2 files changed, 156 insertions, 0 deletions

diff --git a/src/data/things/language.js b/src/data/things/language.js
index d8af9620..fa529a8e 100644
--- a/src/data/things/language.js
+++ b/src/data/things/language.js
@@ -1,3 +1,5 @@
+import { Temporal, toTemporalInstant } from '@js-temporal/polyfill';
+
 import {isLanguageCode} from '#validators';
 import {Tag} from '#html';
 
@@ -284,6 +286,108 @@ export class Language extends Thing {
     return this.intl_date.formatRange(startDate, endDate);
   }
 
+  formatDateDuration({
+    years: numYears = 0,
+    months: numMonths = 0,
+    days: numDays = 0,
+    approximate = false,
+  }) {
+    let basis;
+
+    const years = this.countYears(numYears, {unit: true});
+    const months = this.countMonths(numMonths, {unit: true});
+    const days = this.countDays(numDays, {unit: true});
+
+    if (numYears && numMonths && numDays)
+      basis = this.formatString('count.dateDuration.yearsMonthsDays', {years, months, days});
+    else if (numYears && numMonths)
+      basis = this.formatString('count.dateDuration.yearsMonths', {years, months});
+    else if (numYears && numDays)
+      basis = this.formatString('count.dateDuration.yearsDays', {years, days});
+    else if (numYears)
+      basis = this.formatString('count.dateDuration.years', {years});
+    else if (numMonths && numDays)
+      basis = this.formatString('count.dateDuration.monthsDays', {months, days});
+    else if (numMonths)
+      basis = this.formatzString('count.dateDuration.months', {months});
+    else if (numDays)
+      basis = this.formatString('count.dateDuration.days', {days});
+    else
+      return this.formatString('count.dateDuration.zero');
+
+    if (approximate) {
+      return this.formatString('count.dateDuration.approximate', {
+        duration: basis,
+      });
+    } else {
+      return basis;
+    }
+  }
+
+  formatRelativeDate(currentDate, referenceDate, {
+    considerRoundingDays = false,
+    approximate = true,
+    absolute = true,
+  } = {}) {
+    const currentInstant = toTemporalInstant.apply(currentDate);
+    const referenceInstant = toTemporalInstant.apply(referenceDate);
+
+    const comparison =
+      Temporal.Instant.compare(currentInstant, referenceInstant);
+
+    if (comparison === 0) {
+      return this.formatString('count.dateDuration.same');
+    }
+
+    const currentTDZ = currentInstant.toZonedDateTimeISO('Etc/UTC');
+    const referenceTDZ = referenceInstant.toZonedDateTimeISO('Etc/UTC');
+
+    const earlierTDZ = (comparison === -1 ? currentTDZ : referenceTDZ);
+    const laterTDZ = (comparison === 1 ? currentTDZ : referenceTDZ);
+
+    const {years, months, days} =
+      laterTDZ.since(earlierTDZ, {
+        largestUnit: 'year',
+        smallestUnit:
+          (considerRoundingDays
+            ? (laterTDZ.since(earlierTDZ, {
+                largestUnit: 'year',
+                smallestUnit: 'day',
+              }).years
+                ? 'month'
+                : 'day')
+            : 'day'),
+        roundingMode: 'halfCeil',
+      });
+
+    const duration =
+      this.formatDateDuration({
+        years, months, days,
+        approximate: false,
+      });
+
+    const relative =
+      this.formatString(
+        'count.dateDuration',
+        (approximate
+          ? (comparison === -1
+              ? 'approximateEarlier'
+              : 'approximateLater')
+          : (comparison === -1
+              ? 'earlier'
+              : 'later')),
+        {duration});
+
+    if (absolute) {
+      return this.formatString('count.dateDuration.relativeAbsolute', {
+        relative,
+        absolute: this.formatDate(currentDate),
+      });
+    } else {
+      return relative;
+    }
+  }
+
   formatDuration(secTotal, {approximate = false, unit = false} = {}) {
     if (secTotal === 0) {
       return this.formatString('count.duration.missing');
@@ -442,7 +546,11 @@ Object.assign(Language.prototype, {
   countCommentaryEntries: countHelper('commentaryEntries', 'entries'),
   countContributions: countHelper('contributions'),
   countCoverArts: countHelper('coverArts'),
+  countDays: countHelper('days'),
+  countMonths: countHelper('months'),
   countTimesReferenced: countHelper('timesReferenced'),
   countTimesUsed: countHelper('timesUsed'),
   countTracks: countHelper('tracks'),
+  countWeeks: countHelper('weeks'),
+  countYears: countHelper('years'),
 });
diff --git a/src/strings-default.yaml b/src/strings-default.yaml
index af2ddc42..30b04141 100644
--- a/src/strings-default.yaml
+++ b/src/strings-default.yaml
@@ -129,6 +129,16 @@ count:
       many: ""
       other: "{DAYS} days"
 
+  months:
+    _: "{MONTHS}"
+    withUnit:
+      zero: ""
+      one: "{MONTHS} month"
+      two: ""
+      few: ""
+      many: ""
+      other: "{MONTHS} months"
+
   timesReferenced:
     _: "{TIMES_REFERENCED}"
     withUnit:
@@ -149,6 +159,16 @@ count:
       many: ""
       other: "used {TIMES_USED} times"
 
+  weeks:
+    _: "{WEEKS}"
+    withUnit:
+      zero: ""
+      one: "{WEEKS} week"
+      two: ""
+      few: ""
+      many: ""
+      other: "{WEEKS} weeks"
+
   words:
     _: "{WORDS}"
     thousand: "{WORDS}k"
@@ -160,6 +180,16 @@ count:
       many: ""
       other: "{WORDS} words"
 
+  years:
+    _: "{YEARS}"
+    withUnit:
+      zero: ""
+      one: "{YEARS} year"
+      two: ""
+      few: ""
+      many: ""
+      other: "{YEARS} years"
+
   # Numerical things that aren't exactly counting, per se
 
   duration:
@@ -172,6 +202,24 @@ count:
       _:        "{MINUTES}:{SECONDS}"
       withUnit: "{MINUTES}:{SECONDS} minutes"
 
+  dateDuration:
+    earlier: "{DURATION} earlier"
+    later: "{DURATION} later"
+    same: "on the same date"
+    zero: "no days apart"
+    approximate: "about {DURATION}"
+    approximateEarlier: "about {DURATION} earlier"
+    approximateLater: "about {DURATION} later"
+    relativeAbsolute: "{ABSOLUTE}; {RELATIVE}"
+
+    years: "{YEARS}"
+    months: "{MONTHS}"
+    days: "{DAYS}"
+    yearsMonthsDays: "{YEARS}, {MONTHS}, {DAYS}"
+    yearsMonths: "{YEARS}, {MONTHS}"
+    yearsDays: "{YEARS}, {DAYS}"
+    monthsDays: "{MONTHS}, {DAYS}"
+
   fileSize:
     terabytes: "{TERABYTES} TB"
     gigabytes: "{GIGABYTES} GB"