From 41a1dbeceba274f42142e376ef56f1a78557c536 Mon Sep 17 00:00:00 2001
From: Ian Fijolek <ian@iamthefij.com>
Date: Thu, 10 Aug 2023 16:22:30 -0400
Subject: [PATCH] Add date format functions

---
 README.md | 20 +++++++++++++++++++-
 alert.go  | 35 +++++++++++++++++++++++++++++++++--
 2 files changed, 52 insertions(+), 3 deletions(-)

diff --git a/README.md b/README.md
index 4e0a524..5345fe0 100644
--- a/README.md
+++ b/README.md
@@ -94,10 +94,28 @@ Also, when alerts are executed, they will be passed through Go's format function
 |`{{.AlertCount}}`|Number of times this monitor has alerted|
 |`{{.FailureCount}}`|The total number of sequential failed checks for this monitor|
 |`{{.LastCheckOutput}}`|The last returned value from the check command to either stderr or stdout|
-|`{{.LastSuccess}}`|The ISO datetime of the last successful check|
+|`{{.LastSuccess}}`|The datetime of the last successful check as a go Time struct|
 |`{{.MonitorName}}`|The name of the monitor that failed and triggered the alert|
 |`{{.IsUp}}`|Indicates if the monitor that is alerting is up or not. Can be used in a conditional message template|
 
+To provide flexible formatting, the following non-standard functions are available in templates:
+
+|func|description|
+|---|---|
+|`ANSIC <Time>`|Formats provided time in ANSIC format|
+|`UnixDate <Time>`|Formats provided time in UnixDate format|
+|`RubyDate <Time>`|Formats provided time in RubyDate format|
+|`RFC822Z <Time>`|Formats provided time in RFC822Z format|
+|`RFC850 <Time>`|Formats provided time in RFC850 format|
+|`RFC1123 <Time>`|Formats provided time in RFC1123 format|
+|`RFC1123Z <Time>`|Formats provided time in RFC1123Z format|
+|`RFC3339 <Time>`|Formats provided time in RFC3339 format|
+|`RFC3339Nano <Time>`|Formats provided time in RFC3339Nano format|
+|`FormatTime <Time> <string template>`|Formats provided time according to provided template|
+|`InTZ <Time> <string timezone name>`|Converts provided time to parsed timezone from the provided name|
+
+For more information, check out the [Go documentation for the time module](https://pkg.go.dev/time@go1.20.7#pkg-constants).
+
 ### Metrics
 
 Minitor supports exporting metrics for [Prometheus](https://prometheus.io/). Prometheus is an open source tool for reading and querying metrics from different sources. Combined with another tool, [Grafana](https://grafana.com/), it allows building of charts and dashboards. You could also opt to just use Minitor to log check results, and instead do your alerting with Grafana.
diff --git a/alert.go b/alert.go
index 4935216..2bdca8f 100644
--- a/alert.go
+++ b/alert.go
@@ -57,6 +57,37 @@ func (alert *Alert) BuildTemplates() error {
 
 	slog.Debugf("Building template for alert %s", alert.Name)
 
+	// Time format func factory
+	tff := func(formatString string) func(time.Time) string {
+		return func(t time.Time) string {
+			return t.Format(formatString)
+		}
+	}
+
+	// Create some functions for formatting datetimes in popular formats
+	timeFormatFuncs := template.FuncMap{
+		"ANSIC":       tff(time.ANSIC),
+		"UnixDate":    tff(time.UnixDate),
+		"RubyDate":    tff(time.RubyDate),
+		"RFC822Z":     tff(time.RFC822Z),
+		"RFC850":      tff(time.RFC850),
+		"RFC1123":     tff(time.RFC1123),
+		"RFC1123Z":    tff(time.RFC1123Z),
+		"RFC3339":     tff(time.RFC3339),
+		"RFC3339Nano": tff(time.RFC3339Nano),
+		"FormatTime": func(t time.Time, timeFormat string) string {
+			return t.Format(timeFormat)
+		},
+		"InTZ": func(t time.Time, tzName string) (time.Time, error) {
+			tz, err := time.LoadLocation(tzName)
+			if err != nil {
+				return t, fmt.Errorf("failed to convert time to specified tz: %w", err)
+			}
+
+			return t.In(tz), nil
+		},
+	}
+
 	switch {
 	case alert.commandTemplate == nil && alert.Command.Command != nil:
 		alert.commandTemplate = []*template.Template{}
@@ -66,7 +97,7 @@ func (alert *Alert) BuildTemplates() error {
 			}
 
 			alert.commandTemplate = append(alert.commandTemplate, template.Must(
-				template.New(alert.Name+fmt.Sprint(i)).Parse(cmdPart),
+				template.New(alert.Name+fmt.Sprint(i)).Funcs(timeFormatFuncs).Parse(cmdPart),
 			))
 		}
 	case alert.commandShellTemplate == nil && alert.Command.ShellCommand != "":
@@ -77,7 +108,7 @@ func (alert *Alert) BuildTemplates() error {
 		}
 
 		alert.commandShellTemplate = template.Must(
-			template.New(alert.Name).Parse(shellCmd),
+			template.New(alert.Name).Funcs(timeFormatFuncs).Parse(shellCmd),
 		)
 	default:
 		return fmt.Errorf("No template provided for alert %s: %w", alert.Name, errNoTemplate)