// BEFORE: Too many args, mixed abstraction levels
async function processPod(
  namespace: string,
  name: string,
  action: string,
  force: boolean,
  gracePeriod: number,
  callback: () => void
) {
  const pod = await invoke('get_pod', { namespace, name });
  if (action === 'delete') {
    if (force) {
      await invoke('force_delete', { namespace, name });
    } else {
      await invoke('delete', { namespace, name, gracePeriod });
    }
  }
  callback();
}

// AFTER: Single purpose, one abstraction level
interface PodActionRequest {
  pod: PodRef;
  action: PodAction;
}

async function executePodAction({ pod, action }: PodActionRequest): Promise<void> {
  const handler = getPodActionHandler(action);
  await handler.execute(pod);
}

// VIOLATES Law of Demeter: "Train wreck"
const street = user.getAddress().getCity().getStreet();

// BETTER: Tell, don't ask
const street = user.getStreetAddress();

// Kubeli Example:
// BAD: Navigating through objects
const podName = store.getState().cluster.selectedPod.metadata.name;

// GOOD: Direct access with selector
const podName = useSelectedPodName();

// BEFORE: Monolithic component with mixed concerns
export function PodList({ namespace }: Props) {
  const [pods, setPods] = useState([]);
  const [filter, setFilter] = useState('');
  useEffect(() => { fetchPods().then(setPods); }, []);
  return (
    <div>
      <input value={filter} onChange={e => setFilter(e.target.value)} />
      <ul>{pods.filter(p => p.name.includes(filter)).map(p => <PodItem pod={p} />)}</ul>
    </div>
  );
}

// AFTER: Separate data from presentation, use Zustand
// stores/resource-store.ts
export const useResourceStore = create((set) => ({
  pods: [],
  fetchPods: async (ns) => { /* ... */ },
}));

// components/PodList.tsx
export function PodList() {
  const pods = useResourceStore(s => s.pods);
  const [filter, setFilter] = useState('');
  return <ul>{pods.filter(p => p.name.includes(filter)).map(p => <PodItem pod={p} />)}</ul>;
}

// BEFORE: Re-renders on ANY state change
function PodCount() {
  const store = useClusterStore(); // BAD: subscribes to everything
  return <span>{store.pods.length}</span>;
}

// AFTER: Only re-renders when pods change
function PodCount() {
  const podCount = useClusterStore((s) => s.pods.length); // GOOD: selective
  return <span>{podCount}</span>;
}

// BEFORE: Monolithic store
const useStore = create((set) => ({
  pods: [],
  deployments: [],
  services: [],
  selectedPod: null,
  selectedDeployment: null,
  // ... 50 more properties
}));

// AFTER: Composable slices
// stores/pods-slice.ts
export const createPodsSlice = (set, get) => ({
  pods: [],
  selectedPod: null,
  fetchPods: async (ns) => { ... },
  selectPod: (id) => set({ selectedPod: id }),
});

// stores/deployments-slice.ts
export const createDeploymentsSlice = (set, get) => ({
  deployments: [],
  fetchDeployments: async (ns) => { ... },
});

// stores/index.ts
export const useStore = create((...a) => ({
  ...createPodsSlice(...a),
  ...createDeploymentsSlice(...a),
}));

// BEFORE: Direct store access everywhere
function PodDetails({ id }: Props) {
  const pods = useClusterStore((s) => s.pods);
  const pod = pods.find(p => p.id === id);
  // ...
}

// AFTER: Domain-specific hooks
// hooks/usePod.ts
export function usePod(id: string) {
  return useClusterStore((s) => s.pods.find(p => p.id === id));
}

// components/PodDetails.tsx
function PodDetails({ id }: Props) {
  const pod = usePod(id);
  // ...
}

// BEFORE: All commands in one file
// src-tauri/src/main.rs
#[tauri::command]
fn get_pods() { ... }
#[tauri::command]
fn get_deployments() { ... }
#[tauri::command]
fn get_services() { ... }
// ... 50 more commands

// AFTER: Modular command structure
// src-tauri/src/commands/mod.rs
pub mod pods;
pub mod deployments;
pub mod services;

// src-tauri/src/commands/pods.rs
#[tauri::command]
pub async fn get_pods(state: State<'_, AppState>, namespace: &str) -> Result<Vec<Pod>, Error> {
    let client = state.client_manager.get_client()?;
    client.list_pods(namespace).await
}

