package tg

import (
	"context"
	"fmt"
	"regexp"
	"strings"
	"time"

	"github.com/gotd/td/telegram/uploader"
	"github.com/gotd/td/tg"
)

// BotFather is Telegram's own bot for registering bots. There is no API for
// this: a bot is created by holding a conversation, which is why provisioning
// needs a user session at all.
const botFatherUsername = "BotFather"

// Conversation drives that exchange. It is deliberately literal -- send a
// message, wait for the reply, read it -- because BotFather is a chat partner
// and not an endpoint, and pretending otherwise hides where it can surprise us.
type Conversation struct {
	c    *Client
	peer tg.InputPeerClass
	last int // highest message id already seen, so a reply is never confused with an echo
}

func (c *Client) BotFather(ctx context.Context) (*Conversation, error) {
	resolved, err := c.api.ContactsResolveUsername(ctx, &tg.ContactsResolveUsernameRequest{
		Username: botFatherUsername,
	})
	if err != nil {
		return nil, fmt.Errorf("resolve @%s: %w", botFatherUsername, err)
	}
	if len(resolved.Users) == 0 {
		return nil, fmt.Errorf("@%s did not resolve to a user", botFatherUsername)
	}
	u, ok := resolved.Users[0].(*tg.User)
	if !ok {
		return nil, fmt.Errorf("@%s resolved to %T", botFatherUsername, resolved.Users[0])
	}
	conv := &Conversation{
		c:    c,
		peer: &tg.InputPeerUser{UserID: u.ID, AccessHash: u.AccessHash},
	}
	// Anchor on the current end of the conversation so that a reply is always
	// newer than the request that caused it.
	if id, err := conv.latestID(ctx); err == nil {
		conv.last = id
	}
	return conv, nil
}

// Ask sends text and returns BotFather's next reply.
func (conv *Conversation) Ask(ctx context.Context, text string) (string, error) {
	pause()
	randID, err := conv.c.client.RandInt64()
	if err != nil {
		return "", err
	}
	if err := conv.c.client.SendMessage(ctx, &tg.MessagesSendMessageRequest{
		Peer:     conv.peer,
		Message:  text,
		RandomID: randID,
	}); err != nil {
		return "", fmt.Errorf("send %q to @%s: %w", firstLine(text), botFatherUsername, err)
	}
	return conv.awaitReply(ctx)
}

// awaitReply polls for the next incoming message. Polling rather than an update
// handler keeps provisioning a straight line: the tool is doing one thing, and a
// missed update would strand it rather than fail it.
func (conv *Conversation) awaitReply(ctx context.Context) (string, error) {
	deadline := time.Now().Add(45 * time.Second)
	for time.Now().Before(deadline) {
		msgs, err := conv.history(ctx)
		if err != nil {
			return "", err
		}
		for _, m := range msgs {
			msg, ok := m.(*tg.Message)
			if !ok || msg.Out || msg.ID <= conv.last {
				continue // our own message, or one we have already read
			}
			conv.last = msg.ID
			return msg.Message, nil
		}
		select {
		case <-ctx.Done():
			return "", ctx.Err()
		case <-time.After(1500 * time.Millisecond):
		}
	}
	return "", fmt.Errorf("@%s did not reply within 45s; it may be rate-limiting this "+
		"account, or the conversation may be in a state this tool does not expect -- "+
		"open the chat and look", botFatherUsername)
}

func (conv *Conversation) history(ctx context.Context) ([]tg.MessageClass, error) {
	res, err := conv.c.api.MessagesGetHistory(ctx, &tg.MessagesGetHistoryRequest{
		Peer:  conv.peer,
		Limit: 5,
	})
	if err != nil {
		return nil, fmt.Errorf("read @%s history: %w", botFatherUsername, err)
	}
	switch v := res.(type) {
	case *tg.MessagesMessages:
		return v.Messages, nil
	case *tg.MessagesMessagesSlice:
		return v.Messages, nil
	case *tg.MessagesChannelMessages:
		return v.Messages, nil
	}
	return nil, fmt.Errorf("unexpected history type %T", res)
}

func (conv *Conversation) latestID(ctx context.Context) (int, error) {
	msgs, err := conv.history(ctx)
	if err != nil {
		return 0, err
	}
	best := 0
	for _, m := range msgs {
		if msg, ok := m.(*tg.Message); ok && msg.ID > best {
			best = msg.ID
		}
	}
	return best, nil
}

