package editor

import (
	"strings"
	"testing"
	"time"

	"pad/internal/io/pool/mock"
)

// newStringState builds a minimal State that uses the (small-file) string
// buffer fallback rather than a ChunkedBuffer.
func newStringState(buf string) *State {
	st := NewState()
	TheState = st
	st.Editor.Buffer = buf
	st.Editor.ChunkedBuffer = nil
	st.Editor.CursorPosition = len(buf)
	return st
}

// newChunkedState builds a minimal State backed by a ChunkedBuffer over a
// mock filesystem. chunkSize is small so a short file spans several chunks.
func newChunkedState(t *testing.T, content string, chunkSize int) *State {
	t.Helper()
	mockFS := mock.NewFileSystem()
	filename := "/ime_range.txt"
	mockFS.AddFile(filename, []byte(content), time.Now())
	cb := NewChunkedBuffer(filename, chunkSize, mockFS, "")
	// Full-load via the on-open path (all chunks resident), matching production.
	cb.SetContent([]byte(content))
	st := NewState()
	TheState = st
	st.Editor.Filename = filename
	st.Editor.ChunkedBuffer = cb
	st.Editor.Buffer = ""
	st.Editor.CursorPosition = len(content)
	return st
}

func TestRuneIndexToByteStr(t *testing.T) {
	cases := []struct {
		s    string
		n    int
		want int
	}{
		{"", 0, 0},
		{"abc", 0, 0},
		{"abc", 1, 1},
		{"abc", 3, 3},
		{"abc", 10, 3}, // past end -> len(s)
		// "héllo": h(1) é(2) l(1) l(1) o(1) -> byte offsets 0,1,3,4,5
		{"héllo", 0, 0},
		{"héllo", 1, 1}, // after 'h'
		{"héllo", 2, 3}, // after 'é' (2 bytes)
		{"héllo", 5, 6}, // end
		// "日本語": each rune is 3 bytes
		{"日本語", 0, 0},
		{"日本語", 1, 3},
		{"日本語", 2, 6},
		{"日本語", 3, 9},
	}
	for _, c := range cases {
		if got := runeIndexToByteStr(c.s, c.n); got != c.want {
			t.Errorf("runeIndexToByteStr(%q, %d) = %d, want %d", c.s, c.n, got, c.want)
		}
	}
}

func TestRuneIndexToByte_Chunked(t *testing.T) {
	// Use a 4-byte chunk size so "hello world" (11 bytes) spans 3 chunks.
	st := newChunkedState(t, "hello world", 4)
	cb := st.Editor.ChunkedBuffer

	// All ASCII: rune index == byte offset.
	for n := 0; n <= 11; n++ {
		if got := cb.RuneIndexToByte(n); got != n {
			t.Errorf("ASCII RuneIndexToByte(%d) = %d, want %d", n, got, n)
		}
	}

	// Non-ASCII spanning chunk boundaries. "abéfg" = a(1) b(1) é(2) f(1) g(1)
	// = 6 bytes; rune byte offsets are 0,1,2,4,5 and the end is 6.
	st2 := newChunkedState(t, "abéfg", 2)
	cb2 := st2.Editor.ChunkedBuffer
	want := []int{0, 1, 2, 4, 5, 6}
	for n, w := range want {
		if got := cb2.RuneIndexToByte(n); got != w {
			t.Errorf("RuneIndexToByte(%d) = %d, want %d (s=\"abéfg\", chunk=2)", n, got, w)
		}
	}
}

func TestHandleReplaceRange_Insert_String(t *testing.T) {
	st := newStringState("Hello World")
	// Insert at rune 5 (byte 5, the space) -> "Hello  World"
	HandleReplaceRange(5, 5, "!")
	// Insert before the space: "Hello" + "!" + " World"
	want := "Hello! World"
	if st.Editor.Buffer != want {
		t.Fatalf("buffer = %q, want %q", st.Editor.Buffer, want)
	}
	// Cursor should be at the end of the inserted text: startByte(5) + len("!")
	if st.Editor.CursorPosition != 6 {
		t.Fatalf("cursor = %d, want 6", st.Editor.CursorPosition)
	}
}

