package conversation

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"strings"
	"unicode/utf8"

	"code.chimeric.al/chimerical/odidere/internal/db"
	"code.chimeric.al/chimerical/odidere/internal/llm"
)

// MaxTitleLength is the maximum length of a conversation title in
// Unicode code points.
const MaxTitleLength = 256

// deriveTitle returns a title from the first line of text that
// contains non-whitespace characters. It replaces runs of
// whitespace on that line with single spaces and truncates to
// MaxTitleLength runes. It returns "" if text has no
// non-whitespace characters.
func deriveTitle(text string) string {
	for line := range strings.SplitSeq(text, "\n") {
		title := strings.Join(strings.Fields(line), " ")
		if title == "" {
			continue
		}
		if utf8.RuneCountInString(title) <= MaxTitleLength {
			return title
		}
		runes := []rune(title)
		return string(runes[:MaxTitleLength])
	}
	return ""
}

// setTitle derives a title from msg and sets the conversation
// title if the conversation has no title yet. It does nothing if
// msg has no non-whitespace text or if the conversation already
// has a title.
func (c *Conversation) setTitle(
	ctx context.Context,
	msg llm.Message,
) error {
	title := deriveTitle(msg.Text())
	if title == "" {
		return nil
	}
	_, err := c.dbw.UpdateConversationTitleIfUnset(
		ctx,
		db.UpdateConversationTitleIfUnsetParams{
			Id:    c.id,
			Title: title,
		},
	)
	// sql.ErrNoRows means the conversation already has a title (or
	// does not exist).
	if errors.Is(err, sql.ErrNoRows) {
		return nil
	}
	if err != nil {
		return fmt.Errorf("update conversation title: %w", err)
	}
	return nil
}