package mirko

// Migration support via github.com/golang-migrations/migrate for go_embed data in Bazel.
// For example usage, see go/mirko/tests/sql.

import (
	"bytes"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"strconv"
	"strings"

	"github.com/golang-migrate/migrate/v4/source"
)

func NewMigrationsFromBazel(data map[string][]byte) (source.Driver, error) {
	migrations := make(map[uint]*migration)

	for k, v := range data {
		parts := strings.Split(k, ".")
		errInvalid := fmt.Errorf("invalid migration filename: %q", k)

		if len(parts) != 3 {
			return nil, errInvalid
		}
		if parts[2] != "sql" {
			return nil, errInvalid
		}
		if parts[1] != "up" && parts[1] != "down" {
			return nil, errInvalid
		}
		direction := parts[1]

		nameParts := strings.SplitN(parts[0], "_", 2)
		if len(nameParts) != 2 {
			return nil, errInvalid
		}

		name := nameParts[1]

		version32, err := strconv.ParseUint(nameParts[0], 10, 32)
		if err != nil {
			return nil, errInvalid
		}
		version := uint(version32)

		m, ok := migrations[version]
		if !ok {
			migrations[version] = &migration{
				version: version,
				name:    name,
			}
			m = migrations[version]
		} else {
			if m.name != name {
				if err != nil {
					return nil, fmt.Errorf("migration version %d exists under diffrent names (%q vs %q)", version, name, m.name)
				}
			}
		}

		if direction == "up" {
			m.up = v
		} else {
			m.down = v
		}
	}

	var first uint
	for version, migration := range migrations {
		if migration.up == nil {
			return nil, fmt.Errorf("migration version %d has no up file", version)
		}
		if migration.down == nil {
			return nil, fmt.Errorf("migration version %d has no down file", version)
		}
		if first == 0 {
			first = version
		}
		if version < first {
			first = version
		}
	}

	if first == 0 {
		return nil, fmt.Errorf("no migrations, or lowest migration version is 0")
	}

	return &migrationSource{
		migrations: migrations,
		first:      first,
	}, nil
}

type migrationSource struct {
	migrations map[uint]*migration
	first      uint
}

type migration struct {
	version uint
	name    string
	up      []byte
	down    []byte
}

func (s *migrationSource) Open(url string) (source.Driver, error) {
	if url != "" {
		return nil, fmt.Errorf("bazel migration source is not configure via an URL")
	}
	return s, nil
}

func (s *migrationSource) Close() error {
	return nil
}

func (s *migrationSource) First() (uint, error) {
	return s.first, nil
}

func (s *migrationSource) Prev(version uint) (uint, error) {
	var prev uint
	for ver, _ := range s.migrations {
		if ver > prev && ver < version {
			prev = ver
		}
	}
	if prev == 0 {
		return 0, os.ErrNotExist
	}
	return prev, nil
}

func (s *migrationSource) Next(version uint) (uint, error) {
	var next uint
	for ver, _ := range s.migrations {
		if ver <= version {
			continue
		}
		if next == 0 {
			next = ver
		}
		if ver < next {
			next = ver
		}
	}
	if next <= version {
		return 0, os.ErrNotExist
	}
	return next, nil
}

func (s *migrationSource) ReadUp(version uint) (io.ReadCloser, string, error) {
	m, ok := s.migrations[version]
	if !ok {
		return nil, "", os.ErrNotExist
	}

	return ioutil.NopCloser(bytes.NewReader(m.up)), m.name, nil
}

func (s *migrationSource) ReadDown(version uint) (io.ReadCloser, string, error) {
	m, ok := s.migrations[version]
	if !ok {
		return nil, "", os.ErrNotExist
	}

	return ioutil.NopCloser(bytes.NewReader(m.down)), m.name, nil
}