export type PostPreviewDraftPayload = {
  title: string
  excerpt: string
  bodyMarkdown: string
  visibility: 'private' | 'unlisted' | 'public'
}

const PREVIEW_DRAFT_KEY_PREFIX = 'post-preview-draft:'
const PREVIEW_DRAFT_TTL_MS = 10 * 60 * 1000

type StoredPostPreviewDraftPayload = PostPreviewDraftPayload & {
  createdAt: number
}

function isPostPreviewDraftKey(key: string): boolean {
  return key.startsWith(PREVIEW_DRAFT_KEY_PREFIX)
}

export function createPostPreviewDraft(payload: PostPreviewDraftPayload): string {
  const uniqueId = typeof crypto !== 'undefined' && typeof crypto.randomUUID === 'function'
    ? crypto.randomUUID()
    : `${Date.now()}-${Math.random().toString(16).slice(2)}`
  const key = `${PREVIEW_DRAFT_KEY_PREFIX}${uniqueId}`
  const storedPayload: StoredPostPreviewDraftPayload = {
    ...payload,
    createdAt: Date.now(),
  }
  localStorage.setItem(key, JSON.stringify(storedPayload))
  return uniqueId
}

export function readPostPreviewDraft(uniqueId: string): PostPreviewDraftPayload | null {
  const key = `${PREVIEW_DRAFT_KEY_PREFIX}${uniqueId}`
  const raw = localStorage.getItem(key)
  if (!raw) {
    return null
  }

  try {
    const parsed = JSON.parse(raw) as Partial<StoredPostPreviewDraftPayload>
    if (
      typeof parsed.title !== 'string' ||
      typeof parsed.excerpt !== 'string' ||
      typeof parsed.bodyMarkdown !== 'string' ||
      typeof parsed.createdAt !== 'number' ||
      (parsed.visibility !== 'private' && parsed.visibility !== 'unlisted' && parsed.visibility !== 'public')
    ) {
      localStorage.removeItem(key)
      return null
    }

    if (Date.now() - parsed.createdAt > PREVIEW_DRAFT_TTL_MS) {
      localStorage.removeItem(key)
      return null
    }

    return {
      title: parsed.title,
      excerpt: parsed.excerpt,
      bodyMarkdown: parsed.bodyMarkdown,
      visibility: parsed.visibility,
    }
  } catch {
    localStorage.removeItem(key)
    return null
  }
}

export function clearPostPreviewDrafts(options?: { onlyExpired?: boolean }) {
  const onlyExpired = options?.onlyExpired === true
  const now = Date.now()

  for (let index = localStorage.length - 1; index >= 0; index -= 1) {
    const key = localStorage.key(index)
    if (!key || !isPostPreviewDraftKey(key)) {
      continue
    }

    if (!onlyExpired) {
      localStorage.removeItem(key)
      continue
    }

    const raw = localStorage.getItem(key)
    if (!raw) {
      localStorage.removeItem(key)
      continue
    }

    try {
      const parsed = JSON.parse(raw) as Partial<StoredPostPreviewDraftPayload>
      if (typeof parsed.createdAt !== 'number' || now - parsed.createdAt > PREVIEW_DRAFT_TTL_MS) {
        localStorage.removeItem(key)
      }
    } catch {
      localStorage.removeItem(key)
    }
  }
}