set up project

flake.nix

@@ -0,0 +1,76 @@
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+  };
+
+  outputs = {
+    self,
+    nixpkgs,
+    ...
+  }: let
+    # System types to support.
+    supportedSystems = ["x86_64-linux" "x86_64-darwin" "aarch64-linux" "aarch64-darwin"];
+
+    # Helper function to generate an attrset '{ x86_64-linux = f "x86_64-linux"; ... }'.
+    forAllSystems = nixpkgs.lib.genAttrs supportedSystems;
+
+    # Nixpkgs instantiated for supported system types.
+    nixpkgsFor = forAllSystems (system: import nixpkgs {inherit system;});
+  in {
+    devShells = forAllSystems (system: let
+      pkgs = nixpkgsFor.${system};
+      startPostgres = pkgs.writeScriptBin "postgres_start" ''
+        background() {
+            exec 0>&-
+            exec 1>&-
+            exec 2>&-
+            exec 3>&-
+            "$@" &
+            disown $!
+        }
+
+        echo "Starting postgres server..."
+        # start postgres server
+        background ${pkgs.postgresql}/bin/pg_ctl -l $DB_LOG -o "--unix_socket_directories='$PWD'" start
+        echo "Postgres server started."
+      '';
+    in {
+      default = pkgs.mkShell {
+        buildInputs = with pkgs; [go gopls gotools go-tools postgresql];
+
+        PGDATA = "postgres.db";
+        DB_LOG = "postgres.log";
+        DB_NAME = "vegan-barcode";
+        shellHook = ''
+          echo "Using ${pkgs.postgresql.name}."
+
+          create_db=0
+          # initialize postgres if we have not done so already
+          if [ ! -d $PGDATA ]; then
+              echo "Postgres not found. Initializing postgres at $PGDATA"
+              ${pkgs.postgresql}/bin/initdb > /dev/null
+
+              echo "Setting postgres unix socket directories to $PWD/$SOCKET_DIRECTORIES..."
+              echo "unix_socket_directories = '$PWD'" >> $PGDATA/postgresql.conf
+              echo "unix socket directories set."
+
+              echo "Creating database $DB_NAME..."
+              echo "CREATE DATABASE \"$DB_NAME\";" | postgres --single -E postgres
+              echo "Database created."
+          fi
+
+          export PGHOST="$PWD"
+
+          if [ ! -f "$PWD/.s.PGSQL.5432.lock" ]; then
+              ${startPostgres}/bin/postgres_start
+          fi
+        '';
+      };
+    });
+
+    # The default package for 'nix build'. This makes sense if the
+    # flake provides only one package or there is a clear "main"
+    # package.
+    defaultPackage = forAllSystems (system: self.packages.${system}.go-hello);
+  };
+}