// See documentation here:
//
// Sending notifications
//
// https://firebase.google.com/docs/cloud-messaging/send-message?hl=en
//
// OAuth2.0
//
// https://developers.google.com/identity/protocols/oauth2/service-account?hl=en
package fcm

import (
	"bufio"
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"io/ioutil"
	"mime"
	"mime/multipart"
	"net/http"
	"net/textproto"

	"git.bit5.ru/backend/colog"
	"git.bit5.ru/backend/errors"
	"golang.org/x/oauth2"
)

const (
	fcmErrorType = "type.googleapis.com/google.firebase.fcm.v1.FcmError"

	maxMessages       = 500
	multipartBoundary = "msg_boundary"

	BatchSendEndpoint = "https://fcm.googleapis.com/batch"
)

var (
	AuthScopes = []string{"https://www.googleapis.com/auth/firebase.messaging"}
)

func MakeSendEndpoint(projectId string) string {
	return fmt.Sprintf("https://fcm.googleapis.com/v1/projects/%s/messages:send", projectId)
}

type Credentials struct {
	Type string `json:"type"`

	ProjectID    string `json:"project_id"`
	PrivateKeyID string `json:"private_key_id"`
	PrivateKey   string `json:"private_key"`

	ClientID    string `json:"client_id"`
	ClientEmail string `json:"client_email"`

	AuthURL  string `json:"auth_uri"`
	TokenURL string `json:"token_uri"`
}

func ReadCredentialsFromFile(filename string) (Credentials, error) {
	data, err := ioutil.ReadFile(filename)
	if err != nil {
		return Credentials{}, errors.WithStack(err)
	}

	var c Credentials
	if err := json.Unmarshal(data, &c); err != nil {
		return Credentials{}, errors.WithStack(err)
	}

	return c, nil
}

type ClientConfig struct {
	SendEndpoint      string
	BatchSendEndpoint string
}

type Client struct {
	cfg    ClientConfig
	ts     oauth2.TokenSource
	hc     *http.Client
	logger *colog.CoLog
}

func NewClient(cfg ClientConfig, ts oauth2.TokenSource, hc *http.Client, logger *colog.CoLog) *Client {
	return &Client{
		cfg:    cfg,
		ts:     ts,
		hc:     hc,
		logger: logger,
	}
}

func (c *Client) SendMessage(msg Message) (SendResponse, error) {
	sendRequest := SendRequest{
		ValidateOnly: false,
		Message:      msg,
	}

	return c.doSendRequest(sendRequest)
}

func (c *Client) ValidateMessage(msg Message) (SendResponse, error) {
	sendRequest := SendRequest{
		ValidateOnly: true,
		Message:      msg,
	}

	return c.doSendRequest(sendRequest)
}

func (c *Client) doSendRequest(req SendRequest) (SendResponse, error) {
	accessToken, err := c.ts.Token()
	if err != nil {
		return SendResponse{}, err
	}

	data, err := json.Marshal(req)
	if err != nil {
		return SendResponse{}, errors.WithStack(err)
	}
	c.logger.Logf("sending message: %s", data)

	request, err := http.NewRequest(http.MethodPost, c.cfg.SendEndpoint, bytes.NewReader(data))
	if err != nil {
		return SendResponse{}, errors.WithStack(err)
	}

	accessToken.SetAuthHeader(request)
	request.Header.Set("Content-Type", "application/json")

	response, err := c.hc.Do(request)
	if err != nil {
		return SendResponse{}, errors.WithStack(err)
	}
	defer response.Body.Close()

	if response.StatusCode != http.StatusOK {
		body, err := ioutil.ReadAll(response.Body)
		if err != nil {
			return SendResponse{}, errors.WithStack(err)
		}

		return SendResponse{}, errors.New(string(body))
	}

	var resp SendResponse
	if err := json.NewDecoder(response.Body).Decode(&resp); err != nil {
		return SendResponse{}, errors.WithStack(err)
	}

