Enable domain availability checker

src/api/views.py

@@ -1,7 +1,5 @@
 """Internal API views"""
-
 from django.apps import apps
-from django.core.exceptions import BadRequest
 from django.views.decorators.http import require_http_methods
 from django.http import JsonResponse
 
@@ -17,6 +15,19 @@ DOMAIN_FILE_URL = (
 )
 
 
+DOMAIN_API_MESSAGES = {
+    "required": "Enter the .gov domain you want. Don’t include “www” or “.gov.”"
+        " For example, if you want www.city.gov, you would enter “city”"
+        " (without the quotes).",
+    "extra_dots": "Enter the .gov domain you want without any periods.",
+    "unavailable": "That domain isn’t available. Try entering another one."
+        " Contact us if you need help coming up with a domain.",
+    "invalid": "Enter a domain using only letters,"
+        " numbers, or hyphens (though we don't recommend using hyphens).",
+    "success": "That domain is available!",
+}
+
+
 # this file doesn't change that often, nor is it that big, so cache the result
 # in memory for ten minutes
 @ttl_cache(ttl=600)
@@ -72,6 +83,18 @@ def available(request, domain=""):
         Domain.string_could_be_domain(domain)
         or Domain.string_could_be_domain(domain + ".gov")
     ):
-        raise BadRequest("Invalid request.")
+        return JsonResponse({
+            "available": False,
+            "message": DOMAIN_API_MESSAGES["invalid"]
+        })
     # a domain is available if it is NOT in the list of current domains
-    return JsonResponse({"available": not in_domains(domain)})
+    if in_domains(domain):
+        return JsonResponse({
+            "available": False,
+            "message": DOMAIN_API_MESSAGES["unavailable"]
+        })
+    else:
+        return JsonResponse({
+            "available": True,
+            "message": DOMAIN_API_MESSAGES["success"]
+        })