// 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 a middleware that provides the session management of Macaron.
package session

import (
	"context"
	"encoding/hex"
	"errors"
	"fmt"
	"net/http"
	"net/url"
	"reflect"
	"time"
)

const version = "0.7.0"

// Version returns the version
func Version() string {
	return version
}

// RawStore is the interface that operates the session data.
type RawStore interface {
	// Set sets value to given key in session.
	Set(interface{}, interface{}) error
	// Get gets value by given key in session.
	Get(interface{}) interface{}
	// Delete deletes a key from session.
	Delete(interface{}) error
	// ID returns current session ID.
	ID() string
	// Release releases session resource and save data to provider.
	Release() error
	// Flush deletes all session data.
	Flush() error
}

// Store is the interface that contains all data for one session process with specific ID.
type Store interface {
	RawStore
	// Read returns raw session store by session ID.
	Read(string) (RawStore, error)
	// Destroy deletes a session.
	Destroy(http.ResponseWriter, *http.Request) error
	// RegenerateID regenerates a session store from old session ID to new one.
	RegenerateID(http.ResponseWriter, *http.Request) (RawStore, error)
	// Count counts and returns number of sessions.
	Count() int
	// GC calls GC to clean expired sessions.
	GC()
}

type store struct {
	RawStore
	*Manager
}

var _ Store = &store{}

// Options represents a struct for specifying configuration options for the session middleware.
type Options struct {
	// Name of provider. Default is "memory".
	Provider string
	// Provider configuration, it's corresponding to provider.
	ProviderConfig string
	// Cookie name to save session ID. Default is "MacaronSession".
	CookieName string
	// Cookie path to store. Default is "/".
	CookiePath string
	// GC interval time in seconds. Default is 3600.
	Gclifetime int64
	// Max life time in seconds. Default is whatever GC interval time is.
	Maxlifetime int64
	// Use HTTPS only. Default is false.
	Secure bool
	// Cookie life time. Default is 0.
	CookieLifeTime int
	// SameSite set the cookie SameSite
	SameSite http.SameSite
	// Cookie domain name. Default is empty.
	Domain string
	// Session ID length. Default is 16.
	IDLength int
	// Ignore release for websocket. Default is false.
	IgnoreReleaseForWebSocket bool
	// FlashEncryptionKey sets the encryption key for flash messages
	FlashEncryptionKey string
}

// PrepareOptions gives some default values for options
func PrepareOptions(options []Options) Options {
	var opt Options
	if len(options) > 0 {
		opt = options[0]
	}

	if len(opt.Provider) == 0 {
		opt.Provider = "memory"
	}
	if len(opt.ProviderConfig) == 0 {
		opt.ProviderConfig = "data/sessions"
	}
	if len(opt.CookieName) == 0 {
		opt.CookieName = "MacaronSession"
	}
	if len(opt.CookiePath) == 0 {
		opt.CookiePath = "/"
	}
	if opt.Gclifetime == 0 {
		opt.Gclifetime = 3600
	}
	if opt.Maxlifetime == 0 {
		opt.Maxlifetime = opt.Gclifetime
	}
	if !opt.Secure {
		opt.Secure = false
	}
	if opt.IDLength == 0 {
		opt.IDLength = 16
	}
	if len(opt.FlashEncryptionKey) == 0 {
		opt.FlashEncryptionKey = ""
	}
	if len(opt.FlashEncryptionKey) == 0 {
		opt.FlashEncryptionKey, _ = NewSecret()
	}

	return opt
}

// GetCookie returns given cookie value from request header.
func GetCookie(req *http.Request, name string) string {
	cookie, err := req.Cookie(name)
	if err != nil {
		return ""
	}
	val, _ := url.QueryUnescape(cookie.Value)
	return val
}

// NewCookie creates cookie via given params and value.
// FIXME: IE support? http://golanghome.com/post/620#reply2
func NewCookie(name string, value string, others ...interface{}) *http.Cookie {
	cookie := http.Cookie{}
	cookie.Name = name
	cookie.Value = url.QueryEscape(value)

	if len(others) > 0 {
		switch v := others[0].(type) {
		case int:
			cookie.MaxAge = v
		case int64:
			cookie.MaxAge = int(v)
		case int32:
			cookie.MaxAge = int(v)
		case func(*http.Cookie):
			v(&cookie)
		}
	}

	cookie.Path = "/"
	if len(others) > 1 {
		if v, ok := others[1].(string); ok && len(v) > 0 {
			cookie.Path = v
		} else if v, ok := others[1].(func(*http.Cookie)); ok {
			v(&cookie)
		}
	}

