// SPDX-FileCopyrightText: Copyright The Miniflux Authors. All rights reserved.
// SPDX-License-Identifier: Apache-2.0

package icon // import "miniflux.app/v2/internal/reader/icon"

import (
	"bytes"
	"encoding/base64"
	"fmt"
	"image"
	"image/gif"
	"image/jpeg"
	"image/png"
	"io"
	"log/slog"
	"net/url"
	"regexp"
	"slices"
	"strings"

	"miniflux.app/v2/internal/config"
	"miniflux.app/v2/internal/crypto"
	"miniflux.app/v2/internal/model"
	"miniflux.app/v2/internal/reader/encoding"
	"miniflux.app/v2/internal/reader/fetcher"
	"miniflux.app/v2/internal/urllib"

	"github.com/PuerkitoBio/goquery"
	"github.com/tdewolff/minify/v2"
	"github.com/tdewolff/minify/v2/svg"
	"golang.org/x/image/draw"
	"golang.org/x/image/webp"
)

type iconFinder struct {
	requestBuilder *fetcher.RequestBuilder
	websiteURL     string
	feedIconURL    string
}

func newIconFinder(requestBuilder *fetcher.RequestBuilder, websiteURL, feedIconURL string) *iconFinder {
	return &iconFinder{
		requestBuilder: requestBuilder,
		websiteURL:     websiteURL,
		feedIconURL:    feedIconURL,
	}
}

func (f *iconFinder) findIcon() (*model.Icon, error) {
	slog.Debug("Begin icon discovery process",
		slog.String("website_url", f.websiteURL),
		slog.String("feed_icon_url", f.feedIconURL),
	)

	if f.feedIconURL != "" {
		if icon, err := f.downloadIcon(f.feedIconURL); err != nil {
			slog.Debug("Unable to fetch the feed's icon",
				slog.String("website_url", f.websiteURL),
				slog.String("feed_icon_url", f.feedIconURL),
				slog.Any("error", err),
			)
		} else if icon != nil {
			return icon, nil
		}
	}

	// Try the website URL first, then fall back to the root URL if no icon is found.
	// The website URL may include a subdirectory (e.g., https://example.org/subfolder/), and icons can be referenced relative to that path.
	for _, documentURL := range []string{f.websiteURL, urllib.RootURL(f.websiteURL)} {
		if icon, err := f.fetchIconsFromHTMLDocument(documentURL); err != nil {
			slog.Debug("Unable to fetch icons from HTML document",
				slog.String("document_url", documentURL),
				slog.Any("error", err),
			)
		} else if icon != nil {
			return icon, nil
		}
	}

	return f.fetchDefaultIcon()
}

func (f *iconFinder) fetchDefaultIcon() (*model.Icon, error) {
	slog.Debug("Fetching default icon",
		slog.String("website_url", f.websiteURL),
	)

	iconURL, err := urllib.JoinBaseURLAndPath(urllib.RootURL(f.websiteURL), "favicon.ico")
	if err != nil {
		return nil, fmt.Errorf(`icon: unable to join root URL and path: %w`, err)
	}

	icon, err := f.downloadIcon(iconURL)
	if err != nil {
		return nil, err
	}

	return icon, nil
}

func (f *iconFinder) fetchIconsFromHTMLDocument(documentURL string) (*model.Icon, error) {
	slog.Debug("Searching icons from HTML document",
		slog.String("document_url", documentURL),
	)

	responseHandler := fetcher.NewResponseHandler(f.requestBuilder.ExecuteRequest(documentURL))
	defer responseHandler.Close()

	if localizedError := responseHandler.LocalizedError(); localizedError != nil {
		return nil, fmt.Errorf("icon: unable to download website index page: %w", localizedError.Error())
	}

	iconURLs, err := findIconURLsFromHTMLDocument(
		documentURL,
		responseHandler.Body(config.Opts.HTTPClientMaxBodySize()),
		responseHandler.ContentType(),
	)
	if err != nil {
		return nil, err
	}

	slog.Debug("Searched icon from HTML document",
		slog.String("document_url", documentURL),
		slog.String("icon_urls", strings.Join(iconURLs, ",")),
	)

