SelectionGet.luau

--!strict
local ScriptEditorService = game:GetService("ScriptEditorService")
local Selection = game:GetService("Selection")
local ALIAS = "game.Selection:Get()[%s]"

type AutocompleteItem = {
	label: string,
	kind: Enum.CompletionItemKind?,
	tags: { Enum.CompletionItemTag }?,
	detail: string?,

	documentation: {
		value: string,
	}?,

	overloads: number?,
	learnMoreLink: string?,
	codeSample: string?,
	preselect: boolean?,

	textEdit: {
		newText: string,
		replace: {
			start: { line: number, character: number },
			["end"]: { line: number, character: number },
		},
	}?,
}

type AutocompleteResponse = {
	items: { AutocompleteItem },
}

type AutocompleteRequest = {
	position: {
		line: number,
		character: number,
	},

	textDocument: {
		document: ScriptDocument?,
		script: LuaSourceContainer?,
	},
}

local function snippetCallback(request: AutocompleteRequest, response: AutocompleteResponse)
	local textDoc = request.textDocument
	local scriptDoc = textDoc.document
	
	if not scriptDoc then
		return response
	end
	
	if not scriptDoc:IsCommandBar() then
		if scriptDoc:GetScript() ~= nil then
			return response
		end
	end

	local line = scriptDoc:GetLine()

	if line:sub(-5) == "for _" then
		-- Typing a placeholder, ignore
		return response
	end

	local pos = request.position
	local startAt, endAt, index = line:find("_(%d+)$")

	if startAt and endAt and index then
		local num = tonumber(index)
		local selected = Selection:Get()
		
		local target = num and selected[num]
		local pathTo: string?
		
		if target and target:IsDescendantOf(game) then
			local parent = target.Parent
			local child = parent and parent:FindFirstChild(target.Name)
			
			if child == target then
				local at = target
				local path = ""
				
				while at and at ~= game do
					if at.Name:match("^[A-z_][A-z0-9_]+$") then
						path = `.{at.Name}{path}`
					else
						path = `["{at.Name}"]{path}`
					end
					
					at = at.Parent
				end
				
				if path:sub(1, 10) == ".Workspace" then
					path = "w" .. path:sub(3)
				else
					path = "game" .. path
				end
				
				pathTo = path
			end
		end
		
		local alias = ALIAS:format(index)
		
		if pathTo then
			table.insert(response.items, {
				label = `_{index} (Direct Path)`,
				kind = Enum.CompletionItemKind.Snippet,
				detail = "Direct Path",

				documentation = {
					value = `<code>{alias}</code> as:<br><code>{pathTo}</code>`,
				},

				textEdit = {
					newText = pathTo,

					replace = {
						start = {
							line = pos.line,
							character = startAt,
						},

						["end"] = {
							line = pos.line,
							character = endAt + 1,
						},
					},
				},
			})
		end
		
		table.insert(response.items, {
			label = `_{index} (Selection Alias)`,
			kind = Enum.CompletionItemKind.Snippet,
			detail = "Selection Alias",

			documentation = {
				value = `Exactly: <code>{alias}</code>`,
			},	

			textEdit = {
				newText = alias,

				replace = {
					start = {
						line = pos.line,
						character = startAt,
					},

					["end"] = {
						line = pos.line,
						character = endAt + 1,
					},
				},
			},
		})
	elseif line:sub(-1) == "_" then
		table.insert(response.items, {
			label = "_#",
			kind = Enum.CompletionItemKind.Folder,
			detail = "(Hint)",

			documentation = {
				value = `Type a number after an underscore to auto-complete {ALIAS:format("#")}`,
			},

			textEdit = {
				newText = "",

				replace = {
					start = pos,
					["end"] = pos,
				},
			},
		})
	end

	return response
end

pcall(function()
	-- If testing, deregister the existing callback.
	ScriptEditorService:DeregisterAutocompleteCallback(ALIAS)
end)

ScriptEditorService:RegisterAutocompleteCallback(ALIAS, 1000, snippetCallback)

dude, fuck yes.