inabox/InABox.Core/CoreExpression.cs

using Expressive;
using Expressive.Expressions;
using Expressive.Functions;
using InABox.Clients;
using System.Diagnostics.CodeAnalysis;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using Expressive.Exceptions;

namespace InABox.Core
{
    public interface IExpressionModel { }
    public interface IExpressionModel<TReturn> : IExpressionModel { }

    public abstract class CoreExpressionFunction : FunctionBase
    {
        public abstract string Group { get; }
        public abstract string Description { get; }
        public abstract string[] Parameters { get; }
    }
    
    internal class FormatFunction : CoreExpressionFunction
    {
        #region IFunction Members

        public override object Evaluate(IExpression[] parameters, Context context)
        {
            ValidateParameterCount(parameters,-1, 2);

            string fmt = parameters.First()?.Evaluate(Variables).ToString() ?? "";
            object[] objects = parameters.Skip(1).Select(x => x.Evaluate(Variables)).ToArray();
            return String.Format(fmt, objects);
        }

        public override string Group => "String";
        public override string Name => "Format";
        public override string Description => "Formats a list of objects using the specified format string";
        public override string[] Parameters => new[] { "string format", "object[] parameters" };

        #endregion
    }

    internal class Client_LoadDocumentFunction : CoreExpressionFunction
    {
        public override object? Evaluate(IExpression[] parameters, Context context)
        {
            ValidateParameterCount(parameters, 1, 1);
            
            var id = parameters[0].Evaluate(Variables);
            
            if (id is null)
                return null;
            
            if (!(id is Guid docID))
                return null;

            return new Client<Document>()
                .Query(
                    new Filter<Document>(x => x.ID).IsEqualTo(docID),
                    Columns.None<Document>().Add(x => x.Data))
                .Rows.FirstOrDefault()
                ?.Get<Document, byte[]>(x => x.Data);
        }

        public override string Group => "Other";
        public override string Name => "Client_LoadDocument";
        public override string Description => "Retrieves a database document with the specified id";
        public override string[] Parameters => new[] { "Guid id" };
    }
    
    public class CoreExpression
    {
        private Expression Expression;
        
        public bool IsValid {
            get
            {
                try
                {
                    return Expression.ReferencedVariables != null;
                }
                catch
                {
                    return false;
                }   
            }
        }

        public IReadOnlyCollection<string> ReferencedVariables => Expression.ReferencedVariables;

        protected virtual Type? ReturnType { get; }

        public CoreExpression(string expressionString)
        {
            Expression = new Expression(expressionString, _context);
            if (!IsValid)
            {
                var expr = "\"" + expressionString + "\"";
                var tags = new Regex(@"\[(.*?)\]").Matches(expressionString);
                foreach (var tag in tags)
                    expr = expr.Replace($"{tag}", $"\"+{tag}+\"");
                expr = expr.Replace("+\"\"", "");
                Expression = new Expression(expr);
            }
        }

        public object? Evaluate(Dictionary<string, object?>? variables)
        {
            var result = Expression.Evaluate(variables);
            if(ReturnType != null)
            {
                return CoreUtils.ChangeType(result, ReturnType);
            }
            return result;
        }

        public static List<string> GetModelVariables(Type modelType)
        {
            var props = DatabaseSchema.Properties(modelType).Select(x => x.Name).ToList();
            props.Sort();
            return props;
        }
        public static List<string> GetModelVariables<TModel>() where TModel : IExpressionModel
            => GetModelVariables(typeof(TModel));

        #region Static

        public static List<CoreExpressionFunction> Functions = new List<CoreExpressionFunction>();
        
        private static Context _context = new Context(ExpressiveOptions.None);
        
        static void RegisterFunction<T>() where T : CoreExpressionFunction, new ()
        {
            var function = new T();
            Functions.Add(function);
            _context.RegisterFunction(function);
        }
        
        static CoreExpression()
        {
            RegisterFunction<FormatFunction>();
            RegisterFunction<Client_LoadDocumentFunction>();
        }

        #endregion
    }

    public class CoreExpression<TModel, TReturn> : CoreExpression
        where TModel : IExpressionModel<TReturn>
    {
        protected override Type? ReturnType => typeof(TReturn);

        public CoreExpression(string expressionString): base(expressionString) { }

        [return: MaybeNull]
        public new TReturn Evaluate(Dictionary<string, object?>? variables)
        {
            var result = base.Evaluate(variables);
            if(result is TReturn ret)
            {
                return ret;
            }
            return default;
        }

        public Result<TReturn, Exception> Evaluate(TModel model)
        {
            var values = new Dictionary<string, object?>();
            foreach(var variable in ReferencedVariables)
            {
                values[variable] = CoreUtils.GetPropertyValue(model, variable);
            }

            try
            {
                var result = base.Evaluate(values);
                if(result is TReturn ret)
                {
                    return Result.Ok(ret);
                }
                return Result.Ok<TReturn>(default);
            }
            catch (Exception e)
            {
                return Result.Error(e);
            }
        }
    }
}