Changeset: New API to simplify attribute processing

src/static/js/AttributeMap.js

@@ -0,0 +1,91 @@
+'use strict';
+
+const attributes = require('./attributes');
+
+/**
+ * A `[key, value]` pair of strings describing a text attribute.
+ *
+ * @typedef {[string, string]} Attribute
+ */
+
+/**
+ * A concatenated sequence of zero or more attribute identifiers, each one represented by an
+ * asterisk followed by a base-36 encoded attribute number.
+ *
+ * Examples: '', '*0', '*3*j*z*1q'
+ *
+ * @typedef {string} AttributeString
+ */
+
+/**
+ * Convenience class to convert an Op's attribute string to/from a Map of key, value pairs.
+ */
+class AttributeMap extends Map {
+  /**
+   * Converts an attribute string into an AttributeMap.
+   *
+   * @param {AttributeString} str - The attribute string to convert into an AttributeMap.
+   * @param {AttributePool} pool - Attribute pool.
+   * @returns {AttributeMap}
+   */
+  static fromString(str, pool) {
+    return new AttributeMap(pool).updateFromString(str);
+  }
+
+  /**
+   * @param {AttributePool} pool - Attribute pool.
+   */
+  constructor(pool) {
+    super();
+    /** @public */
+    this.pool = pool;
+  }
+
+  /**
+   * @param {string} k - Attribute name.
+   * @param {string} v - Attribute value.
+   * @returns {AttributeMap} `this` (for chaining).
+   */
+  set(k, v) {
+    k = k == null ? '' : String(k);
+    v = v == null ? '' : String(v);
+    this.pool.putAttrib([k, v]);
+    return super.set(k, v);
+  }
+
+  toString() {
+    return attributes.attribsToString(attributes.sort([...this]), this.pool);
+  }
+
+  /**
+   * @param {Iterable<Attribute>} entries - [key, value] pairs to insert into this map.
+   * @param {boolean} [emptyValueIsDelete] - If true and an entry's value is the empty string, the
+   *     key is removed from this map (if present).
+   * @returns {AttributeMap} `this` (for chaining).
+   */
+  update(entries, emptyValueIsDelete = false) {
+    for (let [k, v] of entries) {
+      k = k == null ? '' : String(k);
+      v = v == null ? '' : String(v);
+      if (!v && emptyValueIsDelete) {
+        this.delete(k);
+      } else {
+        this.set(k, v);
+      }
+    }
+    return this;
+  }
+
+  /**
+   * @param {AttributeString} str - The attribute string identifying the attributes to insert into
+   *     this map.
+   * @param {boolean} [emptyValueIsDelete] - If true and an entry's value is the empty string, the
+   *     key is removed from this map (if present).
+   * @returns {AttributeMap} `this` (for chaining).
+   */
+  updateFromString(str, emptyValueIsDelete = false) {
+    return this.update(attributes.attribsFromString(str, this.pool), emptyValueIsDelete);
+  }
+}
+
+module.exports = AttributeMap;

