package engine

import (
	"errors"
	"os"
	"path/filepath"
	"strings"
	"testing"
	"time"

	"github.com/cdnutter/playlink/internal/fsops"
	"github.com/cdnutter/playlink/internal/store"
)

// A cross-folder upgrade: the slave file sits in another folder than the
// master's, so linking moves it into the master's folder structure.
func crossFolder(t *testing.T) (ev *env, m store.Match, masterAbs, oldAbs, newAbs string) {
	t.Helper()
	ev = setup(t, false)
	enableApprox(t, ev)
	masterAbs = ev.write(ev.master, "Composer/Game1/01 Song.flac", "lossless")
	oldAbs = ev.write(ev.slave, "Composer/Game Rips/01 Song.mp3", "lossy")
	newAbs = filepath.Join(ev.slave, "Composer/Game1/01 Song.flac")
	ev.scan()
	m = ev.match("Composer/Game Rips/01 Song.mp3")
	if m.Kind != store.KindApprox || LinkTarget(m.RelSlave, m.RelMaster, false) != "Composer/Game1/01 Song.flac" {
		t.Fatalf("setup: unexpected match %s -> %s", m.Kind, m.RelMaster)
	}
	t.Cleanup(func() { testHookBeforeRemove = nil })
	return
}

func exists(p string) bool { _, err := os.Lstat(p); return err == nil }

// The reported bug: an unreliable modification time must not leave both the
// original and the new link behind.
func TestCrossFolderLinkIgnoresMtimeNoise(t *testing.T) {
	ev, m, masterAbs, oldAbs, newAbs := crossFolder(t)
	testHookBeforeRemove = func(p string) {
		// What a FUSE filesystem may report after the new links were made.
		_ = os.Chtimes(p, time.Now(), time.Now().Add(-time.Hour))
	}
	op, err := ev.e.Link(ctx, m.ID, LinkOptions{})
	if err != nil {
		t.Fatal(err)
	}
	if exists(oldAbs) {
		t.Fatal("the original must not remain next to the new link")
	}
	if !sameInode(t, masterAbs, newAbs) || ev.read(op.QuarantinePath) != "lossy" {
		t.Fatal("expected the link at the master's path and the original in quarantine")
	}
}

// If the original really cannot be removed, the new link is rolled back and
// the library is left exactly as it was.
func TestCrossFolderLinkRollsBack(t *testing.T) {
	if os.Geteuid() == 0 {
		t.Skip("root ignores directory permissions")
	}
	ev, m, _, oldAbs, newAbs := crossFolder(t)
	dir := filepath.Dir(oldAbs)
	testHookBeforeRemove = func(string) { _ = os.Chmod(dir, 0o555) } // deletion now fails
	t.Cleanup(func() { _ = os.Chmod(dir, 0o755) })
	op, err := ev.e.Link(ctx, m.ID, LinkOptions{})
	if err == nil || !strings.Contains(err.Error(), "nothing was changed") {
		t.Fatalf("want a rollback error, got %v", err)
	}
	_ = os.Chmod(dir, 0o755)
	if exists(newAbs) || exists(filepath.Dir(newAbs)) {
		t.Fatal("the new link (and its folder) should be rolled back")
	}
	if ev.read(oldAbs) != "lossy" {
		t.Fatal("the original must be untouched")
	}
	stored, _ := ev.st.Op(ctx, op.ID)
	if stored.Status != store.OpFailed || stored.QuarantinePath != "" {
		t.Fatalf("op should be failed with no quarantine left, got %s %q", stored.Status, stored.QuarantinePath)
	}
	if entries, _ := os.ReadDir(filepath.Join(ev.slave, ".playlink-trash")); len(entries) != 0 {
		t.Fatalf("quarantine should be empty after rollback, has %d entries", len(entries))
	}
}

// If the original was swapped for another file mid-way, the quarantine copy
// is the only copy of the original's data, so it is kept.
func TestCrossFolderLinkKeepsQuarantineWhenOriginalWasSwapped(t *testing.T) {
	ev, m, _, oldAbs, newAbs := crossFolder(t)
	testHookBeforeRemove = func(p string) {
		_ = os.Remove(p)
		_ = os.WriteFile(p, []byte("someone else's new file"), 0o644)
	}
	op, err := ev.e.Link(ctx, m.ID, LinkOptions{})
	if err == nil || !errors.Is(err, fsops.ErrChanged) {
		t.Fatalf("want a changed-file error, got %v", err)
	}
	if exists(newAbs) {
		t.Fatal("the new link should be rolled back")
	}
	if ev.read(oldAbs) != "someone else's new file" {
		t.Fatal("the new file must not be touched")
	}
	stored, _ := ev.st.Op(ctx, op.ID)
	if stored.QuarantinePath == "" || ev.read(stored.QuarantinePath) != "lossy" {
		t.Fatal("the original's data must stay in quarantine")
	}
}

// Leftovers from the old bug: the master's path already holds the link and
// the original is still there. Linking again only retires the original.
func TestRelinkCleansUpLeftoverOriginal(t *testing.T) {
	ev, _, masterAbs, oldAbs, newAbs := crossFolder(t)
	if err := os.MkdirAll(filepath.Dir(newAbs), 0o755); err != nil {
		t.Fatal(err)
	}
	if err := os.Link(masterAbs, newAbs); err != nil {
		t.Fatal(err)
	}
	ev.scan()
	m := ev.match("Composer/Game Rips/01 Song.mp3")
	op, err := ev.e.Link(ctx, m.ID, LinkOptions{})
	if err != nil {
		t.Fatalf("relinking over an existing link of the master should work: %v", err)
	}
	if exists(oldAbs) || !sameInode(t, masterAbs, newAbs) {
		t.Fatal("the leftover original should be retired and the link kept")
	}
	if err := ev.e.Undo(ctx, op.ID); err != nil {
		t.Fatal(err)
	}
	if ev.read(oldAbs) != "lossy" || !sameInode(t, masterAbs, newAbs) {
		t.Fatal("undo should restore the original and keep the link that existed before")
	}
}

// A different file at the target is still refused.
func TestRelinkRefusesForeignFileAtTarget(t *testing.T) {
	ev, m, _, oldAbs, newAbs := crossFolder(t)
	ev.write(ev.slave, "Composer/Game1/01 Song.flac", "unrelated")
	if _, err := ev.e.Link(ctx, m.ID, LinkOptions{}); !errors.Is(err, fsops.ErrExists) {
		t.Fatalf("want ErrExists, got %v", err)
	}
	if ev.read(newAbs) != "unrelated" || ev.read(oldAbs) != "lossy" {
		t.Fatal("nothing may change")
	}
}