package server

import (
	"context"
	"encoding/json"
	"errors"
	"html"
	"io"
	"net/http"
	"net/url"
	"regexp"
	"strings"
	"time"
)

// Web search for the assistant, when the user turned «Поиск» on: DuckDuckGo's
// plain pages, no key and nothing to install. The light page first, the
// HTML one if that fails; DuckDuckGo turns away too many requests from one
// address, and then the assistant is told so.

type searchResult struct {
	Title   string `json:"title"`
	URL     string `json:"url"`
	Snippet string `json:"snippet"`
}

var (
	reLiteLink    = regexp.MustCompile(`(?s)<a[^>]+href="([^"]+)"[^>]*class='result-link'[^>]*>(.*?)</a>`)
	reLiteSnippet = regexp.MustCompile(`(?s)<td class='result-snippet'>(.*?)</td>`)
	reHTMLLink    = regexp.MustCompile(`(?s)<a[^>]+class="result__a"[^>]+href="([^"]+)"[^>]*>(.*?)</a>`)
	reHTMLSnippet = regexp.MustCompile(`(?s)<a[^>]+class="result__snippet"[^>]*>(.*?)</a>`)
	reTags        = regexp.MustCompile(`<[^>]+>`)
)

// text is a bit of a results page as plain text.
func text(s string) string {
	return strings.Join(strings.Fields(html.UnescapeString(reTags.ReplaceAllString(s, ""))), " ")
}

// realURL takes DuckDuckGo's redirect (/l/?uddg=…) back to the address.
func realURL(h string) string {
	h = html.UnescapeString(h)
	if strings.HasPrefix(h, "//") {
		h = "https:" + h
	}
	if u, err := url.Parse(h); err == nil {
		if t := u.Query().Get("uddg"); t != "" {
			return t
		}
	}
	return h
}

// parseDDG reads the results of the light or the HTML page.
func parseDDG(page string) []searchResult {
	links, snips := reLiteLink.FindAllStringSubmatch(page, -1), reLiteSnippet.FindAllStringSubmatch(page, -1)
	if len(links) == 0 {
		links, snips = reHTMLLink.FindAllStringSubmatch(page, -1), reHTMLSnippet.FindAllStringSubmatch(page, -1)
	}
	var out []searchResult
	for i, l := range links {
		r := searchResult{Title: text(l[2]), URL: realURL(l[1])}
		if i < len(snips) {
			r.Snippet = text(snips[i][1])
		}
		// Ads lead back through DuckDuckGo itself: left out.
		if strings.Contains(r.URL, "duckduckgo.com/y.js") || r.Title == "" {
			continue
		}
		out = append(out, r)
	}
	return out
}

var searchClient = &http.Client{Timeout: 15 * time.Second}

// webSearch asks DuckDuckGo for q: up to n results.
func webSearch(ctx context.Context, q string, n int) ([]searchResult, error) {
	var last error
	for _, base := range []string{"https://lite.duckduckgo.com/lite/?q=", "https://html.duckduckgo.com/html/?q="} {
		req, _ := http.NewRequestWithContext(ctx, http.MethodGet, base+url.QueryEscape(q), nil)
		req.Header.Set("User-Agent", "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0 Safari/537.36")
		req.Header.Set("Accept-Language", "ru,en;q=0.8")
		resp, err := searchClient.Do(req)
		if err != nil {
			last = err
			continue
		}
		b, _ := io.ReadAll(io.LimitReader(resp.Body, 2<<20))
		resp.Body.Close()
		rs := parseDDG(string(b))
		if resp.StatusCode == http.StatusOK && len(rs) > 0 {
			if len(rs) > n {
				rs = rs[:n]
			}
			return rs, nil
		}
		if resp.StatusCode == http.StatusOK {
			last = errors.New("ничего не нашлось")
		} else {
			last = errors.New("поисковик не ответил (" + resp.Status + "), возможно, временно ограничил запросы")
		}
	}
	return nil, last
}

// POST /api/panel/ai/search - {q}: the results, for a user with the
// assistant on (the «Поиск» switch is the page's: it lets the model ask).
func (s *Server) handleAISearch(w http.ResponseWriter, r *http.Request) {
	a := s.currentAdmin(r)
	if on, _ := s.db.GetConfig(aiUserKey(a.ID)); on != "1" {
		writeJSON(w, map[string]any{"ok": false, "error": "ассистент выключен в профиле"})
		return
	}
	var in struct {
		Q string `json:"q"`
	}
	if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, 4<<10)).Decode(&in); err != nil || strings.TrimSpace(in.Q) == "" {
		writeJSON(w, map[string]any{"ok": false, "error": "пустой запрос"})
		return
	}
	rs, err := webSearch(r.Context(), strings.TrimSpace(in.Q), 6)
	if err != nil {
		writeJSON(w, map[string]any{"ok": false, "error": err.Error()})
		return
	}
	writeJSON(w, map[string]any{"ok": true, "data": rs})
}