Add Markdown to Mrkdwn conversion for Slack messages (#2)

* Initial plan

* Initial plan for Markdown to Mrkdwn conversion

Co-authored-by: alexec <1142830+alexec@users.noreply.github.com>

* Add Markdown to Mrkdwn conversion and feature suggestions

Co-authored-by: alexec <1142830+alexec@users.noreply.github.com>

* Address code review feedback - fix italic conversion and language specifier patterns

Co-authored-by: alexec <1142830+alexec@users.noreply.github.com>

* Fix code consistency - use ${N} syntax and reuse compiled regex patterns

Co-authored-by: alexec <1142830+alexec@users.noreply.github.com>

* Remove FEATURES.md and suggested features section from README

Co-authored-by: alexec <1142830+alexec@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: alexec <1142830+alexec@users.noreply.github.com>
Co-authored-by: Alex Collins <alexec@users.noreply.github.com>

Author: Copilot

.gitignore

@@ -0,0 +1,22 @@
+# Binaries for programs and plugins
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+
+# Test binary, built with `go test -c`
+*.test
+
+# Output of the go coverage tool
+*.out
+
+# Build artifacts
+slack-cli
+slack_*
+
+# Dependency directories
+vendor/
+
+# Go workspace file
+go.work

README.md

@@ -20,6 +20,7 @@ Add this to your prompt (e.g. `AGENTS.md`):
 
 ```markdown
 - You can send messages to a Slack user by using the `slack send-message <channel|email> "<message>"` command.
+- The message supports Markdown formatting which will be automatically converted to Slack's Mrkdwn format.
 ```
 
 ## Usage

main.go

@@ -79,7 +79,10 @@ func sendMessage(ctx context.Context, identifier, body string) error {
 		channel = identifier
 	}
 
-	if _, _, err := api.PostMessageContext(ctx, channel, slack.MsgOptionText(body, false)); err != nil {
+	// Convert Markdown to Mrkdwn format
+	mrkdwnBody := convertMarkdownToMrkdwn(body)
+
+	if _, _, err := api.PostMessageContext(ctx, channel, slack.MsgOptionText(mrkdwnBody, false)); err != nil {
 		return fmt.Errorf("failed to send message: %w", err)
 	}
 

markdown.go

@@ -0,0 +1,73 @@
+package main
+
+import (
+	"regexp"
+	"strings"
+)
+
+// convertMarkdownToMrkdwn converts Markdown format to Slack's Mrkdwn format
+// See: https://api.slack.com/reference/surfaces/formatting
+func convertMarkdownToMrkdwn(markdown string) string {
+	text := markdown
+
+	// Placeholder to protect already-converted bold text
+	const boldPlaceholder = "\x00BOLD\x00"
+	
+	// Store bold conversions with placeholders
+	boldMatches := []string{}
+	
+	// Convert bold: **text** or __text__ -> placeholder
+	boldPattern := regexp.MustCompile(`\*\*(.+?)\*\*`)
+	text = boldPattern.ReplaceAllStringFunc(text, func(match string) string {
+		content := boldPattern.FindStringSubmatch(match)
+		if len(content) > 1 {
+			replacement := "*" + content[1] + "*"
+			boldMatches = append(boldMatches, replacement)
+			return boldPlaceholder
+		}
+		return match
+	})
+	
+	boldUnderscorePattern := regexp.MustCompile(`__(.+?)__`)
+	text = boldUnderscorePattern.ReplaceAllStringFunc(text, func(match string) string {
+		content := boldUnderscorePattern.FindStringSubmatch(match)
+		if len(content) > 1 {
+			replacement := "*" + content[1] + "*"
+			boldMatches = append(boldMatches, replacement)
+			return boldPlaceholder
+		}
+		return match
+	})
+
+	// Convert italic: single *text* -> _text_ (only single asterisks)
+	italicAsteriskPattern := regexp.MustCompile(`\*([^*\n]+?)\*`)
+	text = italicAsteriskPattern.ReplaceAllString(text, `_${1}_`)
+
+	// Convert italic: _text_ -> _text_ (already in Mrkdwn format, no change needed)
+
+	// Restore bold text from placeholders
+	for _, boldText := range boldMatches {
+		text = strings.Replace(text, boldPlaceholder, boldText, 1)
+	}
+
+	// Convert strikethrough: ~~text~~ -> ~text~
+	strikethroughPattern := regexp.MustCompile(`~~(.+?)~~`)
+	text = strikethroughPattern.ReplaceAllString(text, `~${1}~`)
+
+	// Convert links: [text](url) -> <url|text>
+	linkPattern := regexp.MustCompile(`\[([^\]]+)\]\(([^\)]+)\)`)
+	text = linkPattern.ReplaceAllString(text, `<${2}|${1}>`)
+
+	// Convert code blocks: ```lang\ncode\n``` -> ```code```
+	// Remove language specifier from code blocks (supports alphanumeric, hyphens, plus, etc.)
+	codeBlockPattern := regexp.MustCompile("```[a-zA-Z0-9+#\\-]*\n")
+	text = codeBlockPattern.ReplaceAllString(text, "```\n")
+
+	// Convert unordered lists: * item or - item -> • item
+	listPattern := regexp.MustCompile(`(?m)^[\*\-]\s+`)
+	text = listPattern.ReplaceAllString(text, "• ")
+
+	// Convert ordered lists: 1. item -> 1. item (no change needed)
+
+	return text
+}

