package main

import (
	"encoding/json"
	"fmt"
	"io"
	"log"
	"net/http"
	"net/url"
	"strings"
	"time"
)

const (
	wikidataSparql = "https://query.wikidata.org/sparql"
	wikiBatchSize  = 30
	wikiDelay      = 2 * time.Second // ~15 req/min, safe under 20 req/min limit
	wikiMaxRetries = 3
	wikiRetryBackoff = 15 * time.Second
)

var wikiClient = &http.Client{Timeout: 120 * time.Second}

// wikiAcc accumulates per-ID results from a SPARQL batch.
type wikiAcc struct {
	wikiArticle string
	title       string
}

// type alias for SPARQL JSON response
type sparqlResponse struct {
	Results struct {
		BindingList []map[string]jsonNode `json:"bindings"`
	} `json:"results"`
}

type jsonNode struct {
	Type  string `json:"type"`
	Value string `json:"value"`
	Lang  string `json:"xml:lang,omitempty"`
}

// getMissingWikiArticles returns imdb_ids where wiki_article IS NULL.
func (a *App) getMissingWikiArticles() ([]string, error) {
	rows, err := a.DB.Query(`SELECT imdb_id FROM imdb WHERE wiki_article IS NULL AND has_no_wiki_article = 0 AND imdb_id LIKE 'tt%'`)
	if err != nil {
		return nil, fmt.Errorf("query missing wiki articles: %w", err)
	}
	defer rows.Close()

	var ids []string
	for rows.Next() {
		var id string
		if err := rows.Scan(&id); err != nil {
			return nil, fmt.Errorf("scan imdb_id: %w", err)
		}
		ids = append(ids, id)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("rows iteration: %w", err)
	}
	return ids, nil
}

// wikiArticleFetch carries a resolved wiki article to the data consumer.
type wikiArticleFetch struct {
	imdbID string
	name   string // decoded wiki article name
}

// fetchWikiArticles pipelines SPARQL batches with wiki data extraction.
// SPARQL producer feeds batches into a channel; DB commits per batch.
// Resolved articles are forwarded to a wiki data consumer running in parallel.
func (a *App) fetchWikiArticles() error {
	ids, err := a.getMissingWikiArticles()
	if err != nil {
		return err
	}
	if len(ids) == 0 {
		log.Println("fetchWikiArticles: all entries have wiki_article, skipping")
		return nil
	}

	// Also pre-load existing entries that need wiki data extraction
	existing, err := a.getExistingWikiArticles()
	if err != nil {
		return err
	}

	// Channel for wiki article fetch tasks (buffered for pipelining)
	artCh := make(chan wikiArticleFetch, wikiBatchSize*2)

	// Consumer processes wiki data extraction in background
	consumerDone := make(chan struct{})
	go a.wikiDataConsumer(artCh, consumerDone)

	// Feed existing entries to consumer first
	for _, e := range existing {
		select {
		case artCh <- wikiArticleFetch{imdbID: e.imdbID, name: e.wikiArticle}:
		default:
			// Channel full, will pick up on next run
			log.Printf("wiki data channel full, deferring %s", e.imdbID)
		}
	}

	// SPARQL producer: fetches batches, commits to DB, forwards resolved
	sparqlDone := make(chan struct{})
	go a.sparqlPipeline(ids, artCh, sparqlDone)

	// Wait for SPARQL to finish
	<-sparqlDone

	// Close channel and wait for consumer to drain
	close(artCh)
	<-consumerDone

	log.Printf("fetchWikiArticles: pipeline complete")
	return nil
}

type existingWikiArticle struct {
	imdbID      string
	wikiArticle string
}

// getExistingWikiArticles returns entries that have a wiki_article but need data extraction.
func (a *App) getExistingWikiArticles() ([]existingWikiArticle, error) {
	rows, err := a.DB.Query(`
		SELECT imdb_id, wiki_article FROM imdb
		WHERE wiki_article IS NOT NULL
		AND wiki_status_code != 404
		AND (synopsis IS NULL OR description IS NULL OR year IS NULL
			OR poster_url IS NULL OR license IS NULL OR license_url IS NULL OR num_accolades IS NULL)
	`)
	if err != nil {
		return nil, fmt.Errorf("query existing wiki articles: %w", err)
	}
	defer rows.Close()

	var articles []existingWikiArticle
	for rows.Next() {
		var e existingWikiArticle
		if err := rows.Scan(&e.imdbID, &e.wikiArticle); err != nil {
			return nil, fmt.Errorf("scan existing wiki: %w", err)
		}
		articles = append(articles, e)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("rows iteration: %w", err)
	}
	return articles, nil
}

