# Simple way to store an `HashMap[K1, HashMap[K2, V]]`
#
# ~~~~
# var hm2 = new HashMap2[Int, String, Float]
# hm2[1, "one"] = 1.0
# hm2[2, "two"] = 2.0
# assert hm2[1, "one"] == 1.0
# assert hm2[2, "not-two"] == null
# ~~~~
class HashMap2[K1, K2, V]

	private var level1 = new HashMap[K1, HashMap[K2, V]]

	# Return the value associated to the keys `k1` and `k2`.
	# Return `null` if no such a value.
	fun [](k1: K1, k2: K2): nullable V
	do
		var level1 = self.level1
		var level2 = level1.get_or_null(k1)
		if level2 == null then return null
		return level2.get_or_null(k2)
	end

	# Set `v` the value associated to the keys `k1` and `k2`.
	fun []=(k1: K1, k2: K2, v: V)
	do
		var level1 = self.level1
		var level2 = level1.get_or_null(k1)
		if level2 == null then
			level2 = new HashMap[K2, V]
			level1[k1] = level2
		end
		level2[k2] = v
	end

	# Remove the item at `k1` and `k2`
	fun remove_at(k1: K1, k2: K2)
	do
		var level1 = self.level1
		var level2 = level1.get_or_null(k1)
		if level2 == null then return
		level2.keys.remove(k2)
	end

	# Is there a value at `k1, k2`?
	fun has(k1: K1, k2: K2): Bool
	do
		if not level1.keys.has(k1) then return false
		return level1[k1].keys.has(k2)
	end

	# Remove all items
	fun clear do level1.clear
end