playlistdb: Implement shuffle

Initial implementation of shuffle with a naive algorithm.

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

software/src/utils/playlistdb.py

@@ -2,6 +2,8 @@
 # Copyright (c) 2025 Matthias Blankertz <matthias@blankertz.org>
 
 import btree
+import random
+import time
 try:
     import typing
     from typing import TYPE_CHECKING, Iterable  # type: ignore
@@ -38,6 +40,39 @@ class BTreeDB(IPlaylistDB):
             self.persist = persist
             self.shuffle = shuffle
             self.length = self.parent._getPlaylistLength(self.tag)
+            self._shuffle()
+
+        def _getPlaylistPos(self):
+            """
+            Gets the position to pass to parent._getPlaylistEntry etc.
+            """
+            if self.shuffle == BTreeDB.SHUFFLE_YES:
+                return self.shuffle_order[self.pos]
+            else:
+                return self.pos
+
+        def _shuffle(self, reshuffle=False):
+            if self.shuffle == BTreeDB.SHUFFLE_NO:
+                return
+
+            self.shuffle_seed = None
+            # Try to get seed from DB if persisted
+            if self.persist != BTreeDB.PERSIST_NO and not reshuffle:
+                self.shuffle_seed = self.parent._getPlaylistShuffleSeed(self.tag)
+            if self.shuffle_seed is None:
+                # Either not persisted or could not read from db
+                self.shuffle_seed = time.ticks_cpu()
+                if self.persist != BTreeDB.PERSIST_NO:
+                    self.parent._setPlaylistShuffleSeed(self.tag, self.shuffle_seed)
+            # TODO: Find an algorithm for shuffling that does not use O(n) memory for playlist of length n
+            random.seed(self.shuffle_seed)
+            entries = list(range(0, self.length))
+            # We don't have random.shuffle in micropython, so emulate it with random.choice
+            self.shuffle_order = []
+            while len(entries) > 0:
+                chosen = random.choice(entries)
+                self.shuffle_order.append(chosen)
+                entries.remove(chosen)
 
         def getPaths(self):
             """
@@ -49,7 +84,7 @@ class BTreeDB(IPlaylistDB):
             """
             Get path of file that should be played.
             """
-            return self.parent._getPlaylistEntry(self.tag, self.pos)
+            return self.parent._getPlaylistEntry(self.tag, self._getPlaylistPos())
 
         def getNextPath(self):
             """
@@ -60,6 +95,7 @@ class BTreeDB(IPlaylistDB):
                 if self.persist != BTreeDB.PERSIST_NO:
                     self.parent._setPlaylistPos(self.tag, self.pos)
                     self.setPlaybackOffset(0)
+                    self._shuffle(True)
                 return None
 
             self.pos += 1
@@ -100,6 +136,10 @@ class BTreeDB(IPlaylistDB):
     def _keyPlaylistShuffle(tag):
         return b''.join([tag, b'/playlistshuffle'])
 
+    @staticmethod
+    def _keyPlaylistShuffleSeed(tag):
+        return b''.join([tag, b'/playlistshuffleseed'])
+
     @staticmethod
     def _keyPlaylistPersist(tag):
         return b''.join([tag, b'/playlistpersist'])
@@ -145,6 +185,17 @@ class BTreeDB(IPlaylistDB):
     def _getPlaylistPosOffset(self, tag: bytes) -> int:
         return int(self.db.get(self._keyPlaylistPosOffset(tag), b'0'))
 
+    def _getPlaylistShuffleSeed(self, tag: bytes) -> int | None:
+        try:
+            return int(self.db[self._keyPlaylistShuffleSeed(tag)])
+        except (ValueError, KeyError):
+            return None
+
+    def _setPlaylistShuffleSeed(self, tag, seed: int, flush=True):
+        self.db[self._keyPlaylistShuffleSeed(tag)] = str(seed).encode()
+        if flush:
+            self._flush()
+
     def _getPlaylistLength(self, tag: bytes) -> int:
         start, end = self._keyPlaylistStartEnd(tag)
         for k in self.db.keys(end, start, btree.DESC):
@@ -178,7 +229,8 @@ class BTreeDB(IPlaylistDB):
             except KeyError:
                 pass
         for k in (self._keyPlaylistPos(tag), self._keyPlaylistPosOffset(tag),
-                  self._keyPlaylistPersist(tag), self._keyPlaylistShuffle(tag)):
+                  self._keyPlaylistPersist(tag), self._keyPlaylistShuffle(tag),
+                  self._keyPlaylistShuffleSeed(tag)):
             try:
                 del self.db[k]
             except KeyError:
@@ -271,7 +323,7 @@ class BTreeDB(IPlaylistDB):
                 val = self.db[k]
                 if val not in (b'no', b'yes'):
                     fail(f'Bad playlistshuffle value for {last_tag}: {val!r}')
-                if dump and val == 'yes':
+                if dump and val == b'yes':
                     print('\tShuffle')
             elif fields[1] == b'playlistpersist':
                 val = self.db[k]
@@ -280,8 +332,11 @@ class BTreeDB(IPlaylistDB):
                 elif dump:
                     print(f'\tPersist: {val.decode()}')
             elif fields[1] == b'playlistshuffleseed':
-                # Format TBD
+                val = self.db[k]
-                pass
+                try:
+                    _ = int(val)
+                except ValueError:
+                    fail(f' Bad playlistshuffleseed value for {last_tag}: {val!r}')
             elif fields[1] == b'playlistposoffset':
                 val = self.db[k]
                 try:

software/tests/utils_test/test_btreedb.py

@@ -3,9 +3,19 @@
 
 import btree
 import pytest
+import time
 from utils import BTreeDB
 
 
+@pytest.fixture(autouse=True)
+def micropythonify():
+    def time_ticks_cpu():
+        return time.time_ns()
+    time.ticks_cpu = time_ticks_cpu
+    yield
+    del time.ticks_cpu
+
+
 class FakeDB:
     def __init__(self, contents):
         self.contents = contents
@@ -165,3 +175,23 @@ def test_playlist_resets_offset_on_next_track():
     pl = uut.getPlaylistForTag(b'foo')
     assert pl.getCurrentPath() == b'track2'
     assert pl.getPlaybackOffset() == 0
+
+
+def test_playlist_shuffle():
+    contents_dict = {b'foo/playlistpersist': b'track',
+                     b'foo/playlistshuffle': b'yes',
+                     }
+    for i in range(256):
+        contents_dict['foo/playlist/{:05}'.format(i).encode()] = 'track{}'.format(i).encode()
+    contents = FakeDB(contents_dict)
+    uut = BTreeDB(contents)
+    pl = uut.getPlaylistForTag(b'foo')
+    shuffled = False
+    last_idx = int(pl.getCurrentPath().removeprefix(b'track'))
+    while (t := pl.getNextPath()) is not None:
+        idx = int(t.removeprefix(b'track'))
+        if idx != last_idx + 1:
+            shuffled = True
+            break
+    # A false negative ratr of 1 in 256! should be good enough for this test
+    assert shuffled