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index.js
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index.js
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const timeUnits = { second: 1000 };
timeUnits.seconds = timeUnits.secs = timeUnits.sec = timeUnits.second;
timeUnits.minute = timeUnits.minutes = timeUnits.min = timeUnits.mins = timeUnits.second * 60;
timeUnits.hour = timeUnits.hours = timeUnits.minute * 60;
timeUnits.day = timeUnits.days = timeUnits.hour * 24;
timeUnits.week = timeUnits.weeks = timeUnits.day * 7;
timeUnits.month = timeUnits.months = timeUnits.mth = timeUnits.mths = timeUnits.day * 30;
timeUnits.year = timeUnits.years = timeUnits.day * 365;
const futurePrefix = 'in';
const futureSuffix = 'from now';
const getCurrentDateInMs = () => {
return Math.floor(Date.now() / timeUnits.day) * timeUnits.day;
};
/**
* Splits expression string to amount expression, unit and suffix.
*
* @param {string} timeExpression
*
* @throws {Error}
* @return {object}
*/
const splitExpression = (timeExpression) => {
const timeArr = timeExpression.split(' ');
const time = {
amountExpr: null,
unit: null,
suffix: null,
prefix: null,
};
// Special future prefix case
if (timeArr[0] === futurePrefix) {
time.prefix = timeArr.splice(0, 1)[0];
}
// Less than a minute special case
if (timeExpression.includes('less than a minute')) {
time.amountExpr = 30;
time.unit = 'seconds';
return time;
}
// Cases starting with about
if (timeArr[0] === 'about' && (timeArr[1] === 'a' || timeArr[1] === 'an')) {
time.amountExpr = timeArr.splice(0, 2).join(' ');
// Cases starting with articles
} else if (timeArr[0] === 'a' || timeArr[0] === 'an' || timeArr[0] === 'few') {
time.amountExpr = timeArr.splice(0, 1)[0];
// Cases with no time amount expression (which start with a unit)
} else if (timeUnits[timeArr[0]] == null) {
time.amountExpr = timeArr.splice(0, 1)[0];
}
if (timeArr.length === 0) {
throw new Error('Cannot find time unit in timeago expression');
}
time.unit = timeArr.splice(0, 1)[0];
if (timeArr.length > 0) {
time.suffix = timeArr.join(' ');
}
return time;
};
/**
* Parses time amount expression and returns time multiplier
*
* @param {string} amountExpr
*
* @throws {Error}
* @return {number}
*/
const parseTimeAmount = (amountExpr) => {
let amount = null;
// Special approximate 1 case ie. "about a minute ago", "an hour ago"
if (amountExpr === 'about a' || amountExpr === 'about an'
|| amountExpr === 'a' || amountExpr === 'an') {
amount = 1;
// Special few case ie. "few seconds ago"
} else if (amountExpr === 'few') {
amount = 3;
// In case of empty amount expression
} else if (amountExpr == null) {
amount = 1;
// Regular case ie. "3 hours ago"
} else {
amount = parseInt(amountExpr);
}
if (isNaN(amount)) {
throw new Error(
'First part of timeago string must be a time amount (parsable positive integer)'
);
}
if (amount < 0) {
throw new Error('Amount should be a positive integer');
}
return amount;
};
/**
* Gets unit multiplier from unit name
*
* @param {string} unit
*
* @throws {Error}
* @return {number}
*/
const getUnitMultiplier = (unit) => {
if (timeUnits[unit] == null) {
throw new Error(
`Timeago unit "${unit}" is not supported.
Use one of "${Object.keys(timeUnits).join('", "')}"`
);
}
return timeUnits[unit];
};
/**
* Gets time direction multiplier
*
* @param {string} suffix
*
* @return {number}
*/
const getTimeDirection = (affix) => {
return (affix === futureSuffix || affix === futurePrefix) ? +1 : -1;
};
/**
* Counts date from amount, unitMultiplier and timeDirection
*
* @param {object} o
* @param {number} o.amount
* @param {number} o.unitMultiplier
* @param {number} o.timeDirection
*
* @return {Date}
*/
const countDate = ({ amount, unitMultiplier, timeDirection }) => {
const now = Date.now();
const parsedMs = now + amount * unitMultiplier * timeDirection;
return new Date(parsedMs);
};
/**
* Parses timeago string and returns approximate Date object
*
* @param {string} timeago
*
* @return {Date}
*/
const parse = (timeago) => {
timeago = timeago.toLowerCase();
if (timeago.includes('tomorrow')) {
const ms = getCurrentDateInMs() + timeUnits.day;
return new Date(ms);
}
// Handling now cases
if (timeago === 'now'
|| timeago.includes('just now')
|| timeago.includes('any moment now')) {
return new Date();
}
if (timeago.includes('today')) {
const ms = getCurrentDateInMs();
return new Date(ms);
}
if (timeago.includes('yesterday')) {
const ms = getCurrentDateInMs() - timeUnits.day;
return new Date(ms);
}
const splittedTimeExpr = splitExpression(timeago);
const time = {
amount: parseTimeAmount(splittedTimeExpr.amountExpr),
unitMultiplier: getUnitMultiplier(splittedTimeExpr.unit),
timeDirection: getTimeDirection(splittedTimeExpr.prefix || splittedTimeExpr.suffix),
};
return countDate(time);
};
module.exports = { parse };