feat: add recursive file fetching

flake.nix

@@ -1,17 +1,12 @@
 {
-  description = "A very basic flake";
+  description = "A declarative wallpaper collection.";
 
-  outputs =
-    _:
-    let
-      lib = import ./lib;
-    in
-    {
-      wallpapers = lib.toWallpkgs ./wallpapers [
-        "png"
-        "jpg"
-        "jpeg"
-        "gif"
-      ];
-    };
+  outputs = _: {
+    wallpapers = (import ./lib).toWallpkgs ./wallpapers [
+      "png"
+      "jpg"
+      "jpeg"
+      "gif"
+    ];
+  };
 }

lib/default.nix

@@ -52,41 +52,55 @@ let
       }) names
     );
 
-  # TODO: This needs to be extensible, possibly in order to allow additional directories.
-  # In theory, we should only need to handle path*s* instead of a path, and search multiple
-  # paths by extension instead of just once, right?
+  hasSuffix =
+    suffix: content:
+    let
+      lenContent = builtins.stringLength content;
+      lenSuffix = builtins.stringLength suffix;
+    in
+    (
+      lenContent >= lenSuffix && builtins.substring (lenContent - lenSuffix) lenContent content == suffix
+    );
+
   toWallpkgs =
     path: extensions:
     let
-      fileExts = extensions;
-    in
-    builtins.listToAttrs (
-      map
-        (
-          n:
-          let
-            filesByExtension = builtins.filter builtins.pathExists (map (ext: path + /${n}.${ext}) fileExts);
-            file =
-              if filesByExtension == [ ] then
-                builtins.throw "Either ${n} is not a file or it does not have the ${builtins.concatStringsSep ", " fileExts} extensions."
+
+      hasValidExtension =
+        file: builtins.foldl' (acc: elem: (hasSuffix elem "${file}") || acc) false extensions;
+
+      fetchPath =
+        path:
+        filterAttrs (n: t: t == "directory" || (t == "regular" && hasValidExtension n)) (
+          builtins.readDir path
+        );
+
+      getFiles =
+        path:
+        builtins.listToAttrs (
+          builtins.attrValues (
+            builtins.mapAttrs (
+              n: v:
+              if v == "directory" then
+                {
+                  name = n;
+                  value = getFiles "${path}/${n}";
+                }
               else
-                builtins.head filesByExtension;
-          in
-          {
-            name = n;
-            value = {
-              path = file;
-              tags = splitString "-" n;
-              hash = builtins.hashFile "md5" file; # in theory, md5 is the fastest option because it produces a 128-bit hash instead of >= 160
-            };
-          }
-        )
-        (
-          map (n: builtins.head (splitString "." n)) (
-            builtins.attrNames (filterAttrs (n: _: n != "README.md") (builtins.readDir path))
+                {
+                  name = builtins.head (splitString "." n);
+                  value = {
+                    path = "${path}/${n}";
+                    tags = splitString "-" (builtins.head (splitString "." n));
+                    hash = builtins.hashFile "md5" "${path}/${n}";
+                  };
+                }
+            ) (fetchPath path)
           )
-        )
-    );
+        );
+
+    in
+    getFiles path;
 in
 {
   # Partial re-implementations of functions from Nixpkgs.