// 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 (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"sync"

	"git.bit5.ru/backend/errors"

	"github.com/go-logr/logr"
	"golang.org/x/oauth2"

	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/codes"
	"go.opentelemetry.io/otel/trace"
)

const tracerName = "git.bit5.ru/backend/fcm"

var tracer = otel.Tracer(tracerName)

//-----------------------------------------------------------------------------

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

	maxMessages       = 500
	multipartBoundary = "msg_boundary"
)

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 := os.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
}

type Client struct {
	sendEndpoint string
	ts           oauth2.TokenSource
	hc           *http.Client
	logger       logr.Logger
}

func NewClient(projectId string, cfg ClientConfig, ts oauth2.TokenSource, hc *http.Client, logger logr.Logger) *Client {
	return &Client{
		sendEndpoint: MakeSendEndpoint(projectId),
		ts:           ts,
		hc:           hc,
		logger:       logger,
	}
}

func (c *Client) SendMessage(ctx context.Context, msg Message) (SendResponse, error) {

	ctx, span := tracer.Start(ctx, "Client.SendMessage")
	defer span.End()

	sendRequest := SendRequest{
		ValidateOnly: false,
		Message:      msg,
	}

	return c.doSendRequest(ctx, sendRequest, true)
}

func (c *Client) ValidateMessage(ctx context.Context, msg Message) (SendResponse, error) {

	ctx, span := tracer.Start(ctx, "Client.ValidateMessage")
	defer span.End()

	sendRequest := SendRequest{
		ValidateOnly: true,
		Message:      msg,
	}

	return c.doSendRequest(ctx, sendRequest, true)
}

func (c *Client) Send(ctx context.Context, message Message) (string, error) {

	ctx, span := tracer.Start(ctx, "Client.Send")
	defer span.End()

	sendRequest := SendRequest{
		ValidateOnly: false,
		Message:      message,
	}

	resp, err := c.doSendRequest(ctx, sendRequest, false)
	if err != nil {
		span.SetStatus(codes.Error, err.Error())
		span.RecordError(err)
		return "", err
	}

	return resp.MessageName, nil
}

func (c *Client) Validate(ctx context.Context, message Message) (string, error) {

	ctx, span := tracer.Start(ctx, "Client.Validate")
	defer span.End()

	sendRequest := SendRequest{
		ValidateOnly: true,
		Message:      message,
	}

	resp, err := c.doSendRequest(ctx, sendRequest, false)
	if err != nil {
		span.SetStatus(codes.Error, err.Error())
		span.RecordError(err)
		return "", err
	}

	return resp.MessageName, nil
}

func (c *Client) doSendRequest(ctx context.Context, req SendRequest, loggerEnabled bool) (SendResponse, error) {

	spanAttrs := trace.WithAttributes(
		attribute.String("token", req.Message.Token),
	)

	_, span := tracer.Start(ctx, "Client.doSendRequest", spanAttrs)
	defer span.End()

	accessToken, err := c.ts.Token()
	if err != nil {
		span.SetStatus(codes.Error, err.Error())
		span.RecordError(err)
		return SendResponse{}, err
	}

	data, err := json.Marshal(req)
	if err != nil {
		span.SetStatus(codes.Error, err.Error())
		span.RecordError(err)
		return SendResponse{}, errors.WithStack(err)
	}
	span.SetAttributes(
		attribute.String("request.body", string(data)),
	)
	if loggerEnabled {
		c.logger.Info("sending", "message", data)
	}

	request, err := http.NewRequest(http.MethodPost, c.sendEndpoint, bytes.NewReader(data))
	if err != nil {
		span.SetStatus(codes.Error, err.Error())
		span.RecordError(err)
		return SendResponse{}, errors.WithStack(err)
	}

