using System.Text.Json;

namespace Speckle.Automate.Sdk.Schema;

public static class FunctionRunDataParser
{
  private static readonly JsonSerializerOptions s_jsonSerializerSettings = new()
  {
    PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
  };

  /// <summary>
  /// Function run data parser from json file path./>
  /// </summary>
  /// <param name="inputLocation"> Path to retrieve function run data.</param>
  /// <typeparam name="T"> Type for function inputs.</typeparam>
  /// <returns>The data to be able to run function.</returns>
  /// <exception cref="JsonException">Json was not valid</exception>
  /// <exception cref="FileNotFoundException"> Throws unless file exists.</exception>
  public static FunctionRunData<T> FromPath<T>(string inputLocation)
  {
    string inputJsonString = ReadInputData(inputLocation);
    //It's important to use System.Text.Json here. The template FunctionInputs are decorated with STJ attributes
    FunctionRunData<T>? functionRunData = JsonSerializer.Deserialize<FunctionRunData<T>>(
      inputJsonString,
      s_jsonSerializerSettings
    );

    if (functionRunData is null)
    {
      throw new JsonException($"Function run data couldn't deserialized at {inputLocation}");
    }

    return functionRunData;
  }

  /// <summary>
  /// Read text from file.
  /// </summary>
  /// <param name="inputLocation"> Path to check file is exist.</param>
  /// <returns>Text in file.</returns>
  /// <exception cref="FileNotFoundException"> Throws unless file exists.</exception>
  private static string ReadInputData(string inputLocation)
  {
    if (!File.Exists(inputLocation))
    {
      throw new FileNotFoundException($"Cannot find the function inputs file at {inputLocation}");
    }

    return File.ReadAllText(inputLocation);
  }
}