packet: add system expression

Author: vaibhavsagar

packet/default.nix

@@ -0,0 +1,11 @@
+let
+  fetcher = { owner, repo, rev, sha256, ... }: builtins.fetchTarball {
+    inherit sha256;
+    url = "https://github.com/${owner}/${repo}/tarball/${rev}";
+  };
+  nixpkgs = fetcher (builtins.fromJSON (builtins.readFile ./versions.json)).nixpkgs;
+  nixos = import "${nixpkgs}/nixos" {
+    configuration = import ./configuration.nix;
+  };
+in
+  nixos.system

packet/updater

@@ -0,0 +1,26 @@
+#! /usr/bin/env nix-shell
+#! nix-shell -i bash
+#! nix-shell -p curl jq nix
+
+set -eufo pipefail
+
+FILE=$1
+PROJECT=$2
+
+OWNER=$(jq -r '.[$project].owner' --arg project "$PROJECT" < "$FILE")
+REPO=$(jq -r '.[$project].repo' --arg project "$PROJECT" < "$FILE")
+DEFAULT_BRANCH=$(jq -r '.[$project].branch // "master"' --arg project "$PROJECT" < "$FILE")
+
+BRANCH=${3:-$DEFAULT_BRANCH}
+
+REV=$(curl "https://api.github.com/repos/$OWNER/$REPO/branches/$BRANCH" | jq -r '.commit.sha')
+SHA256=$(nix-prefetch-url --unpack "https://github.com/$OWNER/$REPO/tarball/$REV")
+TJQ=$(jq '.[$project] = {owner: $owner, repo: $repo, branch: $branch, rev: $rev, sha256: $sha256}' \
+  --arg project "$PROJECT" \
+  --arg owner "$OWNER" \
+  --arg repo "$REPO" \
+  --arg branch "$BRANCH" \
+  --arg rev "$REV" \
+  --arg sha256 "$SHA256" \
+  < "$FILE")
+[[ $? == 0 ]] && echo "${TJQ}" >| "$FILE"

packet/versions.json

@@ -0,0 +1,9 @@
+{
+  "nixpkgs": {
+    "owner": "NixOS",
+    "repo": "nixpkgs-channels",
+    "branch": "nixos-19.03",
+    "rev": "77295b0bd26555c39a1ba9c1da72dbdb651fd280",
+    "sha256": "18v866h12xk6l1s37nk1vns869pvzphmnnlhrnm2b1zklg2hd1nq"
+  }
+}