package fog

// Diff 是一份待导入快照与当前迷雾之间的差异画像。
//
// 导入有两种语义完全不同的模式：叠加只做按位或、不可能丢数据；整体替换会先清空，
// 快照里没有的块一律消失。以前两种模式在界面上只是一个下拉框，站长在下手之前
// 看不到「这次能补多少」和「这次会丢多少」，实测里整体替换静默丢掉过 14% 的已探索区域。
type Diff struct {
	CurBlocks, CurCells int // 库里现有
	IncBlocks, IncCells int // 快照本身

	// GainBlocks/GainCells 是叠加模式真正新增的部分：快照里当前完全没有的整块，
	// 加上重叠块里补亮的格。
	GainBlocks int
	GainCells  int

	// OverlapBlocks 是与现有块坐标相同的块数，其中 SameBlocks 是一格都不会变的。
	OverlapBlocks int
	SameBlocks    int

	// LostBlocks/LostCells 是快照里完全没有、只有整体替换才会消失的部分。
	LostBlocks int
	LostCells  int

	curAreaM2, incAreaM2, gainAreaM2, lostAreaM2 float64
}

// DiffBlocks 比对当前块集与一份待导入快照。入参块集不要求有序。
func DiffBlocks(cur, inc []Block) Diff {
	var d Diff
	d.CurBlocks, d.IncBlocks = len(cur), len(inc)

	curMap := make(map[[2]int][]byte, len(cur))
	for _, b := range cur {
		curMap[[2]int{b.GX, b.GY}] = b.Bitmap
		n := popcountSum(b.Bitmap)
		d.CurCells += n
		d.curAreaM2 += float64(n) * cellAreaM2(b.GX, b.GY)
	}

	incSet := make(map[[2]int]struct{}, len(inc))
	for _, b := range inc {
		incSet[[2]int{b.GX, b.GY}] = struct{}{}
		n := popcountSum(b.Bitmap)
		d.IncCells += n
		d.incAreaM2 += float64(n) * cellAreaM2(b.GX, b.GY)

		old, ok := curMap[[2]int{b.GX, b.GY}]
		if !ok {
			d.GainBlocks++
			d.GainCells += n
			d.gainAreaM2 += float64(n) * cellAreaM2(b.GX, b.GY)
			continue
		}
		d.OverlapBlocks++
		gain := 0
		for i := range b.Bitmap {
			gain += int(popcount[b.Bitmap[i]&^old[i]])
		}
		if gain == 0 {
			d.SameBlocks++
			continue
		}
		d.GainCells += gain
		d.gainAreaM2 += float64(gain) * cellAreaM2(b.GX, b.GY)
	}

	for _, b := range cur {
		if _, ok := incSet[[2]int{b.GX, b.GY}]; ok {
			continue
		}
		n := popcountSum(b.Bitmap)
		d.LostBlocks++
		d.LostCells += n
		d.lostAreaM2 += float64(n) * cellAreaM2(b.GX, b.GY)
	}
	return d
}

func (d Diff) CurAreaKm2() float64  { return d.curAreaM2 / 1e6 }
func (d Diff) IncAreaKm2() float64  { return d.incAreaM2 / 1e6 }
func (d Diff) GainAreaKm2() float64 { return d.gainAreaM2 / 1e6 }
func (d Diff) LostAreaKm2() float64 { return d.lostAreaM2 / 1e6 }

// MergeAreaKm2 是叠加后的总量，CoverAreaKm2 是整体替换后的总量。
func (d Diff) MergeAreaKm2() float64 { return (d.curAreaM2 + d.gainAreaM2) / 1e6 }
func (d Diff) CoverAreaKm2() float64 { return d.incAreaM2 / 1e6 }

// Changed 报告叠加是否会让地图有任何变化——为假说明这份快照已经被完全覆盖过。
func (d Diff) Changed() bool { return d.GainCells > 0 }