package postgres

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

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

const migrationLockID int64 = 674301

func Migrate(ctx context.Context, database Database) (err error) {
	tx, err := database.Begin(ctx)
	if err != nil {
		return fmt.Errorf("begin migrations: %w", err)
	}
	defer func() {
		if err != nil {
			_ = tx.Rollback(ctx)
		}
	}()

	if _, err = tx.Exec(ctx, "SELECT pg_advisory_xact_lock($1)", migrationLockID); err != nil {
		return fmt.Errorf("lock migrations: %w", err)
	}
	if _, err = tx.Exec(ctx, `CREATE TABLE IF NOT EXISTS ledger_schema_migrations (
        version bigint PRIMARY KEY,
        applied_at timestamptz NOT NULL DEFAULT clock_timestamp()
    )`); err != nil {
		return fmt.Errorf("create migration ledger: %w", err)
	}

	files, err := fs.Glob(migrationFiles, "migrations/*.up.sql")
	if err != nil {
		return fmt.Errorf("list migrations: %w", err)
	}
	sort.Strings(files)
	for _, name := range files {
		versionText := strings.SplitN(strings.TrimPrefix(name, "migrations/"), "_", 2)[0]
		version, parseErr := strconv.ParseInt(versionText, 10, 64)
		if parseErr != nil {
			return fmt.Errorf("parse migration %s: %w", name, parseErr)
		}

		var applied bool
		if err = tx.QueryRow(ctx, "SELECT EXISTS (SELECT 1 FROM ledger_schema_migrations WHERE version = $1)", version).Scan(&applied); err != nil {
			return fmt.Errorf("check migration %s: %w", name, err)
		}
		if applied {
			continue
		}

		contents, readErr := migrationFiles.ReadFile(name)
		if readErr != nil {
			return fmt.Errorf("read migration %s: %w", name, readErr)
		}
		if _, err = tx.Exec(ctx, string(contents)); err != nil {
			return fmt.Errorf("apply migration %s: %w", name, err)
		}
		if _, err = tx.Exec(ctx, "INSERT INTO ledger_schema_migrations (version) VALUES ($1) ON CONFLICT DO NOTHING", version); err != nil {
			return fmt.Errorf("record migration %s: %w", name, err)
		}
	}

	if err = tx.Commit(ctx); err != nil {
		return fmt.Errorf("commit migrations: %w", err)
	}
	return nil
}