From ffc148b4bf413f45cff4fd35be05301ce9939641 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Ritzl?= <bjorn.ritzl@gmail.com>
Date: Sun, 3 Jun 2018 17:32:13 +0200
Subject: [PATCH] Added preload()

---
 README.md           |  8 ++++++++
 monarch/monarch.lua | 41 +++++++++++++++++++++++++++++++++++++++--
 2 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index 7acfcd7..8770903 100644
--- a/README.md
+++ b/README.md
@@ -227,6 +227,14 @@ Go back to a previous Monarch screen
 * ```callback``` (function) - Optional function to call when the previous screen is visible.
 
 
+### monarch.preload(screen_id, [callback])
+Preload a Monarch screen. This will load but not enable the screen. This is useful for content heavy screens that you wish to be able to show without having to wait for it load.
+
+**PARAMETERS**
+* ```screen_id``` (hash) - Id of the screen to preload.
+* ```callback``` (function) - Optional function to call when the new screen is preloaded.
+
+
 ### monarch.data(screen_id)
 Get the data associated with a screen (from a call to ```monarch.show()``` or ```monarch.back()```).
 
diff --git a/monarch/monarch.lua b/monarch/monarch.lua
index b36e60f..bfe63af 100644
--- a/monarch/monarch.lua
+++ b/monarch/monarch.lua
@@ -253,10 +253,17 @@ local function show_in(screen, previous_screen, reload, cb)
 			log("show_in() reloading", screen.id)
 			unload(screen)
 		end
+		-- if the screen has been preloaded we need to enable it
+		if screen.preloaded then
+			log("show_in() screen was preloaded", screen.id)
+			msg.post(screen.proxy, ENABLE)
+			screen.loaded = true
+			screen.preloaded = false
 		-- the screen could be loaded if the previous screen was a popup
 		-- and the popup asked to show this screen again
 		-- in that case we shouldn't attempt to load it again
-		if not screen.loaded then
+		elseif not screen.loaded then
+			log("show_in() loading screen", screen.id)
 			async_load(screen)
 		end
 		stack[#stack + 1] = screen
@@ -275,7 +282,13 @@ local function back_in(screen, previous_screen, cb)
 	co = coroutine.create(function()
 		screen.co = co
 		change_context(screen)
-		if not screen.loaded then
+		if screen.preloaded then
+			log("back_in() screen was preloaded", screen.id)
+			msg.post(screen.proxy, ENABLE)
+			screen.preloaded = false
+			screen.loaded = true
+		elseif not screen.loaded then
+			log("back_in() loading screen", screen.id)
 			async_load(screen)
 		end
 		if previous_screen and not previous_screen.popup then
@@ -413,6 +426,30 @@ function M.back(data, cb)
 	end
 end
 
+--- Preload a screen. This will load but not enable and show a screen. Useful for "heavier" screens
+-- that you wish to show without any delay.
+-- @param id (string|hash) - Id of the screen to preload
+-- @param cb (function) - Optional callback to invoke when screen is loaded
+function M.preload(id, cb)
+	assert(id, "You must provide a screen id")
+	id = tohash(id)
+	assert(screens[id], ("There is no screen registered with id %s"):format(tostring(id)))
+
+	local screen = screens[id]
+	local co
+	co = coroutine.create(function()
+		screen.co = co
+		change_context(screen)
+		screen.wait_for = PROXY_LOADED
+		msg.post(screen.proxy, ASYNC_LOAD)
+		coroutine.yield()
+		screen.preloaded = true
+		screen.wait_for = nil
+		if cb then cb() end
+	end)
+	coroutine.resume(co)
+end
+
 
 function M.on_message(message_id, message, sender)
 	if message_id == PROXY_LOADED then