	for _, iconURL := range iconURLs {
		if strings.HasPrefix(iconURL, "data:") {
			slog.Debug("Found icon with data URL",
				slog.String("document_url", documentURL),
			)
			return parseImageDataURL(iconURL)
		}

		if icon, err := f.downloadIcon(iconURL); err != nil {
			slog.Debug("Unable to download icon from HTML document",
				slog.String("document_url", documentURL),
				slog.String("icon_url", iconURL),
				slog.Any("error", err),
			)
		} else if icon != nil {
			slog.Debug("Downloaded icon from HTML document",
				slog.String("document_url", documentURL),
				slog.String("icon_url", iconURL),
			)
			return icon, nil
		}
	}

	return nil, nil
}

func (f *iconFinder) downloadIcon(iconURL string) (*model.Icon, error) {
	slog.Debug("Downloading icon",
		slog.String("website_url", f.websiteURL),
		slog.String("icon_url", iconURL),
	)

	if err := ensureRemoteIconURLAllowed(iconURL, config.Opts.IconFetchAllowPrivateNetworks()); err != nil {
		return nil, err
	}

	responseHandler := fetcher.NewResponseHandler(f.requestBuilder.ExecuteRequest(iconURL))
	defer responseHandler.Close()

	if localizedError := responseHandler.LocalizedError(); localizedError != nil {
		return nil, fmt.Errorf("icon: unable to download website icon: %w", localizedError.Error())
	}

	responseBody, localizedError := responseHandler.ReadBody(config.Opts.HTTPClientMaxBodySize())
	if localizedError != nil {
		return nil, fmt.Errorf("icon: unable to read response body: %w", localizedError.Error())
	}

	icon := &model.Icon{
		Hash:     crypto.HashFromBytes(responseBody),
		MimeType: responseHandler.ContentType(),
		Content:  responseBody,
	}

	icon = resizeIcon(icon)

	return icon, nil
}

func resizeIcon(icon *model.Icon) *model.Icon {
	if icon.MimeType == "image/svg+xml" {
		minifier := minify.New()
		minifier.AddFunc("image/svg+xml", svg.Minify)
		var err error
		// minifier.Bytes returns the data unchanged in case of error.
		icon.Content, err = minifier.Bytes("image/svg+xml", icon.Content)
		if err != nil {
			slog.Error("Unable to minify SVG icon", slog.Any("error", err))
		}
		return icon
	}

	if !slices.Contains([]string{"image/jpeg", "image/png", "image/gif", "image/webp"}, icon.MimeType) {
		slog.Debug("Icon resize skipped: unsupported MIME type", slog.String("mime_type", icon.MimeType))
		return icon
	}

	r := bytes.NewReader(icon.Content)

	// Don't resize icons that we can't decode, or that already have the right size.
	config, _, err := image.DecodeConfig(r)
	if err != nil {
		slog.Warn("Unable to decode icon metadata", slog.Any("error", err))
		return icon
	}
	if config.Height <= 32 && config.Width <= 32 {
		slog.Debug("Icon doesn't need to be resized", slog.Int("height", config.Height), slog.Int("width", config.Width))
		return icon
	}

	r.Seek(0, io.SeekStart)

	var src image.Image
	switch icon.MimeType {
	case "image/jpeg":
		src, err = jpeg.Decode(r)
	case "image/png":
		src, err = png.Decode(r)
	case "image/gif":
		src, err = gif.Decode(r)
	case "image/webp":
		src, err = webp.Decode(r)
	}
	if err != nil || src == nil {
		slog.Warn("Unable to decode icon image", slog.Any("error", err))
		return icon
	}

	dst := image.NewRGBA(image.Rect(0, 0, 32, 32))
	draw.BiLinear.Scale(dst, dst.Rect, src, src.Bounds(), draw.Over, nil)

	var b bytes.Buffer
	if err = png.Encode(io.Writer(&b), dst); err != nil {
		slog.Warn("Unable to encode resized icon", slog.Any("error", err))
		return icon
	}

