New time formatter, time.Format(formatString)

The model is that formatString is a a representation of a standard time,
and that Format converts the time to that representation.
Standard representaitons are defined for ANSIC, RFC850, RFC1123, and ISO8601.
There's also a humane Kitchen fomat: 3:04PM.

R=rsc, benolive, cw
CC=golang-dev
http://codereview.appspot.com/181130

4 files changed, 259 insertions, 155 deletions

diff --git a/src/pkg/time/Makefile b/src/pkg/time/Makefile
index ac4415069..f73fc8878 100644
--- a/src/pkg/time/Makefile
+++ b/src/pkg/time/Makefile
@@ -6,6 +6,7 @@ include ../../Make.$(GOARCH)
 
 TARG=time
 GOFILES=\
+	format.go \
 	sleep.go\
 	tick.go\
 	time.go\
diff --git a/src/pkg/time/format.go b/src/pkg/time/format.go
new file mode 100644
index 000000000..52d62a908
--- /dev/null
+++ b/src/pkg/time/format.go
@@ -0,0 +1,227 @@
+package time
+
+import (
+	"strconv"
+)
+
+const (
+	numeric = iota
+	alphabetic
+	separator
+)
+
+// These are predefined layouts for use in Time.Format.
+// The standard time used in the layouts is:
+//	Mon Jan  2 15:04:05 PST 2006  (PST is GMT-0800)
+// which is Unix time 1136243045.
+const (
+	ANSIC    = "Mon Jan  2 15:04:05 2006"
+	UnixDate = "Mon Jan  2 15:04:05 PST 2006"
+	RFC850   = "Monday, 02-Jan-06 15:04:05 PST"
+	RFC1123  = "Mon, 02 Jan 2006 15:04:05 PST"
+	Kitchen  = "3:04PM"
+	// Special case: use Z to get the time zone formatted according to ISO 8601,
+	// which is -0800 or Z for UTC
+	ISO8601 = "2006-01-02T15:04:05Z"
+)
+
+const (
+	stdLongMonth   = "January"
+	stdMonth       = "Jan"
+	stdNumMonth    = "1"
+	stdZeroMonth   = "01"
+	stdLongWeekDay = "Monday"
+	stdWeekDay     = "Mon"
+	stdDay         = "2"
+	stdZeroDay     = "02"
+	stdHour        = "15"
+	stdHour12      = "3"
+	stdZeroHour12  = "03"
+	stdMinute      = "4"
+	stdZeroMinute  = "04"
+	stdSecond      = "5"
+	stdZeroSecond  = "05"
+	stdLongYear    = "2006"
+	stdYear        = "06"
+	stdZulu        = "1504"
+	stdPM          = "PM"
+	stdpm          = "pm"
+	stdTZ          = "PST"
+	stdISO8601TZ   = "Z"
+)
+
+var longDayNames = []string{
+	"Sunday",
+	"Monday",
+	"Tuesday",
+	"Wednesday",
+	"Thursday",
+	"Friday",
+	"Saturday",
+}
+
+var shortDayNames = []string{
+	"Sun",
+	"Mon",
+	"Tue",
+	"Wed",
+	"Thu",
+	"Fri",
+	"Sat",
+}
+
+var shortMonthNames = []string{
+	"---",
+	"Jan",
+	"Feb",
+	"Mar",
+	"Apr",
+	"May",
+	"Jun",
+	"Jul",
+	"Aug",
+	"Sep",
+	"Oct",
+	"Nov",
+	"Dec",
+}
+
+var longMonthNames = []string{
+	"---",
+	"January",
+	"February",
+	"March",
+	"April",
+	"May",
+	"June",
+	"July",
+	"August",
+	"September",
+	"October",
+	"November",
+	"December",
+}
+
+func charType(c uint8) int {
+	switch {
+	case '0' <= c && c <= '9':
+		return numeric
+	case 'a' <= c && c < 'z', 'A' <= c && c <= 'Z':
+		return alphabetic
+	}
+	return separator
+}
+
+func pieces(s string) []string {
+	p := make([]string, 20)
+	i := 0
+	// Each iteration generates one piece
+	for n := range p {
+		if i >= len(s) {
+			p = p[0:n]
+			break
+		}
+		start := i
+		c := s[i]
+		pieceType := charType(c)
+		for i < len(s) && charType(s[i]) == pieceType {
+			i++
+		}
+		p[n] = s[start:i]
+	}
+	return p
+}
+
+func zeroPad(i int) string {
+	s := strconv.Itoa(i)
+	if i < 10 {
+		s = "0" + s
+	}
+	return s
+}
+
+// Format returns a textual representation of the time value formatted
+// according to layout.  The layout defines the format by showing the
+// representation of a standard time, which is then used to describe
+// the time to be formatted.  Predefined layouts ANSIC, UnixDate,
+// ISO8601 and others describe standard representations.
+func (t *Time) Format(layout string) string {
+	pc := pieces(layout)
+	s := ""
+	for _, p := range pc {
+		switch p {
+		case stdYear:
+			p = strconv.Itoa64(t.Year % 100)
+		case stdLongYear:
+			p = strconv.Itoa64(t.Year)
+		case stdMonth:
+			p = shortMonthNames[t.Month]
+		case stdLongMonth:
+			p = longMonthNames[t.Month]
+		case stdNumMonth:
+			p = strconv.Itoa(t.Month)
+		case stdZeroMonth:
+			p = zeroPad(t.Month)
+		case stdWeekDay:
+			p = shortDayNames[t.Weekday]
+		case stdLongWeekDay:
+			p = longDayNames[t.Weekday]
+		case stdDay:
+			p = strconv.Itoa(t.Day)
+		case stdZeroDay:
+			p = zeroPad(t.Day)
+		case stdHour:
+			p = zeroPad(t.Hour)
+		case stdHour12:
+			p = strconv.Itoa(t.Hour % 12)
+		case stdZeroHour12:
+			p = zeroPad(t.Hour % 12)
+		case stdMinute:
+			p = strconv.Itoa(t.Minute)
+		case stdZeroMinute:
+			p = zeroPad(t.Minute)
+		case stdSecond:
+			p = strconv.Itoa(t.Second)
+		case stdZeroSecond:
+			p = zeroPad(t.Second)
+		case stdZulu:
+			p = zeroPad(t.Hour) + zeroPad(t.Minute)
+		case stdISO8601TZ:
+			// Rather ugly special case, required because the time zone is too broken down
+			// in this format to recognize easily.  We cheat and take "Z" to mean "the time
