#![forbid(unsafe_code)]

use std::sync::Arc;
use std::sync::atomic::{AtomicU64, Ordering};

use tokio::sync::Mutex;
use tonic::Status;
use tracing::info;

use crate::{camera, uvc_runtime, video};

struct CameraRelaySlot {
    cfg: camera::CameraConfig,
    relay: Arc<video::CameraRelay>,
}

/// Manage the currently active camera relay instance.
///
/// Inputs: camera configurations requested by incoming RPC streams.
/// Outputs: a reusable relay handle plus a monotonically increasing session id.
/// Why: only one camera output should own the physical sink at a time, but we
/// still want identical stream requests to reuse the existing pipeline.
pub struct CameraRuntime {
    generation: AtomicU64,
    slot: Mutex<Option<CameraRelaySlot>>,
}

impl CameraRuntime {
    /// Create an empty runtime with no active relay.
    ///
    /// Inputs: none.
    /// Outputs: a fresh runtime with generation zero.
    /// Why: keeping construction trivial lets the main server handler create
    /// camera state early and share it across RPCs.
    #[must_use]
    pub fn new() -> Self {
        Self {
            generation: AtomicU64::new(0),
            slot: Mutex::new(None),
        }
    }

    /// Activate the relay matching the current configuration.
    ///
    /// Inputs: the desired camera configuration selected from the environment.
    /// Outputs: a session id plus a relay that is either reused or recreated.
    /// Why: UVC/HDMI sinks are expensive to churn, so identical requests should
    /// reuse the active pipeline instead of rebuilding it every time.
    pub async fn activate(
        &self,
        cfg: &camera::CameraConfig,
    ) -> Result<(u64, Arc<video::CameraRelay>), Status> {
        let session_id = self.generation.fetch_add(1, Ordering::SeqCst) + 1;
        let mut slot = self.slot.lock().await;
        let mut reused = false;

        let relay = if let Some(existing) = slot.as_ref() {
            if camera_cfg_eq(&existing.cfg, cfg) {
                reused = true;
                existing.relay.clone()
            } else {
                self.make_relay(cfg)?
            }
        } else {
            self.make_relay(cfg)?
        };

        if !reused {
            *slot = Some(CameraRelaySlot {
                cfg: cfg.clone(),
                relay: relay.clone(),
            });
            info!(
                session_id,
                output = cfg.output.as_str(),
                codec = cfg.codec.as_str(),
                width = cfg.width,
                height = cfg.height,
                fps = cfg.fps,
                "🎥 camera relay (re)created"
            );
        } else {
            info!(session_id, "🎥 camera relay reused");
        }

        Ok((session_id, relay))
    }

    /// Check whether a previously issued session id is still current.
    ///
    /// Inputs: a session id returned by `activate`.
    /// Outputs: `true` only when the session is still the most recent owner of
    /// the active camera relay.
    /// Why: superseded streams must stop writing frames into a sink that has
    /// already been reconfigured for a newer client session.
    #[must_use]
    pub fn is_active(&self, session_id: u64) -> bool {
        self.generation.load(Ordering::Relaxed) == session_id
    }

    fn make_relay(&self, cfg: &camera::CameraConfig) -> Result<Arc<video::CameraRelay>, Status> {
        let relay = match cfg.output {
            camera::CameraOutput::Uvc => {
                if std::env::var("LESAVKA_DISABLE_UVC").is_ok() {
                    return Err(Status::failed_precondition(
                        "UVC output disabled (LESAVKA_DISABLE_UVC set)",
                    ));
                }
                let uvc = uvc_runtime::pick_uvc_device()
                    .map_err(|e| Status::internal(format!("{e:#}")))?;
                info!(%uvc, "🎥 stream_camera using UVC sink");
                video::CameraRelay::new_uvc(0, &uvc, cfg)
                    .map_err(|e| Status::internal(format!("{e:#}")))?
            }
            camera::CameraOutput::Hdmi => video::CameraRelay::new_hdmi(0, cfg)
                .map_err(|e| Status::internal(format!("{e:#}")))?,
        };
        Ok(Arc::new(relay))
    }
}

/// Compare two camera configurations for sink reuse.
///
/// Inputs: the currently active camera config and the requested config.
/// Outputs: `true` when both configs target the same sink and stream profile.
/// Why: reusing a pipeline is only safe when both the transport parameters and
/// the HDMI connector identity still match.
#[must_use]
pub fn camera_cfg_eq(a: &camera::CameraConfig, b: &camera::CameraConfig) -> bool {
    if a.output != b.output
        || a.codec != b.codec
        || a.width != b.width
        || a.height != b.height
        || a.fps != b.fps
    {
        return false;
    }

    match (&a.hdmi, &b.hdmi) {
        (Some(left), Some(right)) => left.name == right.name && left.id == right.id,
        (None, None) => true,
        _ => false,
    }
}

#[cfg(test)]
mod tests {
    use super::camera_cfg_eq;
    use crate::camera::{CameraCodec, CameraConfig, CameraOutput, HdmiConnector};

    #[test]
    fn camera_cfg_eq_requires_matching_sink_profile() {
        let base = CameraConfig {
            output: CameraOutput::Hdmi,
            codec: CameraCodec::H264,
            width: 1920,
            height: 1080,
            fps: 30,
            hdmi: Some(HdmiConnector {
                name: String::from("HDMI-A-1"),
                id: Some(42),
            }),
        };

        let same = base.clone();
        assert!(camera_cfg_eq(&base, &same));

        let mut changed = base.clone();
        changed.fps = 25;
        assert!(!camera_cfg_eq(&base, &changed));

        changed = base.clone();
        changed.hdmi = Some(HdmiConnector {
            name: String::from("HDMI-A-2"),
            id: Some(42),
        });
        assert!(!camera_cfg_eq(&base, &changed));
    }
}