	return resp, nil
}

func (c *Client) SendMessages(messages []Message) (MultiSendResponse, error) {
	return c.doSendMessages(messages, false)
}

func (c *Client) ValidateMessages(messages []Message) (MultiSendResponse, error) {
	return c.doSendMessages(messages, true)
}

func (c *Client) doSendMessages(messages []Message, validateOnly bool) (MultiSendResponse, error) {
	messageCount := len(messages)
	if messageCount == 0 {
		return MultiSendResponse{}, nil
	}
	if messageCount > maxMessages {
		return MultiSendResponse{}, errors.New(fmt.Sprintf("messages limit (%d) exceeded: %d", maxMessages, messageCount))
	}

	accessToken, err := c.ts.Token()
	if err != nil {
		return MultiSendResponse{}, err
	}

	var body bytes.Buffer
	w := multipart.NewWriter(&body)
	w.SetBoundary(multipartBoundary)

	for index, msg := range messages {
		req := SendRequest{
			ValidateOnly: validateOnly,
			Message:      msg,
		}

		body, err := c.makeMessageRequest(req)
		if err != nil {
			return MultiSendResponse{}, err
		}

		if err := writePartTo(w, body, index); err != nil {
			return MultiSendResponse{}, err
		}
	}

	if err := w.Close(); err != nil {
		return MultiSendResponse{}, errors.WithStack(err)
	}

	request, err := http.NewRequest(http.MethodPost, c.cfg.BatchSendEndpoint, &body)
	if err != nil {
		return MultiSendResponse{}, errors.WithStack(err)
	}

	accessToken.SetAuthHeader(request)
	request.Header.Set("Content-Type", fmt.Sprintf(`multipart/mixed; boundary="%s"`, multipartBoundary))

	response, err := c.hc.Do(request)
	if err != nil {
		return MultiSendResponse{}, errors.WithStack(err)
	}
	defer response.Body.Close()

	return c.makeMultiSendResponse(response, messageCount)
}

func (c *Client) makeMessageRequest(req SendRequest) ([]byte, error) {
	reqJson, err := json.Marshal(req)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	request, err := http.NewRequest(http.MethodPost, c.cfg.SendEndpoint, bytes.NewBuffer(reqJson))
	if err != nil {
		return nil, errors.WithStack(err)
	}

	request.Header.Set("Content-Type", "application/json; charset=UTF-8")
	request.Header.Set("User-Agent", "")

	var body bytes.Buffer
	if err := request.Write(&body); err != nil {
		return nil, errors.WithStack(err)
	}

	return body.Bytes(), nil
}

func writePartTo(w *multipart.Writer, bytes []byte, index int) error {
	header := make(textproto.MIMEHeader)
	header.Set("Content-Type", "application/http")
	header.Set("Content-Transfer-Encoding", "binary")
	header.Set("Content-ID", fmt.Sprintf("%d", index+1))

	part, err := w.CreatePart(header)
	if err != nil {
		return errors.WithStack(err)
	}
	if _, err := part.Write(bytes); err != nil {
		return errors.WithStack(err)
	}

	return nil
}

func (c *Client) makeMultiSendResponse(response *http.Response, totalCount int) (MultiSendResponse, error) {
	responses := make([]SendResponse, 0, totalCount)
	var fails int

