package git

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"syscall"

	"github.com/karrick/godirwalk"
	"github.com/pkg/errors"
)

// errSkipNode is used as an error indicating that .git directory has been found.
// It's handled by ErrorsCallback to tell the WalkCallback to skip this dir.
var errSkipNode = errors.New(".git directory found, skipping this node")

// errDirectoryAccess indicates a directory doesn't exists or can't be accessed
var errDirectoryAccess = errors.New("directory doesn't exist or can't be accessed")

// Exists returns true if a directory exists. If it doesn't or the directory can't be accessed it returns an error.
func Exists(path string) (bool, error) {
	_, err := os.Stat(path)

	if err == nil {
		return true, nil
	}

	if err != nil {
		if os.IsNotExist(err) {
			return false, errDirectoryAccess
		}
	}

	// Directory exists but can't be accessed
	return true, errDirectoryAccess
}

// RepoFinder finds paths to git repos inside given path.
type RepoFinder struct {
	root  string
	repos []string
}

// NewRepoFinder returns a RepoFinder pointed at given root path.
func NewRepoFinder(root string) *RepoFinder {
	return &RepoFinder{
		root: root,
	}
}

// Find returns a sorted list of paths to git repos found inside a given root path.
// Returns error if root repo path can't be found or accessed.
func (r *RepoFinder) Find() ([]string, error) {
	if _, err := Exists(r.root); err != nil {
		return nil, err
	}

	walkOpts := &godirwalk.Options{
		ErrorCallback: r.errorCb,
		Callback:      r.walkCb,
		// Use Unsorted to improve speed because repos will be processed by goroutines in a random order anyway.
		Unsorted: true,
	}

	err := godirwalk.Walk(r.root, walkOpts)
	if err != nil {
		return nil, err
	}

	if len(r.repos) == 0 {
		return nil, fmt.Errorf("no git repos found in root path %s", r.root)
	}

	return r.repos, nil
}

func (r *RepoFinder) walkCb(path string, ent *godirwalk.Dirent) error {
	// Do not traverse .git directories
	if ent.IsDir() && ent.Name() == ".git" {
		r.repos = append(r.repos, strings.TrimSuffix(path, ".git"))
		return errSkipNode
	}
	// Do not traverse directories containing a .git directory
	if ent.IsDir() {
		_, err := os.Stat(filepath.Join(path, ".git"))
		if err == nil {
			r.repos = append(r.repos, strings.TrimSuffix(path, ".git"))
			return ErrSkipNode
		}
	}
	return nil
}

func (r *RepoFinder) errorCb(_ string, err error) godirwalk.ErrorAction {
	// Skip .git directory and directories we don't have permissions to access
	// TODO: Will syscall.EACCES work on windows?
	if errors.Is(err, errSkipNode) || errors.Is(err, syscall.EACCES) {
		return godirwalk.SkipNode
	}
	return godirwalk.Halt
}