package feed

import (
	"encoding/xml"
	"os"
	"path/filepath"
	"strings"
	"testing"
	"time"
)

func writeFiles(t *testing.T, names ...string) string {
	t.Helper()
	dir := t.TempDir()
	for i, n := range names {
		// Distinct sizes so enclosure length is verifiably per-file.
		body := strings.Repeat("x", 100+i)
		if err := os.WriteFile(filepath.Join(dir, n), []byte(body), 0o644); err != nil {
			t.Fatalf("writing %s: %v", n, err)
		}
	}
	return dir
}

func build(t *testing.T, dir string, opts ...func(*Options)) *RSS {
	t.Helper()
	o := Options{
		Dir:     dir,
		BaseURL: "https://example.com/audio/",
		Title:   "Personal Physics Lectures",
		Epoch:   time.Date(2020, time.March, 1, 12, 0, 0, 0, time.UTC),
	}
	for _, f := range opts {
		f(&o)
	}
	r, err := Build(o, nil)
	if err != nil {
		t.Fatalf("Build: %v", err)
	}
	return r
}

func TestParseName(t *testing.T) {
	cases := []struct {
		in    string
		track int
		title string
	}{
		{"01 - The Law of Gravitation.mp3", 1, "The Law of Gravitation"},
		{"07 - Seeking New Laws.mp3", 7, "Seeking New Laws"},
		{"10 - Probability & Uncertainty.mp3", 10, "Probability & Uncertainty"},
		{"3 - Short Prefix.mp3", 3, "Short Prefix"},
		{"04 – En Dash Separator.mp3", 4, "En Dash Separator"},
		{"No Number Here.mp3", 0, "No Number Here"},
		{"  Padded Name  .mp3", 0, "Padded Name"},
	}
	for _, c := range cases {
		track, title := ParseName(c.in)
		if track != c.track || title != c.title {
			t.Errorf("ParseName(%q) = (%d, %q), want (%d, %q)", c.in, track, title, c.track, c.title)
		}
	}
}

// Filenames routinely contain spaces and ampersands. Pasting them into the
// enclosure URL unescaped produces both an invalid URL and invalid XML — the
// single most likely way a hand-rolled feed fails to load at all.
func TestEnclosureURL_EscapesFilenames(t *testing.T) {
	got, err := EnclosureURL("https://example.com/audio/", "10 - Probability & Uncertainty.mp3", "")
	if err != nil {
		t.Fatalf("EnclosureURL: %v", err)
	}
	if strings.ContainsAny(got, " ") {
		t.Errorf("URL still contains a raw space: %q", got)
	}
	for _, want := range []string{"%20", "&"} {
		_ = want
	}
	if !strings.Contains(got, "10%20-%20Probability") {
		t.Errorf("spaces not percent-encoded: %q", got)
	}
	if !strings.HasPrefix(got, "https://example.com/audio/") {
		t.Errorf("base URL mangled: %q", got)
	}
}

func TestEnclosureURL_HandlesMissingTrailingSlash(t *testing.T) {
	got, err := EnclosureURL("https://example.com/audio", "01 - One.mp3", "")
	if err != nil {
		t.Fatalf("EnclosureURL: %v", err)
	}
	if !strings.Contains(got, "/audio/01") {
		t.Errorf("expected a separator to be inserted, got %q", got)
	}
}

func TestEnclosureURL_RejectsBadBase(t *testing.T) {
	for _, bad := range []string{"", "not-a-url", "/just/a/path"} {
		if _, err := EnclosureURL(bad, "a.mp3", ""); err == nil {
			t.Errorf("EnclosureURL(%q) should have failed", bad)
		}
	}
}

// Zero-padding is a convention, not a guarantee. Ordering has to come from the
// parsed track number, or a series with ten or more parts plays 1, 10, 2.
func TestBuild_OrdersByTrackNumberNotFilename(t *testing.T) {
	dir := writeFiles(t,
		"1 - One.mp3",
		"10 - Ten.mp3",
		"2 - Two.mp3",
	)
	r := build(t, dir)

	var titles []string
	for _, it := range r.Channel.Items {
		titles = append(titles, it.Title)
	}
	want := []string{"One", "Two", "Ten"}
	for i := range want {
		if titles[i] != want[i] {
			t.Fatalf("order = %v, want %v", titles, want)
		}
	}
}

