--[[
Explosion API mod for Minetest (adapted to MineClone 2)

This mod is based on the Minetest explosion API mod, but has been changed
to have the same explosion mechanics as Minecraft and work with MineClone.
The computation-intensive parts of the mod has been optimized to allow for
larger explosions and faster world updating.

This mod was created by Elias Astrom <ryvnf@riseup.net> and is released
under the LGPLv2.1 license.
--]]

mcl_explosions = {}

local creative_mode = minetest.settings:get_bool("creative_mode")
local mod_death_messages = minetest.get_modpath("mcl_death_messages") ~= nil
local mod_fire = minetest.get_modpath("mcl_fire") ~= nil
local CONTENT_FIRE = minetest.get_content_id("mcl_fire:fire")

local S = minetest.get_translator("mcl_explosions")

-- Saved sphere explosion shapes for various radiuses
local sphere_shapes = {}

-- Saved node definitions in table using cid-keys for faster look-up.
local node_blastres = {}
local node_on_blast = {}
local node_walkable = {}

-- The step length for the rays (Minecraft uses 0.3)
local STEP_LENGTH = 0.3

-- How many rays to compute entity exposure to explosion
local N_EXPOSURE_RAYS = 16

minetest.register_on_mods_loaded(function()
	-- Store blast resistance values by content ids to improve performance.
	for name, def in pairs(minetest.registered_nodes) do
		local id = minetest.get_content_id(name)
		node_blastres[id] = def._mcl_blast_resistance or 0
		node_on_blast[id] = def.on_blast
		node_walkable[id] = def.walkable
	end
end)

-- Compute the rays which make up a sphere with radius.	Returns a list of rays
-- which can be used to trace explosions. This function is not efficient
-- (especially for larger radiuses), so the generated rays for various radiuses
-- should be cached and reused.
--
-- Should be possible to improve by using a midpoint circle algorithm multiple
-- times to create the sphere, currently uses more of a brute-force approach.
local function compute_sphere_rays(radius)
	local rays = {}
	local sphere = {}

	for i=1, 2 do
		for y = -radius, radius do
			for z = -radius, radius do
				for x = -radius, 0, 1 do
					local d = x * x + y * y + z * z
					if d <= radius * radius then
						local pos = { x = x, y = y, z = z }
						sphere[minetest.hash_node_position(pos)] = pos
						break
					end
				end
			end
		end
	end

	for i=1,2 do
		for x = -radius, radius do
			for z = -radius, radius do
				for y = -radius, 0, 1 do
					local d = x * x + y * y + z * z
					if d <= radius * radius then
						local pos = { x = x, y = y, z = z }
						sphere[minetest.hash_node_position(pos)] = pos
						break
					end
				end
			end
		end
	end

	for i=1,2 do
		for x = -radius, radius do
			for y = -radius, radius do
				for z = -radius, 0, 1 do
					local d = x * x + y * y + z * z
					if d <= radius * radius then
						local pos = { x = x, y = y, z = z }
						sphere[minetest.hash_node_position(pos)] = pos
						break
					end
				end
			end
		end
	end

	for _, pos in pairs(sphere) do
		rays[#rays + 1] = vector.normalize(pos)
	end

	return rays
end

-- Add particles from explosion
--
-- Parameters:
-- pos - The position of the explosion
-- radius - The radius of the explosion
local function add_particles(pos, radius)
	minetest.add_particlespawner({
		amount = 64,
		time = 0.125,
		minpos = pos,
		maxpos = pos,
		minvel = {x = -radius, y = -radius, z = -radius},
		maxvel = {x = radius, y = radius, z = radius},
		minacc = vector.new(),
		maxacc = vector.new(),
		minexptime = 0.5,
		maxexptime = 1.0,
		minsize = radius * 0.5,
		maxsize = radius * 1.0,
		texture = "tnt_smoke.png",
	})
end

-- Traces the rays of an explosion, and updates the environment.
--
-- Parameters:
-- pos - Where the rays in the explosion should start from
-- strength - The strength of each ray
-- raydirs - The directions for each ray
-- radius - The maximum distance each ray will go
-- drop_chance - The chance that destroyed nodes will drop their items
-- fire - If true, 1/3 of destroyed nodes become fire
-- puncher - object that punches other objects (optional)
--
-- Note that this function has been optimized, it contains code which has been
-- inlined to avoid function calls and unnecessary table creation. This was
-- measured to give a significant performance increase.
local function trace_explode(pos, strength, raydirs, radius, drop_chance, fire, puncher)
	local vm = minetest.get_voxel_manip()

	local emin, emax = vm:read_from_map(vector.subtract(pos, radius),
		vector.add(pos, radius))
	local emin_x = emin.x
	local emin_y = emin.y
	local emin_z = emin.z

	local ystride = (emax.x - emin_x + 1)
	local zstride = ystride * (emax.y - emin_y + 1)
	local pos_x = pos.x
	local pos_y = pos.y
	local pos_z = pos.z

	local area = VoxelArea:new {
		MinEdge = emin,
		MaxEdge = emax
	}
	local data = vm:get_data()
	local destroy = {}

