package e2e_test

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

	"gioui.org/io/key"
	"pad/internal/editor"
	"pad/internal/io/pool/real"
	"pad/internal/test/e2e"
	"pad/internal/ui"
)

// realFileHarness writes content to <tempdir>/name, builds a harness whose
// browser root and editor both use the real filesystem, opens /name and waits
// for the load + line index. Returns the harness and the on-disk path.
func realFileHarness(t *testing.T, name, content string) (*e2e.Harness, string) {
	t.Helper()
	dir := t.TempDir()
	diskPath := filepath.Join(dir, name)
	if err := os.WriteFile(diskPath, []byte(content), 0644); err != nil {
		t.Fatal(err)
	}

	h := e2e.NewHarness(e2e.WithFileSystem(real.NewRealFileSystem(dir), "/"))
	h.Run()

	if err := h.WithState(func(st *editor.State) { editor.GoToBrowser(nil) }); err != nil {
		t.Fatalf("GoToBrowser: %v", err)
	}
	time.Sleep(100 * time.Millisecond)
	if err := h.WithState(func(st *editor.State) { editor.OpenFile("/" + name) }); err != nil {
		t.Fatalf("OpenFile: %v", err)
	}
	// "Loaded" means both async results are fully applied: the ReadFile
	// content (len(FullContent) == FileLen) AND the BuildLineIndex result
	// (LineIndex.Size == FileLen). Waiting on FileLen>0 && LineIndex!=nil
	// alone is a race: stat sets FileLen, and the two worker results can
	// interleave with test edits.
	loaded := false
	for i := 0; i < 100; i++ {
		v, err := h.Inspect(func(st *editor.State) any {
			cb := st.Editor.ChunkedBuffer
			if cb == nil || cb.FileLen() == 0 || cb.LineIndex == nil {
				return false
			}
			full, err := cb.FullContent()
			return err == nil && int64(len(full)) == cb.FileLen() &&
				cb.LineIndex.Size == cb.FileLen()
		})
		if err != nil {
			t.Fatalf("Inspect: %v", err)
		}
		if v.(bool) {
			loaded = true
			break
		}
		time.Sleep(50 * time.Millisecond)
	}
	if !loaded {
		t.Fatal("timed out waiting for real file to load")
	}
	return h, diskPath
}

// readDisk reads the on-disk content of a test file.
func readDisk(t *testing.T, path string) string {
	t.Helper()
	data, err := os.ReadFile(path)
	if err != nil {
		t.Fatalf("reading disk: %v", err)
	}
	return string(data)
}

// TestRealFile_BasicInsert verifies an insert on a small real file lands in
// the buffer, flushes, and matches on disk.
func TestRealFile_BasicInsert(t *testing.T) {
	h, path := realFileHarness(t, "small.txt", "hello world")
	defer h.Cleanup()

	if err := h.WithState(func(st *editor.State) {
		st.Editor.CursorPosition = 5
		editor.HandleInsert(" there")
	}); err != nil {
		t.Fatalf("insert: %v", err)
	}
	got, _ := h.FullContent()
	if got != "hello there world" {
		t.Fatalf("buffer = %q, want %q", got, "hello there world")
	}
	if err := h.Flush(); err != nil {
		t.Fatalf("flush: %v", err)
	}
	if disk := readDisk(t, path); disk != "hello there world" {
		t.Fatalf("disk = %q, want %q", disk, "hello there world")
	}
}

// TestRealFile_BackspaceAndDelete verifies deletion edits on a real file,
// including across the line-index update path.
func TestRealFile_BackspaceAndDelete(t *testing.T) {
	h, path := realFileHarness(t, "small.txt", "0123456789")
	defer h.Cleanup()

