package vfs

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

// Glob returns the names of all files matching pattern or nil
// if there is no matching file. The syntax of patterns is the same
// as in Match. The pattern may describe hierarchical names such as
// /usr/*/bin/ed (assuming the Separator is '/').
//
// Glob ignores file system errors such as I/O errors reading directories.
// The only possible returned error is ErrBadPattern, when pattern
// is malformed.
//
// Function originally from https://golang.org/src/path/filepath/match_test.go
func Glob(fs VFS, pattern string) (matches []string, err error) {
	if !hasMeta(pattern) {
		if _, err = fs.Lstat(pattern); err != nil {
			return nil, nil
		}
		return []string{pattern}, nil
	}

	dir, file := filepath.Split(pattern)
	// Prevent infinite recursion. See issue 15879.
	if dir == pattern {
		return nil, filepath.ErrBadPattern
	}

	var m []string
	m, err = Glob(fs, cleanGlobPath(dir))
	if err != nil {
		return
	}
	for _, d := range m {
		matches, err = glob(fs, d, file, matches)
		if err != nil {
			return
		}
	}
	return
}

// cleanGlobPath prepares path for glob matching.
func cleanGlobPath(path string) string {
	switch path {
	case "":
		return "."
	case string(filepath.Separator):
		// do nothing to the path
		return path
	default:
		return path[0 : len(path)-1] // chop off trailing separator
	}
}

// glob searches for files matching pattern in the directory dir
// and appends them to matches. If the directory cannot be
// opened, it returns the existing matches. New matches are
// added in lexicographical order.
func glob(fs VFS, dir, pattern string, matches []string) (m []string, e error) {
	m = matches
	fi, err := fs.Stat(dir)
	if err != nil {
		return
	}

	if !fi.IsDir() {
		return
	}

	names, _ := readdirnames(fs, dir)
	sort.Strings(names)

	for _, n := range names {
		matched, err := filepath.Match(pattern, n)
		if err != nil {
			return m, err
		}
		if matched {
			m = append(m, filepath.Join(dir, n))
		}
	}
	return
}

// hasMeta reports whether path contains any of the magic characters
// recognized by Match.
func hasMeta(path string) bool {
	// TODO(niemeyer): Should other magic characters be added here?
	return strings.ContainsAny(path, "*?[")
}

func readdirnames(fs VFS, dir string) ([]string, error) {
	files, err := fs.ReadDir(dir)
	if err != nil {
		return nil, err
	}

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

	return names, nil
}
