// SPDX-License-Identifier: GPL-3.0-or-later

package dup

import (
	"bytes"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"strings"
	"testing"
	"time"

	"krino/internal/scan"
)

var base = time.Date(2026, 9, 1, 0, 0, 0, 0, time.UTC)

// put writes content at dir/name with an mtime `age` hours after base.
func put(t *testing.T, dir, name string, content []byte, hours int) scan.File {
	t.Helper()
	p := filepath.Join(dir, name)
	if err := os.MkdirAll(filepath.Dir(p), 0o755); err != nil {
		t.Fatal(err)
	}
	if err := os.WriteFile(p, content, 0o644); err != nil {
		t.Fatal(err)
	}
	mt := base.Add(time.Duration(hours) * time.Hour)
	if err := os.Chtimes(p, mt, mt); err != nil {
		t.Fatal(err)
	}
	return scan.File{Path: p, Rel: name, Name: filepath.Base(name), Size: int64(len(content)), ModTime: mt}
}

func lookup(t *testing.T, x *Index, f scan.File) (string, bool) {
	t.Helper()
	orig, dup, err := x.Lookup(f.Path)
	if err != nil {
		t.Fatal(err)
	}
	return orig, dup
}

func TestDuplicatesInScan(t *testing.T) {
	d := t.TempDir()
	a := put(t, d, "report.pdf", []byte("same content"), 1)
	b := put(t, d, "report (1).pdf", []byte("same content"), 5)
	c := put(t, d, "other.pdf", []byte("diff content"), 0) // same size, different bytes
	e1 := put(t, d, "empty1", nil, 0)
	e2 := put(t, d, "empty2", nil, 1)
	x, errs := NewIndex([]scan.File{a, b, c, e1, e2}, nil)
	if len(errs) > 0 {
		t.Fatal(errs)
	}
	if orig, dup := lookup(t, x, b); !dup || orig != a.Path {
		t.Errorf("copy: dup=%v orig=%s, want dup of %s", dup, orig, a.Path)
	}
	if _, dup := lookup(t, x, a); dup {
		t.Error("the original reported as a duplicate")
	}
	if _, dup := lookup(t, x, c); dup {
		t.Error("same size, different content reported as a duplicate")
	}
	if _, dup := lookup(t, x, e2); dup {
		t.Error("empty files reported as duplicates")
	}
}

func TestExtraDirHoldsTheOriginal(t *testing.T) {
	scanned, filed := t.TempDir(), t.TempDir()
	dl := put(t, scanned, "invoice.pdf", []byte("invoice 42"), 0) // older than the filed copy
	put(t, filed, "2026/invoice-42.pdf", []byte("invoice 42"), 9)
	x, errs := NewIndex([]scan.File{dl}, []string{filed, filepath.Join(filed, "missing")})
	if len(errs) != 1 {
		t.Errorf("want one error for the missing extra dir, got %v", errs)
	}
	if orig, dup := lookup(t, x, dl); !dup || orig != filepath.Join(filed, "2026/invoice-42.pdf") {
		t.Errorf("dup=%v orig=%s, want the filed copy as original", dup, orig)
	}
}

func TestTieBreaks(t *testing.T) {
	d := t.TempDir()
	long := put(t, d, "longer-name.txt", []byte("x"), 0)
	short := put(t, d, "b.txt", []byte("x"), 0)
	same := put(t, d, "a.txt", []byte("x"), 0)
	x, _ := NewIndex([]scan.File{long, short, same}, nil)
	for _, f := range []scan.File{long, short} {
		if orig, dup := lookup(t, x, f); !dup || orig != same.Path {
			t.Errorf("%s: dup=%v orig=%s, want %s (shortest name, then path order)", f.Name, dup, orig, same.Path)
		}
	}
}

func TestPartialHashCollisionResolvedByFullHash(t *testing.T) {
	d := t.TempDir()
	head, tail := bytes.Repeat([]byte("h"), 70<<10), bytes.Repeat([]byte("t"), 70<<10)
	one := append(append(append([]byte{}, head...), []byte("MIDDLE-ONE")...), tail...)
	two := append(append(append([]byte{}, head...), []byte("MIDDLE-TWO")...), tail...)
	a := put(t, d, "a.bin", one, 0)
	b := put(t, d, "b.bin", two, 1)
	x, _ := NewIndex([]scan.File{a, b}, nil)
	if _, dup := lookup(t, x, b); dup {
		t.Error("files differing only in the middle reported as duplicates")
	}
}

func TestLookupUnknownPath(t *testing.T) {
	x, _ := NewIndex(nil, nil)
	if _, _, err := x.Lookup("/nowhere"); err == nil {
		t.Fatal("no error for a path that was not scanned")
	}
}

