package world

// renderCirclesStageA performs a full expanded-canvas redraw but renders ONLY Circle primitives.
func (w *World) renderCirclesStageA(drawer PrimitiveDrawer, params RenderParams) error {
	plan, err := w.buildRenderPlanStageA(params)
	if err != nil {
		return err
	}

	drawCirclesFromPlan(drawer, plan, w.W, w.H)
	return nil
}

// drawCirclesFromPlan executes a circles-only draw from an already built render plan.
func drawCirclesFromPlan(drawer PrimitiveDrawer, plan RenderPlan, worldW, worldH int) {
	for _, td := range plan.Tiles {
		if td.ClipW <= 0 || td.ClipH <= 0 {
			continue
		}

		// Filter only circles; skip tiles that have no circles.
		circles := make([]Circle, 0, len(td.Candidates))
		for _, it := range td.Candidates {
			c, ok := it.(Circle)
			if !ok {
				continue
			}
			circles = append(circles, c)
		}
		if len(circles) == 0 {
			continue
		}

		// Determine which circle copies actually intersect this tile segment.
		type circleCopy struct {
			c  Circle
			dx int
			dy int
		}
		copiesToDraw := make([]circleCopy, 0, len(circles))

		for _, c := range circles {
			shifts := circleWrapShifts(c, worldW, worldH)
			for _, s := range shifts {
				if circleCopyIntersectsTile(c, s.dx, s.dy, td.Tile, worldW, worldH) {
					copiesToDraw = append(copiesToDraw, circleCopy{c: c, dx: s.dx, dy: s.dy})
				}
			}
		}

		if len(copiesToDraw) == 0 {
			continue
		}

		drawer.Save()
		drawer.ClipRect(float64(td.ClipX), float64(td.ClipY), float64(td.ClipW), float64(td.ClipH))

		for _, cc := range copiesToDraw {
			c := cc.c

			// Project the circle center for this tile copy (tile offset + wrap shift).
			cxPx := worldSpanFixedToCanvasPx((c.X+td.Tile.OffsetX+cc.dx)-plan.WorldRect.minX, plan.ZoomFp)
			cyPx := worldSpanFixedToCanvasPx((c.Y+td.Tile.OffsetY+cc.dy)-plan.WorldRect.minY, plan.ZoomFp)

			// Radius is a world span.
			rPx := worldSpanFixedToCanvasPx(c.Radius, plan.ZoomFp)

			drawer.AddCircle(float64(cxPx), float64(cyPx), float64(rPx))
		}

		drawer.Fill()
		drawer.Restore()
	}
}

type wrapShift struct {
	dx int
	dy int
}

// circleWrapShifts returns 1..4 wrap shifts (multiples of worldW/worldH) required to render
// all torus copies of the circle inside the canonical world domain.
// The (0,0) shift is always present.
func circleWrapShifts(c Circle, worldW, worldH int) []wrapShift {
	// If radius covers the whole axis, additional copies are not useful.
	// (One copy already covers everything under any reasonable clip.)
	if c.Radius >= worldW || c.Radius >= worldH {
		return []wrapShift{{dx: 0, dy: 0}}
	}

	xShifts := []int{0}
	yShifts := []int{0}

	if c.X+c.Radius >= worldW {
		xShifts = append(xShifts, -worldW)
	}
	if c.X-c.Radius < 0 {
		xShifts = append(xShifts, worldW)
	}

	if c.Y+c.Radius >= worldH {
		yShifts = append(yShifts, -worldH)
	}
	if c.Y-c.Radius < 0 {
		yShifts = append(yShifts, worldH)
	}

	out := make([]wrapShift, 0, len(xShifts)*len(yShifts))
	for _, dx := range xShifts {
		for _, dy := range yShifts {
			out = append(out, wrapShift{dx: dx, dy: dy})
		}
	}
	return out
}

// circleCopyIntersectsTile checks whether the circle copy (shifted by dx/dy) intersects the tile segment.
// We use the tile's unwrapped segment bounds: [offset+rect.min, offset+rect.max) per axis.
func circleCopyIntersectsTile(c Circle, dx, dy int, tile WorldTile, worldW, worldH int) bool {
	// Unwrapped tile segment bounds.
	segMinX := tile.OffsetX + tile.Rect.minX
	segMaxX := tile.OffsetX + tile.Rect.maxX
	segMinY := tile.OffsetY + tile.Rect.minY
	segMaxY := tile.OffsetY + tile.Rect.maxY

	// Circle bbox in the same unwrapped space (apply shift + tile offset).
	cx := c.X + tile.OffsetX + dx
	cy := c.Y + tile.OffsetY + dy

	minX := cx - c.Radius
	maxX := cx + c.Radius
	minY := cy - c.Radius
	maxY := cy + c.Radius

	// Treat bbox as half-open for intersection checks.
	if maxX <= segMinX || minX >= segMaxX || maxY <= segMinY || minY >= segMaxY {
		return false
	}
	return true
}