feat: fetch Wikipedia article titles via Wikidata SPARQL

- Query Wikidata SPARQL in batches of 30 for entries missing wiki_article
- Store wiki_article title in imdb table
- Respect rate limits with configurable delay and retry on 5xx/429
- Skip entries that have no Wikipedia article
- Removed unique constraint on wiki_article (multiple entries can share one)

3 files changed, 243 insertions, 1 deletions

diff --git a/schema/schema.sql b/schema/schema.sql
index 9b1e5ab..f957079 100644
--- a/schema/schema.sql
+++ b/schema/schema.sql
@@ -34,7 +34,6 @@ CREATE TABLE `imdb` (
   `num_votes` int(11) DEFAULT NULL,
   PRIMARY KEY (`id`),
   UNIQUE KEY `imdb_id` (`imdb_id`),
-  UNIQUE KEY `wiki_article` (`wiki_article`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci;
 
 
diff --git a/src/main.go b/src/main.go
index 123cc64..272e4b6 100644
--- a/src/main.go
+++ b/src/main.go
@@ -194,4 +194,8 @@ func main() {
 	if err = app.fetchAndUpdateImdbData(); err != nil {
 		log.Fatalf("fetchAndUpdateImdbData: %v", err)
 	}
+
+	if err = app.fetchWikiArticles(); err != nil {
+		log.Fatalf("fetchWikiArticles: %v", err)
+	}
 }
diff --git a/src/wikidata.go b/src/wikidata.go
new file mode 100644
index 0000000..b3018e5
--- /dev/null
+++ b/src/wikidata.go
@@ -0,0 +1,239 @@
+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
+}
+