use std::fmt;
use std::time::Duration;

use sea_orm::{ActiveValue::Set, DatabaseConnection};

use shanty_db::entities::download_queue::DownloadStatus;
use shanty_db::entities::wanted_item::WantedStatus;
use shanty_db::queries;

use crate::backend::{BackendConfig, DownloadBackend, DownloadTarget};
use crate::error::{DlError, DlResult};

/// Statistics from a queue processing run.
#[derive(Debug, Default, Clone)]
pub struct DlStats {
    pub downloads_attempted: u64,
    pub downloads_completed: u64,
    pub downloads_failed: u64,
    pub downloads_skipped: u64,
}

impl fmt::Display for DlStats {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(
            f,
            "attempted: {}, completed: {}, failed: {}, skipped: {}",
            self.downloads_attempted,
            self.downloads_completed,
            self.downloads_failed,
            self.downloads_skipped,
        )
    }
}

const MAX_RETRIES: i32 = 3;
const RETRY_DELAYS: [Duration; 3] = [
    Duration::from_secs(30),
    Duration::from_secs(120),
    Duration::from_secs(600),
];

/// Progress callback: (current, total, message).
pub type ProgressFn = Box<dyn Fn(u64, u64, &str) + Send + Sync>;

/// Process all pending items in the download queue.
pub async fn run_queue(
    conn: &DatabaseConnection,
    backend: &impl DownloadBackend,
    config: &BackendConfig,
    dry_run: bool,
) -> DlResult<DlStats> {
    run_queue_with_progress(conn, backend, config, dry_run, None).await
}

/// Process all pending items in the download queue, with optional progress reporting.
pub async fn run_queue_with_progress(
    conn: &DatabaseConnection,
    backend: &impl DownloadBackend,
    config: &BackendConfig,
    dry_run: bool,
    on_progress: Option<ProgressFn>,
) -> DlResult<DlStats> {
    let mut stats = DlStats::default();

    // Count total for progress reporting
    let total = queries::downloads::list(conn, Some(DownloadStatus::Pending))
        .await
        .map(|v| v.len() as u64)
        .unwrap_or(0);

    if let Some(ref cb) = on_progress {
        cb(0, total, "Starting downloads...");
    }

    loop {
        let item = match queries::downloads::get_next_pending(conn).await? {
            Some(item) => item,
            None => break,
        };

        stats.downloads_attempted += 1;

        if let Some(ref cb) = on_progress {
            cb(stats.downloads_attempted, total, &format!("Downloading: {}", item.query));
        }

        tracing::info!(
            id = item.id,
            query = %item.query,
            retry = item.retry_count,
            "processing download"
        );

        if dry_run {
            tracing::info!(id = item.id, query = %item.query, "DRY RUN: would download");
            stats.downloads_skipped += 1;
            // Mark as failed temporarily so we don't loop forever on the same item
            queries::downloads::update_status(
                conn,
                item.id,
                DownloadStatus::Failed,
                Some("dry run"),
            )
            .await?;
            continue;
        }

        // Mark as downloading
        queries::downloads::update_status(conn, item.id, DownloadStatus::Downloading, None)
            .await?;

        // Determine download target
        let target = if let Some(ref url) = item.source_url {
            DownloadTarget::Url(url.clone())
        } else {
            DownloadTarget::Query(item.query.clone())
        };

        // Attempt download
        match backend.download(&target, config).await {
            Ok(result) => {
                tracing::info!(
                    id = item.id,
                    path = %result.file_path.display(),
                    title = %result.title,
                    "download completed"
                );

                queries::downloads::update_status(
                    conn,
                    item.id,
                    DownloadStatus::Completed,
                    None,
                )
                .await?;

                // Update wanted item status and create track record with MBID
                if let Some(wanted_id) = item.wanted_item_id {
                    if let Ok(wanted) = queries::wanted::get_by_id(conn, wanted_id).await {
                        // Create a track record with the MBID so the tagger
                        // can skip searching and go straight to the right recording
                        let now = chrono::Utc::now().naive_utc();
                        let file_path = result.file_path.to_string_lossy().to_string();
                        let file_size = std::fs::metadata(&result.file_path)
                            .map(|m| m.len() as i64)
                            .unwrap_or(0);

                        let track_active = shanty_db::entities::track::ActiveModel {
                            file_path: Set(file_path),
                            title: Set(Some(result.title.clone())),
                            artist: Set(result.artist.clone()),
                            file_size: Set(file_size),
                            musicbrainz_id: Set(wanted.musicbrainz_id.clone()),
                            artist_id: Set(wanted.artist_id),
                            added_at: Set(now),
                            updated_at: Set(now),
                            ..Default::default()
                        };
                        if let Err(e) = queries::tracks::upsert(conn, track_active).await {
                            tracing::warn!(error = %e, "failed to create track record after download");
                        }

