jellyfin-smart-playlist/Jellyfin.Plugin.SmartPlaylist/Lisp/Expression.cs

namespace Jellyfin.Plugin.SmartPlaylist.Lisp {
    interface IAddable<T> where T : IAddable<T> {
        static abstract T operator +(T left, T right);
    }

    interface ISubtractable<T> where T : ISubtractable<T> {
        static abstract T operator -(T left, T right);
    }

    interface IMultiplicatable<T> where T : IMultiplicatable<T> {
        static abstract T operator *(T left, T right);
    }

    interface IDivisible<T> where T : IDivisible<T> {
        static abstract T operator /(T left, T right);
        static abstract T operator %(T left, T right);
    }

    interface ISortable<T, E> where T : ISortable<T, E> {
        static abstract E operator >(T left, T right);
        static abstract E operator <(T left, T right);
        static abstract E operator >=(T left, T right);
        static abstract E operator <=(T left, T right);
    }

    interface IComparable<T, E> where T : IComparable<T, E> {
        static abstract E operator ==(T left, T right);
        static abstract E operator !=(T left, T right);
        E Equals(T other);
    }

    interface IInner {
        public object Inner();
    }

    public abstract class Expression: IComparable<Expression, bool> {
        public override abstract string? ToString();
        public abstract override int GetHashCode();
        public abstract bool Equals(Expression other);
        public override bool Equals(object? other) {
            if (other is Expression other_e) {
                return Equals(other_e);
            }
            return false;
        }
        public static bool operator ==(Expression left, Expression right) {
            return left.Equals(right);
        }
        public static bool operator !=(Expression left, Expression right) {
            return !left.Equals(right);
        }
    }

    public abstract class Atom : Expression {}
    public class Scalar<V> : Atom, IInner where V : notnull {
        protected V _value;
        public Scalar(V value) {
            _value = value;
        }
        public override int GetHashCode() {
            return 17 * 23 + _value.GetHashCode();
        }
        public override bool Equals(Expression other) {
            if (other is Scalar<V> other_scalar) {
                return _value.Equals(other_scalar._value);
            }
            return false;
        }
        public override string? ToString() {
            return _value.ToString();
        }
        public V Value() {
            return _value;
        }
        public object Inner() {
            return _value;
        }
    }
    public class Symbol : Atom {
        private string _name;
        public Symbol(string name) {
            _name = name;
        }
        public override int GetHashCode() {
            return 17 * 23 + _name.GetHashCode();
        }
        public override bool Equals(Expression other) {
            if (other is Symbol other_symbol) {
                return _name.Equals(other_symbol._name);
            }
            return false;
        }
        public override string? ToString() {
            return _name.ToString();
        }
        public string Name() {
            return _name;
        }
    }
    public class Integer : Scalar<int>, IAddable<Integer>, ISubtractable<Integer>, IMultiplicatable<Integer>, IDivisible<Integer>, ISortable<Integer, Boolean> {
        public Integer(int value) : base(value) {}
        public static Integer operator +(Integer a, Integer b) {
            return new Integer(a._value + b._value);
        }
        public static Integer operator -(Integer a, Integer b) {
            return new Integer(a._value - b._value);
        }
        public static Integer operator *(Integer a, Integer b) {
            return new Integer(a._value * b._value);
        }
        public static Integer operator /(Integer a, Integer b) {
            return new Integer(a._value / b._value);
        }
        public static Integer operator %(Integer a, Integer b) {
            return new Integer(a._value % b._value);
        }
        public static Boolean operator >(Integer a, Integer b) {
            return (a._value > b._value) ? Boolean.TRUE : Boolean.FALSE;
        }
        public static Boolean operator <(Integer a, Integer b) {
            return (a._value < b._value) ? Boolean.TRUE : Boolean.FALSE;
        }
        public static Boolean operator >=(Integer a, Integer b) {
            return (a._value >= b._value) ? Boolean.TRUE : Boolean.FALSE;
        }
        public static Boolean operator <=(Integer a, Integer b) {
            return (a._value <= b._value) ? Boolean.TRUE : Boolean.FALSE;
        }
        public override int GetHashCode() {
            return base.GetHashCode();
        }
        public override bool Equals(object? other) {
            return base.Equals(other);
        }
        public static Boolean operator ==(Integer a, Integer b) {
            return (a._value == b._value) ? Boolean.TRUE : Boolean.FALSE;
        }
        public static Boolean operator !=(Integer a, Integer b) {
            return (a._value != b._value) ? Boolean.TRUE : Boolean.FALSE;
        }
    }

