// 前后端共用的 Yjs 文档结构。
//
// 文档划分：
// - `meta`：空间（标签）列表。客户端只读，增删改都走 REST 接口由服务端写入。
// - `board:<spaceId>`：一个空间的画布。`cards` 和 `edges` 两个 Y.Map。
//
// 每张卡片是一个嵌套 Y.Map，这样位置、尺寸、文字等字段可以分别合并，
// 两台设备同时改同一张卡片的不同字段不会互相覆盖。
import * as Y from 'yjs'

export const META_DOC = 'meta'
const BOARD_PREFIX = 'board:'

export type CardKind = 'note' | 'image'
export type CardColor = 'paper' | 'sun' | 'mint' | 'sky' | 'rose'

export const CARD_COLORS: CardColor[] = ['paper', 'sun', 'mint', 'sky', 'rose']

export interface SpaceInfo {
  id: string
  name: string
  emoji: string
  createdAt: number
  updatedAt: number
  cardCount: number
}

export interface CardFields {
  kind: CardKind
  title: string
  content: string
  /** 图片地址（服务端 /api/images/...），仅图片卡片有 */
  image?: string
  color: CardColor
  x: number
  y: number
  width: number
  height: number
  /** 叠放顺序，越大越靠上 */
  z: number
  createdAt: number
  updatedAt: number
}

export interface Card extends CardFields {
  id: string
}

export interface EdgeFields {
  source: string
  target: string
  sourceHandle?: string | null
  targetHandle?: string | null
}

export interface Edge extends EdgeFields {
  id: string
}

export function boardDocName(spaceId: string) {
  return `${BOARD_PREFIX}${spaceId}`
}

export function spaceIdFromDocName(name: string): string | null {
  return name.startsWith(BOARD_PREFIX) ? name.slice(BOARD_PREFIX.length) : null
}

export function metaSpaces(doc: Y.Doc) {
  return doc.getMap<Y.Map<unknown>>('spaces')
}

export function boardCards(doc: Y.Doc) {
  return doc.getMap<Y.Map<unknown>>('cards')
}

export function boardEdges(doc: Y.Doc) {
  return doc.getMap<EdgeFields>('edges')
}

function num(value: unknown, fallback: number) {
  return typeof value === 'number' && Number.isFinite(value) ? value : fallback
}

function str(value: unknown, fallback = '') {
  return typeof value === 'string' ? value : fallback
}

export function readSpace(id: string, map: Y.Map<unknown>): SpaceInfo {
  return {
    id,
    name: str(map.get('name'), '未命名空间'),
    emoji: str(map.get('emoji'), '✦'),
    createdAt: num(map.get('createdAt'), 0),
    updatedAt: num(map.get('updatedAt'), 0),
    cardCount: num(map.get('cardCount'), 0),
  }
}

export function readSpaces(doc: Y.Doc): SpaceInfo[] {
  const spaces: SpaceInfo[] = []
  metaSpaces(doc).forEach((map, id) => spaces.push(readSpace(id, map)))
  return spaces.sort((a, b) => a.createdAt - b.createdAt || a.id.localeCompare(b.id))
}

export function readCard(id: string, map: Y.Map<unknown>): Card {
  const kind = map.get('kind') === 'image' ? 'image' : 'note'
  const color = map.get('color')
  const image = map.get('image')
  return {
    id,
    kind,
    title: str(map.get('title')),
    content: str(map.get('content')),
    image: typeof image === 'string' && image ? image : undefined,
    color: CARD_COLORS.includes(color as CardColor) ? (color as CardColor) : 'paper',
    x: num(map.get('x'), 0),
    y: num(map.get('y'), 0),
    width: num(map.get('width'), 300),
    height: num(map.get('height'), 220),
    z: num(map.get('z'), 0),
    createdAt: num(map.get('createdAt'), 0),
    updatedAt: num(map.get('updatedAt'), 0),
  }
}

export function readCards(doc: Y.Doc): Card[] {
  const cards: Card[] = []
  boardCards(doc).forEach((map, id) => cards.push(readCard(id, map)))
  return cards.sort((a, b) => a.z - b.z || a.createdAt - b.createdAt)
}

export function readEdges(doc: Y.Doc): Edge[] {
  const edges: Edge[] = []
  boardEdges(doc).forEach((edge, id) => edges.push({ ...edge, id }))
  return edges
}

/** 新建卡片的 Y.Map。只能在事务内调用并立即放进 cards。 */
export function createCardMap(fields: CardFields): Y.Map<unknown> {
  const map = new Y.Map<unknown>()
  for (const [key, value] of Object.entries(fields)) {
    if (value !== undefined) map.set(key, value)
  }
  return map
}

/** 只写入真正变化的字段，避免产生多余的同步数据。 */
export function patchCardMap(map: Y.Map<unknown>, patch: Partial<CardFields>) {
  let changed = false
  for (const [key, value] of Object.entries(patch)) {
    if (value === undefined) {
      if (map.has(key)) {
        map.delete(key)
        changed = true
      }
    } else if (map.get(key) !== value) {
      map.set(key, value)
      changed = true
    }
  }
  return changed
}

/** 用另一份文档的内容整体替换画布（恢复历史版本时使用）。 */
export function replaceBoardContent(target: Y.Doc, source: Y.Doc) {
  const cards = boardCards(target)
  const edges = boardEdges(target)
  for (const id of [...cards.keys()]) cards.delete(id)
  for (const id of [...edges.keys()]) edges.delete(id)
  for (const card of readCards(source)) {
    const { id, ...fields } = card
    cards.set(id, createCardMap(fields))
  }
  for (const edge of readEdges(source)) {
    const { id, ...fields } = edge
    if (cards.has(fields.source) && cards.has(fields.target)) edges.set(id, fields)
  }
}

export function docFromUpdate(update: Uint8Array) {
  const doc = new Y.Doc()
  Y.applyUpdate(doc, update)
  return doc
}