using System;
using System.Collections.Concurrent;
using System.Linq.Expressions;
using System.Threading.Tasks;

namespace Blazor.Diagrams.Interop
{
    public static class TcsUtil
    {
        private static readonly Type _tcsType = typeof(TaskCompletionSource<>);
        private static readonly ConcurrentDictionary<Type, Action<object, object>> _setResults = new ConcurrentDictionary<Type, Action<object, object>>();
        private static readonly ConcurrentDictionary<Type, Action<object, Exception>> _setExceptions = new ConcurrentDictionary<Type, Action<object, Exception>>();

        public static void SetResult(object tcs, Type resultType, object result)
        {
            var tcsSpecificType = _tcsType.MakeGenericType(resultType);
            var setResult = _setResults.GetOrAdd(tcsSpecificType, (tcsSpecificType) =>
            {
                var tcsParamExpr = Expression.Parameter(typeof(object), "tcs");
                var resultParamExpr = Expression.Parameter(typeof(object), "result");

                var tcsConvertExpr = Expression.Convert(tcsParamExpr, tcsSpecificType);
                var resultConvertExpr = Expression.Convert(resultParamExpr, resultType);
                var setResultExpr = Expression.Call(tcsConvertExpr, "TrySetResult", Type.EmptyTypes, resultConvertExpr);

                return Expression.Lambda<Action<object, object>>(setResultExpr, tcsParamExpr, resultParamExpr).Compile();
            });

            setResult(tcs, result);
        }

        public static void SetException(object tcs, Type resultType, Exception exception)
        {
            var tcsSpecificType = _tcsType.MakeGenericType(resultType);
            var setException = _setExceptions.GetOrAdd(tcsSpecificType, (tcsSpecificType) =>
            {
                var tcsParamExpr = Expression.Parameter(typeof(object), "tcs");
                var exParamExpr = Expression.Parameter(typeof(Exception), "ex");

                var tcsConvertExpr = Expression.Convert(tcsParamExpr, tcsSpecificType);
                var setResultExpr = Expression.Call(tcsConvertExpr, "TrySetException", Type.EmptyTypes, exParamExpr);

                return Expression.Lambda<Action<object, Exception>>(setResultExpr, tcsParamExpr, exParamExpr).Compile();
            });

            setException(tcs, exception);
        }
    }
}