package library

import (
	"testing"
	"time"
)

func TestProposeSurvivor(t *testing.T) {
	older := time.Date(2025, 1, 1, 0, 0, 0, 0, time.UTC)
	newer := older.Add(24 * time.Hour)
	cases := []struct {
		name       string
		cands      []SurvivorCandidate
		wantID     string
		wantReason string
	}{
		{
			// Lossless wins even against a much larger lossy file, and even
			// when the lossy copy has been in the library longer.
			name: "lossless beats larger and older",
			cands: []SurvivorCandidate{
				{TrackID: "mp3", FileFormat: "mp3", FileSize: 90_000_000, AddedAt: older},
				{TrackID: "flac", FileFormat: "FLAC", FileSize: 30_000_000, AddedAt: newer},
			},
			wantID: "flac", wantReason: "lossless (flac)",
		},
		{
			// m4a may be AAC; it must not outrank an mp3 just for being m4a.
			name: "m4a is not treated as lossless",
			cands: []SurvivorCandidate{
				{TrackID: "m4a", FileFormat: "m4a", FileSize: 5_000_000, AddedAt: older},
				{TrackID: "mp3", FileFormat: "mp3", FileSize: 9_000_000, AddedAt: newer},
			},
			wantID: "mp3", wantReason: "largest file",
		},
		{
			name: "larger file wins among lossy copies",
			cands: []SurvivorCandidate{
				{TrackID: "128k", FileFormat: "mp3", FileSize: 3_400_000, AddedAt: older},
				{TrackID: "320k", FileFormat: "mp3", FileSize: 8_600_000, AddedAt: newer},
			},
			wantID: "320k", wantReason: "largest file",
		},
		{
			// The #3885 pair: identical audio, sizes equal but for the tags.
			name: "the longest-standing copy wins when size ties",
			cands: []SurvivorCandidate{
				{TrackID: "www-02", FileFormat: "mp3", FileSize: 6_900_000, AddedAt: newer},
				{TrackID: "www-01", FileFormat: "mp3", FileSize: 6_900_000, AddedAt: older},
			},
			wantID: "www-01", wantReason: "in the library longest",
		},
		{
			name: "a full tie falls back to the lowest id, stably",
			cands: []SurvivorCandidate{
				{TrackID: "b", FileFormat: "mp3", FileSize: 1, AddedAt: older},
				{TrackID: "a", FileFormat: "mp3", FileSize: 1, AddedAt: older},
			},
			wantID: "a", wantReason: "copies are otherwise identical",
		},
		{
			name:   "one copy",
			cands:  []SurvivorCandidate{{TrackID: "only", FileFormat: "mp3", FileSize: 1, AddedAt: older}},
			wantID: "only", wantReason: "the only copy",
		},
	}
	for _, tc := range cases {
		t.Run(tc.name, func(t *testing.T) {
			id, reason := ProposeSurvivor(tc.cands)
			if id != tc.wantID || reason != tc.wantReason {
				t.Fatalf("ProposeSurvivor = (%q, %q), want (%q, %q)", id, reason, tc.wantID, tc.wantReason)
			}
		})
	}
}

// The reason must name the rule that decided. Across three copies that is the
// comparison between first and second place, not the first rule any pair
// differs on: here the lossy copy differs from the others by format, but the
// two FLACs are separated by size.
func TestProposeSurvivor_ReasonIsTheDecidingRule(t *testing.T) {
	at := time.Date(2025, 1, 1, 0, 0, 0, 0, time.UTC)
	id, reason := ProposeSurvivor([]SurvivorCandidate{
		{TrackID: "mp3", FileFormat: "mp3", FileSize: 99_000_000, AddedAt: at},
		{TrackID: "flac-small", FileFormat: "flac", FileSize: 20_000_000, AddedAt: at},
		{TrackID: "flac-big", FileFormat: "flac", FileSize: 40_000_000, AddedAt: at},
	})
	if id != "flac-big" || reason != "largest file" {
		t.Fatalf("got (%q, %q), want (flac-big, largest file)", id, reason)
	}
}