QueryContextExtensions.cs

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using System;
using System.Linq.Expressions;
 
using GreenDonut.Data;
 
using Tgstation.Server.Host.Authority.Core;
 
namespace Tgstation.Server.Host.Extensions
{
    static class QueryContextExtensions
    {
        public static QueryContext<AuthorityResponse<TResult>> AuthorityResponseWrap<TResult>(this QueryContext<TResult> queryContext)
        {
            ArgumentNullException.ThrowIfNull(queryContext);
 
            Expression<Func<AuthorityResponse<TResult>, TResult>> responseToResult = response => response.Result!;
 
            var authorityParameter = Expression.Parameter(typeof(AuthorityResponse<TResult>), "authorityResponse");
            var resultFromAuthority = Expression.Invoke(
                responseToResult,
                authorityParameter);
 
            // we don't need to do much
            Expression<Func<AuthorityResponse<TResult>, AuthorityResponse<TResult>>>? selector = null;
            if (queryContext.Selector != null)
            {
                var innerInvoke = Expression.Invoke(
                    queryContext.Selector,
                    resultFromAuthority);
 
                var outerInvoke = Expression.Invoke(
                    AuthorityResponse<TResult>.MappingExpression,
                    innerInvoke);
 
                selector = Expression.Lambda<Func<AuthorityResponse<TResult>, AuthorityResponse<TResult>>>(
                    outerInvoke,
                    authorityParameter);
            }
 
            Expression<Func<AuthorityResponse<TResult>, bool>>? predicate = null;
            if (queryContext.Predicate != null)
            {
                predicate = Expression.Lambda<Func<AuthorityResponse<TResult>, bool>>(
                    Expression.Invoke(
                        queryContext.Predicate,
                        resultFromAuthority),
                    authorityParameter);
            }
 
            if (queryContext.Sorting?.Operations.Length > 0)
            {
                throw new NotImplementedException();
            }
 
            return new QueryContext<AuthorityResponse<TResult>>(
                selector,
                predicate);
        }
 
        public static QueryContext<TResult> AuthorityResponseUnwrap<TResult>(this QueryContext<AuthorityResponse<TResult>> queryContext)
        {
            ArgumentNullException.ThrowIfNull(queryContext);
 
            // assuming we were wrapped with AuthorityResponseWrap. This is hacky but it works
            // UNLESS it was compiled down, in which case we are D-O-N-E-FUCKED
            Expression<Func<TResult, TResult>>? selector = null;
            if (queryContext.Selector != null)
            {
                selector = (Expression<Func<TResult, TResult>>?)((InvocationExpression)((InvocationExpression)queryContext.Selector.Body).Arguments[0]).Expression;
            }
 
            Expression<Func<TResult, bool>>? predicate = null;
            if (queryContext.Predicate != null)
            {
                predicate = (Expression<Func<TResult, bool>>?)((InvocationExpression)queryContext.Predicate.Body).Expression;
            }
 
            if (queryContext.Sorting?.Operations.Length > 0)
            {
                throw new NotImplementedException();
            }
 
            return new QueryContext<TResult>(
                selector,
                predicate);
        }
    }
}