	-- Trace rays for environment destruction
	for i = 1, #raydirs do
		local rpos_x = pos.x
		local rpos_y = pos.y
		local rpos_z = pos.z
		local rdir_x = raydirs[i].x
		local rdir_y = raydirs[i].y
		local rdir_z = raydirs[i].z
		local rstr = (0.7 + math.random() * 0.6) * strength

		for r = 0, math.ceil(radius * (1.0 / STEP_LENGTH)) do
			local npos_x = math.floor(rpos_x + 0.5)
			local npos_y = math.floor(rpos_y + 0.5)
			local npos_z = math.floor(rpos_z + 0.5)
			local idx = (npos_z - emin_z) * zstride + (npos_y - emin_y) * ystride +
					npos_x - emin_x + 1

			local cid = data[idx]
			local br = node_blastres[cid]
			local hash = minetest.hash_node_position({x=npos_x, y=npos_y, z=npos_z})

			rpos_x = rpos_x + STEP_LENGTH * rdir_x
			rpos_y = rpos_y + STEP_LENGTH * rdir_y
			rpos_z = rpos_z + STEP_LENGTH * rdir_z

			rstr = rstr - 0.75 * STEP_LENGTH - (br + 0.3) * STEP_LENGTH

			if rstr <= 0 then
				break
			end

			if cid ~= minetest.CONTENT_AIR then
				destroy[hash] = idx
			end
		end
	end

	-- Entities in radius of explosion
	local punch_radius = 2 * strength
	local objs = minetest.get_objects_inside_radius(pos, punch_radius)

	-- Trace rays for entity damage
	for _, obj in pairs(objs) do
		local ent = obj:get_luaentity()

		-- Ignore items to lower lag
		if obj:is_player() or (ent and ent.name ~= '__builtin.item') then
			local opos = obj:get_pos()
			local collisionbox = nil

			if obj:is_player() then
				collisionbox = { -0.3, 0.0, -0.3, 0.3, 1.77, 0.3 }
			elseif ent.name then
				local def = minetest.registered_entities[ent.name]
				collisionbox = def.collisionbox
			end

			if collisionbox then
				-- Create rays from random points in the collision box
				local x1 = collisionbox[1] * 2
				local y1 = collisionbox[2] * 2
				local z1 = collisionbox[3] * 2
				local x2 = collisionbox[4] * 2
				local y2 = collisionbox[5] * 2
				local z2 = collisionbox[6] * 2
				local x_len = math.abs(x2 - x1)
				local y_len = math.abs(y2 - y1)
				local z_len = math.abs(z2 - z1)

				-- Move object position to the center of its bounding box
				opos.x = opos.x + x1 + x2
				opos.y = opos.y + y1 + y2
				opos.z = opos.z + z1 + z2

				-- Count number of rays from collision box which are unobstructed
				local count = N_EXPOSURE_RAYS

				for i = 1, N_EXPOSURE_RAYS do
					local rpos_x = opos.x + math.random() * x_len - x_len / 2
					local rpos_y = opos.y + math.random() * y_len - y_len / 2
					local rpos_z = opos.z + math.random() * z_len - z_len / 2
					local rdir_x = pos.x - rpos_x
					local rdir_y = pos.y - rpos_y
					local rdir_z = pos.z - rpos_z
					local rdir_len = math.hypot(rdir_x, math.hypot(rdir_y, rdir_z))
					rdir_x = rdir_x / rdir_len
					rdir_y = rdir_y / rdir_len
					rdir_z = rdir_z / rdir_len

					for i=0, rdir_len / STEP_LENGTH do
						rpos_x = rpos_x + rdir_x * STEP_LENGTH
						rpos_y = rpos_y + rdir_y * STEP_LENGTH
						rpos_z = rpos_z + rdir_z * STEP_LENGTH
						local npos_x = math.floor(rpos_x + 0.5)
						local npos_y = math.floor(rpos_y + 0.5)
						local npos_z = math.floor(rpos_z + 0.5)
						local idx = (npos_z - emin_z) * zstride + (npos_y - emin_y) * ystride +
								npos_x - emin_x + 1


						local cid = data[idx]
						local walkable = node_walkable[cid]

						if walkable then
							count = count - 1
							break
						end
					end
				end

