Add cron mode support

Ability to run in a daemon mode, where the schedule is configured
with the cron-like spec.

README.md

@@ -35,9 +35,22 @@ In addition to the config.yaml file, the following environment variables can be
 - `PROJECTS`: A comma-separated list of GitLab project IDs to check for merge requests.
 - `GROUPS`: A comma-separated list of GitLab group IDs to check for merge requests.
 - `CONFIG_PATH` (optional): The path to the config.yaml configuration file. Defaults to config.yaml.
+- `CRON_SCHEDULE` (optional): The cron schedule for the bot to run. See [Run mode](#run-mode) and [supported format](https://github.com/reugn/go-quartz?tab=readme-ov-file#cron-expression-format).
 
 Environment variables take precedence over the config.yaml file.
 
+### Run mode
+
+The bot can run in two modes: one-shot and cron.
+
+When no `CRON_SCHEDULE` variable or `cron_schedule` config parameter specified, the bot will execute in one-shot mode.
+In this mode, the bot will check for merge requests and send a message to the Slack channel once, then exit.
+It is useful for testing or integrating with something like CI pipeline or Kubernetes CronJob.
+
+When the cron schedule is specified, the bot will run in cron mode.
+In this mode, the bot will check for merge requests and send a message to the Slack channel according to the specified cron schedule.
+Well suited for running as as a container or daemon process.
+
 ## Building and Running the Application
 
 ### Locally
@@ -85,6 +98,8 @@ kubectl -n mergentle-reminder create secret generic mergentle-reminder-secrets -
 Edit `schedule` in `k8s/cronjob.yaml` to specify the desired schedule. Set to run every hour by default.
 See the [CronJob documentation](https://kubernetes.io/docs/concepts/workloads/controllers/cron-jobs/) for more information.
 
