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+;;; PLS.fnl
+;; a parser for *.pls files
+;; Copyright (C) 2022 Case Duckworth <acdw@acdw.net>
+;; License: Good Choices (https://acdw.casa/gcl)
+
+;; https://en.wikipedia.org/wiki/PLS_(file_format)
+
+(fn split-lines [str]
+  "Split STR into a list of lines."
+  (icollect [ln (: str :gmatch "([^\n]*)\n?")]
+    ln))
+
+(fn parse [str]
+  "Parse a list of LINES into a playlist."
+  ;; This /maybe/ should take a string, I suppose.
+  (let [t []]
+    (each [_ l (ipairs (split-lines str))]
+      (let [(ltype num title) (: l :match "^(.*)([0-9]+)=(.*)")]
+        (when (and ltype num title)
+          (let [ltype (string.lower ltype)
+                num (tonumber num)]
+            (if (. t num)
+                (tset t num ltype title)
+                (tset t num {ltype title}))))))
+    t))
+
+(fn read [file]
+  "Read a .pls FILE into a playlist."
+  (with-open [p (io.open file)]
+    (parse (: p :read :*a))))
+
+(fn serialize [playlist]
+  "Serialize a PLAYLIST into a .pls-formatted string."
+  (let [s (icollect [n i (ipairs playlist)]
+            (.. (string.format "File%d=%s\n" n (. i :file))
+                (if (. i :title)
+                    (string.format "Title%d=%s\n" n (. i :title))
+                    "")
+                (if (. i :length)
+                    (string.format "Length%d=%s\n" n (. i :length))
+                    "")))]
+    (.. "[playlist]\n\n" (table.concat s "\n") "\n\n" :NumberOfEntries=
+        (length s) "\n" "Version=2\n")))
+
+(fn write [playlist file]
+  "Write PLAYLIST to FILE."
+  (with-open [p (io.open file :w)]
+    (: p :write (serialize playlist))))
+
+{: parse : read : serialize : write}
+