// Files with no track number should not displace the numbered sequence.
func TestBuild_UntrackedFilesSortLast(t *testing.T) {
	dir := writeFiles(t, "Intro.mp3", "01 - One.mp3", "02 - Two.mp3")
	r := build(t, dir)
	last := r.Channel.Items[len(r.Channel.Items)-1]
	if last.Title != "Intro" {
		t.Errorf("last item = %q, want the untracked Intro", last.Title)
	}
}

// Anything that is not audio must be ignored, including the .part files an
// interrupted download leaves behind and any cover art.
func TestBuild_IgnoresNonAudio(t *testing.T) {
	dir := writeFiles(t,
		"01 - One.mp3",
		"cover.jpg",
		"02 - Two.mp3.part",
		"notes.txt",
	)
	r := build(t, dir)
	if len(r.Channel.Items) != 1 {
		var got []string
		for _, i := range r.Channel.Items {
			got = append(got, i.Title)
		}
		t.Errorf("got %d items %v, want only the mp3", len(r.Channel.Items), got)
	}
}

func TestBuild_EnclosureLengthIsTheFileSize(t *testing.T) {
	dir := writeFiles(t, "01 - One.mp3")
	info, err := os.Stat(filepath.Join(dir, "01 - One.mp3"))
	if err != nil {
		t.Fatal(err)
	}
	r := build(t, dir)
	if got := r.Channel.Items[0].Enclosure.Length; got != info.Size() {
		t.Errorf("Length = %d, want %d", got, info.Size())
	}
}

// Every item needs a distinct, increasing date or clients are free to order
// the series however they like.
func TestBuild_PubDatesAreDistinctAndAscending(t *testing.T) {
	dir := writeFiles(t, "01 - One.mp3", "02 - Two.mp3", "03 - Three.mp3")
	r := build(t, dir)

	var prev time.Time
	for i, it := range r.Channel.Items {
		got, err := time.Parse(time.RFC1123Z, it.PubDate)
		if err != nil {
			t.Fatalf("item %d has an unparseable pubDate %q: %v", i, it.PubDate, err)
		}
		if i > 0 && !got.After(prev) {
			t.Errorf("item %d pubDate %v is not after the previous %v", i, got, prev)
		}
		prev = got
	}
}

func TestBuild_EpisodeNumbersFollowTracks(t *testing.T) {
	dir := writeFiles(t, "01 - One.mp3", "02 - Two.mp3")
	r := build(t, dir)
	for i, want := range []int{1, 2} {
		if r.Channel.Items[i].Episode != want {
			t.Errorf("item %d episode = %d, want %d", i, r.Channel.Items[i].Episode, want)
		}
	}
}

// A lecture course must be presented oldest-first; the default for a podcast
// is newest-first, which would start the listener at the final lecture.
func TestBuild_MarkedAsSerial(t *testing.T) {
	r := build(t, writeFiles(t, "01 - One.mp3"))
	if r.Channel.ITunesType != "serial" {
		t.Errorf("itunes:type = %q, want serial", r.Channel.ITunesType)
	}
}

func TestBuild_RequiresATitle(t *testing.T) {
	_, err := Build(Options{Dir: t.TempDir(), BaseURL: "https://e.com/"}, nil)
	if err == nil {
		t.Error("expected an error when no feed title is given")
	}
}

// A missing directory must be an error, not an empty feed that looks like a
// working setup with nothing in it.
func TestBuild_MissingDirectoryIsAnError(t *testing.T) {
	_, err := Build(Options{
		Dir: filepath.Join(t.TempDir(), "nope"), BaseURL: "https://e.com/", Title: "T",
	}, nil)
	if err == nil {
		t.Error("expected an error for a missing directory")
	}
}

func TestBuild_ChannelHasRequiredElements(t *testing.T) {
	r := build(t, writeFiles(t, "01 - One.mp3"))
	if r.Channel.Title == "" {
		t.Error("channel title is empty")
	}
	if r.Channel.Description == "" {
		t.Error("channel description is empty — many clients reject a feed without one")
	}
	if r.Channel.Link == "" {
		t.Error("channel link is empty")
	}
}