+Make sure that the config does not include `cron_schedule` field, see
+
 Apply the Kubernetes manifests:
 
 ```sh

config.go

@@ -5,6 +5,8 @@ import (
 	"os"
 	"strconv"
 	"strings"
+
+	"gopkg.in/yaml.v2"
 )
 
 type Config struct {
@@ -15,8 +17,9 @@ type Config struct {
 	Slack struct {
 		WebhookURL string `yaml:"webhook_url"`
 	} `yaml:"slack"`
-	Projects []ConfigProject
-	Groups   []ConfigGroup
+	Projects     []ConfigProject
+	Groups       []ConfigGroup
+	CronSchedule string `yaml:"cron_schedule"`
 }
 
 type ConfigGroup struct {
@@ -91,13 +94,33 @@ func loadConfig(env Env) (*Config, error) {
 		return nil, fmt.Errorf("SLACK_WEBHOOK_URL environment variable is required")
 	}
 
+	cronSchedule := env.Getenv("CRON_SCHEDULE")
+	if cronSchedule != "" {
+		config.CronSchedule = cronSchedule
+	}
+
 	if len(config.Projects) == 0 && len(config.Groups) == 0 {
 		return nil, fmt.Errorf("Neither groups nor projects were provided")
 	}
 
 	return config, nil
 }
 
+func readConfig(file string) (*Config, error) {
+	data, err := os.ReadFile(file)
+	if err != nil {
+		return nil, err
+	}
+
+	var config Config
+	err = yaml.Unmarshal(data, &config)
+	if err != nil {
+		return nil, err
+	}
+
+	return &config, nil
+}
+
 func parseIDsAsConfigProjects(env string) ([]ConfigProject, error) {
 	ids, err := parseIDs(env)
 	if err != nil {

config.test.yaml

@@ -9,3 +9,4 @@ projects:
 groups:
   - id: 1
   - id: 2
+cron_schedule: "0 7,13 * * 1-5"

config.yaml.example

@@ -9,3 +9,4 @@ projects:
 groups:
   - id: 1
   - id: 2
+cron_schedule: "0 7,13 * * 1-5"

config_test.go

@@ -44,6 +44,7 @@ func TestLoadConfig(t *testing.T) {
 			"SLACK_WEBHOOK_URL": "webhook",
 			"CONFIG_PATH":       "NONEXISTING.yaml",
 			"PROJECTS":          "1,2,3",
+			"CRON_SCHEDULE":     "0 1 * * *",
 		}}
 
 		config, err := loadConfig(env)
@@ -54,6 +55,7 @@ func TestLoadConfig(t *testing.T) {
 			{ID: 2},
 			{ID: 3},
 		}, config.Projects)
+		assert.Equal(t, "0 1 * * *", config.CronSchedule)
 	})
 
 	// Test loading config from file
@@ -76,5 +78,6 @@ func TestLoadConfig(t *testing.T) {
 			{ID: 1},
 			{ID: 2},
 		}, config.Groups)
+		assert.Equal(t, "0 7,13 * * 1-5", config.CronSchedule)
 	})
 }

go.mod

@@ -9,6 +9,8 @@ require (
 	gopkg.in/yaml.v2 v2.4.0
 )
 
+require github.com/reugn/go-quartz v0.13.0
+
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/google/go-querystring v1.1.0 // indirect

go.sum

@@ -20,6 +20,8 @@ github.com/mattn/go-colorable v0.1.13 h1:fFA4WZxdEF4tXPZVKMLwD8oUnCTTo08duU7wxec
 github.com/mattn/go-isatty v0.0.20 h1:xfD0iDuEKnDkl03q4limB+vH+GxLEtL/jb4xVJSWWEY=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/reugn/go-quartz v0.13.0 h1:0eMxvj28Qu1npIDdN9Mzg9hwyksGH6XJt4Cz0QB8EUk=
+github.com/reugn/go-quartz v0.13.0/go.mod h1:0ghKksELp8MJ4h84T203aTHRF3Kug5BrxEW3ErBvhzY=
 github.com/slack-go/slack v0.13.1 h1:6UkM3U1OnbhPsYeb1IMkQ6HSNOSikWluwOncJt4Tz/o=
 github.com/slack-go/slack v0.13.1/go.mod h1:hlGi5oXA+Gt+yWTPP0plCdRKmjsDxecdHxYQdlMQKOw=
 github.com/stretchr/objx v0.5.2 h1:xuMeJ0Sdp5ZMRXx/aWO6RZxdr3beISkG5/G/aIRr3pY=

main.go

@@ -1,40 +1,81 @@
 package main
 
 import (
+	"context"
 	"fmt"
-	"io/ioutil"
+	"log"
 	"os"
 	"strings"
 
+	"github.com/reugn/go-quartz/job"
+	"github.com/reugn/go-quartz/quartz"
 	"github.com/xanzy/go-gitlab"
-	"gopkg.in/yaml.v2"
 )
 
 func main() {
 	// Load configuration
 	config, err := loadConfig(&OsEnv{})
 	if err != nil {
-		fmt.Printf("%v\n", err)
+		log.Printf("Error loading configuration: %v", err)
 		os.Exit(1)
 	}
 
+	if config.CronSchedule == "" {
+		log.Printf("Running in one-shot mode")
+		execute(config)
+		return
+	}
+
+	runScheduler(config)
+}
+
+func runScheduler(config *Config) {
+	log.Printf("Running in cron mode with schedule: %s\n", config.CronSchedule)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	sched := quartz.NewStdScheduler()
+	sched.Start(ctx)
+
+	cronTrigger, err := quartz.NewCronTrigger(config.CronSchedule)
+	if err != nil {
+		log.Printf("Error creating cron trigger: %v\n", err)
+		os.Exit(1)
+	}
+
+	executeJob := job.NewFunctionJob(func(_ context.Context) (int, error) {
+		execute(config)
+		return 0, nil
+	})
+
+	err = sched.ScheduleJob(quartz.NewJobDetail(executeJob, quartz.NewJobKey("executeJob")), cronTrigger)
+	if err != nil {
+		log.Printf("Error scheduling job: %v\n", err)
+		os.Exit(1)
+	}
+
+	<-ctx.Done()
+}
+
+func execute(config *Config) {
 	glClient, err := gitlab.NewClient(os.Getenv("GITLAB_TOKEN"),
 		gitlab.WithBaseURL(config.GitLab.URL))
 	if err != nil {
-		fmt.Printf("Error creating GitLab client: %v\n", err)
+		log.Printf("Error creating GitLab client: %v\n", err)
 		os.Exit(1)
 	}
 
 	gitlabClient := &gitLabClient{client: glClient}
 
 	mrs, err := fetchOpenedMergeRequests(config, gitlabClient)
 	if err != nil {
-		fmt.Printf("Error fetching opened merge requests: %v\n", err)
+		log.Printf("Error fetching opened merge requests: %v\n", err)
 		os.Exit(1)
 	}
 
 	if len(mrs) == 0 {
-		fmt.Println("No opened merge requests found.")
+		log.Println("No opened merge requests found.")
 		os.Exit(0)
 	}
 
@@ -43,26 +84,11 @@ func main() {
 	slackClient := &slackClient{webhookURL: os.Getenv("SLACK_WEBHOOK_URL")}
 	err = sendSlackMessage(slackClient, summary)
 	if err != nil {
-		fmt.Printf("Error sending Slack message: %v\n", err)
+		log.Printf("Error sending Slack message: %v\n", err)
 		os.Exit(1)
 	}
 
-	fmt.Println("Successfully sent merge request summary to Slack.")
-}
-
-func readConfig(file string) (*Config, error) {
-	data, err := ioutil.ReadFile(file)
-	if err != nil {
-		return nil, err
-	}
-
-	var config Config
-	err = yaml.Unmarshal(data, &config)
-	if err != nil {
-		return nil, err
-	}
-
-	return &config, nil
+	log.Println("Successfully sent merge request summary to Slack.")
 }
 
 func formatMergeRequestsSummary(mrs []*MergeRequestWithApprovals) string {