package notes

import (
	"os"
	"path/filepath"
	"strings"
	"sync"
	"testing"
)

func seed(t *testing.T, dir, rel, content string) string {
	t.Helper()
	abs := filepath.Join(dir, rel)
	if err := os.MkdirAll(filepath.Dir(abs), 0o755); err != nil {
		t.Fatal(err)
	}
	if err := os.WriteFile(abs, []byte(content), 0o644); err != nil {
		t.Fatal(err)
	}
	return abs
}

func read(t *testing.T, abs string) string {
	t.Helper()
	b, err := os.ReadFile(abs)
	if err != nil {
		t.Fatal(err)
	}
	return string(b)
}

func TestRead_ReturnsVerbatimBytes(t *testing.T) {
	dir := newBrain(t)
	const body = "---\ntitle: 'x'\n---\n\nbody with  double  spaces\r\nand a CRLF line\nno trailing newline"
	seed(t, dir, "knowledge/verbatim.md", body)

	got, err := Read(dir, "knowledge/verbatim.md")
	if err != nil {
		t.Fatalf("Read: %v", err)
	}
	if string(got) != body {
		t.Errorf("Read returned %q, want the file byte-for-byte", got)
	}
}

func TestRead_RefusesNonUTF8RatherThanCorruptingIt(t *testing.T) {
	// The response is marshalled into a JSON string, and encoding/json
	// replaces invalid UTF-8 with U+FFFD. Returning it would mean every
	// old_str the caller derives from that region can never match, and
	// pasting it back would write the corruption to disk permanently.
	dir := newBrain(t)
	seed(t, dir, "knowledge/bad.md", "ok \xff\xfe broken\n")

	if _, err := Read(dir, "knowledge/bad.md"); err == nil {
		t.Fatal("Read accepted invalid UTF-8; it must refuse rather than silently substitute")
	}
}

func TestEdit_ReplacesExactlyOnceAndLeavesEveryOtherByteAlone(t *testing.T) {
	dir := newBrain(t)
	const body = "---\ntitle: 'x'\n---\n\nalpha\nbeta\ngamma\n"
	abs := seed(t, dir, "knowledge/n.md", body)

	res, err := Edit(dir, "knowledge/n.md", "beta", "BETA", ScopeNotes)
	if err != nil {
		t.Fatalf("Edit: %v", err)
	}
	want := strings.Replace(body, "beta", "BETA", 1)
	if got := read(t, abs); got != want {
		t.Errorf("file = %q, want %q", got, want)
	}
	if res.ContentHash == "" {
		t.Error("result should carry a content hash for read-after-write confirmation")
	}
}

func TestEdit_RefusesAmbiguousAndAbsentMatchesWithoutWriting(t *testing.T) {
	dir := newBrain(t)
	const body = "alpha\nalpha\n"
	abs := seed(t, dir, "knowledge/n.md", body)

	cases := []struct{ name, old, want string }{
		{"two matches", "alpha", "2"},
		{"no match", "delta", "0"},
	}
	for _, tc := range cases {
		t.Run(tc.name, func(t *testing.T) {
			_, err := Edit(dir, "knowledge/n.md", tc.old, "x", ScopeNotes)
			if err == nil {
				t.Fatal("want a loud refusal")
			}
			if !strings.Contains(err.Error(), tc.want) {
				t.Errorf("error must state the match count, got %v", err)
			}
			if got := read(t, abs); got != body {
				t.Errorf("file changed on a refused edit: %q", got)
			}
		})
	}
}

func TestEdit_CountsOverlappingMatches(t *testing.T) {
	// bytes.Count counts NON-overlapping occurrences: "aa" in "aaa" is 1, so
	// a Count-based uniqueness check calls an ambiguous edit unique.
	dir := newBrain(t)
	seed(t, dir, "knowledge/n.md", "aaa\n")

	if _, err := Edit(dir, "knowledge/n.md", "aa", "b", ScopeNotes); err == nil {
		t.Fatal("overlapping matches must be reported as ambiguous")
	}
}

func TestEdit_RejectsDegenerateArguments(t *testing.T) {
	dir := newBrain(t)
	seed(t, dir, "knowledge/n.md", "alpha\n")

	if _, err := Edit(dir, "knowledge/n.md", "", "x", ScopeNotes); err == nil {
		t.Error("empty old_str must be rejected")
	}
	if _, err := Edit(dir, "knowledge/n.md", "alpha", "alpha", ScopeNotes); err == nil {
		t.Error("a no-op edit must be rejected rather than burning a sync cycle")
	}
}

func TestEdit_DeletionIsLegal(t *testing.T) {
	dir := newBrain(t)
	abs := seed(t, dir, "knowledge/n.md", "keep\ndrop\n")

	if _, err := Edit(dir, "knowledge/n.md", "drop\n", "", ScopeNotes); err != nil {
		t.Fatalf("Edit: %v", err)
	}
	if got := read(t, abs); got != "keep\n" {
		t.Errorf("file = %q, want %q", got, "keep\n")
	}
}

func TestEdit_ReportsWhenOnlyLineEndingsDiffer(t *testing.T) {
	// The likeliest real failure: the caller's old_str lost its \r. Never
	// normalise silently — that breaks byte-identity — but say so, because an
	// opaque "no match" is unfixable from the caller's side.
	dir := newBrain(t)
	seed(t, dir, "knowledge/n.md", "alpha\r\nbeta\r\n")