+			// zone as formatted for ISO 8601".
+			if t.ZoneOffset == 0 {
+				p = "Z"
+			} else {
+				zone := t.ZoneOffset / 60 // minutes
+				if zone < 0 {
+					p = "-"
+					zone = -zone
+				} else {
+					p = "+"
+				}
+				p += zeroPad(zone / 60)
+				p += zeroPad(zone % 60)
+			}
+		case stdPM:
+			if t.Hour >= 12 {
+				p = "PM"
+			} else {
+				p = "AM"
+			}
+		case stdpm:
+			if t.Hour >= 12 {
+				p = "pm"
+			} else {
+				p = "am"
+			}
+		case stdTZ:
+			p = t.Zone
+		}
+		s += p
+	}
+	return s
+}
+
+// String returns a Unix-style representation of the time value.
+func (t *Time) String() string { return t.Format(UnixDate) }
diff --git a/src/pkg/time/time.go b/src/pkg/time/time.go
index ff696e0ac..d84807e83 100644
--- a/src/pkg/time/time.go
+++ b/src/pkg/time/time.go
@@ -227,155 +227,3 @@ func (t *Time) Seconds() int64 {
 	sec -= int64(t.ZoneOffset)
 	return sec
 }
-
-var longDayNames = []string{
-	"Sunday",
-	"Monday",
-	"Tuesday",
-	"Wednesday",
-	"Thursday",
-	"Friday",
-	"Saturday",
-}
-
-var shortDayNames = []string{
-	"Sun",
-	"Mon",
-	"Tue",
-	"Wed",
-	"Thu",
-	"Fri",
-	"Sat",
-}
-
-var shortMonthNames = []string{
-	"---",
-	"Jan",
-	"Feb",
-	"Mar",
-	"Apr",
-	"May",
-	"Jun",
-	"Jul",
-	"Aug",
-	"Sep",
-	"Oct",
-	"Nov",
-	"Dec",
-}
-
-func copy(dst []byte, s string) {
-	for i := 0; i < len(s); i++ {
-		dst[i] = s[i]
-	}
-}
-
-func decimal(dst []byte, n int) {
-	if n < 0 {
-		n = 0
-	}
-	for i := len(dst) - 1; i >= 0; i-- {
-		dst[i] = byte(n%10 + '0')
-		n /= 10
-	}
-}
-
-func addString(buf []byte, bp int, s string) int {
-	n := len(s)
-	copy(buf[bp:bp+n], s)
-	return bp + n
-}
-
-// Just enough of strftime to implement the date formats below.
-// Not exported.
-func format(t *Time, fmt string) string {
-	buf := make([]byte, 128)
-	bp := 0
-
-	for i := 0; i < len(fmt); i++ {
-		if fmt[i] == '%' {
-			i++
-			switch fmt[i] {
-			case 'A': // %A full weekday name
-				bp = addString(buf, bp, longDayNames[t.Weekday])
-			case 'a': // %a abbreviated weekday name
-				bp = addString(buf, bp, shortDayNames[t.Weekday])
-			case 'b': // %b abbreviated month name
-				bp = addString(buf, bp, shortMonthNames[t.Month])
-			case 'd': // %d day of month (01-31)
-				decimal(buf[bp:bp+2], t.Day)
-				bp += 2
-			case 'e': // %e day of month ( 1-31)
-				if t.Day >= 10 {
-					decimal(buf[bp:bp+2], t.Day)
-				} else {
-					buf[bp] = ' '
-					buf[bp+1] = byte(t.Day + '0')
-				}
-				bp += 2
-			case 'H': // %H hour 00-23
-				decimal(buf[bp:bp+2], t.Hour)
-				bp += 2
-			case 'M': // %M minute 00-59
-				decimal(buf[bp:bp+2], t.Minute)
-				bp += 2
-			case 'm': // %m month 01-12
-				decimal(buf[bp:bp+2], t.Month)
-				bp += 2
-			case 'S': // %S second 00-59
-				decimal(buf[bp:bp+2], t.Second)
-				bp += 2
-			case 'Y': // %Y year 2008
-				decimal(buf[bp:bp+4], int(t.Year))
-				bp += 4
-			case 'y': // %y year 08
-				decimal(buf[bp:bp+2], int(t.Year%100))
-				bp += 2
-			case 'z': // %z tz in the form -0500
-				if t.ZoneOffset == 0 {
-					bp = addString(buf, bp, "Z")
-				} else if t.ZoneOffset < 0 {
-					bp = addString(buf, bp, "-")
-					decimal(buf[bp:bp+2], -t.ZoneOffset/3600)
-					decimal(buf[bp+2:bp+4], (-t.ZoneOffset%3600)/60)
-					bp += 4
-				} else {
-					bp = addString(buf, bp, "+")
-					decimal(buf[bp:bp+2], t.ZoneOffset/3600)
-					decimal(buf[bp+2:bp+4], (t.ZoneOffset%3600)/60)
-					bp += 4
-				}
-			case 'Z':
-				bp = addString(buf, bp, t.Zone)
-			default:
-				buf[bp] = '%'
-				buf[bp+1] = fmt[i]
-				bp += 2
-			}
-		} else {
-			buf[bp] = fmt[i]
-			bp++
-		}
-	}
-	return string(buf[0:bp])
-}
-
-// Asctime formats the parsed time value in the style of
-// ANSI C asctime: Sun Nov  6 08:49:37 1994
-func (t *Time) Asctime() string { return format(t, "%a %b %e %H:%M:%S %Y") }
-
-// RFC850 formats the parsed time value in the style of
-// RFC 850: Sunday, 06-Nov-94 08:49:37 UTC
-func (t *Time) RFC850() string { return format(t, "%A, %d-%b-%y %H:%M:%S %Z") }
-
-// RFC1123 formats the parsed time value in the style of
-// RFC 1123: Sun, 06 Nov 1994 08:49:37 UTC
-func (t *Time) RFC1123() string { return format(t, "%a, %d %b %Y %H:%M:%S %Z") }
-
-// ISO8601 formats the parsed time value in the style of
-// ISO 8601: 1994-11-06T08:49:37Z
-func (t *Time) ISO8601() string { return format(t, "%Y-%m-%dT%H:%M:%S%z") }
-
-// String formats the parsed time value in the style of
-// date(1): Sun Nov  6 08:49:37 UTC 1994
-func (t *Time) String() string { return format(t, "%a %b %e %H:%M:%S %Z %Y") }
diff --git a/src/pkg/time/time_test.go b/src/pkg/time/time_test.go
index 97787f30b..4dfdea445 100644
--- a/src/pkg/time/time_test.go
+++ b/src/pkg/time/time_test.go
@@ -114,10 +114,38 @@ var iso8601Formats = []TimeFormatTest{
 
