package world

import (
	"testing"

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

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

	plan, err := PlanIncrementalPan(200, 100, 50, 30, 0, 0)
	require.NoError(t, err)
	require.Equal(t, IncrementalNoOp, plan.Mode)
	require.Empty(t, plan.Dirty)
}

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

	_, err := PlanIncrementalPan(0, 100, 10, 10, 1, 0)
	require.ErrorIs(t, err, errInvalidCanvasSize)
}

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

	plan, err := PlanIncrementalPan(100, 80, 40, 40, 100, 0)
	require.NoError(t, err)
	require.Equal(t, IncrementalFullRedraw, plan.Mode)

	plan, err = PlanIncrementalPan(100, 80, 40, 40, 0, -80)
	require.NoError(t, err)
	require.Equal(t, IncrementalFullRedraw, plan.Mode)
}

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

	plan, err := PlanIncrementalPan(100, 80, 0, 20, 1, 0)
	require.NoError(t, err)
	require.Equal(t, IncrementalFullRedraw, plan.Mode)

	plan, err = PlanIncrementalPan(100, 80, 20, 0, 0, 1)
	require.NoError(t, err)
	require.Equal(t, IncrementalFullRedraw, plan.Mode)
}

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

	// marginX=20 => threshold=10, dx=11 => full redraw
	plan, err := PlanIncrementalPan(200, 100, 20, 20, 11, 0)
	require.NoError(t, err)
	require.Equal(t, IncrementalFullRedraw, plan.Mode)
}

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

	// marginY=20 => threshold=10, dy=-11 => full redraw
	plan, err := PlanIncrementalPan(200, 100, 20, 20, 0, -11)
	require.NoError(t, err)
	require.Equal(t, IncrementalFullRedraw, plan.Mode)
}

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

	// marginX=40 => threshold=20, dx=5 => shift ok
	plan, err := PlanIncrementalPan(200, 100, 40, 40, 5, 0)
	require.NoError(t, err)
	require.Equal(t, IncrementalShift, plan.Mode)
	require.Equal(t, 5, plan.DxPx)
	require.Equal(t, 0, plan.DyPx)

	require.Equal(t, []RectPx{
		{X: 0, Y: 0, W: 6, H: 100},
	}, plan.Dirty)
}

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

	plan, err := PlanIncrementalPan(200, 100, 40, 40, -7, 0)
	require.NoError(t, err)
	require.Equal(t, IncrementalShift, plan.Mode)

	require.Equal(t, []RectPx{
		{X: 200 - 8, Y: 0, W: 8, H: 100},
	}, plan.Dirty)
}

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

	plan, err := PlanIncrementalPan(200, 100, 40, 40, 0, 9)
	require.NoError(t, err)
	require.Equal(t, IncrementalShift, plan.Mode)

	require.Equal(t, []RectPx{
		{X: 0, Y: 0, W: 200, H: 10},
	}, plan.Dirty)
}

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

	plan, err := PlanIncrementalPan(200, 100, 40, 40, 0, -9)
	require.NoError(t, err)
	require.Equal(t, IncrementalShift, plan.Mode)

	require.Equal(t, []RectPx{
		{X: 0, Y: 100 - 10, W: 200, H: 10},
	}, plan.Dirty)
}

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

	plan, err := PlanIncrementalPan(200, 100, 40, 40, -6, 8)
	require.NoError(t, err)
	require.Equal(t, IncrementalShift, plan.Mode)

	// Overlap is allowed; we just require both strips exist.
	require.Len(t, plan.Dirty, 2)
	require.ElementsMatch(t, []RectPx{
		{X: 200 - 7, Y: 0, W: 7, H: 100}, // right strip
		{X: 0, Y: 0, W: 200, H: 9},       // top strip
	}, plan.Dirty)
}

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

	plan, err := PlanIncrementalPan(200, 100, 40, 40, -7, 0)
	require.NoError(t, err)
	require.Equal(t, IncrementalShift, plan.Mode)

	// Right strip width should be abs(dx)+1 = 8.
	require.Equal(t, []RectPx{
		{X: 200 - 8, Y: 0, W: 8, H: 100},
	}, plan.Dirty)
}