// Copyright 2018 The Hugo Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package hugofs

import (
	"os"

	"github.com/spf13/afero"
)

var (
	_ afero.Fs      = (*languageCompositeFs)(nil)
	_ afero.Lstater = (*languageCompositeFs)(nil)
)

type languageCompositeFs struct {
	*afero.CopyOnWriteFs
}

// NewLanguageCompositeFs creates a composite and language aware filesystem.
// This is a hybrid filesystem. To get a specific file in Open, Stat etc., use the full filename
// to the target filesystem. This information is available in Readdir, Stat etc. via the
// special LanguageFileInfo FileInfo implementation.
func NewLanguageCompositeFs(base, overlay afero.Fs) afero.Fs {
	return &languageCompositeFs{afero.NewCopyOnWriteFs(base, overlay).(*afero.CopyOnWriteFs)}
}

// Open takes the full path to the file in the target filesystem. If it is a directory, it gets merged
// using the language as a weight.
func (fs *languageCompositeFs) Open(name string) (afero.File, error) {
	f, err := fs.CopyOnWriteFs.Open(name)
	if err != nil {
		return nil, err
	}

	fu, ok := f.(*afero.UnionFile)
	if ok {
		// This is a directory: Merge it.
		fu.Merger = LanguageDirsMerger
	}
	return f, nil
}

// LanguageDirsMerger implements the afero.DirsMerger interface, which is used
// to merge two directories.
var LanguageDirsMerger = func(lofi, bofi []os.FileInfo) ([]os.FileInfo, error) {
	for _, fi1 := range bofi {
		fim1 := fi1.(FileMetaInfo)
		var found bool
		for _, fi2 := range lofi {
			fim2 := fi2.(FileMetaInfo)
			if fi1.Name() == fi2.Name() && fim1.Meta().Lang == fim2.Meta().Lang {
				found = true
				break
			}
		}
		if !found {
			lofi = append(lofi, fi1)
		}
	}

	return lofi, nil
}