Relative time, fixes.

util/sql3util/arg.go

@@ -1,6 +1,9 @@
 package sql3util
 
-import "strings"
+import (
+	"strings"
+	"time"
+)
 
 // NamedArg splits an named arg into a key and value,
 // around an equals sign.
@@ -63,3 +66,115 @@ func ParseBool(s string) (b, ok bool) {
 	}
 	return false, false
 }
+
+// ParseTimeShift parses a time shift modifier,
+// also the output of timediff.
+//
+// https://sqlite.org/lang_datefunc.html
+func ParseTimeShift(s string) (years, months, days int, duration time.Duration, ok bool) {
+	// Sign part: ±
+	neg := strings.HasPrefix(s, "-")
+	sign := neg || strings.HasPrefix(s, "+")
+	if sign {
+		s = s[1:]
+	}
+
+	if ok = len(s) >= 5; !ok {
+		return // !ok
+	}
+
+	defer func() {
+		if neg {
+			years = -years
+			months = -months
+			days = -days
+			duration = -duration
+		}
+	}()
+
+	// Date part: YYYY-MM-DD
+	if s[4] == '-' {
+		if ok = sign && len(s) >= 10 && s[7] == '-'; !ok {
+			return // !ok
+		}
+		if years, ok = parseInt(s[0:4]); !ok {
+			return // !ok
+		}
+		if months, ok = parseInt(s[5:7]); !ok {
+			return // !ok
+		}
+		if days, ok = parseInt(s[8:10]); !ok {
+			return // !ok
+		}
+		if len(s) == 10 {
+			return
+		}
+		if ok = s[10] == ' '; !ok {
+			return // !ok
+		}
+		s = s[11:]
+	}
+
+	// Time part: HH:MM
+	if ok = len(s) >= 5 && s[2] == ':'; !ok {
+		return // !ok
+	}
+
+	var hours, minutes int
+	if hours, ok = parseInt(s[0:2]); !ok {
+		return
+	}
+	if minutes, ok = parseInt(s[3:5]); !ok {
+		return
+	}
+	duration = time.Duration(hours)*time.Hour + time.Duration(minutes)*time.Minute
+
+	if len(s) == 5 {
+		return
+	}
+	if ok = len(s) >= 8 && s[5] == ':'; !ok {
+		return // !ok
+	}
+
+	// Seconds part: HH:MM:SS
+	var seconds int
+	if seconds, ok = parseInt(s[6:8]); !ok {
+		return
+	}
+	duration += time.Duration(seconds) * time.Second
+
+	if len(s) == 8 {
+		return
+	}
+	if ok = len(s) >= 10 && s[8] == '.'; !ok {
+		return // !ok
+	}
+	s = s[9:]
+
+	// Nanosecond part: HH:MM:SS.SSS
+	var nanos int
+	if nanos, ok = parseInt(s[0:min(9, len(s))]); !ok {
+		return
+	}
+	for i := len(s); i < 9; i++ {
+		nanos *= 10
+	}
+	duration += time.Duration(nanos)
+
+	// Subnanosecond part.
+	if len(s) > 9 {
+		_, ok = parseInt(s[9:])
+	}
+	return
+}
+
+func parseInt(s string) (i int, _ bool) {
+	for _, r := range []byte(s) {
+		r -= '0'
+		if r > 9 {
+			return
+		}
+		i = i*10 + int(r)
+	}
+	return i, true
+}