package main

import (
	"context"
	"os"
	"regexp"
	"strings"
	"time"

	"github.com/sirupsen/logrus"
)

var sentenceSplitRegex = regexp.MustCompile(`(?m)(?:[^.!?\n]+[.!?]|[^.!?\n]+$)`)

// configurable via env (seconds); defaults chosen for model cold start friendliness
func envDuration(key string, def time.Duration) time.Duration {
	if v := os.Getenv(key); v != "" {
		if d, err := time.ParseDuration(v); err == nil {
			return d
		}
	}
	return def
}

// startSentenceEmbeddingBackfill launches a background goroutine that iterates all visits
// and stores (visit_id, sentence, translated, embedding) records in sentence_embeddings table
// if they do not already exist (relying on unique index ON CONFLICT DO NOTHING).
func startSentenceEmbeddingBackfill(repo *PGChatRepository, llm LLMClientAPI, vdb *VisitDB) {
	if repo == nil || llm == nil || vdb == nil {
		logrus.Info("Sentence embedding backfill skipped (missing repo, llm or vdb)")
		return
	}
	if disable := strings.ToLower(os.Getenv("SENTENCE_BACKFILL_DISABLE")); disable == "1" || disable == "true" {
		logrus.Info("Sentence embedding backfill disabled via SENTENCE_BACKFILL_DISABLE env var")
		return
	}
	translateTimeout := envDuration("TRANSLATE_TIMEOUT", 45*time.Second)
	embeddingTimeout := envDuration("EMBEDDING_TIMEOUT", 45*time.Second)
	maxTranslateAttempts := 3
	maxEmbeddingAttempts := 3
	go func() {
		start := time.Now()
		logrus.WithFields(logrus.Fields{"translateTimeout": translateTimeout, "embeddingTimeout": embeddingTimeout}).Info("Sentence embedding backfill started")
		processed := 0
		inserted := 0
		skippedExisting := 0
		skippedDueToFailures := 0
		for _, visit := range vdb.visitsDB { // visitsDB accessible within package
			if strings.TrimSpace(visit.Visit) == "" {
				continue
			}
			sentences := extractSentences(visit.Visit)
			for _, s := range sentences {
				processed++
				trimmed := strings.TrimSpace(s)
				if len(trimmed) < 3 {
					continue
				}
				// Existence check before any LLM calls
				existsCtx, existsCancel := context.WithTimeout(context.Background(), 2*time.Second)
				exists, err := repo.ExistsSentenceEmbedding(existsCtx, visit.ID, trimmed)
				existsCancel()
				if err != nil {
					logrus.WithError(err).Warnf("Exists check failed visit=%s sentence=%q", visit.ID, trimmed)
				} else if exists {
					skippedExisting++
					continue
				}

				// Translation with retry/backoff
				var translated string
				translateErr := retry(maxTranslateAttempts, 0, func(at int) error {
					ctx, cancel := context.WithTimeout(context.Background(), translateTimeout)
					defer cancel()
					resp, err := llm.TranslateToEnglish(ctx, trimmed)
					if err != nil {
						logrus.WithError(err).Warnf("Translate attempt=%d failed visit=%s sentence=%q", at+1, visit.ID, trimmed)
						return err
					}
					translated = strings.TrimSpace(resp)
					return nil
				})
				if translateErr != nil || translated == "" {
					translated = trimmed // fallback keep original language
				}

				// Embedding with retry/backoff (skip if translation totally failed with deadline each time)
				var emb []float64
				embErr := retry(maxEmbeddingAttempts, 0, func(at int) error {
					ctx, cancel := context.WithTimeout(context.Background(), embeddingTimeout)
					defer cancel()
					vec, err := llm.GetEmbeddings(ctx, translated)
					if err != nil {
						logrus.WithError(err).Warnf("Embeddings attempt=%d failed visit=%s sentence=%q", at+1, visit.ID, trimmed)
						return err
					}
					emb = vec
					return nil
				})
				if embErr != nil {
					skippedDueToFailures++
					continue
				}

				persistCtx, pcancel := context.WithTimeout(context.Background(), 5*time.Second)
				if err := repo.InsertSentenceEmbedding(persistCtx, visit.ID, trimmed, translated, emb); err == nil {
					inserted++
				}
				pcancel()
				// Throttle (configurable?)
				time.Sleep(50 * time.Millisecond)
			}
		}
		logrus.Infof("Sentence embedding backfill complete processed=%d inserted=%d skipped_existing=%d skipped_failures=%d elapsed=%s", processed, inserted, skippedExisting, skippedDueToFailures, time.Since(start))
	}()
}

// retry executes fn up to attempts times with exponential backoff starting at base (or 200ms if base==0)
func retry(attempts int, base time.Duration, fn func(attempt int) error) error {
	if attempts <= 0 {
		return nil
	}
	if base <= 0 {
		base = 200 * time.Millisecond
	}
	var err error
	for a := 0; a < attempts; a++ {
		err = fn(a)
		if err == nil {
			return nil
		}
		// backoff except after last attempt
		if a < attempts-1 {
			backoff := base << a // exponential
			time.Sleep(backoff)
		}
	}
	return err
}

// extractSentences splits a block of text into sentence-like units.
func extractSentences(text string) []string {
	// First replace newlines with space to keep regex simpler, keep periods.
	normalized := strings.ReplaceAll(text, "\n", " ")
	matches := sentenceSplitRegex.FindAllString(normalized, -1)
	var out []string
	for _, m := range matches {
		m = strings.TrimSpace(m)
		if m != "" {
			out = append(out, m)
		}
	}
	return out
}