feat(quando-dsx): implement snap operations StartOf and EndOf
- Implement StartOf(unit) for Weeks, Months, Quarters, Years - Implement EndOf(unit) for Weeks, Months, Quarters, Years - Week snapping follows ISO 8601 (Monday start, Sunday end) - Month-end handling for all month lengths (28/29/30/31 days) - Quarter definitions: Q1=Jan-Mar, Q2=Apr-Jun, Q3=Jul-Sep, Q4=Oct-Dec - Comprehensive unit tests for all units and edge cases - Leap year handling for February - Timezone preservation tests - Immutability verification tests - Performance benchmarks (all <200ns, well under 1µs target) - Zero allocations for all operations - 97.3% test coverage (exceeds 95% requirement) - Godoc comments with usage examples All acceptance criteria met: ✓ StartOf(Week) returns Monday 00:00:00 ✓ EndOf(Week) returns Sunday 23:59:59 ✓ StartOf(Month) returns 1st day 00:00:00 ✓ EndOf(Month) handles all month lengths correctly ✓ StartOf(Quarter) returns correct quarter start ✓ EndOf(Quarter) returns correct quarter end ✓ StartOf(Year) returns Jan 1 00:00:00 ✓ EndOf(Year) returns Dec 31 23:59:59 ✓ Leap year handling for February ✓ Unit tests for all units and edge cases ✓ ISO 8601 week compliance tests ✓ Benchmarks meet <1µs target (all <200ns) ✓ Godoc comments with examples
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4 changed files with 727 additions and 2 deletions
143
snap.go
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143
snap.go
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package quando
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import "time"
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// StartOf returns a new Date snapped to the beginning of the specified unit.
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// Time is set to 00:00:00.000 unless otherwise specified.
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//
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// Supported units:
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// - Week: Returns Monday 00:00:00 (ISO 8601 convention)
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// - Month: Returns 1st day of month, 00:00:00
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// - Quarter: Returns first day of quarter (Q1=Jan 1, Q2=Apr 1, Q3=Jul 1, Q4=Oct 1)
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// - Year: Returns Jan 1, 00:00:00
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//
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// Example:
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//
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// date := quando.From(time.Date(2026, 2, 9, 15, 30, 45, 0, time.UTC))
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// monday := date.StartOf(quando.Week) // Feb 9, 2026 00:00:00 (Monday)
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// month := date.StartOf(quando.Month) // Feb 1, 2026 00:00:00
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// quarter := date.StartOf(quando.Quarter) // Jan 1, 2026 00:00:00 (Q1)
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// year := date.StartOf(quando.Year) // Jan 1, 2026 00:00:00
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func (d Date) StartOf(unit Unit) Date {
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t := d.t
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loc := t.Location()
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switch unit {
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case Weeks:
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// Find Monday of current week (ISO 8601: Monday is day 1)
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// time.Weekday: Sunday=0, Monday=1, ..., Saturday=6
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weekday := int(t.Weekday())
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if weekday == 0 { // Sunday
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weekday = 7 // Treat Sunday as day 7 for ISO 8601
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}
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daysToMonday := weekday - 1
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mondayDate := t.AddDate(0, 0, -daysToMonday)
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result := time.Date(mondayDate.Year(), mondayDate.Month(), mondayDate.Day(), 0, 0, 0, 0, loc)
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return Date{t: result, lang: d.lang}
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case Months:
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// First day of month, 00:00:00
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result := time.Date(t.Year(), t.Month(), 1, 0, 0, 0, 0, loc)
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return Date{t: result, lang: d.lang}
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case Quarters:
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// Q1=Jan-Mar (start: Jan 1), Q2=Apr-Jun (start: Apr 1),
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// Q3=Jul-Sep (start: Jul 1), Q4=Oct-Dec (start: Oct 1)
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month := t.Month()
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var quarterStart time.Month
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switch {
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case month >= 1 && month <= 3:
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quarterStart = time.January
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case month >= 4 && month <= 6:
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quarterStart = time.April
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case month >= 7 && month <= 9:
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quarterStart = time.July
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default: // month >= 10 && month <= 12
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quarterStart = time.October
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}
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result := time.Date(t.Year(), quarterStart, 1, 0, 0, 0, 0, loc)
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return Date{t: result, lang: d.lang}
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case Years:
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// Jan 1, 00:00:00
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result := time.Date(t.Year(), time.January, 1, 0, 0, 0, 0, loc)
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return Date{t: result, lang: d.lang}
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default:
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// For other units, return the date unchanged
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return d
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}
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}
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// EndOf returns a new Date snapped to the end of the specified unit.
