feat(liquidsoap): deck-shuffle playlist with peek-ahead

config/liquidsoap.liq

@@ -6,6 +6,46 @@ settings.log.level.set(3)
 
 source_pw = environment.get(default="", "SOURCE_PW")
 
+# deck-shuffle: full shuffle once, hand out in order, reshuffle on exhaustion.
+# returns a record with .source (request.dynamic) and .peek (returns next N filenames).
+def make_deck(dir) =
+  files = ref([])
+  cursor = ref(0)
+
+  def reload_and_shuffle() =
+    files := list.shuffle(file.ls(dir, recursive=true, absolute=true))
+    cursor := 0
+  end
+
+  def next_file() =
+    if !cursor >= list.length(!files) then reload_and_shuffle() end
+    f = list.nth(default="", !files, !cursor)
+    cursor := !cursor + 1
+    f
+  end
+
+  def next_request() =
+    f = next_file()
+    if f == "" then null() else request.create(f) end
+  end
+
+  def peek(n) =
+    needed = !cursor + n
+    if needed > list.length(!files) and list.length(!files) > 0 then
+      # would exhaust the deck during peek; not worth pre-reshuffling.
+      # return whatever's left, the caller pads.
+      ()
+    end
+    list.init(
+      min(n, list.length(!files) - !cursor),
+      fun(i) -> list.nth(default="", !files, !cursor + i)
+    )
+  end
+
+  reload_and_shuffle()
+  { source = request.dynamic(next_request), peek = peek }
+end
+
 def emit_now_playing(station, m) =
   filename = m["filename"]
   if filename != "" then
@@ -68,13 +108,10 @@ def append_history(station, m) =
 end
 
 # === station: minecraft ===
-minecraft = playlist(
-  reload_mode="watch",
-  mode="randomize",
-  "/library/minecraft/tracks"
-)
+minecraft_deck = make_deck("/library/minecraft/tracks")
+minecraft = minecraft_deck.source
 minecraft.on_track(fun (m) -> begin
-  emit_now_playing("minecraft", m)
+  emit_now_playing("minecraft", m, minecraft_deck.peek(4))
   append_history("minecraft", m)
 end)
 minecraft = crossfade(minecraft)