class GEO_Line {

  /**
   * Get coordinates of point at line's position
   *
   * @param {Object} line - line object
   * @param {number} percentage - position on line in percents
   *
   * @return {Object} - point with coordinates
   */
  getPoint(line, position) {
    let equation = this.getLineEquation(line);

    let dx = line.end.x - line.start.x;

    let x = line.start.x + (dx * position / 100);
    let y = equation(x);

    return {x, y};
  }

  /**
   * Get length of a given line
   *
   * @param {Object} line - line object
   *
   * @return {number} - absolute value of line's length
   */
  getLength(line) {
    let dx = line.end.x - line.start.x;
    let dy = line.end.y - line.start.y;

    return Math.abs( Math.sqrt(dx*dx + dy*dy) );
  }

  /**
   * Get line equation for given line
   *
   * @param {Object} line - line object
   *
   * @return {function}
   */
  getLineEquation(line) {
    let m = this.getSlope(line);

    /**
     * Get y coordinate from x coordinate
     *
     * @param {number} x - x coordinate
     *
     * @return {number} - y coordinate
     */
    let equation = function(x) {
      return m*x - m*line.start.x + line.start.y;
    }

    return equation;
  }

  /**
   * Get line's slope for line equation
   *
   * @param {Object} line - line object
   *
   * @return {number} - slope
   */
  getSlope(line) {
    return (line.end.y - line.start.y)/(line.end.x - line.start.x);
  }

  /**
   * Creates proper line object
   *
   * @param {number} x1 - start x
   * @param {number} y1 - start y
   * @param {number} x2 - end x
   * @param {number} y2 - end y
   *
   * @return {Object} - line object
   */
  new(x1, y1, x2, y2) {
    return {
      start: {x: x1, y: y1},
      end:   {x: x2, y: y2}
    }
  }
}

const Line = new GEO_Line();