	if len(others) > 2 {
		if v, ok := others[2].(string); ok && len(v) > 0 {
			cookie.Domain = v
		} else if v, ok := others[1].(func(*http.Cookie)); ok {
			v(&cookie)
		}
	}

	if len(others) > 3 {
		switch v := others[3].(type) {
		case bool:
			cookie.Secure = v
		case func(*http.Cookie):
			v(&cookie)
		default:
			if others[3] != nil {
				cookie.Secure = true
			}
		}
	}

	if len(others) > 4 {
		if v, ok := others[4].(bool); ok && v {
			cookie.HttpOnly = true
		} else if v, ok := others[1].(func(*http.Cookie)); ok {
			v(&cookie)
		}
	}

	if len(others) > 5 {
		if v, ok := others[5].(time.Time); ok {
			cookie.Expires = v
			cookie.RawExpires = v.Format(time.UnixDate)
		} else if v, ok := others[1].(func(*http.Cookie)); ok {
			v(&cookie)
		}
	}

	if len(others) > 6 {
		for _, other := range others[6:] {
			if v, ok := other.(func(*http.Cookie)); ok {
				v(&cookie)
			}
		}
	}
	return &cookie
}

// Sessioner is a middleware that maps a session.SessionStore service into the Macaron handler chain.
// An single variadic session.Options struct can be optionally provided to configure.
func Sessioner(options ...Options) func(next http.Handler) http.Handler {
	opt := PrepareOptions(options)
	manager, err := NewManager(opt.Provider, opt)
	if err != nil {
		panic(err)
	}
	go manager.startGC()

	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
			sess, err := manager.Start(w, req)
			if err != nil {
				panic("session(start): " + err.Error())
			}

			var s = store{
				RawStore: sess,
				Manager:  manager,
			}

			req = req.WithContext(context.WithValue(req.Context(), interface{}("Session"), &s))

			next.ServeHTTP(w, req)

			if manager.opt.IgnoreReleaseForWebSocket && req.Header.Get("Upgrade") == "websocket" {
				return
			}

			if err = sess.Release(); err != nil {
				panic("session(release): " + err.Error())
			}
		})
	}
}

// GetSession returns session store
func GetSession(req *http.Request) Store {
	sessCtx := req.Context().Value("Session")
	sess, _ := sessCtx.(*store)
	return sess
}

// Provider is the interface that provides session manipulations.
type Provider interface {
	// Init initializes session provider.
	Init(gclifetime int64, config string) error
	// Read returns raw session store by session ID.
	Read(sid string) (RawStore, error)
	// Exist returns true if session with given ID exists.
	Exist(sid string) bool
	// Destroy deletes a session by session ID.
	Destroy(sid string) error
	// Regenerate regenerates a session store from old session ID to new one.
	Regenerate(oldsid, sid string) (RawStore, error)
	// Count counts and returns number of sessions.
	Count() int
	// GC calls GC to clean expired sessions.
	GC()
}

var providers = make(map[string]func() Provider)

// Register registers a provider.
func Register(name string, provider Provider) {
	if reflect.TypeOf(provider).Kind() == reflect.Ptr {
		// Pointer:
		RegisterFn(name, func() Provider {
			return reflect.New(reflect.ValueOf(provider).Elem().Type()).Interface().(Provider)
		})
		return
	}

	// Not a Pointer
	RegisterFn(name, func() Provider {
		return reflect.New(reflect.TypeOf(provider)).Elem().Interface().(Provider)
	})
}

// RegisterFn registers a provider function.
func RegisterFn(name string, providerfn func() Provider) {
	if providerfn == nil {
		panic("session: cannot register provider with nil value")
	}
	if _, dup := providers[name]; dup {
		panic(fmt.Errorf("session: cannot register provider '%s' twice", name))
	}

	providers[name] = providerfn
}

//    _____
//   /     \ _____    ____ _____     ____   ___________
//  /  \ /  \\__  \  /    \\__  \   / ___\_/ __ \_  __ \
// /    Y    \/ __ \|   |  \/ __ \_/ /_/  >  ___/|  | \/
// \____|__  (____  /___|  (____  /\___  / \___  >__|
//         \/     \/     \/     \//_____/      \/

// Manager represents a struct that contains session provider and its configuration.
type Manager struct {
	provider Provider
	opt      Options
}

