feat: the assistant's search engine in Настройки - DuckDuckGo, a SearXNG of one's own, Brave Search or Tavily, with DuckDuckGo behind the chosen one

internal/server/search.go

@@ -9,6 +9,7 @@ import (
 	"net/http"
 	"net/url"
 	"regexp"
+	"strconv"
 	"strings"
 	"time"
 )
@@ -74,6 +75,127 @@ func parseDDG(page string) []searchResult {
 
 var searchClient = &http.Client{Timeout: 15 * time.Second}
 
+// The engine is the admins' choice (Настройки › ИИ-ассистент): DuckDuckGo,
+// a SearXNG of one's own, Brave Search or Tavily; when the chosen one fails,
+// DuckDuckGo answers instead.
+const (
+	cfgSearchEngine = "ai_search"
+	cfgSearchURL    = "ai_search_url"
+	cfgSearchKey    = "ai_search_key"
+)
+
+type searchConf struct{ Engine, URL, Key string }
+
+func (s *Server) searchConf() searchConf {
+	e, _ := s.db.GetConfig(cfgSearchEngine)
+	u, _ := s.db.GetConfig(cfgSearchURL)
+	k, _ := s.db.GetConfig(cfgSearchKey)
+	return searchConf{Engine: e, URL: strings.TrimRight(u, "/"), Key: k}
+}
+
+var (
+	braveURL  = "https://api.search.brave.com/res/v1/web/search"
+	tavilyURL = "https://api.tavily.com/search"
+	ddgSearch = webSearch
+)
+
+// searchWith asks the engine c names; DuckDuckGo if that one fails.
+func searchWith(ctx context.Context, c searchConf, q string, n int) ([]searchResult, error) {
+	var rs []searchResult
+	var err error
+	switch c.Engine {
+	case "searxng":
+		rs, err = searchSearx(ctx, c, q)
+	case "brave":
+		rs, err = searchBrave(ctx, c, q, n)
+	case "tavily":
+		rs, err = searchTavily(ctx, c, q, n)
+	default:
+		return ddgSearch(ctx, q, n)
+	}
+	if err != nil || len(rs) == 0 {
+		return ddgSearch(ctx, q, n)
+	}
+	if len(rs) > n {
+		rs = rs[:n]
+	}
+	return rs, nil
+}
+
+// getJSON fetches url (with the headers) into v.
+func getJSON(ctx context.Context, method, url string, body io.Reader, hdr map[string]string, v any) error {
+	req, err := http.NewRequestWithContext(ctx, method, url, body)
+	if err != nil {
+		return err
+	}
+	req.Header.Set("Accept", "application/json")
+	for k, val := range hdr {
+		req.Header.Set(k, val)
+	}
+	resp, err := searchClient.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode/100 != 2 {
+		return errors.New("поисковик ответил " + resp.Status)
+	}
+	return json.NewDecoder(io.LimitReader(resp.Body, 4<<20)).Decode(v)
+}
+
+// searchSearx: a SearXNG with JSON output on (search.formats: json).
+func searchSearx(ctx context.Context, c searchConf, q string) ([]searchResult, error) {
+	if c.URL == "" {
+		return nil, errors.New("не задан адрес SearXNG")
+	}
+	var out struct {
+		Results []struct{ Title, URL, Content string } `json:"results"`
+	}
+	if err := getJSON(ctx, http.MethodGet, c.URL+"/search?format=json&q="+url.QueryEscape(q), nil, nil, &out); err != nil {
+		return nil, err
+	}
+	var rs []searchResult
+	for _, r := range out.Results {
+		rs = append(rs, searchResult{Title: r.Title, URL: r.URL, Snippet: text(r.Content)})
+	}
+	return rs, nil
+}
+
+func searchBrave(ctx context.Context, c searchConf, q string, n int) ([]searchResult, error) {
+	var out struct {
+		Web struct {
+			Results []struct{ Title, URL, Description string } `json:"results"`
+		} `json:"web"`
+	}
+	err := getJSON(ctx, http.MethodGet, braveURL+"?count="+strconv.Itoa(n)+"&q="+url.QueryEscape(q), nil,
+		map[string]string{"X-Subscription-Token": c.Key}, &out)
+	if err != nil {
+		return nil, err
+	}
+	var rs []searchResult
+	for _, r := range out.Web.Results {
+		rs = append(rs, searchResult{Title: text(r.Title), URL: r.URL, Snippet: text(r.Description)})
+	}
+	return rs, nil
+}
+
+func searchTavily(ctx context.Context, c searchConf, q string, n int) ([]searchResult, error) {
+	b, _ := json.Marshal(map[string]any{"query": q, "max_results": n})
+	var out struct {
+		Results []struct{ Title, URL, Content string } `json:"results"`
+	}
+	err := getJSON(ctx, http.MethodPost, tavilyURL, strings.NewReader(string(b)),
+		map[string]string{"Authorization": "Bearer " + c.Key, "Content-Type": "application/json"}, &out)
+	if err != nil {
+		return nil, err
+	}
+	var rs []searchResult
+	for _, r := range out.Results {
+		rs = append(rs, searchResult{Title: r.Title, URL: r.URL, Snippet: r.Content})
+	}
+	return rs, nil
+}
+
 // webSearch asks DuckDuckGo for q: up to n results.
 func webSearch(ctx context.Context, q string, n int) ([]searchResult, error) {
 	var last error
@@ -119,7 +241,7 @@ func (s *Server) handleAISearch(w http.ResponseWriter, r *http.Request) {
 		writeJSON(w, map[string]any{"ok": false, "error": "пустой запрос"})
 		return
 	}
-	rs, err := webSearch(r.Context(), strings.TrimSpace(in.Q), 6)
+	rs, err := searchWith(r.Context(), s.searchConf(), strings.TrimSpace(in.Q), 6)
 	if err != nil {
 		writeJSON(w, map[string]any{"ok": false, "error": err.Error()})
 		return