 func TestISO8601Conversion(t *testing.T) {
 	for _, f := range iso8601Formats {
-		if f.time.ISO8601() != f.formattedValue {
-			t.Error("ISO8601():")
+		if f.time.Format(ISO8601) != f.formattedValue {
+			t.Error("ISO8601:")
 			t.Errorf("  want=%+v", f.formattedValue)
-			t.Errorf("  have=%+v", f.time.ISO8601())
+			t.Errorf("  have=%+v", f.time.Format(ISO8601))
+		}
+	}
+}
+
+type FormatTest struct {
+	name   string
+	format string
+	result string
+}
+
+var formatTests = []FormatTest{
+	FormatTest{"ANSIC", ANSIC, "Thu Feb  4 21:00:57 2010"},
+	FormatTest{"UnixDate", UnixDate, "Thu Feb  4 21:00:57 PST 2010"},
+	FormatTest{"RFC850", RFC850, "Thursday, 04-Feb-10 21:00:57 PST"},
+	FormatTest{"RFC1123", RFC1123, "Thu, 04 Feb 2010 21:00:57 PST"},
+	FormatTest{"ISO8601", ISO8601, "2010-02-04T21:00:57-0800"},
+	FormatTest{"Kitchen", Kitchen, "9:00PM"},
+	FormatTest{"am/pm", "3pm", "9pm"},
+	FormatTest{"AM/PM", "3PM", "9PM"},
+}
+
+func TestFormat(t *testing.T) {
+	// The numeric time represents Thu Feb  4 21:00:57 EST 2010
+	time := SecondsToLocalTime(1265346057)
+	for _, test := range formatTests {
+		result := time.Format(test.format)
+		if result != test.result {
+			t.Errorf("%s expected %q got %q", test.name, test.result, result)
 		}
 	}
 }