package world

import (
	"image/color"
	"testing"

	"github.com/stretchr/testify/require"
)

func TestRender_AppliesStyleBeforeAddCommands_ForFirstItemInTile(t *testing.T) {
	t.Parallel()

	w := NewWorld(10, 10)
	w.resetGrid(2 * SCALE)

	// Create a derived circle style so we can observe a style application transition.
	red := color.RGBA{R: 255, A: 255}
	styleID := w.AddStyleCircle(StyleOverride{FillColor: red})

	_, err := w.AddCircle(5, 5, 1, CircleWithStyleID(styleID), CircleWithPriority(100))
	require.NoError(t, err)

	for _, obj := range w.objects {
		w.indexObject(obj)
	}

	params := RenderParams{
		ViewportWidthPx:  10,
		ViewportHeightPx: 10,
		MarginXPx:        0,
		MarginYPx:        0,
		CameraXWorldFp:   5 * SCALE,
		CameraYWorldFp:   5 * SCALE,
		CameraZoom:       1.0,
		Options: &RenderOptions{
			BackgroundColor: color.RGBA{A: 255},
		},
	}

	d := &fakePrimitiveDrawer{}
	require.NoError(t, w.Render(d, params))

	cmds := d.Commands()

	iSetFill := indexOfFirstName(cmds, "SetFillColor")
	iAddCircle := indexOfFirstName(cmds, "AddCircle")
	require.NotEqual(t, -1, iSetFill)
	require.NotEqual(t, -1, iAddCircle)

	require.Less(t, iSetFill, iAddCircle, "style must be applied before AddCircle")
}

func TestRender_DoesNotReapplySameStyleAcrossMultipleObjects(t *testing.T) {
	t.Parallel()

	w := NewWorld(10, 10)
	w.resetGrid(2 * SCALE)

	// Two lines with the same default line style and same priority.
	_, err := w.AddLine(1, 5, 9, 5, LineWithPriority(100))
	require.NoError(t, err)
	_, err = w.AddLine(1, 6, 9, 6, LineWithPriority(101)) // ensure deterministic order by priority
	require.NoError(t, err)

	for _, obj := range w.objects {
		w.indexObject(obj)
	}

	params := RenderParams{
		ViewportWidthPx:  10,
		ViewportHeightPx: 10,
		MarginXPx:        0,
		MarginYPx:        0,
		CameraXWorldFp:   5 * SCALE,
		CameraYWorldFp:   5 * SCALE,
		CameraZoom:       1.0,
		Options: &RenderOptions{
			BackgroundColor: color.RGBA{A: 255},
		},
	}

	d := &fakePrimitiveDrawer{}
	require.NoError(t, w.Render(d, params))

	// We expect style application at least once.
	setWidth := d.CommandsByName("SetLineWidth")
	require.NotEmpty(t, setWidth)

	// The key batching assertion: style setters should not be called twice *between* two AddLine calls.
	cmds := d.Commands()
	line1 := indexOfFirstName(cmds, "AddLine")
	require.NotEqual(t, -1, line1)

	line2 := indexOfNextName(cmds, "AddLine", line1+1)
	require.NotEqual(t, -1, line2)

	// Between line1 and line2 there must be no SetLineWidth / SetStrokeColor / SetDash / SetDashOffset,
	// because StyleID is the same and the renderer caches lastStyleID.
	for i := line1 + 1; i < line2; i++ {
		switch cmds[i].Name {
		case "SetLineWidth", "SetStrokeColor", "SetDash", "SetDashOffset", "SetFillColor":
			t.Fatalf("unexpected style setter %q between two AddLine commands at index %d", cmds[i].Name, i)
		}
	}
}

func TestRender_ReappliesStyleWhenStyleIDChanges(t *testing.T) {
	t.Parallel()

	w := NewWorld(10, 10)
	w.resetGrid(2 * SCALE)

	// Two circles, different derived fill colors => different StyleIDs.
	red := color.RGBA{R: 255, A: 255}
	green := color.RGBA{G: 255, A: 255}

	styleRed := w.AddStyleCircle(StyleOverride{FillColor: red})
	styleGreen := w.AddStyleCircle(StyleOverride{FillColor: green})

	_, err := w.AddCircle(4, 5, 1, CircleWithStyleID(styleRed), CircleWithPriority(100))
	require.NoError(t, err)
	_, err = w.AddCircle(6, 5, 1, CircleWithStyleID(styleGreen), CircleWithPriority(101))
	require.NoError(t, err)

	for _, obj := range w.objects {
		w.indexObject(obj)
	}

	params := RenderParams{
		ViewportWidthPx:  10,
		ViewportHeightPx: 10,
		MarginXPx:        0,
		MarginYPx:        0,
		CameraXWorldFp:   5 * SCALE,
		CameraYWorldFp:   5 * SCALE,
		CameraZoom:       1.0,
		Options: &RenderOptions{
			BackgroundColor: color.RGBA{A: 255},
		},
	}

	d := &fakePrimitiveDrawer{}
	require.NoError(t, w.Render(d, params))

	cmds := d.Commands()
	firstCircle := indexOfFirstName(cmds, "AddCircle")
	secondCircle := indexOfNextName(cmds, "AddCircle", firstCircle+1)
	require.NotEqual(t, -1, firstCircle)
	require.NotEqual(t, -1, secondCircle)

	// There must be at least one SetFillColor before each circle.
	// And importantly, we expect a SetFillColor BETWEEN the two circles due to style change.
	setBeforeFirst := lastIndexOfNameBefore(cmds, "SetFillColor", firstCircle)
	require.NotEqual(t, -1, setBeforeFirst)

	setBetween := indexOfFirstNameInRange(cmds, "SetFillColor", firstCircle+1, secondCircle)
	require.NotEqual(t, -1, setBetween, "expected style reapply (SetFillColor) between circles with different StyleIDs")
}

/* ---------- helper functions for fake command slices ---------- */

func indexOfFirstName(cmds []fakeDrawerCommand, name string) int {
	for i, c := range cmds {
		if c.Name == name {
			return i
		}
	}
	return -1
}

func indexOfNextName(cmds []fakeDrawerCommand, name string, start int) int {
	for i := start; i < len(cmds); i++ {
		if cmds[i].Name == name {
			return i
		}
	}
	return -1
}

func lastIndexOfNameBefore(cmds []fakeDrawerCommand, name string, before int) int {
	if before > len(cmds) {
		before = len(cmds)
	}
	for i := before - 1; i >= 0; i-- {
		if cmds[i].Name == name {
			return i
		}
	}
	return -1
}

func indexOfFirstNameInRange(cmds []fakeDrawerCommand, name string, start, end int) int {
	if start < 0 {
		start = 0
	}
	if end > len(cmds) {
		end = len(cmds)
	}
	for i := start; i < end; i++ {
		if cmds[i].Name == name {
			return i
		}
	}
	return -1
}