add nix flake

Signed-off-by: Vladislav Fursov <github@ghost.im>

Author: ghostiam

flake.lock

@@ -0,0 +1,65 @@
+{
+  description = "A flake that builds a repo";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs =
+    inputs@{
+      nixpkgs,
+      flake-utils,
+      ...
+    }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = import nixpkgs { inherit system; };
+        buildInputs = with pkgs; [
+          go
+          coreutils
+          curl
+          xmlstarlet
+
+          # Protobuf + gRPC
+          protobuf
+          protoc-gen-go
+          protoc-gen-go-grpc
+          grpc
+        ];
+
+        defaultShellHook = ''
+          export FLAKE_ROOT=$(nix flake metadata | grep 'Resolved URL' | awk '{print $3}' | awk -F'://' '{print $2}')
+          export HISTFILE="$FLAKE_ROOT/.nix_bash_history"
+
+          export GOROOT="${pkgs.go}/share/go"
+        '';
+      in
+      {
+        # run: `nix develop`
+        devShells = {
+          default = pkgs.mkShell {
+            inherit buildInputs;
+            shellHook = defaultShellHook;
+          };
+
+          # Update IDEA paths. Use only if nix installed in whole system.
+          # run: `nix develop .#idea`
+          idea = pkgs.mkShell {
+            inherit buildInputs;
+
+            shellHook = pkgs.lib.concatLines [
+              defaultShellHook
+              ''
+                echo "Replace GOPATH"
+                xmlstarlet ed -L -u '//project/component[@name="GOROOT"]/@url' -v 'file://${pkgs.go}/share/go' .idea/workspace.xml
+
+                exit 0
+              ''
+            ];
+          };
+        };
+      }
+    );
+}