	icon.Content = b.Bytes()
	icon.MimeType = "image/png"
	return icon
}

func findIconURLsFromHTMLDocument(documentURL string, body io.Reader, contentType string) ([]string, error) {
	htmlDocumentReader, err := encoding.NewCharsetReader(body, contentType)
	if err != nil {
		return nil, fmt.Errorf("icon: unable to create charset reader: %w", err)
	}

	doc, err := goquery.NewDocumentFromReader(htmlDocumentReader)
	if err != nil {
		return nil, fmt.Errorf("icon: unable to read document: %v", err)
	}

	queries := [...]string{
		"link[rel='icon' i][href]",
		"link[rel='shortcut icon' i][href]",
		"link[rel='icon shortcut' i][href]",
		"link[rel='apple-touch-icon'][href]",
	}

	var iconURLs []string
	for _, query := range queries {
		slog.Debug("Searching icon URL in HTML document", slog.String("query", query))

		for _, s := range doc.Find(query).EachIter() {
			href, _ := s.Attr("href")
			href = strings.TrimSpace(href)
			if href == "" {
				continue
			}

			if absoluteIconURL, err := urllib.AbsoluteURL(documentURL, href); err != nil {
				slog.Warn("Unable to convert icon URL to absolute URL", slog.Any("error", err), slog.String("icon_href", href))
			} else {
				iconURLs = append(iconURLs, absoluteIconURL)
				slog.Debug("Found icon URL in HTML document",
					slog.String("query", query),
					slog.String("icon_href", href),
					slog.String("absolute_icon_url", absoluteIconURL),
				)
			}
		}
	}

	return iconURLs, nil
}

// https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/Data_URIs#syntax
// data:[<mediatype>][;encoding],<data>
// we consider <mediatype> to be mandatory, and it has to start with `image/`.
// we consider `base64`, `utf8` and the empty string to be the only valid encodings
func parseImageDataURL(value string) (*model.Icon, error) {
	re := regexp.MustCompile(`^data:` +
		`(?P<mediatype>image/[^;,]+)` +
		`(?:;(?P<encoding>base64|utf8))?` +
		`,(?P<data>.+)$`)

	matches := re.FindStringSubmatch(value)
	if matches == nil {
		return nil, fmt.Errorf(`icon: invalid data URL %q`, value)
	}

	mediaType := matches[re.SubexpIndex("mediatype")]
	encoding := matches[re.SubexpIndex("encoding")]
	data := matches[re.SubexpIndex("data")]

	var blob []byte
	switch encoding {
	case "base64":
		var err error
		blob, err = base64.StdEncoding.DecodeString(data)
		if err != nil {
			return nil, fmt.Errorf(`icon: invalid data %q (%v)`, value, err)
		}
	case "":
		decodedData, err := url.QueryUnescape(data)
		if err != nil {
			return nil, fmt.Errorf(`icon: unable to decode data URL %q`, value)
		}
		blob = []byte(decodedData)
	case "utf8":
		blob = []byte(data)
	}

	return &model.Icon{
		Hash:     crypto.HashFromBytes(blob),
		Content:  blob,
		MimeType: mediaType,
	}, nil
}

func ensureRemoteIconURLAllowed(iconURL string, allowPrivateNetworks bool) error {
	parsedURL, err := url.Parse(iconURL)
	if err != nil {
		return fmt.Errorf("icon: invalid icon URL %q: %w", iconURL, err)
	}

	if !parsedURL.IsAbs() {
		return fmt.Errorf("icon: icon URL %q must be absolute", iconURL)
	}

	scheme := strings.ToLower(parsedURL.Scheme)
	if scheme != "http" && scheme != "https" {
		return fmt.Errorf("icon: unsupported icon URL scheme %q", parsedURL.Scheme)
	}

	hostname := parsedURL.Hostname()
	if hostname == "" {
		return fmt.Errorf("icon: icon URL %q has no hostname", iconURL)
	}

	if allowPrivateNetworks {
		return nil
	}

	isPrivate, err := urllib.ResolvesToPrivateIP(hostname)
	if err != nil {
		return fmt.Errorf("icon: unable to resolve icon hostname %q: %w", hostname, err)
	}

	if isPrivate {
		return fmt.Errorf("icon: refusing to download icon from private network host %q", hostname)
	}

	return nil
}
