import type { ApplicationFormDto } from '~~/.api-client'
import { useLogger } from '~/composables/useLogger'

interface LocalStorageBackup {
  formId: string
  sectionIndex: number
  timestamp: number
  formData: ApplicationFormDto
}

const STORAGE_KEY_PREFIX = 'lch-form-backup-'

export function useLocalStorageBackup(formId: string) {
  const storageKey = `${STORAGE_KEY_PREFIX}${formId}`
  const logger = useLogger().withTag('localStorageBackup')

  const hasBackup = ref(false)
  const backupTimestamp = ref<Date | null>(null)
  const backupSectionIndex = ref<number | null>(null)

  function checkForBackup(): boolean {
    if (import.meta.server) return false

    try {
      const storedApplicationForm = localStorage.getItem(storageKey)
      if (storedApplicationForm) {
        const backup = JSON.parse(storedApplicationForm) as LocalStorageBackup
        hasBackup.value = true
        backupTimestamp.value = new Date(backup.timestamp)
        backupSectionIndex.value = backup.sectionIndex
        return true
      }
    } catch {
      clearBackup()
    }
    return false
  }

  function saveBackup(formData: ApplicationFormDto, currentSectionIndex: number): void {
    if (import.meta.server) return

    try {
      const backup: LocalStorageBackup = {
        formId,
        sectionIndex: currentSectionIndex,
        timestamp: Date.now(),
        formData
      }
      localStorage.setItem(storageKey, JSON.stringify(backup))
      hasBackup.value = true
      backupTimestamp.value = new Date(backup.timestamp)
      backupSectionIndex.value = currentSectionIndex
    } catch (e) {
      // localStorage might be full or unavailable
      logger.error('Error saving backup', e)
    }
  }

  function loadBackup(): ApplicationFormDto | null {
    if (import.meta.server) return null

    try {
      const stored = localStorage.getItem(storageKey)
      if (stored) {
        const backup = JSON.parse(stored) as LocalStorageBackup
        return backup.formData
      }
    } catch {
      clearBackup()
    }
    return null
  }

  function clearBackup(): void {
    if (import.meta.server) return

    localStorage.removeItem(storageKey)
    hasBackup.value = false
    backupTimestamp.value = null
    backupSectionIndex.value = null
  }

  // Call synchronously - import.meta.server guard handles SSR safety.
  // Do NOT use onMounted here: this composable is called after `await` in async setup(),
  // which means Vue's active component instance is gone and lifecycle hooks cannot be registered.
  checkForBackup()

  return {
    hasBackup: readonly(hasBackup),
    backupTimestamp: readonly(backupTimestamp),
    backupSectionIndex: readonly(backupSectionIndex),
    saveBackup,
    loadBackup,
    clearBackup,
    checkForBackup
  }
}