	_, err := Edit(dir, "knowledge/n.md", "alpha\nbeta", "x", ScopeNotes)
	if err == nil {
		t.Fatal("want a refusal")
	}
	if !strings.Contains(err.Error(), "line ending") {
		t.Errorf("error should point at CRLF, got %v", err)
	}
}

func TestEdit_RefusesWhileGitIsMidOperation(t *testing.T) {
	// brain-sync runs `git merge -X ours origin/main`, and aborts on conflict
	// with a hard reset. An edit landing inside that window is either erased
	// or committed as a wrongly-resolved conflict, and the caller was told it
	// succeeded.
	dir := newBrain(t)
	seed(t, dir, "knowledge/n.md", "alpha\n")

	for _, marker := range []string{"MERGE_HEAD", "index.lock", "REBASE_HEAD"} {
		t.Run(marker, func(t *testing.T) {
			p := filepath.Join(dir, ".git", marker)
			if err := os.WriteFile(p, []byte("x"), 0o644); err != nil {
				t.Fatal(err)
			}
			defer func() { _ = os.Remove(p) }()

			if _, err := Edit(dir, "knowledge/n.md", "alpha", "beta", ScopeNotes); err == nil {
				t.Errorf("edit accepted while %s exists", marker)
			}
		})
	}
}

func TestEdit_RefusesAFileHoldingConflictMarkers(t *testing.T) {
	dir := newBrain(t)
	seed(t, dir, "knowledge/n.md", "<<<<<<< HEAD\nours\n=======\ntheirs\n>>>>>>> origin/main\n")

	if _, err := Edit(dir, "knowledge/n.md", "ours", "x", ScopeNotes); err == nil {
		t.Fatal("editing one side of an unresolved conflict must be refused")
	}
}

func TestEdit_ConcurrentEditsBothApply(t *testing.T) {
	// Read-modify-write with no lock loses one update AND reports success for
	// both. old_str uniqueness does not protect against it: uniqueness is
	// evaluated against the stale read.
	dir := newBrain(t)
	abs := seed(t, dir, "knowledge/n.md", "alpha\nbeta\n")

	var wg sync.WaitGroup
	errs := make([]error, 2)
	for i, pair := range [][2]string{{"alpha", "ALPHA"}, {"beta", "BETA"}} {
		wg.Add(1)
		go func(i int, old, new string) {
			defer wg.Done()
			_, errs[i] = Edit(dir, "knowledge/n.md", old, new, ScopeNotes)
		}(i, pair[0], pair[1])
	}
	wg.Wait()

	for i, err := range errs {
		if err != nil {
			t.Fatalf("edit %d failed: %v", i, err)
		}
	}
	if got := read(t, abs); got != "ALPHA\nBETA\n" {
		t.Errorf("file = %q, want both edits applied", got)
	}
}

func TestEdit_LeavesNoTemporaryFileBehind(t *testing.T) {
	dir := newBrain(t)
	seed(t, dir, "knowledge/n.md", "alpha\n")

	if _, err := Edit(dir, "knowledge/n.md", "alpha", "beta", ScopeNotes); err != nil {
		t.Fatal(err)
	}
	entries, err := os.ReadDir(filepath.Join(dir, "knowledge"))
	if err != nil {
		t.Fatal(err)
	}
	for _, e := range entries {
		if e.Name() != "note.md" && e.Name() != "n.md" {
			t.Errorf("stray file left in the tree: %q (git add -A would commit it)", e.Name())
		}
	}
}

func TestEdit_PreservesReadableMode(t *testing.T) {
	// Other uids write this tree (brain-fix, brain-enrich). os.CreateTemp
	// yields 0600 and rename preserves it, which would break them silently.
	dir := newBrain(t)
	abs := seed(t, dir, "knowledge/n.md", "alpha\n")

	if _, err := Edit(dir, "knowledge/n.md", "alpha", "beta", ScopeNotes); err != nil {
		t.Fatal(err)
	}
	fi, err := os.Stat(abs)
	if err != nil {
		t.Fatal(err)
	}
	if fi.Mode().Perm() != 0o644 {
		t.Errorf("mode = %v, want 0644", fi.Mode().Perm())
	}
}

func TestEdit_RefusesNonUTF8Replacement(t *testing.T) {
	dir := newBrain(t)
	seed(t, dir, "knowledge/n.md", "alpha\n")

	if _, err := Edit(dir, "knowledge/n.md", "alpha", "bad \xff", ScopeNotes); err == nil {
		t.Fatal("new_str with invalid UTF-8 must be refused, not written")
	}
}