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

using System.Reflection;

using Jellyfin.Plugin.SmartPlaylist.Lisp.Compiler;

namespace Jellyfin.Plugin.SmartPlaylist.Lisp {
    using Function = Func<IList<Expression>, Expression>;
    using FunctionLater = Func<Executor, IList<Expression>, Expression>;

    public class Procedure : Expression {
        private Compiler.List _parameters;
        private Expression _body;
        public Procedure(Compiler.List parameters, Expression body) {
            _parameters = parameters;
            _body = body;
        }
        private static IEnumerable<(T1, T2)> Zip<T1, T2>(IEnumerable<T1> a, IEnumerable<T2> b) {
            using (var e1 = a.GetEnumerator()) using (var e2 = b.GetEnumerator()) {
                while (e1.MoveNext() && e2.MoveNext()) {
                    yield return (e1.Current, e2.Current);
                }
            }
        }
        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 object Inner() {
            throw new ApplicationException("This is not sensible");
        }
        public override string ToString() {
            return $"(lambda {_parameters} {_body})";
        }

        public Expression Call(Executor e, IList<Expression> args) {
            var p = _parameters.expressions.Select(x => x.Inner().ToString()).ToList();
            Executor new_e = new Executor(new SubEnvironment(e.environment), e.builtins, e.builtinsLater);
            foreach (var tuple in Zip<string, Expression>(p, args)) {
                new_e.environment.Set(tuple.Item1, tuple.Item2);
            }
            return new_e.eval(_body);
        }
    }

    public interface IEnvironment<K, V> {
        public V Get(K k);
        public void Set(K k, V v);
        public IEnvironment<K, V>? Find(K k);
    }

    public class Environment : Dictionary<string, Expression>, IEnvironment<string, Expression> {
        public Expression? Get(string k) {
            if (TryGetValue(k, out Expression v)) {
                return v;
            }
            return null;
        }
        public void Set(string k, Expression v) {
            Add(k, v);
        }

        public IEnvironment<string, Expression>? Find(string k) {
            if (ContainsKey(k)) {
                return this;
            }
            return null;
        }
    }

    public class SubEnvironment : Dictionary<string, Expression>, IEnvironment<string, Expression> {
        private IEnvironment<string, Expression> _super;
        public SubEnvironment(IEnvironment<string, Expression> super) {
            _super = super;
        }
        public Expression? Get(string k) {
            if (TryGetValue(k, out Expression v)) {
                return v;
            }
            return null;
        }
        public void Set(string k, Expression v) {
            Add(k, v);
        }

        public IEnvironment<string, Expression>? Find(string k) {
            if (ContainsKey(k)) {
                return this;
            }
            return _super.Find(k);
        }
    }

    public class Builtins : Dictionary<string, Function> {
        public Builtins() : base() {
            this["+"] = _add;
            this["-"] = _sub;
            this["*"] = _mul;
            this["/"] = _div;
            this["%"] = _mod;
            this[">"] = _gt;
            this["<"] = _lt;
            this[">="] = _ge;
            this["<="] = _le;
            this["eq?"] = _eq;
            this["="] = _eq;
            this["!="] = _ne;
            this["abs"] = _abs;
            this["append"] = _append;
            this["begin"] = _begin;
            this["car"] = _car;
            this["cdr"] = _cdr;
            this["cons"] = _cons;
            this["not"] = _not;
            this["length"] = _length;
            this["haskeys"] = _haskeys;
            this["getitems"] = _getitems;
            this["invoke"] = _invoke;
        }

