package migration

import (
	"context"

	"github.com/pkg/errors"
)

var (
	ErrNoAvailableMigration = errors.New("no available migration")
	ErrMigrationNotFound    = errors.New("migration not found")
)

type Manager struct {
	migrations []Migration
	resolver   VersionResolver
}

func (m *Manager) Up(ctx context.Context) error {
	currentVersion, err := m.resolver.Current(ctx)
	if err != nil {
		return errors.Wrap(err, "could not retrieve current version")
	}

	migrate := func(up Migration) error {
		if err := up.Up(ctx); err != nil {
			return errors.Wrapf(err, "could not apply '%s' up migration", up.Version())
		}

		if err := m.resolver.Set(ctx, up.Version()); err != nil {
			return errors.Wrapf(err, "could not update schema version to '%s'", up.Version())
		}

		return nil
	}

	if currentVersion == "" {
		up := m.migrations[0]

		return migrate(up)
	}

	for i, mi := range m.migrations {
		if mi.Version() != currentVersion && currentVersion != "" {
			continue
		}

		// Already at latest, do nothing
		if i >= len(m.migrations)-1 {
			return nil
		}

		up := m.migrations[i+1]

		return migrate(up)
	}

	return errors.WithStack(ErrMigrationNotFound)
}

func (m *Manager) Down(ctx context.Context) error {
	currentVersion, err := m.resolver.Current(ctx)
	if err != nil {
		return errors.Wrap(err, "could not retrieve current version")
	}

	for i, mi := range m.migrations {
		if mi.Version() != currentVersion {
			continue
		}

		if err := mi.Down(ctx); err != nil {
			return errors.Wrapf(err, "could not apply '%s' down migration", mi.Version())
		}

		var version string

		// Already at oldest, do nothing
		if i != 0 {
			down := m.migrations[i-1]
			version = down.Version()
		}

		if err := m.resolver.Set(ctx, version); err != nil {
			return errors.Wrapf(err, "could not update schema version to '%s'", version)
		}

		return nil
	}

	return errors.WithStack(ErrMigrationNotFound)
}

func (m *Manager) Latest(ctx context.Context) error {
	for {
		isLatest, err := m.IsLatest(ctx)
		if err != nil {
			return errors.Wrap(err, "could not retrieve schema state")
		}

		if isLatest {
			return nil
		}

		if err := m.Up(ctx); err != nil {
			return errors.WithStack(err)
		}
	}
}

func (m *Manager) Register(migrations ...Migration) {
	m.migrations = migrations
}

func (m *Manager) CurrentVersion(ctx context.Context) (string, error) {
	return m.resolver.Current(ctx)
}

func (m *Manager) LatestVersion() (string, error) {
	if len(m.migrations) == 0 {
		return "", errors.WithStack(ErrNoAvailableMigration)
	}

	return m.migrations[len(m.migrations)-1].Version(), nil
}

func (m *Manager) IsLatest(ctx context.Context) (bool, error) {
	currentVersion, err := m.resolver.Current(ctx)
	if err != nil {
		return false, errors.Wrap(err, "could not retrieve current version")
	}

	latestVersion, err := m.LatestVersion()
	if err != nil {
		return false, errors.Wrap(err, "could not retrieve latest version")
	}

	return currentVersion == latestVersion, nil
}

func NewManager(resolver VersionResolver) *Manager {
	return &Manager{
		resolver:   resolver,
		migrations: make([]Migration, 0),
	}
}