markdown_test.go

@@ -0,0 +1,98 @@
+package main
+
+import (
+	"testing"
+)
+
+func TestConvertMarkdownToMrkdwn(t *testing.T) {
+	tests := []struct {
+		name     string
+		markdown string
+		expected string
+	}{
+		{
+			name:     "bold with double asterisks",
+			markdown: "This is **bold** text",
+			expected: "This is *bold* text",
+		},
+		{
+			name:     "bold with double underscores",
+			markdown: "This is __bold__ text",
+			expected: "This is *bold* text",
+		},
+		{
+			name:     "strikethrough",
+			markdown: "This is ~~strikethrough~~ text",
+			expected: "This is ~strikethrough~ text",
+		},
+		{
+			name:     "inline code",
+			markdown: "This is `code` text",
+			expected: "This is `code` text",
+		},
+		{
+			name:     "link",
+			markdown: "Check out [Google](https://google.com)",
+			expected: "Check out <https://google.com|Google>",
+		},
+		{
+			name:     "code block with language",
+			markdown: "```python\nprint('hello')\n```",
+			expected: "```\nprint('hello')\n```",
+		},
+		{
+			name:     "code block without language",
+			markdown: "```\ncode here\n```",
+			expected: "```\ncode here\n```",
+		},
+		{
+			name:     "unordered list with asterisk",
+			markdown: "* Item 1\n* Item 2",
+			expected: "• Item 1\n• Item 2",
+		},
+		{
+			name:     "unordered list with dash",
+			markdown: "- Item 1\n- Item 2",
+			expected: "• Item 1\n• Item 2",
+		},
+		{
+			name:     "ordered list",
+			markdown: "1. First\n2. Second",
+			expected: "1. First\n2. Second",
+		},
+		{
+			name:     "mixed formatting",
+			markdown: "This is **bold** and ~~strike~~ with a [link](https://example.com)",
+			expected: "This is *bold* and ~strike~ with a <https://example.com|link>",
+		},
+		{
+			name:     "italic with single asterisk",
+			markdown: "This is *italic* text",
+			expected: "This is _italic_ text",
+		},
+		{
+			name:     "code block with complex language specifier",
+			markdown: "```c++\nint main() {}\n```",
+			expected: "```\nint main() {}\n```",
+		},
+		{
+			name:     "code block with c# language",
+			markdown: "```c#\npublic void Main() {}\n```",
+			expected: "```\npublic void Main() {}\n```",
+		},
+		{
+			name:     "code block with hyphenated language",
+			markdown: "```objective-c\n@interface MyClass\n```",
+			expected: "```\n@interface MyClass\n```",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := convertMarkdownToMrkdwn(tt.markdown)
+			if result != tt.expected {
+				t.Errorf("convertMarkdownToMrkdwn() = %q, want %q", result, tt.expected)
+			}
+		})
+	}
+}