/**

* Problem 17 - Number letter counts

*

* @see {@link https://projecteuler.net/problem=17}

*

* If the numbers 1 to 5 are written out in words: one, two, three, four, five, then there are 3 + 3 + 5 + 4 + 4 = 19 letters used in total.

* If all the numbers from 1 to 1000 (one thousand) inclusive were written out in words, how many letters would be used?

*

* @author Chetan07j

*/

// Array of number word length from 0 -> 19

const ones = [4, 3, 3, 5, 4, 4, 3, 5, 5, 4, 3, 6, 6, 8, 8, 7, 7, 9, 8, 8]

// Array for tens from 20, 30, 40, 50, 60, 70, 80, 90 in words length

const tens = [6, 6, 5, 5, 5, 7, 6, 6]

// Word length for words thousand, hundred, and

const thousandLength = 8

const hundredLength = 7

const andLength = 3

/**

* Function to convert number to word

*

* This function is called recursively to handle thousand and its sub part

*/

const numberToWordLength = (n) => {

let count = 0

// If number is < 20 then return its corresponding value from ones

if (n < 20) {

return ones[n]

}

/**

* To calculate tens value "n / 10 - 2" is performed, which might return decimal value

* to extract proper integer value Math.floor is added

* Here "-2" is performed as our tens array start with index 0

* To get appropriate value from that for our number it is required

* e.g.,

* -> 34 -> 34/10= 3.4 -> Math.floor(3.4) = 3

* -> ones[3] = 5 // this is wrong

* -> 3 - 2 = 1 -> ones[1] = 6

*

* To find ones part, unit is identified by n % 10

* If > 0 then ones word is appended to tens word otherwise nothing

* e.g.,

* 1. 34 -> 10

* 2. 30 -> 6

*/

if (n >= 20 && n < 100) {

const unit = n % 10

return tens[Math.floor(n / 10 - 2)] + ((unit !== 0) ? ones[unit] : 0)

}

// Find thousand, hundred and sub part

const hundred = Math.floor(n / 100) % 10

const thousand = Math.floor(n / 1000)

const sub = n % 100

// Find ones for thousand part number

// e.g., thousand = 2 => inWord = twothousand

if (n > 999) {

count += numberToWordLength(thousand) + thousandLength

}

// Find ones for hundred part number

// e.g., hundred = 1 => inWord = onehundred

if (hundred !== 0) {

count += ones[hundred] + hundredLength

}

// Find and part of number

// e.g., 922 => ninehundred"andtwentytwo"

if (sub !== 0) {

count += andLength + numberToWordLength(sub)

}

// return number in word format

return count

}

/**

* Function responsible for calculating total number word length

* for provided input number

* Validation is performed for input

* Loop is executed to find total word length for given number range

* starting from 1

*

*

* @param {number} number

* @returns {number}

*/

const countNumberWordLength = (number) => {

let count = 0

// Not a number check

if (Number.isNaN(parseInt(number))) {

throw new Error('Invalid input, please provide valid number')

}

// Number should be greater than 1

if (number < 1) {

throw new Error('Please provide number greater that 1')

}

// Loop to calculate word length by calling {@link numberToWord}

for (let i = 1; i <= number; i++) {

count += numberToWordLength(i)

}

// return final count for number word length

return count

}

export { countNumberWordLength }