// TestTieBreakNameBeforePath: same-length names, same mtime, in directories
// that sort in the opposite order from the names — the base name decides,
// not the full path (spec §5.5's flat chain, not a path-only fallback).
func TestTieBreakNameBeforePath(t *testing.T) {
	d := t.TempDir()
	catInZzz := put(t, d, "zzz/cat.txt", []byte("x"), 0)
	dogInAaa := put(t, d, "aaa/dog.txt", []byte("x"), 0)
	x, _ := NewIndex([]scan.File{catInZzz, dogInAaa}, nil)
	for _, f := range []scan.File{catInZzz, dogInAaa} {
		if orig, dup := lookup(t, x, f); orig != catInZzz.Path || dup != (f.Path != catInZzz.Path) {
			t.Errorf("%s: orig=%s dup=%v, want %s (name sorts before path)", f.Rel, orig, dup, catInZzz.Path)
		}
	}
}

// TestTieBreakExtraVsExtra: two extra directories hold identical copies;
// the one under the lexically later directory is older and must still win
// on ModTime — extra-vs-extra ties are not resolved by path alone.
func TestTieBreakExtraVsExtra(t *testing.T) {
	common := t.TempDir()
	aaa, zzz := filepath.Join(common, "aaa"), filepath.Join(common, "zzz")
	newer := put(t, aaa, "copy.txt", []byte("invoice 42"), 5) // lexically first, newer
	older := put(t, zzz, "copy.txt", []byte("invoice 42"), 0) // lexically last, older
	scanned := t.TempDir()
	dl := put(t, scanned, "download.txt", []byte("invoice 42"), 3)
	x, errs := NewIndex([]scan.File{dl}, []string{aaa, zzz})
	if len(errs) != 0 {
		t.Fatal(errs)
	}
	if orig, dup := lookup(t, x, dl); !dup || orig != older.Path {
		t.Errorf("dup=%v orig=%s, want %s (older extra copy, despite sorting after %s)", dup, orig, older.Path, newer.Path)
	}
}

// TestUnreadableSubdirReported: an unreadable subdirectory under an extra
// directory is reported as its own error, and the rest of that extra
// directory is still indexed.
func TestUnreadableSubdirReported(t *testing.T) {
	if os.Geteuid() == 0 {
		t.Skip("permissions are not enforced running as root")
	}
	filed := t.TempDir()
	blocked := filepath.Join(filed, "blocked")
	if err := os.MkdirAll(blocked, 0o755); err != nil {
		t.Fatal(err)
	}
	put(t, blocked, "secret.pdf", []byte("secret 42"), 0)
	put(t, filed, "visible.pdf", []byte("visible content"), 0)
	if err := os.Chmod(blocked, 0o000); err != nil {
		t.Fatal(err)
	}
	t.Cleanup(func() {
		if err := os.Chmod(blocked, 0o755); err != nil {
			t.Fatal(err)
		}
	})

	scanned := t.TempDir()
	dl := put(t, scanned, "visible.pdf", []byte("visible content"), 1)

	x, errs := NewIndex([]scan.File{dl}, []string{filed})
	if len(errs) != 1 || !strings.Contains(errs[0].Error(), blocked) {
		t.Fatalf("want one error naming %s, got %v", blocked, errs)
	}
	if orig, dup := lookup(t, x, dl); !dup || orig != filepath.Join(filed, "visible.pdf") {
		t.Errorf("dup=%v orig=%s, want the filed copy (visible.pdf still indexed despite the unreadable sibling)", dup, orig)
	}
}

