Supabase Reliability Patterns

// lib/circuit-breaker.ts
import { createClient } from '@supabase/supabase-js'
import type { Database } from './database.types'

type CircuitState = 'CLOSED' | 'OPEN' | 'HALF_OPEN'

interface CircuitBreakerOptions {
  failureThreshold: number    // failures before opening
  resetTimeoutMs: number      // ms before trying again (half-open)
  halfOpenSuccesses: number   // successes in half-open to close
  name: string                // for logging
}

class CircuitBreaker {
  private state: CircuitState = 'CLOSED'
  private failures = 0
  private lastFailureTime = 0
  private halfOpenSuccesses = 0

  constructor(private opts: CircuitBreakerOptions) {}

  async call<T>(fn: () => Promise<T>, fallback?: () => T): Promise<T> {
    // Check if circuit should transition from OPEN to HALF_OPEN
    if (this.state === 'OPEN') {
      if (Date.now() - this.lastFailureTime > this.opts.resetTimeoutMs) {
        this.state = 'HALF_OPEN'
        this.halfOpenSuccesses = 0
        console.log(`[CircuitBreaker:${this.opts.name}] OPEN → HALF_OPEN`)
      } else {
        if (fallback) return fallback()
        throw new Error(`Circuit breaker ${this.opts.name} is OPEN`)
      }
    }

    try {
      const result = await fn()

      // Success in HALF_OPEN: count toward recovery
      if (this.state === 'HALF_OPEN') {
        this.halfOpenSuccesses++
        if (this.halfOpenSuccesses >= this.opts.halfOpenSuccesses) {
          this.state = 'CLOSED'
          this.failures = 0
          console.log(`[CircuitBreaker:${this.opts.name}] HALF_OPEN → CLOSED`)
        }
      } else {
        this.failures = 0  // reset on success in CLOSED state
      }

      return result
    } catch (error) {
      this.failures++
      this.lastFailureTime = Date.now()

      if (this.failures >= this.opts.failureThreshold) {
        this.state = 'OPEN'
        console.error(
          `[CircuitBreaker:${this.opts.name}] CLOSED → OPEN after ${this.failures} failures`
        )
      }

      if (fallback) return fallback()
      throw error
    }
  }

  get currentState() {
    return { state: this.state, failures: this.failures }
  }
}

// One circuit breaker per Supabase service domain
export const dbCircuit = new CircuitBreaker({
  name: 'database',
  failureThreshold: 5,
  resetTimeoutMs: 30_000,
  halfOpenSuccesses: 3,
})

export const authCircuit = new CircuitBreaker({
  name: 'auth',
  failureThreshold: 3,
  resetTimeoutMs: 15_000,
  halfOpenSuccesses: 2,
})

export const storageCircuit = new CircuitBreaker({
  name: 'storage',
  failureThreshold: 3,
  resetTimeoutMs: 60_000,
  halfOpenSuccesses: 2,
})

// lib/retry.ts
interface RetryOptions {
  maxRetries: number
  baseDelayMs: number
  maxDelayMs: number
  retryableErrors?: string[]  // Supabase error codes to retry
}

const DEFAULT_RETRYABLE = [
  'PGRST301',   // connection error
  '08006',      // connection failure
  '57014',      // query cancelled (timeout)
  '40001',      // serialization failure
  '53300',      // too many connections
]

export async function withRetry<T>(
  fn: () => Promise<{ data: T | null; error: any }>,
  opts: RetryOptions = { maxRetries: 3, baseDelayMs: 200, maxDelayMs: 5000 }
): Promise<{ data: T | null; error: any }> {
  const retryable = opts.retryableErrors ?? DEFAULT_RETRYABLE

  for (let attempt = 0; attempt <= opts.maxRetries; attempt++) {
    const result = await fn()

    if (!result.error) return result

    // Don't retry non-retryable errors (auth, RLS, validation)
    const errorCode = result.error.code ?? ''
    if (!retryable.includes(errorCode) && attempt > 0) {
      return result
    }

    if (attempt < opts.maxRetries) {
      // Exponential backoff with full jitter
      const delay = Math.min(
        opts.baseDelayMs * Math.pow(2, attempt) * (0.5 + Math.random() * 0.5),
        opts.maxDelayMs
      )
      console.warn(
        `[Retry] Attempt ${attempt + 1}/${opts.maxRetries} failed (${errorCode}), ` +
        `retrying in ${Math.round(delay)}ms`
      )
      await new Promise(resolve => setTimeout(resolve, delay))
    }
  }

  // Should not reach here, but return last result
  return fn()
}

// services/todo-service.ts
import { createClient } from '@supabase/supabase-js'
import type { Database } from '../lib/database.types'
import { dbCircuit } from '../lib/circuit-breaker'
import { withRetry } from '../lib/retry'

const supabase = createClient<Database>(
  process.env.SUPABASE_URL!,
  process.env.SUPABASE_ANON_KEY!
)

export const TodoService = {
  async list(userId: string) {
    return dbCircuit.call(
      // Retry transient errors inside the circuit breaker
      () => withRetry(() =>
        supabase
          .from('todos')
          .select('id, title, is_complete, created_at')
          .eq('user_id', userId)
          .order('created_at', { ascending: false })
      ),
      // Fallback when circuit is OPEN: return empty list
      () => ({ data: [], error: null })
    )
  },

  async create(todo: { title: string; user_id: string }) {
    return dbCircuit.call(
      () => withRetry(() =>
        supabase
          .from('todos')
          .insert(todo)
          .select('id, title, is_complete, created_at')
          .single()
      )
      // No fallback for writes — let the error propagate to the offline queue
    )
  },
}