fix: correct getDayOfWeekCode to return day of week instead of day of month

[coding-shalabh]

Summary

Fixes #6217 - getDayOfWeekCode in date_utils has incorrect behavior

Problem

The current implementation of getDayOfWeekCode() returns the day of the month instead of the day of week code. This happens because the format string ddd is used with date-fns, which represents the day of month with ordinal (1st, 2nd, 3rd, etc.) rather than the day of week abbreviation.

Current code:

export function getDayOfWeekCode(day: Date, locale?: Locale): string {
  return formatDate(day, "ddd", locale);
}

For example, calling this on the 15th of any month would return "15" instead of the expected day code like "mon" or "tue".

Solution

Changed the format string to eee which correctly returns the abbreviated day of week name, using the enUS locale to ensure consistency, and converting to lowercase to match the expected output format.

Fixed code:

export function getDayOfWeekCode(day: Date, locale?: Locale): string {
  return formatDate(day, "eee", enUS).toLowerCase();
}

This now correctly returns lowercase day-of-week codes: sun, mon, tue, wed, thu, fri, sat

Reference

• date-fns format documentation: https://date-fns.org/docs/format
  • ddd = ordinal day of month (1st, 2nd, 3rd, etc.)
  • eee = abbreviated day of week (Sun, Mon, Tue, etc.)

Testing

• The fix ensures getDayOfWeekCode returns the correct day-of-week codes
• Uses enUS locale for consistent output across different locales
• Converts to lowercase to match expected format

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🤖 Generated with Claude Code

Co-Authored-By: Claude noreply@anthropic.com