From 9f4c03a1363785155df284d1a0f53d33c77ba385 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=89tienne=20Reuh=20Fildadut?= <fildadut@reuh.eu>
Date: Thu, 24 Jun 2021 16:24:54 +0200
Subject: [PATCH] Add callback, children, timer example systems

---
 ecs/callback.can | 35 ++++++++++++++++++++++++++++++++++
 ecs/children.can | 49 ++++++++++++++++++++++++++++++++++++++++++++++++
 ecs/timer.can    | 35 ++++++++++++++++++++++++++++++++++
 3 files changed, 119 insertions(+)
 create mode 100644 ecs/callback.can
 create mode 100644 ecs/children.can
 create mode 100644 ecs/timer.can

diff --git a/ecs/callback.can b/ecs/callback.can
new file mode 100644
index 0000000..dcd62f0
--- /dev/null
+++ b/ecs/callback.can
@@ -0,0 +1,35 @@
+--- Callback system
+-- Allow to call callbacks defined in other systems in entity methods.
+-- Example:
+-- entity.callback:onMove(...) -- call onAdd(system, entitySystemTable, ...) on every system the entity belong to (which has this callback)
+-- Can be also used for onAdd, etc.
+
+--- Recursively get a list of systems with a certain method.
+let recGetSystemsWithMethod = (method, systems, l={})
+	for _, s in ipairs(systems) do
+		if s[method] then
+			table.insert(l, s)
+		end
+		recGetSystemsWithMethod(method, s.systems, l)
+	end
+	return l
+end
+
+return {
+	name = "callback",
+	filter = true,
+	methods = {
+		__index = :(c, k)
+			let s = recGetSystemsWithMethod(k, {@world})
+			@methods[k] = :(c, ...)
+				let e = c.entity
+				for _, sys in ipairs(s) do
+					if sys._previous[e] then
+						sys[k](sys, e[sys.name], ...)
+					end
+				end
+			end
+			return @_methods_mt[k]
+		end
+	}
+}
diff --git a/ecs/children.can b/ecs/children.can
new file mode 100644
index 0000000..b7fa482
--- /dev/null
+++ b/ecs/children.can
@@ -0,0 +1,49 @@
+--- Children system
+-- Allow to build a hierarchy between entities.
+-- Children are stored directly in the .children entity table: they are added when their parent is added, and removed when it is removed from the world.
+
+return {
+	name = "children",
+	filter = true,
+	default = {
+		parent = nil, -- reference to parent entity, if any
+		-- ... list of children
+	},
+	methods = {
+		--- Add a new entity to the world, using this entity as a parent.
+		add = :(c, o)
+			if not o.children then
+				o.children = {}
+			end
+			o.children.parent = c.entity
+			table.insert(c, o)
+			@world:add(o)
+		end,
+		--- Remove an entity from the world and from this entity's children.
+		remove = :(c, o)
+			@world:remove(o)
+			for i=#c, 1, -1 do
+				if c[i] == o then
+					table.remove(c, i)
+					break
+				end
+			end
+			o.children.parent = nil
+		end
+	},
+	onAdd = :(c)
+		for _, o in ipairs(c) do
+			o.children.parent = c.entity
+			@world:add(o)
+		end
+	end,
+	onRemove = :(c)
+		for _, o in ipairs(c) do
+			@world:remove(o)
+			o.children.parent = nil
+		end
+		if c.parent then
+			c.parent.children:remove(c.entity)
+		end
+	end
+}
diff --git a/ecs/timer.can b/ecs/timer.can
new file mode 100644
index 0000000..52405e8
--- /dev/null
+++ b/ecs/timer.can
@@ -0,0 +1,35 @@
+--- Timer system
+-- Handles ubiquitousse timers.
+
+let timer = require((...):match("^(.-)ecs%.timer").."scene")
+
+return {
+	name = "timer",
+	filter = "timer",
+	default = {
+		-- timer object
+	},
+	process = :(t, dt)
+		t:update(dt)
+		if t:dead() then
+			@world:remove(t.entity)
+		end
+	end,
+	--- System methods ---
+	--- Add a new timer
+	run = :(func)
+		local t = timer.run(func)
+		@world:add {
+			timer = t
+		}
+		return t
+	end,
+	--- Add a new tween
+	tween = :(duration, tbl, to, method)
+		local t = timer.tween(duration, tbl, to, method)
+		@world:add {
+			timer = t
+		}
+		return t
+	end
+}