// Package database owns the SQLite connection, pragmas, and migrations.
package database

import (
	"database/sql"
	"embed"
	"fmt"
	"io/fs"
	"sort"
	"strings"

	_ "modernc.org/sqlite"
)

//go:embed migrations/*.sql
var migrationsFS embed.FS

// Open opens (creating if needed) the SQLite database at path, applies
// pragmas suited for a long-running server (WAL, foreign keys, busy
// timeout), and runs any pending migrations.
func Open(path string) (*sql.DB, error) {
	dsn := fmt.Sprintf("file:%s?_pragma=busy_timeout(5000)", path)
	db, err := sql.Open("sqlite", dsn)
	if err != nil {
		return nil, err
	}
	// SQLite only tolerates a single writer; keep the pool modest so
	// writers serialize instead of colliding on SQLITE_BUSY.
	db.SetMaxOpenConns(8)

	pragmas := []string{
		"PRAGMA journal_mode=WAL",
		"PRAGMA synchronous=NORMAL",
		"PRAGMA foreign_keys=ON",
		"PRAGMA busy_timeout=5000",
	}
	for _, p := range pragmas {
		if _, err := db.Exec(p); err != nil {
			db.Close()
			return nil, fmt.Errorf("pragma %q: %w", p, err)
		}
	}

	if err := migrate(db); err != nil {
		db.Close()
		return nil, fmt.Errorf("migrate: %w", err)
	}
	return db, nil
}

func migrate(db *sql.DB) error {
	if _, err := db.Exec(`CREATE TABLE IF NOT EXISTS schema_migrations (
		version TEXT PRIMARY KEY,
		applied_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ','now'))
	)`); err != nil {
		return err
	}

	entries, err := fs.ReadDir(migrationsFS, "migrations")
	if err != nil {
		return err
	}
	var names []string
	for _, e := range entries {
		if !e.IsDir() && strings.HasSuffix(e.Name(), ".sql") {
			names = append(names, e.Name())
		}
	}
	sort.Strings(names)

	for _, name := range names {
		var applied int
		if err := db.QueryRow(`SELECT COUNT(*) FROM schema_migrations WHERE version = ?`, name).Scan(&applied); err != nil {
			return err
		}
		if applied > 0 {
			continue
		}
		content, err := migrationsFS.ReadFile("migrations/" + name)
		if err != nil {
			return err
		}
		tx, err := db.Begin()
		if err != nil {
			return err
		}
		if _, err := tx.Exec(string(content)); err != nil {
			tx.Rollback()
			return fmt.Errorf("applying %s: %w", name, err)
		}
		if _, err := tx.Exec(`INSERT INTO schema_migrations (version) VALUES (?)`, name); err != nil {
			tx.Rollback()
			return err
		}
		if err := tx.Commit(); err != nil {
			return err
		}
	}
	return nil
}