package discord

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"log"
	"os"
	"strings"
	"time"

	"github.com/bwmarrin/discordgo"

	"plumber/internal/events"
	"plumber/internal/store"
)

const discordTimeout = 15 * time.Second

// Bot posts site events to a Discord channel and owns post-to-message links.
type Bot struct {
	channelID string
	links     store.DiscordLinkStore
	api       API
}

// New constructs an outbound subscriber. Tests inject a fake API.
func New(channelID string, links store.DiscordLinkStore, api API) *Bot {
	return &Bot{channelID: strings.TrimSpace(channelID), links: links, api: api}
}

// FromEnv builds a bot when Discord env is set. Missing config is a no-op.
func FromEnv(links store.DiscordLinkStore, bus *events.Bus) (*Bot, error) {
	token := strings.TrimSpace(os.Getenv("DISCORD_BOT_TOKEN"))
	channelID := strings.TrimSpace(os.Getenv("DISCORD_CHANNEL_ID"))
	if token == "" && channelID == "" {
		return nil, nil
	}
	if token == "" {
		return nil, fmt.Errorf("DISCORD_BOT_TOKEN is required when DISCORD_CHANNEL_ID is set")
	}
	if channelID == "" {
		return nil, fmt.Errorf("DISCORD_CHANNEL_ID is required when DISCORD_BOT_TOKEN is set")
	}
	if links == nil {
		return nil, fmt.Errorf("discord links store is required")
	}
	session, err := discordgo.New("Bot " + token)
	if err != nil {
		return nil, err
	}
	bot := New(channelID, links, &sessionAPI{session: session})
	if bus != nil {
		bus.Subscribe(bot.Handle)
	}
	log.Printf("discord: outbound subscriber enabled")
	return bot, nil
}

// Close releases the Discord session.
func (b *Bot) Close() error {
	if b == nil || b.api == nil {
		return nil
	}
	return b.api.Close()
}

// Handle processes one site event. Failures are logged and do not fail the request.
func (b *Bot) Handle(_ context.Context, ev any) {
	if b == nil {
		return
	}
	ctx, cancel := context.WithTimeout(context.Background(), discordTimeout)
	defer cancel()
	switch e := ev.(type) {
	case events.PostCreated:
		b.onCreated(ctx, e.PostEvent)
	case events.PostUpdated:
		b.onUpdated(ctx, e.PostEvent)
	}
}

func (b *Bot) onCreated(ctx context.Context, ev events.PostEvent) {
	if isRoot(ev) {
		b.createRoot(ctx, ev)
		return
	}
	b.createReply(ctx, ev)
}

func (b *Bot) onUpdated(ctx context.Context, ev events.PostEvent) {
	link, err := b.links.GetByPostID(ctx, ev.PostID)
	if err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			b.onCreated(ctx, ev)
			return
		}
		log.Printf("discord: load link %s: %v", ev.PostID, err)
		return
	}
	channelID, err := b.editChannel(ctx, ev, link)
	if err != nil {
		log.Printf("discord: edit channel %s: %v", ev.PostID, err)
		return
	}
	if err := b.api.Edit(ctx, channelID, link.MessageID, formatMessage(ev)); err != nil {
		log.Printf("discord: edit %s: %v", ev.PostID, err)
		return
	}
	log.Printf("discord: edited %s", ev.PostID)
}

func (b *Bot) createRoot(ctx context.Context, ev events.PostEvent) {
	msg := formatMessage(ev)
	messageID, err := b.api.SendToChannel(ctx, b.channelID, msg)
	if err != nil {
		log.Printf("discord: send root %s: %v", ev.PostID, err)
		return
	}
	threadID, err := b.api.StartThread(ctx, b.channelID, messageID, msg.ThreadName)
	if err != nil {
		log.Printf("discord: start thread %s: %v", ev.PostID, err)
		return
	}
	if err := b.links.Upsert(ctx, store.DiscordLink{
		PostID:    ev.PostID,
		MessageID: messageID,
		ThreadID:  threadID,
	}); err != nil {
		log.Printf("discord: save root link %s: %v", ev.PostID, err)
		return
	}
	log.Printf("discord: posted root %s", ev.PostID)
}

func (b *Bot) createReply(ctx context.Context, ev events.PostEvent) {
	root, err := b.links.GetByPostID(ctx, ev.RootID)
	if err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			log.Printf("discord: skip reply %s: no root thread", ev.PostID)
			return
		}
		log.Printf("discord: load root link %s: %v", ev.RootID, err)
		return
	}
	if strings.TrimSpace(root.ThreadID) == "" {
		log.Printf("discord: skip reply %s: no root thread", ev.PostID)
		return
	}
	messageID, err := b.api.SendToThread(ctx, root.ThreadID, formatMessage(ev))
	if err != nil {
		log.Printf("discord: send reply %s: %v", ev.PostID, err)
		return
	}
	if err := b.links.Upsert(ctx, store.DiscordLink{
		PostID:    ev.PostID,
		MessageID: messageID,
	}); err != nil {
		log.Printf("discord: save reply link %s: %v", ev.PostID, err)
		return
	}
	log.Printf("discord: posted reply %s", ev.PostID)
}

func (b *Bot) editChannel(ctx context.Context, ev events.PostEvent, link *store.DiscordLink) (string, error) {
	if strings.TrimSpace(link.ThreadID) != "" {
		return b.channelID, nil
	}
	root, err := b.links.GetByPostID(ctx, ev.RootID)
	if err != nil {
		return "", err
	}
	if strings.TrimSpace(root.ThreadID) == "" {
		return "", fmt.Errorf("root %s has no thread", ev.RootID)
	}
	return root.ThreadID, nil
}