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/*!
 * tree.js - authenticated tree
 * Copyright (c) 2018, Christopher Jeffrey (MIT License).
 * https://github.com/handshake-org/urkel
 */
 
'use strict';
 
const assert = require('bsert');
const common = require('./common');
const errors = require('./errors');
const nodes = require('./nodes');
const Proof = require('./proof');
const store = require('./store');
const {AssertionError} = errors;
 
const {
  hasBit,
  hashValue,
  randomPath
} = common;
 
const {
  types,
  Node,
  NIL,
  Internal,
  Leaf
} = nodes;
 
const {
  NULL,
  INTERNAL,
  LEAF,
  HASH
} = types;
 
const {
  FileStore,
  MemoryStore
} = store;
 
/*
 * Compat
 */
 
const asyncIterator = Symbol.asyncIterator || 'asyncIterator';
 
/**
 * Tree
 */
 
class Tree {
  /**
   * Create a tree.
   * @constructor
   * @param {Object} hash
   * @param {Number} bits
   * @param {String} prefix
   */
 
  constructor(hash, bits, prefix) {
    assert(hash && typeof hash.digest === 'function');
    assert((bits >>> 0) === bits);
    assert(bits > 0 && (bits & 7) === 0);
    assert(!prefix || typeof prefix === 'string');
 
    let Store = FileStore;
 
    Eif (!prefix) {
      Store = MemoryStore;
      prefix = '/store';
    }
 
    this.hash = hash;
    this.bits = bits;
    this.prefix = prefix || null;
    this.store = new Store(prefix, hash, bits);
    this.root = NIL;
  }
 
  isKey(key) {
    Iif (!Buffer.isBuffer(key))
      return false;
    return key.length === (this.bits >>> 3);
  }
 
  isValue(value) {
    Iif (!Buffer.isBuffer(value))
      return false;
    return value.length <= 0x400;
  }
 
  isHash(hash) {
    Iif (!Buffer.isBuffer(hash))
      return false;
    return hash.length === this.hash.size;
  }
 
  leaf(key, value) {
    const hash = hashValue(this.hash, key, value);
    return new Leaf(hash, key, value);
  }
 
  rootHash() {
    return this.root.hash(this.hash);
  }
 
  async getRoot() {
    return this.root;
  }
 
  async open(root) {
    this.root = await this.store.open();
 
    Iif (root)
      await this.inject(root);
  }
 
  async close() {
    this.root = NIL;
    return this.store.close();
  }
 
  async inject(root) {
    this.root = await this.getHistory(root);
  }
 
  async getHistory(root) {
    assert(this.isHash(root));
    return this.store.getHistory(root);
  }
 
  async resolve(node) {
    return this.store.resolve(node);
  }
 
  async retrieve(node) {
    return this.store.retrieve(node);
  }
 
  async _get(root, key) {
    let node = root;
    let depth = 0;
 
    for (;;) {
      switch (node.type()) {
        case NULL: {
          // Empty tree.
          return null;
        }
 
        case INTERNAL: {
          if (!node.prefix.has(key, depth))
            return null;
 
          depth += node.prefix.size;
 
          const bit = hasBit(key, depth);
 
          node = node.get(bit);
          depth += 1;
 
          break;
        }
 
        case LEAF: {
          // Prefix collision.
          if (!key.equals(node.key))
            return null;
 
          return this.retrieve(node);
        }
 
        case HASH: {
          node = await this.resolve(node);
          break;
        }
 
        default: {
          throw new AssertionError('Unknown node type.');
        }
      }
    }
  }
 
  async get(key) {
    assert(this.isKey(key));
    return this._get(this.root, key);
  }
 
  async _insert(node, key, value, depth) {
    switch (node.type()) {
      case NULL: {
        // Replace the empty node.
        return this.leaf(key, value);
      }
 
      case INTERNAL: {
        const bits = node.prefix.count(key, depth);
 
        depth += bits;
 
        const bit = hasBit(key, depth);
 
        if (bits !== node.prefix.size) {
          const leaf = this.leaf(key, value);
          const [front, back] = node.prefix.split(bits);
          const child = new Internal(back, node.left, node.right);
          return Internal.from(front, leaf, child, bit);
        }
 
        const x = node.get(bit);
        const y = node.get(bit ^ 1);
        const z = await this._insert(x, key, value, depth + 1);
 