// src-tauri/src/main.rs
fn main() {
    tauri::Builder::default()
        .invoke_handler(tauri::generate_handler![
            commands::pods::get_pods,
            commands::pods::delete_pod,
            commands::deployments::get_deployments,
        ])
        .run(tauri::generate_context!())
        .expect("error running app");
}

// BEFORE: Logic in main.rs
// src-tauri/src/main.rs
fn main() {
    // 500 lines of logic...
}

// AFTER: main.rs only handles startup, lib.rs has logic
// src-tauri/src/main.rs
fn main() {
    kubeli_lib::run();
}

// src-tauri/src/lib.rs
pub mod commands;
pub mod k8s;
pub mod state;

pub fn run() {
    tauri::Builder::default()
        .manage(state::AppState::new())
        .invoke_handler(tauri::generate_handler![...])
        .run(tauri::generate_context!())
        .expect("error running app");
}

// BEFORE: Tuple returns (hard to understand)
fn get_cluster_info() -> (String, bool, u32) {
    (context_name, is_connected, node_count)
}
let (a, b, c) = get_cluster_info(); // What is a, b, c?

// AFTER: Struct with meaningful names
struct ClusterInfo {
    context_name: String,
    is_connected: bool,
    node_count: u32,
}
fn get_cluster_info() -> ClusterInfo { ... }
let info = get_cluster_info();
println!("Connected: {}", info.is_connected);

// BEFORE: if-else chains
if status == "Running" { ... }
else if status == "Pending" { ... }
else if status == "Failed" { ... }

// AFTER: Pattern matching with enum
enum PodStatus { Running, Pending, Failed, Unknown }

match pod.status {
    PodStatus::Running => { ... }
    PodStatus::Pending => { ... }
    PodStatus::Failed => { ... }
    PodStatus::Unknown => { ... }
}

// BEFORE: Manual error handling everywhere
fn get_pod(name: &str) -> Result<Pod, Error> {
    let pods = self.list_pods()?;
    for pod in pods {
        if pod.name == name {
            return Ok(pod);
        }
    }
    Err(Error::NotFound)
}

// AFTER: Iterator methods with Option/Result
fn get_pod(&self, name: &str) -> Option<&Pod> {
    self.pods.iter().find(|p| p.name == name)
}

// Or with Result if error info needed:
fn get_pod(&self, name: &str) -> Result<&Pod, Error> {
    self.pods.iter()
        .find(|p| p.name == name)
        .ok_or_else(|| Error::PodNotFound(name.to_string()))
}

// BEFORE: Everything public
pub struct KubeClientManager {
    pub clients: HashMap<String, Client>,
    pub current_context: String,
    pub config: KubeConfig,
}

// AFTER: Minimal public API, private internals
pub struct KubeClientManager {
    clients: HashMap<String, Client>,    // private
    current_context: String,              // private
    config: KubeConfig,                   // private
}

impl KubeClientManager {
    pub fn new() -> Result<Self, Error> { ... }
    pub fn get_client(&self) -> Result<&Client, Error> { ... }
    pub fn switch_context(&mut self, name: &str) -> Result<(), Error> { ... }
    // Internal methods stay private
}

// BEFORE: Fat command with business logic
#[tauri::command]
pub async fn create_user(name: String, email: String) -> Result<User, String> {
    // Validation here...
    // Database access here...
    // Business logic here...
    // 100+ lines of mixed concerns
}

// AFTER: Thin handler → Service layer
// src/commands/user_commands.rs
#[tauri::command]
pub async fn create_user(name: String, email: String) -> Result<User, AppError> {
    user_service::create_user(&name, &email).await
}

// src/services/user_service.rs
pub async fn create_user(name: &str, email: &str) -> Result<User, AppError> {
    validate_email(email)?;
    let user = User::new(name, email);
    repository::save_user(&user).await?;
    Ok(user)
}

use thiserror::Error;
use serde::Serialize;

#[derive(Error, Debug)]
pub enum AppError {
    #[error("Database error: {0}")]
    Database(#[from] sqlx::Error),

    #[error("File not found: {path}")]
    FileNotFound { path: String },

    #[error("Kubernetes error: {0}")]
    Kube(#[from] kube::Error),

    #[error(transparent)]
    Other(#[from] anyhow::Error),
}

// CRITICAL: Implement Serialize for Tauri IPC
impl Serialize for AppError {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where S: serde::Serializer {
        serializer.serialize_str(&self.to_string())
    }
}