        private static T _agg<T>(Func<T, T, T> op, IList<T> args) {
            T agg = args[0];
            foreach (var arg in args.Skip(1)) {
                agg = op(agg, arg);
            }
            return agg;
        }
        private static Expression _add(IList<Expression> args) {
            Expression first = args[0];
            switch (first) {
                case Integer i:
                    return _agg((a, b) => a + b, args.Select(x => (Integer) x).ToList());
                case Compiler.String s:
                    return _agg((a, b) => a + b, args.Select(x => (Compiler.String) x).ToList());
            }
            throw new ApplicationException();
        }
        private static Expression _sub(IList<Expression> args) {
            Expression first = args[0];
            switch (first) {
                case Integer i:
                    return _agg((a, b) => a - b, args.Select(x => (Integer) x).ToList());
            }
            throw new ApplicationException();
        }
        private static Expression _mul(IList<Expression> args) {
            Expression first = args[0];
            switch (first) {
                case Integer i:
                    return _agg((a, b) => a * b, args.Select(x => (Integer) x).ToList());
            }
            throw new ApplicationException();
        }
        private static Expression _div(IList<Expression> args) {
            Expression first = args[0];
            switch (first) {
                case Integer i:
                    return _agg((a, b) => a / b, args.Select(x => (Integer) x).ToList());
            }
            throw new ApplicationException();
        }
        private static Expression _mod(IList<Expression> args) {
            Expression first = args[0];
            switch (first) {
                case Integer i:
                    return _agg((a, b) => a % b, args.Select(x => (Integer) x).ToList());
            }
            throw new ApplicationException();
        }
        private static E _cmp<T, E>(Func<T, T, E> op, IList<T> args) {
            T first = args[0];
            T second = args[1];
            return op(first, second);
        }
        private static Expression _gt(IList<Expression> args) {
            Expression first = args[0];
            switch (first) {
                case Integer i:
                    return _cmp((a, b) => a > b, args.Select(x => (Integer) x).ToList());
            }
            throw new ApplicationException();
        }
        private static Expression _lt(IList<Expression> args) {
            Expression first = args[0];
            switch (first) {
                case Integer i:
                    return _cmp((a, b) => a < b, args.Select(x => (Integer) x).ToList());
            }
            throw new ApplicationException();
        }
        private static Expression _ge(IList<Expression> args) {
            Expression first = args[0];
            switch (first) {
                case Integer i:
                    return _cmp((a, b) => a >= b, args.Select(x => (Integer) x).ToList());
            }
            throw new ApplicationException();
        }
        private static Expression _le(IList<Expression> args) {
            Expression first = args[0];
            switch (first) {
                case Integer i:
                    return _cmp((a, b) => a <= b, args.Select(x => (Integer) x).ToList());
            }
            throw new ApplicationException();
        }
        private static Expression _eq(IList<Expression> args) {
            bool r = _cmp((a, b) => a == b, args);
            return new Compiler.Boolean(r);
        }
        private static Expression _ne(IList<Expression> args) {
            bool r = _cmp((a, b) => a != b, args);
            return new Compiler.Boolean(r);
        }
        private static Expression _abs(IList<Expression> args) {
            Expression first = args[0];
            switch (first) {
                case Integer i:
                    return i.value >= 0 ? i : new Integer(-i.value);
            }
            throw new ApplicationException();
        }
        private static Expression _append(IList<Expression> args) {
            Expression first = args[0];
            switch (first) {
                case List l:
                    return l + new List(args);
            }
            throw new ApplicationException();
        }
        private static Expression _begin(IList<Expression> args) {
            return args.Last();
        }
        private static Expression _car(IList<Expression> args) {
            return ((List) args.First()).expressions.First();
        }
        private static Expression _cdr(IList<Expression> args) {
            return new List(((List) args.First()).expressions.Skip(1).ToList());
        }
        private static Expression _cons(IList<Expression> args) {
            switch (args[1]) {
                case Compiler.List other_list:
                    return (new Compiler.List(new []{args[0]}.ToList()) + new Compiler.List(other_list.expressions));
                case Atom other_atom:
                    return new Compiler.List(new[]{args[0], args[1]}.ToList());
            }
            throw new ApplicationException();
        }
        private static Expression _not(IList<Expression> args) {
            if (args[0] == new Compiler.Boolean(false)) {
                return new Compiler.Boolean(true);
            }
            return new Compiler.Boolean(false);
        }
        private static Expression _length(IList<Expression> args) {
            return new Integer(((Compiler.List)args[0]).expressions.Count());
        }
        private static Expression _haskeys(IList<Expression> args) {
            Compiler.Object o = (Compiler.Object) args[0];
            foreach (var e in args.Skip(1)) {
                Compiler.String s = (Compiler.String) e;
                PropertyInfo? pi = o.value.GetType().GetProperty(s.value);
                if (pi != null) {
                    continue;
                }
                MethodInfo? mi = o.value.GetType().GetMethod(s.value);
                if (mi != null) {
                    continue;
                }
                FieldInfo? fi = o.value.GetType().GetField(s.value);
                if (fi != null) {
                    continue;
                }
                return new Compiler.Boolean(false);
            }
            return new Compiler.Boolean(true);
        }
        private static Expression _getitems(IList<Expression> args) {
            Compiler.Object o = (Compiler.Object) args[0];
            IList<Expression> r = new List<Expression>();
            foreach (var e in args.Skip(1)) {
                Compiler.String s = (Compiler.String) e;
                PropertyInfo? pi = o.value.GetType().GetProperty(s.value);
                if (pi != null) {
                    r.Add(Compiler.Object.FromBase(pi.GetValue(o.value)));
                    continue;
                }
                FieldInfo? fi = o.value.GetType().GetField(s.value);
                if (fi != null) {
                    r.Add(Compiler.Object.FromBase(fi.GetValue(o.value)));
                    continue;
                }
                throw new ApplicationException($"{o.value} has no property or field {s.value}");
            }
            return new Compiler.List(r);
        }

        private static Expression _invoke(IList<Expression> args) {
            Compiler.Object o = (Compiler.Object) args[0];
            Compiler.String s = (Compiler.String) args[1];
            Compiler.List l = (Compiler.List) args[2];
            IList<Expression> r = new List<Expression>();
            MethodInfo? mi = o.value.GetType().GetMethod(s.value);
            if (mi == null) {
                throw new ApplicationException($"{o.value} has not method {s.value}");
            }
            return Compiler.Object.FromBase(mi.Invoke(o.value, (object?[]?) l.Inner()));
        }
    }

