| 4 | 4 | // |
| 5 | 5 | |
| 6 | 6 | /** |
| 7 | | * @param {number} year |
| 8 | | * @param {number} month |
| 9 | | * @param {string} week |
| 10 | | * @param {string} dayOfWeek |
| 11 | | * @returns {Date} |
| 7 | * Calculates the date of a meetup based on year, month, week descriptor, and day of week. |
| 8 | * |
| 9 | * @param {number} year - The year of the meetup |
| 10 | * @param {number} month - The month of the meetup (1-12) |
| 11 | * @param {string} week - The week descriptor ('first', 'second', 'third', 'fourth', 'last', 'teenth') |
| 12 | * @param {string} dayOfWeek - The day of the week ('Sunday', 'Monday', etc.) |
| 13 | * @returns {Date} - The calculated date of the meetup |
| 14 | * |
| 15 | * @example |
| 16 | * meetup(2018, 1, 'first', 'Monday') // Returns Date for January 1, 2018 |
| 17 | * meetup(1953, 8, 'teenth', 'Saturday') // Returns Date for August 15, 1953 |
| 12 | 18 | */ |
| 13 | 19 | export const meetup = (year, month, week, dayOfWeek) => { |
| 14 | | throw new Error('Remove this line and implement the function'); |
| 20 | // Validate inputs |
| 21 | if (typeof year !== 'number' || year < 1) { |
| 22 | throw new Error('Invalid year'); |
| 23 | } |
| 24 | |
| 25 | if (typeof month !== 'number' || month < 1 || month > 12) { |
| 26 | throw new Error('Invalid month'); |
| 27 | } |
| 28 | |
| 29 | const validWeeks = ['first', 'second', 'third', 'fourth', 'last', 'teenth']; |
| 30 | if (!validWeeks.includes(week)) { |
| 31 | throw new Error('Invalid week descriptor'); |
| 32 | } |
| 33 | |
| 34 | const validDays = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday']; |
| 35 | if (!validDays.includes(dayOfWeek)) { |
| 36 | throw new Error('Invalid day of week'); |
| 37 | } |
| 38 | |
| 39 | // Convert day name to index (0-6) |
| 40 | const dayIndex = validDays.indexOf(dayOfWeek); |
| 41 | |
| 42 | // Create a date object for the first day of the month |
| 43 | // Note: JavaScript months are 0-indexed, but our input is 1-indexed |
| 44 | const firstOfMonth = new Date(year, month - 1, 1); |
| 45 | |
| 46 | // Edge Case: Handle 'teenth' week (13th through 19th) |
| 47 | if (week === 'teenth') { |
| 48 | // Start checking from the 13th day of the month |
| 49 | for (let day = 13; day <= 19; day++) { |
| 50 | const date = new Date(year, month - 1, day); |
| 51 | if (date.getDay() === dayIndex) { |
| 52 | return date; |
| 53 | } |
| 54 | } |
| 55 | // This should never happen with valid inputs |
| 56 | throw new Error('Could not find teenth day'); |
| 57 | } |
| 58 | |
| 59 | // Edge Case: Handle 'last' week |
| 60 | if (week === 'last') { |
| 61 | // Get the last day of the month by going to the first day of next month and subtracting one day |
| 62 | const nextMonth = new Date(year, month, 1); |
| 63 | const lastDay = new Date(nextMonth.getTime() - 86400000); // 86400000 ms = 1 day |
| 64 | |
| 65 | // Work backwards to find the last occurrence of the specified day |
| 66 | let current = lastDay; |
| 67 | while (current.getMonth() === month - 1) { // Still in the target month |
| 68 | if (current.getDay() === dayIndex) { |
| 69 | return current; |
| 70 | } |
| 71 | // Move to previous day |
| 72 | current = new Date(current.getTime() - 86400000); |
| 73 | } |
| 74 | // This should never happen with valid inputs |
| 75 | throw new Error('Could not find last day'); |
| 76 | } |
| 77 | |
| 78 | // Edge Case: Handle 'first', 'second', 'third', 'fourth' weeks |
| 79 | // Find the first occurrence of the specified day in the month |
| 80 | const firstDay = firstOfMonth.getDay(); |
| 81 | let daysUntilTarget = dayIndex - firstDay; |
| 82 | |
| 83 | // If the target day has already passed in the first week, move to next week |
| 84 | if (daysUntilTarget < 0) { |
| 85 | daysUntilTarget += 7; |
| 86 | } |
| 87 | |
| 88 | // Calculate the date of the first occurrence |
| 89 | const firstOccurrence = 1 + daysUntilTarget; |
| 90 | |
| 91 | // Calculate which occurrence we want (1st, 2nd, 3rd, 4th) |
| 92 | const weekIndex = ['first', 'second', 'third', 'fourth'].indexOf(week); |
| 93 | |
| 94 | // Calculate the final date |
| 95 | const targetDate = firstOccurrence + (weekIndex * 7); |
| 96 | |
| 97 | // Verify the date is still in the correct month |
| 98 | const result = new Date(year, month - 1, targetDate); |
| 99 | |
| 100 | // Edge Case: Handle case where calculated date is in a different month |
| 101 | if (result.getMonth() !== month - 1) { |
| 102 | throw new Error(`The ${week} ${dayOfWeek} does not exist in the given month`); |
| 103 | } |
| 104 | |
| 105 | return result; |
| 106 | |
| 107 | // Handled Edge Cases: Invalid inputs (year, month, week, dayOfWeek), teenth week calculation, |
| 108 | // last week calculation, first/second/third/fourth week calculation, date overflow into next month |
| 15 | 109 | }; |