Add slack integration

Signed-off-by: Sacha Al Himdani <sacha@getprobo.com>

pkg/slack/client.go

@@ -0,0 +1,105 @@
+// Copyright (c) 2025 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package slack
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+)
+
+type (
+	Client struct {
+		webhookURL string
+		httpClient *http.Client
+	}
+
+	webhookMessage struct {
+		Text   string  `json:"text,omitempty"`
+		Blocks []block `json:"blocks,omitempty"`
+	}
+
+	block struct {
+		Type string    `json:"type"`
+		Text *textItem `json:"text,omitempty"`
+	}
+
+	textItem struct {
+		Type string `json:"type"`
+		Text string `json:"text"`
+	}
+)
+
+func NewClient(webhookURL string, httpClient *http.Client) *Client {
+	return &Client{
+		webhookURL: webhookURL,
+		httpClient: httpClient,
+	}
+}
+
+func (c *Client) PostMessage(ctx context.Context, text string) error {
+	msg := webhookMessage{
+		Text: text,
+		Blocks: []block{
+			{
+				Type: "section",
+				Text: &textItem{
+					Type: "mrkdwn",
+					Text: text,
+				},
+			},
+		},
+	}
+
+	var buf bytes.Buffer
+	if err := json.NewEncoder(&buf).Encode(msg); err != nil {
+		return fmt.Errorf("cannot marshal message: %w", err)
+	}
+	body := buf.Bytes()
+
+	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, c.webhookURL, bytes.NewReader(body))
+	if err != nil {
+		return fmt.Errorf("cannot create request: %w", err)
+	}
+
+	httpReq.Header.Set("Content-Type", "application/json")
+
+	resp, err := c.httpClient.Do(httpReq)
+	if err != nil {
+		return fmt.Errorf("cannot send request: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		body, err := io.ReadAll(resp.Body)
+		if err != nil {
+			return fmt.Errorf("unexpected status code: %d, failed to read response body: %w", resp.StatusCode, err)
+		}
+
+		var errorResponse map[string]any
+		var buf bytes.Buffer
+		buf.Write(body)
+		if err := json.NewDecoder(&buf).Decode(&errorResponse); err != nil {
+			return fmt.Errorf("unexpected status code: %d, response body: %s", resp.StatusCode, string(body))
+		}
+
+		return fmt.Errorf("unexpected status code: %d, response: %+v", resp.StatusCode, errorResponse)
+	}
+
+	return nil
+}