Pinia State Management Skill

File Organization: This skill uses split structure. See references/ for advanced patterns and security examples.

1. Overview

This skill provides Pinia expertise for managing application state in the JARVIS AI Assistant, including system metrics, user preferences, and HUD configuration.

Risk Level: MEDIUM - Manages sensitive state, SSR considerations, potential data exposure

Primary Use Cases:

• System metrics and status tracking
• User preferences and settings
• HUD configuration state
• Command history and queue
• Real-time data synchronization

2. Core Responsibilities

2.1 Core Principles

1. TDD First: Write store tests before implementation
2. Performance Aware: Optimize subscriptions and computed values
3. Type Safety: Define stores with full TypeScript typing
4. SSR Security: Prevent state leakage between requests
5. Composition API: Use setup stores for better TypeScript support
6. Minimal State: Store only necessary data, derive the rest
7. Action Validation: Validate inputs in actions before mutations
8. Persistence Security: Never persist sensitive data to localStorage

3. Technology Stack & Versions

3.1 Recommended Versions

3.2 Nuxt Configuration

// nuxt.config.ts
export default defineNuxtConfig({
  modules: ['@pinia/nuxt'],
  pinia: {
    storesDirs: ['./stores/**']
  }
})

3.3 Implementation Workflow (TDD)

Follow this workflow for every store:

Step 1: Write Failing Test First

// tests/stores/metrics.test.ts
import { describe, it, expect, beforeEach } from 'vitest'
import { setActivePinia, createPinia } from 'pinia'
import { useMetricsStore } from '~/stores/metrics'

describe('MetricsStore', () => {
  beforeEach(() => {
    setActivePinia(createPinia())
  })

  it('should initialize with default values', () => {
    const store = useMetricsStore()
    expect(store.cpu).toBe(0)
    expect(store.memory).toBe(0)
  })

  it('should clamp values within valid range', () => {
    const store = useMetricsStore()
    store.updateCpu(150)
    expect(store.cpu).toBe(100)
    store.updateCpu(-50)
    expect(store.cpu).toBe(0)
  })

  it('should compute health status correctly', () => {
    const store = useMetricsStore()
    store.updateCpu(95)
    store.updateMemory(90)
    expect(store.healthStatus).toBe('critical')
  })
})

Step 2: Implement Minimum to Pass

// stores/metrics.ts
export const useMetricsStore = defineStore('metrics', () => {
  const cpu = ref(0)
  const memory = ref(0)

  const healthStatus = computed(() => {
    const avg = (cpu.value + memory.value) / 2
    if (avg > 90) return 'critical'
    if (avg > 70) return 'warning'
    return 'healthy'
  })

  function updateCpu(value: number) {
    cpu.value = Math.max(0, Math.min(100, value))
  }

  function updateMemory(value: number) {
    memory.value = Math.max(0, Math.min(100, value))
  }

  return { cpu, memory, healthStatus, updateCpu, updateMemory }
})

Step 3: Refactor Following Patterns

• Extract validation logic
• Add TypeScript interfaces
• Optimize computed dependencies

Step 4: Run Full Verification

npm run test -- --filter=stores
npm run typecheck
npm run build

4. Implementation Patterns

4.1 Setup Store with TypeScript

// stores/jarvis.ts
import { defineStore } from 'pinia'
import { ref, computed } from 'vue'

interface SystemMetrics {
  cpu: number
  memory: number
  network: number
  timestamp: number
}

interface JARVISState {
  status: 'idle' | 'listening' | 'processing' | 'responding'
  securityLevel: 'normal' | 'elevated' | 'lockdown'
}

export const useJarvisStore = defineStore('jarvis', () => {
  // State
  const state = ref<JARVISState>({
    status: 'idle',
    securityLevel: 'normal'
  })

  const metrics = ref<SystemMetrics>({
    cpu: 0,
    memory: 0,
    network: 0,
    timestamp: Date.now()
  })