// TestUnreadableCandidateSkipped: three files share a size; one of them
// (not the subject of either Lookup call) is unreadable. A1: the other two
// are still reported as a duplicate pair, and the unreadable one is
// recorded exactly once as a candidate error, not returned as a Lookup
// error.
func TestUnreadableCandidateSkipped(t *testing.T) {
	if os.Geteuid() == 0 {
		t.Skip("permissions are not enforced running as root")
	}
	d := t.TempDir()
	a := put(t, d, "a.bin", []byte("same content"), 0)
	b := put(t, d, "b.bin", []byte("same content"), 1)
	c := put(t, d, "c.bin", []byte("diff content"), 2) // same size, different bytes
	if err := os.Chmod(c.Path, 0o000); err != nil {
		t.Fatal(err)
	}
	t.Cleanup(func() { os.Chmod(c.Path, 0o644) })

	x, errs := NewIndex([]scan.File{a, b, c}, nil)
	if len(errs) != 0 {
		t.Fatalf("NewIndex errors: %v", errs)
	}
	if orig, dup := lookup(t, x, b); !dup || orig != a.Path {
		t.Errorf("a/b duplicate pair broken by unreadable sibling: dup=%v orig=%s", dup, orig)
	}
	if orig, dup := lookup(t, x, a); dup {
		t.Errorf("a reported as a duplicate: orig=%s", orig)
	}
	cerrs := x.Errors()
	if len(cerrs) != 1 {
		t.Fatalf("got %d candidate errors, want 1: %v", len(cerrs), cerrs)
	}
	if cerrs[0].Path != c.Path {
		t.Errorf("candidate error names %q, want %q", cerrs[0].Path, c.Path)
	}
}

// TestVanishedCandidateSkippedSilently: a candidate that vanishes between
// being indexed and being hashed is dropped with no error recorded at all.
func TestVanishedCandidateSkippedSilently(t *testing.T) {
	d := t.TempDir()
	a := put(t, d, "a.bin", []byte("same content"), 0)
	b := put(t, d, "b.bin", []byte("same content"), 1)
	c := put(t, d, "c.bin", []byte("diff content"), 2)
	x, errs := NewIndex([]scan.File{a, b, c}, nil)
	if len(errs) != 0 {
		t.Fatalf("NewIndex errors: %v", errs)
	}
	if err := os.Remove(c.Path); err != nil {
		t.Fatal(err)
	}
	if orig, dup := lookup(t, x, b); !dup || orig != a.Path {
		t.Errorf("a/b duplicate pair broken by vanished sibling: dup=%v orig=%s", dup, orig)
	}
	if got := x.Errors(); len(got) != 0 {
		t.Errorf("vanished candidate recorded as an error: %v", got)
	}
}

// TestLookupFailsWhenSubjectUnreadable: Lookup still fails outright when
// the file it was asked about (not some other candidate) cannot be read.
func TestLookupFailsWhenSubjectUnreadable(t *testing.T) {
	if os.Geteuid() == 0 {
		t.Skip("permissions are not enforced running as root")
	}
	d := t.TempDir()
	a := put(t, d, "a.bin", []byte("same content"), 0)
	b := put(t, d, "b.bin", []byte("same content"), 1)
	if err := os.Chmod(a.Path, 0o000); err != nil {
		t.Fatal(err)
	}
	t.Cleanup(func() { os.Chmod(a.Path, 0o644) })
	x, _ := NewIndex([]scan.File{a, b}, nil)
	if _, _, err := x.Lookup(a.Path); err == nil {
		t.Fatal("no error looking up an unreadable subject")
	}
}

// TestSameContentEqualSizeDifferentContent: two files of identical size but
// different bytes must not be reported as the same content — the partial
// hash (not just the size check) has to separate them.
func TestSameContentEqualSizeDifferentContent(t *testing.T) {
	d := t.TempDir()
	a := filepath.Join(d, "a.bin")
	b := filepath.Join(d, "b.bin")
	one := []byte("acme-invoice-01")
	two := []byte("acme-invoice-02")
	if len(one) != len(two) {
		t.Fatal("fixture bug: files must be the same size")
	}
	if err := os.WriteFile(a, one, 0o644); err != nil {
		t.Fatal(err)
	}
	if err := os.WriteFile(b, two, 0o644); err != nil {
		t.Fatal(err)
	}
	if ok, err := SameContent(a, b); err != nil || ok {
		t.Errorf("SameContent(a, b) = %v, %v; want false, nil", ok, err)
	}
}

// fakeDirEntry is an fs.DirEntry whose Info() returns a canned result, for
// exercising addEntry's Info()-failure handling directly (A3) — a real
// filepath.WalkDir gives no hook to inject a stat failure deterministically
// and without root.
type fakeDirEntry struct {
	name    string
	info    fs.FileInfo
	infoErr error
}

func (f fakeDirEntry) Name() string               { return f.name }
func (f fakeDirEntry) IsDir() bool                { return false }
func (f fakeDirEntry) Type() fs.FileMode          { return 0 }
func (f fakeDirEntry) Info() (fs.FileInfo, error) { return f.info, f.infoErr }

