//! Transcoding service for media files using FFmpeg.

use std::collections::HashMap;
use std::path::{Path, PathBuf};
use std::sync::Arc;

use chrono::{DateTime, Utc};
use serde::{Deserialize, Serialize};
use tokio::sync::{RwLock, Semaphore};
use uuid::Uuid;

use crate::config::{TranscodeProfile, TranscodingConfig};
use crate::model::MediaId;
use crate::storage::DynStorageBackend;
use crate::users::UserId;

/// A transcoding session for a media item.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct TranscodeSession {
    pub id: Uuid,
    pub media_id: MediaId,
    pub user_id: Option<UserId>,
    pub profile: String,
    pub cache_path: PathBuf,
    pub status: TranscodeStatus,
    pub progress: f32,
    pub created_at: DateTime<Utc>,
    pub expires_at: Option<DateTime<Utc>>,
    /// Duration of the source media in seconds, used for progress calculation.
    #[serde(default)]
    pub duration_secs: Option<f64>,
    /// Handle to cancel the child FFmpeg process.
    #[serde(skip)]
    pub child_cancel: Option<Arc<tokio::sync::Notify>>,
}

/// Status of a transcode session.
#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(rename_all = "snake_case", tag = "state")]
pub enum TranscodeStatus {
    Pending,
    Transcoding,
    Complete,
    Failed { error: String },
    Cancelled,
}

impl TranscodeStatus {
    pub fn as_str(&self) -> &str {
        match self {
            Self::Pending => "pending",
            Self::Transcoding => "transcoding",
            Self::Complete => "complete",
            Self::Failed { .. } => "failed",
            Self::Cancelled => "cancelled",
        }
    }

    pub fn from_db(status: &str, error_message: Option<&str>) -> Self {
        match status {
            "pending" => Self::Pending,
            "transcoding" => Self::Transcoding,
            "complete" => Self::Complete,
            "failed" => Self::Failed {
                error: error_message.unwrap_or("unknown error").to_string(),
            },
            "cancelled" => Self::Cancelled,
            other => {
                tracing::warn!(
                    "unknown transcode status '{}', defaulting to Pending",
                    other
                );
                Self::Pending
            }
        }
    }

    pub fn error_message(&self) -> Option<&str> {
        match self {
            Self::Failed { error } => Some(error),
            _ => None,
        }
    }
}

/// Service managing transcoding sessions and FFmpeg invocations.
pub struct TranscodeService {
    pub config: TranscodingConfig,
    pub sessions: Arc<RwLock<HashMap<Uuid, TranscodeSession>>>,
    semaphore: Arc<Semaphore>,
}

impl TranscodeService {
    pub fn new(config: TranscodingConfig) -> Self {
        let max_concurrent = config.max_concurrent.max(1);
        Self {
            sessions: Arc::new(RwLock::new(HashMap::new())),
            semaphore: Arc::new(Semaphore::new(max_concurrent)),
            config,
        }
    }

    pub fn is_enabled(&self) -> bool {
        self.config.enabled
    }

    pub fn cache_dir(&self) -> PathBuf {
        self.config
            .cache_dir
            .clone()
            .unwrap_or_else(|| PathBuf::from("/tmp/pinakes-transcode"))
    }

    /// Start a transcode job for a media item.
    pub async fn start_transcode(
        &self,
        media_id: MediaId,
        source_path: &Path,
        profile_name: &str,
        duration_secs: Option<f64>,
        storage: &DynStorageBackend,
    ) -> crate::error::Result<Uuid> {
        let profile = self
            .config
            .profiles
            .iter()
            .find(|p| p.name == profile_name)
            .cloned()
            .ok_or_else(|| {
                crate::error::PinakesError::InvalidOperation(format!(
                    "unknown transcode profile: {}",
                    profile_name
                ))
            })?;

        let session_id = Uuid::now_v7();
        let session_dir = self.cache_dir().join(session_id.to_string());
        tokio::fs::create_dir_all(&session_dir).await.map_err(|e| {
            crate::error::PinakesError::InvalidOperation(format!(
                "failed to create session directory: {}",
                e
            ))
        })?;

        let expires_at =
            Some(Utc::now() + chrono::Duration::hours(self.config.cache_ttl_hours as i64));

        let cancel_notify = Arc::new(tokio::sync::Notify::new());

        let session = TranscodeSession {
            id: session_id,
            media_id,
            user_id: None,
            profile: profile_name.to_string(),
            cache_path: session_dir.clone(),
            status: TranscodeStatus::Pending,
            progress: 0.0,
            created_at: Utc::now(),
            expires_at,
            duration_secs,
            child_cancel: Some(cancel_notify.clone()),
        };