	_, params, err := mime.ParseMediaType(response.Header.Get("Content-Type"))
	if err != nil {
		return MultiSendResponse{}, errors.WithStack(err)
	}

	reader := multipart.NewReader(response.Body, params["boundary"])
	for {
		part, err := reader.NextPart()
		if err == io.EOF {
			break
		} else if err != nil {
			return MultiSendResponse{}, errors.WithStack(err)
		}

		resp, err := makeSendResponseFromPart(part)
		if err != nil {
			return MultiSendResponse{}, err
		}

		responses = append(responses, resp)
		if resp.HasError() {
			c.logger.Logf("error: %+v", *resp.Error)
			fails++
		}
	}

	return MultiSendResponse{
		Responses: responses,
		Sent:      totalCount - fails,
		Failed:    fails,
	}, nil
}

func makeSendResponseFromPart(part *multipart.Part) (SendResponse, error) {
	response, err := http.ReadResponse(bufio.NewReader(part), nil)
	if err != nil {
		return SendResponse{}, errors.WithStack(err)
	}
	defer response.Body.Close()

	body, err := ioutil.ReadAll(response.Body)
	if err != nil {
		return SendResponse{}, errors.WithStack(err)
	}

	var resp SendResponse
	if err := json.Unmarshal(body, &resp); err != nil {
		return SendResponse{}, errors.WithMessagef(err, "response body: %s", body)
	}

	return resp, nil
}

type SendRequest struct {
	// Flag for testing the request without actually delivering the message.
	ValidateOnly bool `json:"validate_only,omitempty"`

	Message Message `json:"message"`
}

type SendResponse struct {
	MessageName string `json:"name"`

	Error *SendError `json:"error"`
}

func (sr SendResponse) HasError() bool {
	return sr.Error != nil
}

type SendErrorCode string

const (
	SendErrorCode_UNSPECIFIED_ERROR      SendErrorCode = "UNSPECIFIED_ERROR"
	SendErrorCode_UNREGISTERED           SendErrorCode = "UNREGISTERED"
	SendErrorCode_SENDER_ID_MISMATCH     SendErrorCode = "SENDER_ID_MISMATCH"
	SendErrorCode_QUOTA_EXCEEDED         SendErrorCode = "QUOTA_EXCEEDED"
	SendErrorCode_THIRD_PARTY_AUTH_ERROR SendErrorCode = "THIRD_PARTY_AUTH_ERROR"
)

type SendError struct {
	Code    int    `json:"code"`
	Message string `json:"message"`
	Status  string `json:"status"`
	Details []struct {
		Type      string        `json:"@type"`
		ErrorCode SendErrorCode `json:"errorCode"`
	} `json:"details"`
}

func (se *SendError) IsUnregistered() bool {
	if se == nil {
		return false
	}

	for _, d := range se.Details {
		if d.Type == fcmErrorType && d.ErrorCode == SendErrorCode_UNREGISTERED {
			return true
		}
	}

	return false
}

type MultiSendResponse struct {
	Responses []SendResponse
	Sent      int
	Failed    int
}

type Message struct {
	Token        string            `json:"token,omitempty"`
	Topic        string            `json:"topic,omitempty"`
	Condition    string            `json:"condition,omitempty"`
	Data         map[string]string `json:"data,omitempty"`
	Notification *Notification     `json:"notification,omitempty"`
	FcmOptions   *FcmOptions       `json:"fcm_options,omitempty"`
	Android      *AndroidConfig    `json:"android,omitempty"`
	Webpush      *WebpushConfig    `json:"webpush,omitempty"`
	Apns         *ApnsConfig       `json:"apns,omitempty"`
}

// Basic notification template to use across all platforms.
type Notification struct {
	Title string `json:"title,omitempty"`
	Body  string `json:"body,omitempty"`
	Image string `json:"image,omitempty"`
}

type FcmOptions struct {
	// Label associated with the message's analytics data.
	//   Format: ^[a-zA-Z0-9-_.~%]{1,50}$
	AnalyticsLabel string `json:"analytics_label,omitempty"`
}

type AndroidConfig struct {
	CollapseKey           string                 `json:"collapse_key,omitempty"`
	Priority              AndroidMessagePriority `json:"priority,omitempty"`
	TTL                   string                 `json:"ttl,omitempty"`
	RestrictedPackageName string                 `json:"restricted_package_name,omitempty"`
	Data                  map[string]string      `json:"data,omitempty"`
	Notification          *AndroidNotification   `json:"notification,omitempty"`
	FcmOptions            *AndroidFcmOptions     `json:"fcm_options,omitempty"`
	DirectBootOk          bool                   `json:"direct_boot_ok,omitempty"`
}

type AndroidMessagePriority uint8

const (
	// Default priority for data messages.
	//
	// Normal priority messages won't open network connections on a sleeping device,
	// and their delivery may be delayed to conserve the battery.
	AndroidMessagePriority_NORMAL AndroidMessagePriority = 0

