/*
Copyright 2016 The Kubernetes 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 driver // import "k8s.io/helm/pkg/storage/driver"

import (
	"sync"

	rspb "k8s.io/helm/pkg/proto/hapi/release"
)

// MemoryDriverName is the string name of this driver.
const MemoryDriverName = "Memory"

// Memory is the in-memory storage driver implementation.
type Memory struct {
	sync.RWMutex
	cache map[string]*rspb.Release
}

// NewMemory initializes a new memory driver.
func NewMemory() *Memory {
	return &Memory{cache: map[string]*rspb.Release{}}
}

// Name returns the name of the driver.
func (mem *Memory) Name() string {
	return MemoryDriverName
}

// Get returns the release named by key or returns ErrReleaseNotFound.
func (mem *Memory) Get(key string) (*rspb.Release, error) {
	defer unlock(mem.rlock())

	if rls, ok := mem.cache[key]; ok {
		return rls, nil
	}
	return nil, ErrReleaseNotFound
}

// List returns the list of all releases such that filter(release) == true
func (mem *Memory) List(filter func(*rspb.Release) bool) ([]*rspb.Release, error) {
	defer unlock(mem.rlock())

	var releases []*rspb.Release
	for k := range mem.cache {
		if filter(mem.cache[k]) {
			releases = append(releases, mem.cache[k])
		}
	}
	return releases, nil
}

// Create creates a new release or returns ErrReleaseExists.
func (mem *Memory) Create(rls *rspb.Release) error {
	defer unlock(mem.wlock())

	if _, ok := mem.cache[rls.Name]; ok {
		return ErrReleaseExists
	}
	mem.cache[rls.Name] = rls
	return nil
}

// Update updates a release or returns ErrReleaseNotFound.
func (mem *Memory) Update(rls *rspb.Release) error {
	defer unlock(mem.wlock())

	if _, ok := mem.cache[rls.Name]; ok {
		mem.cache[rls.Name] = rls
		return nil
	}
	return ErrReleaseNotFound
}

// Delete deletes a release or returns ErrReleaseNotFound.
func (mem *Memory) Delete(key string) (*rspb.Release, error) {
	defer unlock(mem.wlock())

	if old, ok := mem.cache[key]; ok {
		delete(mem.cache, key)
		return old, nil
	}
	return nil, ErrReleaseNotFound
}

// wlock locks mem for writing
func (mem *Memory) wlock() func() {
	mem.Lock()
	return func() {
		mem.Unlock()
	}
}

// rlock locks mem for reading
func (mem *Memory) rlock() func() {
	mem.RLock()
	return func() {
		mem.RUnlock()
	}
}

// unlock calls fn which reverses a mem.rlock or mem.wlock. e.g:
// ```defer unlock(mem.rlock())```, locks mem for reading at the
// call point of defer and unlocks upon exiting the block.
func unlock(fn func()) { fn() }