        // Store session in DB
        storage.create_transcode_session(&session).await?;

        // Store in memory
        {
            let mut sessions = self.sessions.write().await;
            sessions.insert(session_id, session);
        }

        // Spawn the FFmpeg task
        let sessions = self.sessions.clone();
        let semaphore = self.semaphore.clone();
        let source = source_path.to_path_buf();
        let hw_accel = self.config.hardware_acceleration.clone();
        let storage = storage.clone();
        let cancel = cancel_notify.clone();

        tokio::spawn(async move {
            // Acquire semaphore permit to limit concurrency
            let _permit = match semaphore.acquire().await {
                Ok(permit) => permit,
                Err(e) => {
                    tracing::error!("failed to acquire transcode semaphore: {}", e);
                    let error_msg = format!("semaphore closed: {}", e);
                    let mut s = sessions.write().await;
                    if let Some(sess) = s.get_mut(&session_id) {
                        sess.status = TranscodeStatus::Failed {
                            error: error_msg.clone(),
                        };
                    }
                    if let Err(e) = storage
                        .update_transcode_status(
                            session_id,
                            TranscodeStatus::Failed { error: error_msg },
                            0.0,
                        )
                        .await
                    {
                        tracing::error!("failed to update transcode status: {}", e);
                    }
                    return;
                }
            };

            // Mark as transcoding
            {
                let mut s = sessions.write().await;
                if let Some(sess) = s.get_mut(&session_id) {
                    sess.status = TranscodeStatus::Transcoding;
                }
            }
            if let Err(e) = storage
                .update_transcode_status(session_id, TranscodeStatus::Transcoding, 0.0)
                .await
            {
                tracing::error!("failed to update transcode status: {}", e);
            }

            // Build FFmpeg args and run
            let args = get_ffmpeg_args(&source, &session_dir, &profile, hw_accel.as_deref());
            match run_ffmpeg(&args, &sessions, session_id, duration_secs, cancel).await {
                Ok(()) => {
                    let mut s = sessions.write().await;
                    if let Some(sess) = s.get_mut(&session_id) {
                        sess.status = TranscodeStatus::Complete;
                        sess.progress = 1.0;
                    }
                    if let Err(e) = storage
                        .update_transcode_status(session_id, TranscodeStatus::Complete, 1.0)
                        .await
                    {
                        tracing::error!("failed to update transcode status: {}", e);
                    }
                }
                Err(e) => {
                    let error_msg = e.to_string();
                    let mut s = sessions.write().await;
                    if let Some(sess) = s.get_mut(&session_id) {
                        // Don't overwrite Cancelled status
                        if matches!(sess.status, TranscodeStatus::Cancelled) {
                            return;
                        }
                        sess.status = TranscodeStatus::Failed {
                            error: error_msg.clone(),
                        };
                    }
                    drop(s);
                    if let Err(e) = storage
                        .update_transcode_status(
                            session_id,
                            TranscodeStatus::Failed { error: error_msg },
                            0.0,
                        )
                        .await
                    {
                        tracing::error!("failed to update transcode status: {}", e);
                    }
                }
            }
        });

        Ok(session_id)
    }

    /// Cancel a transcode session and clean up cache files.
    pub async fn cancel_transcode(
        &self,
        session_id: Uuid,
        storage: &DynStorageBackend,
    ) -> crate::error::Result<()> {
        let (cache_path, cancel_notify) = {
            let mut sessions = self.sessions.write().await;
            if let Some(sess) = sessions.get_mut(&session_id) {
                sess.status = TranscodeStatus::Cancelled;
                let cancel = sess.child_cancel.take();
                (Some(sess.cache_path.clone()), cancel)
            } else {
                (None, None)
            }
        };

