// Package db handles the SQLite connection and migrations.
package db

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

	_ "modernc.org/sqlite"
)

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

// Open opens (and creates if needed) the SQLite database at the given path,
// enables performance PRAGMAs, and applies embedded migrations.
func Open(path string) (*sql.DB, error) {
	dsn := fmt.Sprintf("file:%s?_pragma=journal_mode(WAL)&_pragma=foreign_keys(on)&_pragma=synchronous(normal)&_pragma=busy_timeout(5000)", path)
	conn, err := sql.Open("sqlite", dsn)
	if err != nil {
		return nil, fmt.Errorf("open sqlite: %w", err)
	}
	if err := conn.Ping(); err != nil {
		_ = conn.Close()
		return nil, fmt.Errorf("ping sqlite: %w", err)
	}
	if err := migrate(conn); err != nil {
		_ = conn.Close()
		return nil, err
	}
	return conn, nil
}

// migrate applies all embedded *.sql migrations in alphabetical order,
// skipping those already applied. Intentionally minimal in-house system
// (no external dependency).
func migrate(conn *sql.DB) error {
	if _, err := conn.Exec(`CREATE TABLE IF NOT EXISTS schema_migrations (
        name TEXT PRIMARY KEY,
        applied_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now'))
    )`); err != nil {
		return fmt.Errorf("create schema_migrations: %w", err)
	}

	entries, err := migrationsFS.ReadDir("migrations")
	if err != nil {
		return fmt.Errorf("read migrations dir: %w", err)
	}
	names := make([]string, 0, len(entries))
	for _, e := range entries {
		if e.IsDir() || !strings.HasSuffix(e.Name(), ".sql") {
			continue
		}
		names = append(names, e.Name())
	}
	sort.Strings(names)

	for _, name := range names {
		var dummy string
		err := conn.QueryRow(`SELECT name FROM schema_migrations WHERE name = ?`, name).Scan(&dummy)
		if err == nil {
			continue // already applied
		}
		if err != sql.ErrNoRows {
			return fmt.Errorf("check migration %s: %w", name, err)
		}
		content, err := migrationsFS.ReadFile("migrations/" + name)
		if err != nil {
			return fmt.Errorf("read migration %s: %w", name, err)
		}
		tx, err := conn.Begin()
		if err != nil {
			return fmt.Errorf("begin tx for %s: %w", name, err)
		}
		if _, err := tx.Exec(string(content)); err != nil {
			_ = tx.Rollback()
			return fmt.Errorf("apply migration %s: %w", name, err)
		}
		if _, err := tx.Exec(`INSERT INTO schema_migrations(name) VALUES(?)`, name); err != nil {
			_ = tx.Rollback()
			return fmt.Errorf("record migration %s: %w", name, err)
		}
		if err := tx.Commit(); err != nil {
			return fmt.Errorf("commit migration %s: %w", name, err)
		}
	}
	return nil
}