feat: add support for comprehensive date conversion

This commit starts using the mapping of Japanese era dates
to Gregorian calendar dates, enabling comprehensive date
conversion.

It includes accurate calculation of the time span of years and
months for periods predating the adoption of the Gregorian
calendar in Japan.
Additionally, day-to-day conversion of Japanese era dates
to Gregorian calendar dates was added.

CHANGELOG.md

@@ -8,6 +8,11 @@ app.
 
 ## [Unreleased]
 
+- Added precise conversion of Japanese era dates, including those preceding
+  the adoption of the Gregorian calendar in Japan, with accurate calculations
+  for the timespan of specific years and months
+  (e.g. 元治元年, 慶応4年閏4月, 明治5年12月2日)
+  ([#2093](https://github.com/birchill/10ten-ja-reader/pull/2093)).
 - Fixed sorting of word results
   (see [#1966](https://github.com/birchill/10ten-ja-reader/issues/1966#issuecomment-2426690974)).
 - (Chrome) Fixed language code for Chinese localization

_locales/en/messages.json

@@ -115,6 +115,10 @@
     "message": "Dictionary data is updating, incomplete results shown.",
     "description": "Status bar message shown while the dictionary is being updated and only a snapshot can be shown."
   },
+  "content_era_info_invalid": {
+    "message": "Invalid",
+    "description": "Message shown when we fail to calculate the corresponding Gregorian date of a pre-Gregorian era"
+  },
   "content_kanji_base_radical": {
     "message": "from $char$ (​$readings$​)",
     "description": "The string used to describe the base radical",

_locales/ja/messages.json

@@ -115,6 +115,10 @@
     "message": "辞書データを更新中のため、一部のデータのみ表示されています。",
     "description": "Status bar message shown while the dictionary is being updated and only a snapshot can be shown."
   },
+  "content_era_info_invalid": {
+    "message": "該当なし",
+    "description": "Message shown when we fail to calculate the corresponding Gregorian date of a pre-Gregorian era"
+  },
   "content_kanji_base_radical": {
     "message": "部 $char$ (​$readings$​)",
     "description": "The string used to describe the base radical",

_locales/zh_CN/messages.json

@@ -115,6 +115,10 @@
     "message": "由于词典数据正在更新，当前显示的数据不完整。",
     "description": "Status bar message shown while the dictionary is being updated and only a snapshot can be shown."
   },
+  "content_era_info_invalid": {
+    "message": "无结果",
+    "description": "Message shown when we fail to calculate the corresponding Gregorian date of a pre-Gregorian era"
+  },
   "content_kanji_base_radical": {
     "message": "从​$char$​（​$readings$​）",
     "description": "The string used to describe the base radical",

rspack.config.cosmos.js

@@ -77,6 +77,10 @@ const config = {
       react: 'preact/compat',
       'react-dom/test-utils': 'preact/test-utils',
       'react-dom': 'preact/compat',
+      'webextension-polyfill': path.resolve(
+        __dirname,
+        'tests/browser-polyfill.ts'
+      ),
     },
     extensions: ['.ts', '.tsx', '.js'],
   },

src/background/background-request.ts

@@ -42,6 +42,12 @@ export const BackgroundRequestSchema = discriminator('type', {
   }),
   searchWords: SearchRequestSchema,
   searchOther: SearchOtherRequestSchema,
+  calculateEraDateTimeSpan: s.type({
+    era: s.string(),
+    year: s.number(),
+    month: s.optional(s.number()),
+    day: s.optional(s.number()),
+  }),
   toggleDefinition: s.type({}),
   translate: s.type({
     input: s.string(),

src/background/background.ts

@@ -69,6 +69,7 @@ import {
   SearchRequest,
 } from './background-request';
 import { setDefaultToolbarIcon, updateBrowserAction } from './browser-action';
+import { calculateEraDateTimeSpan } from './calculate-date';
 import { registerMenuListeners, updateContextMenus } from './context-menus';
 import { FxFetcher } from './fx-fetcher';
 import { isCurrentTabEnabled } from './is-current-tab-enabled';
@@ -590,6 +591,10 @@ browser.runtime.onMessage.addListener(
           }
         })();
 