	// Default priority for notification messages.
	//
	// FCM attempts to deliver high priority messages immediately,
	// allowing the FCM service to wake a sleeping device when possible
	// and open a network connection to your app server.
	AndroidMessagePriority_HIGH AndroidMessagePriority = 1
)

type AndroidFcmOptions struct {
	AnalyticsLabel string `json:"analytics_label,omitempty"`
}

type NotificationPriority uint8

const (
	NotificationPriority_UNSPECIFIED NotificationPriority = 0

	// Notifications might not be shown to the user except under special circumstances, such as detailed notification logs.
	NotificationPriority_MIN NotificationPriority = 1

	// The UI may choose to show the notifications smaller, or at a different position in the list, compared with notifications with DEFAULT.
	NotificationPriority_LOW NotificationPriority = 2

	// If the application does not prioritize its own notifications, use this value for all notifications.
	NotificationPriority_DEFAULT NotificationPriority = 3

	// Use this for more important notifications or alerts.
	//
	// The UI may choose to show these notifications larger, or at a different position in the notification lists, compared with notifications with DEFAULT.
	NotificationPriority_HIGH NotificationPriority = 4

	// Use this for the application's most important items that require the user's prompt attention or input.
	NotificationPriority_MAX NotificationPriority = 5
)

type NotificationVisibility uint8

const (
	NotificationVisibility_UNSPECIFIED NotificationVisibility = 0

	// Show this notification on all lockscreens, but conceal sensitive or private information on secure lockscreens.
	NotificationVisibility_PRIVATE NotificationVisibility = 1

	// Show this notification in its entirety on all lockscreens.
	NotificationVisibility_PUBLIC NotificationVisibility = 2

	// Do not reveal any part of this notification on a secure lockscreen.
	NotificationVisibility_SECRET NotificationVisibility = 3
)

type LightSettings struct {
	Color       Color  `json:"color,omitempty"`
	OnDuration  string `json:"light_on_duration,omitempty"`
	OffDuration string `json:"light_off_duration,omitempty"`
}

type Color struct {
	Red   float32 `json:"red,omitempty"`
	Green float32 `json:"green,omitempty"`
	Blue  float32 `json:"blue,omitempty"`
	Alpha float32 `json:"alpha,omitempty"`
}

type AndroidNotification struct {
	Title                    string                 `json:"title,omitempty"`
	Body                     string                 `json:"body,omitempty"`
	Image                    string                 `json:"image,omitempty"`
	Icon                     string                 `json:"icon,omitempty"`
	Color                    string                 `json:"color,omitempty"`
	Sound                    string                 `json:"sound,omitempty"`
	Tag                      string                 `json:"tag,omitempty"`
	ClickAction              string                 `json:"click_action,omitempty"`
	ChannelID                string                 `json:"channel_id,omitempty"`
	BodyLocalizationKey      string                 `json:"body_loc_key,omitempty"`
	BodyLocalizationArgs     []string               `json:"body_loc_args,omitempty"`
	TitleLocalizationKey     string                 `json:"title_loc_key,omitempty"`
	TitleLocalizationArgs    []string               `json:"title_loc_args,omitempty"`
	Ticker                   string                 `json:"ticker,omitempty"`
	Sticky                   bool                   `json:"sticky,omitempty"`
	EventTime                string                 `json:"event_time,omitempty"`
	LocalOnly                bool                   `json:"local_only,omitempty"`
	Priority                 NotificationPriority   `json:"notification_priority,omitempty"`
	UseDefaultSound          bool                   `json:"default_sound,omitempty"`
	UseDefaultVibrateTimings bool                   `json:"default_vibrate_timings,omitempty"`
	UseDefaultLightSettings  bool                   `json:"default_light_settings,omitempty"`
	VibrateTimings           []string               `json:"vibrate_timings,omitempty"`
	Visibility               NotificationVisibility `json:"visibility,omitempty"`
	Count                    int                    `json:"notification_count,omitempty"`
	LightSettings            *LightSettings         `json:"light_settings,omitempty"`
}

