1 files changed, 122 insertions, 0 deletions
diff --git a/cmd/gen-imworkingon/calendar.go b/cmd/gen-imworkingon/calendar.go
new file mode 100644
index 0000000..29c3318
--- /dev/null
+++ b/cmd/gen-imworkingon/calendar.go
@@ -0,0 +1,122 @@
+package main
+
+import (
+	"time"
+)
+
+//////////////////////////////////////////////////////////////////////
+
+type Date struct {
+	Year  int
+	Month time.Month
+	Day   int
+}
+
+func DateOf(t time.Time) Date {
+	y, m, d := t.Date()
+	return Date{Year: y, Month: m, Day: d}
+}
+
+func (d Date) Time() time.Time {
+	return time.Date(d.Year, d.Month, d.Day, 0, 0, 0, 0, time.Local)
+}
+
+func (d Date) AddDays(delta int) Date {
+	return DateOf(d.Time().AddDate(0, 0, delta))
+}
+
+func (d Date) Weekday() time.Weekday {
+	return d.Time().Weekday()
+}
+
+func (a Date) Cmp(b Date) int {
+	switch {
+	case a.Year < b.Year:
+		return -1
+	case a.Year > b.Year:
+		return 1
+	}
+	switch {
+	case a.Month < b.Month:
+		return -1
+	case a.Month > b.Month:
+		return 1
+	}
+	switch {
+	case a.Day < b.Day:
+		return -1
+	case a.Day > b.Day:
+		return 1
+	}
+	return 0
+}
+
+//////////////////////////////////////////////////////////////////////
+
+type CalendarDay[T any] struct {
+	Date
+	Data T
+}
+
+//////////////////////////////////////////////////////////////////////
+
+// keyed by time.Weekday
+type CalendarWeek[T any] [7]CalendarDay[T]
+
+//////////////////////////////////////////////////////////////////////
+
+// must be sorted, must be non-sparse
+type Calendar[T any] []CalendarWeek[T]
+
+func (c Calendar[T]) NumWeekdaysInMonth(weekday time.Weekday, target Date) int {
+	num := 0
+	for _, w := range c {
+		if w[weekday].Date == (Date{}) {
+			continue
+		}
+		switch {
+		case w[weekday].Year == target.Year:
+			switch {
+			case w[weekday].Month == target.Month:
+				num++
+			case w[weekday].Month > target.Month:
+				return num
+			}
+		case w[weekday].Year > target.Year:
+			return num
+		}
+	}
+	return num
+}
+
+//////////////////////////////////////////////////////////////////////
+
+func BuildCalendar[T any](things []T, dateOfThing func(T) Date) Calendar[T] {
+	if len(things) == 0 {
+		return nil
+	}
+
+	newestDate := DateOf(time.Now().Local())
+
+	oldestDate := dateOfThing(things[0])
+	byDate := make(map[Date]T, len(things))
+	for _, thing := range things {
+		date := dateOfThing(thing)
+		if oldestDate.Cmp(date) > 0 {
+			oldestDate = date
+		}
+		byDate[date] = thing
+	}
+
+	var ret Calendar[T]
+	for date := oldestDate; date.Cmp(newestDate) <= 0; date = date.AddDays(1) {
+		if len(ret) == 0 || date.Weekday() == 0 {
+			ret = append(ret, CalendarWeek[T]{})
+		}
+		ret[len(ret)-1][date.Weekday()] = CalendarDay[T]{
+			Date: date,
+			Data: byDate[date],
+		}
+	}
+	return ret
+}