        Iif (!z)
          return null;
 
        return Internal.from(node.prefix, z, y, bit);
      }
 
      case LEAF: {
        // Current key.
        Iif (key.equals(node.key)) {
          // Exact leaf already exists.
          if (node.value && value.equals(node.value))
            return null;
 
          // The branch doesn't grow.
          // Replace the current node.
          return this.leaf(key, value);
        }
 
        assert(depth !== this.bits);
 
        const prefix = node.bits.collide(key, depth);
 
        depth += prefix.size;
 
        const leaf = this.leaf(key, value);
        const bit = hasBit(key, depth);
 
        return Internal.from(prefix, leaf, node, bit);
      }
 
      case HASH: {
        const rn = await this.resolve(node);
        return this._insert(rn, key, value, depth);
      }
 
      default: {
        throw new AssertionError('Unknown node.');
      }
    }
  }
 
  async _remove(node, key, depth) {
    switch (node.type()) {
      case NULL: {
        // Empty tree.
        return null;
      }
 
      case INTERNAL: {
        Iif (!node.prefix.has(key, depth))
          return null;
 
        depth += node.prefix.size;
 
        const bit = hasBit(key, depth);
        const x = node.get(bit);
        const y = node.get(bit ^ 1);
        const z = await this._remove(x, key, depth + 1);
 
        Iif (!z)
          return null;
 
        if (z.isNull()) {
          const side = await this.resolve(y);
 
          if (side.isInternal()) {
            const prefix = node.prefix.join(side.prefix, bit ^ 1);
            return new Internal(prefix, side.left, side.right);
          }
 
          return side;
        }
 
        return Internal.from(node.prefix, z, y, bit);
      }
 
      case LEAF: {
        // Not our key.
        Iif (!key.equals(node.key))
          return null;
 
        return NIL;
      }
 
      case HASH: {
        const rn = await this.resolve(node);
        return this._remove(rn, key, depth);
      }
 
      default: {
        throw new AssertionError('Unknown node.');
      }
    }
  }
 
  async _commit(node) {
    const root = this._write(node);
 
    await this.store.commit(root);
 
    this.root = root;
 
    return root;
  }
 
  _write(node) {
    switch (node.type()) {
      case NULL: {
        return node;
      }
 
      case INTERNAL: {
        node.left = this._write(node.left);
        node.right = this._write(node.right);
 
        Eif (!node.ptr) {
          this.store.writeNode(node);
 
          // if (this.store.needsFlush())
          //   await this.store.flush();
        }
 
        assert(node.ptr);
 
        return node.toHash(this.hash);
      }
 
      case LEAF: {
        if (!node.ptr) {
          assert(node.value);
 
          this.store.writeValue(node);
          this.store.writeNode(node);
 
          // if (this.store.needsFlush())
          //   await this.store.flush();
        }
 
        assert(node.ptr);
 
        return node.toHash(this.hash);
      }
 
      case HASH: {
        assert(node.ptr);
        return node;
      }
    }
 
    throw new AssertionError('Unknown node.');
  }
 
  async prove(key) {
    assert(this.isKey(key));
    return this._prove(this.root, key);
  }
 
  async _prove(root, key) {
    const proof = new Proof();
 
    let node = root;
    let depth = 0;
 
    // Traverse bits left to right.
outer:
    for (;;) {
      switch (node.type()) {
        case NULL: {
          proof.type = Proof.TYPE_DEADEND;
          proof.depth = depth;
          break outer;
        }
 
        case INTERNAL: {
          if (!node.prefix.has(key, depth)) {
            const left = node.left.hash(this.hash);
            const right = node.right.hash(this.hash);
 
            proof.type = Proof.TYPE_SHORT;
            proof.depth = depth;
            proof.prefix = node.prefix.clone();
            proof.left = Buffer.from(left);
            proof.right = Buffer.from(right);
 
            break outer;
          }
 
          depth += node.prefix.size;
 
          const bit = hasBit(key, depth);
          const side = node.get(bit ^ 1);
          const hash = side.hash(this.hash);
 
          proof.push(node.prefix.clone(), hash);
 
          node = node.get(bit);
          depth += 1;
 
          break;
        }
 
        case LEAF: {
          const value = await this.retrieve(node);
 
