package main

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

const (
	wikidataSparql = "https://query.wikidata.org/sparql"
	wikiBatchSize  = 30
	wikiDelay      = 1 * 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 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
}

// fetchWikiArticles queries Wikidata SPARQL in batches and updates wiki_article in the DB.
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
	}
	log.Printf("fetchWikiArticles: %d entries missing wiki_article", len(ids))

	tx, err := a.DB.Begin()
	if err != nil {
		return fmt.Errorf("begin tx: %w", err)
	}

	stmt, err := tx.Prepare(`UPDATE imdb SET wiki_article = ? WHERE imdb_id = ?`)
	if err != nil {
		tx.Rollback()
		return fmt.Errorf("prepare wiki update: %w", err)
	}
	defer stmt.Close()

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

		results, err := a.queryWikidataBatch(chunk)
		if err != nil {
			log.Printf("wikidata batch error at offset %d: %v", i, err)
			// skip batch, continue
			continue
		}

		for id, acc := range results {
			if acc.title == "" {
				continue
			}
			if _, err := stmt.Exec(acc.title, id); err != nil {
				tx.Rollback()
				return fmt.Errorf("update wiki_article for %s: %w", id, err)
			}
			updated++
		}

		done := i + len(chunk)
		log.Printf("fetchWikiArticles: [%d/%d]", done, len(ids))

		// rate limit between batches
		if i+wikiBatchSize < len(ids) {
			time.Sleep(wikiDelay)
		}
	}

	if err := tx.Commit(); err != nil {
		return fmt.Errorf("commit wiki articles: %w", err)
	}

	log.Printf("fetchWikiArticles: %d wiki articles updated", updated)
	return nil
}

// 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 := 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
}