Corona SDK - on back tap

BackEvent.lua

module("BackEvent", package.seeall)

local composer = require "composer"

local event = {}
local stack = {}
local platform = system.getInfo("platform")

local init
, executeEvent
, openPrevScene
, requestExit
, onKeyEvent

function BackEvent.back()
	if composer.getSceneName("overlay") then
		composer.hideOverlay("fade", 400)
	else		
		if #stack > 1 then
			openPrevScene()
		else
			native.showAlert( "Hey Listen!", "Do you really want to exit?", { "Yes", "No" }, requestExit )
		end
	end
end

function BackEvent.add(listener)
	if not table.isValueExists(event, listener) then
		table.insert(event, listener)
	end
end

function BackEvent.remove(listener)
	local key = table.getKeyByValue(event, listener)

	if key then
		table.remove(event, key)
	end
end

function init()
	for name, super in pairs(composer) do
		if name == "gotoScene" then
			composer[name] = function(...)
				super(...)
				table.insert(stack, {...})
			end
		end

		if name == "removeScene" then
			composer[name] = function(...)
				super(...)
				
				local sceneName = ...
				local stack_id
				
				for i = 1, #stack do
					if table.isValueExists(stack[i], sceneName) then
						stack_id = i
						break
					end
				end

				if stack_id then
					table.remove(stack, stack_id)
				end
			end
		end
	end

	if platform == "android" then
		Runtime:addEventListener("key", onKeyEvent)
	end
end

function executeEvent()
	local isExecuted = true

	for i = 1, #event do
		if not event[i]() then
			isExecuted = false
		end 
	end

	return isExecuted
end

function openPrevScene()
	table.remove(stack, #stack)
	local sceneName = stack[#stack][1]
	local options = stack[#stack][2]

	composer.gotoScene(sceneName, options)
end

function requestExit(event)
	if event.action == "clicked" then
		if event.index == 1 then
			native.requestExit()
		elseif event.index == 2 then

		end
	end
end

function onKeyEvent(event)
	if platform == "android" then
		if event.keyName == "back" then
			if event.phase == "down" then
				if executeEvent() then
					BackEvent.back()
				end
			end
		end

		return true
	end

	return false
end

init()