package fn_operations

import (
	"database/sql"
	"embed"
	"fmt"
	"path"
	"sort"
	"strconv"
	"strings"
	"time"
)

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

const migrationTableSQL = `
CREATE TABLE IF NOT EXISTS schema_migrations (
	version    INTEGER PRIMARY KEY,
	name       TEXT NOT NULL,
	applied_at TEXT NOT NULL
);`

// migrate applies pending migrations to the database.
func migrate(conn *sql.DB) error {
	if _, err := conn.Exec(migrationTableSQL); err != nil {
		return fmt.Errorf("creating schema_migrations table: %w", err)
	}

	current, err := currentVersion(conn)
	if err != nil {
		return err
	}

	files, err := listMigrations()
	if err != nil {
		return err
	}

	for _, mf := range files {
		if mf.version <= current {
			continue
		}

		content, err := migrationsFS.ReadFile(path.Join("migrations", mf.filename))
		if err != nil {
			return fmt.Errorf("reading migration %s: %w", mf.filename, err)
		}

		tx, err := conn.Begin()
		if err != nil {
			return fmt.Errorf("beginning transaction for migration %d: %w", mf.version, err)
		}

		if _, err := tx.Exec(string(content)); err != nil {
			tx.Rollback()
			return fmt.Errorf("applying migration %s: %w", mf.filename, err)
		}

		if _, err := tx.Exec(
			"INSERT INTO schema_migrations (version, name, applied_at) VALUES (?, ?, ?)",
			mf.version, mf.filename, time.Now().UTC().Format(time.RFC3339),
		); err != nil {
			tx.Rollback()
			return fmt.Errorf("recording migration %s: %w", mf.filename, err)
		}

		if err := tx.Commit(); err != nil {
			return fmt.Errorf("committing migration %s: %w", mf.filename, err)
		}
	}

	return nil
}

func currentVersion(conn *sql.DB) (int, error) {
	var v int
	err := conn.QueryRow("SELECT COALESCE(MAX(version), 0) FROM schema_migrations").Scan(&v)
	if err != nil {
		return 0, fmt.Errorf("reading current schema version: %w", err)
	}
	return v, nil
}

type migrationFile struct {
	version  int
	filename string
}

func listMigrations() ([]migrationFile, error) {
	entries, err := migrationsFS.ReadDir("migrations")
	if err != nil {
		return nil, fmt.Errorf("reading migrations directory: %w", err)
	}

	var files []migrationFile
	for _, e := range entries {
		if e.IsDir() || !strings.HasSuffix(e.Name(), ".sql") {
			continue
		}
		parts := strings.SplitN(e.Name(), "_", 2)
		if len(parts) < 2 {
			continue
		}
		v, err := strconv.Atoi(parts[0])
		if err != nil {
			continue
		}
		files = append(files, migrationFile{version: v, filename: e.Name()})
	}

	sort.Slice(files, func(i, j int) bool {
		return files[i].version < files[j].version
	})

	return files, nil
}