add solicitation task and validations

lib/workload_service/aggregates/solicitation_task.ex

@@ -4,7 +4,47 @@ defmodule WorkloadService.Aggregates.SolicitationTask do
     commands: WorkloadService.Commands.SolicitationTask,
     submission_type: map()
 
-  def validate_submission(_) do
-    :ok
+  def validate_submission(submission) when is_map(submission) do
+    with {:ok, provider_policy_number} <- validate_required_string(submission, "provider_policy_number"),
+         {:ok, effective_date} <- validate_date_string(submission, "effective_date"),
+         {:ok, expiry_date} <- validate_date_string(submission, "expiry_date"),
+         {:ok, _} <- validate_expiry_after_effective(effective_date, expiry_date) do
+      :ok
+    end
+  end
+
+  def validate_submission(_), do: {:error, :invalid_submission_format}
+
+  defp validate_required_string(submission, field) do
+    case Map.get(submission, field) do
+      nil -> {:error, {:missing_field, field}}
+      value when is_binary(value) and byte_size(value) > 0 -> {:ok, value}
+      _ -> {:error, {:invalid_field, field}}
+    end
+  end
+
+  defp validate_date_string(submission, field) do
+    case Map.get(submission, field) do
+      nil -> {:error, {:missing_field, field}}
+      value when is_binary(value) ->
+        case Date.from_iso8601(value) do
+          {:ok, _date} -> {:ok, value}
+          {:error, _} -> {:error, {:invalid_date_format, field}}
+        end
+      _ -> {:error, {:invalid_field, field}}
+    end
+  end
+
+  defp validate_expiry_after_effective(effective_date, expiry_date) do
+    case {Date.from_iso8601(effective_date), Date.from_iso8601(expiry_date)} do
+      {{:ok, effective}, {:ok, expiry}} ->
+        if Date.compare(expiry, effective) == :gt do
+          {:ok, :valid_date_range}
+        else
+          {:error, :expiry_must_be_after_effective}
+        end
+      _ ->
+        {:error, :invalid_date_comparison}
+    end
   end
 end