{
  description = "LightRAG + Graphiti dev environments";

  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";

  outputs = { self, nixpkgs }:
    let
      system = "x86_64-linux";
      pkgs = nixpkgs.legacyPackages.${system};

      startNeo4j = pkgs.writeShellScript "start-neo4j" ''
        set -e
        : "''${RAGS_ROOT:=$PWD}"
        NEO4J_DATA="$RAGS_ROOT/data/neo4j"
        mkdir -p "$NEO4J_DATA"/{data,logs,run,plugins,import,conf}

        cat > "$NEO4J_DATA/conf/neo4j.conf" <<CONF
        server.directories.data=$NEO4J_DATA/data
        server.directories.logs=$NEO4J_DATA/logs
        server.directories.run=$NEO4J_DATA/run
        server.directories.plugins=$NEO4J_DATA/plugins
        server.directories.import=$NEO4J_DATA/import
        server.bolt.listen_address=:7687
        server.http.listen_address=:7474
        dbms.security.auth_enabled=false
        CONF

        export NEO4J_CONF="$NEO4J_DATA/conf"
        ${pkgs.neo4j}/bin/neo4j start
        echo ""
        echo "Neo4j running:"
        echo "  bolt: bolt://localhost:7687"
        echo "  http: http://localhost:7474"
        echo "  stop: RAGS_ROOT=$RAGS_ROOT nix run .#neo4j-stop"
        echo ""
      '';

      stopNeo4j = pkgs.writeShellScript "stop-neo4j" ''
        : "''${RAGS_ROOT:=$PWD}"
        export NEO4J_CONF="$RAGS_ROOT/data/neo4j/conf"
        ${pkgs.neo4j}/bin/neo4j stop
      '';

    in {
      devShells.${system} = {

        lightrag = pkgs.mkShell {
          packages = [ pkgs.uv pkgs.python312 pkgs.curl pkgs.bun ];

          shellHook = ''
            RAGS_ROOT="$PWD"
            export VIRTUAL_ENV="$RAGS_ROOT/lightrag/.venv"
            export UV_PROJECT_ENVIRONMENT="$VIRTUAL_ENV"
            export UV_PYTHON="${pkgs.python312}/bin/python3.12"
            export LD_LIBRARY_PATH="${pkgs.lib.makeLibraryPath [ pkgs.stdenv.cc.cc pkgs.zlib ]}:$LD_LIBRARY_PATH"
            cd "$RAGS_ROOT/lightrag"

            echo "Syncing lightrag venv..."
            uv sync --extra api --extra offline-llm --quiet
            source .venv/bin/activate

            if [ ! -d lightrag/api/webui ]; then
              echo "Building frontend (first time, ~1min)..."
              cd lightrag_webui
              bun install --frozen-lockfile --silent
              bun run build:bun
              cd ..
            fi

            if [ -f "$RAGS_ROOT/.env.lightrag" ]; then
              set -a; source "$RAGS_ROOT/.env.lightrag"; set +a
            fi

            echo ""
            echo "LightRAG shell ready."
            echo "  start:  lightrag-server"
            echo "  config: $RAGS_ROOT/.env.lightrag"
            echo "  needs:  ollama with qwen2.5:7b + nomic-embed-text"
            echo ""
          '';
        };

        graphiti = pkgs.mkShell {
          packages = [ pkgs.uv pkgs.python312 pkgs.neo4j pkgs.curl ];

          shellHook = ''
            RAGS_ROOT="$PWD"
            export VIRTUAL_ENV="$RAGS_ROOT/graphiti/.venv"
            export UV_PROJECT_ENVIRONMENT="$VIRTUAL_ENV"
            export UV_PYTHON="${pkgs.python312}/bin/python3.12"
            export LD_LIBRARY_PATH="${pkgs.lib.makeLibraryPath [ pkgs.stdenv.cc.cc pkgs.zlib ]}:$LD_LIBRARY_PATH"
            cd "$RAGS_ROOT/graphiti"

            echo "Syncing graphiti venv..."
            uv sync --quiet
            source .venv/bin/activate

            if [ -f "$RAGS_ROOT/.env.graphiti" ]; then
              set -a; source "$RAGS_ROOT/.env.graphiti"; set +a
            fi

            echo ""
            echo "Graphiti shell ready."
            echo "  neo4j:  nix run .#neo4j-start   (in another terminal, run first)"
            echo "  config: $RAGS_ROOT/.env.graphiti"
            echo "  needs:  ollama with qwen2.5:7b + nomic-embed-text"
            echo ""
          '';
        };

      };

      apps.${system} = {
        neo4j-start = { type = "app"; program = "${startNeo4j}"; };
        neo4j-stop  = { type = "app"; program = "${stopNeo4j}"; };
      };
    };
}