feat(preload): Add a menu script

Closes #26.

Signed-off-by: Rahix <rahix@rahix.de>

preload/menu.py

+"""
+Menu Script
+===========
+You can customize this script however you want :)  If you want to go back to
+the default version, just delete this file; the firmware will recreate it on
+next run.
+"""
+import buttons
+import color
+import display
+import os
+
+
+def list_apps():
+    """Create a list of available apps."""
+    apps = sorted(os.listdir("."))
+
+    # Filter for apps
+    apps = [app for app in apps if app.endswith(".elf") or app.endswith(".py")]
+
+    if "menu.py" in apps:
+        apps.remove("menu.py")
+
+    return apps
+
+
+def button_events():
+    """Iterate over button presses (event-loop)."""
+    yield 0
+    button_pressed = False
+    while True:
+        v = buttons.read(buttons.BOTTOM_LEFT | buttons.BOTTOM_RIGHT | buttons.TOP_RIGHT)
+
+        if v == 0:
+            button_pressed = False
+
+        if not button_pressed and v & buttons.BOTTOM_LEFT != 0:
+            button_pressed = True
+            yield buttons.BOTTOM_LEFT
+
+        if not button_pressed and v & buttons.BOTTOM_RIGHT != 0:
+            button_pressed = True
+            yield buttons.BOTTOM_RIGHT
+
+        if not button_pressed and v & buttons.TOP_RIGHT != 0:
+            button_pressed = True
+            yield buttons.TOP_RIGHT
+
+
+COLOR1, COLOR2 = (color.CHAOSBLUE_DARK, color.CHAOSBLUE)
+
+
+def draw_menu(disp, applist, idx, offset):
+    disp.clear()
+
+    # Wrap around the app-list and draw entries from idx - 3 to idx + 4
+    for y, i in enumerate(range(len(applist) + idx - 3, len(applist) + idx + 4)):
+        disp.print(
+            " " + applist[i % len(applist)] + "      ",
+            posy=offset + y * 20 - 40,
+            bg=COLOR1 if i % 2 == 0 else COLOR2,
+        )
+
+    disp.print(">", posy=20, fg=color.COMMYELLOW, bg=COLOR1 if idx % 2 == 0 else COLOR2)
+    disp.update()
+
+
+def main():
+    disp = display.open()
+    applist = list_apps()
+    numapps = len(applist)
+    current = 0
+    for ev in button_events():
+        if ev == buttons.BOTTOM_RIGHT:
+            # Scroll down
+            draw_menu(disp, applist, current, -8)
+            current = (current + 1) % numapps
+        elif ev == buttons.BOTTOM_LEFT:
+            # Scroll up
+            draw_menu(disp, applist, current, 8)
+            current = (current + numapps - 1) % numapps
+        elif ev == buttons.TOP_RIGHT:
+            # Select & start
+            disp.clear().update()
+            disp.close()
+            try:
+                os.exec(applist[current])
+            except OSError as e:
+                print("Loading failed: ", e)
+                os.exit(1)
+
+        draw_menu(disp, applist, current, 0)
+
+
+if __name__ == "__main__":
+    main()