// For typed frontend errors, use tagged serialization:
#[derive(Serialize)]
#[serde(tag = "kind", content = "message")]
#[serde(rename_all = "camelCase")]
pub enum TypedError {
    Io(String),
    Validation(String),
    NotFound(String),
}
// Produces: { kind: 'io' | 'validation' | 'notFound', message: string }

// SYNC commands: Use std::sync::Mutex
use std::sync::Mutex;

#[tauri::command]
fn increment(state: State<'_, Mutex<AppState>>) -> u32 {
    let mut state = state.lock().unwrap();
    state.counter += 1;
    state.counter
}

// ASYNC commands: Use tokio::sync::Mutex (avoids blocking!)
use tokio::sync::Mutex;

#[tauri::command]
async fn async_increment(state: State<'_, Mutex<AppState>>) -> Result<u32, ()> {
    let mut state = state.lock().await;  // .await not .unwrap()!
    state.counter += 1;
    Ok(state.counter)
}

// CRITICAL: Async commands with borrowed args need Result return type
// ❌ Won't compile
async fn cmd(state: State<'_, AppState>) { }

// ✅ Correct pattern
async fn cmd(state: State<'_, AppState>) -> Result<(), ()> { Ok(()) }

#[tauri::command]
async fn read_file(path: String, app: AppHandle) -> Result<String, String> {
    let path = std::path::Path::new(&path);

    // Prevent path traversal attacks
    if path.components().any(|c| matches!(c, std::path::Component::ParentDir)) {
        return Err("Invalid path: directory traversal not allowed".into());
    }

    // Validate against allowed base directory
    let base = app.path().app_data_dir().unwrap();
    let full_path = base.join(&path);
    let canonical = full_path.canonicalize()
        .map_err(|e| format!("Invalid path: {}", e))?;

    if !canonical.starts_with(&base) {
        return Err("Access denied: path outside allowed scope".into());
    }

    std::fs::read_to_string(canonical).map_err(|e| e.to_string())
}

// CPU-intensive work should use spawn_blocking
#[tauri::command]
async fn heavy_computation(data: Vec<u8>) -> Result<Vec<u8>, String> {
    tokio::task::spawn_blocking(move || {
        process_heavy_data(data)  // Runs on blocking thread pool
    }).await.map_err(|e| e.to_string())
}

// I/O work uses regular async
#[tauri::command]
async fn fetch_data(url: String) -> Result<Data, String> {
    reqwest::get(&url).await
        .map_err(|e| e.to_string())?
        .json().await
        .map_err(|e| e.to_string())
}

pub trait AppHandleExt {
    fn get_database(&self) -> Arc<Database>;
    fn emit_global(&self, event: &str, payload: impl Serialize);
}

impl AppHandleExt for tauri::AppHandle {
    fn get_database(&self) -> Arc<Database> {
        self.state::<Arc<Database>>().inner().clone()
    }

    fn emit_global(&self, event: &str, payload: impl Serialize) {
        self.emit(event, payload).unwrap();
    }
}

// Usage in commands:
#[tauri::command]
async fn get_pods(app: AppHandle) -> Result<Vec<Pod>, AppError> {
    let db = app.get_database();
    db.query_pods().await
}

use tauri::{AppHandle, Emitter};

#[derive(Clone, Serialize)]
struct ProgressUpdate { percent: u32, status: String }

#[tauri::command]
async fn long_operation(app: AppHandle) -> Result<(), String> {
    for i in 0..=100 {
        app.emit("progress", ProgressUpdate {
            percent: i,
            status: format!("Processing {}%", i)
        }).unwrap();
        tokio::time::sleep(Duration::from_millis(50)).await;
    }
    Ok(())
}

// Frontend: Always cleanup listeners!
import { listen } from '@tauri-apps/api/event';

const unlisten = await listen<ProgressUpdate>('progress', (event) => {
  console.log(`Progress: ${event.payload.percent}%`);
});

// Cleanup on unmount
onCleanup(() => unlisten());

// src-tauri/capabilities/default.json
{
  "$schema": "../gen/schemas/desktop-schema.json",
  "identifier": "main-capability",
  "windows": ["main"],
  "permissions": [
    "core:default",
    "fs:default",
    {
      "identifier": "fs:allow-read",
      "allow": [{ "path": "$APPDATA/*" }],
      "deny": [{ "path": "$HOME/.ssh/*" }]
    }
  ]
}

undefined