// ID3 tags, when present, are better than a filename guess.
func TestBuild_PrefersTagsOverFilenames(t *testing.T) {
	dir := writeFiles(t, "01 - filename title.mp3")
	r, err := Build(Options{
		Dir: dir, BaseURL: "https://example.com/a/", Title: "T",
	}, func(string) (string, int, bool) {
		return "Tagged Title", 5, true
	})
	if err != nil {
		t.Fatalf("Build: %v", err)
	}
	if r.Channel.Items[0].Title != "Tagged Title" {
		t.Errorf("title = %q, want the tag value", r.Channel.Items[0].Title)
	}
	if r.Channel.Items[0].Episode != 5 {
		t.Errorf("episode = %d, want the tag track", r.Channel.Items[0].Episode)
	}
}

// A tag reader that finds nothing must not blank out the filename-derived title.
func TestBuild_FallsBackWhenTagsAreAbsent(t *testing.T) {
	dir := writeFiles(t, "01 - Filename Title.mp3")
	r, err := Build(Options{Dir: dir, BaseURL: "https://e.com/a/", Title: "T"},
		func(string) (string, int, bool) { return "", 0, false })
	if err != nil {
		t.Fatalf("Build: %v", err)
	}
	if r.Channel.Items[0].Title != "Filename Title" {
		t.Errorf("title = %q, want the filename fallback", r.Channel.Items[0].Title)
	}
}

// The whole document must be well-formed and round-trip through a parser —
// this is what a podcast client does first, and the thing most likely to fail
// on unescaped content.
func TestMarshal_ProducesParseableXML(t *testing.T) {
	dir := writeFiles(t, "10 - Probability & Uncertainty.mp3", "01 - One <thing>.mp3")
	r := build(t, dir)

	out, err := Marshal(r)
	if err != nil {
		t.Fatalf("Marshal: %v", err)
	}
	if !strings.HasPrefix(string(out), xml.Header) {
		t.Error("missing XML declaration")
	}

	var parsed struct {
		Channel struct {
			Title string `xml:"title"`
			Items []struct {
				Title     string `xml:"title"`
				Enclosure struct {
					URL    string `xml:"url,attr"`
					Length int64  `xml:"length,attr"`
				} `xml:"enclosure"`
			} `xml:"item"`
		} `xml:"channel"`
	}
	if err := xml.Unmarshal(out, &parsed); err != nil {
		t.Fatalf("generated feed does not parse: %v\n%s", err, out)
	}
	if len(parsed.Channel.Items) != 2 {
		t.Fatalf("parsed %d items, want 2", len(parsed.Channel.Items))
	}
	for _, it := range parsed.Channel.Items {
		if it.Enclosure.URL == "" {
			t.Error("an item has no enclosure URL")
		}
		if it.Enclosure.Length == 0 {
			t.Error("an item has a zero enclosure length")
		}
	}
}

// The original hand-rolled struct had a field with no xml tag, which the
// marshaller emitted as a stray <EnclosureURL> element. Guard against any
// element leaking in that a reader would not expect.
func TestMarshal_NoStrayElements(t *testing.T) {
	out, err := Marshal(build(t, writeFiles(t, "01 - One.mp3")))
	if err != nil {
		t.Fatal(err)
	}
	if strings.Contains(string(out), "EnclosureURL") {
		t.Error("stray EnclosureURL element in output")
	}
	if strings.Contains(string(out), "XMLName") {
		t.Error("stray XMLName element in output")
	}
}

func TestMarshal_GUIDIsNotAPermalink(t *testing.T) {
	out, _ := Marshal(build(t, writeFiles(t, "01 - One.mp3")))
	if !strings.Contains(string(out), `isPermaLink="false"`) {
		t.Error(`guid should carry isPermaLink="false"; it is not a URL`)
	}
}

func TestBuild_EmptyDirectoryProducesAValidEmptyFeed(t *testing.T) {
	r := build(t, t.TempDir())
	if len(r.Channel.Items) != 0 {
		t.Errorf("got %d items, want 0", len(r.Channel.Items))
	}
	if _, err := Marshal(r); err != nil {
		t.Errorf("an empty feed should still marshal: %v", err)
	}
}