using System;
using System.Threading.Tasks;

using Newtonsoft.Json.Linq;

using AIRuntime.Runtime.Capabilities.Permissions;


namespace AIRuntime.Runtime.Capabilities
{
    /// <summary>
    /// Base class for strongly typed capabilities.
    ///
    /// Responsibilities:
    /// • Automatic JSON Schema generation
    /// • Strongly typed argument casting
    ///
    /// The runtime is responsible for:
    /// • JSON deserialization
    /// • Validation
    /// • Middleware execution
    /// • Result serialization
    /// • Providing the execution context
    /// </summary>
    /// <typeparam name="TArguments">
    /// Strongly typed argument class for this capability.
    /// </typeparam>
    public abstract class CapabilityBase<TArguments> :
        ICapability
    {
        /// <inheritdoc/>
        public abstract string Name
        {
            get;
        }


        /// <inheritdoc/>
        public abstract string Description
        {
            get;
        }


        /// <summary>
        /// Permission required by this capability.
        ///
        /// Every capability must explicitly declare its permission
        /// category so unsafe operations cannot silently inherit
        /// read-only access.
        /// </summary>
        public abstract CapabilityPermission Permission
        {
            get;
        }


        /// <inheritdoc/>
        public virtual JObject Parameters
        {
            get
            {
                return SchemaGenerator.Generate<TArguments>();
            }
        }


        /// <inheritdoc/>
        public virtual Type ArgumentType
        {
            get
            {
                return typeof(TArguments);
            }
        }


        /// <inheritdoc/>
        async Task<object> ICapability.ExecuteObjectAsync(
            object arguments,
            CapabilityContext context)
        {
            if (context == null)
            {
                throw new ArgumentNullException(
                    nameof(context));
            }


            TArguments typedArguments;


            if (arguments == null)
            {
                typedArguments =
                    Activator.CreateInstance<TArguments>();
            }
            else
            {
                typedArguments =
                    (TArguments)arguments;
            }


            return await ExecuteAsync(
                typedArguments,
                context);
        }


        /// <summary>
        /// Executes the capability.
        /// </summary>
        protected abstract Task<object> ExecuteAsync(
            TArguments arguments,
            CapabilityContext context);
    }
}