package database

import (
	"context"
	"embed"
	"fmt"
	"io/fs"
	"log"
	"sort"
	"strings"

	"github.com/jackc/pgx/v5/pgxpool"
)

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

func Migrate(ctx context.Context, pool *pgxpool.Pool) error {
	_, err := pool.Exec(ctx, `
		CREATE TABLE IF NOT EXISTS schema_migrations (
			version TEXT PRIMARY KEY,
			applied_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
		)
	`)
	if err != nil {
		return fmt.Errorf("creating migrations table: %w", err)
	}

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

	// Sort by filename to ensure order.
	sort.Slice(entries, func(i, j int) bool {
		return entries[i].Name() < entries[j].Name()
	})

	for _, entry := range entries {
		if entry.IsDir() || !strings.HasSuffix(entry.Name(), ".sql") {
			continue
		}

		version := strings.TrimSuffix(entry.Name(), ".sql")

		var exists bool
		err := pool.QueryRow(ctx, "SELECT EXISTS(SELECT 1 FROM schema_migrations WHERE version = $1)", version).Scan(&exists)
		if err != nil {
			return fmt.Errorf("checking migration %s: %w", version, err)
		}
		if exists {
			continue
		}

		sql, err := migrationsFS.ReadFile("migrations/" + entry.Name())
		if err != nil {
			return fmt.Errorf("reading migration %s: %w", version, err)
		}

		tx, err := pool.Begin(ctx)
		if err != nil {
			return fmt.Errorf("beginning transaction for %s: %w", version, err)
		}

		if _, err := tx.Exec(ctx, string(sql)); err != nil {
			tx.Rollback(ctx)
			return fmt.Errorf("executing migration %s: %w", version, err)
		}

		if _, err := tx.Exec(ctx, "INSERT INTO schema_migrations (version) VALUES ($1)", version); err != nil {
			tx.Rollback(ctx)
			return fmt.Errorf("recording migration %s: %w", version, err)
		}

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

		log.Printf("Applied migration: %s", version)
	}

	return nil
}