Keep/keep-notes/lib/i18n/detect-user-language.ts

/**
 * Detect user's preferred language from their existing notes
 * Analyzes language distribution across all user's notes
 */

import { auth } from '@/auth'
import { prisma } from '@/lib/prisma'
import { SupportedLanguage } from './load-translations'

export async function detectUserLanguage(): Promise<SupportedLanguage> {
  const session = await auth()

  // Default to English for non-logged-in users
  if (!session?.user?.id) {
    return 'en'
  }

  try {
    // Get all user's notes with detected languages
    const notes = await prisma.note.findMany({
      where: {
        userId: session.user.id,
        language: { not: null }
      },
      select: {
        language: true,
        languageConfidence: true
      }
    })

    if (notes.length === 0) {
      return 'en' // Default for new users
    }

    // Count language occurrences weighted by confidence
    const languageScores: Record<string, number> = {}

    for (const note of notes) {
      if (note.language) {
        const confidence = note.languageConfidence || 0.8
        languageScores[note.language] = (languageScores[note.language] || 0) + confidence
      }
    }

    // Find language with highest score
    const sortedLanguages = Object.entries(languageScores)
      .sort(([, a], [, b]) => b - a)

    if (sortedLanguages.length > 0) {
      const topLanguage = sortedLanguages[0][0] as SupportedLanguage
      // Verify it's a supported language
      if (['en', 'fr', 'es', 'de', 'fa', 'it', 'pt', 'ru', 'zh', 'ja', 'ko', 'ar', 'hi', 'nl', 'pl'].includes(topLanguage)) {
        return topLanguage
      }
    }

    return 'en'
  } catch (error) {
    console.error('Error detecting user language:', error)
    return 'en'
  }
}