38 lines
1.3 KiB
JavaScript
38 lines
1.3 KiB
JavaScript
const {DateTime} = require('luxon');
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const {IncorrectUsageError} = require('@tryghost/errors');
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const messages = {
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invalidInterval: 'Invalid interval specified. Only "month" value is accepted.'
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};
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const SUPPORTED_INTERVALS = ['month'];
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/**
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* Calculates the start of the last period (billing, cycle, etc.) based on the start date
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* and the interval at which the cycle renews.
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*
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* @param {String} startDate - date in ISO 8601 format (https://en.wikipedia.org/wiki/ISO_8601)
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* @param {('month')} interval - currently only supports 'month' value, in the future might support 'year', etc.
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*
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* @returns {String} - date in ISO 8601 format (https://en.wikipedia.org/wiki/ISO_8601) of the last period start
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*/
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const lastPeriodStart = (startDate, interval) => {
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if (interval === 'month') {
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const startDateISO = DateTime.fromISO(startDate, {zone: 'UTC'});
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const now = DateTime.now().setZone('UTC');
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const fullPeriodsPast = Math.floor(now.diff(startDateISO, 'months').months);
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const lastPeriodStartDate = startDateISO.plus({months: fullPeriodsPast});
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return lastPeriodStartDate.toISO();
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}
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throw new IncorrectUsageError({
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message: messages.invalidInterval
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});
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};
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module.exports = {
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lastPeriodStart,
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SUPPORTED_INTERVALS
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};
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