package migration

import (
	"context"
	"database/sql"
	"github.com/Southclaws/fault"
	"github.com/lmika/gopkgs/fp/maps"
	"io/fs"
	"log/slog"
	"regexp"
	"sort"
	"strconv"
)

type Migrator struct {
	fs fs.FS
	db *sql.DB

	preStepHooks []func(filename string)
}

func New(fs fs.FS, db *sql.DB, opts ...Option) *Migrator {
	migrator := &Migrator{
		db: db,
		fs: fs,
	}

	for _, opt := range opts {
		opt(migrator)
	}
	return migrator
}

func (m *Migrator) Version(ctx context.Context) (userVersion int, err error) {
	if err := m.inTX(ctx, func(tx *sql.Tx) error {
		userVersion, err = m.getVersion(ctx, tx)
		return err
	}); err != nil {
		return 0, fault.Wrap(err)
	}

	return int(userVersion), nil
}

func (m *Migrator) MigrateUp(ctx context.Context) error {
	sf, err := m.readFiles()
	if err != nil {
		return fault.Wrap(err)
	} else if len(sf) == 0 {
		return nil
	}

	return m.inTX(ctx, func(tx *sql.Tx) error {
		latestVersion := sf[len(sf)-1].ver

		currentVersion, err := m.getVersion(ctx, tx)
		if err != nil {
			return fault.Wrap(err)
		}

		if currentVersion == latestVersion {
			slog.Debug("no DB migration necessary", "current_version", currentVersion, "latest_version", latestVersion)
			return nil
		}

		slog.Debug("starting migration", "current_version", currentVersion, "latest_version", latestVersion)
		for _, mf := range sf {
			if mf.ver <= currentVersion {
				continue
			}

			for _, h := range m.preStepHooks {
				h(mf.upFile)
			}

			if err := m.runMigrationFile(ctx, tx, mf.upFile); err != nil {
				return err
			}
		}

		return m.setVersion(ctx, tx, latestVersion)
	})
}

func (m *Migrator) readFiles() ([]schemaFiles, error) {
	de, err := fs.ReadDir(m.fs, ".")
	if err != nil {
		return nil, fault.Wrap(err)
	}

	verFiles := make(map[int]schemaFiles)
	for _, f := range de {
		parts := migrateFileName.FindStringSubmatch(f.Name())
		if len(parts) != 3 {
			continue
		}

		versionID, err := strconv.Atoi(parts[1])
		if err != nil {
			continue
		}

		vf := verFiles[versionID]
		vf.ver = versionID
		if parts[2] == "up" {
			vf.upFile = f.Name()
		} else {
			vf.downFile = f.Name()
		}

		verFiles[versionID] = vf
	}

	files := maps.Values(verFiles)
	sort.Slice(files, func(i, j int) bool { return files[i].ver < files[j].ver })
	return files, nil
}

var migrateFileName = regexp.MustCompile(`0*([0-9]+)[-_].*\.(up|down)\.sql`)

type schemaFiles struct {
	ver      int
	upFile   string
	downFile string
}