// sparqlPipeline fetches SPARQL batches, commits each to DB, forwards resolved articles.
func (a *App) sparqlPipeline(ids []string, artCh chan<- wikiArticleFetch, done chan<- struct{}) {
	defer close(done)

	log.Printf("fetchWikiArticles: %d entries missing wiki_article", len(ids))
	batchNum := 0
	totalResolved := 0
	totalNoWiki := 0

	for i := 0; i < len(ids); i += wikiBatchSize {
		batchNum++
		chunk := ids[i:min(i+wikiBatchSize, len(ids))]

		results, err := a.queryWikidataBatch(chunk)
		if err != nil {
			log.Printf("sparql batch %d error: %v, marking all as no-wiki", batchNum, err)
			// Mark all in failed batch as no-wiki
			tx, _ := a.DB.Begin()
			stmt, _ := tx.Prepare(`UPDATE imdb SET has_no_wiki_article = 1 WHERE imdb_id = ?`)
			for _, id := range chunk {
				stmt.Exec(id)
				totalNoWiki++
			}
			stmt.Close()
			tx.Commit()
			continue
		}

		// Commit batch to DB
		tx, err := a.DB.Begin()
		if err != nil {
			log.Printf("sparql batch %d begin tx error: %v", batchNum, err)
			continue
		}

		wikiStmt, err := tx.Prepare(`UPDATE imdb SET wiki_article = ? WHERE imdb_id = ?`)
		if err != nil {
			tx.Rollback()
			log.Printf("sparql batch %d prepare error: %v", batchNum, err)
			continue
		}

		noWikiStmt, err := tx.Prepare(`UPDATE imdb SET has_no_wiki_article = 1 WHERE imdb_id = ?`)
		if err != nil {
			wikiStmt.Close()
			tx.Rollback()
			log.Printf("sparql batch %d prepare no_wiki error: %v", batchNum, err)
			continue
		}

		resolved := 0
		for _, imdbID := range chunk {
			acc, found := results[imdbID]
			if found && acc.title != "" {
				wikiStmt.Exec(acc.title, imdbID)
				resolved++
				// Forward to consumer
				select {
				case artCh <- wikiArticleFetch{imdbID: imdbID, name: acc.title}:
				default:
					log.Printf("wiki data channel full, deferring %s", imdbID)
				}
			} else {
				noWikiStmt.Exec(imdbID)
				totalNoWiki++
			}
		}
		totalResolved += resolved

		wikiStmt.Close()
		noWikiStmt.Close()

		tx.Commit()

		log.Printf("fetchWikiArticles: sparql batch %d/%d - %d/%d resolved",
			batchNum, (len(ids)+wikiBatchSize-1)/wikiBatchSize, resolved, len(chunk))

		// Rate limit between SPARQL requests
		if i+wikiBatchSize < len(ids) {
			time.Sleep(wikiDelay)
		}
	}

	log.Printf("fetchWikiArticles: SPARQL done - %d resolved, %d no-wiki", totalResolved, totalNoWiki)
}

// wikiDataConsumer fetches wiki article data from the custom server.
func (a *App) wikiDataConsumer(artCh <-chan wikiArticleFetch, done chan<- struct{}) {
	defer close(done)

	updated := 0
	skipped := 0

	for art := range artCh {
		// Wait between requests (rate limit)
		time.Sleep(2 * time.Second)

		entry, statusCode, err := a.queryWikiArticle(art.name)
		if err != nil {
			log.Printf("wiki error %s (%s): HTTP %d - %v", art.imdbID, art.name, statusCode, err)
			skipped++
		}

