feat: add incoming webhook API support with configurable endpoints

- Implemented the incoming webhook API to handle alerts from external applications.
- Added configuration options for webhook listening address, port, and endpoints in config.go.
- Created WebhookReceiverConfig and WebhookEndpointConfig structures to manage webhook settings.
- Developed WebhookHandler to process incoming requests, validate tokens, and deliver alerts to specified channels.
- Enhanced existing controller interfaces to support alert delivery.
- Updated message rendering to respect Markdown settings for different channels.
- Added tests for webhook functionality and ensured proper error handling.

internal/template/template.go

@@ -19,6 +19,9 @@ type Params struct {
 	Message             string
 	Command             string
 	Result              string
+	Subject             string // Alert subject (see AlertParams)
+	Source              string // Alert source (see AlertParams)
+	Content             string // Alert content (see AlertParams)
 	OnlineServers       string // Pre-formatted multi-line list
 	OfflineServers      string // Pre-formatted multi-line list
 	SoftwareVersion     string
@@ -30,6 +33,37 @@ type Params struct {
 	SoftwareDescription string
 }
 
+// AlertTemplate is the body format of an alert submitted by an external
+// application through the incoming webhook API.
+const AlertTemplate = "{{ subject }}\n- Source: {{ source }}\n- Content:\n{{ content }}\n\n- Time: {{ time }}\nSent by Nukumizu Alert System"
+
+// AlertParams holds the parameters of an alert submitted through the incoming
+// webhook API.
+type AlertParams struct {
+	Subject string // Short one-line title of the alert
+	Source  string // Name of the webhook endpoint the alert was submitted to
+	Content string // Free-form alert body
+	Time    string // Submission time
+}
+
+// RenderAlert renders the body of an alert for a channel. The alert source and
+// content may be wrapped in Markdown — the source in inline code, the content
+// in a fenced code block — when the target channel has markdown enabled
+// (markdown); everything else, the timestamp included, stays plain text.
+func RenderAlert(alert AlertParams, markdown bool) string {
+	params := Params{
+		Time:    alert.Time,
+		Subject: alert.Subject,
+		Source:  alert.Source,
+		Content: alert.Content,
+	}
+	if markdown {
+		params.Source = "`" + params.Source + "`"
+		params.Content = "```\n" + params.Content + "\n```"
+	}
+	return Render(AlertTemplate, params, false)
+}
+
 // BuildBotInitializationMsgParams creates template parameters for the bot initialization message.
 func BuildBotInitializationMsgParams() Params {
 	return Params{
@@ -80,7 +114,13 @@ func BuildParamsFromExecResult(serverName, serverUUID, command, result string) P
 	}
 }
 
-// Render substitutes {{ paramName }} placeholders in a template string.
+// Render substitutes {{ paramName }} placeholders in a template string. The
+// markdown argument is the target channel's markdown setting: when true the
+// values that are meant to be read verbatim (UUIDs, messages, commands, command
+// results) are wrapped in Markdown code spans and blocks, otherwise every value
+// is inserted as plain text. Whether a channel renders Markdown comes from the
+// configuration alone — the renderer never infers it from the channel name.
+//
 // Supported placeholders:
 //   - {{ time }} — current server time
 //   - {{ serverName }} — server name
@@ -90,6 +130,9 @@ func BuildParamsFromExecResult(serverName, serverUUID, command, result string) P
 //   - {{ message }} — event descriptive message
 //   - {{ command }} — executed command
 //   - {{ result }} — command execution result
+//   - {{ subject }} — alert subject
+//   - {{ source }} — alert source
+//   - {{ content }} — alert content
 //   - {{ list.onlineServers }} — multi-line online server list
 //   - {{ list.offlineServers }} — multi-line offline server list
 //   - {{ softwareVersion }} — software version
@@ -99,19 +142,20 @@ func BuildParamsFromExecResult(serverName, serverUUID, command, result string) P
 //   - {{ softwareBuildTime }} — software build time
 //   - {{ softwareDeveloper }} — software developer
 //   - {{ softwareDescription }} — software description
-func Render(tmpl string, params Params, source ...string) string {
+func Render(tmpl string, params Params, markdown bool) string {
 	result := tmpl
 
-	if len(source) > 0 && source[0] == "telegram" {
-		// Telegram requires special formatting for code blocks and inline code.
-		result = strings.ReplaceAll(result, "{{ time }}", "**" + params.Time + "**")
-		result = strings.ReplaceAll(result, "{{ serverName }}", "**" + params.ServerName + "**")
-		result = strings.ReplaceAll(result, "{{ serverUUID }}", "`" + params.ServerUUID + "`")
-		result = strings.ReplaceAll(result, "{{ upStatus }}", "**" + params.UpStatus + "**")
-		result = strings.ReplaceAll(result, "{{ event }}", "**" + params.Event + "**")
-		result = strings.ReplaceAll(result, "{{ message }}", "`" + params.Message + "`")
-		result = strings.ReplaceAll(result, "{{ command }}", "`" + params.Command + "`")
-		result = strings.ReplaceAll(result, "{{ result }}", "```bash\n" + params.Result + "\n```")
+	if markdown {
+		// Channels that render Markdown get code blocks and inline code for the
+		// values that are read verbatim.
+		result = strings.ReplaceAll(result, "{{ time }}", "**"+params.Time+"**")
+		result = strings.ReplaceAll(result, "{{ serverName }}", "**"+params.ServerName+"**")
+		result = strings.ReplaceAll(result, "{{ serverUUID }}", "`"+params.ServerUUID+"`")
+		result = strings.ReplaceAll(result, "{{ upStatus }}", "**"+params.UpStatus+"**")
+		result = strings.ReplaceAll(result, "{{ event }}", "**"+params.Event+"**")
+		result = strings.ReplaceAll(result, "{{ message }}", "`"+params.Message+"`")
+		result = strings.ReplaceAll(result, "{{ command }}", "`"+params.Command+"`")
+		result = strings.ReplaceAll(result, "{{ result }}", "```bash\n"+params.Result+"\n```")
 		result = strings.ReplaceAll(result, "{{ list.onlineServers }}", params.OnlineServers)
 		result = strings.ReplaceAll(result, "{{ list.offlineServers }}", params.OfflineServers)
 		result = strings.ReplaceAll(result, "{{ softwareVersion }}", params.SoftwareVersion)
@@ -140,6 +184,13 @@ func Render(tmpl string, params Params, source ...string) string {
 		result = strings.ReplaceAll(result, "{{ softwareDeveloper }}", params.SoftwareDeveloper)
 		result = strings.ReplaceAll(result, "{{ softwareDescription }}", params.SoftwareDescription)
 	}
+
+	// Alert values carry their own formatting (see RenderAlert), so they are
+	// substituted identically in both branches.
+	result = strings.ReplaceAll(result, "{{ subject }}", params.Subject)
+	result = strings.ReplaceAll(result, "{{ source }}", params.Source)
+	result = strings.ReplaceAll(result, "{{ content }}", params.Content)
+
 	return result
 }