type WebpushConfig struct {
	Headers      map[string]string   `json:"headers,omitempty"`
	Data         map[string]string   `json:"data,omitempty"`
	Notification WebpushNotification `json:"notification,omitempty"`
	FcmOptions   WebpushFcmOptions   `json:"fcm_options,omitempty"`
}

type WebpushNotification struct{}

type WebpushFcmOptions struct {
	Link           string `json:"link,omitempty"`
	AnalyticsLabel string `json:"analytics_label,omitempty"`
}

// Apple specific options for message
type ApnsConfig struct {
	Headers      *ApnsHeaders    `json:"headers,omitempty"`
	Notification *ApnsPayload    `json:"payload,omitempty"`
	FcmOptions   *ApnsFcmOptions `json:"fcm_options,omitempty"`
}

type ApnsHeaders struct {
	PushType   string `json:"apns-push-type,omitempty"`
	Id         string `json:"apns-id,omitempty"`
	Expiration int64  `json:"apns-expiration,omitempty"`
	Priority   uint8  `json:"apns-priority,omitempty"`
	Topic      string `json:"apns-topic,omitempty"`
	CollapseId string `json:"apns-collapse-id,omitempty"`
}

type ApnsPayload struct {
	Aps ApnsPayloadKeys `json:"aps"`

	// TODO: add support for custom keys
	// https://developer.apple.com/documentation/usernotifications/setting_up_a_remote_notification_server/generating_a_remote_notification
	customKeys map[string]interface{}
}

type ApnsPayloadKeys struct {
	Alert             *ApnsAlert `json:"alert,omitempty"`
	Badge             int        `json:"badge,omitempty"`
	Sound             string     `json:"sound,omitempty"`
	ThreadId          string     `json:"thread-id,omitempty"`
	Category          string     `json:"category,omitempty"`
	ContentAvailable  int        `json:"content-available,omitempty"`
	MutableContent    int        `json:"mutable-content,omitempty"`
	TargetContentId   string     `json:"target-content-id,omitempty"`
	InterruptionLevel string     `json:"interruption-level,omitempty"`
	RelevanceScore    int        `json:"relevance-score,omitempty"`

	CriticalSound *ApnsCriticalSound `json:"-"`
}

type ApnsAlert struct {
	Title           string   `json:"title,omitempty"`
	Subtitle        string   `json:"subtitle,omitempty"`
	Body            string   `json:"body,omitempty"`
	LaunchImg       string   `json:"launch-image,omitempty"`
	TitleLocKey     string   `json:"title-loc-key,omitempty"`
	TitleLocArgs    []string `json:"title-loc-args,omitempty"`
	SubtitleLocKey  string   `json:"subtitle-loc-key,omitempty"`
	SubtitleLocArgs []string `json:"subtitle-loc-args,omitempty"`
	LocKey          string   `json:"loc-key,omitempty"`
	LocArgs         []string `json:"loc-args,omitempty"`
}

type ApnsCriticalSound struct {
	Critical int    `json:"critical,omitempty"`
	Name     string `json:"name,omitempty"`
	Volume   int    `json:"volume,omitempty"`
}

type ApnsFcmOptions struct {
	AnalyticsLabel string `json:"analytics_label,omitempty"`
	Image          string `json:"image,omitempty"`
}