// OpenSAPS - Open Slack API server for everyone.
//
// Copyright (c) 2017, Stanislav N. aka pztrn.
// All rights reserved.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.
package matrixpusher

import (
    // stdlib
    "bytes"
    crand "crypto/rand"
    "encoding/json"
    "errors"
    "fmt"
    "io/ioutil"
    "net/http"

    // local
    "lab.pztrn.name/pztrn/opensaps/slack/message"
)

// Constants for random transaction ID.
const (
    letterBytes = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789" // 36 possibilities
    letterIdxBits = 6                    // 6 bits to represent 64 possibilities / indexes
    letterIdxMask = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits
)

type MatrixConnection struct {
    // API root for connection.
    api_root string
    // Connection name.
    conn_name string
    // Our device ID.
    device_id string
    // Password for user.
    password string
    // Room ID.
    room_id string
    // Token we obtained after logging in.
    token string
    // Our username for logging in to server.
    username string
}

func (mxc *MatrixConnection) doPostRequest(endpoint string, data string) ([]byte, error) {
    c.Log.Debugln("Data to send:", data)

    api_root := mxc.api_root + endpoint
    if mxc.token != "" {
        api_root += fmt.Sprintf("?access_token=%s", mxc.token)
    }
    c.Log.Debugln("Request URL:", api_root)
    req, _ := http.NewRequest("POST", api_root, bytes.NewBuffer([]byte(data)))
    req.Header.Set("Content-Type", "application/json")

    client := &http.Client{}
    resp, err := client.Do(req)
    if err != nil {
        return nil, errors.New("Failed to perform POST request to Matrix as '" + mxc.username + "' (conn " + mxc.conn_name + "): " + err.Error())
    }
    defer resp.Body.Close()
    body, _ := ioutil.ReadAll(resp.Body)

    if resp.Status == "200 OK" {
        // Return body.
        return body, nil
    } else {
        return nil, errors.New("Status: " + resp.Status + ", body: " + string(body))
    }
}

func (mxc *MatrixConnection) doPutRequest(endpoint string, data string) ([]byte, error) {
    c.Log.Debugln("Data to send:", data)
api_root := mxc.api_root + endpoint
    if mxc.token != "" {
        api_root += fmt.Sprintf("?access_token=%s", mxc.token)
    }
    c.Log.Debugln("Request URL:", api_root)
    req, _ := http.NewRequest("PUT", api_root, bytes.NewBuffer([]byte(data)))
    req.Header.Set("Content-Type", "application/json")

    client := &http.Client{}
    resp, err := client.Do(req)
    if err != nil {
        return nil, errors.New("Failed to perform PUT request to Matrix as '" + mxc.username + "' (conn " + mxc.conn_name + "): " + err.Error())
    }
    defer resp.Body.Close()
    body, _ := ioutil.ReadAll(resp.Body)

    if resp.Status == "200 OK" {
        // Return body.
        return body, nil
    } else {
        return nil, errors.New("Status: " + resp.Status + ", body: " + string(body))
    }
}

func (mxc *MatrixConnection) generateTnxId() string {
    // Random tnxid - 16 chars.
    length := 16

    result := make([]byte, length)
    bufferSize := int(float64(length)*1.3)

    // Making sure that we have only letters and numbers and resulted
    // string will be exactly requested length.
    for i, j, randomBytes := 0, 0, []byte{}; i < length; j++ {
        if j%bufferSize == 0 {
            randomBytes = mxc.generateTnxIdSecureBytes(bufferSize)
        }
        if idx := int(randomBytes[j%length] & letterIdxMask); idx < len(letterBytes) {
            result[i] = letterBytes[idx]
            i++
        }
    }
    return string(result)
}

func (mxc *MatrixConnection) generateTnxIdSecureBytes(length int) []byte {
    // Get random bytes.
    var randomBytes = make([]byte, length)
    _, err := crand.Read(randomBytes)
    if err != nil {
        c.Log.Fatalln("Unable to generate random bytes for transaction ID!")
    }

    return randomBytes
}

func (mxc *MatrixConnection) Initialize(conn_name string, api_root string, user string, password string, room_id string) {
    mxc.conn_name = conn_name
    mxc.api_root = api_root
    mxc.username = user
    mxc.password = password
    mxc.room_id = room_id
    mxc.token = ""

    c.Log.Debugln("Trying to connect to", mxc.conn_name, "(" + api_root + ")")

    loginStr := fmt.Sprintf(`{"type": "m.login.password", "user": "%s", "password": "%s"}`, mxc.username, mxc.password)
    c.Log.Debugln("Login string:", loginStr)
    reply, err := mxc.doPostRequest("/login", loginStr)
    if err != nil {
        c.Log.Fatalf("Failed to login to Matrix with user '%s' (conn %s): '%s'", mxc.username, mxc.conn_name, err.Error())
    }
    // Parse received JSON and get access token.
    data := make(map[string]string)
    err1 := json.Unmarshal(reply, &data)
    if err1 != nil {
        c.Log.Fatalf("Failed to parse received JSON from Matrix for user '%s' (conn %s): %s", mxc.username, mxc.conn_name, err1.Error())
    }
    mxc.token = data["access_token"]
    mxc.device_id = data["device_id"]

    c.Log.Debugf("Login successful for conn '%s', access token is '%s', our device_id is '%s'", mxc.conn_name, mxc.token, mxc.device_id)

    // We should check if we're already in room and, if not, join it.
    // We will do this by simply trying to join. We don't care about reply
    // here.
    _, err2 := mxc.doPostRequest("/rooms/" + mxc.room_id + "/join", "{}")
    if err2 != nil {
        c.Log.Fatalf("Failed to join room: %s", err2.Error())
    }

    // If we're here - everything is okay and we already in room. Send
    // greeting message.
    mxc.SendMessage("OpenSAPS is back in business for connection '" + mxc.conn_name + "'!")
}

// This function launches when new data was received thru Slack API.
// It will prepare a message which will be passed to mxc.SendMessage().
func (mxc *MatrixConnection) ProcessMessage(message slackmessage.SlackMessage) {
    // Prepare message body.
    message_body := message.Text

    // ToDo: attachments handling.

    // Send message.
    mxc.SendMessage(message_body)
}

// This function sends already prepared message to room.
func (mxc *MatrixConnection) SendMessage(message string) {
    c.Log.Debugf("Sending message to connection '%s': '%s'", mxc.conn_name, message)

    // We should send notices as it is preferred behaviour for bots and
    // appservices.
    //msgStr := fmt.Sprintf(`{"msgtype": "m.text", "body": "%s", "format": "org.matrix.custom.html", "formatted_body": "%s"}`, message, message)
    msgStr := fmt.Sprintf(`{"msgtype": "m.notice", "body": "%s"}`, message)
    reply, err := mxc.doPutRequest("/rooms/" + mxc.room_id + "/send/m.room.message/" + mxc.generateTnxId(), msgStr)
    if err != nil {
        c.Log.Fatalf("Failed to send message to room '%s' (conn: '%s'): %s", mxc.room_id, mxc.conn_name, err.Error())
    }
    c.Log.Debugf("Message sent, reply: %s", string(reply))
}

func (mxc *MatrixConnection) Shutdown() {
    c.Log.Infof("Shutting down connection '%s'...", mxc.conn_name)

    _, err := mxc.doPostRequest("/logout", "{}")
    if err != nil {
        c.Log.Errorf("Error occured while trying to log out from Matrix (conn %s): %s", mxc.conn_name, err.Error())
    }
    mxc.token = ""
    c.Log.Infof("Connection '%s' successfully shutted down", mxc.conn_name)
}