// Copyright 2013 Beego Authors
// Copyright 2014 The Macaron Authors
//
// 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 session

import (
	"container/list"
	"fmt"
	"sync"
	"time"
)

// MemStore represents a in-memory session store implementation.
type MemStore struct {
	sid        string
	lock       sync.RWMutex
	data       map[interface{}]interface{}
	lastAccess time.Time
}

// NewMemStore creates and returns a memory session store.
func NewMemStore(sid string) *MemStore {
	return &MemStore{
		sid:        sid,
		data:       make(map[interface{}]interface{}),
		lastAccess: time.Now(),
	}
}

// Set sets value to given key in session.
func (s *MemStore) Set(key, val interface{}) error {
	s.lock.Lock()
	defer s.lock.Unlock()

	s.data[key] = val
	return nil
}

// Get gets value by given key in session.
func (s *MemStore) Get(key interface{}) interface{} {
	s.lock.RLock()
	defer s.lock.RUnlock()

	return s.data[key]
}

// Delete deletes a key from session.
func (s *MemStore) Delete(key interface{}) error {
	s.lock.Lock()
	defer s.lock.Unlock()

	delete(s.data, key)
	return nil
}

// ID returns current session ID.
func (s *MemStore) ID() string {
	return s.sid
}

// Release releases resource and save data to provider.
func (*MemStore) Release() error {
	return nil
}

// Flush deletes all session data.
func (s *MemStore) Flush() error {
	s.lock.Lock()
	defer s.lock.Unlock()

	s.data = make(map[interface{}]interface{})
	return nil
}

// MemProvider represents a in-memory session provider implementation.
type MemProvider struct {
	lock        sync.RWMutex
	maxLifetime int64
	data        map[string]*list.Element
	// A priority list whose lastAccess newer gets higer priority.
	list *list.List
}

// Init initializes memory session provider.
func (p *MemProvider) Init(maxLifetime int64, _ string) error {
	p.lock.Lock()
	p.list = list.New()
	p.data = make(map[string]*list.Element)
	p.maxLifetime = maxLifetime
	p.lock.Unlock()
	return nil
}

// update expands time of session store by given ID.
func (p *MemProvider) update(sid string) error {
	p.lock.Lock()
	defer p.lock.Unlock()

	if e, ok := p.data[sid]; ok {
		e.Value.(*MemStore).lastAccess = time.Now()
		p.list.MoveToFront(e)
		return nil
	}
	return nil
}

// Read returns raw session store by session ID.
func (p *MemProvider) Read(sid string) (_ RawStore, err error) {
	p.lock.RLock()
	e, ok := p.data[sid]
	p.lock.RUnlock()

	// Only restore if the session is still alive.
	if ok && (e.Value.(*MemStore).lastAccess.Unix()+p.maxLifetime) >= time.Now().Unix() {
		if err = p.update(sid); err != nil {
			return nil, err
		}
		return e.Value.(*MemStore), nil
	}

	// Create a new session.
	p.lock.Lock()
	defer p.lock.Unlock()
	if ok {
		p.list.Remove(e)
		delete(p.data, sid)
	}
	s := NewMemStore(sid)
	p.data[sid] = p.list.PushBack(s)
	return s, nil
}

// Exist returns true if session with given ID exists.
func (p *MemProvider) Exist(sid string) bool {
	p.lock.RLock()
	defer p.lock.RUnlock()

	_, ok := p.data[sid]
	return ok
}

// Destroy deletes a session by session ID.
func (p *MemProvider) Destroy(sid string) error {
	p.lock.Lock()
	defer p.lock.Unlock()

	e, ok := p.data[sid]
	if !ok {
		return nil
	}

	p.list.Remove(e)
	delete(p.data, sid)
	return nil
}

// Regenerate regenerates a session store from old session ID to new one.
func (p *MemProvider) Regenerate(oldsid, sid string) (RawStore, error) {
	if p.Exist(sid) {
		return nil, fmt.Errorf("new sid '%s' already exists", sid)
	}

	s, err := p.Read(oldsid)
	if err != nil {
		return nil, err
	}

	if err = p.Destroy(oldsid); err != nil {
		return nil, err
	}

	s.(*MemStore).sid = sid

	p.lock.Lock()
	defer p.lock.Unlock()
	p.data[sid] = p.list.PushBack(s)
	return s, nil
}

// Count counts and returns number of sessions.
func (p *MemProvider) Count() int {
	return p.list.Len()
}

// GC calls GC to clean expired sessions.
func (p *MemProvider) GC() {
	p.lock.RLock()
	for {
		// No session in the list.
		e := p.list.Back()
		if e == nil {
			break
		}

		if (e.Value.(*MemStore).lastAccess.Unix() + p.maxLifetime) < time.Now().Unix() {
			p.lock.RUnlock()
			p.lock.Lock()
			p.list.Remove(e)
			delete(p.data, e.Value.(*MemStore).sid)
			p.lock.Unlock()
			p.lock.RLock()
		} else {
			break
		}
	}
	p.lock.RUnlock()
}

func init() {
	Register("memory", &MemProvider{})
}
