ripple-binary-codec/src/shamap.ts

XRP Ledger binary codec

import { coreTypes } from './types'
import { HashPrefix } from './hash-prefixes'
import { Sha512Half } from './hashes'
import { Hash256 } from './types/hash-256'
import { BytesList } from './serdes/binary-serializer'

/**
 * Abstract class describing a SHAMapNode
 */
abstract class ShaMapNode {
  abstract hashPrefix(): Uint8Array
  abstract isLeaf(): boolean
  abstract isInner(): boolean
  abstract toBytesSink(list: BytesList): void
  abstract hash(): Hash256
}

/**
 * Class describing a Leaf of SHAMap
 */
class ShaMapLeaf extends ShaMapNode {
  constructor(public index: Hash256, public item?: ShaMapNode) {
    super()
  }

  /**
   * @returns true as ShaMapLeaf is a leaf node
   */
  isLeaf(): boolean {
    return true
  }

  /**
   * @returns false as ShaMapLeaf is not an inner node
   */
  isInner(): boolean {
    return false
  }

  /**
   * Get the prefix of the this.item
   *
   * @returns The hash prefix, unless this.item is undefined, then it returns an empty Uint8Array
   */
  hashPrefix(): Uint8Array {
    return this.item === undefined ? new Uint8Array(0) : this.item.hashPrefix()
  }

  /**
   * Hash the bytes representation of this
   *
   * @returns hash of this.item concatenated with this.index
   */
  hash(): Hash256 {
    const hash = Sha512Half.put(this.hashPrefix())
    this.toBytesSink(hash)
    return hash.finish()
  }

  /**
   * Write the bytes representation of this to a BytesList
   * @param list BytesList to write bytes to
   */
  toBytesSink(list: BytesList): void {
    if (this.item !== undefined) {
      this.item.toBytesSink(list)
    }
    this.index.toBytesSink(list)
  }
}

/**
 * Class defining an Inner Node of a SHAMap
 */
class ShaMapInner extends ShaMapNode {
  private slotBits = 0
  private branches: Array<ShaMapNode> = Array(16)

  constructor(private depth: number = 0) {
    super()
  }

  /**
   * @returns true as ShaMapInner is an inner node
   */
  isInner(): boolean {
    return true
  }

  /**
   * @returns false as ShaMapInner is not a leaf node
   */
  isLeaf(): boolean {
    return false
  }

  /**
   * Get the hash prefix for this node
   *
   * @returns hash prefix describing an inner node
   */
  hashPrefix(): Uint8Array {
    return HashPrefix.innerNode
  }

  /**
   * Set a branch of this node to be another node
   *
   * @param slot Slot to add branch to this.branches
   * @param branch Branch to add
   */
  setBranch(slot: number, branch: ShaMapNode): void {
    this.slotBits = this.slotBits | (1 << slot)
    this.branches[slot] = branch
  }

  /**
   * @returns true if node is empty
   */
  empty(): boolean {
    return this.slotBits === 0
  }

  /**
   * Compute the hash of this node
   *
   * @returns The hash of this node
   */
  hash(): Hash256 {
    if (this.empty()) {
      return (coreTypes.Hash256 as typeof Hash256).ZERO_256
    }
    const hash = Sha512Half.put(this.hashPrefix())
    this.toBytesSink(hash)
    return hash.finish()
  }

  /**
   * Writes the bytes representation of this node to a BytesList
   *
   * @param list BytesList to write bytes to
   */
  toBytesSink(list: BytesList): void {
    for (let i = 0; i < this.branches.length; i++) {
      const branch = this.branches[i]
      const hash = branch
        ? branch.hash()
        : (coreTypes.Hash256 as typeof Hash256).ZERO_256
      hash.toBytesSink(list)
    }
  }

  /**
   * Add item to the SHAMap
   *
   * @param index Hash of the index of the item being inserted
   * @param item Item to insert in the map
   * @param leaf Leaf node to insert when branch doesn't exist
   */
  addItem(index?: Hash256, item?: ShaMapNode, leaf?: ShaMapLeaf): void {
    if (index === undefined) {
      throw new Error()
    }
    if (index !== undefined) {
      const nibble = index.nibblet(this.depth)
      const existing = this.branches[nibble]

      if (existing === undefined) {
        this.setBranch(nibble, leaf || new ShaMapLeaf(index, item))
      } else if (existing instanceof ShaMapLeaf) {
        const newInner = new ShaMapInner(this.depth + 1)
        newInner.addItem(existing.index, undefined, existing)
        newInner.addItem(index, item, leaf)
        this.setBranch(nibble, newInner)
      } else if (existing instanceof ShaMapInner) {
        existing.addItem(index, item, leaf)
      } else {
        throw new Error('invalid ShaMap.addItem call')
      }
    }
  }
}

class ShaMap extends ShaMapInner {}

export { ShaMap, ShaMapNode, ShaMapLeaf }