feat(3p/radicle-explorer): package radicle web interface

For some reason this is not included. The build is based on their experimental
Nix code upstream which I copy&pasted and modified a bit.

Change-Id: I523f9e90a3f5feca0deb317eec1d5283e2a3ca98
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12487
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

third_party/radicle-explorer/default.nix

@@ -0,0 +1,47 @@
+# radicle-explorer is the web UI for Radicle.
+#
+# They have an upstream Nix derivation, but it only works with experimental
+# features Nix and is quite messy, so this is a copy of the relevant parts.
+{ pkgs, ... }:
+
+let
+  twemoji-assets = pkgs.fetchFromGitHub {
+    owner = "twitter";
+    repo = "twemoji";
+    rev = "v14.0.2";
+    hash = "sha256-YoOnZ5uVukzi/6bLi22Y8U5TpplPzB7ji42l+/ys5xI=";
+  };
+
+  httpdSrc = pkgs.radicle-httpd.src;
+in
+pkgs.buildNpmPackage rec {
+  pname = "radicle-explorer";
+  version = (builtins.fromJSON (builtins.readFile "${src}/package.json")).version;
+
+  # source should be synced with the httpd, which is already in nixpkgs
+  src = pkgs.fetchgit {
+    inherit (httpdSrc) url rev;
+    hash = "sha256:09m13238h6j7g02r6332ihgyyzbjx90pgz14rz29pgv7936h6il8";
+  };
+
+  # This might change during nixpkgs bumps and will need updating. Need to fix
+  # upstream so that there is a normal, callable derivation.
+  npmDepsHash = "sha256:0kw6rvqm0s21j1rss35idvgcrzzczfy6qi3323y385djw4ygk5xs";
+
+  postPatch = ''
+    patchShebangs --build ./scripts
+    mkdir -p "public/twemoji"
+    cp -t public/twemoji -r -- ${twemoji-assets}/assets/svg/*
+    : >scripts/install-twemoji-assets
+  '';
+  dontConfigure = true;
+  doCheck = false;
+
+  installPhase = ''
+    runHook preInstall
+    mkdir -p "$out"
+    cp -r -t "$out" build/*
+    runHook postInstall
+  '';
+
+}