#!/usr/bin/env elixir

# Test script to understand why ISOMsg.set fails
# This will help us understand the root cause of the set_value issue

Mix.install([
  {:jason, "~> 1.3"}
])

defmodule TestISOSetBehavior do
  @moduledoc """
  Test to understand why ISOMsg.set/3 is failing
  """

  require Logger

  # Mock the structure of fields to understand the issue
  defmodule TestISOComponent do
    defstruct [:field_number, :value, :validated, :packager]
    
    def new(field_number, value \\ nil) do
      %__MODULE__{
        field_number: field_number,
        value: value,
        validated: false
      }
    end
    
    def set_value(%__MODULE__{} = component, value) do
      %{component | value: value, validated: false}
    end
    
    # This is what causes the original error - if the first argument is not a struct
    def set_value(not_a_struct, value) when not is_struct(not_a_struct) do
      raise FunctionClauseError, 
        module: __MODULE__, 
        function: :set_value, 
        arity: 2,
        args: [not_a_struct, value]
    end
    
    def get_value(%__MODULE__{value: value}), do: value
  end

  defmodule TestISOMsg do
    defstruct [:mti, :fields]
    
    def new(mti) do
      %__MODULE__{mti: mti, fields: %{}}
    end
    
    def set(%__MODULE__{fields: fields} = msg, field_number, value) do
      Logger.info("Setting field #{field_number} to '#{value}'")
      
      # This is the logic from the real ISOMsg.set/3
      component = 
        case Map.get(fields, field_number) do
          nil -> 
            Logger.info("Field #{field_number} is nil, creating new component")
            TestISOComponent.new(field_number, value)
          existing -> 
            Logger.info("Field #{field_number} exists: #{inspect(existing)}")
            TestISOComponent.set_value(existing, value)  # This is where it can fail!
        end

      updated_fields = Map.put(fields, field_number, component)
      %{msg | fields: updated_fields}
    end
    
    def get(%__MODULE__{fields: fields}, field_number) do
      case Map.get(fields, field_number) do
        nil -> nil
        component -> TestISOComponent.get_value(component)
      end
    end
  end

  def test_iso_set_behavior do
    Logger.info("=== Testing ISOMsg.set behavior ===")
    
    # Test 1: Normal case - set field on empty message
    Logger.info("\n--- Test 1: Setting field on empty message ---")
    msg1 = TestISOMsg.new("0200")
    msg2 = TestISOMsg.set(msg1, 24, "782")
    Logger.info("✅ Successfully set field 24 to '782'")
    Logger.info("Field 24 value: #{TestISOMsg.get(msg2, 24)}")
    
    # Test 2: Set same field again with same value
    Logger.info("\n--- Test 2: Setting same field with same value ---")
    try do
      msg3 = TestISOMsg.set(msg2, 24, "782")
      Logger.info("✅ Successfully set field 24 to '782' again")
      Logger.info("Field 24 value: #{TestISOMsg.get(msg3, 24)}")
    rescue
      exception ->
        Logger.error("❌ Failed to set same field with same value: #{inspect(exception)}")
    end
    
    # Test 3: What if the field contains a plain string instead of ISOComponent?
    Logger.info("\n--- Test 3: Field contains plain string (corrupted state) ---")
    corrupted_msg = %TestISOMsg{
      mti: "0200",
      fields: %{24 => "782"}  # Plain string instead of ISOComponent struct!
    }
    
    Logger.info("Corrupted message fields: #{inspect(corrupted_msg.fields)}")
    
    try do
      TestISOMsg.set(corrupted_msg, 24, "782")
      Logger.info("✅ Unexpectedly succeeded with corrupted field")
    rescue
      exception ->
      Logger.error("❌ Failed with corrupted field (plain string): #{inspect(exception)}")
        Logger.error("This explains the original error!")
    end
    
    Logger.info("\n=== Test completed ===")
  end
end

# Run the test
TestISOSetBehavior.test_iso_set_behavior()