datezone/dist/output/offset.pub.js

A lightweight and comprehensive date and timeZone utility library for JavaScript.

import { HOUR } from "./constants.pub.js";
import { calcOffset, offsetCache } from "./offset.internal.js";
import { isDST, isUTC } from "./timezone.pub.js";
/**
 * Get UTC to timezone offset minutes.
 *
 * @param ts - Timestamp in milliseconds
 * @param tz - Target timezone (null/undefined for local)
 * @returns Offset in minutes (positive if ahead of UTC, negative if behind)
 * @see https://datezone.dev/docs/reference/offset#getutctotimezoneoffsetminutes
 */
export function getUTCtoTimezoneOffsetMinutes(ts, tz) {
    if (isUTC(tz) || !isDST(tz)) {
        const cached = offsetCache.fixedOffset.get(tz);
        if (cached !== undefined)
            return cached;
        const offset = calcOffset(ts, tz);
        offsetCache.fixedOffset.set(tz, offset);
        return offset;
    }
    const hourStart = Math.floor(ts / HOUR) * HOUR;
    const cache = offsetCache.perHourOffset.get(tz);
    if (cache && cache.hourStart === hourStart) {
        return cache.offset;
    }
    const offset = calcOffset(ts, tz);
    offsetCache.perHourOffset.set(tz, { hourStart, offset });
    return offset;
}
/**
 * Get UTC to local timezone offset minutes.
 *
 * @param ts - Timestamp in milliseconds
 * @returns Offset in minutes (positive if ahead of UTC, negative if behind)
 * @see https://datezone.dev/docs/reference/offset#getutctolocaloffsetminutes
 */
export function getUTCtoLocalOffsetMinutes(ts) {
    // Fast path for fixed offset local zone
    if (!offsetCache.checkedLocalDST) {
        const jan = new Date(Date.UTC(new Date().getFullYear(), 0, 1)).getTimezoneOffset();
        const jul = new Date(Date.UTC(new Date().getFullYear(), 6, 1)).getTimezoneOffset();
        if (jan === jul) {
            offsetCache.localFixedOffset = -jan;
        }
        offsetCache.checkedLocalDST = true;
    }
    if (offsetCache.localFixedOffset !== null) {
        return offsetCache.localFixedOffset;
    }
    // Per-hour cache for non-fixed local zones
    const hourStart = Math.floor(ts / HOUR) * HOUR;
    if (offsetCache.lastLocalHourStart === hourStart &&
        offsetCache.lastLocalOffset !== null) {
        return offsetCache.lastLocalOffset;
    }
    const offset = -new Date(ts).getTimezoneOffset();
    offsetCache.lastLocalHourStart = hourStart;
    offsetCache.lastLocalOffset = offset;
    return offset;
}
/**
 * Get timezone offset minutes.
 *
 * @see https://datezone.dev/docs/reference/offset#gettimezoneoffsetminutes
 */
export function getTimezoneOffsetMinutes(ts, fromZone, toZone) {
    // Default both timeZones to local if not specified
    const from = fromZone || undefined;
    const to = toZone || undefined;
    // Fast path: UTC zones with optimized lookups
    if (from === "Etc/UTC" || from === "UTC") {
        if (!to) {
            // If 'to' is undefined, treat as local time offset
            return getUTCtoLocalOffsetMinutes(ts);
        }
        return getUTCtoTimezoneOffsetMinutes(ts, to);
    }
    if (to === "Etc/UTC" || to === "UTC") {
        if (!from) {
            // If 'from' is undefined, treat as local time offset
            return -getUTCtoLocalOffsetMinutes(ts);
        }
        return -getUTCtoTimezoneOffsetMinutes(ts, from);
    }
    // If both are local (undefined), return 0
    if (!from && !to) {
        return 0;
    }
    // If one is local and one is specified
    if (!from && to) {
        // Local to specified timeZone
        const localOffset = getUTCtoLocalOffsetMinutes(ts);
        const toOffset = getUTCtoTimezoneOffsetMinutes(ts, to);
        return toOffset - localOffset;
    }
    if (from && !to) {
        // Specified timeZone to local
        const fromOffset = getUTCtoTimezoneOffsetMinutes(ts, from);
        const localOffset = getUTCtoLocalOffsetMinutes(ts);
        return localOffset - fromOffset;
    }
    // General case: calculate both offsets
    const fromOffset = getUTCtoTimezoneOffsetMinutes(ts, from);
    const toOffset = getUTCtoTimezoneOffsetMinutes(ts, to);
    return toOffset - fromOffset;
}
/**
 * Get fixed offset cache info.
 *
 * @returns Object containing cache size and cached timeZones
 * @see https://datezone.dev/docs/reference/offset#getfixedoffsetcacheinfo
 */
export function getFixedOffsetCacheInfo() {
    return {
        cachedTimezones: Array.from(offsetCache.fixedOffset.keys()).filter((tz) => tz !== null),
        size: offsetCache.fixedOffset.size,
    };
}
/**
 * Clear fixed offset cache.
 *
 * @see https://datezone.dev/docs/reference/offset#clearfixedoffsetcache
 */
export function clearFixedOffsetCache() {
    offsetCache.fixedOffset.clear();
}
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