package service

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"os"
	"strings"
	"time"

	"github.com/gochat/gochat/internal/model"
	"github.com/gochat/gochat/internal/repository"
	applogger "github.com/gochat/gochat/pkg/logger"
)

var ErrSlackInvalidChannel = errors.New("invalid slack channel")

// SlackIntegrationService implements Slack integration business logic.
// Reference: Chatwoot Integrations::SlackController + SlackService
// Slack integration sends conversation notifications to a Slack channel and
// supports Slack slash commands for ticket creation.
type SlackIntegrationService struct {
	hookRepo *repository.IntegrationHookRepo
	client   *slackAPIClient
}

// NewSlackIntegrationService creates a new SlackIntegrationService.
func NewSlackIntegrationService(hookRepo *repository.IntegrationHookRepo) *SlackIntegrationService {
	return &SlackIntegrationService{hookRepo: hookRepo, client: newSlackAPIClientFromEnv()}
}

// CreateSlackRequest is the DTO for creating/updating a Slack integration.
// Reference: Chatwoot SlackController#create — params: {code, inbox_id}
type CreateSlackRequest struct {
	Code        string `json:"code,omitempty"`
	InboxID     *uint  `json:"inbox_id,omitempty"`
	ChannelID   string `json:"channel_id" validate:"required"`
	ChannelName string `json:"channel_name,omitempty"`
	SlackToken  string `json:"slack_token,omitempty"`
}

// UpdateSlackRequest is the DTO for updating a Slack integration.
type UpdateSlackRequest struct {
	ReferenceID string `json:"reference_id,omitempty"`
	ChannelID   string `json:"channel_id,omitempty"`
	ChannelName string `json:"channel_name,omitempty"`
	SlackToken  string `json:"slack_token,omitempty"`
}

// Create creates a Slack integration hook for an account.
func (s *SlackIntegrationService) Create(ctx context.Context, accountID uint, req CreateSlackRequest) (*model.IntegrationHook, error) {
	accessToken := strings.TrimSpace(req.SlackToken)
	if accessToken == "" {
		var err error
		accessToken, err = s.client.exchangeOAuthCode(ctx, accountID, req.Code)
		if err != nil {
			return nil, err
		}
	}

	settingsJSON, err := json.Marshal(slackSettingsFromCreate(req))
	if err != nil {
		return nil, fmt.Errorf("failed to marshal Slack settings: %w", err)
	}

	hook := &model.IntegrationHook{
		AccountID:   accountID,
		AppID:       "slack",
		InboxID:     req.InboxID,
		HookType:    model.HookTypeSlack,
		Status:      model.HookStatusInactive,
		AccessToken: accessToken,
		Settings:    settingsJSON,
	}

	if err := s.hookRepo.Create(ctx, hook); err != nil {
		return nil, fmt.Errorf("failed to create Slack integration: %w", err)
	}

	applogger.L().Infof("Slack integration created: account=%d", accountID)
	return hook, nil
}

// Update updates a Slack integration hook.
func (s *SlackIntegrationService) Update(ctx context.Context, accountID uint, req UpdateSlackRequest) (*model.IntegrationHook, error) {
	hooks, err := s.findSlackHooks(ctx, accountID)
	if err != nil || len(hooks) == 0 {
		return nil, fmt.Errorf("Slack integration not found for account %d", accountID)
	}

	hook := &hooks[0]
	referenceID := firstNonBlank(req.ReferenceID, req.ChannelID)
	channel, err := s.findChannel(ctx, *hook, referenceID)
	if err != nil {
		return nil, err
	}
	if channel == nil {
		return nil, ErrSlackInvalidChannel
	}
	if !channel.IsPrivate {
		if err := s.client.joinChannel(ctx, hook.AccessToken, channel.ID); err != nil {
			return nil, err
		}
	}

	settings := model.SlackSettings{ChannelName: channel.Name}
	if req.SlackToken != "" {
		hook.AccessToken = req.SlackToken
		settings.SlackToken = req.SlackToken
	}

	settingsJSON, err := json.Marshal(settings)
	if err != nil {
		return nil, fmt.Errorf("failed to marshal Slack settings: %w", err)
	}
	hook.Settings = settingsJSON
	hook.AppID = "slack"
	hook.ReferenceID = channel.ID
	hook.Status = model.HookStatusActive

	if err := s.hookRepo.Update(ctx, hook); err != nil {
		return nil, fmt.Errorf("failed to update Slack integration: %w", err)
	}

	applogger.L().Infof("Slack integration updated: account=%d", accountID)
	return hook, nil
}