func TestHandleReplaceRange_Replace_String(t *testing.T) {
	// This is the core of item 3: a swipe/autocorrect commit replaces the
	// selected region without duplicating it.
	st := newStringState("Hello World")
	// Replace runes [6,11) == "World" with "there"
	HandleReplaceRange(6, 11, "there")
	want := "Hello there"
	if st.Editor.Buffer != want {
		t.Fatalf("buffer = %q, want %q", st.Editor.Buffer, want)
	}
	// Cursor at end of inserted text: startByte(6) + len("there") = 11
	if st.Editor.CursorPosition != 11 {
		t.Fatalf("cursor = %d, want 11", st.Editor.CursorPosition)
	}
}

func TestHandleReplaceRange_Delete_String(t *testing.T) {
	st := newStringState("Hello World")
	// Delete runes [5,11) == " World" (empty text)
	HandleReplaceRange(5, 11, "")
	want := "Hello"
	if st.Editor.Buffer != want {
		t.Fatalf("buffer = %q, want %q", st.Editor.Buffer, want)
	}
	if st.Editor.CursorPosition != 5 {
		t.Fatalf("cursor = %d, want 5", st.Editor.CursorPosition)
	}
}

func TestHandleReplaceRange_Unicoded_String(t *testing.T) {
	// "héllo wörld": replace the 2nd word's runes.
	// runes: h(0) é(1) l(2) l(3) o(4) ' '(5) w(6) ö(7) r(8) l(9) d(10)
	st := newStringState("héllo wörld")
	// Replace runes [6,11) == "wörld" with "there"
	HandleReplaceRange(6, 11, "there")
	want := "héllo there"
	if st.Editor.Buffer != want {
		t.Fatalf("buffer = %q, want %q", st.Editor.Buffer, want)
	}
	// startByte for rune 6 = 7 (h=1,é=2,l=1,l=1,o=1,' '=1 -> 7 bytes), + len("there")=5
	if st.Editor.CursorPosition != 12 {
		t.Fatalf("cursor = %d, want 12", st.Editor.CursorPosition)
	}
}

func TestHandleReplaceRange_Replace_Chunked(t *testing.T) {
	// Chunked path: replace a region that spans multiple small chunks.
	content := "Hello World, this is a test."
	st := newChunkedState(t, content, 8)
	cb := st.Editor.ChunkedBuffer

	// Replace runes [12,15) == "this"[0:3]="thi"? let's pick [5,11) = " World"
	HandleReplaceRange(5, 11, " there")
	want := "Hello there, this is a test."
	got, err := cb.FullContent()
	if err != nil {
		t.Fatalf("FullContent: %v", err)
	}
	if got != want {
		t.Fatalf("buffer = %q, want %q", got, want)
	}
	// startByte for rune 5 = 5 (ASCII), + len(" there") = 6 -> 11
	if st.Editor.CursorPosition != 11 {
		t.Fatalf("cursor = %d, want 11", st.Editor.CursorPosition)
	}
}

func TestHandleReplaceRange_Unicode_Chunked(t *testing.T) {
	// Non-ASCII content in a chunked buffer, replacing across rune/byte
	// mismatch. "héllo" -> replace rune 1 ('é') with 'e'.
	st := newChunkedState(t, "héllo", 2)
	cb := st.Editor.ChunkedBuffer
	HandleReplaceRange(1, 2, "e")
	want := "hello"
	got, err := cb.FullContent()
	if err != nil {
		t.Fatalf("FullContent: %v", err)
	}
	if got != want {
		t.Fatalf("buffer = %q, want %q", got, want)
	}
	// startByte for rune 1 = 1, + len("e") = 1 -> 2
	if st.Editor.CursorPosition != 2 {
		t.Fatalf("cursor = %d, want 2", st.Editor.CursorPosition)
	}
}