        // Signal the child process to be killed
        if let Some(notify) = cancel_notify {
            notify.notify_one();
        }

        storage
            .update_transcode_status(session_id, TranscodeStatus::Cancelled, 0.0)
            .await?;

        // Clean up cache directory
        if let Some(path) = cache_path
            && let Err(e) = tokio::fs::remove_dir_all(&path).await {
                tracing::error!("failed to remove transcode cache directory: {}", e);
            }

        Ok(())
    }

    /// Remove expired transcode sessions and their cache directories.
    pub async fn cleanup_expired(&self) {
        let now = Utc::now();

        // Collect expired entries and remove them from the map under the lock.
        let expired: Vec<(Uuid, PathBuf)> = {
            let mut sessions = self.sessions.write().await;
            let expired: Vec<(Uuid, PathBuf)> = sessions
                .iter()
                .filter_map(|(id, sess)| {
                    if let Some(expires) = sess.expires_at
                        && now > expires {
                            return Some((*id, sess.cache_path.clone()));
                        }
                    None
                })
                .collect();

            for (id, _) in &expired {
                sessions.remove(id);
            }

            expired
        };
        // Lock is dropped here; perform filesystem cleanup outside the lock.

        for (_id, path) in expired {
            if let Err(e) = tokio::fs::remove_dir_all(&path).await {
                tracing::error!("failed to remove expired transcode cache directory: {}", e);
            }
        }
    }

    /// Get a session by ID from the in-memory store.
    pub async fn get_session(&self, session_id: Uuid) -> Option<TranscodeSession> {
        let sessions = self.sessions.read().await;
        sessions.get(&session_id).cloned()
    }

    /// Resolve the path to a specific segment file on disk.
    pub fn segment_path(&self, session_id: Uuid, segment_name: &str) -> PathBuf {
        // Sanitize segment_name to prevent path traversal
        let safe_name = std::path::Path::new(segment_name)
            .file_name()
            .map(|n| n.to_string_lossy().to_string())
            .unwrap_or_default();
        if safe_name.is_empty() || safe_name.contains('\0') || safe_name.starts_with('.') {
            // Return a non-existent path that will fail safely
            return self
                .cache_dir()
                .join(session_id.to_string())
                .join("__invalid__");
        }
        self.cache_dir()
            .join(session_id.to_string())
            .join(safe_name)
    }

    /// Find a session for a given media_id and profile.
    pub async fn find_session(&self, media_id: MediaId, profile: &str) -> Option<TranscodeSession> {
        let sessions = self.sessions.read().await;
        sessions
            .values()
            .find(|s| s.media_id == media_id && s.profile == profile)
            .cloned()
    }
}

/// Parse a resolution string like "360p", "720p", "1080p" into (width, height).
pub fn parse_resolution(res: &str) -> (u32, u32) {
    match res.trim_end_matches('p') {
        "360" => (640, 360),
        "480" => (854, 480),
        "720" => (1280, 720),
        "1080" => (1920, 1080),
        "1440" => (2560, 1440),
        "2160" | "4k" => (3840, 2160),
        _ => (1280, 720), // default to 720p
    }
}

/// Estimate bandwidth (bits/sec) from a profile's max_bitrate_kbps.
pub fn estimate_bandwidth(profile: &TranscodeProfile) -> u32 {
    profile.max_bitrate_kbps * 1000
}

/// Build FFmpeg CLI arguments for transcoding.
fn get_ffmpeg_args(
    source: &Path,
    output_dir: &Path,
    profile: &TranscodeProfile,
    hw_accel: Option<&str>,
) -> Vec<String> {
    let (w, h) = parse_resolution(&profile.max_resolution);
    let playlist = output_dir.join("playlist.m3u8");
    let segment_pattern = output_dir.join("segment%d.ts");

    let mut args = Vec::new();