// Delete removes a Slack integration hook for an account.
func (s *SlackIntegrationService) Delete(ctx context.Context, accountID uint) error {
	hooks, err := s.findSlackHooks(ctx, accountID)
	if err != nil || len(hooks) == 0 {
		return fmt.Errorf("Slack integration not found for account %d", accountID)
	}

	for _, hook := range hooks {
		if err := s.hookRepo.Delete(ctx, hook.ID); err != nil {
			return fmt.Errorf("failed to delete Slack integration: %w", err)
		}
	}

	applogger.L().Infof("Slack integration deleted: account=%d", accountID)
	return nil
}

// ListAllChannels returns available Slack channels (proxy to Slack API).
// GET /api/v1/accounts/:account_id/integrations/slack/list_all_channels
func (s *SlackIntegrationService) ListAllChannels(ctx context.Context, accountID uint) ([]map[string]interface{}, error) {
	hooks, err := s.findSlackHooks(ctx, accountID)
	if err != nil || len(hooks) == 0 {
		return nil, fmt.Errorf("Slack integration not found for account %d", accountID)
	}

	channels, err := s.client.listChannels(ctx, hooks[0].AccessToken)
	if err != nil {
		return nil, err
	}

	applogger.L().Infof("Listing Slack channels for account=%d", accountID)
	return slackChannelsToMaps(channels), nil
}

func (s *SlackIntegrationService) ListHooks(ctx context.Context, accountID uint) ([]model.IntegrationHook, error) {
	return s.findSlackHooks(ctx, accountID)
}

func (s *SlackIntegrationService) findSlackHooks(ctx context.Context, accountID uint) ([]model.IntegrationHook, error) {
	hooks, err := s.hookRepo.FindByAccountAndApp(ctx, accountID, "slack")
	if err != nil {
		return nil, err
	}
	if len(hooks) > 0 {
		return hooks, nil
	}
	return s.hookRepo.FindByAccountAndType(ctx, accountID, model.HookTypeSlack)
}

func (s *SlackIntegrationService) findChannel(ctx context.Context, hook model.IntegrationHook, referenceID string) (*slackChannel, error) {
	if referenceID == "" {
		return nil, ErrSlackInvalidChannel
	}
	channels, err := s.client.listChannels(ctx, hook.AccessToken)
	if err != nil {
		return nil, err
	}
	for _, channel := range channels {
		if channel.ID == referenceID {
			return &channel, nil
		}
	}
	return nil, nil
}

func slackSettingsFromCreate(req CreateSlackRequest) model.SlackSettings {
	return model.SlackSettings{
		ChannelID:   req.ChannelID,
		ChannelName: req.ChannelName,
		SlackToken:  req.SlackToken,
	}
}

func firstNonBlank(values ...string) string {
	for _, value := range values {
		if strings.TrimSpace(value) != "" {
			return strings.TrimSpace(value)
		}
	}
	return ""
}

type slackAPIClient struct {
	baseURL    string
	httpClient *http.Client
}

type slackChannel struct {
	ID        string `json:"id"`
	Name      string `json:"name"`
	IsPrivate bool   `json:"is_private"`
}

func newSlackAPIClientFromEnv() *slackAPIClient {
	baseURL := strings.TrimRight(os.Getenv("SLACK_API_BASE"), "/")
	if baseURL == "" {
		baseURL = "https://slack.com/api"
	}
	return &slackAPIClient{baseURL: baseURL, httpClient: &http.Client{Timeout: 15 * time.Second}}
}