// TestHandleReplaceRange_SwappedBounds guards against start>end (the IME can
// deliver either order); it must normalize and behave as [min, max).
func TestHandleReplaceRange_SwappedBounds(t *testing.T) {
	st := newStringState("abcdef")
	// Provide swapped bounds for range [1,3) ("bc") -> replace with "XY"
	HandleReplaceRange(3, 1, "XY")
	want := "aXYdef"
	if !strings.Contains(st.Editor.Buffer, "XY") {
		t.Fatalf("buffer = %q, want to contain %q", st.Editor.Buffer, "XY")
	}
	if st.Editor.Buffer != want {
		t.Fatalf("buffer = %q, want %q", st.Editor.Buffer, want)
	}
}

// TestHandleReplaceRange_WindowOffset_Chunked verifies the scrolled-viewport
// path: the IME snippet starts mid-file, so the EditEvent.Range (absolute
// file runes, addressed from IMEOffsetRune) must be mapped through the
// leading context and the window to address the buffer.
func TestHandleReplaceRange_WindowOffset_Chunked(t *testing.T) {
	newChunkedState(t, "Hello World, this is a test.", 8)
	// Simulate a scrolled viewport: layout would have set the visible window
	// to start at byte 6 ("World, this is a test."), with no leading context
	// (all ASCII, so rune offset == byte offset).
	TheState.Editor.IMEWindowStartByte = 6
	TheState.Editor.IMEWindowText = "World, this is a test."
	TheState.Editor.IMEContext = ""
	TheState.Editor.IMEContextStartByte = 6
	TheState.Editor.IMEOffsetRune = 6
	// The IME reports absolute file runes: "World" is runes [6,11).
	HandleReplaceRange(6, 11, "There")
	cb := TheState.Editor.ChunkedBuffer
	got, err := cb.FullContent()
	if err != nil {
		t.Fatal("FullContent failed: ", err)
	}
	if want := "Hello There, this is a test."; got != want {
		t.Fatalf("windowed replace: got %q, want %q", got, want)
	}
	// Cursor: window start (6) + len("There") (5) = 11.
	if cp := TheState.Editor.CursorPosition; cp != 11 {
		t.Fatalf("cursor = %d, want 11", cp)
	}
}

// TestHandleReplaceRange_WindowOffset_String verifies the same absolute-rune
// mapping on the small-file (string) buffer.
func TestHandleReplaceRange_WindowOffset_String(t *testing.T) {
	st := newStringState("Hello World, this is a test.")
	st.Editor.IMEWindowStartByte = 6
	st.Editor.IMEWindowText = "World, this is a test."
	st.Editor.IMEContext = ""
	st.Editor.IMEContextStartByte = 6
	st.Editor.IMEOffsetRune = 6
	HandleReplaceRange(6, 11, "There")
	if want := "Hello There, this is a test."; st.Editor.Buffer != want {
		t.Fatalf("windowed replace: got %q, want %q", st.Editor.Buffer, want)
	}
	if cp := TheState.Editor.CursorPosition; cp != 11 {
		t.Fatalf("cursor = %d, want 11", cp)
	}
}