// TestAddEntryInfoFailure: A3. A vanished entry's Info() failure
// (fs.ErrNotExist) is dropped with no error recorded; any other Info()
// failure is dropped too, but recorded in errs, naming the entry.
func TestAddEntryInfoFailure(t *testing.T) {
	x := &Index{bySize: make(map[int64][]int), scanned: make(map[string]int)}
	var errs []error

	x.addEntry("/extra/vanished.txt", fakeDirEntry{
		name: "vanished.txt", infoErr: fmt.Errorf("stat vanished.txt: %w", fs.ErrNotExist),
	}, &errs)
	if len(errs) != 0 {
		t.Fatalf("vanished entry recorded an error: %v", errs)
	}
	if len(x.candidates) != 0 {
		t.Fatalf("vanished entry was indexed: %v", x.candidates)
	}

	x.addEntry("/extra/denied.txt", fakeDirEntry{
		name: "denied.txt", infoErr: errors.New("permission denied"),
	}, &errs)
	if len(errs) != 1 || !strings.Contains(errs[0].Error(), "/extra/denied.txt") {
		t.Fatalf("want one error naming /extra/denied.txt, got %v", errs)
	}
	if len(x.candidates) != 0 {
		t.Fatalf("denied entry was indexed: %v", x.candidates)
	}
}

// TestExtraDirSymlinkNotFollowed: A4. An extra directory that is itself a
// symlink to a real directory is not silently treated as empty:
// filepath.WalkDir Lstats its root, so without a check for this the walk
// would report no error and index nothing, misleading the user into
// thinking an archive was consulted when it never was.
func TestExtraDirSymlinkNotFollowed(t *testing.T) {
	real := t.TempDir()
	put(t, real, "invoice.pdf", []byte("invoice 42"), 0)
	link := filepath.Join(t.TempDir(), "link")
	if err := os.Symlink(real, link); err != nil {
		t.Fatal(err)
	}

	scanned := t.TempDir()
	dl := put(t, scanned, "download.pdf", []byte("invoice 42"), 1)

	x, errs := NewIndex([]scan.File{dl}, []string{link})
	if len(errs) != 1 || !strings.Contains(errs[0].Error(), link) || !strings.Contains(errs[0].Error(), "symlink") {
		t.Fatalf("want one error naming %s as a symlink, got %v", link, errs)
	}
	if orig, dup := lookup(t, x, dl); dup {
		t.Errorf("symlinked extra dir was indexed despite the error: dup=%v orig=%s", dup, orig)
	}
}

// linked builds a scan.File for a hardlink of an already-put file: same
// inode, so same content and metadata by construction, under a new name.
func linked(t *testing.T, dir, name string, target scan.File) scan.File {
	t.Helper()
	p := filepath.Join(dir, name)
	if err := os.Link(target.Path, p); err != nil {
		t.Fatal(err)
	}
	fi, err := os.Stat(p)
	if err != nil {
		t.Fatal(err)
	}
	return scan.File{Path: p, Rel: name, Name: name, Size: fi.Size(), ModTime: fi.ModTime()}
}

// TestHardlinksAreNotDuplicatesOfEachOther: spec §5.5 groups duplicate
// candidates by size and hash, with no inode check, so two hardlinked names
// - one inode, byte-identical by construction - were judged a duplicate
// pair. A rule of (when (duplicate)) (delete) would then remove a name the
// user relies on even though nothing was ever actually copied. os.SameFile
// must stop a file being judged a duplicate of itself under another name.
func TestHardlinksAreNotDuplicatesOfEachOther(t *testing.T) {
	d := t.TempDir()
	a := put(t, d, "a.pdf", []byte("same content"), 0)
	b := linked(t, d, "b.pdf", a)

	x, errs := NewIndex([]scan.File{a, b}, nil)
	if len(errs) > 0 {
		t.Fatal(errs)
	}
	if orig, dup := lookup(t, x, a); dup {
		t.Errorf("a.pdf reported as a duplicate of its own hardlink b.pdf (orig=%s)", orig)
	}
	if orig, dup := lookup(t, x, b); dup {
		t.Errorf("b.pdf reported as a duplicate of its own hardlink a.pdf (orig=%s)", orig)
	}
}

