local math = math

local get_node = minetest.get_node
local get_item_group = minetest.get_item_group

local registered_nodes = minetest.registered_nodes

flowlib = {}

--sum of direction vectors must match an array index

--(sum,root)
--(0,1), (1,1+0=1), (2,1+1=2), (3,1+2^2=5), (4,2^2+2^2=8)

local inv_roots = {
	[0] = 1,
	[1] = 1,
	[2] = 0.70710678118655,
	[4] = 0.5,
	[5] = 0.44721359549996,
	[8] = 0.35355339059327,
}

local function to_unit_vector(dir_vector)
	local sum = dir_vector.x * dir_vector.x + dir_vector.z * dir_vector.z
	return {x = dir_vector.x * inv_roots[sum], y = dir_vector.y, z = dir_vector.z * inv_roots[sum]}
end

local function is_touching(realpos,nodepos,radius)
	local boarder = 0.5 - radius
	return math.abs(realpos - nodepos) > (boarder)
end

flowlib.is_touching = is_touching

local function is_water(pos)
	return get_item_group(get_node(pos).name, "water") ~= 0
end

flowlib.is_water = is_water

local function node_is_water(node)
	return get_item_group(node.name, "water") ~= 0
end

flowlib.node_is_water = node_is_water

local function is_lava(pos)
	return get_item_group(get_node(pos).name, "lava") ~= 0
end

flowlib.is_lava = is_lava

local function node_is_lava(node)
	return get_item_group(node.name, "lava") ~= 0
end

flowlib.node_is_lava = node_is_lava


local function is_liquid(pos)
	return get_item_group(get_node(pos).name, "liquid") ~= 0
end

flowlib.is_liquid = is_liquid

local function node_is_liquid(node)
	return get_item_group(node.name, "liquid") ~= 0
end

flowlib.node_is_liquid = node_is_liquid

--This code is more efficient
local function quick_flow_logic(node, pos_testing, direction)
	local name = node.name
	if not registered_nodes[name] then
		return 0
	end
	if registered_nodes[name].liquidtype == "source" then
		local node_testing = get_node(pos_testing)
		if not registered_nodes[node_testing.name] then
			return 0
		end
		if registered_nodes[node_testing.name].liquidtype ~= "flowing" then
			return 0
		else
			return direction
		end
	elseif registered_nodes[name].liquidtype == "flowing" then
		local node_testing = get_node(pos_testing)
		local param2_testing = node_testing.param2
		if not registered_nodes[node_testing.name] then
			return 0
		end
		if registered_nodes[node_testing.name].liquidtype == "source" then
			return -direction
		elseif registered_nodes[node_testing.name].liquidtype == "flowing" then
			if param2_testing < node.param2 then
				if (node.param2 - param2_testing) > 6 then
					return -direction
				else
					return direction
				end
			elseif param2_testing > node.param2 then
				if (param2_testing - node.param2) > 6 then
					return direction
				else
					return -direction
				end
			end
		end
	end
	return 0
end

local function quick_flow(pos, node)
	if not node_is_liquid(node)  then
		return {x = 0, y = 0, z = 0}
	end
	local x = quick_flow_logic(node,{x = pos.x-1, y = pos.y, z = pos.z},-1) + quick_flow_logic(node,{x = pos.x+1, y = pos.y, z = pos.z}, 1)
	local z = quick_flow_logic(node,{x = pos.x, y = pos.y, z = pos.z-1},-1) + quick_flow_logic(node,{x = pos.x, y = pos.y, z = pos.z+1}, 1)
	return to_unit_vector({x = x, y = 0, z = z})
end

flowlib.quick_flow = quick_flow

--if not in water but touching, move centre to touching block
--x has higher precedence than z
--if pos changes with x, it affects z

local function move_centre(pos, realpos, node, radius)
	if is_touching(realpos.x, pos.x, radius) then
		if is_liquid({x = pos.x-1, y = pos.y, z = pos.z}) then
			node = get_node({x=pos.x-1, y = pos.y, z = pos.z})
			pos = {x = pos.x-1, y = pos.y, z = pos.z}
		elseif is_liquid({x = pos.x+1, y = pos.y, z = pos.z}) then
			node = get_node({x = pos.x+1, y = pos.y, z = pos.z})
			pos = {x = pos.x+1, y = pos.y, z = pos.z}
		end
	end
	if is_touching(realpos.z, pos.z, radius) then
		if is_liquid({x = pos.x, y = pos.y, z = pos.z - 1}) then
			node = get_node({x = pos.x, y = pos.y, z = pos.z - 1})
			pos = {x = pos.x, y = pos.y, z = pos.z - 1}
		elseif is_liquid({x = pos.x, y = pos.y, z = pos.z + 1}) then
			node = get_node({x = pos.x, y = pos.y, z = pos.z + 1})
			pos = {x = pos.x, y = pos.y, z = pos.z + 1}
		end
	end
	return pos, node
end

flowlib.move_centre = move_centre

--BEGIN getCornerLevel
local function get_corner_level(x, z, c_flowing, c_source, neighbors)
	local sum = 0
	local count = 0
	local air_count = 0
	for dz=0,1 do
		for dx=0,1 do
			local neighbor_data = neighbors[z + dz][x + dx]
			if neighbor_data.top_is_same_liquid then
				return 0.5 --- REPLACE returns
			end
			if neighbor_data.content == c_source then
				return 0.5
			end
			if neighbor_data.content == c_flowing then
				sum = sum + neighbor_data.level
				count = count + 1
			elseif neighbor_data.content == "air" then
				air_count = air_count + 1
			end
		end
	end

	if air_count >= 2 then
		return -0.5 + (0.2/10)
	end
	if count > 0 then
		return sum/count
	end
	return 0
end
--END getCornerLevel


