Show command errors

I went with placing htis logic at the command level since it plays well with the composite structure, where you don't know whether you are handling one command or many commands, and you want to aggregate all the errors. I didn't leverage the existing support with rails' model errors because that customizing those message is cumbersome (either i18n or using custom validation logic for everything).

app/controllers/commands_controller.rb

@@ -68,6 +68,7 @@ class CommandsController < ApplicationController
     end
 
     def respond_with_error(command)
-      render json: { error: command.errors.full_messages.join(", "), context_url: command.context.url }, status: :unprocessable_entity
+      error_message = command.error_messages.map { |msg| "- #{msg}\n" }.join
+      render json: { error: error_message, context_url: command.context.url }, status: :unprocessable_entity
     end
 end

app/javascript/controllers/terminal_controller.js

@@ -64,6 +64,7 @@ export default class extends Controller {
   }
 
   hideError() {
+    this.#hideOutput()
     this.element.classList.remove(this.errorClass)
   }
 
@@ -113,13 +114,15 @@ export default class extends Controller {
     const status = response.status
 
     if (status === HttpStatus.UNPROCESSABLE) {
-      this.#showError()
+      this.#showError(response)
     } else if (status === HttpStatus.CONFLICT) {
       await this.#handleConflictResponse(response)
     }
   }
 
-  #showError() {
+  async #showError(response) {
+    const message = await response.json()
+    this.#showOutput(message.error)
     this.element.classList.add(this.errorClass)
   }
 

app/models/command.rb

@@ -37,8 +37,35 @@ class Command < ApplicationRecord
     false
   end
 
+  def error_messages
+    errors.to_hash.flat_map do |attribute, message|
+      error_message_for(attribute, message)
+    end.uniq
+  end
+
   private
     def redirect_to(...)
       Command::Result::Redirection.new(...)
     end
+
+    def error_message_for(attribute, message)
+      case attribute.to_sym
+      when :cards, :card_ids
+        "No cards in this context"
+      when :card
+        "Can't find the card"
+      when :collection
+        "The collection is missing"
+      when :assignee_ids
+        "Assignees are missing"
+      when :user
+        "Can't find that user"
+      when :stage
+        "Can't find that workflow stage"
+      when :tag_title
+        "A tag is required"
+      else
+        message
+      end
+    end
 end

app/models/command/composite.rb

@@ -34,6 +34,10 @@ class Command::Composite < Command
     commands.any?(&:needs_confirmation?)
   end
 
+  def error_messages
+    commands.flat_map(&:error_messages).uniq
+  end
+
   private
     def commands_excluding_redirections
       commands.reject { it.is_a?(Command::VisitUrl) }