    // Hardware acceleration
    if let Some(accel) = hw_accel {
        args.extend_from_slice(&["-hwaccel".to_string(), accel.to_string()]);
    }

    args.extend_from_slice(&[
        "-i".to_string(),
        source.to_string_lossy().to_string(),
        "-c:v".to_string(),
        profile.video_codec.clone(),
        "-c:a".to_string(),
        profile.audio_codec.clone(),
        "-b:v".to_string(),
        format!("{}k", profile.max_bitrate_kbps),
        "-vf".to_string(),
        format!("scale={}:{}", w, h),
        "-f".to_string(),
        "hls".to_string(),
        "-hls_time".to_string(),
        "10".to_string(),
        "-hls_segment_filename".to_string(),
        segment_pattern.to_string_lossy().to_string(),
        "-progress".to_string(),
        "pipe:1".to_string(),
        "-y".to_string(),
        playlist.to_string_lossy().to_string(),
    ]);

    args
}

/// Run FFmpeg as a child process, parsing progress from stdout.
async fn run_ffmpeg(
    args: &[String],
    sessions: &Arc<RwLock<HashMap<Uuid, TranscodeSession>>>,
    session_id: Uuid,
    duration_secs: Option<f64>,
    cancel: Arc<tokio::sync::Notify>,
) -> Result<(), crate::error::PinakesError> {
    use tokio::io::{AsyncBufReadExt, BufReader};
    use tokio::process::Command;

    let mut child = Command::new("ffmpeg")
        .args(args)
        .stdout(std::process::Stdio::piped())
        .stderr(std::process::Stdio::piped())
        .spawn()
        .map_err(|e| {
            crate::error::PinakesError::InvalidOperation(format!("failed to spawn ffmpeg: {}", e))
        })?;

    // Capture stderr in a spawned task for error reporting
    let stderr_handle = if let Some(stderr) = child.stderr.take() {
        let reader = BufReader::new(stderr);
        Some(tokio::spawn(async move {
            let mut lines = reader.lines();
            let mut collected = Vec::new();
            while let Ok(Some(line)) = lines.next_line().await {
                collected.push(line);
            }
            collected
        }))
    } else {
        None
    };

    // Parse progress from stdout
    let stdout_handle = if let Some(stdout) = child.stdout.take() {
        let reader = BufReader::new(stdout);
        let mut lines = reader.lines();
        let sessions = sessions.clone();

        Some(tokio::spawn(async move {
            while let Ok(Some(line)) = lines.next_line().await {
                // FFmpeg progress output: "out_time_us=12345678"
                if let Some(time_str) = line.strip_prefix("out_time_us=")
                    && let Ok(us) = time_str.trim().parse::<f64>() {
                        let secs = us / 1_000_000.0;
                        // Calculate progress based on known duration
                        let progress = match duration_secs {
                            Some(dur) if dur > 0.0 => (secs / dur).min(0.99) as f32,
                            _ => {
                                // Duration unknown; don't update progress
                                continue;
                            }
                        };
                        let mut s = sessions.write().await;
                        if let Some(sess) = s.get_mut(&session_id) {
                            sess.progress = progress;
                        }
                    }
            }
        }))
    } else {
        None
    };

    // Wait for child, but also listen for cancellation
    let status = tokio::select! {
        result = child.wait() => {
            result.map_err(|e| {
                crate::error::PinakesError::InvalidOperation(format!("ffmpeg process error: {}", e))
            })?
        }
        _ = cancel.notified() => {
            // Kill the child process on cancel
            if let Err(e) = child.kill().await {
                tracing::error!("failed to kill ffmpeg process: {}", e);
            }
            return Err(crate::error::PinakesError::InvalidOperation(
                "cancelled by user".to_string(),
            ));
        }
    };

    // Await the stdout reader task
    if let Some(handle) = stdout_handle {
        let _ = handle.await;
    }

    // Collect stderr output for error reporting
    let stderr_output = if let Some(handle) = stderr_handle {
        handle.await.unwrap_or_default()
    } else {
        Vec::new()
    };

    if !status.success() {
        let last_stderr = stderr_output
            .iter()
            .rev()
            .take(10)
            .rev()
            .cloned()
            .collect::<Vec<_>>()
            .join("\n");
        return Err(crate::error::PinakesError::InvalidOperation(format!(
            "ffmpeg exited with status: {}\nstderr:\n{}",
            status, last_stderr
        )));
    }

    Ok(())
}