    public class Boolean: Scalar<bool> {
        public static Boolean TRUE = new Boolean(true);
        public static Boolean FALSE = new Boolean(false);
        private Boolean(bool value) : base(value) {}
        public override string? ToString() {
            if (_value) {
                return "t";
            }
            return "nil";
        }
        public IList<Expression> ToList() {
            if (_value) {
                throw new ApplicationException("Cannot use t as list");
            }
            return new List<Expression>();
        }
    }
    public class String: Scalar<string> {
        public String(string value) : base(value) {}
        public override string? ToString() {
            return $"\"{base.ToString()}\"";
        }
    }
    public class Cons: Expression {
        public Expression Item1;
        public Expression Item2;
        public Cons(Expression item1, Expression item2) {
            Item1 = item1;
            Item2 = item2;
        }
        public static Expression FromList(IEnumerable<Expression> expressions) {
            var e = expressions.ToList();
            if (e.Count == 0) {
                return Boolean.FALSE;
            }
            var item1 = expressions.First();
            if (e.Count == 1) {
                return new Cons(item1, Boolean.FALSE);
            }
            var item2 = expressions.Skip(1).ToList();
            return new Cons(item1, FromList(item2));
        }
        public IEnumerable<Expression> ToList() {
            var l = new List<Expression>();
            l.Add(Item1);
            if (Item2 == Boolean.FALSE) {
                return l;
            }
            if (Item2 is Cons item2_cons) {
                l.AddRange(item2_cons.ToList());
                return l;
            }
            l.Add(Item2);
            return l;
        }
        public override int GetHashCode() {
            var hash = 17;
            hash *= 23;
            hash += Item1.GetHashCode();
            hash *= 23;
            hash += Item2.GetHashCode();
            return hash;
        }
        public override bool Equals(Expression other) {
            if (other is Cons other_list) {
                return Item1.Equals(other_list.Item1) && Item2.Equals(other_list.Item2);
            }
            return false;
        }
        private string? ToStringSimple() {
            if (Item2.Equals(Boolean.FALSE)) {
                return Item1.ToString();
            }
            if (Item2 is Cons item2_cons) {
                return $"{Item1} {item2_cons.ToStringSimple()}";
            }
            return $"{Item1} . {Item2}";
        }
        public override string? ToString() {
            return $"({ToStringSimple()})";
        }
    }

    public class Object : Scalar<object> {
        public Object(object value) : base(value) { }
        public static Expression FromBase(object? o) {
            if (o == null) {
                return Boolean.FALSE;
            }
            switch (o) {
                case bool b:
                    return b ? Boolean.TRUE : Boolean.FALSE;
                case int i:
                    return new Integer(i);
                case string s:
                    return new String(s);
                case Expression e:
                    return e;
                case IEnumerable<object> e:
                    return Cons.FromList(e.Select(x => FromBase(x)));
                default:
                    return new Object(o);
            }
        }
    }

    public class Procedure : Expression {
        private IEnumerable<Symbol> _parameters;
        private Expression _body;
        private bool _eval_args;
        public Procedure(IEnumerable<Symbol> parameters, Expression body, bool eval_args) {
            _parameters = parameters;
            _body = body;
            _eval_args = eval_args;
        }
        public override int GetHashCode() {
            int hash = 17;
            hash *= 23;
            hash += _parameters.GetHashCode();
            hash *= 23;
            hash += _body.GetHashCode();
            return hash;
        }
        public override bool Equals(Expression? other) {
            if (other is Procedure other_p) {
                return _parameters == other_p._parameters && _body == other_p._body;
            }
            return false;
        }
        public override string ToString() {
            var star = _eval_args ? "" : "*";
            return $"(lambda{star} {Cons.FromList(_parameters)} {_body})";
        }

        private Expression __eval(Executor e, Expression exp) {
            if (!_eval_args) return exp;
            return e.eval(exp);
        }

        private Expression _eval(Executor e, Expression exp) {
            var r = __eval(e, exp);
            //Console.WriteLine($"{exp} = {r}");
            return r;
        }

        public Expression Call(Executor e, IList<Expression> args) {
            Executor new_e = new Executor(new SubEnvironment(e.environment), e.builtins, e.builtinsLater);
            var _params = _parameters.Select(x => x.Name()).ToArray();
            var idx_rest = -1;

            IList<(string, Expression)> name_args = new List<(string, Expression)>();
            for (var i = 0; i < _parameters.Count(); i++) {
                var name = _params[i];
                if (name.Equals(".")) {
                    idx_rest = i + 1;
                    break;
                }
                name_args.Add((name, _eval(e, args[i])));
            }
            if (idx_rest > 0) {
                name_args.Add((_params[idx_rest], Cons.FromList(args.Skip(idx_rest - 1).Select(x => _eval(e, x)))));
            }
            foreach (var na in name_args) {
                new_e.environment.Set(na.Item1, na.Item2);
            }
            var r = new_e.eval(_body);
            return r;
        }
    }

}