use sqlx::{SqlitePool, sqlite::SqlitePoolOptions};
use std::path::Path;

/// Creates and initializes a connection pool to the SQLite database.
///
/// This function:
/// - Creates the database file if it doesn't exist
/// - Ensures parent directories are created
/// - Configures a connection pool with max 5 connections
/// - Enables foreign key constraints for referential integrity
/// - Runs database migrations to set up the schema
///
/// # Arguments
/// * `db_path` - Path to the SQLite database file (e.g., "pickleball.db")
///
/// # Returns
/// * `Ok(SqlitePool)` - Initialized connection pool ready to use
/// * `Err(sqlx::Error)` - If connection or migration fails
pub async fn create_pool(db_path: &str) -> Result<SqlitePool, sqlx::Error> {
    // Create database file if it doesn't exist
    let path = Path::new(db_path);
    let db_exists = path.exists();
    
    // Ensure parent directory exists
    if let Some(parent) = path.parent() {
        std::fs::create_dir_all(parent).ok();
    }
    
    // Create connection pool with correct SQLite connection string
    let pool = SqlitePoolOptions::new()
        .max_connections(5)
        .connect(&format!("sqlite://{}?mode=rwc", db_path))
        .await?;
    
    // Enable foreign keys
    sqlx::query("PRAGMA foreign_keys = ON")
        .execute(&pool)
        .await?;
    
    // Run migrations
    run_migrations(&pool).await?;
    
    Ok(pool)
}

/// Runs database migrations to create tables and indexes if they don't exist.
///
/// Creates the following schema:
/// - **players**: Stores player profiles with separate singles/doubles Glicko2 ratings
/// - **sessions**: Tracks play sessions with optional summaries
/// - **matches**: Individual matches within sessions (singles or doubles)
/// - **match_participants**: Records each player's performance in a match with before/after ratings
///
/// All tables include foreign keys and appropriate indexes for query performance.
/// Idempotent - safe to call multiple times.
pub async fn run_migrations(pool: &SqlitePool) -> Result<(), sqlx::Error> {
    let schema = include_str!("../../migrations/001_initial_schema.sql");
    
    // Execute each statement
    let statements = vec![
        "PRAGMA foreign_keys = ON",
        // Players table: Stores player profiles with separate Glicko2 ratings for singles and doubles
        // Each player maintains independent rating systems since skill in singles vs doubles may differ
        "CREATE TABLE IF NOT EXISTS players (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            name TEXT NOT NULL UNIQUE,
            email TEXT,
            -- Glicko2 Rating: Skill estimate (1500 = average)
            singles_rating REAL NOT NULL DEFAULT 1500.0,
            -- Glicko2 RD (Rating Deviation): Confidence in rating (lower = more confident; ~30 = highly confident)
            singles_rd REAL NOT NULL DEFAULT 350.0,
            -- Glicko2 Volatility: Unpredictability of performance (0.06 = starting volatility)
            singles_volatility REAL NOT NULL DEFAULT 0.06,
            doubles_rating REAL NOT NULL DEFAULT 1500.0,
            doubles_rd REAL NOT NULL DEFAULT 350.0,
            doubles_volatility REAL NOT NULL DEFAULT 0.06,
            created_at TEXT NOT NULL DEFAULT (datetime('now')),
            last_played TEXT NOT NULL DEFAULT (datetime('now'))
        )",
        // Sessions table: Groups matches that occurred during a play session
        "CREATE TABLE IF NOT EXISTS sessions (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            start_time TEXT NOT NULL DEFAULT (datetime('now')),
            end_time TEXT,
            summary_sent BOOLEAN NOT NULL DEFAULT 0,
            notes TEXT
        )",
        // Matches table: Individual games (singles or doubles) within a session
        "CREATE TABLE IF NOT EXISTS matches (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            session_id INTEGER NOT NULL,
            match_type TEXT NOT NULL CHECK(match_type IN ('singles', 'doubles')),
            timestamp TEXT NOT NULL DEFAULT (datetime('now')),
            team1_score INTEGER NOT NULL,
            team2_score INTEGER NOT NULL,
            FOREIGN KEY (session_id) REFERENCES sessions(id) ON DELETE CASCADE
        )",
        // Match participants table: Records each player's participation and rating changes per match
        // Stores before/after ratings to allow recalculation and audit trails
        "CREATE TABLE IF NOT EXISTS match_participants (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            match_id INTEGER NOT NULL,
            player_id INTEGER NOT NULL,
            team INTEGER NOT NULL CHECK(team IN (1, 2)),
            -- Rating state before match
            rating_before REAL NOT NULL,
            rd_before REAL NOT NULL,
            volatility_before REAL NOT NULL,
            -- Rating state after Glicko2 calculation
            rating_after REAL NOT NULL,
            rd_after REAL NOT NULL,
            volatility_after REAL NOT NULL,
            -- Net change in rating from this match
            rating_change REAL NOT NULL,
            FOREIGN KEY (match_id) REFERENCES matches(id) ON DELETE CASCADE,
            FOREIGN KEY (player_id) REFERENCES players(id) ON DELETE CASCADE
        )",
        // Indexes for query performance
        "CREATE INDEX IF NOT EXISTS idx_matches_session ON matches(session_id)",
        "CREATE INDEX IF NOT EXISTS idx_matches_timestamp ON matches(timestamp DESC)",
        "CREATE INDEX IF NOT EXISTS idx_participants_match ON match_participants(match_id)",
        "CREATE INDEX IF NOT EXISTS idx_participants_player ON match_participants(player_id)",
        "CREATE INDEX IF NOT EXISTS idx_players_name ON players(name)",
        "CREATE INDEX IF NOT EXISTS idx_players_singles_rating ON players(singles_rating DESC)",
        "CREATE INDEX IF NOT EXISTS idx_players_doubles_rating ON players(doubles_rating DESC)",
    ];
    
    for statement in &statements {
        if !statement.trim().is_empty() {
            match sqlx::query(statement).execute(pool).await {
                Ok(_) => {},
                Err(e) => {
                    // Ignore "table already exists" errors
                    if !e.to_string().contains("already exists") {
                        eprintln!("Migration error: {}", e);
                    }
                }
            }
        }
    }
    
    Ok(())
}