		// Record status code
		if statusCode > 0 {
			a.DB.Exec(`UPDATE imdb SET wiki_status_code = ? WHERE imdb_id = ?`, statusCode, art.imdbID)
		}

		// Update data fields on success
		if statusCode == 200 {
			a.DB.Exec(`
				UPDATE imdb SET synopsis = ?, description = ?, year = ?, poster_url = ?,
					license = ?, license_url = ?, num_accolades = ?
				WHERE imdb_id = ?`,
				entry.Synopsis, entry.Description, entry.Year, entry.PosterURL,
				entry.License, entry.LicenseURL, entry.NumAccolades, art.imdbID)
			updated++
		}
	}

	log.Printf("fetchWikiArticlesData: %d updated, %d skipped (non-200)", updated, skipped)
}

// queryWikidataBatch sends a SPARQL query for the given IDs and returns a map of id -> wikiAcc.
func (a *App) queryWikidataBatch(ids []string) (map[string]wikiAcc, error) {
	sparql := buildSparql(ids)
	time.Sleep(wikiDelay)

	endpoint := wikidataSparql + "?" + url.Values{
		"query":  {sparql},
		"format": {"json"},
	}.Encode()

	raw, err := doGETWithRetry(endpoint, a.Config.UserAgent)
	if err != nil {
		return nil, fmt.Errorf("SPARQL request: %w", err)
	}

	var data sparqlResponse
	if err := json.Unmarshal(raw, &data); err != nil {
		return nil, fmt.Errorf("SPARQL JSON parse: %w", err)
	}

	results := make(map[string]wikiAcc)
	for _, b := range data.Results.BindingList {
		imdb := b["imdbVal"].Value
		if !strings.HasPrefix(imdb, "tt") {
			continue
		}

		if n, ok := b["article"]; ok && n.Value != "" {
			// Extract title from URL: strip "https://en.wikipedia.org/wiki/"
			title, _ := url.PathUnescape(strings.TrimPrefix(n.Value, "https://en.wikipedia.org/wiki/"))
			results[imdb] = wikiAcc{
				wikiArticle: n.Value,
				title:       title,
			}
		}
	}

	return results, nil
}

// buildSparql creates a SPARQL query that resolves IMDb IDs to English Wikipedia article URLs.
func buildSparql(ids []string) string {
	var vals strings.Builder
	for _, id := range ids {
		vals.WriteString(fmt.Sprintf("    \"%s\"\n", id))
	}

	return fmt.Sprintf(`PREFIX schema: <http://schema.org/>
PREFIX wdt: <http://www.wikidata.org/prop/direct/>

SELECT ?imdbVal ?article
WHERE {
  VALUES ?imdbVal {
%s
  }
  ?item wdt:P345 ?imdbVal .
  OPTIONAL {
    ?article schema:about ?item ;
             schema:isPartOf <https://en.wikipedia.org/> .
  }
}
ORDER BY ?imdbVal`, vals.String())
}

// doGET performs a GET request with the configured User-Agent.
func doGET(uri, userAgent string) ([]byte, error) {
	req, err := http.NewRequest("GET", uri, nil)
	if err != nil {
		return nil, err
	}
	req.Header.Set("User-Agent", userAgent)
	resp, err := wikiClient.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		body, _ := io.ReadAll(io.LimitReader(resp.Body, 2048))
		return nil, fmt.Errorf("HTTP %d: %s", resp.StatusCode, body)
	}
	return io.ReadAll(resp.Body)
}

// doGETWithRetry retries on 5xx errors.
func doGETWithRetry(uri, userAgent string) ([]byte, error) {
	var lastErr error
	for attempt := 0; attempt < wikiMaxRetries; attempt++ {
		if attempt > 0 {
			backoff := wikiRetryBackoff * time.Duration(1<<(attempt-1))
			log.Printf("  retry %d/%d after %v", attempt+1, wikiMaxRetries, backoff)
			time.Sleep(backoff)
		}
		raw, err := doGET(uri, userAgent)
		if err == nil {
			return raw, nil
		}
		lastErr = err
		if !strings.Contains(err.Error(), "HTTP 5") {
			break
		}
	}
	return nil, lastErr
}

// min returns the smaller of a and b.
func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}