package main

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

//chat state that we might be use for collecting infomation from user
type chatState struct {
	//back pointer style information
	OpenID    string `json:"OpenID"`    //whom is this belongs to
	Procedure string `json:"Procedure"` //which procedure this belongs to

	//real state information
	Name   string   `json:"Name"`   //state name
	Expire int32    `json:"Expire"` //unix timestamp  when this state expire
	Send   struct { //anything we need to send?
		Type    string            `json:"Type"`    //what type of message
		Message map[string]string `json:"Message"` //the message to be sent,key value pair to describe the message
	} `json:"Send"`

	Receive struct { //anything we expect to receive
		Validator string            `json:"Validator"`
		Hint      string            `json:"Hint"`
		Message   map[string]string `json:"Message"` //the description for receiving message
	} `json:"Receive"`

	Save map[string]string `json:"Save"` //the state save some data for later usage
}

//for individual state
func getCurrentState(openID string, procedure string) (result chatState, err error) {
	path := getProcedurePath(openID, procedure)
	log.Printf("read state from %s\r\n", path)
	body, err := ioutil.ReadFile(path)
	if err != nil { //read file error
		if isFileExist(path) {
			log.Println("Error session reading " + path)
		}
		return //empty and expired session
	}
	err = json.Unmarshal(body, &result)
	if err != nil {
		log.Printf("Session Content [path=%s] not correct: ", path)
		log.Println(err)
	}
	//we don't check Expire, we give the caller full control on
	//how to deal wiht expired session

	//check whether state is for the correct openID and procedure
	if result.OpenID != openID {
		err = errors.New("Error: State for " + openID + " is actually for " + result.OpenID)
		return
	}

	if result.Procedure != procedure {
		err = errors.New("Error: Proecdure for " + procedure + " is actually for " + result.Procedure)
		return
	}
	return
}

func setCurrentState(openID, procedure string, state chatState) (newState chatState, err error) {
	state.OpenID = openID
	state.Procedure = procedure

	j, err := json.Marshal(state)
	if err != nil {
		return
	}
	path := getProcedurePath(openID, procedure)
	err = ioutil.WriteFile(path, j, 0600)
	if err != nil {
		log.Println("write state error" + path)
		log.Println(err)
		return
	}
	newState = state
	return
}

func deleteChatState(openID, procedure string) (err error) {
	path := getProcedurePath(openID, procedure)
	err = os.Remove(path)
	return
}

//ValidationResult After input validation, what is the result
type ValidationResult struct {
	accept  bool
	Hint    string
	Error   string
	Warning string
}

//Validator function type for validating all wechat inputs
type Validator func(s chatState) ValidationResult

//start a procedure
func startProcedure(openID, procedure string) (err error) {
	//init procedure state
	init := getProcedureInit(openID, procedure)
	if init == nil {
		msg := "FATAL: cannot initialize procedure [" + procedure + "] "
		err = errors.New(msg)
		return
	}
	//init and get initial state
	state := init(openID)

	//do the real concret work for processing the state
	err = processProcedureState(state)

	return
}

//resume a previous Procedure's state
func resumeProcedure(openID, procedure string) (err error) {
	state, err := getCurrentState(openID, procedure)
	if err != nil {
		return
	}
	return processProcedureState(state)
}

//finish a procedure, regardless its been finished or not
//normally not finished normally
func stopProcedure(openID, procedure string) {
	path := getProcedurePath(openID, procedure)
	os.Remove(path)
	log.Println("Clearing [" + openID + "] @ [" + procedure + "]")
}

func processProcedureState(state chatState) (err error) {
	//send what we need to send
	if isExpired(state.Expire) {
		return errors.New("State has expired " + state.Name)
	}
	//mark we have sent.

	//do we need input? waiting for input

	//if not, what is next state

	log.Println(state)
	return
}

type initProcedureFunction func(openid string) (initState chatState)

func getProcedureInit(openID, procedure string) initProcedureFunction {
	initFunc := map[string]initProcedureFunction{
		"TestDummy":        nil,
		"TestEcho":         initTestEcho,
		"GetBasicUserInfo": initGetBasicUserInfo,
		"GetEmailAddr":     initGetBasicUserInfo,
	}
	return initFunc[procedure]
}

func initTestEcho(openid string) (r chatState) {
	r.Name = openid
	r.Expire = int32(time.Now().Unix() + 100)
	return
}