_age_p95_ms,
        config.max_queue_age_p95_ms,
    ) {
        return BlindHealDecision::Wait("client-queue-p95-unstable");
    }
    if exceeds(
        snapshot.camera_sink_late_p95_ms,
        config.max_sink_late_p95_ms,
    ) || exceeds(
        snapshot.microphone_sink_late_p95_ms,
        config.max_sink_late_p95_ms,
    ) {
        return BlindHealDecision::Wait("sink-late-p95-unstable");
    }

    let correction_us = clamp_step(skew_ms * config.gain * 1000.0, config.max_step_us);
    if correction_us == 0 {
        return BlindHealDecision::Wait("rounded-zero");
    }
    let (audio_delta_us, video_delta_us) = match config.target {
        BlindHealTarget::Audio => (correction_us, 0),
        BlindHealTarget::Video => (0, -correction_us),
    };
    BlindHealDecision::Apply(BlindHealAction {
        audio_delta_us,
        video_delta_us,
        observed_sink_handoff_skew_ms: skew_ms,
        observed_client_send_abs_p95_ms: snapshot.client_send_abs_skew_p95_ms.unwrap_or(0.0),
        note: format!(
            "runtime blind healer: sink handoff skew {skew_ms:+.1}ms, target={:?}, applying audio {:+.1}ms/video {:+.1}ms",
            config.target,
            audio_delta_us as f64 / 1000.0,
            video_delta_us as f64 / 1000.0
        ),
    })
}

fn exceeds(value: Option<f64>, limit: f64) -> bool {
    value.is_none_or(|value| !value.is_finite() || value.abs() > limit)
}

fn clamp_step(value: f64, max_step_us: i64) -> i64 {
    let limit = max_step_us.abs().max(1);
    (value.round() as i64).clamp(-limit, limit)
}

impl BlindHealConfig {
    #[cfg(not(coverage))]
    fn from_env() -> Self {
        Self {
            enabled: env_bool("LESAVKA_UPSTREAM_BLIND_HEAL", true),
            target: match std::env::var("LESAVKA_UPSTREAM_BLIND_HEAL_TARGET")
                .unwrap_or_else(|_| "video".to_string())
                .trim()
                .to_ascii_lowercase()
                .as_str()
            {
                "audio" | "mic" | "microphone" => BlindHealTarget::Audio,
                _ => BlindHealTarget::Video,
            },
            min_samples: env_u64("LESAVKA_UPSTREAM_BLIND_HEAL_MIN_SAMPLES", 30),
            deadband_ms: env_f64("LESAVKA_UPSTREAM_BLIND_HEAL_DEADBAND_MS", 35.0),
            max_handoff_abs_p95_ms: env_f64(
                "LESAVKA_UPSTREAM_BLIND_HEAL_MAX_HANDOFF_P95_MS",
                250.0,
            ),
            max_client_send_abs_p95_ms: env_f64(
                "LESAVKA_UPSTREAM_BLIND_HEAL_MAX_CLIENT_SEND_P95_MS",
                250.0,
            ),
            max_server_receive_abs_p95_ms: env_f64(
                "LESAVKA_UPSTREAM_BLIND_HEAL_MAX_SERVER_RECEIVE_P95_MS",
                250.0,
            ),
            max_queue_age_p95_ms: env_f64(
                "LESAVKA_UPSTREAM_BLIND_HEAL_MAX_QUEUE_AGE_P95_MS",
                150.0,
            ),
            max_sink_late_p95_ms: env_f64(
                "LESAVKA_UPSTREAM_BLIND_HEAL_MAX_SINK_LATE_P95_MS",
                120.0,
            ),
            gain: env_f64("LESAVKA_UPSTREAM_BLIND_HEAL_GAIN", 0.25).clamp(0.01, 1.0),
            max_step_us: env_i64("LESAVKA_UPSTREAM_BLIND_HEAL_MAX_STEP_US", 25_000)
                .abs()
                .max(1),
            interval: Duration::from_millis(env_u64(
                "LESAVKA_UPSTREAM_BLIND_HEAL_INTERVAL_MS",
                2_000,
            )),
            cooldown: Duration::from_millis(env_u64(
                "LESAVKA_UPSTREAM_BLIND_HEAL_COOLDOWN_MS",
                8_000,
            )),
        }
    }
}

#[cfg(not(coverage))]
fn env_bool(name: &str, default: bool) -> bool {
    std::env::var(name)
        .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(default)
}

#[cfg(not(coverage))]
fn env_u64(name: &str, default: u64) -> u64 {
    std::env::var(name)
        .ok()
        .and_then(|value| value.trim().parse::<u64>().ok())
        .filter(|value| *value > 0)
        .unwrap_or(default)
}

