feat(docs): add template preview (#1777)

tplprev/main.go

@@ -0,0 +1,49 @@
+//go:build !wasm
+
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+
+	"github.com/containrrr/watchtower/internal/meta"
+	"github.com/containrrr/watchtower/pkg/notifications/preview"
+	"github.com/containrrr/watchtower/pkg/notifications/preview/data"
+)
+
+func main() {
+	fmt.Fprintf(os.Stderr, "watchtower/tplprev %v\n\n", meta.Version)
+
+	var states string
+	var entries string
+
+	flag.StringVar(&states, "states", "cccuuueeekkktttfff", "sCanned, Updated, failEd, sKipped, sTale, Fresh")
+	flag.StringVar(&entries, "entries", "ewwiiidddd", "Fatal,Error,Warn,Info,Debug,Trace")
+
+	flag.Parse()
+
+	if len(flag.Args()) < 1 {
+		fmt.Fprintln(os.Stderr, "Missing required argument TEMPLATE")
+		flag.Usage()
+		os.Exit(1)
+		return
+	}
+
+	input, err := os.ReadFile(flag.Arg(0))
+	if err != nil {
+
+		fmt.Fprintf(os.Stderr, "Failed to read template file %q: %v\n", flag.Arg(0), err)
+		os.Exit(1)
+		return
+	}
+
+	result, err := preview.Render(string(input), data.StatesFromString(states), data.LevelsFromString(entries))
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Failed to read template file %q: %v\n", flag.Arg(0), err)
+		os.Exit(1)
+		return
+	}
+
+	fmt.Println(result)
+}