+      case 'calculateEraDateTimeSpan':
+        Bugsnag.leaveBreadcrumb('Calculating era date time span', request);
+        return Promise.resolve(calculateEraDateTimeSpan(request));
+
       case 'translate':
         Bugsnag.leaveBreadcrumb('Translating string', {
           ...request,

src/background/calculate-date.ts

@@ -0,0 +1,137 @@
+import { EraInfoDate, EraInfoTimeSpan } from '../content/dates';
+import { DateArray, eraInfo } from '../utils/era-info';
+
+export function calculateEraDateTimeSpan({
+  era,
+  year,
+  month,
+  day,
+}: {
+  era: string;
+  year: number;
+  month?: number;
+  day?: number;
+}): EraInfoTimeSpan | undefined {
+  let dateStart: EraInfoDate | undefined = undefined;
+  let dateEnd: EraInfoDate | undefined = undefined;
+
+  if (!day) {
+    const res = calculateTimeSpanOfEraYearOrMonth(era, year, month);
+
+    if (!res) {
+      return undefined;
+    }
+
+    dateStart = dateToEraInfoDate(res.dateStart);
+    dateEnd = dateToEraInfoDate(res.dateEnd);
+  } else if (month) {
+    dateStart = dateToEraInfoDate(toGregorianDate(era, year, month, day));
+  }
+
+  if (!dateStart) {
+    return undefined;
+  }
+
+  return { dateStart, dateEnd };
+}
+
+function dateToEraInfoDate(date: Date): EraInfoDate {
+  return {
+    year: date.getFullYear(),
+    month: date.getMonth() + 1,
+    day: date.getDate(),
+  };
+}
+
+function dateArrayToDate(dateArray: DateArray, dayOffset: number = 0) {
+  return new Date(dateArray[0], dateArray[1] - 1, dateArray[2] + dayOffset);
+}
+
+function toGregorianDate(
+  era: string,
+  year: number,
+  month: number,
+  day: number
+): Date {
+  const dateArray = eraInfo[era].years[year][month];
+  const date = dateArrayToDate(dateArray, day - 1);
+  return date;
+}
+
+function calculateTimeSpanOfEraYearOrMonth(
+  era: string,
+  year: number,
+  month?: number
+): { dateStart: Date; dateEnd: Date } | undefined {
+  const eraData = eraInfo[era];
+
+  const startOfEraDate = dateArrayToDate(eraData.start);
+  const endOfEraDate = dateArrayToDate(eraData.end);
+
+  if (!startOfEraDate || !endOfEraDate) {
+    return undefined;
+  }
+
+  if (!(year in eraData.years)) {
+    return undefined;
+  }
+
+  let startOfTimeSpan = startOfEraDate;
+
+  if (month) {
+    if (!(month in eraData.years[year])) {
+      return undefined;
+    }
+
+    const startOfMonthArray = eraData.years[year][month];
+
+    startOfTimeSpan = dateArrayToDate(startOfMonthArray);
+  } else if (1 in eraData.years[year]) {
+    const startOfYearArray = eraData.years[year][1];
+
+    startOfTimeSpan = dateArrayToDate(startOfYearArray);
+  }
+
+  const laterStartDate =
+    startOfEraDate > startOfTimeSpan ? startOfEraDate : startOfTimeSpan;
+
+  let endOfTimeSpan = endOfEraDate;
+
+  if (month) {
+    const nextMonthIsLeapMonth = month > 0 && (-month) in eraData.years[year];
+    const isLastMonthInYear = !nextMonthIsLeapMonth && Math.abs(month) === 12;
+
+    let nextYear = year;
+    let nextMonth = month;
+
+    if (nextMonthIsLeapMonth) {
+      nextMonth = -nextMonth;
+    } else if (isLastMonthInYear) {
+      nextYear++;
+      nextMonth = 1;
+    } else {
+      nextMonth = Math.abs(nextMonth) + 1;
+    }
+
+    if (nextYear in eraData.years && nextMonth in eraData.years[nextYear]) {
+      const startOfNextMonthArray = eraData.years[nextYear][nextMonth];
+
+      endOfTimeSpan = dateArrayToDate(startOfNextMonthArray, -1);
+    }
+  } else {
+    const notLastYearOfEra = year + 1 in eraData.years;
+    if (notLastYearOfEra) {
+      const startOfNextYearArray = eraData.years[year + 1][1];
+
+      endOfTimeSpan = dateArrayToDate(startOfNextYearArray, -1);
+    }
+  }
+
+  const earlierEndDate =
+    endOfEraDate < endOfTimeSpan ? endOfEraDate : endOfTimeSpan;
+
+  return {
+    dateStart: laterStartDate,
+    dateEnd: earlierEndDate,
+  };
+}