feat: add support for block kit slack body (#774)

docs/content/3.cookbooks/2.slack-hook-build-kit-examples.md

@@ -0,0 +1,73 @@
+# Slack Hook Build Kit Examples
+
+## Overview
+
+When using the Slack Hook you can provide a simple message or a [Slack Block Kit](https://api.slack.com/block-kit) message. You can leverage the [Block Kit Builder](https://app.slack.com/block-kit-builder) to Preview the message.
+
+## Clean Job Summary
+
+<div style="text-align: center;">
+<img src="/screenshots/slack-clean-job.png" alt="Settings View" style="width: 700px; height: auto;" />
+</div>
+
+```
+{
+  "blocks": [
+    {
+      "type": "section",
+      "text": {
+        "type": "mrkdwn",
+        "text": "Backup: *{{ .Plan.Id }}* ➝ *{{ .Repo.Id }}* at *{{ .FormatTime .CurTime }}*"
+      }
+    },
+    {
+      "type": "divider"
+    },
+    {{ if .Error }}
+    {
+      "type": "section",
+      "text": {
+        "type": "mrkdwn",
+        "text": ":x: *Snapshot failed:*\n```{{ .Error }}```"
+      }
+    }
+    {{ else }}
+    {
+      "type": "section",
+      "text": {
+        "type": "mrkdwn",
+        "text": ":white_check_mark: *Snapshot `{{ .SnapshotId }}` created*"
+      }
+    },
+    {
+      "type": "section",
+      "fields": [
+        {
+          "type": "mrkdwn",
+          "text": "*Total Added:*\n`{{ .FormatSizeBytes .SnapshotStats.DataAdded }}`"
+        },
+        {
+          "type": "mrkdwn",
+          "text": "*Files Processed:*\n`{{ .SnapshotStats.TotalFilesProcessed }}`"
+        },
+        {
+          "type": "mrkdwn",
+          "text": "*Bytes Processed:*\n`{{ .FormatSizeBytes .SnapshotStats.TotalBytesProcessed }}`"
+        },
+        {
+          "type": "mrkdwn",
+          "text": "*Time:*\n`{{ .SnapshotStats.TotalDuration }}s`"
+        }
+      ]
+    },
+    {
+      "type": "section",
+      "text": {
+        "type": "mrkdwn",
+        "text": "*Backup Stats:*\n• *Files:* `{{ .SnapshotStats.FilesNew }} new`, `{{ .SnapshotStats.FilesChanged }} changed`, `{{ .SnapshotStats.FilesUnmodified }} unmodified`\n• *Dirs:* `{{ .SnapshotStats.DirsNew }} new`, `{{ .SnapshotStats.DirsChanged }} changed`, `{{ .SnapshotStats.DirsUnmodified }} unmodified`"
+      }
+    }
+    {{ end }}
+  ]
+}
+```

internal/hook/types/slack.go

@@ -20,25 +20,30 @@ func (slackHandler) Name() string {
 }
 
 func (slackHandler) Execute(ctx context.Context, cmd *v1.Hook, vars interface{}, runner tasks.TaskRunner, event v1.Hook_Condition) error {
+
 	payload, err := hookutil.RenderTemplateOrDefault(cmd.GetActionSlack().GetTemplate(), hookutil.DefaultTemplate, vars)
 	if err != nil {
 		return fmt.Errorf("template rendering: %w", err)
 	}
 
 	l := runner.Logger(ctx)
-	l.Sugar().Infof("Sending slack message to %s", cmd.GetActionSlack().GetWebhookUrl())
-	l.Debug("Sending slack message", zap.String("payload", payload))
 
-	type Message struct {
-		Text string `json:"text"`
+	var requestBytes []byte
+	if json.Valid([]byte(payload)) {
+		l.Sugar().Infof("Sending advanced slack message to %s", cmd.GetActionSlack().GetWebhookUrl())
+		l.Sugar().Debugf("Sending advanced slack message: %s", payload)
+		requestBytes = []byte(payload)
+	} else {
+		l.Sugar().Infof("Sending slack message to %s", cmd.GetActionSlack().GetWebhookUrl())
+		l.Debug("Sending slack message", zap.String("payload", payload))
+		request := struct {
+			Text string `json:"text"`
+		}{
+			Text: "Backrest Notification\n" + payload,
+		}
+		requestBytes, _ = json.Marshal(request)
 	}
 
-	request := Message{
-		Text: "Backrest Notification\n" + payload, // leading newline looks better in discord.
-	}
-
-	requestBytes, _ := json.Marshal(request)
-
 	body, err := hookutil.PostRequest(cmd.GetActionSlack().GetWebhookUrl(), "application/json", bytes.NewReader(requestBytes))
 	if err != nil {
 		return fmt.Errorf("sending slack message to %q: %w", cmd.GetActionSlack().GetWebhookUrl(), err)