func (c *slackAPIClient) exchangeOAuthCode(ctx context.Context, accountID uint, code string) (string, error) {
	if strings.TrimSpace(code) == "" {
		return "", fmt.Errorf("slack oauth code is required")
	}
	form := url.Values{}
	form.Set("client_id", os.Getenv("SLACK_CLIENT_ID"))
	form.Set("client_secret", os.Getenv("SLACK_CLIENT_SECRET"))
	form.Set("code", code)
	form.Set("redirect_uri", fmt.Sprintf("%s/app/accounts/%d/settings/integrations/slack", strings.TrimRight(os.Getenv("FRONTEND_URL"), "/"), accountID))

	var payload struct {
		OK          bool   `json:"ok"`
		AccessToken string `json:"access_token"`
		Error       string `json:"error"`
	}
	if err := c.postForm(ctx, "/oauth.v2.access", "", form, &payload); err != nil {
		return "", err
	}
	if !payload.OK || payload.AccessToken == "" {
		return "", fmt.Errorf("slack oauth failed: %s", payload.Error)
	}
	return payload.AccessToken, nil
}

func (c *slackAPIClient) listChannels(ctx context.Context, token string) ([]slackChannel, error) {
	var channels []slackChannel
	for _, channelType := range []string{"private_channel", "public_channel"} {
		cursor := ""
		for {
			batch, nextCursor, err := c.listChannelsByType(ctx, token, channelType, cursor)
			if err != nil {
				return nil, err
			}
			channels = append(channels, batch...)
			if nextCursor == "" {
				break
			}
			cursor = nextCursor
		}
	}
	return channels, nil
}

func (c *slackAPIClient) listChannelsByType(ctx context.Context, token, channelType, cursor string) ([]slackChannel, string, error) {
	query := url.Values{}
	query.Set("types", channelType)
	query.Set("exclude_archived", "true")
	query.Set("limit", "1000")
	if cursor != "" {
		query.Set("cursor", cursor)
	}

	var payload struct {
		OK               bool           `json:"ok"`
		Channels         []slackChannel `json:"channels"`
		Error            string         `json:"error"`
		ResponseMetadata struct {
			NextCursor string `json:"next_cursor"`
		} `json:"response_metadata"`
	}
	if err := c.get(ctx, "/conversations.list?"+query.Encode(), token, &payload); err != nil {
		return nil, "", err
	}
	if !payload.OK {
		return nil, "", fmt.Errorf("slack conversations.list failed: %s", payload.Error)
	}
	return payload.Channels, payload.ResponseMetadata.NextCursor, nil
}

func (c *slackAPIClient) joinChannel(ctx context.Context, token, channelID string) error {
	form := url.Values{}
	form.Set("channel", channelID)
	var payload struct {
		OK    bool   `json:"ok"`
		Error string `json:"error"`
	}
	if err := c.postForm(ctx, "/conversations.join", token, form, &payload); err != nil {
		return err
	}
	if !payload.OK {
		return fmt.Errorf("slack conversations.join failed: %s", payload.Error)
	}
	return nil
}

func (c *slackAPIClient) get(ctx context.Context, path, token string, out interface{}) error {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, c.baseURL+path, nil)
	if err != nil {
		return err
	}
	if token != "" {
		req.Header.Set("Authorization", "Bearer "+token)
	}
	return c.do(req, out)
}

func (c *slackAPIClient) postForm(ctx context.Context, path, token string, form url.Values, out interface{}) error {
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.baseURL+path, strings.NewReader(form.Encode()))
	if err != nil {
		return err
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
	if token != "" {
		req.Header.Set("Authorization", "Bearer "+token)
	}
	return c.do(req, out)
}

func (c *slackAPIClient) do(req *http.Request, out interface{}) error {
	resp, err := c.httpClient.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return err
	}
	if resp.StatusCode >= 400 {
		return fmt.Errorf("slack api returned %d: %s", resp.StatusCode, strings.TrimSpace(string(body)))
	}
	if err := json.Unmarshal(body, out); err != nil {
		return err
	}
	return nil
}

func slackChannelsToMaps(channels []slackChannel) []map[string]interface{} {
	items := make([]map[string]interface{}, 0, len(channels))
	for _, channel := range channels {
		items = append(items, map[string]interface{}{
			"id":         channel.ID,
			"name":       channel.Name,
			"is_private": channel.IsPrivate,
		})
	}
	return items
}