// server/db.rs — Database connection pool and migrations
//
// This module provides two functions called once at server startup:
//   - `create_pool`    : opens a connection pool to the database
//   - `run_migrations` : applies all pending SQL migrations
//
// `AnyPool` lets the same Rust code target both SQLite (dev) and
// PostgreSQL (production) — only DATABASE_URL changes.

use sqlx::AnyPool;
use thiserror::Error;

use crate::server::config::{AppConfig, DatabaseBackend};

// ─── Errors ───────────────────────────────────────────────────────────────────

#[derive(Debug, Error)]
pub enum DbError {
    #[error("Database connection failed: {0}")]
    Connection(#[from] sqlx::Error),

    #[error("Migration failed: {0}")]
    Migration(#[from] sqlx::migrate::MigrateError),

    #[error("Record not found: {0}")]
    NotFound(String),
}

// ─── Pool creation ────────────────────────────────────────────────────────────

/// Opens a connection pool to the database specified in `config.database_url`.
///
/// A pool maintains multiple open connections so concurrent requests
/// do not block each other waiting for a single connection.
///
/// `install_default_drivers()` must be called before `AnyPool::connect`
/// to register both the SQLite and PostgreSQL drivers in the `Any` registry.
///
/// For SQLite, this function also creates the database file and its parent
/// directory if they do not exist yet. The `AnyPool` driver cannot create
/// a new SQLite file by itself — unlike the `SqlitePool` which has an
/// explicit `create_if_missing` option.
pub async fn create_pool(config: &AppConfig) -> Result<AnyPool, DbError> {
    // Register SQLite and PostgreSQL drivers so `AnyPool` can dispatch
    // to the correct one based on the URL scheme (sqlite:// vs postgres://).
    sqlx::any::install_default_drivers();

    // SQLite-specific setup: ensure the file exists before connecting.
    //
    // `AnyPool` does not expose `create_if_missing` like `SqlitePool` does,
    // so we must touch the file ourselves.
    //
    // The URL is parsed the same way SQLx does it internally:
    //   sqlite://data/ipam.db → strip sqlite:// → path = data/ipam.db
    if let DatabaseBackend::Sqlite = &config.backend {
        // Strip both possible prefixes (SQLx accepts both forms)
        let path_str = config
            .database_url
            .trim_start_matches("sqlite://")
            .trim_start_matches("sqlite:");

        // Skip special filenames (in-memory, shared cache)
        if path_str != ":memory:" && !path_str.is_empty() {
            let path = std::path::Path::new(path_str);

            // Create the parent directory if it does not exist
            if let Some(parent) = path.parent() {
                if !parent.as_os_str().is_empty() {
                    std::fs::create_dir_all(parent)
                        .map_err(|e| sqlx::Error::Io(e))?;
                }
            }

            // Create an empty file so SQLite can open it
            if !path.exists() {
                std::fs::File::create(path)
                    .map_err(|e| sqlx::Error::Io(e))?;
            }
        }
    }

    let pool = AnyPool::connect(&config.database_url).await?;
    Ok(pool)
}

// ─── Migrations ───────────────────────────────────────────────────────────────

/// Applies all pending migrations from the directory matching the active backend.
///
/// Two separate directories handle SQL syntax differences:
///   - `migrations/sqlite/`   : uses `INTEGER PRIMARY KEY AUTOINCREMENT`
///   - `migrations/postgres/` : uses `BIGSERIAL PRIMARY KEY`
///
/// SQLx tracks applied migrations in a `_sqlx_migrations` table, so running
/// this function on an already-migrated database is always safe (idempotent).
///
/// `sqlx::migrate!("path")` is a compile-time macro: it embeds all `.sql`
/// files from the given path directly into the binary. The path is relative
/// to the project root (where Cargo.toml lives).
pub async fn run_migrations(pool: &AnyPool, backend: &DatabaseBackend) -> Result<(), DbError> {
    match backend {
        DatabaseBackend::Sqlite => {
            sqlx::migrate!("migrations/sqlite").run(pool).await?;
        }
        DatabaseBackend::Postgres => {
            sqlx::migrate!("migrations/postgres").run(pool).await?;
        }
    }
    Ok(())
}