package main

import (
	"encoding/json"
	"io/ioutil"
	"log"
	"os"
	"path/filepath"
	"time"
)

//openSession is the biggest description for a user's openID
// | it contains a name called procedure, whose data is stored elsewhere
// |
// +-- a Procedure name is a alphanumerical string lessthan 128 bytes.
//     |
//     +--- state is part of procedure, a procedure consists of sequence of states

//where to find session data
var sessionDir = "sessions"

//where to find the procedure state information
var procedureDir = "procedure"

//openIDSessionData  openID user's session
type openIDSessionData struct {
	OpenID    string            `json:"OpenID"`    //who's session this is belongs to
	Procedure string            `json:"Procedure"` //name of the current current process, alphanumerical
	CreateAt  int32             `json:"CreateAt"`  //when is this session created
	UpdateAt  int32             `json:"UpdateAt"`  //when is this session updated
	Expire    int32             `json:"Expire"`    //unix timestamp of when this Procedure expires
	KvPair    map[string]string `json:"KvPair"`    //key value pair persistant for this session
	//
	//
	//current state for the prcedure
	state chatState
}

func writeSession(ss openIDSessionData) (err error) {
	openID := ss.OpenID
	path := getSessionPath(openID)
	r, err := json.Marshal(ss)
	if err == nil {
		err = ioutil.WriteFile(path, r, 0600)
		if err != nil {
			log.Printf("Error writing session %s: \r\n %s \r\n", openID, r)
			log.Println(err)
		} else {
			log.Println("write session to " + path)
		}
	} else {
		log.Printf("Error encoding session %s ", openID)
		log.Println(err)
	}
	return
}

func isExpired(timestamp int32) bool {
	now := int32(time.Now().Unix())
	return now > timestamp
}

func getSessionPath(openID string) (path string) {
	path = sessionDir + string(os.PathSeparator) + openID + ".json"
	ensurePathExist(path)
	return path
}

func getProcedurePath(openID, ProcedureName string) (path string) {
	path = procedureDir + string(os.PathSeparator) + ProcedureName + string(os.PathSeparator) + openID + ".json"
	ensurePathExist(path)
	return
}

func ensurePathExist(path string) {
	d := filepath.Dir(path)
	if !isFileExist(d) {
		log.Println("Creating path [" + d + "]")
		os.MkdirAll(d, 0700)
	}
}

func deleteSession(openID string) {
	path := getSessionPath(openID)
	if isFileExist(path) {
		err := os.Remove(path)
		if err != nil {
			log.Println(err)
		}
	}
}

type initProcFunc func(openid string) (newstate chatState)
type sendProcMsgFunc func(openid string) (newstate chatState)
type recvProcMsgFunc func(openid string) (newstate chatState)
type cleanProcFunc func(openid string) (newstate chatState)

//Procedure  a description about all procedure
type Procedure struct {
	init  initProcFunc    //init function
	send  sendProcMsgFunc //function for sending customized message
	recv  recvProcMsgFunc //function for receiving message, possibly transfer to new state
	clean cleanProcFunc   //function for cleanning up
}

func (c *openIDSessionData) Save() {
	//invalid procedure
	if isExpired(c.Expire) || c.Procedure == "" {
		deleteSession(c.OpenID)
	} else {
		writeSession(*c)
	}
}

//read sessions/openID.json to check whether its a Procedure for ongoing dialog
func getCurrentSesssion(openID string) (result openIDSessionData, err error) {
	result = createEmptySession(openID, 3600)
	path := getSessionPath(openID)
	if isFileExist(path) {
		log.Printf("read session from %s\r\n", path)
		body, err := ioutil.ReadFile(path)
		if err != nil { //read file error
			log.Println("Error session reading " + path)
		} else {
			err = json.Unmarshal(body, &result)
			if err != nil {
				log.Printf("Session Content [path=%s] not correct: ", path)
				result = createEmptySession(openID, 3600)
			}
		}
	}
	return
}

func createEmptySession(openID string, expire int32) (result openIDSessionData) {
	result.OpenID = openID
	result.Procedure = ""
	now := int32(time.Now().Unix())
	result.CreateAt = now
	result.UpdateAt = now
	result.Expire = now + expire
	result.KvPair = map[string]string{}
	return
}

func (c *openIDSessionData) setProcedure(procedure string) {
	c.Procedure = procedure
	c.UpdateAt = int32(time.Now().Unix())
}

func (c *openIDSessionData) setKvPair(key, val string) {
	c.KvPair[key] = val
	c.UpdateAt = int32(time.Now().Unix())
}

//main entry point for processing each incoming message
//this stage has session date available
func (c *openIDSessionData) incomingMsg(v InWechatMsg) {
	openID := v.header.FromUserName
	//are we in an existing procedure
	inProc, state := isInProc(openID) //if inside a procedure, resume last saved state
	if inProc {
		c.state = serveProc(state, v) //transit to new state
	} else {
		state, processed := serveCommand(openID, v) //menu or txt command e.g. search
		if !processed {                             // transfer to Customer Service (kf)
			kfSendTxt(openID, "未识别的命令，已转接校友会理事会，稍后答复您")
		}
		c.state = state
	}

	if !isEndingState(state) {
		err := saveChatState(openID, state.Procedure, state)
		if err != nil {
			log.Println("Error Cannot Save chat sate")
			log.Println(err)
			log.Println(state)
		}
	} else { //state ending
		cleanProcedure(openID, state.Procedure)
	}
	return
}