fix(main): Make upgrade from tag directories more ergonomical

As we don't have an API to upload files and create playlists yet, we
used the convention "tag uid as directory name" to allow testing
playback. With the introduction of the database in #39 "Add playlist db"
a builddb() function to initialize the database from the tag directories
was added, but it is not automatically called. To make the developer
experience more ergonomical, add a check for that automatically runs
builddb() when no database exists.

Signed-off-by: Matthias Blankertz <matthias@blankertz.org>

software/src/main.py

@@ -3,8 +3,10 @@
 
 import aiorepl  # type: ignore
 import asyncio
+from errno import ENOENT
 import machine
 import micropython
+import os
 import time
 from math import pi, sin, pow
 
@@ -54,6 +56,9 @@ async def rainbow(np, period=10):
 machine.mem32[0x40030000 + 0x00] = 0x10
 
 
+DB_PATH = '/sd/tonberry.db'
+
+
 def run():
     asyncio.new_event_loop()
     # Setup LEDs
@@ -62,27 +67,36 @@ def run():
 
     # Setup MP3 player
     with SDContext(mosi=hwconfig.SD_DI, miso=hwconfig.SD_DO, sck=hwconfig.SD_SCK, ss=hwconfig.SD_CS,
-                   baudrate=hwconfig.SD_CLOCKRATE), \
-         BTreeFileManager('/sd/tonberry.db') as playlistdb, \
-         AudioContext(hwconfig.I2S_DIN, hwconfig.I2S_DCLK, hwconfig.I2S_LRCLK) as audioctx:
+                   baudrate=hwconfig.SD_CLOCKRATE):
+        # Temporary hack: build database from folders if no database exists
+        # Can be removed once playlists can be created via API
+        try:
+            _ = os.stat(DB_PATH)
+        except OSError as ex:
+            if ex.errno == ENOENT:
+                print("No playlist DB found, trying to build DB from tag dirs")
+                builddb()
 
-        # Setup NFC
-        reader = MFRC522(spi_id=hwconfig.RC522_SPIID, sck=hwconfig.RC522_SCK, miso=hwconfig.RC522_MISO,
-                         mosi=hwconfig.RC522_MOSI, cs=hwconfig.RC522_SS, rst=hwconfig.RC522_RST, tocard_retries=20)
+        with BTreeFileManager(DB_PATH) as playlistdb, \
+             AudioContext(hwconfig.I2S_DIN, hwconfig.I2S_DCLK, hwconfig.I2S_LRCLK) as audioctx:
 
-        # Setup app
-        deps = app.Dependencies(mp3player=lambda the_app: MP3Player(audioctx, the_app),
-                                nfcreader=lambda the_app: Nfc(reader, the_app),
-                                buttons=lambda the_app: Buttons(the_app, pin_volup=hwconfig.BUTTON_VOLUP,
-                                                                pin_voldown=hwconfig.BUTTON_VOLDOWN,
-                                                                pin_next=hwconfig.BUTTON_NEXT),
-                                playlistdb=lambda _: playlistdb)
-        the_app = app.PlayerApp(deps)
+            # Setup NFC
+            reader = MFRC522(spi_id=hwconfig.RC522_SPIID, sck=hwconfig.RC522_SCK, miso=hwconfig.RC522_MISO,
+                             mosi=hwconfig.RC522_MOSI, cs=hwconfig.RC522_SS, rst=hwconfig.RC522_RST, tocard_retries=20)
 
-        # Start
-        asyncio.create_task(aiorepl.task({'timer_manager': TimerManager(),
-                                          'app': the_app}))
-        asyncio.get_event_loop().run_forever()
+            # Setup app
+            deps = app.Dependencies(mp3player=lambda the_app: MP3Player(audioctx, the_app),
+                                    nfcreader=lambda the_app: Nfc(reader, the_app),
+                                    buttons=lambda the_app: Buttons(the_app, pin_volup=hwconfig.BUTTON_VOLUP,
+                                                                    pin_voldown=hwconfig.BUTTON_VOLDOWN,
+                                                                    pin_next=hwconfig.BUTTON_NEXT),
+                                    playlistdb=lambda _: playlistdb)
+            the_app = app.PlayerApp(deps)
+
+            # Start
+            asyncio.create_task(aiorepl.task({'timer_manager': TimerManager(),
+                                              'app': the_app}))
+            asyncio.get_event_loop().run_forever()
 
 
 def builddb():
@@ -90,10 +104,11 @@ def builddb():
     For testing, build a playlist db based on the previous tag directory format.
     Can be removed once uploading files / playlist via the web api is possible.
     """
-    import os
-
-    os.unlink('/sd/tonberry.db')
-    with BTreeFileManager('/sd/tonberry.db') as db:
+    try:
+        os.unlink(DB_PATH)
+    except OSError:
+        pass
+    with BTreeFileManager(DB_PATH) as db:
         for name, type_, _, _ in os.ilistdir(b'/sd'):
             if type_ != 0x4000:
                 continue