Split the layout, checksum and transform declarations out of builtins.go

layout.go

@@ -0,0 +1,146 @@
+package fejkdata
+
+import (
+	"fmt"
+	"strings"
+	"time"
+)
+
+const dayLayout = "2006-01-02"
+
+// The instants a layout is proved against: layoutProbe2 is alike in no field, while
+// layoutDay differs from layoutProbe in its date fields alone and layoutClock in its
+// clock fields alone, so formatting two of them tells which kind a layout names.
+var (
+	layoutProbe  = time.Date(2001, 2, 3, 4, 5, 6, 0, time.UTC)
+	layoutProbe2 = time.Date(2010, 11, 12, 13, 14, 15, 0, time.UTC)
+	layoutDay    = time.Date(2010, 11, 12, 4, 5, 6, 0, time.UTC)
+	layoutClock  = time.Date(2001, 2, 3, 13, 14, 15, 0, time.UTC)
+)
+
+func namesAField(layout string) bool {
+	return layoutProbe.Format(layout) != layoutProbe2.Format(layout)
+}
+func namesADateField(layout string) bool {
+	return layoutProbe.Format(layout) != layoutDay.Format(layout)
+}
+func namesAClockField(layout string) bool {
+	return layoutProbe.Format(layout) != layoutClock.Format(layout)
+}
+
+// quotedLayout reports whether an arg carries the single quotes a layout is written in.
+func quotedLayout(a string) bool {
+	return len(a) >= 2 && a[0] == '\'' && a[len(a)-1] == '\''
+}
+
+// layoutArg is the Go layout a quoted arg holds, refused when unquoted or constant.
+func layoutArg(a string) (string, error) {
+	if !quotedLayout(a) {
+		bare := strings.Trim(a, `'"`)
+		if strings.HasPrefix(a, `"`) || strings.HasSuffix(a, `"`) {
+			return "", fmt.Errorf("layout %s is double-quoted; write '%s'", a, bare)
+		}
+		return "", fmt.Errorf("layout %s is not quoted; write '%s'", a, bare)
+	}
+	layout := a[1 : len(a)-1]
+	if !namesAField(layout) {
+		return "", fmt.Errorf("layout '%s' names no field, so it is the constant %q; write it as text", layout, layout)
+	}
+	return layout, nil
+}
+
+// layoutOf is layoutArg for an arg a check already validated.
+func layoutOf(a string) string {
+	layout, err := layoutArg(a)
+	if err != nil {
+		panic(fmt.Sprintf("fejkdata: builtin arg %q reached prep unvalidated: %v", a, err))
+	}
+	return layout
+}
+
+// layoutArity checks a call ending in a layout takes n args, naming the quoted
+// layout where an unquoted one split into more.
+func layoutArity(name string, n int, a []string) error {
+	if len(a) == n {
+		return nil
+	}
+	hint := ""
+	if len(a) > n && !holdsQuotedLayout(a[n-1:]) {
+		hint = fmt.Sprintf("; a layout holding a comma is quoted: '%s'", strings.Join(a[n-1:], ", "))
+	}
+	return fmt.Errorf("%s takes %d argument%s, got %d%s", name, n, plural(n), len(a), hint)
+}
+
+// holdsQuotedLayout reports whether the surplus args already carry a quoted layout,
+// which no comma split apart.
+func holdsQuotedLayout(a []string) bool {
+	for _, arg := range a {
+		if quotedLayout(arg) {
+			return true
+		}
+	}
+	return false
+}
+func dateArgs(_ map[string]node, a []string) error {
+	if err := layoutArity("date", 3, a); err != nil {
+		return err
+	}
+	from, err := time.Parse(dayLayout, a[0])
+	if err != nil {
+		return fmt.Errorf("date(from,to,layout): from %q is not a YYYY-MM-DD date", a[0])
+	}
+	to, err := time.Parse(dayLayout, a[1])
+	if err != nil {
+		return fmt.Errorf("date(from,to,layout): to %q is not a YYYY-MM-DD date", a[1])
+	}
+	if to.Before(from) {
+		return fmt.Errorf("date(from,to,layout): from %s is after to %s", a[0], a[1])
+	}
+	layout, err := layoutArg(a[2])
+	if err != nil {
+		return err
+	}
+	if !namesADateField(layout) {
+		return fmt.Errorf("date(from,to,layout): '%s' names no date field; write time('%s')", layout, layout)
+	}
+	if from.Equal(to) && !namesAClockField(layout) {
+		return fmt.Errorf("date(%s,%s,'%s') is the constant %q; write it as text", a[0], a[1], layout, from.Format(layout))
+	}
+	return nil
+}
+func timeArg(_ map[string]node, a []string) error {
+	if err := layoutArity("time", 1, a); err != nil {
+		return err
+	}
+	layout, err := layoutArg(a[0])
+	if err != nil {
+		return err
+	}
+	if namesADateField(layout) {
+		return fmt.Errorf("time(layout): '%s' names a date field; write date(from,to,layout)", layout)
+	}
+	return nil
+}
+
+// datePrep draws a second in [from 00:00:00, to 23:59:59] UTC; the span is counted
+// in seconds, since a Duration overflows past 292 years.
+func datePrep(a []string) callFn {
+	from, err := time.Parse(dayLayout, a[0])
+	if err != nil {
+		panic(fmt.Sprintf("fejkdata: builtin arg %q reached prep unvalidated: %v", a[0], err))
+	}
+	to, err := time.Parse(dayLayout, a[1])
+	if err != nil {
+		panic(fmt.Sprintf("fejkdata: builtin arg %q reached prep unvalidated: %v", a[1], err))
+	}
+	layout, start, span := layoutOf(a[2]), from.Unix(), int(to.Unix()-from.Unix())+86400
+	return func(s *session, _ string, _ []string) string {
+		return time.Unix(start+int64(s.IntN(span)), 0).UTC().Format(layout)
+	}
+}
+func timePrep(a []string) callFn {
+	layout := layoutOf(a[0])
+	return func(s *session, _ string, _ []string) string {
+		return time.Unix(int64(s.IntN(86400)), 0).UTC().Format(layout)
+	}
+}