feat: TOML 1.0 parser and encoder

Assisted-by: GLM 5.3 Flash

datetime.go

@@ -0,0 +1,133 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: MIT
+
+package interpres
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+	"time"
+)
+
+// TOML distinguishes four date-time kinds. interpres decodes an offset
+// date-time to a plain time.Time (it carries a zone), and uses the wrapper
+// types below for the local variants so callers can tell them apart.
+
+// LocalDateTime is a TOML local date-time with no offset, e.g.
+// 1979-05-27T07:32:00. The embedded time.Time is in UTC.
+type LocalDateTime struct{ time.Time }
+
+// LocalDate is a TOML local date with no time or offset, e.g. 1979-05-27.
+// The embedded time.Time is at midnight UTC.
+type LocalDate struct{ time.Time }
+
+// LocalTime is a TOML local time with no date or offset, e.g. 07:32:00.999999.
+// The embedded time.Time uses the zero date.
+type LocalTime struct{ time.Time }
+
+// String returns the TOML-canonical rendering of the local date-time, e.g.
+// "1979-05-27T07:32:00" or "...:00.000000123" when the time has a fractional
+// second. The fractional component is zero-padded to nanosecond precision.
+func (ldt LocalDateTime) String() string {
+	base := ldt.Format("2006-01-02T15:04:05")
+	if ns := ldt.Nanosecond(); ns > 0 {
+		return base + "." + fmt.Sprintf("%09d", ns)
+	}
+	return base
+}
+
+// String returns the TOML-canonical rendering of the local date, e.g.
+// "1979-05-27".
+func (ld LocalDate) String() string { return ld.Format("2006-01-02") }
+
+// String returns the TOML-canonical rendering of the local time, e.g.
+// "07:32:00" or "...:00.000000123" when the time has a fractional second.
+// The fractional component is zero-padded to nanosecond precision.
+func (lt LocalTime) String() string {
+	base := lt.Format("15:04:05")
+	if ns := lt.Nanosecond(); ns > 0 {
+		return base + "." + fmt.Sprintf("%09d", ns)
+	}
+	return base
+}
+
+var (
+	offsetDateTimeLayouts = []string{
+		"2006-01-02T15:04:05.999999999Z07:00",
+		"2006-01-02T15:04:05Z07:00",
+		"2006-01-02 15:04:05.999999999Z07:00",
+		"2006-01-02 15:04:05Z07:00",
+	}
+	localDateTimeLayouts = []string{
+		"2006-01-02T15:04:05.999999999",
+		"2006-01-02T15:04:05",
+		"2006-01-02 15:04:05.999999999",
+		"2006-01-02 15:04:05",
+	}
+	localTimeLayouts = []string{
+		"15:04:05.999999999",
+		"15:04:05",
+	}
+)
+
+// dateTimeShape enforces the strict TOML grammar (two-digit components) that
+// time.Parse would otherwise accept loosely (e.g. a single-digit hour).
+var dateTimeShape = regexp.MustCompile(
+	`^\d{4}-\d{2}-\d{2}([Tt ]\d{2}:\d{2}:\d{2}(\.\d+)?([Zz]|[+-]\d{2}:\d{2})?)?$` +
+		`|^\d{2}:\d{2}:\d{2}(\.\d+)?$`,
+)
+
+// parseDateTime classifies and parses a bare token as a TOML date-time value.
+// It returns the decoded value (time.Time, LocalDateTime, LocalDate, or
+// LocalTime) and whether the token was a date-time at all.
+func parseDateTime(tok string) (any, bool) {
+	if tok == "" || tok[0] < '0' || tok[0] > '9' {
+		return nil, false
+	}
+	if !strings.ContainsAny(tok, "-:") {
+		return nil, false
+	}
+	if !dateTimeShape.MatchString(tok) {
+		return nil, false
+	}
+	// The ABNF accepts lowercase "t"/"z"; time.Parse only matches uppercase.
+	norm := strings.ToUpper(tok)
+	for _, layout := range offsetDateTimeLayouts {
+		if t, err := time.Parse(layout, norm); err == nil {
+			return t, true
+		}
+	}
+	for _, layout := range localDateTimeLayouts {
+		if t, err := time.Parse(layout, norm); err == nil {
+			return LocalDateTime{t}, true
+		}
+	}
+	if t, err := time.Parse("2006-01-02", norm); err == nil {
+		return LocalDate{t}, true
+	}
+	for _, layout := range localTimeLayouts {
+		if t, err := time.Parse(layout, norm); err == nil {
+			return LocalTime{t}, true
+		}
+	}
+	return nil, false
+}
+
+// isDateToken reports whether s is exactly a YYYY-MM-DD date, used to detect a
+// space-separated date-time written as "date<space>time".
+func isDateToken(s string) bool {
+	if len(s) != 10 {
+		return false
+	}
+	for i := range len(s) {
+		if i == 4 || i == 7 {
+			if s[i] != '-' {
+				return false
+			}
+		} else if !isDecDigit(s[i]) {
+			return false
+		}
+	}
+	return true
+}