package database

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

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

func ApplyMigrations(ctx context.Context, db *sql.DB) error {
	if _, err := db.ExecContext(ctx, `
		CREATE TABLE IF NOT EXISTS schema_migrations (
			version TEXT PRIMARY KEY,
			applied_at TEXT NOT NULL
		);
	`); err != nil {
		return fmt.Errorf("ensure schema_migrations: %w", err)
	}

	entries, err := fs.ReadDir(migrationFiles, "migrations")
	if err != nil {
		return fmt.Errorf("read migrations: %w", err)
	}

	var names []string
	for _, entry := range entries {
		if entry.IsDir() || !strings.HasSuffix(entry.Name(), ".up.sql") {
			continue
		}
		names = append(names, entry.Name())
	}
	sort.Strings(names)

	for _, name := range names {
		applied, err := migrationApplied(ctx, db, name)
		if err != nil {
			return err
		}
		if applied {
			continue
		}

		body, err := migrationFiles.ReadFile("migrations/" + name)
		if err != nil {
			return fmt.Errorf("read migration %s: %w", name, err)
		}

		tx, err := db.BeginTx(ctx, nil)
		if err != nil {
			return fmt.Errorf("begin migration %s: %w", name, err)
		}

		for _, statement := range splitStatements(string(body)) {
			if _, err := tx.ExecContext(ctx, statement); err != nil {
				_ = tx.Rollback()
				return fmt.Errorf("execute migration %s: %w", name, err)
			}
		}

		if _, err := tx.ExecContext(ctx, `INSERT INTO schema_migrations(version, applied_at) VALUES (?, datetime('now'))`, 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
}

func migrationApplied(ctx context.Context, db *sql.DB, version string) (bool, error) {
	var count int
	if err := db.QueryRowContext(ctx, `SELECT COUNT(1) FROM schema_migrations WHERE version = ?`, version).Scan(&count); err != nil {
		return false, fmt.Errorf("lookup migration %s: %w", version, err)
	}
	return count > 0, nil
}

func splitStatements(body string) []string {
	raw := strings.Split(body, ";")
	statements := make([]string, 0, len(raw))
	for _, statement := range raw {
		statement = strings.TrimSpace(statement)
		if statement == "" {
			continue
		}
		statements = append(statements, statement)
	}
	return statements
}