package ingestion

import (
	"context"
	"encoding/json"
	"net/http"
	"net/url"
	"time"
)

var waybackClient = &http.Client{Timeout: 10 * time.Second}

type waybackResp struct {
	ArchivedSnapshots struct {
		Closest struct {
			Available bool   `json:"available"`
			URL       string `json:"url"`
			Status    string `json:"status"`
		} `json:"closest"`
	} `json:"archived_snapshots"`
}

// ResolveWayback asks the Internet Archive's Wayback availability API for the
// closest snapshot of the given URL. Returns the snapshot URL (https) or ""
// if no snapshot exists or the request fails.
func ResolveWayback(articleURL string) string {
	if articleURL == "" {
		return ""
	}
	api := "https://archive.org/wayback/available?url=" + url.QueryEscape(articleURL)
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()

	req, err := http.NewRequestWithContext(ctx, "GET", api, nil)
	if err != nil {
		return ""
	}
	req.Header.Set("User-Agent", userAgent)

	resp, err := waybackClient.Do(req)
	if err != nil {
		return ""
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return ""
	}

	var wr waybackResp
	if err := json.NewDecoder(resp.Body).Decode(&wr); err != nil {
		return ""
	}
	snap := wr.ArchivedSnapshots.Closest
	if !snap.Available || snap.Status != "200" || snap.URL == "" {
		return ""
	}
	// Wayback sometimes returns http:// even when https is available.
	if len(snap.URL) > 7 && snap.URL[:7] == "http://" {
		return "https://" + snap.URL[7:]
	}
	return snap.URL
}