          if (node.key.equals(key)) {
            proof.type = Proof.TYPE_EXISTS;
            proof.depth = depth;
            proof.value = value;
          } else {
            proof.type = Proof.TYPE_COLLISION;
            proof.depth = depth;
            proof.key = Buffer.from(node.key);
            proof.hash = this.hash.digest(value);
          }
 
          break outer;
        }
 
        case HASH: {
          node = await this.resolve(node);
          break;
        }
 
        default: {
          throw new AssertionError('Unknown node type.');
        }
      }
    }
 
    return proof;
  }
 
  async compact() {
    const prefix = randomPath(this.prefix);
    const store = this.store.clone(prefix);
 
    await store.open();
 
    const root = await this._compact(this.root, store);
 
    await store.commit(root);
    await store.close();
 
    await this.store.close();
    await this.store.destroy();
 
    await store.rename(this.prefix);
    await store.open();
 
    this.store = store;
    this.root = root;
  }
 
  async _compact(node, store) {
    switch (node.type()) {
      case NULL: {
        return node;
      }
 
      case INTERNAL: {
        node.left = await this._compact(node.left, store);
        node.right = await this._compact(node.right, store);
 
        node.ptr = null;
 
        store.writeNode(node);
 
        Iif (store.needsFlush())
          await store.flush();
 
        return node.toHash(this.hash);
      }
 
      case LEAF: {
        node.ptr = null;
        node.value = await this.retrieve(node);
 
        store.writeValue(node);
        store.writeNode(node);
 
        Iif (store.needsFlush())
          await store.flush();
 
        return node.toHash(this.hash);
      }
 
      case HASH: {
        const rn = await this.resolve(node);
        return this._compact(rn, store);
      }
    }
 
    throw new AssertionError('Unknown node.');
  }
 
  snapshot(hash) {
    let root = null;
 
    if (hash == null) {
      hash = this.rootHash();
      root = this.root;
    }
 
    return new Snapshot(this, hash, root);
  }
 
  transaction() {
    return new Transaction(this);
  }
 
  iterator(read = true) {
    const iter = new Iterator(this, this, read);
    iter.root = this.root;
    return iter;
  }
 
  [asyncIterator]() {
    return this.entries();
  }
 
  keys() {
    const iter = this.iterator(false);
    return iter.keys();
  }
 
  values() {
    const iter = this.iterator(true);
    return iter.values();
  }
 
  entries() {
    const iter = this.iterator(true);
    return iter.entries();
  }
 
  batch() {
    return this.transaction();
  }
 
  txn() {
    return this.transaction();
  }
}
 
/**
 * Snapshot
 */
 
class Snapshot {
  constructor(tree, hash, root) {
    assert(tree instanceof Tree);
    assert(tree.isHash(hash));
    assert(root === null || (root instanceof Node));
 
    this.tree = tree;
    this.hash = hash;
    this.root = root;
  }
 
  rootHash() {
    return this.hash;
  }
 
  async getRoot() {
    Eif (!this.root)
      this.root = await this.tree.getHistory(this.hash);
    return this.root;
  }
 
  async inject(root) {
    this.root = await this.tree.getHistory(root);
    this.hash = root;
  }
 
  async get(key) {
    assert(this.tree.isKey(key));
 
    Eif (!this.root)
      this.root = await this.getRoot();
 
    return this.tree._get(this.root, key);
  }
 
  async prove(key) {
    if (!this.root)
      this.root = await this.getRoot();
 
    return this.tree._prove(this.root, key);
  }
 
  iterator(read = true) {
    const iter = new Iterator(this.tree, this, read);
    iter.root = this.root;
    return iter;
  }
 
  [asyncIterator]() {
    return this.entries();
  }
 
  keys() {
    const iter = this.iterator(false);
    return iter.keys();
  }
 
  values() {
    const iter = this.iterator(true);
    return iter.values();
  }
 
  entries() {
    const iter = this.iterator(true);
    return iter.entries();
  }
}
 
/**
 * Transaction
 */
 
class Transaction extends Snapshot {
  constructor(tree) {
    assert(tree instanceof Tree);
    super(tree, tree.rootHash(), tree.root);
  }
 
  rootHash() {
    return this.root.hash(this.tree.hash);
  }
 
  async getRoot() {
    return this.root;
  }
 
  async insert(key, value) {
    assert(this.tree.isKey(key));
    assert(this.tree.isValue(value));
 
    const root = await this.tree._insert(this.root, key, value, 0);
 
