package migrations

import (
	"context"
	"database/sql"
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"
)

const migrationTableSQL = `CREATE TABLE IF NOT EXISTS schema_migrations (
    version TEXT PRIMARY KEY,
    applied_at TIMESTAMPTZ NOT NULL DEFAULT now()
)`

// Apply executes numbered SQL files in lexical order. A transaction-level
// advisory lock serializes concurrent API/worker starts, while each migration
// is committed together with its schema_migrations marker so a failed
// migration can be retried safely.
func Apply(ctx context.Context, db *sql.DB, directory string) error {
	if db == nil || strings.TrimSpace(directory) == "" {
		return fmt.Errorf("database and migration directory are required")
	}
	paths, err := filepath.Glob(filepath.Join(directory, "*.sql"))
	if err != nil {
		return fmt.Errorf("find migrations: %w", err)
	}
	sort.Slice(paths, func(i, j int) bool { return filepath.Base(paths[i]) < filepath.Base(paths[j]) })
	if len(paths) == 0 {
		return fmt.Errorf("no migrations found in %s", directory)
	}
	if _, err := db.ExecContext(ctx, migrationTableSQL); err != nil {
		return fmt.Errorf("create migration table: %w", err)
	}
	for _, path := range paths {
		version := filepath.Base(path)
		sqlBytes, err := os.ReadFile(path)
		if err != nil {
			return fmt.Errorf("read migration %s: %w", version, err)
		}
		tx, err := db.BeginTx(ctx, nil)
		if err != nil {
			return fmt.Errorf("begin migration %s: %w", version, err)
		}
		committed := false
		defer func() {
			if !committed {
				_ = tx.Rollback()
			}
		}()
		if _, err := tx.ExecContext(ctx, `SELECT pg_advisory_xact_lock(hashtext('cosmic-clash:migrations'))`); err != nil {
			return fmt.Errorf("lock migration %s: %w", version, err)
		}
		var applied bool
		if err := tx.QueryRowContext(ctx, `SELECT EXISTS (SELECT 1 FROM schema_migrations WHERE version = $1)`, version).Scan(&applied); err != nil {
			return fmt.Errorf("check migration %s: %w", version, err)
		}
		if !applied {
			if _, err := tx.ExecContext(ctx, string(sqlBytes)); err != nil {
				return fmt.Errorf("apply migration %s: %w", version, err)
			}
			if _, err := tx.ExecContext(ctx, `INSERT INTO schema_migrations (version) VALUES ($1)`, version); err != nil {
				return fmt.Errorf("record migration %s: %w", version, err)
			}
		}
		if err := tx.Commit(); err != nil {
			return fmt.Errorf("commit migration %s: %w", version, err)
		}
		committed = true
	}
	return nil
}

// Rollback reverses the `steps` most recently applied migrations, newest
// first, by running each one's down file from the `down/` subdirectory of
// `directory` (e.g. `down/0006_match_allocation_claims.sql` undoes
// `0006_match_allocation_claims.sql`) and deleting its schema_migrations
// marker. Each rollback is committed in its own transaction, same as Apply,
// so a failure partway through leaves the schema at a consistent, resumable
// state rather than a half-applied one. A missing down file for a migration
// being rolled back is a hard error — better a stuck rollback than a schema
// silently left half-reversed.
func Rollback(ctx context.Context, db *sql.DB, directory string, steps int) error {
	if db == nil || strings.TrimSpace(directory) == "" || steps <= 0 {
		return fmt.Errorf("database, migration directory and a positive step count are required")
	}
	if _, err := db.ExecContext(ctx, migrationTableSQL); err != nil {
		return fmt.Errorf("create migration table: %w", err)
	}
	rows, err := db.QueryContext(ctx, `SELECT version FROM schema_migrations ORDER BY version DESC LIMIT $1`, steps)
	if err != nil {
		return fmt.Errorf("list applied migrations: %w", err)
	}
	var versions []string
	for rows.Next() {
		var version string
		if err := rows.Scan(&version); err != nil {
			rows.Close()
			return fmt.Errorf("scan applied migration: %w", err)
		}
		versions = append(versions, version)
	}
	if err := rows.Err(); err != nil {
		return fmt.Errorf("list applied migrations: %w", err)
	}
	if err := rows.Close(); err != nil {
		return fmt.Errorf("list applied migrations: %w", err)
	}
	for _, version := range versions {
		sqlBytes, err := os.ReadFile(filepath.Join(directory, "down", version))
		if err != nil {
			return fmt.Errorf("read down migration for %s: %w", version, err)
		}
		tx, err := db.BeginTx(ctx, nil)
		if err != nil {
			return fmt.Errorf("begin rollback %s: %w", version, err)
		}
		committed := false
		defer func() {
			if !committed {
				_ = tx.Rollback()
			}
		}()
		if _, err := tx.ExecContext(ctx, `SELECT pg_advisory_xact_lock(hashtext('cosmic-clash:migrations'))`); err != nil {
			return fmt.Errorf("lock rollback %s: %w", version, err)
		}
		var applied bool
		if err := tx.QueryRowContext(ctx, `SELECT EXISTS (SELECT 1 FROM schema_migrations WHERE version = $1)`, version).Scan(&applied); err != nil {
			return fmt.Errorf("check rollback %s: %w", version, err)
		}
		if applied {
			if _, err := tx.ExecContext(ctx, string(sqlBytes)); err != nil {
				return fmt.Errorf("apply down migration %s: %w", version, err)
			}
			if _, err := tx.ExecContext(ctx, `DELETE FROM schema_migrations WHERE version = $1`, version); err != nil {
				return fmt.Errorf("unrecord migration %s: %w", version, err)
			}
		}
		if err := tx.Commit(); err != nil {
			return fmt.Errorf("commit rollback %s: %w", version, err)
		}
		committed = true
	}
	return nil
}