  // Getters
  const isActive = computed(() =>
    state.value.status !== 'idle'
  )

  const systemHealth = computed(() => {
    const avg = (metrics.value.cpu + metrics.value.memory) / 2
    if (avg > 90) return 'critical'
    if (avg > 70) return 'warning'
    return 'healthy'
  })

  // Actions
  function updateMetrics(newMetrics: Partial<SystemMetrics>) {
    // ✅ Validate input
    if (newMetrics.cpu !== undefined) {
      metrics.value.cpu = Math.max(0, Math.min(100, newMetrics.cpu))
    }
    if (newMetrics.memory !== undefined) {
      metrics.value.memory = Math.max(0, Math.min(100, newMetrics.memory))
    }
    if (newMetrics.network !== undefined) {
      metrics.value.network = Math.max(0, newMetrics.network)
    }
    metrics.value.timestamp = Date.now()
  }

  function setStatus(newStatus: JARVISState['status']) {
    state.value.status = newStatus
  }

  function setSecurityLevel(level: JARVISState['securityLevel']) {
    state.value.securityLevel = level

    // ✅ Audit security changes
    console.info(`Security level changed to: ${level}`)
  }

  return {
    state,
    metrics,
    isActive,
    systemHealth,
    updateMetrics,
    setStatus,
    setSecurityLevel
  }
})

4.2 User Preferences Store (with Persistence)

// stores/preferences.ts
export const usePreferencesStore = defineStore('preferences', () => {
  const preferences = ref({
    theme: 'dark' as 'dark' | 'light',
    hudOpacity: 0.8,
    soundEnabled: true
  })

  function updatePreference<K extends keyof typeof preferences.value>(
    key: K, value: typeof preferences.value[K]
  ) {
    if (key === 'hudOpacity' && (value < 0 || value > 1)) return
    preferences.value[key] = value
  }

  return { preferences, updatePreference }
}, {
  persist: {
    key: 'jarvis-preferences',
    paths: ['preferences.theme', 'preferences.hudOpacity']
    // ❌ Never persist: tokens, passwords, API keys
  }
})

4.3 Command Queue Store

// stores/commands.ts
interface Command {
  id: string
  action: string
  status: 'pending' | 'executing' | 'completed' | 'failed'
}

export const useCommandStore = defineStore('commands', () => {
  const queue = ref<Command[]>([])
  const history = ref<Command[]>([])
  const MAX_HISTORY = 100

  const pendingCommands = computed(() =>
    queue.value.filter(cmd => cmd.status === 'pending')
  )

  function addCommand(action: string) {
    const cmd: Command = { id: crypto.randomUUID(), action, status: 'pending' }
    queue.value.push(cmd)
    return cmd.id
  }

  function completeCommand(id: string, status: 'completed' | 'failed') {
    const idx = queue.value.findIndex(cmd => cmd.id === id)
    if (idx !== -1) {
      const [cmd] = queue.value.splice(idx, 1)
      cmd.status = status
      history.value = [cmd, ...history.value].slice(0, MAX_HISTORY)
    }
  }

  return { queue, history, pendingCommands, addCommand, completeCommand }
})

4.4 SSR-Safe Store Usage

<script setup lang="ts">
// ✅ Safe for SSR - store initialized per-request
const jarvisStore = useJarvisStore()

// ✅ Fetch data on server
const { data } = await useFetch('/api/metrics')

// Update store with fetched data
if (data.value) {
  jarvisStore.updateMetrics(data.value)
}
</script>

4.5 Store Composition

// stores/dashboard.ts
export const useDashboardStore = defineStore('dashboard', () => {
  // ✅ Compose from other stores
  const jarvisStore = useJarvisStore()
  const commandStore = useCommandStore()

  const dashboardStatus = computed(() => ({
    systemHealth: jarvisStore.systemHealth,
    pendingCommands: commandStore.pendingCommands.length,
    isActive: jarvisStore.isActive
  }))

  return {
    dashboardStatus
  }
})