#[cfg(not(coverage))]
fn env_i64(name: &str, default: i64) -> i64 {
    std::env::var(name)
        .ok()
        .and_then(|value| value.trim().parse::<i64>().ok())
        .filter(|value| *value != 0)
        .unwrap_or(default)
}

#[cfg(not(coverage))]
fn env_f64(name: &str, default: f64) -> f64 {
    std::env::var(name)
        .ok()
        .and_then(|value| value.trim().parse::<f64>().ok())
        .filter(|value| value.is_finite() && *value > 0.0)
        .unwrap_or(default)
}

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

    fn config() -> BlindHealConfig {
        BlindHealConfig {
            enabled: true,
            target: BlindHealTarget::Video,
            min_samples: 30,
            deadband_ms: 35.0,
            max_handoff_abs_p95_ms: 250.0,
            max_client_send_abs_p95_ms: 250.0,
            max_server_receive_abs_p95_ms: 250.0,
            max_queue_age_p95_ms: 150.0,
            max_sink_late_p95_ms: 120.0,
            gain: 0.25,
            max_step_us: 25_000,
            interval: Duration::from_millis(2_000),
            cooldown: Duration::from_millis(8_000),
        }
    }

    fn snapshot() -> UpstreamPlannerSnapshot {
        UpstreamPlannerSnapshot {
            session_id: 7,
            phase: "live",
            latest_camera_remote_pts_us: Some(1),
            latest_microphone_remote_pts_us: Some(1),
            last_video_presented_pts_us: Some(1),
            last_audio_presented_pts_us: Some(1),
            live_lag_ms: Some(100.0),
            planner_skew_ms: Some(0.0),
            stale_audio_drops: 0,
            stale_video_drops: 0,
            skew_video_drops: 0,
            freshness_reanchors: 0,
            startup_timeouts: 0,
            video_freezes: 0,
            last_reason: "live".to_string(),
            client_capture_skew_ms: Some(0.0),
            client_send_skew_ms: Some(0.0),
            server_receive_skew_ms: Some(0.0),
            camera_client_queue_age_ms: Some(5.0),
            microphone_client_queue_age_ms: Some(5.0),
            camera_server_receive_age_ms: Some(5.0),
            microphone_server_receive_age_ms: Some(5.0),
            client_capture_abs_skew_p95_ms: Some(20.0),
            client_send_abs_skew_p95_ms: Some(20.0),
            server_receive_abs_skew_p95_ms: Some(20.0),
            camera_client_queue_age_p95_ms: Some(20.0),
            microphone_client_queue_age_p95_ms: Some(20.0),
            sink_handoff_skew_ms: Some(100.0),
            sink_handoff_abs_skew_p95_ms: Some(110.0),
            camera_sink_late_ms: Some(0.0),
            microphone_sink_late_ms: Some(0.0),
            camera_sink_late_p95_ms: Some(10.0),
            microphone_sink_late_p95_ms: Some(10.0),
            client_timing_window_samples: 60,
            sink_handoff_window_samples: 60,
        }
    }

    #[test]
    fn blind_healer_nudges_video_opposite_sink_handoff_skew() {
        let decision = evaluate_blind_heal_snapshot(&snapshot(), config());
        assert_eq!(
            decision,
            BlindHealDecision::Apply(BlindHealAction {
                audio_delta_us: 0,
                video_delta_us: -25_000,
                observed_sink_handoff_skew_ms: 100.0,
                observed_client_send_abs_p95_ms: 20.0,
                note: "runtime blind healer: sink handoff skew +100.0ms, target=Video, applying audio +0.0ms/video -25.0ms".to_string(),
            })
        );
    }

    #[test]
    fn blind_healer_refuses_when_under_sampled_or_unstable() {
        let mut low_samples = snapshot();
        low_samples.sink_handoff_window_samples = 1;
        assert_eq!(
            evaluate_blind_heal_snapshot(&low_samples, config()),
            BlindHealDecision::Wait("not-enough-sink-samples")
        );

        let mut noisy_network = snapshot();
        noisy_network.server_receive_abs_skew_p95_ms = Some(400.0);
        assert_eq!(
            evaluate_blind_heal_snapshot(&noisy_network, config()),
            BlindHealDecision::Wait("server-receive-p95-unstable")
        );
    }

    #[test]
    fn blind_healer_can_target_audio_when_requested() {
        let mut config = config();
        config.target = BlindHealTarget::Audio;
        let decision = evaluate_blind_heal_snapshot(&snapshot(), config);
        assert!(matches!(
            decision,
            BlindHealDecision::Apply(BlindHealAction {
                audio_delta_us: 25_000,
                video_delta_us: 0,
                ..
            })
        ));
    }
}