// Licensed to the Apache Software Foundation (ASF) under one or more
// contributor license agreements.  See the NOTICE file distributed with
// this work for additional information regarding copyright ownership.
// The ASF licenses this file to You 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 memfs contains a in-memory Beam filesystem. Useful for testing.
package memfs

import (
	"bytes"
	"context"
	"io"
	"io/ioutil"
	"os"
	"sort"
	"strings"
	"sync"

	"github.com/apache/beam/sdks/go/pkg/beam/io/filesystem"
)

func init() {
	filesystem.Register("memfs", New)
}

var instance = &fs{m: make(map[string][]byte)}

type fs struct {
	m  map[string][]byte
	mu sync.Mutex
}

// New returns the global memory filesystem.
func New(_ context.Context) filesystem.Interface {
	return instance
}

func (f *fs) Close() error {
	return nil
}

func (f *fs) List(_ context.Context, _ string) ([]string, error) {
	f.mu.Lock()
	defer f.mu.Unlock()

	var ret []string
	for k := range f.m {
		ret = append(ret, k)
	}
	sort.Strings(ret)
	return ret, nil
}

func (f *fs) OpenRead(_ context.Context, filename string) (io.ReadCloser, error) {
	f.mu.Lock()
	defer f.mu.Unlock()

	if v, ok := f.m[normalize(filename)]; ok {
		return ioutil.NopCloser(bytes.NewReader(v)), nil
	}
	return nil, os.ErrNotExist
}

func (f *fs) OpenWrite(_ context.Context, filename string) (io.WriteCloser, error) {
	return &commitWriter{key: filename}, nil
}

func (f *fs) Size(_ context.Context, filename string) (int64, error) {
	f.mu.Lock()
	defer f.mu.Unlock()

	if v, ok := f.m[normalize(filename)]; ok {
		return int64(len(v)), nil
	}
	return -1, os.ErrNotExist
}

// Write stores the given key and value in the global store.
func Write(key string, value []byte) {
	instance.mu.Lock()
	defer instance.mu.Unlock()

	cp := make([]byte, len(value))
	copy(cp, value)

	instance.m[normalize(key)] = cp
}

func normalize(key string) string {
	if strings.HasPrefix(key, "memfs://") {
		return key
	}
	return "memfs://" + key
}

type commitWriter struct {
	key string
	buf bytes.Buffer
}

func (w *commitWriter) Write(p []byte) (n int, err error) {
	return w.buf.Write(p)
}

func (w *commitWriter) Close() error {
	Write(w.key, w.buf.Bytes())
	return nil
}