	// Backspace at 5 deletes '4' (index 4); cursor moves to 4 (before '5').
	if err := h.WithState(func(st *editor.State) {
		st.Editor.CursorPosition = 5
		editor.HandleBackspace()
	}); err != nil {
		t.Fatalf("backspace: %v", err)
	}
	got, _ := h.FullContent()
	if got != "012356789" {
		t.Fatalf("buffer = %q, want %q", got, "012356789")
	}
	// Delete at cursor 4 removes '5' (the character now at index 4).
	if err := h.WithState(func(st *editor.State) {
		editor.HandleDelete()
	}); err != nil {
		t.Fatalf("delete: %v", err)
	}
	got, _ = h.FullContent()
	if got != "01236789" {
		t.Fatalf("buffer = %q, want %q", got, "01236789")
	}
	if err := h.Flush(); err != nil {
		t.Fatalf("flush: %v", err)
	}
	if disk := readDisk(t, path); disk != "01236789" {
		t.Fatalf("disk = %q, want %q", disk, "01236789")
	}
}

// TestRealFile_IMEReplaceRange simulates an IME commit replacing a range
// (swipe-to-delete + replacement semantics) on a real file.
func TestRealFile_IMEReplaceRange(t *testing.T) {
	h, path := realFileHarness(t, "small.txt", "hello world")
	defer h.Cleanup()

	// IME replaces [0,5) "hello" with "goodbye".
	if err := h.WithState(func(st *editor.State) {
		editor.HandleReplaceRange(0, 5, "goodbye")
	}); err != nil {
		t.Fatalf("replace: %v", err)
	}
	got, _ := h.FullContent()
	if got != "goodbye world" {
		t.Fatalf("buffer = %q, want %q", got, "goodbye world")
	}
	if pos, _ := h.CursorPosition(); pos != 7 {
		t.Fatalf("cursor = %d, want 7", pos)
	}
	if err := h.Flush(); err != nil {
		t.Fatalf("flush: %v", err)
	}
	if disk := readDisk(t, path); disk != "goodbye world" {
		t.Fatalf("disk = %q, want %q", disk, "goodbye world")
	}
}

// TestRealFile_IMEInsertAtCaret simulates a plain IME commit (empty range at
// the caret) through the real HandleKeyDown event path.
func TestRealFile_IMEInsertAtCaret(t *testing.T) {
	h, path := realFileHarness(t, "small.txt", "abc")
	defer h.Cleanup()

	if err := h.WithState(func(st *editor.State) { st.Editor.CursorPosition = 3 }); err != nil {
		t.Fatalf("set cursor: %v", err)
	}
	// Go through the full event handler, as main.go delivers it.
	h.SendInput([]ui.InputEvent{
		{Handler: editor.HandleKeyDown, Data: key.EditEvent{Range: key.Range{Start: 3, End: 3}, Text: "def"}},
	})
	time.Sleep(50 * time.Millisecond)
	got, _ := h.FullContent()
	if got != "abcdef" {
		t.Fatalf("buffer = %q, want %q", got, "abcdef")
	}
	if err := h.Flush(); err != nil {
		t.Fatalf("flush: %v", err)
	}
	if disk := readDisk(t, path); disk != "abcdef" {
		t.Fatalf("disk = %q, want %q", disk, "abcdef")
	}
}

// TestRealFile_AutosavePersists verifies the 1s-debounced autosave writes the
// edit to disk without an explicit Flush.
func TestRealFile_AutosavePersists(t *testing.T) {
	h, path := realFileHarness(t, "small.txt", "before")
	defer h.Cleanup()

	if err := h.WithState(func(st *editor.State) {
		st.Editor.CursorPosition = 6
		editor.HandleInsert("-after")
	}); err != nil {
		t.Fatalf("insert: %v", err)
	}

	// Wait for the autosave debounce (1 s) plus margin.
	deadline := time.Now().Add(5 * time.Second)
	for {
		if disk := readDisk(t, path); disk == "before-after" {
			break
		}
		if time.Now().After(deadline) {
			t.Fatalf("disk = %q, want %q (autosave did not fire)", readDisk(t, path), "before-after")
		}
		time.Sleep(100 * time.Millisecond)
	}
}

