// Try opening up your terminal and typing 'node'.
// Then in the node REPL, copy and paste the commands in this docuemnt.
// You can copy and paste the entire line of code including the comments into the REPL.

// Intro: REPLS
// A REPL is a 'Read Evaluate Print Loop'. It allows you to run commands in JS in your
// terminal and then see the 'printed' result back in your screen.
console.log('You can', 'chain multiple messages', 'inside console.log');

// I. Basic data types
// 1. Numbers
1 + 1; // add
1 - 1; // subtract
5 * 5; // multiply
10 / 2; // divide
6 % 3; // modulo: the remainder of division

// 2. Strings
'hello world!';
// Provide the number of chartacters in the string
'hello world!'.length;
// Slice a piece of the string
'hello world!'.substring(1,5);
// convert the string to upper case
'hello world!'.toUpperCase();
// convert the string to lower case
'hello world!'.toLowerCase();
// access a specific character in the string
'hello world!'[0];

//2.1 String interpolation
const message = 'world';
const say = `Hello, ${message}!`; //you must use the ` sign. The ' sign will not allow interpolation.
console.log(say);

// 3. Boolean
true;
false;

// 4. Null and undefined
// Both these values can be used interchangeably. They describe a variable that has no content.
null;
undefined;

// 4. Checking the data type
typeof 1;
typeof 'hello';
typeof true;
typeof false;

// 5. Type conversion
// 5.1 convert a string '5' into a number 5.
parseInt('5', 10);

// 5.2 convert an integer 5 into a string '5'.
String(5);




// II. Variables
// 1. let
// We use let when we want to re-assign a variable. Re-assignment is wehn we use '='.
let fruit = 'banana';
fruit = [1,2,3];

// 2. const
// We use const when we do not want to re-assign a variable. It has a unchanging value.
const tropicalFruit = 'pineapple';
tropicalFruit = 'mango'; // This line of code cannot be executed!

// Note: In JS we use camelCase when naming variables. In ruby we used snake_case.
// camelcase
anotherVariable = undefined;
// snake_case
another_variable = undefined;





// III. Arrays
// 1.1 CRUD on arrays
// Create an array
const numbers = [1,2,3,4,5];
// Read from an array
numbers[0];
// Update an array
numbers.push(99); // Add 99 to the array
numbers[0] = 99; // reassigned value at index 0 to 99
numbers.splice(0,0,99); // at index 0, delete 0 items, and insert a number 99.
// Delete from an array
numbers.splice(0,1); // at index 0, delete 1 item.
numbers.splice(0,2); // at index 0, delete 2 items.

// 1.2 Other array operations
// Split a string into an array of characters
'hello world'.split('');

// Give an array length
numbers.length;

// The spread operator
const male = ['hamlet', 'falstaff'];
const female = ['gertrude', 'ophelia'];
const people = [...male, ...female];
console.log(people);

// 1.3 Looping through an array
numbers.forEach( (number, index) => {
  console.log(`${number} is at index: ${index}`);
});




// III. Control Flow
// 1. If-Else statements
const age = 12;
if (age > 18) {
  console.log('can vote');
} else if (age > 99) {
  console.log('can vote, and also very old.')l;
} else {
  console.log('Too young to vote');
}

// 2. Ternary operator
// This operation has two stages:
// stage 1: check if the condition is true (is the variable 'age' > 18?)
// stage 2: depending on the result, assign the value to 'result').
// If the condition passes, result is set to the value to the left ('can vote')
// If the condition does not passe, result is set to the value to the right ('cannot vote')
const result = (age > 18) ? 'can vote' : 'cannot vote';
console.log(result);

// 2.2 Falsy and Truthy values
// JS allows some values to function as if they were boolean 'false'.
1 == false
// => true

'' == false
// => true




// IV. Objects
// 1. CRUD on objects
// Create an object
const characters = { hamlet: 'hello.', harry: 'hi.'};
// read from an object
chracters.hamlet
characters['hamlet'] // the dot notation is preferred
// update an object
chracters.hamlet = 'hello world';
// delete from an object
delete characters.hamlet

// 1.1 Looping through an object
Object.keys(characters).forEach( key => {
  console.log(key);
});
Object.values(characters).forEach( value => {
  console.log(value);
});





// V. Maps
// A map is like a JS Object, except you can set any data type as the key.
// In a JS object, the kety MUST be a string.
// 1. CRUD on maps
// Create a map
const myMap = new Map();
myMap.set('hello', 'world'); // create a new key value pair in the map such that ['hello', 'world']
// read from a map
myMap.get('hello');
// update a map
myMap.set('hello', 'some new value');
// delete from an object
myMap.delete('hamlet');

// 1.1 Looping through a map
// A map is treated like an array: the first parameter is the 'value', the second parameter is the 'index'.
myMap.forEach( (value, key) => {
  console.log(value, key);
});





// VI. Functions
// 1. Arrow Functions
// I define the function here
const sayHello = () => {
  console.log('hello!'); // this is the 'block' passed into the function
};
sayHello(); // I execute the function here

// 1.1 Single Line Functions
// If your block (the { ... } of the function) contains 1 line of code, you can write your
// function like this:
const sayHi = () => console.log('hi!');
sayHi();


// 2. Building a Capitalise function
// JS does not include a .capitalize function in its standards library. Let's make one.
const capitalize = (string) => {
  // capitalize the firct character of the word and save it to a variable
  const firstLetter = string[0].toUpperCase();
  // make sure the rest of the string excluding the first character is lower case, and save it to a variable
  const restOfWord = string.substring(1, string.length).toLowerCase();
  // return the capitalized first letter + the rest of the word in lower case
  return firstLetter + restOfWord;
};
console.log(capitalize('all lower case.'));

// 3. Going further: Let's build a function that will capitalize every word in a sentence.
// Try saving this code in a file and run the following command in your terminal:
// node --inspect-brk file_name.js
// This will allow you to pause the script during execution so you can see what is happenning
// in it line by line.
const capitalizeSentence = (string) => {
  // Define an array that will collect our capitalised words.
  let arr = [];
  // Split the string into an array of words
  string.split(' ').forEach( word => {
    // capitalize the firct character of the word and save it to a variable
    let firstLetter = word[0].toUpperCase();
    // make sure the rest of the string excluding the first character is lower case, and save it to a variable
    let restOfTheWord = word.substring(1).toLowerCase();
    // create a new variable that combines the two new variables we just created
    let newWord = firstLetter + restOfTheWord;
    // push this new variable to the array we defined earlier
    arr.push(newWord);
  });
  // convert the array of capitalized words into a string again
  return arr.join(' ');
}
console.log(capitalizeSentence('all lower case.'));