1 files changed, 117 insertions, 0 deletions
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..515407f
--- /dev/null
+++ b/main.go
@@ -0,0 +1,117 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"log"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"time"
+
+	"github.com/robfig/cron/v3"
+)
+
+type inputLine struct {
+	Schedule string
+	Task     string
+}
+
+var lastSeenInput = map[inputLine]struct{}{}
+
+func main() {
+	p, err := inputFilePath()
+	if err != nil {
+		log.Fatalf("getting input file: %s", err)
+	}
+
+	c := cron.New()
+
+	for {
+		input, err := readInput(p)
+		if err != nil {
+			log.Printf("reading input: %s", err)
+		}
+		changed := inputChanged(lastSeenInput, input)
+		if changed {
+			fmt.Println("changed!")
+			lastSeenInput = input
+			c.Stop()
+			c := cron.New()
+			err := addJobs(c)
+			if err != nil {
+				log.Printf("adding jobs: %s", err)
+			}
+			c.Start()
+		} else {
+			fmt.Println("not changed!")
+		}
+
+		time.Sleep(time.Minute) // re-read the input file every minute
+	}
+
+}
+
+func inputFilePath() (string, error) {
+	args := os.Args
+	if len(args) != 2 {
+		return "", fmt.Errorf("expected one argument (input file path), got %d", len(args)-1)
+	}
+	p := filepath.Clean(args[1])
+
+	// While we're here, check that the input path actually exists and
+	// is stat-able.
+	if _, err := os.Stat(p); err != nil {
+		return "", fmt.Errorf("cannot stat input file: %w", err)
+	}
+
+	return p, nil
+}
+
+var inputFileRe = regexp.MustCompile(`([^\s]+\s+[^\s]+\s+[^\s]+\s+[^\s]+\s+[^\s]+)\s+(.*)`)
+
+func readInput(p string) (map[inputLine]struct{}, error) {
+	input := map[inputLine]struct{}{}
+
+	f, err := os.Open(p)
+	if err != nil {
+		return nil, fmt.Errorf("opening '%s': %w", p, err)
+	}
+	defer f.Close()
+
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		line := strings.TrimSpace(scanner.Text())
+		if line == "" {
+			continue
+		}
+
+		matches := inputFileRe.FindStringSubmatch(line)
+		if matches == nil || len(matches) != 1+2 {
+			log.Printf("failed to parse input line: '%s'", line)
+		}
+
+		input[inputLine{Schedule: matches[1], Task: matches[2]}] = struct{}{}
+	}
+
+	if err := scanner.Err(); err != nil {
+		return nil, fmt.Errorf("scanning: %w", err)
+	}
+
+	return input, nil
+}
+
+func inputChanged(old, new map[inputLine]struct{}) bool {
+	if len(new) != len(old) {
+		return true
+	}
+	for k := range old {
+		if _, ok := new[k]; !ok {
+			return true
+		}
+	}
+	return false
+}
+
+func addJobs(c *cron.Cron) error { return nil }