                        if let Err(e) = queries::wanted::update_status(
                            conn,
                            wanted_id,
                            WantedStatus::Downloaded,
                        )
                        .await
                        {
                            tracing::warn!(
                                wanted_id = wanted_id,
                                error = %e,
                                "failed to update wanted item status"
                            );
                        }
                    }
                }

                stats.downloads_completed += 1;
            }
            Err(e) => {
                let error_msg = e.to_string();
                tracing::error!(
                    id = item.id,
                    query = %item.query,
                    error = %error_msg,
                    "download failed"
                );

                queries::downloads::update_status(
                    conn,
                    item.id,
                    DownloadStatus::Failed,
                    Some(&error_msg),
                )
                .await?;

                // Auto-retry transient errors
                if e.is_transient() && item.retry_count < MAX_RETRIES {
                    let delay_idx = item.retry_count.min(RETRY_DELAYS.len() as i32 - 1) as usize;
                    let delay = RETRY_DELAYS[delay_idx];
                    tracing::info!(
                        id = item.id,
                        retry = item.retry_count + 1,
                        delay_secs = delay.as_secs(),
                        "scheduling retry"
                    );
                    queries::downloads::retry_failed(conn, item.id).await?;

                    // If rate limited, pause before continuing
                    if matches!(e, DlError::RateLimited(_)) {
                        tracing::warn!("rate limited — pausing queue processing");
                        tokio::time::sleep(delay).await;
                    }
                }

                stats.downloads_failed += 1;
            }
        }
    }

    tracing::info!(%stats, "queue processing complete");
    Ok(stats)
}

/// Sync stats from a queue sync operation.
#[derive(Debug, Default)]
pub struct SyncStats {
    pub found: u64,
    pub enqueued: u64,
    pub skipped: u64,
}

impl fmt::Display for SyncStats {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(
            f,
            "found: {}, enqueued: {}, skipped (already queued): {}",
            self.found, self.enqueued, self.skipped,
        )
    }
}

/// Sync wanted items to the download queue.
/// Finds all Track-type Wanted items and enqueues them for download,
/// skipping any that already have a queue entry.
pub async fn sync_wanted_to_queue(
    conn: &DatabaseConnection,
    dry_run: bool,
) -> DlResult<SyncStats> {
    let wanted = queries::wanted::list(conn, Some(WantedStatus::Wanted)).await?;
    let mut stats = SyncStats::default();

    for item in &wanted {
        stats.found += 1;

        // Build search query from the name + artist
        let artist_name = if let Some(id) = item.artist_id {
            queries::artists::get_by_id(conn, id)
                .await
                .map(|a| a.name)
                .ok()
        } else {
            None
        };

        let query = match artist_name {
            Some(ref artist) if !item.name.is_empty() => format!("{} {}", artist, item.name),
            _ if !item.name.is_empty() => item.name.clone(),
            Some(ref artist) => artist.clone(),
            None => {
                tracing::warn!(id = item.id, "cannot build query — no name or artist");
                continue;
            }
        };

        // Check if already queued
        if let Some(_existing) = queries::downloads::find_by_wanted_item_id(conn, item.id).await? {
            tracing::debug!(id = item.id, name = %item.name, "already in queue, skipping");
            stats.skipped += 1;
            continue;
        }

        if dry_run {
            println!("Would enqueue: {query}");
            stats.enqueued += 1;
            continue;
        }

        queries::downloads::enqueue(conn, &query, Some(item.id), "ytdlp").await?;
        tracing::info!(id = item.id, query = %query, "enqueued for download");
        stats.enqueued += 1;
    }

    tracing::info!(%stats, "sync complete");
    Ok(stats)
}

/// Download a single item directly (not from queue).
pub async fn download_single(
    backend: &impl DownloadBackend,
    target: DownloadTarget,
    config: &BackendConfig,
    dry_run: bool,
) -> DlResult<()> {
    if dry_run {
        match &target {
            DownloadTarget::Url(url) => {
                tracing::info!(url = %url, "DRY RUN: would download URL");
            }
            DownloadTarget::Query(q) => {
                tracing::info!(query = %q, "DRY RUN: would search and download");

                // Still run the search to show what would be downloaded
                let results = backend.search(q).await?;
                if let Some(best) = results.first() {
                    tracing::info!(
                        title = %best.title,
                        artist = ?best.artist,
                        url = %best.url,
                        "would download"
                    );
                } else {
                    tracing::warn!(query = %q, "no results found");
                }
            }
        }
        return Ok(());
    }

    let result = backend.download(&target, config).await?;
    println!(
        "Downloaded: {} → {}",
        result.title,
        result.file_path.display()
    );
    Ok(())
}