From 380295c94d7421194e1c6083d20cf30b55a69768 Mon Sep 17 00:00:00 2001
From: Iron-E <code.iron.e@gmail.com>
Date: Mon, 25 May 2020 19:58:25 -0400
Subject: [PATCH] Initial PromptLayer implementation

---
 lua/libmodal/src/PromptLayer.lua | 101 +++++++++++++++++++++++++++++++
 1 file changed, 101 insertions(+)

diff --git a/lua/libmodal/src/PromptLayer.lua b/lua/libmodal/src/PromptLayer.lua
index e69de29..fdd68dc 100644
--- a/lua/libmodal/src/PromptLayer.lua
+++ b/lua/libmodal/src/PromptLayer.lua
@@ -0,0 +1,101 @@
+--[[
+	/*
+	 * IMPORTS
+	 */
+--]]
+
+local classes = require('libmodal/src/classes')
+
+--[[
+	/*
+	 * MODULE
+	 */
+--]]
+
+local PromptLayer = {['TYPE'] = 'libmodal-prompt-layer'}
+
+--[[
+	/*
+	 * META `PromptLayer`
+	 */
+--]]
+
+local _metaPromptLayer = classes.new(PromptLayer.TYPE)
+
+-------------------------------
+--[[ SUMMARY:
+	* Enter the `PromptLayer`, replacing any conflicting executes.
+]]
+-------------------------------
+function _metaPromptLayer:enter()
+	-- Create aliases.
+	local layerPrompt      = self._prompt
+	local layerInstruction = self._instruction
+
+	-- Create a new `priorInstruction`.
+	local priorInstruction = nil
+
+	if self._isTable then -- the layer is a table
+		local promptInstruction = prompt._instruction
+		priorInstruction = {}
+
+		for command, execute in pairs(layerInstruction) do
+			priorInstruction[command] = promptInstruction[command]
+			promptInstruction[command]  = execute
+		end
+	else -- the layer is a function
+		priorInstruction  = layerPrompt._instruction
+		prompt._instruction = layerInstruction
+	end
+
+	self._priorInstruction = priorInstruction
+end
+
+-------------------------------
+--[[ SUMMARY:
+	* Exit the `PromptLayer`, and restore any overwritten executes.
+]]
+-------------------------------
+function _metaPromptLayer:exit()
+	if self._isTable then
+		local promptInstruction  = self._prompt._instruction
+
+		for command, execute in pairs(self._priorInstruction) do
+			promptInstruction[command] = execute
+		end
+	else
+		self._prompt._instruction = self._priorInstruction
+	end
+
+	self._priorInstruction = nil
+end
+
+--[[
+	/*
+	 * CLASS `PromptLayer`
+	 */
+--]]
+
+-----------------------------------------
+--[[ SUMMARY:
+	* Create a new `PromptLayer`.
+]]
+-----------------------------------------
+function PromptLayer.new(prompt, instruction)
+	if classes.type(prompt) == require('libmodal/src/Prompt').TYPE
+		and type(prompt._instruction) == type(instruction)
+	then
+		return setmetatable(
+			{
+				['_isTable'] = type(instruction) == require('libmodal/src/globals').TYPE_TBL,
+				['_instruction'] = instruction,
+				['_prompt']        = prompt
+			}, _metaPromptLayer
+		)
+	else
+		error('Either `prompt` is not a `Prompt`, '
+			.. 'or `instruction` is not the same type '
+			.. 'as it was when `prompt` was created.'
+		)
+	end
+end