// TestRealFile_ShiftSelectionInsert verifies shift+arrow selection through the
// real key event path and that typing replaces the selection; also checks the
// selection reaches the rendered TextField element.
func TestRealFile_ShiftSelectionInsert(t *testing.T) {
	h, path := realFileHarness(t, "small.txt", "hello world")
	defer h.Cleanup()

	if err := h.WithState(func(st *editor.State) { st.Editor.CursorPosition = 0 }); err != nil {
		t.Fatalf("set cursor: %v", err)
	}
	// Select "hello" (5 chars) with shift+right.
	for i := 0; i < 5; i++ {
		h.SendInput([]ui.InputEvent{
			{Handler: editor.HandleKeyDown, Data: ui.KeyEvent{Name: key.NameRightArrow, Shift: true}},
		})
	}
	time.Sleep(50 * time.Millisecond)

	// Selection must be visible in state...
	v, err := h.Inspect(func(st *editor.State) any {
		return [2]int{st.Editor.SelectionStart, st.Editor.SelectionEnd}
	})
	if err != nil {
		t.Fatalf("inspect: %v", err)
	}
	sel := v.([2]int)
	s, e := sel[0], sel[1]
	if s != 0 || e != 5 {
		t.Fatalf("selection = [%d,%d), want [0,5)", s, e)
	}

	// ...and in the rendered TextField element (window-relative; at scroll 0
	// window == file, so same values). Only the latest frame matters: earlier
	// frames predate the selection.
	time.Sleep(100 * time.Millisecond) // let the post-input frame be captured
	frames := h.GetFrames()
	last := frames[len(frames)-1]
	var found bool
	for _, elem := range last {
		if tf, ok := elem.(ui.TextField); ok && tf.ID() == "editor_text" {
			found = true
			if tf.SelectionStart != 0 || tf.SelectionEnd != 5 {
				t.Fatalf("TextField selection = [%d,%d), want [0,5)", tf.SelectionStart, tf.SelectionEnd)
			}
		}
	}
	if !found {
		t.Fatal("no editor_text TextField in latest frame")
	}

	// Typing replaces the selection.
	h.SendInput([]ui.InputEvent{
		{Handler: editor.HandleKeyDown, Data: key.EditEvent{Range: key.Range{Start: 5, End: 5}, Text: "goodbye"}},
	})
	time.Sleep(50 * time.Millisecond)
	got, _ := h.FullContent()
	if got != "goodbye world" {
		t.Fatalf("buffer = %q, want %q", got, "goodbye world")
	}
	if err := h.Flush(); err != nil {
		t.Fatalf("flush: %v", err)
	}
	if disk := readDisk(t, path); disk != "goodbye world" {
		t.Fatalf("disk = %q, want %q", disk, "goodbye world")
	}
}

// TestRealFile_ShiftSelectionBackspace verifies backspace deletes a
// shift-selected range through the real key event path.
func TestRealFile_ShiftSelectionBackspace(t *testing.T) {
	h, path := realFileHarness(t, "small.txt", "0123456789")
	defer h.Cleanup()

	if err := h.WithState(func(st *editor.State) { st.Editor.CursorPosition = 2 }); err != nil {
		t.Fatalf("set cursor: %v", err)
	}
	// Shift+right x3 selects [2,5) = "234".
	for i := 0; i < 3; i++ {
		h.SendInput([]ui.InputEvent{
			{Handler: editor.HandleKeyDown, Data: ui.KeyEvent{Name: key.NameRightArrow, Shift: true}},
		})
	}
	h.SendInput([]ui.InputEvent{
		{Handler: editor.HandleKeyDown, Data: ui.KeyEvent{Name: key.NameDeleteBackward, Shift: false}},
	})
	time.Sleep(50 * time.Millisecond)
	got, _ := h.FullContent()
	if got != "0156789" {
		t.Fatalf("buffer = %q, want %q", got, "0156789")
	}
	if err := h.Flush(); err != nil {
		t.Fatalf("flush: %v", err)
	}
	if disk := readDisk(t, path); disk != "0156789" {
		t.Fatalf("disk = %q, want %q", disk, "0156789")
	}
}

