yjs/src/utils/StructStore.js

import {
  GC,
  splitItem,
  Transaction, ID, Item, DSDecoderV2 // eslint-disable-line
} from '../internals.js'

import * as math from 'lib0/math'
import * as error from 'lib0/error'

export class StructStore {
  constructor () {
    /**
     * @type {Map<number,Array<GC|Item>>}
     */
    this.clients = new Map()
    /**
     * @type {null | { missing: Map<number, number>, update: Uint8Array }}
     */
    this.pendingStructs = null
    /**
     * @type {null | Uint8Array}
     */
    this.pendingDs = null
  }
}

/**
 * Return the states as a Map<client,clock>.
 * Note that clock refers to the next expected clock id.
 *
 * @param {StructStore} store
 * @return {Map<number,number>}
 *
 * @public
 * @function
 */
export const getStateVector = store => {
  const sm = new Map()
  store.clients.forEach((structs, client) => {
    const struct = structs[structs.length - 1]
    sm.set(client, struct.id.clock + struct.length)
  })
  return sm
}

/**
 * @param {StructStore} store
 * @param {number} client
 * @return {number}
 *
 * @public
 * @function
 */
export const getState = (store, client) => {
  const structs = store.clients.get(client)
  if (structs === undefined) {
    return 0
  }
  const lastStruct = structs[structs.length - 1]
  return lastStruct.id.clock + lastStruct.length
}

/**
 * @param {StructStore} store
 *
 * @private
 * @function
 */
export const integretyCheck = store => {
  store.clients.forEach(structs => {
    for (let i = 1; i < structs.length; i++) {
      const l = structs[i - 1]
      const r = structs[i]
      if (l.id.clock + l.length !== r.id.clock) {
        throw new Error('StructStore failed integrety check')
      }
    }
  })
}

/**
 * @param {StructStore} store
 * @param {GC|Item} struct
 *
 * @private
 * @function
 */
export const addStruct = (store, struct) => {
  let structs = store.clients.get(struct.id.client)
  if (structs === undefined) {
    structs = []
    store.clients.set(struct.id.client, structs)
  } else {
    const lastStruct = structs[structs.length - 1]
    if (lastStruct.id.clock + lastStruct.length !== struct.id.clock) {
      throw error.unexpectedCase()
    }
  }
  structs.push(struct)
}

/**
 * Perform a binary search on a sorted array
 * @param {Array<Item|GC>} structs
 * @param {number} clock
 * @return {number}
 *
 * @private
 * @function
 */
export const findIndexSS = (structs, clock) => {
  let left = 0
  let right = structs.length - 1
  let mid = structs[right]
  let midclock = mid.id.clock
  if (midclock === clock) {
    return right
  }
  // @todo does it even make sense to pivot the search?
  // If a good split misses, it might actually increase the time to find the correct item.
  // Currently, the only advantage is that search with pivoting might find the item on the first try.
  let midindex = math.floor((clock / (midclock + mid.length - 1)) * right) // pivoting the search
  while (left <= right) {
    mid = structs[midindex]
    midclock = mid.id.clock
    if (midclock <= clock) {
      if (clock < midclock + mid.length) {
        return midindex
      }
      left = midindex + 1
    } else {
      right = midindex - 1
    }
    midindex = math.floor((left + right) / 2)
  }
  // Always check state before looking for a struct in StructStore
  // Therefore the case of not finding a struct is unexpected
  throw error.unexpectedCase()
}

/**
 * Expects that id is actually in store. This function throws or is an infinite loop otherwise.
 *
 * @param {StructStore} store
 * @param {ID} id
 * @return {GC|Item}
 *
 * @private
 * @function
 */
export const find = (store, id) => {
  /**
   * @type {Array<GC|Item>}
   */
  // @ts-ignore
  const structs = store.clients.get(id.client)
  return structs[findIndexSS(structs, id.clock)]
}

/**
 * Expects that id is actually in store. This function throws or is an infinite loop otherwise.
 * @private
 * @function
 */
export const getItem = /** @type {function(StructStore,ID):Item} */ (find)

/**
 * @param {Transaction} transaction
 * @param {Array<Item|GC>} structs
 * @param {number} clock
 */
export const findIndexCleanStart = (transaction, structs, clock) => {
  const index = findIndexSS(structs, clock)
  const struct = structs[index]
  if (struct.id.clock < clock && struct instanceof Item) {
    structs.splice(index + 1, 0, splitItem(transaction, struct, clock - struct.id.clock))
    return index + 1
  }
  return index
}

/**
 * Expects that id is actually in store. This function throws or is an infinite loop otherwise.
 *
 * @param {Transaction} transaction
 * @param {ID} id
 * @return {Item}
 *
 * @private
 * @function
 */
export const getItemCleanStart = (transaction, id) => {
  const structs = /** @type {Array<Item>} */ (transaction.doc.store.clients.get(id.client))
  return structs[findIndexCleanStart(transaction, structs, id.clock)]
}

/**
 * Expects that id is actually in store. This function throws or is an infinite loop otherwise.
 *
 * @param {Transaction} transaction
 * @param {StructStore} store
 * @param {ID} id
 * @return {Item}
 *
 * @private
 * @function
 */
export const getItemCleanEnd = (transaction, store, id) => {
  /**
   * @type {Array<Item>}
   */
  // @ts-ignore
  const structs = store.clients.get(id.client)
  const index = findIndexSS(structs, id.clock)
  const struct = structs[index]
  if (id.clock !== struct.id.clock + struct.length - 1 && struct.constructor !== GC) {
    structs.splice(index + 1, 0, splitItem(transaction, struct, id.clock - struct.id.clock + 1))
  }
  return struct
}

/**
 * Replace `item` with `newitem` in store
 * @param {StructStore} store
 * @param {GC|Item} struct
 * @param {GC|Item} newStruct
 *
 * @private
 * @function
 */
export const replaceStruct = (store, struct, newStruct) => {
  const structs = /** @type {Array<GC|Item>} */ (store.clients.get(struct.id.client))
  structs[findIndexSS(structs, struct.id.clock)] = newStruct
}

/**
 * Iterate over a range of structs
 *
 * @param {Transaction} transaction
 * @param {Array<Item|GC>} structs
 * @param {number} clockStart Inclusive start
 * @param {number} len
 * @param {function(GC|Item):void} f
 *
 * @function
 */
export const iterateStructs = (transaction, structs, clockStart, len, f) => {
  if (len === 0) {
    return
  }
  const clockEnd = clockStart + len
  let index = findIndexCleanStart(transaction, structs, clockStart)
  let struct
  do {
    struct = structs[index++]
    if (clockEnd < struct.id.clock + struct.length) {
      findIndexCleanStart(transaction, structs, clockEnd)
    }
    f(struct)
  } while (index < structs.length && structs[index].id.clock < clockEnd)
}