//! Peer-to-peer game distribution system.
//!
//! This crate provides the core P2P networking engine for `LanSpread`, handling:
//! - Peer discovery via mDNS
//! - QUIC-based communication
//! - Game file synchronization with chunked transfers
//! - Consensus validation for file integrity

#![allow(clippy::missing_errors_doc)]

// =============================================================================
// Module declarations
// =============================================================================

mod config;
mod context;
mod download;
mod error;
mod events;
mod handlers;
mod identity;
mod install;
mod library;
mod local_games;
mod migration;
mod network;
mod path_validation;
mod peer;
mod peer_db;
mod remote_peer;
mod services;
mod startup;
mod state_paths;
#[cfg(test)]
mod test_support;

// =============================================================================
// Public re-exports
// =============================================================================

use std::{collections::HashSet, net::SocketAddr, path::PathBuf, sync::Arc};

pub use config::{CHUNK_SIZE, MAX_RETRY_COUNT};
pub use error::PeerError;
pub use install::{UnpackFuture, Unpacker};
use lanspread_db::db::{Game, GameFileDescription};
pub use migration::{MigrationReport, migrate_legacy_state};
pub use peer_db::{
    MajorityValidationResult,
    PeerGameDB,
    PeerId,
    PeerInfo,
    PeerSnapshot,
    PeerUpsert,
};
use tokio::sync::{
    RwLock,
    mpsc::{UnboundedReceiver, UnboundedSender},
};
use tokio_util::{sync::CancellationToken, task::TaskTracker};

use crate::{
    context::Ctx,
    handlers::{
        GameDetailSource,
        handle_cancel_download_command,
        handle_connect_peer_command,
        handle_download_game_files_command,
        handle_get_game_command,
        handle_get_peer_count_command,
        handle_install_game_command,
        handle_list_games_command,
        handle_remove_downloaded_game_command,
        handle_set_game_dir_command,
        handle_uninstall_game_command,
        load_local_library,
    },
    state_paths::resolve_state_dir,
};
pub use crate::{startup::PeerRuntimeHandle, state_paths::setup_done_path};

// =============================================================================
// Public API types
// =============================================================================

/// Events sent from the peer system to the UI.
#[derive(Debug, strum::IntoStaticStr)]
pub enum PeerEvent {
    /// The local QUIC server is listening and ready to accept peer connections.
    LocalPeerReady { peer_id: String, addr: SocketAddr },
    /// List of available games from peers.
    ListGames(Vec<Game>),
    /// File descriptions for a specific game.
    GotGameFiles {
        id: String,
        file_descriptions: Vec<GameFileDescription>,
    },
    /// Download has started for a game.
    DownloadGameFilesBegin { id: String },
    /// A file chunk has been downloaded from a peer.
    DownloadGameFileChunkFinished {
        id: String,
        peer_addr: SocketAddr,
        relative_path: String,
        offset: u64,
        length: u64,
    },
    /// Download progress sampled while game files are being received.
    DownloadGameFilesProgress(DownloadProgress),
    /// Download has completed successfully.
    DownloadGameFilesFinished { id: String },
    /// Download has failed.
    DownloadGameFilesFailed { id: String },
    /// All peers with the game have disconnected during download.
    DownloadGameFilesAllPeersGone { id: String },
    /// Install or update transaction has started for a game.
    InstallGameBegin {
        id: String,
        operation: InstallOperation,
    },
    /// Install or update transaction has completed successfully.
    InstallGameFinished { id: String },
    /// Install or update transaction has failed after rollback.
    InstallGameFailed { id: String },
    /// Uninstall transaction has started for a game.
    UninstallGameBegin { id: String },
    /// Uninstall transaction has completed successfully.
    UninstallGameFinished { id: String },
    /// Uninstall transaction has failed after rollback.
    UninstallGameFailed { id: String },
    /// Downloaded archive removal has started for an uninstalled game.
    RemoveDownloadedGameBegin { id: String },
    /// Downloaded archive removal has completed successfully.
    RemoveDownloadedGameFinished { id: String },
    /// Downloaded archive removal has failed before deleting the game root.
    RemoveDownloadedGameFailed { id: String },
    /// No peers have the requested game.
    NoPeersHaveGame { id: String },
    /// A peer has connected.
    PeerConnected(SocketAddr),
    /// A peer has disconnected.
    PeerDisconnected(SocketAddr),
    /// A new peer was discovered via mDNS.
    PeerDiscovered(SocketAddr),
    /// A peer was lost (timed out or disconnected).
    PeerLost(SocketAddr),
    /// The total peer count has changed.
    PeerCountUpdated(usize),
    /// The local library contents changed after a scan.
    LocalLibraryChanged { games: Vec<Game> },
    /// The set of in-progress local operations changed.
    ActiveOperationsChanged {
        active_operations: Vec<ActiveOperation>,
    },
    /// A required peer runtime component failed.
    RuntimeFailed {
        component: PeerRuntimeComponent,
        error: String,
    },
}