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

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

	body, err := io.ReadAll(response.Body)
	if err != nil {
		span.SetStatus(codes.Error, err.Error())
		span.RecordError(err)
		return SendResponse{}, errors.WithStack(err)
	}

	bodyStr := string(body)

	span.SetAttributes(
		attribute.Int("response.status_code", response.StatusCode),
		attribute.String("response.body", bodyStr),
	)

	if response.StatusCode != http.StatusOK {
		err := errors.Errorf("Status is not OK. Status: %d. Body: %q.", response.StatusCode, bodyStr)
		span.SetStatus(codes.Error, err.Error())
		span.RecordError(err)
		return SendResponse{}, err
	}

	var resp SendResponse
	if err := json.Unmarshal(body, &resp); err != nil {
		newErr := errors.Errorf("Can not parse send response as JSON. Response: %q. Error: %v", bodyStr, err)
		span.SetStatus(codes.Error, err.Error())
		span.RecordError(err)
		return SendResponse{}, newErr
	}

	return resp, nil
}

func (c *Client) SendEach(ctx context.Context, messages []Message) (MessageMultiSendResponse, error) {

	ctx, span := tracer.Start(ctx, "Client.SendEach")
	defer span.End()

	resp, err := c.doSendEachInBatch(ctx, messages, false)
	if err != nil {
		span.SetStatus(codes.Error, err.Error())
		span.RecordError(err)
		return MessageMultiSendResponse{}, err
	}

	if resp.Failed > 0 {
		span.SetStatus(codes.Error, "Some notifications not sent.")
	}

	return resp, nil
}

func (c *Client) doSendEachInBatch(
	ctx context.Context,
	messages []Message,
	validateOnly bool,
) (MessageMultiSendResponse, error) {

	ctx, span := tracer.Start(ctx, "Client.doSendEachInBatch")
	defer span.End()

	messageCount := len(messages)
	if messageCount == 0 {
		return MessageMultiSendResponse{}, nil
	}

	if messageCount > maxMessages {
		err := errors.New(fmt.Sprintf("messages limit (%d) exceeded: %d", maxMessages, messageCount))
		span.SetStatus(codes.Error, err.Error())
		span.RecordError(err)
		return MessageMultiSendResponse{}, err
	}

	var responses = make([]MessageSendResponse, len(messages))
	var wg sync.WaitGroup

	for idx, m := range messages {
		//if err := validateMessage(m); err != nil {
		//	return nil, fmt.Errorf("invalid message at index %d: %v", idx, err)
		//}
		wg.Add(1)
		go func(idx int, m Message, validateOnly bool, responses []MessageSendResponse) {
			defer wg.Done()
			var resp string
			var err error
			if validateOnly {
				resp, err = c.Validate(ctx, m)
			} else {
				resp, err = c.Send(ctx, m)
			}
			if err == nil {
				responses[idx] = MessageSendResponse{
					Success:   true,
					MessageID: resp,
				}
			} else {
				span.SetStatus(codes.Error, "Some notifications not sent.")
				responses[idx] = MessageSendResponse{
					Success: false,
					Error:   err,
				}
			}
		}(idx, m, validateOnly, responses)
	}
	// Wait for all Validate/Send calls to finish
	wg.Wait()

	sentAmount := 0
	for _, r := range responses {
		if r.Success {
			sentAmount++
		}
	}

	failedAmount := len(responses) - sentAmount

	span.SetAttributes(
		attribute.Int("resp.total", len(responses)),
		attribute.Int("resp.sent_amount", sentAmount),
		attribute.Int("resp.failed_amount", failedAmount),
	)

	resp := MessageMultiSendResponse{
		Responses: responses,
		Sent:      sentAmount,
		Failed:    failedAmount,
	}

	return resp, nil
}

type MessageSendResponse struct {
	Success   bool
	MessageID string
	Error     error
}

type MessageMultiSendResponse struct {
	Responses []MessageSendResponse
	Sent      int
	Failed    int
}

// Запрос на отправку пуш-оповещения.
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
}