Feature 02 task 2: Store helpers: transactions, ULIDs and time conventions (#11)

Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com>
Co-committed-by: dev_agent <dev_agent@cubecraftlabs.com>

internal/store/time.go

@@ -0,0 +1,119 @@
+package store
+
+import (
+	"database/sql/driver"
+	"errors"
+	"fmt"
+	"time"
+)
+
+// timestampLayout is RFC 3339 in UTC with fixed millisecond precision, so
+// stored timestamps sort lexicographically in time order.
+const timestampLayout = "2006-01-02T15:04:05.000Z"
+
+// Timestamp is an instant stored as UTC RFC 3339 TEXT with millisecond
+// precision. Sub-millisecond precision is dropped on write. Use
+// sql.Null[Timestamp] for a nullable column.
+type Timestamp struct {
+	time.Time
+}
+
+// Now returns the current instant as a Timestamp, in UTC at millisecond
+// precision, so it equals its stored form.
+func Now() Timestamp {
+	return Timestamp{time.Now().UTC().Truncate(time.Millisecond)}
+}
+
+// String returns the stored TEXT form.
+func (t Timestamp) String() string {
+	return t.UTC().Format(timestampLayout)
+}
+
+// Value implements driver.Valuer. The zero Timestamp is an error, as is a UTC
+// year outside 0000–9999, which the four-digit stored form cannot represent.
+func (t Timestamp) Value() (driver.Value, error) {
+	if t.IsZero() {
+		return nil, errors.New("store: zero Timestamp")
+	}
+	if y := t.UTC().Year(); y < 0 || y > 9999 {
+		return nil, fmt.Errorf("store: Timestamp year %d outside 0000-9999", y)
+	}
+	return t.String(), nil
+}
+
+// Scan implements sql.Scanner. It accepts only TEXT in the stored form, and
+// rejects the zero instant, which Value refuses to write.
+func (t *Timestamp) Scan(src any) error {
+	s, ok := src.(string)
+	if !ok {
+		return fmt.Errorf("store: scan Timestamp: want TEXT, got %T", src)
+	}
+	parsed, err := time.Parse(timestampLayout, s)
+	if err != nil {
+		return fmt.Errorf("store: scan Timestamp %q: %w", s, err)
+	}
+	if parsed.Format(timestampLayout) != s {
+		return fmt.Errorf("store: scan Timestamp %q: want %s", s, timestampLayout)
+	}
+	if parsed.IsZero() {
+		return fmt.Errorf("store: scan Timestamp %q: zero Timestamp", s)
+	}
+	t.Time = parsed
+	return nil
+}
+
+// localDateLayout is the household-local calendar date form.
+const localDateLayout = "2006-01-02"
+
+// LocalDate is a household-local calendar date with no time or zone, stored
+// as YYYY-MM-DD TEXT. The zero LocalDate is invalid and cannot be stored.
+type LocalDate struct {
+	year  int
+	month time.Month
+	day   int
+}
+
+// ParseLocalDate parses a YYYY-MM-DD date, rejecting any other form and any
+// date that does not exist on the calendar.
+func ParseLocalDate(s string) (LocalDate, error) {
+	t, err := time.Parse(localDateLayout, s)
+	if err != nil {
+		return LocalDate{}, fmt.Errorf("store: invalid date %q: %w", s, err)
+	}
+	if t.Format(localDateLayout) != s {
+		return LocalDate{}, fmt.Errorf("store: invalid date %q: want YYYY-MM-DD", s)
+	}
+	return LocalDate{t.Year(), t.Month(), t.Day()}, nil
+}
+
+// String returns the YYYY-MM-DD form.
+func (d LocalDate) String() string {
+	return fmt.Sprintf("%04d-%02d-%02d", d.year, int(d.month), d.day)
+}
+
+// IsZero reports whether d is the zero LocalDate.
+func (d LocalDate) IsZero() bool {
+	return d == LocalDate{}
+}
+
+// Value implements driver.Valuer. The zero LocalDate is an error.
+func (d LocalDate) Value() (driver.Value, error) {
+	if d.IsZero() {
+		return nil, errors.New("store: zero LocalDate")
+	}
+	return d.String(), nil
+}
+
+// Scan implements sql.Scanner. It accepts only YYYY-MM-DD TEXT.
+func (d *LocalDate) Scan(src any) error {
+	s, ok := src.(string)
+	if !ok {
+		return fmt.Errorf("store: scan LocalDate: want TEXT, got %T", src)
+	}
+	parsed, err := ParseLocalDate(s)
+	if err != nil {
+		return fmt.Errorf("store: scan LocalDate: %w", err)
+	}
+	*d = parsed
+	return nil
+}