local Reconciler = {}

--[[
	The set of file names that should pass as init files
	These files usurp their parents.
]]
local initNames = {
	["init.lua"] = true,
	["init.server.lua"] = true,
	["init.client.lua"] = true,
}

local function isInit(item, itemFileName)
	if item and item.type == "dir" then
		return
	end

	return initNames[itemFileName] or false
end

--[[
	Determines if the given VFS item has an init file. Yields information about
	the file.
]]
local function findInit(item)
	if item.type ~= "dir" then
		return nil, nil
	end

	for childFileName, childItem in pairs(item.children) do
		if isInit(childItem, childFileName) then
			return childItem, childFileName
		end
	end

	return nil, nil
end

--[[
	Given a VFS item, returns a Name and ClassName for a corresponding Roblox
	instance.

	Doesn't take into account init files.
]]
local function itemToName(item, fileName)
	if item and item.type == "dir" then
		return fileName, "Folder"
	elseif item and item.type == "file" or not item then
		if fileName:find("%.server%.lua$") then
			return fileName:match("^(.-)%.server%.lua$"), "Script"
		elseif fileName:find("%.client%.lua$") then
			return fileName:match("^(.-)%.client%.lua$"), "LocalScript"
		elseif fileName:find("%.lua") then
			return fileName:match("^(.-)%.lua$"), "ModuleScript"
		else
			return fileName, "StringValue"
		end
	else
		error("unknown item type " .. tostring(item.type))
	end
end

--[[
	Given a VFS item, assigns all relevant values (except Name!) to a Roblox
	instance.
]]
local function setValues(rbx, item, fileName)
	local _, className = itemToName(item, fileName)

	if className:find("Script") then
		rbx.Source = item.contents
	else
		rbx.Value = item.contents
	end
end

function Reconciler._reifyShallow(item, fileName)
	if item.type == "dir" then
		local initItem, initFileName = findInit(item)

		if initItem then
			local rbx = Reconciler._reify(initItem, initFileName)
			rbx.Name = fileName

			return rbx
		else
			local rbx = Instance.new("Folder")
			rbx.Name = fileName

			return rbx
		end
	elseif item.type == "file" then
		local objectName, className = itemToName(item, fileName)

		local rbx = Instance.new(className)
		rbx.Name = objectName

		setValues(rbx, item, fileName)

		return rbx
	else
		error("unknown item type " .. tostring(item.type))
	end
end

--[[
	Construct a new Roblox instance tree that corresponds to the given VFS item.
]]
function Reconciler._reify(item, fileName, parent)
	local rbx = Reconciler._reifyShallow(item, fileName)

	if item.type == "dir" then
		for childFileName, childItem in pairs(item.children) do
			if not isInit(childItem, childFileName) then
				local childRbx = Reconciler._reify(childItem, childFileName)
				childRbx.Parent = rbx
			end
		end
	end

	rbx.Parent = parent

	return rbx
end

function Reconciler.reconcile(rbx, item, fileName, parent)
	-- Item was deleted!
	if not item then
		if isInit(item, fileName) then
			if not parent then
				return
			end

			-- Un-usurp parent!
			local newParent = Instance.new("Folder")
			newParent.Name = parent.Name

			for _, child in ipairs(parent:GetChildren()) do
				child.Parent = newParent
			end

			newParent.Parent = parent.Parent
			parent:Destroy()

			return
		else
			if rbx then
				rbx:Destroy()
			end

			return
		end
	end

	if item.type == "dir" then
		-- Folder was created!
		if not rbx then
			return Reconciler._reify(item, fileName, parent)
		end

		local initItem, initFileName = findInit(item)

		if initItem then
			local _, initClassName = itemToName(initItem, initFileName)

			if rbx.ClassName == initClassName then
				setValues(rbx, initItem, initFileName)
			else
				rbx:Destroy()
				return Reconciler._reify(item, fileName, parent)
			end
		else
			if rbx.ClassName ~= "Folder" then
				rbx:Destroy()
				return Reconciler._reify(item, fileName, parent)
			end
		end

		local visitedChildren = {}

		for childFileName, childItem in pairs(item.children) do
			if not isInit(childItem, childFileName) then
				local childName = itemToName(childItem, childFileName)

				visitedChildren[childName] = true

				Reconciler.reconcile(rbx:FindFirstChild(childName), childItem, childFileName, rbx)
			end
		end

		for _, childRbx in ipairs(rbx:GetChildren()) do
			-- Child was deleted!
			if not visitedChildren[childRbx.Name] then
				childRbx:Destroy()
			end
		end

		return rbx
	elseif item.type == "file" then
		if isInit(item, fileName) then
			-- Usurp our container!
			local _, className = itemToName(item, fileName)

			if parent.ClassName == className then
				rbx = parent
			else
				rbx = Reconciler._reify(item, fileName, parent.Parent)
				rbx.Name = parent.Name

				for _, child in ipairs(parent:GetChildren()) do
					child.Parent = rbx
				end

				parent:Destroy()
			end

			setValues(rbx, item, fileName)

			return rbx
		else
			if not rbx then
				return Reconciler._reify(item, fileName, parent)
			end

			local _, className = itemToName(item, fileName)

			if rbx.ClassName ~= className then
				rbx:Destroy()
				return Reconciler._reify(item, fileName, parent)
			end

			setValues(rbx, item, fileName)

			return rbx
		end
	else
		error("unknown item type " .. tostring(item.type))
	end
end

function Reconciler.reconcileRoute(route, item)
	local location = game

	for i = 1, #route - 1 do
		local piece = route[i]
		local newLocation = location:FindFirstChild(piece)

		if not newLocation then
			newLocation = Instance.new("Folder")
			newLocation.Name = piece
			newLocation.Parent = location
		end

		location = newLocation
	end

	local fileName = route[#route]

	local name = itemToName(item, fileName)
	local rbx = location:FindFirstChild(name)
	Reconciler.reconcile(rbx, item, fileName, location)
end

return Reconciler