const STOP_CRAWLING = {};

type SerializerNamespace = { [name: string]: { new (): any } };

/**
 * A deep serializer of javascript objects.
 */
export class Serializer {
  private namespace: SerializerNamespace;
  private namespace_rev: { [classname: string]: string };
  private ignored: string[] = [];
  private stats: any = {};

  constructor(namespace: any) {
    if (Array.isArray(namespace)) {
      this.namespace = {};
      for (let construct of namespace) {
        this.namespace[construct.name] = construct;
      }
    } else {
      this.namespace = namespace;
    }

    this.namespace_rev = {};
    for (let [key, value] of Object.entries(this.namespace)) {
      this.namespace_rev[value.name] = key;
    }
  }

  /**
   * Add a class to the ignore list
   */
  addIgnoredClass(cl: string | { new (): any }) {
    this.ignored.push(typeof cl === "string" ? cl : cl.name);
  }

  /**
   * Serialize an object to a string
   */
  serialize(obj: any): string {
    // Collect objects
    var objects: Object[] = [];
    var stats: any = {};

    function add(value: any): void {
      if (objects.indexOf(value) < 0) {
        objects.push(value);
      }
    }

    crawl(obj, (value) => {
      if (isObject(value)) {
        var vtype = classname(value);
        if (vtype != "" && this.ignored.indexOf(vtype) < 0) {
          stats[vtype] = (stats[vtype] || 0) + 1;
          add(value);
          return value;
        } else {
          return STOP_CRAWLING;
        }
      } else if (typeof value == "function") {
        const found = Object.entries(this.namespace).find(([_, cons]) =>
          cons === value
        );
        if (found && this.ignored.indexOf(found[0]) < 0) {
          // Keep references to constructors in the namespace
          add(value);
        }
        return STOP_CRAWLING;
      } else {
        return value;
      }
    });
    this.stats = stats;

    // Serialize objects list, transforming deeper objects to links
    var fobjects = objects.map((value) => this.encodeObject(value));
    return JSON.stringify(fobjects, (key, value) => {
      if (
        key != "$f" && (isObject(value) || typeof value == "function") &&
        !value.hasOwnProperty("$c") &&
        !value.hasOwnProperty("$i")
      ) {
        return { $i: objects.indexOf(value) };
      } else {
        return value;
      }
    });
  }

  /**
   * Unserialize a string to an object
   */
  unserialize(data: string): any {
    // Unserialize objects list
    var fobjects = JSON.parse(data);

    // Reconstruct objects
    var objects = fobjects.map((objdata: any) => this.decodeObject(objdata));

    // Reconnect links
    crawl(objects, (value) => {
      if (value instanceof Object && value.hasOwnProperty("$i")) {
        return objects[value["$i"]];
      } else {
        return value;
      }
    }, true);

    // Post unserialize hooks
    crawl(objects[0], (value) => {
      if (
        value instanceof Object && typeof value.postUnserialize === "function"
      ) {
        value.postUnserialize();
      }
    });

    // First object was the root
    return objects[0];
  }

  /**
   * Construct an object from a constructor name
   */
  private constructObject(ctype: string): Object {
    if (ctype == "Object") {
      return {};
    } else {
      let cl = this.namespace[ctype];
      if (cl) {
        return Object.create(cl.prototype);
      } else {
        console.error("Can't find class", ctype);
        return {};
      }
    }
  }

  /**
   * Transform an object into encoded representation
   */
  private encodeObject(obj: Object) {
    const ctype = classname(obj);
    if (obj instanceof Set || obj instanceof Map) {
      return {
        $c: ctype,
        $f: Array.from(obj),
      };
    } else if (typeof obj == "function") {
      return {
        $c: obj.name,
      };
    } else {
      return {
        $c: this.namespace_rev[ctype] || ctype,
        $f: Object.assign({}, obj),
      };
    }
  }

  /**
   * Decode back an encoded representation to a full object
   */
  private decodeObject(objdata: any) {
    const ctype = objdata.$c;
    if (ctype == "Set") {
      return new Set(objdata.$f);
    } else if (ctype == "Map") {
      return new Map(objdata.$f);
    } else if (objdata.$f) {
      return Object.assign(this.constructObject(ctype), objdata.$f);
    } else {
      return this.namespace[ctype];
    }
  }
}

/**
 * Check if the argument is an instance of a class
 */
function isObject(value: any): boolean {
  return typeof value == "object" && value instanceof Object &&
    !Array.isArray(value);
}

/**
 * Recursively crawl through an object, yielding any defined value found along the way
 *
 * If *replace* is set to true, the current object is replaced (in array or object attribute) by the result of the callback
 *
 * *memo* is used to prevent circular references to be traversed
 */
function crawl(
  obj: any,
  callback: (item: any) => any,
  replace = false,
  memo: any[] = [],
): any {
  if (isObject(obj)) {
    if (memo.indexOf(obj) >= 0) {
      return obj;
    } else {
      memo.push(obj);
    }
  }

  if (obj !== undefined && obj !== null) {
    const result = callback(obj);

    if (result === STOP_CRAWLING) {
      return undefined;
    }

    if (Array.isArray(obj)) {
      const subresult = obj.map((value) =>
        crawl(value, callback, replace, memo)
      );
      if (replace) {
        subresult.forEach((value, index) => {
          obj[index] = value;
        });
      }
    } else if (obj instanceof Set) {
      const subresult = new Set();
      for (const item of obj) {
        subresult.add(crawl(item, callback, replace, memo));
      }
      if (replace) {
        obj.clear();
        for (const item of subresult) {
          obj.add(item);
        }
      }
    } else if (obj instanceof Map) {
      const subresult = new Map();
      for (const [key, item] of obj.entries()) {
        subresult.set(
          crawl(key, callback, replace, memo),
          crawl(item, callback, replace, memo),
        );
      }
      if (replace) {
        obj.clear();
        for (const [key, item] of subresult.entries()) {
          obj.set(key, item);
        }
      }
    } else if (obj instanceof Object) {
      const subresult: any = {};
      for (const key in obj) {
        subresult[key] = crawl(obj[key], callback, replace, memo);
      }
      if (replace) {
        Object.assign(obj, subresult);
      }
    }

    return result;
  } else {
    return obj;
  }
}

/**
 * Get the class name of an object.
 */
function classname(obj: Object): string {
  return obj.constructor.name;
}