url-json.ts

url-json.ts

/*

URL safe json

cf.
- https://www.json.org/json-en.html
- https://github.com/Sage/jsurl
- https://url.spec.whatwg.org/#application-x-www-form-urlencoded-percent-encode-set
  - ASCII alphanumeric, U+002A (*), U+002D (-), U+002E (.), and U+005F (_)

AST

  <value>
    <object>
    <array>
    <tagged-primitive>

  <object>
    _~ <members> ~_

  <members>
    <member>
    <member> . <members>

  <member>
    * <string> . * - <value>

  <array>
    .~ <values> ~.

  <values>
    <value>
    <value> . <values>

  <tagged-primitive>
    * <primitive> *

  <primitive>
    <string> .
    <number> _
    true
    false
    null


Token
   _~
   ~_
   .~
   ~.
   -
   .
   <tagged-primitive>

*/

const OBJECT_L = "_~";
const OBJECT_R = "~_";
const OBJECT_REL = "-";
const OBJECT_SEP = ".";
const ARRAY_L = ".~";
const ARRAY_R = "~.";
const ARRAY_SEP = ".";
const PRIMITIVE_L = "*";
const PRIMITIVE_R = "*";
const STRING_TAG = ".";
const NUMBER_TAG = "_";

export function stringify(data: any): string {
  //
  // Primitives
  //
  if (data === true) {
    return PRIMITIVE_L + "true" + PRIMITIVE_R;
  }
  if (data === false) {
    return PRIMITIVE_L + "false" + PRIMITIVE_R;
  }
  if (data === null) {
    return PRIMITIVE_L + "null" + PRIMITIVE_R;
  }
  if (typeof data === "string") {
    return (
      PRIMITIVE_L +
      JSON.stringify(data)
        .slice(1, -1)
        .replace(PRIMITIVE_R, "\\" + PRIMITIVE_R) +
      STRING_TAG +
      PRIMITIVE_R
    );
  }
  if (typeof data === "number") {
    return PRIMITIVE_L + JSON.stringify(data) + NUMBER_TAG + PRIMITIVE_R;
  }
  //
  // Array
  //
  if (Array.isArray(data)) {
    return ARRAY_L + data.map(stringify).join(ARRAY_SEP) + ARRAY_R;
  }
  //
  // Object
  //
  const members: string[] = [];
  for (const [key, value] of Object.entries(data)) {
    if (typeof value === "undefined") {
      continue;
    }
    members.push(stringify(key) + OBJECT_REL + stringify(value));
  }
  return OBJECT_L + members.join(OBJECT_SEP) + OBJECT_R;
}

class Parser {
  private cursor: number = 0;
  constructor(private text: string) {}

  match(prefix: string): boolean {
    return this.text.slice(this.cursor).startsWith(prefix);
  }

  consume(expected: string) {
    assert.ok(this.match(expected));
    this.cursor += expected.length;
  }

  parse(): any {
    if (this.match(PRIMITIVE_L)) {
      return this.parsePrimitive();
    }
    if (this.match(ARRAY_L)) {
      return this.parseArray();
    }
    if (this.match(OBJECT_L)) {
      return this.parseObject();
    }
    assert.ok(false);
  }

  parsePrimitive(): any {
    const start = this.cursor;
    let tagged: string | undefined = undefined;
    for (let i = start + 1; i < this.text.length; i++) {
      if (this.text[i] === "\\") {
        i++;
        continue;
      }
      if (this.text[i] === PRIMITIVE_R) {
        tagged = this.text.substring(start, i + 1);
        break;
      }
    }
    assert.ok(typeof tagged === "string");
    this.consume(tagged);
    if (tagged === PRIMITIVE_L + "true" + PRIMITIVE_R) {
      return true;
    }
    if (tagged === PRIMITIVE_L + "false" + PRIMITIVE_R) {
      return false;
    }
    if (tagged === PRIMITIVE_L + "null" + PRIMITIVE_R) {
      return null;
    }
    if (tagged.endsWith(STRING_TAG + PRIMITIVE_R)) {
      const slice_l = PRIMITIVE_L.length;
      const slice_r = STRING_TAG.length + PRIMITIVE_L.length;
      const data = JSON.parse(
        '"' +
          tagged
            .slice(slice_l, -slice_r)
            .replace("\\" + PRIMITIVE_R, PRIMITIVE_R) +
          '"'
      );
      assert.ok(typeof data === "string");
      return data;
    }
    if (tagged.endsWith(NUMBER_TAG + PRIMITIVE_R)) {
      const slice_l = PRIMITIVE_L.length;
      const slice_r = NUMBER_TAG.length + PRIMITIVE_L.length;
      const data = JSON.parse(tagged.slice(slice_l, -slice_r));
      assert.ok(typeof data === "number");
      return data;
    }
    assert.ok(false, "");
  }

  parseArray(): any {
    let first = true;
    let result = [];
    this.consume(ARRAY_L);
    while (!this.match(ARRAY_R)) {
      if (first) {
        first = false;
      } else {
        this.consume(ARRAY_SEP);
      }
      const element = this.parse();
      result.push(element);
    }
    this.consume(ARRAY_R);
    return result;
  }

  parseObject(): any {
    let first = true;
    let result: Record<string, any> = {};
    this.consume(OBJECT_L);
    while (!this.match(OBJECT_R)) {
      if (first) {
        first = false;
      } else {
        this.consume(OBJECT_SEP);
      }
      const key = this.parse();
      assert.ok(typeof key === "string");
      this.consume(OBJECT_REL);
      const value = this.parse();
      result[key] = value;
    }
    this.consume(OBJECT_R);
    return result;
  }
}

export function parse(stringified: string): any {
  return new Parser(stringified).parse();
}