coder · johnstcn · Apr 4, 2022 · Apr 1, 2022 · Apr 4, 2022 · Apr 4, 2022
diff --git a/coderd/autostart/schedule/crontab_test.go b/coderd/autostart/schedule/crontab_test.go
@@ -0,0 +1,67 @@
+package schedule_test
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/coder/coder/coderd/autostart/schedule"
+)
+
+func Test_Weekly(t *testing.T) {
+	t.Parallel()
+	testCases := []struct {
+		name          string
+		spec          string
+		at            time.Time
+		expectedNext  time.Time
+		expectedError string
+	}{
+		{
+			name:          "with timezone",
+			spec:          "CRON_TZ=US/Central 30 9 1-5",
+			at:            time.Date(2022, 4, 1, 14, 29, 0, 0, time.UTC),
+			expectedNext:  time.Date(2022, 4, 1, 14, 30, 0, 0, time.UTC),
+			expectedError: "",
+		},
+		{
+			name:          "without timezone",
+			spec:          "30 9 1-5",
+			at:            time.Date(2022, 4, 1, 9, 29, 0, 0, time.Local),
+			expectedNext:  time.Date(2022, 4, 1, 9, 30, 0, 0, time.Local),
+			expectedError: "",
+		},
+		{
+			name:          "invalid schedule",
+			spec:          "asdfasdfasdfsd",
+			at:            time.Time{},
+			expectedNext:  time.Time{},
+			expectedError: "parse schedule: expected exactly 3 fields, found 1: [asdfasdfasdfsd]",
+		},
+		{
+			name:          "invalid location",
+			spec:          "CRON_TZ=Fictional/Country 30 9 1-5",
+			at:            time.Time{},
+			expectedNext:  time.Time{},
+			expectedError: "parse schedule: provided bad location Fictional/Country: unknown time zone Fictional/Country",
+		},
+	}
+
+	for _, testCase := range testCases {
+		testCase := testCase
+		t.Run(testCase.name, func(t *testing.T) {
+			t.Parallel()
+			actual, err := schedule.Weekly(testCase.spec)
+			if testCase.expectedError == "" {
+				nextTime := actual.Next(testCase.at)
+				require.NoError(t, err)
+				require.Equal(t, testCase.expectedNext, nextTime)
+				require.Equal(t, testCase.spec, actual.String())
+			} else {
+				require.EqualError(t, err, testCase.expectedError)
+				require.Nil(t, actual)
+			}
+		})
+	}
+}
diff --git a/coderd/autostart/schedule/schedule.go b/coderd/autostart/schedule/schedule.go
@@ -0,0 +1,66 @@
+// package schedule provides utilities for parsing and deserializing
+// cron-style expressions.
+package schedule
+
+import (
+	"time"
+
+	"github.com/robfig/cron/v3"
+	"golang.org/x/xerrors"
+)
+
+// For the purposes of this library, we only need minute, hour, and
+// day-of-week.
+const parserFormatWeekly = cron.Minute | cron.Hour | cron.Dow
+
+var defaultParser = cron.NewParser(parserFormatWeekly)
+
+// Weekly parses a Schedule from spec scoped to a recurring weekly event.
+// Spec consists of the following space-delimited fields, in the following order:
+// - timezone e.g. CRON_TZ=US/Central (optional)
+// - minutes of hour e.g. 30 (required)
+// - hour of day e.g. 9 (required)
+// - day of week e.g. 1 (required)
+//
+// Example Usage:
+//  local_sched, _ := schedule.Weekly("59 23 *")
+//  fmt.Println(sched.Next(time.Now().Format(time.RFC3339)))
+//  // Output: 2022-04-04T23:59:00Z
+//  us_sched, _ := schedule.Weekly("CRON_TZ=US/Central 30 9 1-5")
+//  fmt.Println(sched.Next(time.Now()).Format(time.RFC3339))
+//  // Output: 2022-04-04T14:30:00Z
+func Weekly(spec string) (*Schedule, error) {
+	specSched, err := defaultParser.Parse(spec)
+	if err != nil {
+		return nil, xerrors.Errorf("parse schedule: %w", err)
+	}
+
+	schedule, ok := specSched.(*cron.SpecSchedule)
+	if !ok {
+		return nil, xerrors.Errorf("expected *cron.SpecSchedule but got %T", specSched)
+	}
+
+	cronSched := &Schedule{
+		sched: schedule,
+		spec:  spec,
+	}
+	return cronSched, nil
+}
+
+// Schedule represents a cron schedule.
+// It's essentially a thin wrapper for robfig/cron/v3 that implements Stringer.
+type Schedule struct {
+	sched *cron.SpecSchedule
+	// XXX: there isn't any nice way for robfig/cron to serialize
+	spec string
+}
+
+// String serializes the schedule to its original human-friendly format.
+func (s Schedule) String() string {
+	return s.spec
+}
+
+// Next returns the next time in the schedule relative to t.
+func (s Schedule) Next(t time.Time) time.Time {
+	return s.sched.Next(t)
+}
diff --git a/go.mod b/go.mod
@@ -222,6 +222,7 @@ require (
 	github.com/prometheus/procfs v0.7.3 // indirect
 	github.com/rivo/tview v0.0.0-20200712113419-c65badfc3d92 // indirect
 	github.com/rivo/uniseg v0.2.0 // indirect
+	github.com/robfig/cron/v3 v3.0.1
 	github.com/russross/blackfriday/v2 v2.1.0 // indirect
 	github.com/sirupsen/logrus v1.8.1 // indirect
 	github.com/spf13/afero v1.8.1 // indirect

diff --git a/go.sum b/go.sum
@@ -1501,6 +1501,8 @@ github.com/remyoudompheng/bigfft v0.0.0-20200410134404-eec4a21b6bb0/go.mod h1:qq
 github.com/rivo/uniseg v0.1.0/go.mod h1:J6wj4VEh+S6ZtnVlnTBMWIodfgj8LQOQFoIToxlJtxc=
 github.com/rivo/uniseg v0.2.0 h1:S1pD9weZBuJdFmowNwbpi7BJ8TNftyUImj/0WQi72jY=
 github.com/rivo/uniseg v0.2.0/go.mod h1:J6wj4VEh+S6ZtnVlnTBMWIodfgj8LQOQFoIToxlJtxc=
+github.com/robfig/cron/v3 v3.0.1 h1:WdRxkvbJztn8LMz/QEvLN5sBU+xKpSqwwUO1Pjr4qDs=
+github.com/robfig/cron/v3 v3.0.1/go.mod h1:eQICP3HwyT7UooqI/z+Ov+PtYAWygg1TEWWzGIFLtro=
 github.com/rogpeppe/fastuuid v0.0.0-20150106093220-6724a57986af/go.mod h1:XWv6SoW27p1b0cqNHllgS5HIMJraePCO15w5zCzIWYg=
 github.com/rogpeppe/fastuuid v1.2.0/go.mod h1:jVj6XXZzXRy/MSR5jhDC/2q6DgLz+nrA6LYCDYWNEvQ=
 github.com/rogpeppe/go-internal v1.1.0/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFRclV5y23lUDJ4=