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// Time is set to 23:59:59.999999999.
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//
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// Supported units:
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// - Week: Returns Sunday 23:59:59 (ISO 8601 convention)
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// - Month: Returns last day of month, 23:59:59 (handles all month lengths)
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// - Quarter: Returns last day of quarter, 23:59:59
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// - Year: Returns Dec 31, 23:59:59
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//
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// Example:
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//
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// date := quando.From(time.Date(2026, 2, 9, 15, 30, 45, 0, time.UTC))
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// sunday := date.EndOf(quando.Week) // Feb 15, 2026 23:59:59 (Sunday)
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// monthEnd := date.EndOf(quando.Month) // Feb 28, 2026 23:59:59
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// quarterEnd := date.EndOf(quando.Quarter) // Mar 31, 2026 23:59:59 (Q1)
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// yearEnd := date.EndOf(quando.Year) // Dec 31, 2026 23:59:59
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func (d Date) EndOf(unit Unit) Date {
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t := d.t
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loc := t.Location()
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switch unit {
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case Weeks:
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// Find Sunday of current week (ISO 8601: Sunday is day 7)
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// time.Weekday: Sunday=0, Monday=1, ..., Saturday=6
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weekday := int(t.Weekday())
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if weekday == 0 { // Sunday
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weekday = 7
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}
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daysToSunday := 7 - weekday
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sundayDate := t.AddDate(0, 0, daysToSunday)
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result := time.Date(sundayDate.Year(), sundayDate.Month(), sundayDate.Day(), 23, 59, 59, 999999999, loc)
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return Date{t: result, lang: d.lang}
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case Months:
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// Last day of month, 23:59:59
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// Strategy: Go to first day of next month, then subtract one day
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firstOfNextMonth := time.Date(t.Year(), t.Month()+1, 1, 0, 0, 0, 0, loc)
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lastOfMonth := firstOfNextMonth.AddDate(0, 0, -1)
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result := time.Date(lastOfMonth.Year(), lastOfMonth.Month(), lastOfMonth.Day(), 23, 59, 59, 999999999, loc)
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return Date{t: result, lang: d.lang}
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case Quarters:
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// Q1=Jan-Mar (end: Mar 31), Q2=Apr-Jun (end: Jun 30),
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// Q3=Jul-Sep (end: Sep 30), Q4=Oct-Dec (end: Dec 31)
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month := t.Month()
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var quarterEnd time.Month
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switch {
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case month >= 1 && month <= 3:
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quarterEnd = time.March
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case month >= 4 && month <= 6:
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quarterEnd = time.June
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case month >= 7 && month <= 9:
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quarterEnd = time.September
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default: // month >= 10 && month <= 12
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quarterEnd = time.December
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}
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// Get last day of quarter end month
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firstOfNextMonth := time.Date(t.Year(), quarterEnd+1, 1, 0, 0, 0, 0, loc)
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lastOfQuarter := firstOfNextMonth.AddDate(0, 0, -1)
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result := time.Date(lastOfQuarter.Year(), lastOfQuarter.Month(), lastOfQuarter.Day(), 23, 59, 59, 999999999, loc)
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return Date{t: result, lang: d.lang}
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case Years:
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// Dec 31, 23:59:59
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result := time.Date(t.Year(), time.December, 31, 23, 59, 59, 999999999, loc)
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return Date{t: result, lang: d.lang}
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default:
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// For other units, return the date unchanged
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return d
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}
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}
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