// TestRealFile_MultilineEdit verifies insert and backspace across line
// boundaries keep the line index consistent (line count + offsets).
func TestRealFile_MultilineEdit(t *testing.T) {
	h, path := realFileHarness(t, "multi.txt", "aaa\nbbb\nccc")
	defer h.Cleanup()

	// Newline at end of line 1 -> 4 lines.
	if err := h.WithState(func(st *editor.State) {
		st.Editor.CursorPosition = 7 // after "bbb"
		editor.HandleInsert("\n")
	}); err != nil {
		t.Fatalf("insert: %v", err)
	}
	checkLineIndex(t, h, "aaa\nbbb\n\nccc", 4)

	// Backspace #1 removes the inserted '\n' (cursor is right after it).
	if err := h.WithState(func(st *editor.State) {
		editor.HandleBackspace()
	}); err != nil {
		t.Fatalf("backspace 1: %v", err)
	}
	checkLineIndex(t, h, "aaa\nbbb\nccc", 3)

	// Backspace #2 removes the trailing 'b' of line 2.
	if err := h.WithState(func(st *editor.State) {
		editor.HandleBackspace()
	}); err != nil {
		t.Fatalf("backspace 2: %v", err)
	}
	checkLineIndex(t, h, "aaa\nbb\nccc", 3)

	if err := h.Flush(); err != nil {
		t.Fatalf("flush: %v", err)
	}
	if disk := readDisk(t, path); disk != "aaa\nbb\nccc" {
		t.Fatalf("disk = %q, want %q", disk, "aaa\nbb\nccc")
	}
}

// checkLineIndex verifies buffer content and that the incrementally-maintained
// line index matches the expected line count and per-line offsets.
// lo/hi/seg bound a failure-report window around offset at.
func lo(at, n int) int {
	if at < n {
		return 0
	}
	return at - n
}

func hi(at, n int) int { return at + n }
func seg(s string, at, n int) string {
	start := lo(at, n)
	end := at + n
	if end > len(s) {
		end = len(s)
	}
	if start > end {
		start = end
	}
	return s[start:end]
}

func checkLineIndex(t *testing.T, h *e2e.Harness, wantContent string, wantLines int) {
	t.Helper()
	got, err := h.FullContent()
	if err != nil {
		t.Fatalf("FullContent: %v", err)
	}
	if got != wantContent {
		// Report compactly: large files make %q messages megabytes long.
		at := 0
		for at < len(got) && at < len(wantContent) && got[at] == wantContent[at] {
			at++
		}
		t.Fatalf("buffer mismatch at byte %d: got %d bytes, want %d\ngot  [%d:%d]=%q\nwant [%d:%d]=%q",
			at, len(got), len(wantContent), lo(at, 40), hi(at, 40), seg(got, at, 40), lo(at, 40), hi(at, 40), seg(wantContent, at, 40))
	}
	diag, err := h.Inspect(func(st *editor.State) any {
		li := st.Editor.ChunkedBuffer.LineIndex
		if li == nil {
			return "nil index"
		}
		if li.LineCount() != wantLines {
			return fmt.Sprintf("linecount=%d want=%d size=%d head=%v", li.LineCount(), wantLines, li.Size, li.Offsets[:min(10, len(li.Offsets))])
		}
		head := ""
		if len(li.Offsets) > 10 {
			head = fmt.Sprintf(" head=%v", li.Offsets[:10])
		}
		// Offsets must match a fresh computation from the content.
		offset := 0
		for line := 0; line < wantLines; line++ {
			if li.ByteOffset(line) != offset {
				return fmt.Sprintf("mismatch at line %d: index=%d want=%d size=%d%s",
					line, li.ByteOffset(line), offset, li.Size, head)
			}
			idx := strings.IndexByte(got[offset:], '\n')
			if idx < 0 {
				break
			}
			offset += idx + 1
		}
		return "ok"
	})
	if err != nil {
		t.Fatalf("inspect: %v", err)
	}
	if diag.(string) != "ok" {
		t.Fatalf("line index inconsistent: %s (content=%d bytes, want %d lines)", diag, len(wantContent), wantLines)
	}
}