--- ubiquitousse.timer
-- Optional dependencies: ubiquitousse.signal (to bind to update signal in signal.event)
local loaded, signal = pcall(require, (...):match("^(.-)timer").."signal")
if not loaded then signal = nil end

local ease = require((...):match("^.-timer")..".easing")

--- Returns true if all the values in the list are true ; functions in the list will be called and the test will be performed on their return value.
-- Returns default if the list is empty.
local function all(list, default)
	if #list == 0 then
		return default
	else
		local r = true
		for _,v in ipairs(list) do
			if type(v) == "function" then
				r = r and v()
			else
				r = r and v
			end
		end
		return r
	end
end

-- Timer methods.
local timer_mt = {
	--- timer data table
	t = nil,

	--- Wait time milliseconds before running the function.
	-- Specify no time to remove condition.
	after = function(self, time)
		self.t.after = time
		return self
	end,
	--- Run the function every time millisecond.
	-- Specify no time to remove condition.
	every = function(self, time)
		self.t.every = time
		return self
	end,
	--- The function will not execute more than count times.
	-- Specify no time to remove condition.
	times = function(self, count)
		self.t.times = count or -1
		return self
	end,
	--- The TimedFunction will be active for a time duration.
	-- Specify no time to remove condition.
	during = function(self, time)
		self.t.during = time
		return self
	end,

	--- Function conditions ---
	--- Starts the function execution when func() returns true. Checked before the "after" condition,
	-- meaning the "after" countdown starts when func() returns true.
	-- If multiple init functions are added, init will trigger only when all of them returns true.
	initWhen = function(self, func)
		table.insert(self.t.initWhen, func)
		return self
	end,
	--- Starts the function execution when func() returns true. Checked after the "after" condition.
	-- If multiple start functions are added, start will trigger only when all of them returns true.
	startWhen = function(self, func)
		table.insert(self.t.startWhen, func)
		return self
	end,
	--- When the functions ends, the execution won't stop and will repeat as long as func() returns true.
	-- Will cancel timed repeat conditions if false but needs other timed repeat conditions to be true to create a new repeat.
	-- If multiple repeat functions are added, a repeat will trigger only when all of them returns true.
	repeatWhile = function(self, func)
		table.insert(self.t.repeatWhile, func)
		return self
	end,
	--- Stops the function execution when func() returns true. Checked before all timed conditions.
	-- If multiple stop functions are added, stop will trigger only when all of them returns true.
	stopWhen = function(self, func)
		table.insert(self.t.stopWhen, func)
		return self
	end,

	--- Conditions override ---
	--- Force the function to start its execution.
	start = function(self)
		self.t.forceStart = true
		return self
	end,
	--- Force the function to stop its execution.
	stop = function(self)
		self.t.forceStop = true
		return self
	end,
	--- Force the function to stop immediately. Won't trigger onEnd or other callbacks.
	abort = function(self)
		self.t.abort = true
		return self
	end,
	--- Skip some amount of time.
	skip = function(self, time)
		self.t.skip = (self.t.skip or 0) + time
	end,

	--- Callbacks functions ---
	--- Will execute func(self, lag) when the function execution start.
	onStart = function(self, func)
		table.insert(self.t.onStart, func)
		return self
	end,
	--- Will execute func(self, lag) each frame the main function is run.
	onUpdate = function(self, func)
		table.insert(self.t.onUpdate, func)
		return self
	end,
	--- Will execute func(self, lag) when the function execution end.
	onEnd = function(self, func)
		table.insert(self.t.onEnd, func)
		return self
	end,

	--- Chaining ---
	--- Creates another TimedFunction which will be initialized immediately when the current one ends.
	-- Returns the new TimedFunction.
	chain = function(self, func)
		local done = false
		local fn = self:run(func)
			:initWhen(function() return done end)
		self:onEnd(function(self, lag)
			done = true
			fn:skip(lag)
		end)
		return fn
	end
}
timer_mt.__index = timer_mt

--- Registry methods.
local registry_mt = {
	--- Update all the timers in the registry.
	-- Should be called at every game update; called by ubiquitousse.update.
	-- @tparam number dt the delta-time (time spent since last time the function was called) (miliseconds)
	-- @impl ubiquitousse
	update = function(self, dt)
		self.dt = dt

		-- process timers
		for _, timer in ipairs(self.delayed) do
			local t = timer.t
			if not t.dead then
				if t.abort then
					t.dead = true
				elseif all(t.initWhen, true) then
					t.initWhen = {}
					local co = t.coroutine
					-- skip
					dt = self.dt
					if t.skip then dt = dt + t.skip end
					-- start
					if t.after then t.after = t.after - dt end
					if t.forceStart or ((not t.after or t.after <= 0) and all(t.startWhen, true)) then
						local startLag = 0
						if t.after then
							startLag = -t.after
						elseif t.skip then
							startLag = t.skip
						end
						t.after, t.skip = nil, nil
						t.startWhen = {}
						t.dead = true -- niling here cause the next pair iteration to error
						if not co then
							co = coroutine.create(t.func)
							t.coroutine = co
							if t.times > 0 then t.times = t.times - 1 end
							for _, f in ipairs(t.onStart) do f(timer, startLag) end
						end
						-- update
						assert(coroutine.resume(co, timer, dt, 0, function(delay)
							t.after = delay - startLag
							t.dead = false
							local _, _, dt, lag = coroutine.yield()
							return dt, lag
						end))
						for _, f in ipairs(t.onUpdate) do f(t.object, startLag) end
						if t.during then t.during = t.during - startLag - dt end
						-- stopping / repeat
						if all(t.stopWhen, false) then t.forceStop = true end
						if t.forceStop or coroutine.status(co) == "dead" then
							if t.forceStop
								or (t.during and t.during <= 0)
								or (t.times == 0)
								or (not all(t.repeatWhile, true))
								or (t.every == nil and t.times == -1 and t.during == nil and #t.repeatWhile == 0) -- no repeat
							then
								local endLag = t.during and -t.during or 0
								for _, f in ipairs(t.onEnd) do f(timer, endLag) end
							else
								if t.times > 0 then t.times = t.times - 1 end
								if t.every then t.after = t.every - startLag end
								t.coroutine = coroutine.create(t.func)
								t.dead = false
							end
						end
					end
				end
			end
		end

