feat: allow specifying on which weekday a tickInterval should start

docs/syntax/gantt.md

@@ -257,6 +257,12 @@ The pattern is:
 
 More info in: <https://github.com/d3/d3-time#interval_every>
 
+Week-based `tickInterval`s start the week on sunday by default. If you wish to specify another weekday on which the `tickInterval` should start, use the `weekday` option:
+
+```markdown
+weekday monday
+```
+
 ## Output in compact mode
 
 The compact mode allows you to display multiple tasks in the same row. Compact mode can be enabled for a gantt chart by setting the display mode of the graph via preceeding YAML settings.

packages/mermaid/src/defaultConfig.ts

@@ -50,6 +50,7 @@ const config: Partial<MermaidConfig> = {
     ...defaultConfigJson.gantt,
     tickInterval: undefined,
     useWidth: undefined, // can probably be removed since `configKeys` already includes this
+    weekday: 'sunday', // the sane default is a monday, but it's set to sunday for legacy reasons
   },
   c4: {
     ...defaultConfigJson.c4,

packages/mermaid/src/diagrams/gantt/ganttDb.js

@@ -37,6 +37,7 @@ const tags = ['active', 'done', 'crit', 'milestone'];
 let funs = [];
 let inclusiveEndDates = false;
 let topAxis = false;
+let weekday = undefined;
 
 // The serial order of the task in the script
 let lastOrder = 0;
@@ -66,6 +67,7 @@ export const clear = function () {
   lastOrder = 0;
   links = {};
   commonClear();
+  weekday = undefined;
 };
 
 export const setAxisFormat = function (txt) {
@@ -179,6 +181,14 @@ export const isInvalidDate = function (date, dateFormat, excludes, includes) {
   return excludes.includes(date.format(dateFormat.trim()));
 };
 
+export const setWeekday = function (txt) {
+  weekday = txt;
+};
+
+export const getWeekday = function () {
+  return weekday;
+};
+
 /**
  * TODO: fully document what this function does and what types it accepts
  *
@@ -759,6 +769,8 @@ export default {
   bindFunctions,
   parseDuration,
   isInvalidDate,
+  setWeekday,
+  getWeekday,
 };
 
 /**

packages/mermaid/src/diagrams/gantt/ganttRenderer.js

@@ -14,6 +14,12 @@ import {
   timeHour,
   timeDay,
   timeMonday,
+  timeTuesday,
+  timeWednesday,
+  timeThursday,
+  timeFriday,
+  timeSaturday,
+  timeSunday,
   timeMonth,
 } from 'd3';
 import common from '../common/common.js';
@@ -561,6 +567,8 @@ export const draw = function (text, id, version, diagObj) {
     if (resultTickInterval !== null) {
       const every = resultTickInterval[1];
       const interval = resultTickInterval[2];
+      const weekday = diagObj.db.getWeekday() || conf.weekday;
+
       switch (interval) {
         case 'minute':
           bottomXAxis.ticks(timeMinute.every(every));
@@ -572,7 +580,30 @@ export const draw = function (text, id, version, diagObj) {
           bottomXAxis.ticks(timeDay.every(every));
           break;
         case 'week':
-          bottomXAxis.ticks(timeMonday.every(every));
+          switch (weekday) {
+            case 'monday':
+              bottomXAxis.ticks(timeMonday.every(every));
+              break;
+            case 'tuesday':
+              bottomXAxis.ticks(timeTuesday.every(every));
+              break;
+            case 'wednesday':
+              bottomXAxis.ticks(timeWednesday.every(every));
+              break;
+            case 'thursday':
+              bottomXAxis.ticks(timeThursday.every(every));
+              break;
+            case 'friday':
+              bottomXAxis.ticks(timeFriday.every(every));
+              break;
+            case 'saturday':
+              bottomXAxis.ticks(timeSaturday.every(every));
+              break;
+            case 'sunday':
+            default:
+              bottomXAxis.ticks(timeSunday.every(every));
+              break;
+          }
           break;
         case 'month':
           bottomXAxis.ticks(timeMonth.every(every));

packages/mermaid/src/diagrams/gantt/parser/gantt.jison

@@ -86,6 +86,7 @@ that id.
 "includes"\s[^#\n;]+        return 'includes';
 "excludes"\s[^#\n;]+        return 'excludes';
 "todayMarker"\s[^\n;]+      return 'todayMarker';
+"weekday"\s[^#\n;]+         return 'weekday';
 \d\d\d\d"-"\d\d"-"\d\d      return 'date';
 "title"\s[^#\n;]+           return 'title';
 "accDescription"\s[^#\n;]+  return 'accDescription'
@@ -130,6 +131,7 @@ statement
   | excludes {yy.setExcludes($1.substr(9));$$=$1.substr(9);}
   | includes {yy.setIncludes($1.substr(9));$$=$1.substr(9);}
   | todayMarker {yy.setTodayMarker($1.substr(12));$$=$1.substr(12);}
+  | weekday { yy.setWeekday($1.substr(8));$$=$1.substr(8);}
   | title {yy.setDiagramTitle($1.substr(6));$$=$1.substr(6);}
   | acc_title acc_title_value { $$=$2.trim();yy.setAccTitle($$); }
   | acc_descr acc_descr_value { $$=$2.trim();yy.setAccDescription($$); }

packages/mermaid/src/diagrams/gantt/parser/gantt.spec.js

@@ -180,4 +180,9 @@ row2`;
     expect(ganttDb.getAccTitle()).toBe(expectedTitle);
     expect(ganttDb.getAccDescription()).toBe(expectedAccDescription);
   });
+
+  it('should allow for customising the weekday for tick intervals', function () {
+    parser.parse('gantt\nweekday wednesday');
+    expect(ganttDb.getWeekday()).toBe('wednesday');
+  });
 });