/ld27

-- Class: Emitter

-- An emitter periodically emits sprites with varying properties --

-- for example, velocity. These are set with the emitter's min and

-- max properties. For example, you could set the x velocity of

-- particles to range between -100 and 100 with these statements:

--

-- > emitter.min.velocity.x = -100

-- > emitter.max.velocity.x = 100

--

-- Properties can descend two levels deep at most.

--

-- You can specify any property in min and max, and it will be set

-- on sprites as they are emitted. Mins and maxes can only be used

-- with numeric properties.

--

-- Particles when emitted will appear at a random spot inside the

-- rectangle defined by the emitter's x, y, width, and height

-- properties.

--

-- Because emitters are <Group> subclasses, all particles appear at

-- the same z index onscreen. This also means that setting active,

-- visible, and solid properties on the emitter will affect all particles.

--

-- Any sprite may be used as a particle. When a sprite is added as

-- a particle, its die() method is called. When emitted, revive() is

-- called on it. If you want a particle to remain invisible after being

-- emitted, for example, then write an onEmit method on your sprite to do so.

--

-- Extends:

--		<Group>

--

-- Event: onEmit

-- Called on both the parent emitter and the emitted sprite

-- when it is emitted. If multiple particles are emitted at once, the

-- emitter will receive multiple onEmit events.

Emitter = Group:extend{

	-- Property: x

	-- The x coordinate of the upper-left corner of the rectangle where particles may appear.

	x = 0,

	-- Property: y

	-- The y coordinate of the upper-left corner of the rectangle where particles may appear.

	y = 0,

	-- Property: width

	-- The width of the rectangle where particles may appear.

	width = 0,

	-- Property: height

	-- The height of the retangle where particles may appear.

	height = 0,

	-- Property: emitting

	-- Boolean whether this emitter is actually emitting particles.

	emitting = true,

	-- Property: period

	-- How long, in seconds, the emitter should wait before emitting.

	period = math.huge,

	-- Property: emitCount

	-- How many particles to emit at once.

	emitCount = 1,

	-- Property: min

	-- Minimum numeric properties for particles.

	min = {},

	-- Property: max

	-- Maximum numeric properties for particles.

	max = {},

	-- Property: emitTimer

	-- Used to keep track of when the next emit should take place.

	-- To restart the timer, set it to 0. To immediately force a particle

	-- to be emitted, set it to the emitter's period property. (Although

	-- you should probably call emit() instead.)

	emitTimer = 0,

	-- which particle to emit next

	_emitIndex = 1,

	-- Method: loadParticles

	-- Creates a number of particles to use based on a class.

	-- This calls new() on the particle class with no arguments.

	--

	-- Arguments:

	--		class - class object to instantiate

	--		count - number of particles to create

	--

	-- Returns:

	--		nothing

	loadParticles = function (self, class, count)

		for i = 1, count do

			self:add(class:new())

		end

	end,

	-- Method: emit

	-- Emits one or more particles. This ignores the emitting property.

	-- If no particles are ready to be emitted, this does nothing. 

	--

	-- Arguments:

	--		count - how many particles to emit, default 1

	--

	-- Returns:

	--		emitted particle

	emit = function (self, count)

		count = count or 1

		if #self.sprites == 0 then return end

		for i = 1, count do

			local emitted = self.sprites[self._emitIndex]

			self._emitIndex = self._emitIndex + 1

			if self._emitIndex > #self.sprites then self._emitIndex = 1 end

			-- revive it and set properties

			emitted:revive()

			emitted.x = math.random(self.x, self.x + self.width)

			emitted.y = math.random(self.y, self.y + self.height)

			for key, _ in pairs(self.min) do

				if self.max[key] then

					-- simple case, single value

					if type(self.min[key]) == 'number' then

						emitted[key] = self.min[key] + math.random() * (self.max[key] - self.min[key])

					end

					-- complicated case, table

					if type(self.min[key]) == 'table' then

						for subkey, _ in pairs(self.min[key]) do

							if type(self.min[key][subkey]) == 'number' then

								emitted[key][subkey] = self.min[key][subkey] + math.random() *

													   (self.max[key][subkey] - self.min[key][subkey])

							end

						end

					end

				end

			end

			if emitted.onEmit then emitted:onEmit(self) end

			if self.onEmit then self:onEmit(emitted) end

		end

	end,

	-- Method: explode

	-- This emits many particles simultaneously then immediately stops any further

	-- emissions. If you want to keep the emitter going, call emitter.emit(#emitter.sprites).

	--

	-- Arguments:

	--		count - number of particles to emit, defaults to all of them

	--

	-- Returns:

	--		nothing

	explode = function (self, count)

		count = count or #self.sprites

		self:emit(count)

		self.emitting = false

	end,

	-- Method: extinguish

	-- This immediately calls die() on all particles, then the emitter itself.

	-- This differs from a regular die() call in that if you call revive() on the

	-- emitter later, particles will not appear where they last left off.

	--

	-- Arguments:

	--		none

	--

	-- Returns:

	--		nothing

	extinguish = function (self)

		for _, spr in pairs(self.sprites) do

			spr:die()

		end

		self:die()

	end,

	update = function (self, elapsed)

		if not self.active then return end

		if self.emitting then

			self.emitTimer = self.emitTimer + elapsed

			if self.emitTimer > self.period then

				self:emit(self.emitCount)

				self.emitTimer = self.emitTimer - self.period

			end

		end

		Group.update(self, elapsed)

	end,

	add = function (self, sprite)

		sprite:die()

		Group.add(self, sprite)

	end,

	__tostring = function (self)

		local result = 'Emitter (x: ' .. self.x .. ', y: ' .. self.y ..

					   ', w: ' .. self.width .. ', h: ' .. self.height .. ', '

		if self.emitting then

			result = result .. 'emitting with period ' .. self.period .. ', '

		else

			result = result .. 'not emitting, '

		end

		return result

	end

}