// TestHardlinksAreStillDuplicatesOfASeparateIdenticalFile is the direction
// a naive "same size+hash means never a duplicate" fix would get wrong:
// a.pdf and b.pdf are hardlinks of one inode, but c.pdf is a genuinely
// separate, byte-identical copy under an extra (duplicate "DIR") directory,
// so spec §5.5 prefers it as the original. Deleting a.pdf and b.pdf then
// leaves the content intact in c.pdf - they really are duplicates, of
// c.pdf, and must still be reported as such.
func TestHardlinksAreStillDuplicatesOfASeparateIdenticalFile(t *testing.T) {
	scanned, filed := t.TempDir(), t.TempDir()
	a := put(t, scanned, "a.pdf", []byte("same content"), 0)
	b := linked(t, scanned, "b.pdf", a)
	put(t, filed, "c.pdf", []byte("same content"), 0) // extra-dir copy: preferred as the original regardless of mtime

	x, errs := NewIndex([]scan.File{a, b}, []string{filed})
	if len(errs) > 0 {
		t.Fatal(errs)
	}
	cPath := filepath.Join(filed, "c.pdf")
	if orig, dup := lookup(t, x, a); !dup || orig != cPath {
		t.Errorf("a.pdf: dup=%v orig=%s, want a real duplicate of %s", dup, orig, cPath)
	}
	if orig, dup := lookup(t, x, b); !dup || orig != cPath {
		t.Errorf("b.pdf: dup=%v orig=%s, want a real duplicate of %s", dup, orig, cPath)
	}
}

// TestHardlinkUnderExtraDirWithNoOtherCopyIsNotADuplicate: a candidate is
// never a duplicate of a candidate that is the same file, and extra-
// directory candidates are candidates - the rule is not scanned-vs-scanned
// only. This is the shape (duplicate "DIR") exists for: (duplicate
// "~/backup") means "the backup already holds a copy, so the local name can
// go", but if ~/backup/a.pdf is a hardlink of ~/dl/a.pdf, the backup holds
// no copy at all, just the same file under a second name - judging the
// scanned file a duplicate would delete the only copy while the user
// believes it is backed up.
//
// Lookup's os.SameFile check compares the elected original with the file
// asked about whether the original was scanned or found under an extra
// directory, so this case needs no special handling; the test pins it as
// its own named case.
func TestHardlinkUnderExtraDirWithNoOtherCopyIsNotADuplicate(t *testing.T) {
	scanned, backup := t.TempDir(), t.TempDir()
	a := put(t, scanned, "a.pdf", []byte("same content"), 0)
	backupPath := filepath.Join(backup, "a.pdf")
	if err := os.Link(a.Path, backupPath); err != nil {
		t.Fatal(err)
	}

	x, errs := NewIndex([]scan.File{a}, []string{backup})
	if len(errs) > 0 {
		t.Fatal(errs)
	}
	if orig, dup := lookup(t, x, a); dup {
		t.Errorf("a.pdf reported as a duplicate of its own hardlink under the extra dir (orig=%s)", orig)
	}
}

// TestThreeWayHardlinksAreNotDuplicatesOfEachOther is the direct
// generalisation of TestHardlinksAreNotDuplicatesOfEachOther to N names for
// one inode: three names, one inode, no other copy anywhere - none of them
// is a duplicate of either of the others. No special-casing for N > 2: all
// three elect the same original, and Lookup's SameFile check finds each
// name to be that original's own file.
func TestThreeWayHardlinksAreNotDuplicatesOfEachOther(t *testing.T) {
	d := t.TempDir()
	a := put(t, d, "a.pdf", []byte("same content"), 0)
	b := linked(t, d, "b.pdf", a)
	c := linked(t, d, "c.pdf", a)

	x, errs := NewIndex([]scan.File{a, b, c}, nil)
	if len(errs) > 0 {
		t.Fatal(errs)
	}
	for _, f := range []scan.File{a, b, c} {
		if orig, dup := lookup(t, x, f); dup {
			t.Errorf("%s reported as a duplicate (orig=%s)", f.Name, orig)
		}
	}
}

// dupVerdicts looks up every file in fs and returns the paths reported as
// not a duplicate, and the originals the duplicates were reported against.
func dupVerdicts(t *testing.T, x *Index, fs ...scan.File) (kept []string, origs map[string]string) {
	t.Helper()
	origs = make(map[string]string)
	for _, f := range fs {
		orig, dup := lookup(t, x, f)
		if dup {
			origs[f.Path] = orig
		} else {
			kept = append(kept, f.Path)
		}
	}
	return kept, origs
}

