Merge plugin back into main repository (#49)

plugin/src/Reconciler.lua

@@ -0,0 +1,203 @@
+local RouteMap = require(script.Parent.RouteMap)
+
+local function classEqual(rbx, className)
+	if className == "*" then
+		return true
+	end
+
+	return rbx.ClassName == className
+end
+
+local function reparent(rbx, parent)
+	if rbx then
+		-- It's possible that 'rbx' is a service or some other object that we
+		-- can't change the parent of. That's the only reason why Parent would
+		-- fail except for rbx being previously destroyed!
+		pcall(function()
+			rbx.Parent = parent
+		end)
+	end
+end
+
+--[[
+	Attempts to match up Roblox instances and object specifiers for
+	reconciliation.
+
+	An object is considered a match if they have the same Name and ClassName.
+
+	primaryChildren and secondaryChildren can each be either a list of Roblox
+	instances or object specifiers. Since they share a common shape, switching
+	the two around isn't problematic!
+
+	visited is expected to be an empty table initially. It will be filled with
+	the set of children that have been visited so far.
+]]
+local function findNextChildPair(primaryChildren, secondaryChildren, visited)
+	for _, primaryChild in ipairs(primaryChildren) do
+		if not visited[primaryChild] then
+			visited[primaryChild] = true
+
+			for _, secondaryChild in ipairs(secondaryChildren) do
+				if primaryChild.ClassName == secondaryChild.ClassName and primaryChild.Name == secondaryChild.Name then
+					visited[secondaryChild] = true
+
+					return primaryChild, secondaryChild
+				end
+			end
+
+			return primaryChild, nil
+		end
+	end
+
+	return nil, nil
+end
+
+local Reconciler = {}
+Reconciler.__index = Reconciler
+
+function Reconciler.new()
+	local reconciler = {
+		_routeMap = RouteMap.new(),
+	}
+
+	setmetatable(reconciler, Reconciler)
+
+	return reconciler
+end
+
+--[[
+	A semi-smart algorithm that attempts to apply the given item's children to
+	an existing Roblox object.
+]]
+function Reconciler:_reconcileChildren(rbx, item)
+	local visited = {}
+	local rbxChildren = rbx:GetChildren()
+
+	-- Reconcile any children that were added or updated
+	while true do
+		local itemChild, rbxChild = findNextChildPair(item.Children, rbxChildren, visited)
+
+		if not itemChild then
+			break
+		end
+
+		reparent(self:reconcile(rbxChild, itemChild), rbx)
+	end
+
+	-- Reconcile any children that were deleted
+	while true do
+		local rbxChild, itemChild = findNextChildPair(rbxChildren, item.Children, visited)
+
+		if not rbxChild then
+			break
+		end
+
+		reparent(self:reconcile(rbxChild, itemChild), rbx)
+	end
+end
+
+--[[
+	Construct a new Roblox object from the given item.
+]]
+function Reconciler:_reify(item)
+	local className = item.ClassName
+
+	-- "*" represents a match of any class. It reifies as a folder!
+	if className == "*" then
+		className = "Folder"
+	end
+
+	local rbx = Instance.new(className)
+	rbx.Name = item.Name
+
+	for key, property in pairs(item.Properties) do
+		-- TODO: Check for compound types, like Vector3!
+		rbx[key] = property.Value
+	end
+
+	self:_reconcileChildren(rbx, item)
+
+	if item.Route then
+		self._routeMap:insert(item.Route, rbx)
+	end
+
+	return rbx
+end
+
+--[[
+	Apply the changes represented by the given item to a Roblox object that's a
+	child of the given instance.
+]]
+function Reconciler:reconcile(rbx, item)
+	-- Item was deleted
+	if not item then
+		if rbx then
+			rbx:Destroy()
+		end
+
+		return nil
+	end
+
+	-- Item was created!
+	if not rbx then
+		return self:_reify(item)
+	end
+
+	-- Item changed type!
+	if not classEqual(rbx, item.ClassName) then
+		rbx:Destroy()
+
+		rbx = self:_reify(item)
+	end
+
+	-- Apply all properties, Roblox will de-duplicate changes
+	for key, property in pairs(item.Properties) do
+		-- TODO: Transform property value based on property.Type
+		-- Right now, we assume that 'value' is primitive!
+
+		rbx[key] = property.Value
+	end
+
+	-- Use a dumb algorithm for reconciling children
+	self:_reconcileChildren(rbx, item)
+
+	return rbx
+end
+
+function Reconciler:reconcileRoute(route, item, itemRoute)
+	local parent
+	local rbx = game
+
+	for i = 1, #route do
+		local piece = route[i]
+
+		local child = rbx:FindFirstChild(piece)
+
+		-- We should get services instead of making folders here.
+		if rbx == game and not child then
+			local _
+			_, child = pcall(game.GetService, game, piece)
+		end
+
+		-- We don't want to create a folder if we're reaching our target item!
+		if not child and i ~= #route then
+			child = Instance.new("Folder")
+			child.Parent = rbx
+			child.Name = piece
+		end
+
+		parent = rbx
+		rbx = child
+	end
+
+	-- Let's check the route map!
+	if not rbx then
+		rbx = self._routeMap:get(itemRoute)
+	end
+
+	rbx = self:reconcile(rbx, item)
+
+	reparent(rbx, parent)
+end
+
+return Reconciler