define a per-feed update script

it currently has to be run manually:
```
./pkgs/feeds/update.sh <...>
```

it looks like `nix-update` might not really support flakes

modules/data/feeds/default.nix

@@ -2,21 +2,19 @@
 
 let
   inherit (builtins) concatLists concatStringsSep foldl' fromJSON map readDir readFile;
-  inherit (lib) init mapAttrsToList removePrefix removeSuffix splitString;
-  inherit (lib.attrsets) recursiveUpdate setAttrByPath;
-  inherit (lib.filesystem) listFilesRecursive;
+  inherit (lib) hasSuffix listToAttrs mapAttrsToList removeSuffix splitString;
 
   # given a path to a .json file relative to sources, construct the best feed object we can.
   # the .json file could be empty, in which case we make assumptions about the feed based
   # on its fs path.
-  # Type: feedFromSourcePath :: String -> { path = [String]; value = feed; }
+  # Type: feedFromSourcePath :: String -> { name = String; value = feed; }
   feedFromSourcePath = json-path:
+    assert hasSuffix "/default.json" json-path;
     let
-      canonical-name = removeSuffix "/default" (lib.removeSuffix ".json" json-path);
+      canonical-name = removeSuffix "/default.json" json-path;
       default-url = "https://${canonical-name}";
-      attr-path = splitString "/" canonical-name;
       feed-details = { url = default-url; } // (tryImportJson (./sources/${json-path}));
-    in { path = attr-path; value = mkFeed feed-details; };
+    in { name = canonical-name; value = mkFeed feed-details; };
 
   # TODO: for now, feeds are just ordinary Attrs.
   # in the future, we'd like to set them up with an update script.
@@ -49,10 +47,5 @@ let
         )
         (readDir base)
     );
-
-  # like listToAttrs, except takes { path, value } pairs instead of { name, value } pairs.
-  # Type: listToAttrsByPath :: [{ path = [String]; value = Any; }] -> Attrs
-  listToAttrsByPath = items:
-    foldl' (acc: { path, value }: recursiveUpdate acc (setAttrByPath path value)) {} items;
 in
-  listToAttrsByPath (map feedFromSourcePath sources)
+  listToAttrs (map feedFromSourcePath sources)

pkgs/feeds/default.nix

@@ -0,0 +1,17 @@
+{ lib
+, pkgs
+}:
+
+(lib.makeScope pkgs.newScope (self:
+  let
+    # TODO: dependency-inject this.
+    sane-data = import ../../modules/data { inherit lib; };
+    template = self.callPackage ./template.nix;
+  in lib.mapAttrs
+    (name: feed-details: template {
+      feedName = name;
+      jsonPath = "modules/data/feeds/sources/${name}/default.json";
+      inherit (feed-details) url;
+    })
+    sane-data.feeds
+))

pkgs/feeds/template.nix

@@ -0,0 +1,28 @@
+{ lib
+, stdenv
+, callPackage
+, fetchurl
+# feed-specific args
+, feedName
+, jsonPath
+, url
+}:
+
+stdenv.mkDerivation {
+  pname = feedName;
+  version = "20230112";
+  src = fetchurl {
+    inherit url;
+  };
+  passthru.updateScript = [ ./update.sh url jsonPath ];
+  # passthru.updateScript = callPackage ./update.nix {
+  #   inherit url jsonPath;
+  # };
+  meta = {
+    description = "metadata about any feeds available at ${feedName}";
+    homepage = feedName;
+    maintainers = with lib.maintainers; [ colinsane ];
+    platforms = lib.platforms.all;
+  };
+}
+

pkgs/feeds/update.nix

@@ -0,0 +1,18 @@
+{ lib
+, curl
+, jq
+, runtimeShell
+, writeScript
+# feed-specific args
+, jsonPath
+, url
+}:
+
+let
+  apiQuery = "https://feedsearch.dev/api/v1/search?url=${url}";
+in
+writeScript "update-feed" ''
+  #!${runtimeShell}
+  PATH=${lib.makeBinPath [ curl jq  ]}
+  curl -X GET '${apiQuery}' | jq '.[-1]' > '${jsonPath}'
+''

pkgs/feeds/update.sh

@@ -0,0 +1,10 @@
+#!/usr/bin/env nix-shell
+#!nix-shell -i bash -p curl jq
+
+set -xeu -o pipefail
+
+url="$1"
+jsonPath="$2"
+
+apiQuery="https://feedsearch.dev/api/v1/search?url=$url"
+curl -X GET "$apiQuery" | jq '.[-1]' > "$jsonPath"

pkgs/overlay.nix

@@ -1,6 +1,7 @@
 (next: prev: rec {
   #### my own, non-upstreamable packages:
   sane-scripts = prev.callPackage ./sane-scripts { };
+  feeds = prev.callPackage ./feeds { };
   tow-boot-pinephone = prev.callPackage ./tow-boot-pinephone { };
   tow-boot-rpi4 = prev.callPackage ./tow-boot-rpi4 { };
   bootpart-uefi-x86_64 = prev.callPackage ./bootpart-uefi-x86_64 { };