feat: optional param

An option can be set as optional through the syntax:

`$VARIABLE:-default`

`default` can be empty, but `-` is required to make the param optional.

See README for examples.

Closes #3

README.md

@@ -25,8 +25,15 @@ options:
 ## Examples
 
 ```shell
+# Command with no param.
 shell2discord /hello 'echo "World"'
+# Optional param `word` with empty default value.
+shell2discord /hello 'echo "Hello ${word-}"'
+# Optional param `word` with default value of "World".
+shell2discord /hello 'echo "Hello ${word-World}"'
+# Command with required params.
 shell2discord /mirror 'curl "${url}" > "${outfile}"'
+# Command with allowed environment variables.
 shell2discord --export-vars=GOOGLE_MAPS_API_KEY \
     /geocode 'curl "https://maps.googleapis.com/maps/api/geocode/json?latlng=${latlng}&key=$GOOGLE_MAPS_API_KEY"'
 ```

command.go

@@ -11,24 +11,26 @@ import (
 type Command struct {
 	*discordgo.ApplicationCommand
 	Script string
+	Params map[string]string
 	Env    []string
 }
 
 // Creates a new command from `/command 'shell command'`.
 func NewCommand(slashCommand string, shellCommand string) *Command {
 	commandName, params := parseBotCommand(slashCommand, shellCommand)
-	paramsLen := len(params)
 
-	options := make([]*discordgo.ApplicationCommandOption, paramsLen)
-	for i := 0; i < paramsLen; i++ {
-		options[i] = &discordgo.ApplicationCommandOption{
+	options := []*discordgo.ApplicationCommandOption{}
+	for paramName, paramValue := range params {
+		option := &discordgo.ApplicationCommandOption{
 			// Shell variables have no type, so we just use String in Discord.
 			Type: discordgo.ApplicationCommandOptionString,
-			Name: params[i],
+			Name: paramName,
 			// @TODO: Parse option description from flag.
-			Description: params[i],
-			Required:    true,
+			Description: paramName,
+			Required:    paramValue == "",
 		}
+
+		options = append(options, option)
 	}
 
 	return &Command{
@@ -38,6 +40,7 @@ func NewCommand(slashCommand string, shellCommand string) *Command {
 			Options:     options,
 		},
 		Script: shellCommand,
+		Params: params,
 	}
 }
 
@@ -55,10 +58,19 @@ func (command Command) Exec(session *discordgo.Session, interaction *discordgo.I
 	var options = interaction.Data.Options
 
 	shellCommand := command.Script
+	params := command.Params
 	for i := 0; i < len(options); i++ {
 		option := options[i]
-		variable := fmt.Sprintf("${%s}", option.Name)
-		shellCommand = strings.Replace(shellCommand, variable, option.StringValue(), -1)
+		optionName := option.Name
+		defaultValue := params[optionName]
+		variable := fmt.Sprintf("${%s%s}", optionName, defaultValue)
+		value := option.StringValue()
+		// Optional option will have empty value, use default value instead.
+		if value == "" {
+			// Default value has a `-` at the begining.
+			value = defaultValue[1:]
+		}
+		shellCommand = strings.Replace(shellCommand, variable, value, -1)
 	}
 
 	var reply string

utils.go

@@ -10,7 +10,7 @@ import (
 )
 
 // parseBotCommand - parse command-line arguments for one bot command
-func parseBotCommand(slashCommand string, shellCommand string) (commandName string, params []string) {
+func parseBotCommand(slashCommand string, shellCommand string) (commandName string, params map[string]string) {
 	commandRe := regexp.MustCompile(`^/([\w-]{1,32})$`)
 	commandMatches := commandRe.FindStringSubmatch(slashCommand)
 
@@ -19,17 +19,18 @@ func parseBotCommand(slashCommand string, shellCommand string) (commandName stri
 	}
 	commandName = commandMatches[1]
 
-	paramsRe := regexp.MustCompile(`\${(\w+)}`)
+	// Parse variable with optional default value, `${foo-bar}`
+	paramsRe := regexp.MustCompile(`\${(\w+)(-\w*)?}`)
 	matches := paramsRe.FindAllStringSubmatch(shellCommand, -1)
 	matchesLen := len(matches)
 
-	paramsMap := map[string]bool{}
-
+	params = map[string]string{}
 	for i := 0; i < matchesLen; i++ {
-		param := matches[i][1]
-		if !paramsMap[param] {
-			params = append(params, param)
-			paramsMap[param] = true
+		name := matches[i][1]
+		value := matches[i][2]
+
+		if _, ok := params[name]; !ok {
+			params[name] = value
 		}
 	}