package discord

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"net/http"
	"net/url"
	"strings"
	"unicode/utf8"

	"mixmaker/backend/internal/domain"
)

const defaultAPIBaseURL = "https://discord.com/api/v10"

type Config struct {
	BotToken   string
	ChannelID  string
	PublicURL  string
	Locale     string
	APIBaseURL string
	HTTPClient *http.Client
}

type Announcer struct {
	botToken   string
	channelID  string
	publicURL  string
	locale     string
	apiBaseURL string
	httpClient *http.Client
}

type messagePayload struct {
	Content         string          `json:"content"`
	Embeds          []embed         `json:"embeds"`
	Components      []actionRow     `json:"components"`
	AllowedMentions allowedMentions `json:"allowed_mentions"`
}

type embed struct {
	Title       string       `json:"title"`
	Description string       `json:"description,omitempty"`
	URL         string       `json:"url"`
	Color       int          `json:"color"`
	Fields      []embedField `json:"fields"`
}

type embedField struct {
	Name   string `json:"name"`
	Value  string `json:"value"`
	Inline bool   `json:"inline"`
}

type actionRow struct {
	Type       int      `json:"type"`
	Components []button `json:"components"`
}

type button struct {
	Type  int    `json:"type"`
	Style int    `json:"style"`
	Label string `json:"label"`
	URL   string `json:"url"`
}

type allowedMentions struct {
	Parse []string `json:"parse"`
}

type translations struct {
	titlePrefix    string
	startsAt       string
	deadline       string
	registerButton string
}

func New(config Config) (*Announcer, error) {
	if strings.TrimSpace(config.BotToken) == "" {
		return nil, errors.New("discord bot token is required")
	}
	if strings.TrimSpace(config.ChannelID) == "" {
		return nil, errors.New("discord announcement channel ID is required")
	}
	publicURL, err := url.Parse(strings.TrimSpace(config.PublicURL))
	if err != nil || (publicURL.Scheme != "http" && publicURL.Scheme != "https") || publicURL.Host == "" {
		return nil, errors.New("discord announcement public URL must be an absolute HTTP(S) URL")
	}
	locale := strings.ToLower(strings.TrimSpace(config.Locale))
	if locale == "" {
		locale = "ru"
	}
	if locale != "ru" && locale != "en" {
		return nil, fmt.Errorf("unsupported discord announcement locale %q", locale)
	}
	apiBaseURL := strings.TrimRight(config.APIBaseURL, "/")
	if apiBaseURL == "" {
		apiBaseURL = defaultAPIBaseURL
	}
	httpClient := config.HTTPClient
	if httpClient == nil {
		httpClient = http.DefaultClient
	}
	return &Announcer{
		botToken:   config.BotToken,
		channelID:  config.ChannelID,
		publicURL:  strings.TrimRight(strings.TrimSpace(config.PublicURL), "/"),
		locale:     locale,
		apiBaseURL: apiBaseURL,
		httpClient: httpClient,
	}, nil
}

func (a *Announcer) AnnounceEventCreated(ctx context.Context, event domain.Event) error {
	err := a.announceEventCreated(ctx, event)
	if err != nil {
		slog.Error("Discord event announcement failed", "event_id", event.ID, "error", err)
	}
	return err
}

func (a *Announcer) announceEventCreated(ctx context.Context, event domain.Event) error {
	payload, err := json.Marshal(a.createdMessage(event))
	if err != nil {
		return fmt.Errorf("encode Discord message: %w", err)
	}
	endpoint := fmt.Sprintf("%s/channels/%s/messages", a.apiBaseURL, url.PathEscape(a.channelID))
	request, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, bytes.NewReader(payload))
	if err != nil {
		return fmt.Errorf("create Discord request: %w", err)
	}
	request.Header.Set("Authorization", "Bot "+a.botToken)
	request.Header.Set("Content-Type", "application/json")

	response, err := a.httpClient.Do(request)
	if err != nil {
		return fmt.Errorf("send Discord message: %w", err)
	}
	defer response.Body.Close()
	if response.StatusCode < http.StatusOK || response.StatusCode >= http.StatusMultipleChoices {
		body, _ := io.ReadAll(io.LimitReader(response.Body, 4096))
		return fmt.Errorf("Discord returned %s: %s", response.Status, strings.TrimSpace(string(body)))
	}
	return nil
}

func (a *Announcer) createdMessage(event domain.Event) messagePayload {
	text := announcementTranslations(a.locale)
	eventURL := a.publicURL + "/events/" + url.PathEscape(event.ID)
	return messagePayload{
		Content: "@everyone",
		Embeds: []embed{{
			Title:       truncate(text.titlePrefix+event.Name, 256),
			Description: truncate(event.Description, 4096),
			URL:         eventURL,
			Color:       0xe9358f,
			Fields: []embedField{
				{Name: text.startsAt, Value: fmt.Sprintf("<t:%d:F> · <t:%d:R>", event.StartsAt.Unix(), event.StartsAt.Unix()), Inline: true},
				{Name: text.deadline, Value: fmt.Sprintf("<t:%d:F>", event.RegistrationDeadline.Unix()), Inline: true},
			},
		}},
		Components: []actionRow{{
			Type: 1,
			Components: []button{{
				Type:  2,
				Style: 5,
				Label: text.registerButton,
				URL:   eventURL,
			}},
		}},
		AllowedMentions: allowedMentions{Parse: []string{"everyone"}},
	}
}

func announcementTranslations(locale string) translations {
	if locale == "en" {
		return translations{
			titlePrefix:    "New mix: ",
			startsAt:       "Starts",
			deadline:       "Registration deadline",
			registerButton: "Register",
		}
	}
	return translations{
		titlePrefix:    "Новый микс: ",
		startsAt:       "Начало",
		deadline:       "Регистрация до",
		registerButton: "Зарегистрироваться",
	}
}

func truncate(value string, maxRunes int) string {
	if utf8.RuneCountInString(value) <= maxRunes {
		return value
	}
	runes := []rune(value)
	return string(runes[:maxRunes-1]) + "…"
}