export const PAGES_CHANGED = 'computer:pages-changed'

export const notifyPagesChanged = () => window.dispatchEvent(new Event(PAGES_CHANGED))

// Notion-style breadcrumbs: the pages workspace announces which page is open
// so the top bar can show "computer / Pages / <title>" without refetching.
export const ACTIVE_PAGE_CHANGED = 'computer:active-page-changed'

export const notifyActivePage = (title: string | null) =>
  window.dispatchEvent(new CustomEvent<string | null>(ACTIVE_PAGE_CHANGED, { detail: title }))

export type PageSummary = {
  id: string
  title: string
  pinned: boolean
  position: number
  parentId: string | null
  _count?: { bookmarks: number; children?: number }
}

// Connected pages (phase 3): the same link forms the editor understands,
// shared by the page client, sidebar and Markdown preview. Page links use
// `computer:page/<id>`; /pages?id=<id> is accepted for hand-written links.
export function internalPageId(href: string): string | null {
  const value = href.trim().replace(/^<|>$/g, '')
  let raw = ''
  if (value.startsWith('computer://page/')) raw = value.slice('computer://page/'.length)
  else if (value.startsWith('computer:page/')) raw = value.slice('computer:page/'.length)
  else if (value.startsWith('page/')) raw = value.slice('page/'.length)
  else if (value.startsWith('/pages/')) raw = value.slice('/pages/'.length)
  else if (value.startsWith('/pages?') || value.startsWith('computer:page?id=') || value.startsWith('computer://page?id=')) {
    try {
      const id = new URL(value, 'http://localhost').searchParams.get('id')
      raw = id ?? ''
    } catch { raw = '' }
  }
  raw = raw.replace(/\/$/, '')
  return /^[A-Za-z0-9_-]{1,128}$/.test(raw) ? raw : null
}

export const pageLinkMarkdown = (page: Pick<PageSummary, 'id' | 'title'>) =>
  `[${page.title.replace(/[\[\]\n]/g, ' ')}](computer:page/${page.id})`

export type PageEmbedMarker = { collectionId: string; viewId: string | null }

export function parsePageEmbed(value: string): PageEmbedMarker | null {
  const m = /^\{\{\s*collection:([A-Za-z0-9_-]{1,128})(?:\s*\|\s*view=([A-Za-z0-9_-]{1,128}))?\s*\}\}$/.exec(value.trim())
  if (!m) return null
  return { collectionId: m[1], viewId: m[2] ?? null }
}

export const collectionEmbedMarkdown = (collectionId: string, viewId?: string | null) =>
  `{{collection:${collectionId}${viewId ? `|view=${viewId}` : ''}}}`

// Ids below `id` in the current page tree. Used to keep the parent picker
// from offering a descendant (the server rejects the cycle regardless).
export function descendantPageIds(pages: PageSummary[], id: string): Set<string> {
  const out = new Set<string>()
  const children = new Map<string, string[]>()
  for (const p of pages) {
    if (!p.parentId) continue
    const list = children.get(p.parentId) ?? []
    list.push(p.id)
    children.set(p.parentId, list)
  }
  const walk = (parent: string) => {
    for (const child of children.get(parent) ?? []) {
      if (out.has(child)) continue
      out.add(child)
      walk(child)
    }
  }
  walk(id)
  return out
}

// Pages start as "Untitled 1", "Untitled 2", ... until the user renames them.
// Pick the lowest positive integer not already used by an untitled page.
export function nextUntitledTitle(titles: string[]): string {
  const used = new Set<number>()
  for (const t of titles) {
    const m = /^Untitled (\d+)$/.exec(t.trim())
    if (m) used.add(parseInt(m[1], 10))
  }
  let n = 1
  while (used.has(n)) n++
  return `Untitled ${n}`
}