// tokenRe matches a bot token in BotFather's confirmation. The token is
// extracted, written straight to OpenBao, and never logged -- so this is the one
// place it exists in memory, and callers must not print what it returns.
var tokenRe = regexp.MustCompile(`\b(\d{6,}:[A-Za-z0-9_-]{30,})\b`)

// ErrUsernameTaken means the caller should try its next candidate.
var ErrUsernameTaken = fmt.Errorf("username is taken")

// RegisterBot runs /newbot and returns the issued username and token.
func (conv *Conversation) RegisterBot(ctx context.Context, displayName, username string) (string, string, error) {
	reply, err := conv.Ask(ctx, "/newbot")
	if err != nil {
		return "", "", err
	}
	if !strings.Contains(strings.ToLower(reply), "name") {
		return "", "", fmt.Errorf("unexpected reply to /newbot: %q", firstLine(reply))
	}
	if _, err := conv.Ask(ctx, displayName); err != nil {
		return "", "", err
	}
	reply, err = conv.Ask(ctx, username)
	if err != nil {
		return "", "", err
	}

	low := strings.ToLower(reply)
	if strings.Contains(low, "already taken") || strings.Contains(low, "invalid") ||
		strings.Contains(low, "sorry") {
		return "", "", fmt.Errorf("%w: @%s (%s)", ErrUsernameTaken, username, firstLine(reply))
	}
	m := tokenRe.FindStringSubmatch(reply)
	if m == nil {
		return "", "", fmt.Errorf("@%s accepted @%s but no token was found in its reply; "+
			"open the chat and check before retrying, or a second bot will be created",
			botFatherUsername, username)
	}
	return username, m[1], nil
}

// SetProfile applies the spec's editorial fields. Each is idempotent, so it is
// safe to reassert on every apply.
func (conv *Conversation) SetProfile(ctx context.Context, username, about, description string) error {
	steps := []struct{ cmd, arg, label string }{
		{"/setabouttext", about, "about text"},
		{"/setdescription", description, "description"},
	}
	for _, s := range steps {
		if s.arg == "" {
			continue
		}
		if _, err := conv.Ask(ctx, s.cmd); err != nil {
			return err
		}
		if _, err := conv.Ask(ctx, "@"+username); err != nil {
			return err
		}
		reply, err := conv.Ask(ctx, s.arg)
		if err != nil {
			return err
		}
		if !strings.Contains(strings.ToLower(reply), "success") {
			return fmt.Errorf("setting %s did not succeed: %q", s.label, firstLine(reply))
		}
	}
	return nil
}

func firstLine(s string) string {
	if i := strings.IndexByte(s, '\n'); i >= 0 {
		s = s[:i]
	}
	if len(s) > 90 {
		s = s[:90] + "..."
	}
	return s
}

// SetAvatar sends the bot's profile picture through BotFather.
//
// A bot's picture cannot be set through any API: /setuserpic is a conversation
// in which you send a photo, so the file is uploaded and then sent as a message
// like a person would send it.
func (conv *Conversation) SetAvatar(ctx context.Context, username, path string) error {
	reply, err := conv.Ask(ctx, "/setuserpic")
	if err != nil {
		return err
	}
	if strings.Contains(strings.ToLower(reply), "choose a bot") ||
		strings.Contains(reply, "/") {
		if _, err := conv.Ask(ctx, "@"+username); err != nil {
			return err
		}
	}

	pause()
	up := uploader.NewUploader(conv.c.api)
	file, err := up.FromPath(ctx, path)
	if err != nil {
		return fmt.Errorf("upload avatar %s: %w", path, err)
	}

	randID, err := conv.c.client.RandInt64()
	if err != nil {
		return err
	}
	if _, err := conv.c.api.MessagesSendMedia(ctx, &tg.MessagesSendMediaRequest{
		Peer:     conv.peer,
		Media:    &tg.InputMediaUploadedPhoto{File: file},
		RandomID: randID,
	}); err != nil {
		return fmt.Errorf("send avatar to @%s: %w", botFatherUsername, err)
	}

	reply, err = conv.awaitReply(ctx)
	if err != nil {
		return err
	}
	if !strings.Contains(strings.ToLower(reply), "success") {
		return fmt.Errorf("@%s did not confirm the picture: %q", botFatherUsername, firstLine(reply))
	}
	return nil
}