package migrations

import (
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"
)

const maxSearchDepth = 4

var candidateLeaves = []string{
	"migrations",
	filepath.Join("server", "migrations"),
}

// ResolveDir returns the first migrations directory that exists from the
// current working directory.
func ResolveDir() (string, error) {
	seen := make(map[string]bool)
	for _, root := range searchRoots() {
		base := root
		for range maxSearchDepth + 1 {
			for _, leaf := range candidateLeaves {
				dir := filepath.Clean(filepath.Join(base, leaf))
				if seen[dir] {
					continue
				}
				seen[dir] = true
				info, err := os.Stat(dir)
				if err == nil && info.IsDir() {
					return dir, nil
				}
			}
			base = filepath.Join(base, "..")
		}
	}
	return "", fmt.Errorf("migrations directory not found")
}

func searchRoots() []string {
	roots := []string{"."}
	if exe, err := os.Executable(); err == nil {
		roots = append(roots, filepath.Dir(exe))
	}
	return roots
}

// Files returns sorted migration files for the given direction ("up" or
// "down").
func Files(direction string) ([]string, error) {
	dir, err := ResolveDir()
	if err != nil {
		return nil, err
	}

	suffix := "." + direction + ".sql"
	files, err := filepath.Glob(filepath.Join(dir, "*"+suffix))
	if err != nil {
		return nil, err
	}

	if direction == "down" {
		sort.Sort(sort.Reverse(sort.StringSlice(files)))
	} else {
		sort.Strings(files)
	}
	return files, nil
}

// LatestVersion returns the latest "up" migration version found on disk.
func LatestVersion() (string, error) {
	files, err := Files("up")
	if err != nil {
		return "", err
	}
	if len(files) == 0 {
		return "", fmt.Errorf("no up migrations found")
	}
	return ExtractVersion(files[len(files)-1]), nil
}

// ExtractVersion strips the .up.sql / .down.sql suffix from a migration file.
func ExtractVersion(filename string) string {
	base := filepath.Base(filename)
	base = strings.TrimSuffix(base, ".up.sql")
	base = strings.TrimSuffix(base, ".down.sql")
	return base
}