package vfs

import (
	"context"
	"io/fs"
	"path"
	"path/filepath"
	"strings"
	"sync"
	"time"
)

const Separator = "/"

func IsRoot(filename string) bool {
	return path.Clean(filename) == Separator
}

func trimRelPath(p, t string) string {
	return strings.Trim(strings.TrimPrefix(p, t), "/")
}

// func clean(p string) string {
// 	return path.Clean(Separator + strings.ReplaceAll(p, "\\", "/"))
// }

func RelPath(p string) string {
	return strings.TrimLeft(p, Separator)
}

func AbsPath(p string) string {
	if p == "" || p[0] != '/' {
		return Separator + p
	}
	return p
}

func AddTrailSlash(p string) string {
	if p == "" || p[len(p)-1] != '/' {
		return p + Separator
	}
	return p
}

// OnceValueWOErr returns a function that invokes f only once and returns the value
// returned by f . The returned function may be called concurrently.
//
// If f panics, the returned function will panic with the same value on every call.
func OnceValueWOErr[T any](f func() (T, error)) func() (T, error) {
	var (
		mu         sync.Mutex
		isExecuted bool
		r1         T
		err        error
	)

	return func() (T, error) {
		mu.Lock()
		defer mu.Unlock()

		if isExecuted && err == nil {
			return r1, nil
		}

		r1, err = f()
		return r1, err
	}
}

func subTimeout(ctx context.Context) (context.Context, context.CancelFunc) {
	if deadline, ok := ctx.Deadline(); ok {
		timeout := time.Until(deadline) / 2
		return context.WithTimeout(ctx, timeout)
	}

	return ctx, func() {}
}

func Walk(ctx context.Context, vfs Filesystem, root string, walkFn filepath.WalkFunc) error {
	info, err := vfs.Stat(ctx, root)
	if err != nil {
		err = walkFn(root, nil, err)
	} else {
		err = walk(ctx, vfs, root, info, walkFn)
	}

	if err == filepath.SkipDir {
		return nil
	}

	return err
}

// walk recursively descends path, calling walkFn
// adapted from https://golang.org/src/path/filepath/path.go
func walk(ctx context.Context, vfs Filesystem, path string, info fs.FileInfo, walkFn filepath.WalkFunc) error {
	if !info.IsDir() {
		return walkFn(path, info, nil)
	}

	names, err := readdirnames(ctx, vfs, path)
	err1 := walkFn(path, info, err)
	// If err != nil, walk can't walk into this directory.
	// err1 != nil means walkFn want walk to skip this directory or stop walking.
	// Therefore, if one of err and err1 isn't nil, walk will return.
	if err != nil || err1 != nil {
		// The caller's behavior is controlled by the return value, which is decided
		// by walkFn. walkFn may ignore err and return nil.
		// If walkFn returns SkipDir, it will be handled by the caller.
		// So walk should return whatever walkFn returns.
		return err1
	}

	for _, name := range names {
		filename := filepath.Join(path, name)
		fileInfo, err := vfs.Stat(ctx, filename)
		if err != nil {
			if err := walkFn(filename, fileInfo, err); err != nil && err != filepath.SkipDir {
				return err
			}
		} else {
			err = walk(ctx, vfs, filename, fileInfo, walkFn)
			if err != nil {
				if !fileInfo.IsDir() || err != filepath.SkipDir {
					return err
				}
			}
		}
	}
	return nil
}

func readdirnames(ctx context.Context, vfs Filesystem, dir string) ([]string, error) {
	files, err := vfs.ReadDir(ctx, dir)
	if err != nil {
		return nil, err
	}

	var names []string
	for _, file := range files {
		names = append(names, file.Name())
	}

	return names, nil
}