home: direnv: add 'postgres' library file

home/direnv/default.nix

@@ -7,11 +7,26 @@ in
     enable = mkDisableOption "direnv configuration";
   };
 
-  config.programs.direnv = lib.mkIf cfg.enable {
+  config = lib.mkIf cfg.enable {
+    programs.direnv = {
       enable = true;
       nix-direnv = {
         # A better `use_nix`
         enable = true;
       };
     };
+
+    xdg.configFile =
+      let
+        libDir = ./lib;
+        contents = builtins.readDir libDir;
+        names = lib.attrNames contents;
+        files = lib.filter (name: contents.${name} == "regular") names;
+        linkLibFile = name:
+          lib.nameValuePair
+            "direnv/lib/${name}"
+            { source = libDir + "/${name}"; };
+      in
+      lib.my.genAttrs' files linkLibFile;
+  };
 }

home/direnv/lib/postgres.sh

@@ -0,0 +1,22 @@
+#shellcheck shell=bash
+
+layout_postgres() {
+    if ! has postgres || ! has initdb; then
+        # shellcheck disable=2016
+        log_error 'layout_postgres: `postgres` and `initdb` are not in PATH'
+        return 1
+    fi
+
+    # shellcheck disable=2155
+    export PGDATA="$(direnv_layout_dir)/postgres"
+    export PGHOST="$PGDATA"
+
+    if [[ ! -d "$PGDATA" ]]; then
+        initdb
+        cat >> "$PGDATA/postgresql.conf" << EOF
+listen_addresses = ''
+unix_socket_directories = '$PGHOST'
+EOF
+        echo "CREATE DATABASE $USER;" | postgres --single -E postgres
+    fi
+}