use std::collections::HashMap;
use std::path::PathBuf;
use std::sync::Arc;

use chrono::{DateTime, Utc};
use serde::{Deserialize, Serialize};
use serde_json::Value;
use tokio::sync::{RwLock, mpsc};
use tokio_util::sync::CancellationToken;
use uuid::Uuid;

use crate::model::MediaId;

#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(rename_all = "snake_case", tag = "type")]
pub enum JobKind {
    Scan {
        path: Option<PathBuf>,
    },
    GenerateThumbnails {
        media_ids: Vec<MediaId>,
    },
    VerifyIntegrity {
        media_ids: Vec<MediaId>,
    },
    OrphanDetection,
    CleanupThumbnails,
    Export {
        format: ExportFormat,
        destination: PathBuf,
    },
    Transcode {
        media_id: MediaId,
        profile: String,
    },
    Enrich {
        media_ids: Vec<MediaId>,
    },
    CleanupAnalytics,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum ExportFormat {
    Json,
    Csv,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(rename_all = "snake_case", tag = "state")]
pub enum JobStatus {
    Pending,
    Running { progress: f32, message: String },
    Completed { result: Value },
    Failed { error: String },
    Cancelled,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Job {
    pub id: Uuid,
    pub kind: JobKind,
    pub status: JobStatus,
    pub created_at: DateTime<Utc>,
    pub updated_at: DateTime<Utc>,
}

struct WorkerItem {
    job_id: Uuid,
    kind: JobKind,
    cancel: CancellationToken,
}

pub struct JobQueue {
    jobs: Arc<RwLock<HashMap<Uuid, Job>>>,
    cancellations: Arc<RwLock<HashMap<Uuid, CancellationToken>>>,
    tx: mpsc::Sender<WorkerItem>,
}

impl JobQueue {
    /// Create a new job queue and spawn `worker_count` background workers.
    ///
    /// The `executor` callback is invoked for each job; it receives the job kind,
    /// a progress-reporting callback, and a cancellation token.
    pub fn new<F>(worker_count: usize, executor: F) -> Arc<Self>
    where
        F: Fn(
                Uuid,
                JobKind,
                CancellationToken,
                Arc<RwLock<HashMap<Uuid, Job>>>,
            ) -> tokio::task::JoinHandle<()>
            + Send
            + Sync
            + 'static,
    {
        let (tx, rx) = mpsc::channel::<WorkerItem>(256);
        let rx = Arc::new(tokio::sync::Mutex::new(rx));
        let jobs: Arc<RwLock<HashMap<Uuid, Job>>> = Arc::new(RwLock::new(HashMap::new()));
        let cancellations: Arc<RwLock<HashMap<Uuid, CancellationToken>>> =
            Arc::new(RwLock::new(HashMap::new()));

        let executor = Arc::new(executor);

        for _ in 0..worker_count {
            let rx = rx.clone();
            let jobs = jobs.clone();
            let cancellations = cancellations.clone();
            let executor = executor.clone();

            tokio::spawn(async move {
                loop {
                    let item = {
                        let mut guard = rx.lock().await;
                        guard.recv().await
                    };
                    let Some(item) = item else { break };

                    // Mark as running
                    {
                        let mut map = jobs.write().await;
                        if let Some(job) = map.get_mut(&item.job_id) {
                            job.status = JobStatus::Running {
                                progress: 0.0,
                                message: "starting".to_string(),
                            };
                            job.updated_at = Utc::now();
                        }
                    }

                    let handle = executor(item.job_id, item.kind, item.cancel, jobs.clone());
                    let _ = handle.await;

                    // Clean up cancellation token
                    cancellations.write().await.remove(&item.job_id);
                }
            });
        }

        Arc::new(Self {
            jobs,
            cancellations,
            tx,
        })
    }

    /// Submit a new job, returning its ID.
    pub async fn submit(&self, kind: JobKind) -> Uuid {
        let id = Uuid::now_v7();
        let now = Utc::now();
        let cancel = CancellationToken::new();

        let job = Job {
            id,
            kind: kind.clone(),
            status: JobStatus::Pending,
            created_at: now,
            updated_at: now,
        };

        self.jobs.write().await.insert(id, job);
        self.cancellations.write().await.insert(id, cancel.clone());

        let item = WorkerItem {
            job_id: id,
            kind,
            cancel,
        };

        // If the channel is full we still record the job — it'll stay Pending
        let _ = self.tx.send(item).await;
        id
    }

    /// Get the status of a job.
    pub async fn status(&self, id: Uuid) -> Option<Job> {
        self.jobs.read().await.get(&id).cloned()
    }

    /// List all jobs, most recent first.
    pub async fn list(&self) -> Vec<Job> {
        let map = self.jobs.read().await;
        let mut jobs: Vec<Job> = map.values().cloned().collect();
        jobs.sort_by_key(|job| std::cmp::Reverse(job.created_at));
        jobs
    }

    /// Cancel a running or pending job.
    pub async fn cancel(&self, id: Uuid) -> bool {
        if let Some(token) = self.cancellations.read().await.get(&id) {
            token.cancel();
            let mut map = self.jobs.write().await;
            if let Some(job) = map.get_mut(&id) {
                job.status = JobStatus::Cancelled;
                job.updated_at = Utc::now();
            }
            true
        } else {
            false
        }
    }

    /// Update a job's progress. Called by executors.
    pub async fn update_progress(
        jobs: &Arc<RwLock<HashMap<Uuid, Job>>>,
        id: Uuid,
        progress: f32,
        message: String,
    ) {
        let mut map = jobs.write().await;
        if let Some(job) = map.get_mut(&id) {
            job.status = JobStatus::Running { progress, message };
            job.updated_at = Utc::now();
        }
    }

    /// Mark a job as completed.
    pub async fn complete(jobs: &Arc<RwLock<HashMap<Uuid, Job>>>, id: Uuid, result: Value) {
        let mut map = jobs.write().await;
        if let Some(job) = map.get_mut(&id) {
            job.status = JobStatus::Completed { result };
            job.updated_at = Utc::now();
        }
    }

    /// Mark a job as failed.
    pub async fn fail(jobs: &Arc<RwLock<HashMap<Uuid, Job>>>, id: Uuid, error: String) {
        let mut map = jobs.write().await;
        if let Some(job) = map.get_mut(&id) {
            job.status = JobStatus::Failed { error };
            job.updated_at = Utc::now();
        }
    }

    /// Get job queue statistics
    pub async fn stats(&self) -> JobQueueStats {
        let jobs = self.jobs.read().await;
        let mut pending = 0;
        let mut running = 0;
        let mut completed = 0;
        let mut failed = 0;

        for job in jobs.values() {
            match job.status {
                JobStatus::Pending => pending += 1,
                JobStatus::Running { .. } => running += 1,
                JobStatus::Completed { .. } => completed += 1,
                JobStatus::Failed { .. } => failed += 1,
                JobStatus::Cancelled => {} // Don't count cancelled jobs
            }
        }

        JobQueueStats {
            pending,
            running,
            completed,
            failed,
            total: jobs.len(),
        }
    }
}

/// Statistics about the job queue
#[derive(Debug, Clone, Default)]
pub struct JobQueueStats {
    pub pending: usize,
    pub running: usize,
    pub completed: usize,
    pub failed: usize,
    pub total: usize,
}