// TestExtraDirIsTheScannedRoot: (duplicate "DIR") where DIR is the scanned
// root itself, so every scanned file is also indexed as an extra-directory
// candidate under the same path. Two identical files are one duplicate and
// one original, never two duplicates of each other: a (delete) rule must
// leave one copy.
func TestExtraDirIsTheScannedRoot(t *testing.T) {
	d := t.TempDir()
	a := put(t, d, "a.pdf", []byte("same content"), 0) // older: the original
	b := put(t, d, "b.pdf", []byte("same content"), 5)

	x, errs := NewIndex([]scan.File{a, b}, []string{d})
	if len(errs) > 0 {
		t.Fatal(errs)
	}
	kept, origs := dupVerdicts(t, x, a, b)
	if len(kept) != 1 || kept[0] != a.Path {
		t.Errorf("kept = %v, want exactly %s (duplicates: %v)", kept, a.Path, origs)
	}
	if origs[b.Path] != a.Path {
		t.Errorf("b.pdf: original = %q, want %s", origs[b.Path], a.Path)
	}
}

// TestExtraDirInsideRecursiveRoot: DIR is a subdirectory of a recursively
// scanned root, the "the archive already holds a copy, so the loose one can
// go" shape. The copy under DIR is the original even though it is newer;
// only the copy outside DIR is a duplicate.
func TestExtraDirInsideRecursiveRoot(t *testing.T) {
	d := t.TempDir()
	archived := put(t, d, "Archive/x.pdf", []byte("same content"), 5)
	loose := put(t, d, "x-copy.pdf", []byte("same content"), 0) // older, but not under DIR

	x, errs := NewIndex([]scan.File{archived, loose}, []string{filepath.Join(d, "Archive")})
	if len(errs) > 0 {
		t.Fatal(errs)
	}
	kept, origs := dupVerdicts(t, x, archived, loose)
	if len(kept) != 1 || kept[0] != archived.Path {
		t.Errorf("kept = %v, want exactly %s (duplicates: %v)", kept, archived.Path, origs)
	}
	if origs[loose.Path] != archived.Path {
		t.Errorf("x-copy.pdf: original = %q, want %s", origs[loose.Path], archived.Path)
	}
}

// TestExtraDirIsAnAncestorOfTheRoot: DIR contains the scanned root, as
// (duplicate "~") would for a root under the home directory.
func TestExtraDirIsAnAncestorOfTheRoot(t *testing.T) {
	parent := t.TempDir()
	root := filepath.Join(parent, "dl")
	a := put(t, root, "a.pdf", []byte("same content"), 0) // older: the original
	b := put(t, root, "b.pdf", []byte("same content"), 5)

	x, errs := NewIndex([]scan.File{a, b}, []string{parent})
	if len(errs) > 0 {
		t.Fatal(errs)
	}
	kept, origs := dupVerdicts(t, x, a, b)
	if len(kept) != 1 || kept[0] != a.Path {
		t.Errorf("kept = %v, want exactly %s (duplicates: %v)", kept, a.Path, origs)
	}
	if origs[b.Path] != a.Path {
		t.Errorf("b.pdf: original = %q, want %s", origs[b.Path], a.Path)
	}
}

// TestThreeCopiesWithOverlappingExtraDirKeepOne: two copies under DIR and a
// third outside it, all scanned. Exactly one of the three is not a
// duplicate, it lies under DIR, and every duplicate names that same file as
// its original.
func TestThreeCopiesWithOverlappingExtraDirKeepOne(t *testing.T) {
	d := t.TempDir()
	x1 := put(t, d, "Archive/x1.pdf", []byte("same content"), 3)
	x2 := put(t, d, "Archive/x2.pdf", []byte("same content"), 4)
	loose := put(t, d, "x-copy.pdf", []byte("same content"), 0)

	x, errs := NewIndex([]scan.File{x1, x2, loose}, []string{filepath.Join(d, "Archive")})
	if len(errs) > 0 {
		t.Fatal(errs)
	}
	kept, origs := dupVerdicts(t, x, x1, x2, loose)
	if len(kept) != 1 || kept[0] != x1.Path {
		t.Fatalf("kept = %v, want exactly %s (duplicates: %v)", kept, x1.Path, origs)
	}
	for p, orig := range origs {
		if orig != x1.Path {
			t.Errorf("%s: original = %q, want %s", p, orig, x1.Path)
		}
	}
}