Correct Tanakh Yomi calculations by running through entire year

Author: mjradwin

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@hebcal/learning",
-  "version": "5.0.3",
+  "version": "5.0.4",
   "description": "Daily learning schedules: Daf Yomi, Mishna Yomi, etc",
   "main": "dist/index.cjs",
   "module": "dist/index.mjs",

src/masoretic.json

@@ -1,4 +1,23 @@
 {
+ "split":{
+  "Joshua":{
+    "4.1":"6.27-7.26",
+    "4.2":"8.1-32"
+  },
+  "Jeremiah":{
+    "9.1":"17:7-25",
+    "9.2":"17:26-18:18"
+  },
+  "Song of Songs":{
+    "1.1":"1:1-5:1",
+    "1.2":"5:2-8:14"
+  },
+  "Ruth":{
+    "1.1":"1:1-2:11",
+    "1.2":"2:12-4:22"
+  }
+ },
+ "regular":{
  "Joshua":[
   "1:1-3:6",
   "3:7-4:23",
@@ -324,4 +343,5 @@
   "II Chronicles 34:2-35:5",
   "II Chronicles 35:6-36:23"
  ]
+ }
 }

src/tanakhYomi.js

@@ -11,12 +11,13 @@ import masoretic from './masoretic.json.js';
 const startDate = new Date(1948, 9, 26);
 export const tanakhYomiStart = greg.greg2abs(startDate);
 
+const JOSHUA = 'Joshua';
 const JEREMIAH = 'Jeremiah';
 const RUTH = 'Ruth';
 const SHIR_HASHIRIM = 'Song of Songs';
 
 const books = [
-  ['Joshua', 14],
+  [JOSHUA, 14],
   ['Judges', 14],
   ['Samuel', 34],
   ['Kings', 35],
@@ -63,51 +64,48 @@ export function tanakhYomi(date) {
   const hyear = hd.getFullYear();
   const rh = HDate.hebrew2abs(hyear, months.TISHREI, 1);
   const startAbs = rh + 22;
-  const table = books.slice();
-  const longCheshvan = HDate.longCheshvan(hyear);
-  let longRuth = false;
-  if (HDate.isLeapYear(hyear) || longCheshvan) {
-    table[12] = {name: RUTH, blatt: 2}; // Ruth gets 2 days
-    longRuth = true;
-  }
-  let longShirHaShirim = false;
-  if (longCheshvan) {
-    table[11] = {name: SHIR_HASHIRIM, blatt: 2}; // Shir HaShirim gets 2 days
-    longShirHaShirim = true;
-  }
-  let longJeremiah = false;
-  if (longCheshvan && !HDate.shortKislev(hyear)) {
-    table[5] = {name: JEREMIAH, blatt: 32}; // Jeremiah 9 gets split across two days
-    longJeremiah = true;
-  }
-
   if (cday < startAbs) {
-    let blatt = rh % 7 === 6 ? 10 : 12;
+    const rhDow = rh % 7;
+    let blatt = rhDow === 4 ? 11 : rhDow === 6 ? 10 : 12;
     for (let i = rh + 2; i < cday; i++) {
       const hdate = new HDate(i);
       if (!skipDay(hdate)) {
         blatt++;
       }
     }
+    if (blatt === 26) {
+      throw new Error(`${hd.toString()} Chronicles ${blatt}`);
+    }
     return new TanakhYomi('Chronicles', blatt);
   }
-
   let total = 0;
   for (let i = startAbs; i < cday; i++) {
     const hdate = new HDate(i);
     if (!skipDay(hdate)) {
       total++;
     }
   }
+  const readingTable = makeReadingTable(hyear);
+  const table = readingTable.table;
+
   for (let j = 0; j < table.length; j++) {
     if (total < table[j].blatt) {
       const blatt = total + 1;
       const name = table[j].name;
-      if ((longShirHaShirim && name === SHIR_HASHIRIM) ||
-          (longRuth && name === RUTH)) {
+      if ((readingTable.longShirHaShirim && name === SHIR_HASHIRIM) ||
+          (readingTable.longRuth && name === RUTH)) {
         return new TanakhYomi(name, '1.' + blatt);
       }
-      if (longJeremiah && name === JEREMIAH && blatt >= 9) {
+      if (readingTable.longJoshua && name === JOSHUA && blatt >= 4) {
+        if (blatt === 4) {
+          return new TanakhYomi(name, '4.1');
+        } else if (blatt === 5) {
+          return new TanakhYomi(name, '4.2');
+        } else {
+          return new TanakhYomi(name, blatt - 1);
+        }
+      }
+      if (readingTable.longJeremiah && name === JEREMIAH && blatt >= 9) {
         if (blatt === 9) {
           return new TanakhYomi(name, '9.1');
         } else if (blatt === 10) {
@@ -146,11 +144,84 @@ function skipDay(hd) {
   return false;
 }
 