// TestHandleReplaceRange_WithContext verifies the leading-context mapping:
// the snippet is context+window and the IME's absolute rune offsets may land
// inside the context (before the window). The context contains a multi-byte
// rune so rune != byte there, which pins the rune->byte walk. A second, fresh
// state covers a range that spans the context/window boundary.
func TestHandleReplaceRange_WithContext(t *testing.T) {
	// File "héllo world, this" (18 bytes): h(0) é(1-2) l(3) l(4) o(5)
	// sp(6) w(7) o(8) r(9) l(10) d(11) ,(12) sp(13) t(14) h(15) i(16) s(17).
	// Window starts at byte 6 (the space), so window = " world, this"; the
	// context is the preceding runes "héllo" (5 runes, 6 bytes), starting at
	// byte 0. The snippet spans absolute runes [0, ...), so IMEOffsetRune=0.
	st := newStringState("héllo world, this")
	st.Editor.IMEWindowStartByte = 6
	st.Editor.IMEWindowText = " world, this"
	st.Editor.IMEContext = "héllo"
	st.Editor.IMEContextStartByte = 0
	st.Editor.IMEOffsetRune = 0
	// Replace absolute rune [1,2) ("é", bytes 1..3) with "@": inside context.
	HandleReplaceRange(1, 2, "@")
	if want := "h@llo world, this"; st.Editor.Buffer != want {
		t.Fatalf("context replace: got %q, want %q", st.Editor.Buffer, want)
	}
	if cp := TheState.Editor.CursorPosition; cp != 2 {
		t.Fatalf("cursor = %d, want 2", cp)
	}
}

// TestHandleReplaceRange_SpansContextWindow verifies a replace range that
// straddles the context/window boundary maps correctly through both.
func TestHandleReplaceRange_SpansContextWindow(t *testing.T) {
	st := newStringState("héllo world, this")
	st.Editor.IMEWindowStartByte = 6
	st.Editor.IMEWindowText = " world, this"
	st.Editor.IMEContext = "héllo"
	st.Editor.IMEContextStartByte = 0
	st.Editor.IMEOffsetRune = 0
	// Absolute runes [4,7): rune4='o'(context, byte5) + rune5=sp(window,
	// byte6) + rune6='w'(window, byte7) -> bytes [5,8) = "o w". Keeping
	// bytes 0..4 ("héll") and 8+ ("orld, this").
	HandleReplaceRange(4, 7, "ZZ")
	if want := "héllZZorld, this"; st.Editor.Buffer != want {
		t.Fatalf("spanning replace: got %q, want %q", st.Editor.Buffer, want)
	}
	if cp := TheState.Editor.CursorPosition; cp != 7 {
		t.Fatalf("cursor = %d, want 7", cp)
	}
}

// TestRuneAnchorTracking verifies the incremental rune-count cache: it must
// follow edits (imeAnchorEdit) and agree with a naive full count after a
// sequence of mutations at various positions.
func TestRuneAnchorTracking(t *testing.T) {
	st := newChunkedState(t, "hello wörld, this is a test", 8)
	check := func(what string) {
		t.Helper()
		full, _ := st.Editor.ChunkedBuffer.FullContent()
		for _, pos := range []int{0, 3, 9, len(full)} {
			if got, want := st.imeRuneOffsetAt(pos), countRunes(full[:pos]); got != want {
				t.Fatalf("%s: imeRuneOffsetAt(%d) = %d, want %d", what, pos, got, want)
			}
		}
	}
	check("initial")
	testInsertAt(t, st, 3, "é")
	check("insert mid")
	testInsertAt(t, st, int(st.Editor.ChunkedBuffer.FileLen()), "é")
	check("insert end")
	testDeleteAt(t, st, 2, 4)
	check("delete")
}

// testInsertAt inserts text at absolute byte pos on the test state, adjusting
// the IME rune anchor the same way the production edit paths do.
func testInsertAt(t *testing.T, st *State, pos int, text string) {
	t.Helper()
	st.Editor.ChunkedBuffer.Insert(pos, text)
	st.Editor.ChunkedBuffer.UpdateLineIndexAfterInsert(pos, text)
	st.Editor.CursorPosition = pos + len(text)
	imeAnchorEdit(pos, "", text)
}

// testDeleteAt deletes n bytes at absolute byte pos on the test state.
func testDeleteAt(t *testing.T, st *State, pos, n int) {
	t.Helper()
	del := st.Editor.ChunkedBuffer.Content(pos, pos+n)
	st.Editor.ChunkedBuffer.Delete(pos, n)
	st.Editor.ChunkedBuffer.UpdateLineIndexAfterDelete(pos, pos+n)
	imeAnchorEdit(pos, del, "")
}