'use strict';

const internals = {
  kVertexNotFound: 'There is no vertex with the name: ',
  kColors: {
    fulfilled: 'green',
    rejected: 'red'
  }
};

/**
 * The definition of a vertex that can be executed in the graph.
 *
 * @typedef {object} tVertex
 * @property {string} name The name of the vertex
 * @property {string[]} [dependencies=[]] The names of vertices that need to run before this one
 * @property {function} action The action to execute
 */

/**
 * Represents a graph of functions. You can call run on any specific vertex,
 * which will trigger execution of it and its dependencies.
 *
 * It guarantees that each vertex will only run once.
 *
 * It can be represented in graphviz format, highlighting fulfilled and
 * rejected vertices.
 *
 * @class Grafn
 */
module.exports = class Grafn {

  constructor() {

    this._vertices = {};
    this._dependents = {};
    this._state = {};
  }

  /**
   * Executes the named vertex and all its dependents
   * @method run
   * @memberof Grafn
   * @instance
   * @param {string} vertexName the name of the vertex to run
   * @throws Will throw an error if a requested vertex does not exist
   */
  async run(vertexName) {

    const vertex = this._vertices[vertexName];

    if (!vertex) {
      throw new Error(internals.kVertexNotFound + vertexName);
    }

    if (!vertex.isFulfilled && this._dependenciesFulfilled(vertex.dependencies)) {
      try {
        this._state[vertexName] = await vertex.action(this._state);
        vertex.isFulfilled = true;
      }
      catch (error) {
        vertex.isRejected = true;
        throw error;
      }
    }

    await Promise.all(this._dependents[vertexName].map((dependent) => this.run(dependent)));
  }

  /**
   * Adds a vertex to the graph.
   * @method vertex
   * @memberof Grafn
   * @instance
   * @param {tVertex} vertex the definition of the vertex to add
   */
  vertex({ name, action, dependencies = [] }) {

    this._vertices[name] = { action, dependencies, isFulfilled: false, isRejected: false };
    this._dependents[name] = this._dependents[name] || [];

    dependencies.forEach((dependency) => {

      this._dependents[dependency] = this._dependents[dependency] || [];
      this._dependents[dependency].push(name);
    });
  }

  /**
   * Converts the graph to a graphviz digraph. If vertices have been executed,
   * they will be highlighted depending on whether they fulfilled or rejected.
   * @method toString
   * @memberof Grafn
   * @instance
   * @return {string} The graphviz digraph representation
   */
  toString() {

    const string = ['digraph {'];

    Object.entries(this._vertices).forEach(([name, vertex]) => {

      string.push(`    ${name}${this._vertexColor(vertex)}`);
      vertex.dependencies.forEach((dependency) => string.push(`    ${dependency} -> ${name}`));
    });

    string.push('}');

    return string.join('\n');
  }

  // Given a list of dependencies, check that all of them are fulfilled

  _dependenciesFulfilled(dependencies) {

    return dependencies
      .map((dependency) => (this._vertices[dependency] || {}).isFulfilled)
      .reduce((test, isFulfilled) => test && isFulfilled, true);
  }

  // Given the state of a vertex, returns the graphviz color configuration

  _vertexColor(vertex) {

    if (vertex.isFulfilled) {
      return `[color=${internals.kColors.fulfilled}]`;
    }

    if (vertex.isRejected) {
      return `[color=${internals.kColors.rejected}]`;
    }

    return '';
  }
};