package indexer

import (
	"context"
	"encoding/xml"
	"fmt"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"time"
)

// DefaultTimeout is what an unset Timeout means. Longer than a metadata
// call: a feed may itself fan out to several trackers before answering.
const DefaultTimeout = 30 * time.Second

// TorznabConfig is one Torznab feed.
type TorznabConfig struct {
	// Code is the acquisition_services row this client was built from,
	// stamped onto every Result.
	Code string
	// FeedURL is the feed's whole address up to and including /api, as
	// Jackett or a Prowlarr indexer shows it — e.g.
	// http://prowlarr:9696/12/api. Query parameters are appended to it.
	// One field rather than Fabled Librarian's base + path + indexer id: a
	// pasted URL is more reliable than Minstrel being right about a third
	// party's routes.
	FeedURL string
	// APIKey is optional: Torznab makes it so. A feed that needs one says so
	// with Newznab error 100, which is ErrAuth.
	APIKey  string
	Timeout time.Duration
}

// Torznab searches one Torznab feed.
type Torznab struct {
	Config TorznabConfig
	// HTTP is injectable for tests. Nil takes http.DefaultClient.
	HTTP *http.Client
}

// Search asks the feed for q. `t=search` is free text, which every indexer
// supports; `t=music` takes artist and album separately, and a release name
// does not reliably say which of its parts is which.
func (c *Torznab) Search(ctx context.Context, q Query) ([]Result, error) {
	params := url.Values{"t": {"search"}, "q": {q.Text}}
	for _, cat := range q.Categories {
		params.Add("cat", strconv.Itoa(cat))
	}
	body, err := c.get(ctx, c.endpoint(params))
	if err != nil {
		return nil, err
	}
	out, err := parseFeed(body)
	if err != nil {
		return nil, err
	}
	for i := range out {
		out[i].Source = c.Config.Code
	}
	return out, nil
}

// Download fetches a result's .torrent bytes through the feed, which holds
// the tracker's credentials. A result with a magnet needs none of this.
func (c *Torznab) Download(ctx context.Context, r Result) ([]byte, error) {
	if r.DownloadURL == "" {
		return nil, fmt.Errorf("%w: %q has no download URL", ErrUnreachable, r.Title)
	}
	body, err := c.get(ctx, r.DownloadURL)
	if err != nil {
		return nil, err
	}
	return torrentBody(r.Title, body)
}

// torrentBody checks a fetched .torrent. A torrent is a bencoded dictionary
// and starts with 'd'; an expired session gets an HTML login page with HTTP
// 200, which the download client would otherwise reject as an unsupported
// file from a component that did nothing wrong.
func torrentBody(title string, body []byte) ([]byte, error) {
	if err := MagnetBody(body); err != nil {
		return nil, err
	}
	if len(body) == 0 || body[0] != 'd' {
		return nil, fmt.Errorf("%w: %q returned %d bytes that are not a torrent", ErrUnreachable, title, len(body))
	}
	return body, nil
}

// TorrentBody is torrentBody for the other search clients' fetches.
func TorrentBody(title string, body []byte) ([]byte, error) { return torrentBody(title, body) }

func (c *Torznab) endpoint(params url.Values) string {
	if c.Config.APIKey != "" {
		params.Set("apikey", c.Config.APIKey)
	}
	feed := strings.TrimSpace(c.Config.FeedURL)
	sep := "?"
	if strings.Contains(feed, "?") {
		sep = "&"
	}
	return feed + sep + params.Encode()
}

func (c *Torznab) get(ctx context.Context, endpoint string) ([]byte, error) {
	if strings.TrimSpace(c.Config.FeedURL) == "" {
		return nil, ErrUnconfigured
	}
	timeout := c.Config.Timeout
	if timeout <= 0 {
		timeout = DefaultTimeout
	}
	ctx, cancel := context.WithTimeout(ctx, timeout)
	defer cancel()
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
	if err != nil {
		return nil, fmt.Errorf("%w: build request: %v", ErrUnreachable, err)
	}
	req.Header.Set("User-Agent", UserAgent)
	resp, body, err := Send(c.HTTP, req)
	if err != nil {
		return nil, err
	}
	if err := StatusError(resp, "the indexer"); err != nil {
		return nil, err
	}
	// Newznab reports errors as HTTP 200 with an <error> document, so a
	// client checking only the status reads a refused key as an empty result
	// set: search quietly stops finding things.
	if err := errorDocument(body); err != nil {
		return nil, err
	}
	return body, nil
}