    public class BuiltinsLater : Dictionary<string, FunctionLater> {
        public BuiltinsLater() : base() {
            this["if"] = _if;
            this["define"] = _define;
            this["lambda"] = _lambda;
            this["apply"] = _apply;
            this["and"] = _and;
            this["or"] = _or;
        }
        private static Expression _if(Executor e, IList<Expression> args) {
            bool test = e.eval(args[0]) != (new Compiler.Boolean(false));
            return e.eval(args[1 + (test ? 0 : 1)]);
        }
        private static Expression _define(Executor e, IList<Expression> args) {
            var refname = ((Symbol) args[0]).name;
            e.environment.Set(refname, e.eval(args[1]));
            return new Compiler.Boolean(false); // NOOP
        }
        private static Expression _lambda(Executor e, IList<Expression> args) {
            return new Procedure((Compiler.List) args[0], args[1]);
        }
        private static Expression _apply(Executor e, IList<Expression> args) {
            if (args[0].GetType() != typeof(Symbol)) {
                throw new ApplicationException();
            }
            if (args[1].GetType() != typeof(List)) {
                throw new ApplicationException();
            }
            Symbol arg0 = (Compiler.Symbol) args[0];
            Compiler.List other_args = (Compiler.List) args[1];
            return e.EvalFunction(arg0, other_args.expressions);
        }
        private static Expression _and(Executor e, IList<Expression> args) {
            Expression result = new Compiler.Boolean(false);
            foreach (var exp in args) {
                result = e.eval(exp);
                if (result == new Compiler.Boolean(false)) { return result; }
            }
            return result;
        }
        private static Expression _or(Executor e, IList<Expression> args) {
            Expression result = new Compiler.Boolean(false);
            foreach (var exp in args) {
                result = e.eval(exp);
                if (result != new Compiler.Boolean(false)) { return result; }
            }
            return result;
        }
    }

    public class Executor {
        IEnvironment<string, Expression> _environment;
        Builtins _builtins;
        BuiltinsLater _builtinsLater;
        public Executor(IEnvironment<string, Expression> environment, Builtins builtins, BuiltinsLater builtinsLater) {
            _environment = environment;
            _builtins = builtins;
            _builtinsLater = builtinsLater;
        }
        public Executor() {
            _environment = new Environment();
            _builtins = new Builtins();
            _builtinsLater = new BuiltinsLater();
        }

        public IEnvironment<string, Expression> environment { get => _environment; }
        public Builtins builtins { get => _builtins; }
        public BuiltinsLater builtinsLater { get => _builtinsLater; }

        public Expression EvalFunction(Symbol fcname, IList<Expression> args) {
            if (_environment.Find(fcname.name) is IEnvironment<string, Expression> _e) {
                Expression? first = _e.Get(fcname.name);
                return new List(new []{first}.ToList()) + new List(args.Select(x => eval(x)).ToList());
            }
            if (_builtins.ContainsKey(fcname.name)) {
                Function fc = _builtins[fcname.name];
                return fc(args.Select(x => eval(x)).ToList());
            }
            if (_builtinsLater.ContainsKey(fcname.name)) {
                FunctionLater fc = _builtinsLater[fcname.name];
                return fc(this, args);
            }
            throw new ApplicationException($"Key '{fcname.name}' not found in environment or builtins");

        }

        public Expression eval(Expression expression) {
            switch (expression) {
                case Symbol s:
                    return _environment.Find(s.name).Get(s.name);
                case Compiler.Boolean b:
                    return b;
                case Integer i:
                    return i;
                case Compiler.String s:
                    return s;
                case Procedure p:
                    return p;
                case List list:
                    if (list.expressions.Count == 0) {
                        return list;
                    }
                    // do we really want to allow shadowing of builtins?
                    if (list.expressions[0].GetType() == typeof(Symbol)) {
                        return eval(EvalFunction((Symbol) list.expressions[0], list.expressions.Skip(1).ToList()));
                    }
                    if (list.expressions[0].GetType() == typeof(Procedure)) {
                        Procedure procedure = (Procedure) list.expressions[0];
                        return eval(procedure.Call(this, list.expressions.Skip(1).ToList()));
                    }
                    var l = new List(list.expressions.Select(x => eval(x)).ToList());
                    if (l.expressions[0].GetType() == typeof(Procedure)) {
                        return eval(l);
                    }
                    return l;
            }
            throw new ApplicationException($"Not handled case '{expression}'");
        }
        public Expression eval(Parser p) {
            return eval(p.parse());
        }
        public Expression eval(StringTokenStream sts) {
            return eval(new Parser(sts));
        }
        public Expression eval(string p) {
            return eval(StringTokenStream.generate(p));
        }
    }
}