-const splitSeder = {
-  'Jeremiah': {'9.1': '17:7-25', '9.2': '17:26-18:18'},
-  'Song of Songs': {'1.1': '1:1-5:1', '1.2': '5:2-8:14'},
-  'Ruth': {'1.1': '1:1-2:11', '1.2': '2:12-4:22'},
-};
+/**
+ * @private
+ * @param {number} year
+ * @return {number}
+ */
+function calculateNumDaysToRead(year) {
+  const startAbs = HDate.hebrew2abs(year, months.TISHREI, 23);
+  const endAbs = HDate.hebrew2abs(year + 1, months.TISHREI, 22);
+  let included = 0;
+  for (let abs = startAbs; abs <= endAbs; abs++) {
+    const hdate = new HDate(abs);
+    if (!skipDay(hdate)) {
+      included++;
+    }
+  }
+  return included;
+}
+
+/**
+ * A common year can have a length of 353, 354 or 355 days
+ * A leap year can have a length of 383, 384 or 385 days
+ *
+ * Common years can have
+ *   293 chapters - no extra chapters (45%)
+ *   294 chapters - 1 extra chapter (5%)
+ *   295 chapters - 2 extra chapters (31%)
+ *   296 chapters - 3 extra chapters (19%)
+ * Leap years can have
+ *   318 chapters - no extra chapters (10%)
+ *   319 chapters - 1 extra chapter (30%)
+ *   320 chapters - 2 extra chapters (47%)
+ *   222 chapters - 4 extra chapters (12%)
+ *
+ * @private
+ * @param {number} year
+ * @return {any}
+ */
+function makeReadingTable(year) {
+  const numDays = calculateNumDaysToRead(year);
+  const count = HDate.isLeapYear(year) ? numDays - 25 : numDays;
+  const extra = count - 293;
+  const table = books.slice();
+  const result = {
+    numDays,
+    table,
+    longRuth: false,
+    longShirHaShirim: false,
+    longJeremiah: false,
+    longJoshua: false,
+  };
+  switch (extra) {
+    case 0:
+      return result;
+    case 4:
+      // Joshua 4 gets split across two days
+      table[0] = {name: JOSHUA, blatt: 15};
+      result.longJoshua = true;
+      /* FALLTHROUGH */
+    case 3:
+      // Jeremiah 9 gets split across two days
+      table[5] = {name: JEREMIAH, blatt: 32};
+      result.longJeremiah = true;
+      /* FALLTHROUGH */
+    case 2:
+      // Shir HaShirim gets 2 days
+      table[11] = {name: SHIR_HASHIRIM, blatt: 2};
+      result.longShirHaShirim = true;
+      /* FALLTHROUGH */
+    case 1:
+      // Ruth gets 2 days
+      table[12] = {name: RUTH, blatt: 2};
+      result.longRuth = true;
+      break;
+    default:
+      throw new Error(`${year} => ${numDays} ${count} ${extra}`);
+  }
+  return result;
+}
 
 /**
  * Returns the Daf Yomi for given date
@@ -163,9 +234,12 @@ export class TanakhYomi extends DafPage {
    */
   constructor(name, blatt) {
     super(name, blatt);
-    const seders = masoretic[name];
+    const seders = masoretic.regular[name];
     const verses = typeof blatt === 'number' ?
-      seders[blatt - 1] : splitSeder[name][blatt];
+      seders[blatt - 1] : masoretic.split[name][blatt];
+    if (!verses) {
+      throw new Error(`${name} ${blatt}`);
+    }
     const firstChar = verses.charCodeAt(0);
     this.verses = firstChar >= 48 && firstChar <= 57 ?
       `${name} ${verses}` : verses;
@@ -182,10 +256,17 @@ export class TanakhYomi extends DafPage {
       locale = locale.toLowerCase();
     }
     const name = Locale.gettext(this.name, locale);
+    const blatt = this.blatt;
     if (locale === 'he' || locale === 'he-x-nonikud') {
-      return name + ' ס׳ ' + gematriya(this.blatt);
+      const prefix = name + ' ס׳ ';
+      if (typeof blatt === 'string') {
+        const major = blatt[0];
+        const minor = blatt[2];
+        return prefix + gematriya(+major) + minor;
+      }
+      return prefix + gematriya(blatt);
     }
-    return name + ' Seder ' + this.blatt;
+    return name + ' Seder ' + blatt;
   }
 }