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;

namespace InABox.Core
{
    using FncType = Func<IExpression[], IDictionary<string, object>, object?>;

    public class CoreExpressionFunction
    {
        public string Group { get; set; }

        public string Name { get; set; }

        public string? Description { get; set; }

        public List<Parameter> Parameters { get; set; }

        public FncType Function { get; set; }

        public class Parameter
        {
            public string Name { get; set; }

            public string Type { get; set; }

            public Parameter(string name, string type)
            {
                Name = name;
                Type = type;
            }
        }

        public CoreExpressionFunction(string group, string name, FncType function, List<Parameter> parameters, string? description = null)
        {
            Group = group;
            Name = name;
            Parameters = parameters;
            Function = function;
            Description = description;
        }
    }

    public interface IExpressionModel { }
    public interface IExpressionModel<TReturn> : IExpressionModel { }

    public class CoreExpression
    {
        private Expression Expression;

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

        protected virtual Type? ReturnType { get; }

        public CoreExpression(string expressionString)
        {
            Expression = new Expression(expressionString);
            foreach (var function in Functions)
            {
                Expression.RegisterFunction(function.Name, function.Function);
            }
        }

        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)
        {
            return CoreUtils.PropertyList(modelType, x => true).Select(x => x.Name).ToList();
        }
        public static List<string> GetModelVariables<TModel>() where TModel : IExpressionModel
            => GetModelVariables(typeof(TModel));

        #region Static

        public static List<CoreExpressionFunction> Functions = new List<CoreExpressionFunction>();

        static CoreExpression()
        {
            RegisterFunction("String", "Format", (p, v) =>
            {
                if (!(p[0].Evaluate(v) is string format)) throw new Exception("No format string given for Format()");
                return string.Format(format, p.Skip(1).Select(x => x.Evaluate(v)).ToArray());
            }, "string fmt", "...");

            RegisterFunction("Other", "Client_LoadDocument", "Loads a byte array from the database Document table, with the ID {docID}.", Fnc_LoadDocument, "Guid docID");
        }

        private static object? Fnc_LoadDocument(IExpression[] p, IDictionary<string, object> v)
        {
            var id = p[0].Evaluate(v);
            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),
                    new Columns<Document>(x => x.Data))
                .Rows.FirstOrDefault()
                ?.Get<Document, byte[]>(x => x.Data);
        }

        public static void RegisterFunction(string group, string name, FncType function, params string[] parameters)
            => RegisterFunction(group, name, null, function, parameters);

        public static void RegisterFunction(string group, string name, string? description, FncType function, params string[] parameters) =>
            Functions.Add(new CoreExpressionFunction(group, name, function, parameters.Select(x =>
            {
                var parts = x.Split(' ');
                if (parts.Length == 1)
                    return new CoreExpressionFunction.Parameter(parts[0], "");
                return new CoreExpressionFunction.Parameter(parts[1], parts[0]);
            }).ToList(), description));

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

            var result = base.Evaluate(values);
            if(result is TReturn ret)
            {
                return ret;
            }
            return default;
        }
    }
}