package migrate

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"time"

	"github.com/pressly/goose/v3"
)

// ApplyPendingMigrations applies pending migrations and returns the number successfully applied.
// A zero pendingCount is a no-op, a negative value applies all pending migrations,
// and a positive value caps successful applications. Exhausting pending migrations
// is successful even when fewer than the requested cap remain. Versions are identifiers,
// not counts, and may contain gaps or timestamps.
func ApplyPendingMigrations(ctx context.Context, pendingCount int64) (int64, error) {
	migrationsModule.RequireLoaded()
	p, err := Provider()
	if err != nil {
		return 0, err
	}

	count, _, err := applyPendingMigrations(ctx, p, migrationsModule.Logger(), pendingCount)
	return count, err
}

type migrationStepper interface {
	UpByOne(context.Context) (*goose.MigrationResult, error)
}

// The last successful version is used for summaries; it cannot be inferred from count.
func applyPendingMigrations(ctx context.Context, p migrationStepper, logger *slog.Logger, pendingCount int64) (count, lastVersion int64, err error) {
	for pendingCount < 0 || count < pendingCount {
		res, err := p.UpByOne(ctx)
		// A migration itself can fail with ErrNoNextVersion. Goose reports that
		// through PartialError, which must not be mistaken for normal exhaustion.
		var partial *goose.PartialError
		if res == nil && errors.Is(err, goose.ErrNoNextVersion) && !errors.As(err, &partial) {
			return count, lastVersion, nil
		}
		if err := handleMigrationResults(logger, res, err); err != nil {
			return count, lastVersion, err
		}
		if res == nil {
			return count, lastVersion, nil
		}
		count++
		lastVersion = res.Source.Version
	}
	return count, lastVersion, nil
}

// MigrateToBlank rolls back all applied migrations.
func MigrateToBlank(ctx context.Context) (int64, error) {
	migrationsModule.RequireLoaded()
	p, err := Provider()
	if err != nil {
		return 0, err
	}

	current, target, err := p.GetVersions(ctx)
	if err != nil {
		return 0, err
	}
	moduleMigrateBlank.Logger().Info("Database versions", "current", current, "target", target)

	if current == 0 {
		return 0, nil
	}

	results, err := p.DownTo(ctx, 0)
	if err != nil {
		return 0, err
	}
	for _, res := range results {
		if err := handleMigrationResults(moduleMigrateBlank.Logger(), res, nil); err != nil {
			return int64(len(results)), err
		}
	}
	return int64(len(results)), nil
}

// AutoMigrate applies pending migrations when auto-migration is enabled.
func AutoMigrate(ctx context.Context) error {
	migrationsModule.RequireLoaded()
	p, err := Provider()
	if err != nil {
		return err
	}

	current, target, err := p.GetVersions(ctx)
	if err != nil {
		migrationsModule.Logger().Error("Couldn't check for pending migrations", "err", err)
		return err
	}

	fields := []any{"current", current, "target", target}

	if current >= target {
		migrationsModule.Logger().Info("No pending migrations", "version", current)
		return nil
	}
	if !autoMigrateEnabled {
		migrationsModule.Logger().Error(
			"Pending migrations detected, but auto-migration is disabled. Run `migrate up` to apply them.",
			fields...,
		)
		return ErrPendingMigrations
	}

	migrationsModule.Logger().Info("Pending migrations detected, applying them...", fields...)
	now := time.Now()
	count, lastVersion, err := applyPendingMigrations(ctx, p, migrationsModule.Logger(), -1)
	if count > 0 {
		current = lastVersion
	}
	if err != nil {
		migrationsModule.Logger().Error("Couldn't apply pending migrations", "current", current, "target", target, "appliedCount", count, "err", err)
		return err
	}
	migrationsModule.Logger().Info("Applied pending migrations", "current", current, "appliedCount", count, "duration", time.Since(now))
	return nil
}

func handleMigrationResults(logger *slog.Logger, res *goose.MigrationResult, err error) error {
	if err != nil {
		var partial *goose.PartialError
		if errors.As(err, &partial) && partial.Failed != nil {
			_ = handleMigrationResults(logger, partial.Failed, nil)
		}
		return err
	}
	if res == nil {
		return nil
	}

	fields := []any{
		"dir", res.Direction,
		"version", res.Source.Version,
		"source", res.Source.Path,
		"duration", res.Duration,
	}

	if res.Error != nil {
		fields = append(fields, "err", res.Error)
		logger.Error("Couldn't apply migration", fields...)
		return res.Error
	}
	if res.Empty {
		logger.Warn("Applied empty migration", fields...)
	} else {
		logger.Info("Applied migration", fields...)
	}
	return nil
}

// PrintMigrationStatus prints migration status to stdout via the provider.
func PrintMigrationStatus(ctx context.Context) error {
	p, err := Provider()
	if err != nil {
		return err
	}
	statuses, err := p.Status(ctx)
	if err != nil {
		return fmt.Errorf("migration status: %w", err)
	}
	for _, s := range statuses {
		fmt.Printf("%s\t%s\n", s.State, s.Source.Path)
	}
	return nil
}