src/static/js/attributes.js

@@ -0,0 +1,130 @@
+'use strict';
+
+// Low-level utilities for manipulating attribute strings. For a high-level API, see AttributeMap.
+
+/**
+ * A `[key, value]` pair of strings describing a text attribute.
+ *
+ * @typedef {[string, string]} Attribute
+ */
+
+/**
+ * A concatenated sequence of zero or more attribute identifiers, each one represented by an
+ * asterisk followed by a base-36 encoded attribute number.
+ *
+ * Examples: '', '*0', '*3*j*z*1q'
+ *
+ * @typedef {string} AttributeString
+ */
+
+/**
+ * Converts an attribute string into a sequence of attribute identifier numbers.
+ *
+ * WARNING: This only works on attribute strings. It does NOT work on serialized operations or
+ * changesets.
+ *
+ * @param {AttributeString} str - Attribute string.
+ * @yields {number} The attribute numbers (to look up in the associated pool), in the order they
+ *     appear in `str`.
+ * @returns {Generator<number>}
+ */
+exports.decodeAttribString = function* (str) {
+  const re = /\*([0-9a-z]+)|./gy;
+  let match;
+  while ((match = re.exec(str)) != null) {
+    const [m, n] = match;
+    if (n == null) throw new Error(`invalid character in attribute string: ${m}`);
+    yield Number.parseInt(n, 36);
+  }
+};
+
+const checkAttribNum = (n) => {
+  if (typeof n !== 'number') throw new TypeError(`not a number: ${n}`);
+  if (n < 0) throw new Error(`attribute number is negative: ${n}`);
+  if (n !== Math.trunc(n)) throw new Error(`attribute number is not an integer: ${n}`);
+};
+
+/**
+ * Inverse of `decodeAttribString`.
+ *
+ * @param {Iterable<number>} attribNums - Sequence of attribute numbers.
+ * @returns {AttributeString}
+ */
+exports.encodeAttribString = (attribNums) => {
+  let str = '';
+  for (const n of attribNums) {
+    checkAttribNum(n);
+    str += `*${n.toString(36).toLowerCase()}`;
+  }
+  return str;
+};
+
+/**
+ * Converts a sequence of attribute numbers into a sequence of attributes.
+ *
+ * @param {Iterable<number>} attribNums - Attribute numbers to look up in the pool.
+ * @param {AttributePool} pool - Attribute pool.
+ * @yields {Attribute} The identified attributes, in the same order as `attribNums`.
+ * @returns {Generator<Attribute>}
+ */
+exports.attribsFromNums = function* (attribNums, pool) {
+  for (const n of attribNums) {
+    checkAttribNum(n);
+    const attrib = pool.getAttrib(n);
+    if (attrib == null) throw new Error(`attribute ${n} does not exist in pool`);
+    yield attrib;
+  }
+};
+
+/**
+ * Inverse of `attribsFromNums`.
+ *
+ * @param {Iterable<Attribute>} attribs - Attributes. Any attributes not already in `pool` are
+ *     inserted into `pool`. No checking is performed to ensure that the attributes are in the
+ *     canonical order and that there are no duplicate keys. (Use an AttributeMap and/or `sort()` if
+ *     required.)
+ * @param {AttributePool} pool - Attribute pool.
+ * @yields {number} The attribute number of each attribute in `attribs`, in order.
+ * @returns {Generator<number>}
+ */
+exports.attribsToNums = function* (attribs, pool) {
+  for (const attrib of attribs) yield pool.putAttrib(attrib);
+};
+
+/**
+ * Convenience function that is equivalent to `attribsFromNums(decodeAttribString(str), pool)`.
+ *
+ * WARNING: This only works on attribute strings. It does NOT work on serialized operations or
+ * changesets.
+ *
+ * @param {AttributeString} str - Attribute string.
+ * @param {AttributePool} pool - Attribute pool.
+ * @yields {Attribute} The attributes identified in `str`, in order.
+ * @returns {Generator<Attribute>}
+ */
+exports.attribsFromString = function* (str, pool) {
+  yield* exports.attribsFromNums(exports.decodeAttribString(str), pool);
+};
+
+/**
+ * Inverse of `attribsFromString`.
+ *
+ * @param {Iterable<Attribute>} attribs - Attributes. The attributes to insert into the pool (if
+ *     necessary) and encode. No checking is performed to ensure that the attributes are in the
+ *     canonical order and that there are no duplicate keys. (Use an AttributeMap and/or `sort()` if
+ *     required.)
+ * @param {AttributePool} pool - Attribute pool.
+ * @returns {AttributeString}
+ */
+exports.attribsToString =
+    (attribs, pool) => exports.encodeAttribString(exports.attribsToNums(attribs, pool));
+
+/**
+ * Sorts the attributes in canonical order. The order of entries with the same attribute name is
+ * unspecified.
+ *
+ * @param {Attribute[]} attribs - Attributes to sort in place.
+ * @returns {Attribute[]} `attribs` (for chaining).
+ */
+exports.sort =
+    (attribs) => attribs.sort(([keyA], [keyB]) => (keyA > keyB ? 1 : 0) - (keyA < keyB ? 1 : 0));