/// Sampled byte progress for one active game download.
#[derive(Clone, Debug, PartialEq, Eq, serde::Serialize)]
pub struct DownloadProgress {
    pub id: String,
    pub downloaded_bytes: u64,
    pub total_bytes: u64,
    pub bytes_per_second: u64,
    /// Unique peers currently streaming at least one chunk for this download.
    pub active_peer_count: usize,
}

/// Long-running peer runtime components reported in failure events.
#[derive(Clone, Copy, Debug, strum::IntoStaticStr)]
pub enum PeerRuntimeComponent {
    /// Command/control message loop.
    CommandLoop,
    /// Inbound QUIC server and its mDNS advertisement.
    QuicServer,
    /// mDNS peer discovery.
    Discovery,
    /// Peer liveness monitoring.
    Liveness,
    /// Local game directory monitor.
    LocalMonitor,
}

/// Install-side operation represented in lifecycle events.
#[derive(Clone, Copy, Debug, PartialEq, Eq, strum::IntoStaticStr)]
pub enum InstallOperation {
    /// Fresh install into a missing `local/` directory.
    Installing,
    /// Update that replaces an existing `local/` directory.
    Updating,
}

/// In-progress operation snapshot sent when operation state changes.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct ActiveOperation {
    pub id: String,
    pub operation: ActiveOperationKind,
}

/// Operation kinds visible to UI reconciliation.
#[derive(Clone, Copy, Debug, PartialEq, Eq, strum::IntoStaticStr)]
pub enum ActiveOperationKind {
    /// Downloading or replacing archive files.
    Downloading,
    /// Extracting into a previously uninstalled game root.
    Installing,
    /// Replacing an existing `local/` install.
    Updating,
    /// Removing an existing `local/` install.
    Uninstalling,
    /// Removing downloaded archive files for an uninstalled game.
    RemovingDownload,
}

/// Commands sent to the peer system from the UI.
#[derive(Clone, Debug)]
pub enum PeerCommand {
    /// Request a list of all available games.
    ListGames,
    /// Request file details for a specific game, serving local files when available.
    GetGame(String),
    /// Request the latest peer-advertised file details for an update.
    FetchLatestFromPeers { id: String },
    /// Download game files.
    DownloadGameFiles {
        id: String,
        file_descriptions: Vec<GameFileDescription>,
        account_name: Option<String>,
        language: Option<String>,
    },
    /// Download game files with an explicit install policy.
    DownloadGameFilesWithOptions {
        id: String,
        file_descriptions: Vec<GameFileDescription>,
        install_after_download: bool,
        account_name: Option<String>,
        language: Option<String>,
    },
    /// Install already-downloaded archives into `local/`.
    InstallGame {
        id: String,
        account_name: Option<String>,
        language: Option<String>,
    },
    /// Remove only the `local/` install for a game.
    UninstallGame { id: String },
    /// Remove downloaded archive files for an uninstalled game.
    RemoveDownloadedGame { id: String },
    /// Cancel an active peer download without emitting a user-facing failure.
    CancelDownload { id: String },
    /// Set the local game directory.
    SetGameDir(PathBuf),
    /// Request the current peer count.
    GetPeerCount,
    /// Connect directly to a peer address without waiting for mDNS discovery.
    ConnectPeer(SocketAddr),
}

/// Optional startup settings for non-GUI callers and tests.
#[derive(Clone, Debug, Default)]
pub struct PeerStartOptions {
    /// Directory used for peer identity and other state.
    pub state_dir: Option<PathBuf>,
}

// =============================================================================
// Public API functions
// =============================================================================

/// Initialize and start the peer system.
///
/// This is the main entry point for the peer system. It starts all background
/// services (server, discovery, ping, local monitor) and returns a handle that
/// owns the command sender plus a shutdown signal callers can use for clean
/// teardown.
///
/// # Arguments
///
/// * `game_dir` - Path to the local game directory
/// * `tx_notify_ui` - Channel for sending events to the UI
/// * `peer_game_db` - Shared peer game database
#[allow(clippy::implicit_hasher)]
pub fn start_peer(
    game_dir: impl Into<PathBuf>,
    tx_notify_ui: UnboundedSender<PeerEvent>,
    peer_game_db: Arc<RwLock<PeerGameDB>>,
    unpacker: Arc<dyn Unpacker>,
    catalog: Arc<RwLock<HashSet<String>>>,
) -> eyre::Result<PeerRuntimeHandle> {
    start_peer_with_options(
        game_dir,
        tx_notify_ui,
        peer_game_db,
        unpacker,
        catalog,
        PeerStartOptions::default(),
    )
}

/// Initialize and start the peer system with explicit startup settings.
#[allow(clippy::implicit_hasher)]
pub fn start_peer_with_options(
    game_dir: impl Into<PathBuf>,
    tx_notify_ui: UnboundedSender<PeerEvent>,
    peer_game_db: Arc<RwLock<PeerGameDB>>,
    unpacker: Arc<dyn Unpacker>,
    catalog: Arc<RwLock<HashSet<String>>>,
    options: PeerStartOptions,
) -> eyre::Result<PeerRuntimeHandle> {
    let PeerStartOptions { state_dir } = options;
    let state_dir = resolve_state_dir(state_dir.as_deref());
    let game_dir = game_dir.into();
    log::info!(
        "Starting peer system with game directory: {}",
        game_dir.display()
    );
    let peer_id = identity::load_or_create_peer_id(&state_dir)?;

    let (tx_control, rx_control) = tokio::sync::mpsc::unbounded_channel();

