-- LUALOCALS < ---------------------------------------------------------
local ipairs, math, minetest, type
    = ipairs, math, minetest, type
local math_atan2, math_cos, math_pi, math_random, math_sin, math_sqrt
    = math.atan2, math.cos, math.pi, math.random, math.sin, math.sqrt
-- LUALOCALS > ---------------------------------------------------------

local modname = minetest.get_current_modname()

minetest.register_privilege(modname, {
		description = "experimental cinematic camera",
		give_to_singleplayer = false,
		give_to_admin = false
	})

local function lookat(player, target)
	local pos = player:get_pos()
	pos.y = pos.y + player:get_properties().eye_height
	local delta = vector.normalize(vector.subtract(target, pos))
	player:set_look_horizontal(math_atan2(delta.z, delta.x) - math_pi / 2)
	return player:set_look_vertical(-math_atan2(delta.y, math_sqrt(
				delta.x ^ 2 + delta.y ^ 2)))
end

local function fluidmedium(pos)
	local node = minetest.get_node(pos)
	local def = minetest.registered_items[node.name]
	if not def then return node.name end
	if def.sunlight_propagates then return "CLEAR" end
	return def.liquid_alternative_source or node.name
end
local function sightblocked(from, to)
	local fsrc = fluidmedium(from)
	for pt in minetest.raycast(from, to, false, true) do
		if pt.type == "node" then
			if fluidmedium(pt.under) ~= fsrc then
				return vector.multiply(vector.add(pt.under,
						vector.multiply(pt.above, 3)), 0.25)
			end
		end
	end
end

local getdata
do
	local datastore = {}
	function getdata(p)
		local pname = type(p) == "string" and p or p:get_player_name()
		local data = datastore[pname]
		if not data then
			data = {}
			datastore[pname] = data
		end
		return data
	end
	minetest.register_on_leaveplayer(function(player)
			datastore[player:get_player_name()] = nil
		end)
end

local function camcheck(player, dtime)
	local data = getdata(player)

	local text = ""
	if data.target and data.tipttl then
		data.tipttl = data.tipttl - dtime
		if data.tipttl > 0 then
			text = "Watching: " .. data.target
		end
	end
	if data.tip then
		if text ~= data.tip.text then
			player:hud_change(data.tip.id, "text", text)
			data.tip.text = text
		end
	elseif text ~= "" then
		data.tip = {
			id = player:hud_add({
					hud_elem_type = "text",
					position = {x = 0.5, y = 1},
					text = text,
					number = 0xFFFFFF,
					alignment = {x = 0, y = -1},
					offset = {x = 0, y = -8},
				}),
			text = text
		}
	end

	if data.locked then
		data.locked = data.locked - dtime
		if data.locked > 0 then return end
		data.locked = nil
	end

	if data.tracktime then
		data.tracktime = data.tracktime - dtime
		if data.tracktime <= 0 then data.tracktime = nil end
	end
	local target = data.tracktime and data.target
	target = target and minetest.get_player_by_name(target)
	if not target then
		if not (data.queue and #data.queue > 0) then
			local q = {}
			local pname = player:get_player_name()
			for _, p in ipairs(minetest.get_connected_players()) do
				local n = p:get_player_name()
				if n ~= pname then
					local props = p:get_properties()
					local vs = props and props.visual_size
					if vs and vs.x > 0 and vs.y > 0 then
						q[#q + 1] = n
					end
				end
			end
			if #q < 1 then return end
			for i = #q, 2, -1 do
				local j = math_random(1, i)
				local x = q[i]
				q[i] = q[j]
				q[j] = x
			end
			data.queue = q
		end
		data.target = data.queue[#data.queue]
		data.queue[#data.queue] = nil
		data.tracktime = 15

		target = minetest.get_player_by_name(data.target)
		if not target then return end

		data.tipttl = 2
	end

	local pos = player:get_pos()
	pos.y = pos.y + player:get_properties().eye_height
	local tpos = target:get_pos()
	tpos.y = tpos.y + target:get_properties().eye_height

	local tidle = getdata(target).idletime or 0
	if tidle >= 10 then
		data.tracktime = data.tracktime - dtime * 4
	end

	local tlight = nodecore and nodecore.get_node_light(tpos)
	or minetest.get_node_light(tpos)
	if tlight and tlight < 8 then
		data.tracktime = data.tracktime - dtime * 8 / tlight
	end

	local function newcam()
		local theta = math_random() * math_pi * 2
		local trypos = vector.add(tpos, vector.multiply({
					x = math_cos(theta),
					y = math_random() * 2 - 0.5,
					z = math_sin(theta)
				}, 8))
		trypos = vector.add(trypos, vector.multiply(
				target:get_velocity(), -2))
		local dist = vector.distance(trypos, tpos)
		if dist > 4 then
			trypos = vector.add(tpos, vector.multiply(
					vector.direction(tpos, trypos), 4))
		end

		local bpos = sightblocked(tpos, trypos)
		if bpos and vector.distance(tpos, bpos) < 1 then
			return
		end
		trypos = bpos or trypos
		if sightblocked(trypos, tpos) then
			return
		end

		trypos.y = trypos.y - player:get_properties().eye_height
		player:set_pos(trypos)
		lookat(player, tpos)

		data.moved = 0
		data.locked = 1
	end

	local dist = vector.distance(pos, tpos)
	if dist < 1 or dist > 16 then
		return newcam()
	end

	local look = player:get_look_dir()
	local angle = vector.angle(vector.direction(pos, tpos), look)
	if angle > math_pi / 4 then
		return newcam()
	end

	if sightblocked(pos, tpos) then return newcam() end

	data.moved = (data.moved or 0) + dtime
	if data.moved > 15 then return newcam() end
end

minetest.register_globalstep(function(dtime)
		local players = minetest.get_connected_players()
		for _, player in ipairs(players) do
			local pos = player:get_pos()
			local look = player:get_look_dir()
			local ctl = player:get_player_control()
			local data = getdata(player)
			if not (ctl.up or ctl.down or ctl.left or ctl.right
				or ctl.jump or ctl.LMB or ctl.RMB) and data.idlepos
			and data.idlelook and vector.equals(pos, data.idlepos)
			and vector.equals(look, data.idlelook) then
				data.idletime = (data.idletime or 0) + dtime
			else
				data.idletime = 0
			end
			data.idlepos = pos
			data.idlelook = look
		end
		for _, player in ipairs(players) do
			if minetest.check_player_privs(player, modname) then
				camcheck(player, dtime)
			end
		end
	end)