// errorDocument reads an <error code=… description=…/> answer. Newznab's 1xx
// codes (100 wrong key, 101 suspended, 102 insufficient privileges) are all
// about who is asking, so they are ErrAuth.
func errorDocument(body []byte) error {
	head := body
	if len(head) > 512 {
		head = head[:512]
	}
	if !strings.Contains(string(head), "<error") {
		return nil
	}
	var doc struct {
		XMLName     xml.Name `xml:"error"`
		Code        string   `xml:"code,attr"`
		Description string   `xml:"description,attr"`
	}
	if err := xml.Unmarshal(body, &doc); err != nil {
		return nil
	}
	if doc.Code == "" && doc.Description == "" {
		return nil
	}
	if strings.HasPrefix(doc.Code, "1") && len(doc.Code) == 3 {
		return fmt.Errorf("%w: indexer error %s: %s", ErrAuth, doc.Code, doc.Description)
	}
	return fmt.Errorf("%w: indexer error %s: %s", ErrUnreachable, doc.Code, doc.Description)
}

// The Torznab feed: RSS 2.0 with torznab:attr for what RSS has no field for.
type feed struct {
	Channel struct {
		Items []item `xml:"item"`
	} `xml:"channel"`
}

type item struct {
	Title     string `xml:"title"`
	GUID      string `xml:"guid"`
	Link      string `xml:"link"`
	PubDate   string `xml:"pubDate"`
	Size      int64  `xml:"size"`
	Enclosure struct {
		URL    string `xml:"url,attr"`
		Length int64  `xml:"length,attr"`
	} `xml:"enclosure"`
	Attrs []struct {
		Name  string `xml:"name,attr"`
		Value string `xml:"value,attr"`
	} `xml:"attr"`
}

func (i item) attr(name string) string {
	for _, a := range i.Attrs {
		if strings.EqualFold(a.Name, name) {
			return a.Value
		}
	}
	return ""
}

func parseFeed(body []byte) ([]Result, error) {
	var f feed
	if err := xml.Unmarshal(body, &f); err != nil {
		return nil, fmt.Errorf("%w: parse feed: %v", ErrUnreachable, err)
	}
	out := make([]Result, 0, len(f.Channel.Items))
	for _, it := range f.Channel.Items {
		r := Result{
			Title:     strings.TrimSpace(it.Title),
			SizeBytes: it.Size,
			Indexer:   it.attr("indexer"),
			Seeders:   atoi(it.attr("seeders")),
			Peers:     atoi(it.attr("peers")),
			Category:  atoi(it.attr("category")),
		}
		if r.Title == "" {
			continue
		}
		if r.SizeBytes == 0 {
			r.SizeBytes = it.Enclosure.Length
		}
		// The link is a magnet or a .torrent URL; Prowlarr puts it in <link>
		// and repeats it in <enclosure url>, either populated by version.
		for _, candidate := range []string{it.Link, it.Enclosure.URL} {
			if strings.HasPrefix(candidate, "magnet:") && r.Magnet == "" {
				r.Magnet = candidate
			} else if candidate != "" && r.DownloadURL == "" {
				r.DownloadURL = candidate
			}
		}
		// The infohash from the explicit attr, then the magnet, then the GUID
		// only when it is shaped like a hash: Prowlarr puts a URL there as
		// often as a hash.
		r.InfoHash = NormalizeHash(it.attr("infohash"))
		if r.InfoHash == "" {
			r.InfoHash = MagnetHash(r.Magnet)
		}
		if r.InfoHash == "" && IsInfoHash(it.GUID) {
			r.InfoHash = NormalizeHash(it.GUID)
		}
		if t, err := time.Parse(time.RFC1123Z, strings.TrimSpace(it.PubDate)); err == nil {
			r.Published = t
		} else if t, err := time.Parse(time.RFC1123, strings.TrimSpace(it.PubDate)); err == nil {
			r.Published = t
		}
		out = append(out, r)
	}
	return out, nil
}

func atoi(s string) int {
	n, err := strconv.Atoi(strings.TrimSpace(s))
	if err != nil {
		return 0
	}
	return n
}