// Copyright 2019 Google LLC
//
// 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
//
//     https://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 builder

import (
	"context"
	"io"
	"log"
	"os"
	"sync"

	"cloud.google.com/go/storage"
)

type void struct{}

// LocalCache implements the structure used for local caching of
// manifests and layer uploads.
type LocalCache struct {
	mmtx   sync.RWMutex
	mcache map[string]string

	lmtx   sync.RWMutex
	lcache map[string]void
}

func NewCache() LocalCache {
	return LocalCache{
		mcache: make(map[string]string),
		lcache: make(map[string]void),
	}
}

// Has this layer hash already been seen by this Nixery instance? If
// yes, we can skip upload checking and such because it has already
// been done.
func (c *LocalCache) hasSeenLayer(hash string) bool {
	c.lmtx.RLock()
	defer c.lmtx.RUnlock()
	_, seen := c.lcache[hash]
	return seen
}

// Layer has now been seen and should be stored.
func (c *LocalCache) sawLayer(hash string) {
	c.lmtx.Lock()
	defer c.lmtx.Unlock()
	c.lcache[hash] = void{}
}

// Retrieve a cached manifest if the build is cacheable and it exists.
func (c *LocalCache) manifestFromLocalCache(key string) (string, bool) {
	c.mmtx.RLock()
	path, ok := c.mcache[key]
	c.mmtx.RUnlock()

	if !ok {
		return "", false
	}

	return path, true
}

// Adds the result of a manifest build to the local cache, if the
// manifest is considered cacheable.
func (c *LocalCache) localCacheManifest(key, path string) {
	c.mmtx.Lock()
	c.mcache[key] = path
	c.mmtx.Unlock()
}

// Retrieve a manifest from the cache(s). First the local cache is
// checked, then the GCS-bucket cache.
func manifestFromCache(ctx *context.Context, cache *LocalCache, bucket *storage.BucketHandle, key string) (string, bool) {
	path, cached := cache.manifestFromLocalCache(key)
	if cached {
		return path, true
	}

	obj := bucket.Object("manifests/" + key)

	// Probe whether the file exists before trying to fetch it.
	_, err := obj.Attrs(*ctx)
	if err != nil {
		return "", false
	}

	r, err := obj.NewReader(*ctx)
	if err != nil {
		log.Printf("Failed to retrieve manifest '%s' from cache: %s\n", key, err)
		return "", false
	}
	defer r.Close()

	path = os.TempDir() + "/" + key
	f, _ := os.Create(path)
	defer f.Close()

	_, err = io.Copy(f, r)
	if err != nil {
		log.Printf("Failed to read cached manifest for '%s': %s\n", key, err)
	}

	log.Printf("Retrieved manifest for sha1:%s from GCS\n", key)
	cache.localCacheManifest(key, path)

	return path, true
}

func cacheManifest(ctx *context.Context, cache *LocalCache, bucket *storage.BucketHandle, key, path string) {
	cache.localCacheManifest(key, path)

	obj := bucket.Object("manifests/" + key)
	w := obj.NewWriter(*ctx)

	f, err := os.Open(path)
	if err != nil {
		log.Printf("failed to open manifest sha1:%s for cache upload: %s\n", key, err)
		return
	}
	defer f.Close()

	size, err := io.Copy(w, f)
	if err != nil {
		log.Printf("failed to cache manifest sha1:%s: %s\n", key, err)
		return
	}

	if err = w.Close(); err != nil {
		log.Printf("failed to cache manifest sha1:%s: %s\n", key, err)
		return
	}

	log.Printf("Cached manifest sha1:%s (%v bytes written)\n", key, size)
}