gravl/frontend/src/hooks/useDraftWorkout.js

import { useEffect, useState } from 'react'

/**
 * useDraftWorkout - Manages draft workout state with localStorage persistence
 * 
 * @param {number} workoutId - Unique workout ID (used as localStorage key)
 * @param {array} initialExercises - Initial exercise list
 * @returns {object} { exercises, setExercises, clearDraft, hasDraft, restoreDraft }
 */
export function useDraftWorkout(workoutId, initialExercises = []) {
  const [exercises, setExercises] = useState(initialExercises)
  const [hasDraft, setHasDraft] = useState(false)

  const draftKey = `workout-draft-${workoutId}`

  // Load draft from localStorage on mount
  useEffect(() => {
    const saved = localStorage.getItem(draftKey)
    if (saved) {
      try {
        const draft = JSON.parse(saved)
        setExercises(draft)
        setHasDraft(true)
      } catch (err) {
        console.error('Failed to parse draft:', err)
        localStorage.removeItem(draftKey) // Clear corrupted draft
      }
    }
  }, [workoutId, draftKey])

  // Auto-save to localStorage whenever exercises change
  useEffect(() => {
    if (exercises.length > 0) {
      localStorage.setItem(draftKey, JSON.stringify(exercises))
    }
  }, [exercises, draftKey])

  const clearDraft = () => {
    localStorage.removeItem(draftKey)
    setHasDraft(false)
  }

  const restoreDraft = () => {
    const saved = localStorage.getItem(draftKey)
    if (saved) {
      try {
        const draft = JSON.parse(saved)
        setExercises(draft)
        return true
      } catch (err) {
        console.error('Failed to restore draft:', err)
        return false
      }
    }
    return false
  }

  return {
    exercises,
    setExercises,
    clearDraft,
    hasDraft,
    restoreDraft
  }
}