    Eif (root)
      this.root = root;
  }
 
  async remove(key) {
    assert(this.tree.isKey(key));
 
    const root = await this.tree._remove(this.root, key, 0);
 
    Eif (root)
      this.root = root;
  }
 
  async commit() {
    this.root = await this.tree._commit(this.root);
    this.hash = this.rootHash();
    return this.hash;
  }
 
  clear() {
    this.root = this.tree.root;
    return this;
  }
}
 
/**
 * Iterator
 */
 
class Iterator {
  constructor(tree, parent, read) {
    assert(tree instanceof Tree);
    assert(parent && typeof parent.getRoot === 'function');
    assert(typeof read === 'boolean');
 
    this.tree = tree;
    this.parent = parent;
    this.read = read;
    this.root = null;
    this.stack = [];
    this.done = false;
    this.node = NIL;
    this.key = null;
    this.value = null;
  }
 
  [asyncIterator]() {
    return this.entries();
  }
 
  keys() {
    return new AsyncIterator(this, 0);
  }
 
  values() {
    return new AsyncIterator(this, 1);
  }
 
  entries() {
    return new AsyncIterator(this, 2);
  }
 
  push(node, depth) {
    const state = new IteratorState(node, depth);
    return this.stack.push(state);
  }
 
  pop() {
    assert(this.stack.length > 0);
    return this.stack.pop();
  }
 
  top() {
    assert(this.stack.length > 0);
    return this.stack[this.stack.length - 1];
  }
 
  length() {
    return this.stack.length;
  }
 
  async seek() {
    Iif (!this.root)
      this.root = await this.parent.getRoot();
 
    this.node = NIL;
 
    Iif (this.done)
      return false;
 
    if (this.length() === 0) {
      this.push(this.root, 0);
    } else {
      this.pop();
 
      if (this.length() === 0) {
        this.done = true;
        return false;
      }
    }
 
outer:
    for (;;) {
      const parent = this.top();
      const {node, depth} = parent;
 
      switch (node.type()) {
        case NULL: {
          this.node = node;
          break outer;
        }
 
        case INTERNAL: {
          if (parent.child >= 1)
            break outer;
 
          parent.child += 1;
 
          if (parent.child)
            this.push(node.right, depth + node.prefix.size + 1);
          else
            this.push(node.left, depth + node.prefix.size + 1);
 
          break;
        }
 
        case LEAF: {
          this.node = node;
          break outer;
        }
 
        case HASH: {
          if (parent.child >= 0)
            break outer;
 
          parent.child += 1;
 
          const rn = await this.tree.resolve(node);
          this.push(rn, depth);
          break;
        }
 
        default: {
          throw new AssertionError('Unknown node.');
        }
      }
    }
 
    return true;
  }
 
  async next() {
    for (;;) {
      if (!await this.seek())
        break;
 
      if (!this.node.isLeaf())
        continue;
 
      this.key = this.node.key;
      this.value = this.node.value;
 
      Eif (this.read && !this.value)
        this.value = await this.tree.retrieve(this.node);
 
      return true;
    }
 
    this.key = null;
    this.value = null;
 
    return false;
  }
}
 
/**
 * IteratorState
 */
 
class IteratorState {
  constructor(node, depth) {
    this.node = node;
    this.depth = depth;
    this.child = -1;
  }
}
 
/**
 * AsyncIterator
 */
 
class AsyncIterator {
  constructor(iter, type) {
    assert(iter instanceof Iterator);
    assert((type & 3) === type);
    assert(type < 3);
 
    this.iter = iter;
    this.type = type;
  }
 
  async next() {
    if (!await this.iter.next())
      return { value: undefined, done: true };
 
    switch (this.type) {
      case 0:
        return { value: this.iter.key, done: false };
      case 1:
        return { value: this.iter.value, done: false };
      case 2:
        return { value: [this.iter.key, this.iter.value], done: false };
      default:
        throw new AssertionError('Bad value mode.');
    }
  }
}
 
/*
 * Expose
 */
 
module.exports = Tree;