From 4f450ca94522f5c26a631fc4d19bd6eec420cbec Mon Sep 17 00:00:00 2001
From: sanine-a <sanine.not@pm.me>
Date: Tue, 28 Mar 2023 13:15:27 -0500
Subject: implement EntityDb

---
 honey/ecs.lua | 108 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 107 insertions(+), 1 deletion(-)

(limited to 'honey/ecs.lua')

diff --git a/honey/ecs.lua b/honey/ecs.lua
index b4def84..62acce0 100644
--- a/honey/ecs.lua
+++ b/honey/ecs.lua
@@ -5,28 +5,41 @@ setfenv(1, module)
 
 --===== Components =====--
 
+-- Components provide a kind-of-type-safe way of storing values, since they are
+-- guaranteed to have a specific set of keys and no other values in them. They also serialize
+-- nicely for storage.
+
 Component = {}
 
 function Component.newFactory(name, params, serialize)
+	-- create the metatable for this component type
 	local metatable = {}
-	metatable.__tostring = serialize or Component.serialize
+	metatable.__tostring = serialize or Component.serialize -- nice serialization
 	metatable.__newindex = function(tbl, index, value)
 		if params[index] ~= nil then
 			tbl[index] = value
 		else
+			-- throw an error if we try to set a key that is not in the valid set
 			error(string.format("%q is not a valid key for a component of type %q", index, name))
 		end
 	end
+
+	-- the factory function for creating components
 	return function(tbl)
 		local tbl = tbl or {}
 		local self = { __type=name }
+
+		-- ensure that all keys are present
 		for k, v in pairs(params) do
 			self[k] = v
 		end
 		setmetatable(self, metatable)
+
+		-- set the keys from the factory call
 		for k, v in pairs(tbl) do
 			self[k] = v
 		end
+
 		return self
 	end
 end
@@ -45,4 +58,97 @@ function Component.serialize(self)
 	return str
 end
 
+
+--===== EntityDb =====--
+
+EntityDb = {}
+EntityDb.__index = EntityDb
+
+
+function EntityDb.new(_)
+	local self = {
+		entities = {},
+		components = {},
+	}
+	setmetatable(self, EntityDb)
+	return self
+end
+setmetatable(EntityDb, {__call=EntityDb.new})
+
+
+function EntityDb.checkIsValid(self, id)
+	if not self.entities[id] then
+		error(string.format("invalid entity id: 0x%x", id))
+	end
+end
+
+
+local guid = (function()
+	local id = 0
+	return function() id=id+1 return id end
+end)()
+function EntityDb.createEntity(self)
+	local id = guid()
+	self.entities[id] = true
+	return id
+end
+
+
+function EntityDb.addComponent(self, id, name, value)
+	self:checkIsValid(id)
+	if not self.components[name] then
+		self.components[name] = { count=0 }
+	end
+
+	local component = self.components[name]
+	component[id] = value
+	component.count = component.count + 1
+end
+
+
+local function shallowCopy(tbl)
+	local copy = {}
+	for k, v in pairs(tbl) do copy[k] = v end
+	return copy
+end
+
+
+function EntityDb.queryComponent(self, name)
+	local query = shallowCopy(self.components[name])
+	query.count = nil
+	return query
+end
+
+
+function EntityDb.queryEntity(self, id)
+	self:checkIsValid(id)
+	local query = {}
+	for name, component in pairs(self.components) do
+		query[name] = component[id]
+	end
+	return query
+end
+
+
+function EntityDb.removeComponent(self, id, name)
+	self:checkIsValid(id)
+	local component = self.components[name]
+	if component[id] ~= nil then
+		component[id] = nil
+		component.count = component.count - 1
+		if component.count == 0 then
+			self.components[name] = nil
+		end
+	end
+end
+
+
+function EntityDb.deleteEntity(self, id)
+	self:checkIsValid(id)
+	for name in pairs(self.components) do
+		self:removeComponent(id, name)
+	end
+	self.entities[id] = nil
+end
+
 return module
-- 
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