// NewManager creates and returns a new session manager by given provider name and configuration.
// It returns an error when requested provider name isn't registered.
func NewManager(name string, opt Options) (*Manager, error) {
	fn, ok := providers[name]
	if !ok {
		return nil, fmt.Errorf("session: unknown provider '%s'(forgotten import?)", name)
	}

	p := fn()

	return &Manager{p, opt}, p.Init(opt.Maxlifetime, opt.ProviderConfig)
}

// sessionID generates a new session ID with rand string, unix nano time, remote addr by hash function.
func (m *Manager) sessionID() string {
	return hex.EncodeToString(generateRandomKey(m.opt.IDLength / 2))
}

// validSessionID tests whether a provided session ID is a valid session ID.
func (m *Manager) validSessionID(sid string) (bool, error) {
	if len(sid) != m.opt.IDLength {
		return false, fmt.Errorf("invalid 'sid': %s %d != %d", sid, len(sid), m.opt.IDLength)
	}

	for i := range sid {
		switch {
		case '0' <= sid[i] && sid[i] <= '9':
		case 'a' <= sid[i] && sid[i] <= 'f':
		default:
			return false, errors.New("invalid 'sid': " + sid)
		}
	}
	return true, nil
}

// Start starts a session by generating new one
// or retrieve existence one by reading session ID from HTTP request if it's valid.
func (m *Manager) Start(resp http.ResponseWriter, req *http.Request) (RawStore, error) {
	sid := GetCookie(req, m.opt.CookieName)
	valid, _ := m.validSessionID(sid)
	if len(sid) > 0 && valid && m.provider.Exist(sid) {
		return m.provider.Read(sid)
	}

	sid = m.sessionID()
	sess, err := m.provider.Read(sid)
	if err != nil {
		return nil, err
	}

	cookie := &http.Cookie{
		Name:     m.opt.CookieName,
		Value:    sid,
		Path:     m.opt.CookiePath,
		HttpOnly: true,
		Secure:   m.opt.Secure,
		Domain:   m.opt.Domain,
		SameSite: m.opt.SameSite,
	}
	if m.opt.CookieLifeTime >= 0 {
		cookie.MaxAge = m.opt.CookieLifeTime
	}
	http.SetCookie(resp, cookie)
	req.AddCookie(cookie)
	return sess, nil
}

// Read returns raw session store by session ID.
func (m *Manager) Read(sid string) (RawStore, error) {
	// Ensure we're trying to read a valid session ID
	if _, err := m.validSessionID(sid); err != nil {
		return nil, err
	}

	return m.provider.Read(sid)
}

// Destroy deletes a session by given ID.
func (m *Manager) Destroy(resp http.ResponseWriter, req *http.Request) error {
	sid := GetCookie(req, m.opt.CookieName)
	if len(sid) == 0 {
		return nil
	}

	if _, err := m.validSessionID(sid); err != nil {
		return err
	}

	if err := m.provider.Destroy(sid); err != nil {
		return err
	}
	cookie := &http.Cookie{
		Name:     m.opt.CookieName,
		Path:     m.opt.CookiePath,
		HttpOnly: true,
		Expires:  time.Now(),
		MaxAge:   -1,
	}
	http.SetCookie(resp, cookie)
	return nil
}

// RegenerateID regenerates a session store from old session ID to new one.
func (m *Manager) RegenerateID(resp http.ResponseWriter, req *http.Request) (sess RawStore, err error) {
	sid := m.sessionID()
	oldsid := GetCookie(req, m.opt.CookieName)
	_, err = m.validSessionID(oldsid)
	if err != nil {
		return nil, err
	}
	sess, err = m.provider.Regenerate(oldsid, sid)
	if err != nil {
		return nil, err
	}
	cookie := &http.Cookie{
		Name:     m.opt.CookieName,
		Value:    sid,
		Path:     m.opt.CookiePath,
		HttpOnly: true,
		Secure:   m.opt.Secure,
		Domain:   m.opt.Domain,
		SameSite: m.opt.SameSite,
	}
	if m.opt.CookieLifeTime >= 0 {
		cookie.MaxAge = m.opt.CookieLifeTime
	}
	http.SetCookie(resp, cookie)
	req.AddCookie(cookie)
	return sess, nil
}

// Count counts and returns number of sessions.
func (m *Manager) Count() int {
	return m.provider.Count()
}

// GC starts GC job in a certain period.
func (m *Manager) GC() {
	m.provider.GC()
}

// startGC starts GC job in a certain period.
func (m *Manager) startGC() {
	m.GC()
	time.AfterFunc(time.Duration(m.opt.Gclifetime)*time.Second, func() { m.startGC() })
}

// SetSecure indicates whether to set cookie with HTTPS or not.
func (m *Manager) SetSecure(secure bool) {
	m.opt.Secure = secure
}