WhatsApp Reminder (?) I dunno I'm bad at naming things but you get the idea.

main.go

package main

import (
	"context"
	"os"
	"time"

	driver "github.com/chromedp/chromedp"
	"k8s.io/klog/v2"
)

func main() {
	opts := append(driver.DefaultExecAllocatorOptions[:],
		driver.Flag("headless", false),
	)

	ctx, cancel := driver.NewExecAllocator(context.Background(), opts...)
	defer cancel()

	// Create context with logger interface.
	ctx, cancel = driver.NewContext(ctx, driver.WithDebugf(klog.Infof))
	defer cancel()

	// Pre-definitions.
	urlStr := "https://web.whatsapp.com/"
	group := "Heyo!"
	groupSel := `//span[@title="` + group + `"]`
	typeSel := `//div[@title="Type a message"]`
	message := "Avengers assemble!"
	sender := `//span[@data-testid="send"]`
	waitBeforeClose := 10 * time.Second
	var buf []byte
	dir := "artefacts"

	// Current time to string.
	t := time.Now()
	tStr := t.Format("2006-01-02_15-04-05")

	// Run driver.
	err := driver.Run(ctx, driver.Tasks{
		driver.Navigate(urlStr),
		driver.WaitVisible(groupSel),
		driver.Click(groupSel),
		driver.SendKeys(typeSel, message),
		driver.Click(sender),
		driver.Sleep(waitBeforeClose),
		driver.CaptureScreenshot(&buf),
	})
	if err != nil {
		klog.Fatalf("error during run: %v", err)
	}

	// Save screenshot.
	// Create artefacts directory if it doesn't exist.
	if _, err := os.Stat(dir); os.IsNotExist(err) {
		if err := os.Mkdir(dir, 0755); err != nil {
			klog.Fatalf("error on creating artefacts directory: %v", err)
		}
	}

	// Save screenshot to file.
	if err := os.WriteFile(dir+"/screenshot_"+tStr+".png", buf, 0644); err != nil {
		klog.Fatalf("error on saving to buffer: %v", err)
	}

	// Done.
	klog.Info("done!")
}

To use this in a containerized env, use the Dockerfile below.

# Build application.
FROM golang:1.19-alpine3.17 AS build

# Install git.
# Git is required for fetching the dependencies.
RUN apk update && apk add --no-cache git

# Create appuser.
RUN adduser -D -g '' appuser

WORKDIR $GOPATH/src/github.com/rexagod/wa-reminder
COPY . .

# Fetch dependencies.
# Using go get.
RUN go get -d -v

# Build the binary.
RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o /go/bin/wa-reminder .

# Run application.
FROM chromedp/headless-shell:latest

# Import from builder.
COPY --from=build /etc/passwd /etc/passwd
COPY --from=build /go/bin/wa-reminder /go/bin/wa-reminder

# Use an unprivileged user.
USER appuser

# Run the binary.
ENTRYPOINT ["/go/bin/wa-reminder"]