initial stab at setting up nix for local testing with postgres

.gitignore

@@ -3,3 +3,5 @@ target
 Cargo.lock
 docs/book
 docs/doctest_cache
+.vscode
+data

flake.nix

@@ -0,0 +1,58 @@
+{
+  description = "A demo of sqlite-web and multiple postgres services";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    systems.url = "github:nix-systems/default";
+    process-compose-flake.url = "github:Platonic-Systems/process-compose-flake";
+    services-flake.url = "github:juspay/services-flake";
+    flake-parts.url = "github:hercules-ci/flake-parts";
+    rust-overlay.url = "github:oxalica/rust-overlay";
+  };
+
+  outputs = inputs @ { rust-overlay, nixpkgs, ...} :
+    inputs.flake-parts.lib.mkFlake { inherit inputs; } {
+      systems = import inputs.systems;
+
+      imports = [
+        inputs.process-compose-flake.flakeModule
+      ];
+
+      perSystem = { self', system, ... }: let
+        overlays = [ (import rust-overlay) ];
+        pkgs = import nixpkgs {
+          inherit system overlays;
+        };
+        dbName = "atmosphere";
+      in {
+        process-compose."default" = { config, ... }: {
+          imports = [
+            inputs.services-flake.processComposeModules.default
+          ];
+
+          services.postgres."pg1" = {
+            enable = true;
+            initialDatabases = [
+              { name = dbName; }
+            ];
+          };
+
+          settings.processes.test = let 
+            pgconf = config.services.postgres.pg1;
+          in {
+            environment.DATABASE_URL = pgconf.connectionURI { inherit dbName; };
+
+            command = pkgs.writeShellApplication {
+              name = "cargo.test.postgres";
+              runtimeInputs = with pkgs; [
+                darwin.apple_sdk.frameworks.Security
+                darwin.apple_sdk.frameworks.SystemConfiguration
+                rust-bin.stable.latest.default
+              ];
+              text = "cargo test -F postgres";
+            };
+          };
+        };
+      };
+    };
+}