Behavioral Patterns

// Too many parameters, hard to use
class Pizza {
  constructor(size, cheese, pepperoni, mushrooms, onions, basil, oregano) {
    this.size = size;
    this.cheese = cheese;
    this.pepperoni = pepperoni;
    this.mushrooms = mushrooms;
    this.onions = onions;
    this.basil = basil;
    this.oregano = oregano;
  }
}

// Usage (confusing which parameter is which)
const pizza = new Pizza("large", true, true, false, true, false, true);

// Each control talks to others directly
class Button {
  click() {
    this.dialogBox.okClicked();
    this.textBox.enable();
    this.checkbox.update();
  }
}

class DialogBox {
  okClicked() { }
}

class TextBox {
  enable() { }
}

class Checkbox {
  update() { }
}

// Objects are tightly coupled; hard to test individually

// Objects (don't need to know about operations)
class File {
  accept(visitor) {
    return visitor.visitFile(this);
  }
}

class Directory {
  constructor() {
    this.children = [];
  }
  
  add(item) {
    this.children.push(item);
  }
  
  accept(visitor) {
    return visitor.visitDirectory(this);
  }
}

// Visitors (operations)
class FileSizeVisitor {
  visitFile(file) {
    return file.size || 0;
  }
  
  visitDirectory(directory) {
    return directory.children.reduce((total, child) => {
      return total + child.accept(this);
    }, 0);
  }
}

class FileNameVisitor {
  visitFile(file) {
    return file.name;
  }
  
  visitDirectory(directory) {
    return directory.children.map(child => child.accept(this));
  }
}

// Usage
const dir = new Directory();
dir.add(Object.assign(new File(), { name: "file1.txt", size: 100 }));
dir.add(Object.assign(new File(), { name: "file2.txt", size: 200 }));

// Calculate size
const sizeVisitor = new FileSizeVisitor();
console.log(dir.accept(sizeVisitor)); // 300

// Get file names
const nameVisitor = new FileNameVisitor();
console.log(dir.accept(nameVisitor)); // ["file1.txt", "file2.txt"]