package editor

import (
	"math"
	"strings"
	"testing"

	"pad/internal/ui"
)

// dpeq compares two Dp values within 0.01 Dp (all menu geometry is
// float32 Dp; this is far below one screen pixel at any density).
func dpeq(a, b ui.Dp) bool { return math.Abs(float64(a)-float64(b)) < 0.01 }

// menuTrackState builds a small-file state: a 200-line buffer ("aa" per
// line), a selection on line 5 (bytes [15,17)), and a shaped GlyphLayout
// covering the WHOLE buffer (the small-file window is the whole buffer, so
// the layout is identical before and after a scroll — the scroll changes
// only k/r, exactly as in production). Baselines use the shaper's real
// convention (drawWrappedText): ascent + lineHeight*lineIndex, ascent = 14.
func menuTrackState(t *testing.T) (lh float64) {
	const ascent float64 = 14 // FontSize; 0 < ascent < lh is the invariant
	t.Helper()
	lh = float64(EffectiveLineHeight())
	// Long enough that the 1904-Dp test viewport overflows and scrolling is
	// allowed (EditorLayout clamps ScrollOffset to LastLineY-based maxScroll;
	// a short file would clamp the test scroll back to 0).
	lines := 200
	var buf strings.Builder
	for i := 0; i < lines; i++ {
		buf.WriteString("aa\n")
	}
	TheState = NewState()
	TheState.Editor.Buffer = buf.String()
	SetSelection(15, 17) // "aa" on line 5

	gl := ui.GlyphLayout{LineHeight: EffectiveLineHeight()}
	for i := 0; i < lines; i++ {
		for c := 0; c < 2; c++ {
			gl.ByteOffsets = append(gl.ByteOffsets, i*3+c)
			gl.X = append(gl.X, ui.Dp(10+10*c))
			gl.Y = append(gl.Y, ui.Dp(ascent+float64(i)*lh))
			gl.Advance = append(gl.Advance, 10)
		}
	}
	TheState.Editor.GlyphLayout = gl
	// LastLineY is normally set by the shaper's layout feedback; emulate it.
	TheState.LastLineY = ui.Dp(float64(lines) * lh)
	TheState.Editor.IMEWindowStartByte = 0
	TheState.ScrollOffset = 0
	return lh
}

// TestSelectionMenu_FollowsTextAcrossScroll is a regression test for the
// selection menu staying at a FIXED SCREEN POSITION while the user scrolled:
// the menu must track the selected text (the menu is anchored to the text,
// not to where it was first shown). The menu's Y must move down/up by exactly
// the scroll delta while the anchor stays in view.
func TestSelectionMenu_FollowsTextAcrossScroll(t *testing.T) {
	lh := menuTrackState(t)

	// Lay out once so EditorRegion (the text region the menu is placed in)
	// is established, exactly as in production.
	EditorLayout(ui.Dp(1000), ui.Dp(2000), false)

	showSelectionMenu()
	e := &TheState.Editor
	if !e.MenuVisible {
		t.Fatal("menu not shown for a visible selection")
	}
	y0 := e.MenuRect.Y
	// The menu sits ABOVE the anchor's line: lineTop(line 5) = reg.Y + 5*lh
	// (reg.Y = 10+52, the anchor's visual line index is 5).
	wantY0 := ui.Dp(62) + ui.Dp(5*lh) - menuH - 8
	if !dpeq(y0, wantY0) {
		t.Fatalf("initial menu Y = %v, want %v (above the anchor line)", y0, wantY0)
	}

	// Scroll down by exactly 2 lines and lay out again.
	TheState.ScrollOffset = ui.Dp(2 * lh)
	EditorLayout(ui.Dp(1000), ui.Dp(2000), false)

	// The anchor moved up 2 lines on screen; the menu must follow by exactly
	// the same amount.
	want := wantY0 - ui.Dp(2*lh)
	if got := e.MenuRect.Y; !dpeq(got, want) {
		t.Fatalf("menu Y after 2-line scroll = %v, want %v (menu must track the text)", got, want)
	}
	if !e.MenuVisible {
		t.Fatal("menu hidden while its anchor is still in view")
	}
}

// TestSelectionMenu_ClampsWhenTextLeavesView checks the small-file edge: the
// buffer is the whole window, so the anchor never "leaves"; when the selected
// text scrolls off the top, the menu pins to the top of the window (it never
// detaches into mid-screen stale territory).
func TestSelectionMenu_ClampsWhenTextLeavesView(t *testing.T) {
	lh := menuTrackState(t)

	EditorLayout(ui.Dp(1000), ui.Dp(2000), false)

	showSelectionMenu()
	e := &TheState.Editor
	if !e.MenuVisible {
		t.Fatal("menu not shown")
	}

	// Scroll 10 lines: line 5 is 4 lines ABOVE the viewport top.
	TheState.ScrollOffset = ui.Dp(10 * lh)
	EditorLayout(ui.Dp(1000), ui.Dp(2000), false)

	if !e.MenuVisible {
		t.Fatal("menu hidden, but small-file layout can still track it (pinned)")
	}
	if got := e.MenuRect.Y; !dpeq(got, 8) {
		t.Fatalf("menu Y = %v, want 8 (pinned to the window top when the text is above the viewport)", got)
	}
}

// TestSelectionMenu_FlipsBelowOnFirstLine checks the edge where there is no
// room above the anchor (selection on the first line): the menu must flip
// below the line rather than clamping to the window top and sitting over the
// anchor's own text.
func TestSelectionMenu_FlipsBelowOnFirstLine(t *testing.T) {
	lh := menuTrackState(t)

	TheState.Editor.Buffer = "aa\nbb\n"
	SetSelection(0, 2) // "aa" on line 0

	gl := ui.GlyphLayout{LineHeight: EffectiveLineHeight()}
	const ascent float64 = 14
	lines := 2
	for i := 0; i < lines; i++ {
		for c := 0; c < 2; c++ {
			gl.ByteOffsets = append(gl.ByteOffsets, i*3+c)
			gl.X = append(gl.X, ui.Dp(10+10*c))
			gl.Y = append(gl.Y, ui.Dp(ascent+float64(i)*lh))
			gl.Advance = append(gl.Advance, 10)
		}
	}
	TheState.Editor.GlyphLayout = gl
	TheState.LastLineY = ui.Dp(float64(lines) * lh)
	TheState.Editor.IMEWindowStartByte = 0
	TheState.ScrollOffset = 0

	EditorLayout(ui.Dp(1000), ui.Dp(2000), false)
	showSelectionMenu()
	e := &TheState.Editor
	if !e.MenuVisible {
		t.Fatal("menu not shown")
	}
	// Line 0 top = reg.Y = 62; above would be 62-52-8 = 2 < 8, so the menu
	// flips below: 62 + lh + 8.
	wantY := ui.Dp(62) + EffectiveLineHeight() + 8
	if !dpeq(e.MenuRect.Y, wantY) {
		t.Fatalf("menu Y = %v, want %v (flipped below the first line)", e.MenuRect.Y, wantY)
	}
}