		-- remove dead timers
		for i=#self.delayed, 1, -1 do
			if self.delayed[i].t.dead then
				table.remove(self.delayed, i)
			end
		end
	end,

	--- Schedule a function to run.
	-- The function will receive as first parameter the TimedFunction object.
	-- As a second parameter, the function will receive the delta time (dt).
	-- As a third parameter, the function will receive the lag time (difference between the time when the function was run and when it should have been run).
	-- As a fourth parameter, the function will receive as first parameter the wait(time) function, which will pause the function execution for time miliseconds.
	-- @tparam[opt] function func the function to schedule
	-- @treturn timer the object
	-- @impl ubiquitousse
	run = function(self, func)
		local r = setmetatable({
			t = {
				dead = false,
				func = func or function() end,
				coroutine = nil,

				after = nil,
				every = nil,
				times = -1,
				during = nil,

				initWhen = {},
				startWhen = {},
				repeatWhile = {},
				stopWhen = {},

				forceStart = false,
				forceStop = false,
				skip = nil,

				onStart = {},
				onUpdate = {},
				onEnd = {}
			}
		}, timer_mt)

		table.insert(self.delayed, r)

		return r
	end,

	--- Tween some numeric values.
	-- @tparam number duration tween duration (miliseconds)
	-- @tparam table tbl the table containing the values to tween
	-- @tparam table to the new values
	-- @tparam[opt="linear"] string/function method tweening method (string name or the actual function(time, start, change, duration))
	-- @treturn TimedFunction the object. A duration is already defined, and the :chain methods takes the same arguments as tween (and creates a tween).
	-- @impl ubiquitousse
	tween = function(self, duration, tbl, to, method)
		method = method or "linear"
		method = type(method) == "string" and ease[method] or method

		local time = 0 -- tweening time elapsed
		local from = {} -- initial state

		local function update(tbl_, from_, to_) -- apply the method to tbl_ recursively (doesn't handle cycles)
			for k, v in pairs(to_) do
				if type(v) == "table" then
					update(tbl_[k], from_[k], to_[k])
				else
					if time < duration then
						tbl_[k] = method(time, from_[k], v - from_[k], duration)
					else
						tbl_[k] = v
					end
				end
			end
		end

		local r = self:run(function(self, dt)
			time = time + dt
			update(tbl, from, to)
		end):during(duration)
		    :onStart(function()
				local function copy(stencil, source, dest) -- copy initial state recursively
					for k, v in pairs(stencil) do
						if type(v) == "table" then
							if not dest[k] then dest[k] = {} end
							copy(stencil[k], source[k], dest[k])
						else
							dest[k] = source[k]
						end
					end
				end
				copy(to, tbl, from)
			end)

		--- Creates another tween which will be initialized when the current one ends.
		-- If tbl_ and/or method_ are not specified, the values from the current tween will be used.
		-- Returns the new tween.
		r.chain = function(_, duration_, tbl_, to_, method_)
			if not method_ and to_ then
				if type(to_) == "string" then
					tbl_, to_, method_ = tbl, tbl_, to_
				else
					method_ = method
				end
			elseif not method_ and not to_ then
				tbl_, to_, method_ = tbl, tbl_, method
			end

			local done = false
			local fn = self:tween(duration_, tbl_, to_, method_)
				:initWhen(function() return done end)
			r:onEnd(function(self, lag)
				done = true
				fn:skip(lag)
			end)
			return fn
		end

		return r
	end,

	--- Cancels all the running TimedFunctions.
	-- @impl ubiquitousse
	clear = function(self)
		self.delayed = {}
	end
}
registry_mt.__index = registry_mt

--- Time related functions
local timer
timer = {
	--- Creates and return a new TimerRegistry.
	-- A TimerRegistry is a separate ubiquitousse.time instance: its TimedFunctions will be independant
	-- from the one registered using ubiquitousse.time.run (the global TimerRegistry). If you use the scene
	-- system, a scene-specific TimerRegistry is available at ubiquitousse.scene.current.time.
	-- @impl ubiquitousse
	new = function()
		return setmetatable({
			--- Used to store all the functions delayed with ubiquitousse.time.delay
			-- The default implementation use the structure {<key: function> = <value: data table>, ...}
			-- This table is for internal use and shouldn't be used from an external script.
			delayed = {},

			--- Time since last timer update (miliseconds).
			dt = 0
		}, registry_mt)
	end,

	--- Time since last update (miliseconds).
	-- @impl ubiquitousse
	dt = 0,

	--- Global TimerRegistry.
	-- @impl ubiquitousse
	delayed = {},
	update = function(...) -- If ubiquitousse.signal is available, will be bound to the "update" signal in signal.event.
		return registry_mt.update(timer, ...)
	end,
	run = function(...)
		return registry_mt.run(timer, ...)
	end,
	tween = function(...)
		return registry_mt.tween(timer, ...)
	end,
	clear = function(...)
		return registry_mt.clear(timer, ...)
	end
}

-- Bind signals
if signal then
	signal.event:bind("update", timer.update)
end

return timer