				-- Punch entity with damage depending on explosion exposure and
				-- distance to explosion
				local exposure = count / N_EXPOSURE_RAYS
				local punch_vec = vector.subtract(opos, pos)
				local punch_dir = vector.normalize(punch_vec)
				local impact = (1 - vector.length(punch_vec) / punch_radius) * exposure
				if impact < 0 then
					impact = 0
				end
				local damage = math.floor((impact * impact + impact) * 7 * strength + 1)
				if mod_death_messages and obj:is_player() then
					mcl_death_messages.player_damage(obj, S("@1 was caught in an explosion.", obj:get_player_name()))
				end
				local source = puncher
				if not source then
					source = obj
				end
				obj:punch(source, 10, { damage_groups = { full_punch_interval = 1,
						fleshy = damage, knockback = impact * 20.0 } }, punch_dir)

				if obj:is_player() then
					obj:add_player_velocity(vector.multiply(punch_dir, impact * 20))
				elseif ent.tnt_knockback then
					obj:add_velocity(vector.multiply(punch_dir, impact * 20))
				end
			end
		end
	end

	local airs, fires = {}, {}

	-- Remove destroyed blocks and drop items
	for hash, idx in pairs(destroy) do
		local do_drop = not creative_mode and math.random() <= drop_chance
		local on_blast = node_on_blast[data[idx]]
		local remove = true

		if do_drop or on_blast ~= nil then
			local npos = minetest.get_position_from_hash(hash)
			if on_blast ~= nil then
				on_blast(npos, 1.0)
				remove = false
			else
				local name = minetest.get_name_from_content_id(data[idx])
				local drop = minetest.get_node_drops(name, "")

				for _, item in ipairs(drop) do
					if type(item) ~= "string" then
						item = item:get_name() .. item:get_count()
					end
					minetest.add_item(npos, item)
				end
			end
		end
		if remove then
			if mod_fire and fire and math.random(1, 3) == 1 then
				table.insert(fires, minetest.get_position_from_hash(hash))
			else
				table.insert(airs, minetest.get_position_from_hash(hash))
			end
		end
	end
	-- We use bulk_set_node instead of LVM because we want to have on_destruct and
	-- on_construct being called
	if #airs > 0 then
		minetest.bulk_set_node(airs, {name="air"})
	end
	if #fires > 0 then
		minetest.bulk_set_node(fires, {name="mcl_fire:fire"})
	end
	-- Update falling nodes
	for a=1, #airs do
		local p = airs[a]
		minetest.check_for_falling({x=p.x, y=p.y+1, z=p.z})
	end
	for f=1, #fires do
		local p = fires[f]
		minetest.check_for_falling({x=p.x, y=p.y+1, z=p.z})
	end

	-- Log explosion
	minetest.log('action', 'Explosion at ' .. minetest.pos_to_string(pos) ..
		' with strength ' .. strength .. ' and radius ' .. radius)

end

-- Create an explosion with strength at pos.
--
-- Parameters:
-- pos - The position where the explosion originates from
-- strength - The blast strength of the explosion (a TNT explosion uses 4)
-- info - Table containing information about explosion.
-- puncher - object that is reported as source of punches/damage (optional)
--
-- Values in info:
-- drop_chance - If specified becomes the drop chance of all nodes in the
--               explosion (defaults to 1.0 / strength)
-- no_sound - If true then the explosion will not play a sound
-- no_particle - If true then the explosion will not create particles
-- fire - If true, 1/3 nodes become fire (default: false)
function mcl_explosions.explode(pos, strength, info, puncher)
	-- The maximum blast radius (in the air)
	local radius = math.ceil(1.3 * strength / (0.3 * 0.75) * 0.3)

	if not sphere_shapes[radius] then
		sphere_shapes[radius] = compute_sphere_rays(radius)
	end
	local shape = sphere_shapes[radius]

	trace_explode(pos, strength, shape, radius, (info and info.drop_chance) or 1 / strength, info.fire == true, puncher)

	if not (info and info.no_sound) then
		add_particles(pos, radius)
	end
	if not (info and info.no_particle) then
		minetest.sound_play("tnt_explode", {
			pos = pos, gain = 1.0,
			max_hear_distance = strength * 16
		}, true)
	end
end