-- Based on https://github.com/minetest/minetest/blob/master/src/client/content_mapblock.cpp#L536-L813
-- If minetest ever changes liquid flowing rendering this must be changed accordingly
local function get_liquid_corner_heights(pos)
	local cur_liquid = {}
	local node = get_node(pos)
	if not (get_item_group(node.name, "liquid") > 0) then return end
	local ndef = registered_nodes[node.name]
	local node_above = get_node({x=pos.x, y=pos.y+1, z=pos.z})

	-- BEGIN prepareLiquidNodeDrawing
	cur_liquid.content = node.name
	local c_flowing = ndef.liquid_alternative_flowing
	local c_source = ndef.liquid_alternative_source
	cur_liquid.top_is_same_liquid = (node_above.name == c_flowing or node_above.name == c_source)
	-- quick return if the liquid above is the same
	if cur_liquid.top_is_same_liquid then return {0.5, 0.5, 0.5, 0.5} end
	-- END prepareLiquidNodeDrawing

	local c_flowing_ndef = registered_nodes[c_flowing]

	--BEGIN getLiquidNeighborhood
	local range = math.max(1, math.min(c_flowing_ndef.liquid_range, 8))
	local neighbors = {
		{{}, {}, {}},
		{{}, {}, {}},
		{{}, {}, {}},
	}
	for w = -1,1 do
		for u = -1,1 do
			local neighbor = neighbors[w+2][u+2]
			local neighbor_node = get_node({x=pos.x + u, y=pos.y, z=pos.z + w})
			neighbor.content = neighbor_node.name
			neighbor.level = -0.5

			if neighbor.content == c_source then
				neighbor.is_same_liquid = true
				neighbor.level = 0.5
			elseif neighbor.content == c_flowing then
				neighbor.is_same_liquid = true
				local liquid_level = bit.band(neighbor_node.param2, 7)
				liquid_level = math.max(liquid_level - (8 - range), 0)
				neighbor.level = (-0.5 + (liquid_level + 0.5) / range)
			end
			if neighbor.content ~= "ignore" then
				local above_neighbor_node = get_node({x=pos.x + u, y=pos.y + 1, z=pos.z + w})
				if above_neighbor_node.name == c_source or above_neighbor_node.name == c_flowing then
					neighbor.top_is_same_liquid = true
				end
			end
		end
	end
	--END getLiquidNeighborhood

	--BEGIN drawLiquidTop calculateCornerLevels
	local vertices = {
		get_corner_level(1, 2, c_flowing, c_source, neighbors),
		get_corner_level(2, 2, c_flowing, c_source, neighbors),
		get_corner_level(2, 1, c_flowing, c_source, neighbors),
		get_corner_level(1, 1, c_flowing, c_source, neighbors),
	}
	--END drawLiquidTop calculateCornerLevels
	return vertices
end

local function get_liquid_height(pos, pos_offset)
	local pos_origin
	if pos_offset == nil then
		pos_origin = vector.round(pos)
		pos_offset = pos - pos_origin
	else
		pos_origin = pos
	end
	local corner_heights = get_liquid_corner_heights(pos_origin)
	if corner_heights == nil then return end
	-- order: -+ ++ +- --
	--first 3 vertices are connected, so are last 2 and first
	local height_centre, height_x, height_z
	if pos_offset.x + pos_offset.z > 0 then
		-- first triangle
		pos_offset = vector.subtract({x=0.5, y=0, z=0.5}, pos_offset)
		height_centre = corner_heights[2]
		height_x = corner_heights[1]
		height_z = corner_heights[3]
	else
		-- second triangle
		pos_offset = vector.add({x=0.5, y=0, z=0.5}, pos_offset)
		height_centre = corner_heights[4]
		height_x = corner_heights[3]
		height_z = corner_heights[1]
	end
	-- interpolate based on position in triangle
	local height = height_centre + (height_x - height_centre) * pos_offset.x + (height_z - height_centre) * pos_offset.z
	return height + pos_origin.y
end

local function liquid_at_exact(pos, pos_offset)
	local pos_origin
	if pos_offset == nil then
		pos_origin = vector.round(pos)
		pos_offset = pos - pos_origin
	else
		pos_origin = pos
	end
	local liq_height = get_liquid_height(pos_origin, pos_offset)
	if liq_height  == nil then return nil end
	if liq_height > (pos_offset.y + pos_origin.y) then
		return get_node(pos_origin).name
	else
		return nil
	end
end

flowlib.get_liquid_height = get_liquid_height
flowlib.liquid_at_exact = liquid_at_exact