feat: domain blocker plugin

docs/creating-a-plugin.md

@@ -7,6 +7,7 @@ ButterRobot organizes plugins into different categories:
 - **Development**: Utility plugins like `ping`
 - **Fun**: Entertainment plugins like dice rolling, coin flipping
 - **Social**: Social media related plugins like URL transformers/expanders
+- **Security**: Moderation and protection features like domain blocking
 
 When creating a new plugin, consider which category it fits into and place it in the appropriate directory.
 
@@ -59,6 +60,91 @@ func (p *MarcoPlugin) OnMessage(msg *model.Message, config map[string]interface{
 }
 ```
 
+### Configuration-Enabled Plugin
+
+This plugin requires configuration to be set in the admin interface. It demonstrates how to create plugins that need channel-specific configuration:
+
+```go
+package security
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+
+	"git.nakama.town/fmartingr/butterrobot/internal/model"
+	"git.nakama.town/fmartingr/butterrobot/internal/plugin"
+)
+
+// DomainBlockPlugin is a plugin that blocks messages containing links from specific domains
+type DomainBlockPlugin struct {
+	plugin.BasePlugin
+}
+
+// New creates a new DomainBlockPlugin instance
+func New() *DomainBlockPlugin {
+	return &DomainBlockPlugin{
+		BasePlugin: plugin.BasePlugin{
+			ID:             "security.domainblock",
+			Name:           "Domain Blocker",
+			Help:           "Blocks messages containing links from configured domains",
+			ConfigRequired: true, // Mark this plugin as requiring configuration
+		},
+	}
+}
+
+// OnMessage processes incoming messages
+func (p *DomainBlockPlugin) OnMessage(msg *model.Message, config map[string]interface{}) []*model.Message {
+	// Get blocked domains from config
+	blockedDomainsStr, ok := config["blocked_domains"].(string)
+	if !ok || blockedDomainsStr == "" {
+		return nil // No blocked domains configured
+	}
+
+	// Split and clean blocked domains
+	blockedDomains := strings.Split(blockedDomainsStr, ",")
+	for i, domain := range blockedDomains {
+		blockedDomains[i] = strings.ToLower(strings.TrimSpace(domain))
+	}
+
+	// Extract domains from message
+	urlRegex := regexp.MustCompile(`https?://([^\s/$.?#].[^\s]*)`)
+	matches := urlRegex.FindAllStringSubmatch(msg.Text, -1)
+	
+	// Check if any extracted domains are blocked
+	for _, match := range matches {
+		if len(match) < 2 {
+			continue
+		}
+		
+		domain := strings.ToLower(match[1])
+		
+		for _, blockedDomain := range blockedDomains {
+			if blockedDomain == "" {
+				continue
+			}
+			
+			if strings.HasSuffix(domain, blockedDomain) || domain == blockedDomain {
+				// Domain is blocked, create warning message
+				response := &model.Message{
+					Text:    fmt.Sprintf("⚠️ Message contained a link to blocked domain: %s", blockedDomain),
+					Chat:    msg.Chat,
+					ReplyTo: msg.ID,
+					Channel: msg.Channel,
+				}
+				return []*model.Message{response}
+			}
+		}
+	}
+
+	return nil
+}
+
+func init() {
+	plugin.Register(New())
+}
+```
+
 ### Advanced Example: URL Transformer
 
 This more complex plugin transforms URLs, useful for improving media embedding in chat platforms:
@@ -143,6 +229,36 @@ func (p *TwitterExpander) OnMessage(msg *model.Message, config map[string]interf
 }
 ```
 
+## Enabling Configuration for Plugins
+
+To indicate that your plugin requires configuration:
+
+1. Set `ConfigRequired: true` in the BasePlugin struct:
+   ```go
+   BasePlugin: plugin.BasePlugin{
+       ID:             "myplugin.id",
+       Name:           "Plugin Name",
+       Help:           "Help text",
+       ConfigRequired: true,
+   },
+   ```
+
+2. Access the configuration in the OnMessage method:
+   ```go
+   func (p *MyPlugin) OnMessage(msg *model.Message, config map[string]interface{}) []*model.Message {
+       // Extract configuration values
+       configValue, ok := config["some_config_key"].(string)
+       if !ok || configValue == "" {
+           // Handle missing or empty configuration
+           return nil
+       }
+       
+       // Use the configuration...
+   }
+   ```
+
+3. The admin interface will show a "Configure" button for plugins that require configuration.
+
 ## Registering Plugins
 
 To use the plugin, register it in your application:
@@ -161,3 +277,11 @@ func (a *App) Run() error {
     // ...
 }
 ```
+
+Alternatively, you can register your plugin in its init() function:
+
+```go
+func init() {
+    plugin.Register(New())
+}
+```