//! The SQLite pool. Every connection sets `foreign_keys = ON`, `journal_mode = WAL`, `synchronous = NORMAL` and
//! `busy_timeout = 5000` (SPEC §8.9).

use std::path::Path;
use std::time::Duration;

use sqlx::sqlite::{SqliteConnectOptions, SqliteJournalMode, SqlitePoolOptions, SqliteSynchronous};
use sqlx::{Sqlite, SqlitePool, Transaction};

use crate::error::AppError;

/// The pool type used everywhere.
pub type Db = SqlitePool;

/// `busy_timeout` (SPEC §8.9).
pub const BUSY_TIMEOUT: Duration = Duration::from_millis(5000);

/// At most this many connections; two users and one writer at a time need few.
const MAX_CONNECTIONS: u32 = 4;

/// The connect options for the database file at `path` (created if missing).
pub fn options(path: &Path) -> SqliteConnectOptions {
    SqliteConnectOptions::new()
        .filename(path)
        .create_if_missing(true)
        .foreign_keys(true)
        .journal_mode(SqliteJournalMode::Wal)
        .synchronous(SqliteSynchronous::Normal)
        .busy_timeout(BUSY_TIMEOUT)
}

/// Opens the pool for the database file at `path`. The parent directory must exist.
pub async fn connect(path: &Path) -> Result<Db, AppError> {
    let pool = SqlitePoolOptions::new()
        .max_connections(MAX_CONNECTIONS)
        .acquire_timeout(BUSY_TIMEOUT)
        .connect_with(options(path))
        .await?;
    Ok(pool)
}

/// Starts a write transaction with `BEGIN IMMEDIATE` (SPEC §14.1: every write transaction does).
pub async fn begin_immediate(db: &Db) -> Result<Transaction<'static, Sqlite>, AppError> {
    Ok(db.begin_with("BEGIN IMMEDIATE").await?)
}