5. Security Standards

5.1 OWASP Coverage

5.3 Sensitive Data Handling

// ❌ NEVER persist: tokens, API keys, passwords
// ✅ Store sensitive data in memory only (no persist option)
const authStore = defineStore('auth', () => {
  const token = ref<string | null>(null)
  return { token }
})

5.5 Performance Patterns

Pattern 1: Selective Subscriptions

// BAD - Subscribes to entire store
const store = useJarvisStore()
watch(() => store.state, () => { /* ... */ }, { deep: true })

// GOOD - Subscribe to specific properties
const store = useJarvisStore()
watch(() => store.state.status, (newStatus) => {
  console.log('Status changed:', newStatus)
})

Pattern 2: Computed Getters (Memoization)

// BAD - Recalculates on every access
function getFilteredItems() {
  return items.value.filter(i => i.active)
}

// GOOD - Cached until dependencies change
const filteredItems = computed(() =>
  items.value.filter(i => i.active)
)

Pattern 3: Batch Updates

// BAD - Multiple reactive triggers
function updateAll(data: MetricsData) {
  metrics.value.cpu = data.cpu
  metrics.value.memory = data.memory
  metrics.value.network = data.network
}

// GOOD - Single reactive trigger
function updateAll(data: MetricsData) {
  metrics.value = { ...metrics.value, ...data, timestamp: Date.now() }
}

Pattern 4: Lazy Store Initialization

// BAD - Store initializes immediately
const heavyStore = useHeavyDataStore()

// GOOD - Initialize only when needed
const heavyStore = ref<ReturnType<typeof useHeavyDataStore> | null>(null)

function loadHeavyData() {
  if (!heavyStore.value) {
    heavyStore.value = useHeavyDataStore()
  }
  return heavyStore.value
}

Pattern 5: Optimistic Updates

// BAD - Wait for server response
async function deleteItem(id: string) {
  await api.delete(`/items/${id}`)
  items.value = items.value.filter(i => i.id !== id)
}

// GOOD - Update immediately, rollback on error
async function deleteItem(id: string) {
  const backup = [...items.value]
  items.value = items.value.filter(i => i.id !== id)

  try {
    await api.delete(`/items/${id}`)
  } catch (error) {
    items.value = backup  // Rollback
    throw error
  }
}

6. Testing & Quality

See Section 3.3 for complete TDD workflow with vitest examples.

8. Common Anti-Patterns

Security Anti-Patterns

// ❌ Global state leaks between SSR users
const state = reactive({ user: null })

// ✅ Pinia isolates per-request
export const useUserStore = defineStore('user', () => {
  const user = ref(null)
  return { user }
})

// ❌ Never persist auth tokens (XSS risk)
persist: { paths: ['authToken'] }

// ✅ Use httpOnly cookies for auth

Performance Anti-Patterns

See Section 5.5 for detailed performance patterns with Good/Bad examples.

13. Pre-Implementation Checklist

Phase 1: Before Writing Code

• Store interface designed with TypeScript types
• Test file created with failing tests
• Security requirements identified (persistence, SSR)
• Performance patterns selected for use case

Phase 2: During Implementation

• Tests passing after each feature added
• Actions validate all inputs
• Computed values use minimal dependencies
• No sensitive data in persisted state
• SSR state properly isolated

Phase 3: Before Committing

• All store tests passing: npm run test -- --filter=stores
• Type check passing: npm run typecheck
• Build succeeds: npm run build
• No global state outside Pinia
• State shape documented in types

14. Summary

Pinia provides type-safe state management for JARVIS:

1. TDD First: Write store tests before implementation
2. Performance: Optimize subscriptions and computed values
3. Security: Never persist sensitive data, isolate SSR state
4. Type Safety: Use setup stores with full TypeScript

References: See references/ for advanced patterns and security examples.