    Ok(startup::spawn_peer_runtime(
        tx_control,
        rx_control,
        tx_notify_ui,
        peer_game_db,
        peer_id,
        game_dir,
        state_dir,
        unpacker,
        catalog,
    ))
}

/// Main peer execution loop that handles peer commands and manages the peer system.
#[allow(clippy::too_many_arguments, clippy::implicit_hasher)]
async fn run_peer(
    mut rx_control: UnboundedReceiver<PeerCommand>,
    tx_notify_ui: UnboundedSender<PeerEvent>,
    peer_game_db: Arc<RwLock<PeerGameDB>>,
    peer_id: String,
    game_dir: PathBuf,
    state_dir: PathBuf,
    unpacker: Arc<dyn Unpacker>,
    shutdown: CancellationToken,
    task_tracker: TaskTracker,
    catalog: Arc<RwLock<HashSet<String>>>,
) -> eyre::Result<()> {
    let ctx = Ctx::new(
        peer_game_db,
        peer_id,
        game_dir,
        state_dir,
        unpacker,
        shutdown,
        task_tracker,
        catalog,
    );
    if let Err(err) = load_local_library(&ctx, &tx_notify_ui).await {
        log::error!("Failed to load initial local game database: {err}");
    }
    startup::spawn_startup_services(&ctx, &tx_notify_ui);
    if let Err(err) = handle_peer_commands(&ctx, &tx_notify_ui, &mut rx_control).await {
        let error = err.to_string();
        log::error!("Peer command loop failed: {error}");
        events::send(
            &tx_notify_ui,
            PeerEvent::RuntimeFailed {
                component: PeerRuntimeComponent::CommandLoop,
                error,
            },
        );
        ctx.shutdown.cancel();
    }
    startup::send_goodbye_notifications(&ctx).await;

    Ok(())
}

async fn handle_peer_commands(
    ctx: &Ctx,
    tx_notify_ui: &UnboundedSender<PeerEvent>,
    rx_control: &mut UnboundedReceiver<PeerCommand>,
) -> eyre::Result<()> {
    loop {
        let cmd = tokio::select! {
            () = ctx.shutdown.cancelled() => return Ok(()),
            cmd = rx_control.recv() => cmd,
        };

        let Some(cmd) = cmd else {
            if ctx.shutdown.is_cancelled() {
                return Ok(());
            }
            eyre::bail!("peer command channel closed unexpectedly");
        };

        match cmd {
            PeerCommand::ListGames => {
                handle_list_games_command(ctx, tx_notify_ui).await;
            }
            PeerCommand::GetGame(id) => {
                handle_get_game_command(ctx, tx_notify_ui, id, GameDetailSource::LocalOrPeers)
                    .await;
            }
            PeerCommand::FetchLatestFromPeers { id } => {
                handle_get_game_command(ctx, tx_notify_ui, id, GameDetailSource::LatestPeersOnly)
                    .await;
            }
            PeerCommand::DownloadGameFiles {
                id,
                file_descriptions,
                account_name,
                language,
            } => {
                handle_download_game_files_command(
                    ctx,
                    tx_notify_ui,
                    id,
                    file_descriptions,
                    true,
                    account_name,
                    language,
                )
                .await;
            }
            PeerCommand::DownloadGameFilesWithOptions {
                id,
                file_descriptions,
                install_after_download,
                account_name,
                language,
            } => {
                handle_download_game_files_command(
                    ctx,
                    tx_notify_ui,
                    id,
                    file_descriptions,
                    install_after_download,
                    account_name,
                    language,
                )
                .await;
            }
            PeerCommand::InstallGame {
                id,
                account_name,
                language,
            } => {
                handle_install_game_command(ctx, tx_notify_ui, id, account_name, language).await;
            }
            PeerCommand::UninstallGame { id } => {
                handle_uninstall_game_command(ctx, tx_notify_ui, id).await;
            }
            PeerCommand::RemoveDownloadedGame { id } => {
                handle_remove_downloaded_game_command(ctx, tx_notify_ui, id).await;
            }
            PeerCommand::CancelDownload { id } => {
                handle_cancel_download_command(ctx, tx_notify_ui, id).await;
            }
            PeerCommand::SetGameDir(game_dir) => {
                handle_set_game_dir_command(ctx, tx_notify_ui, game_dir).await;
            }
            PeerCommand::GetPeerCount => {
                handle_get_peer_count_command(ctx, tx_notify_ui).await;
            }
            PeerCommand::ConnectPeer(addr) => {
                handle_connect_peer_command(ctx, tx_notify_ui, addr).await;
            }
        }
    }
}