// Copyright (C) 2013-2014, Gabriel Dos Reis.
// All rights reserved.
// Written by Gabriel Dos Reis.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     - Redistributions of source code must retain the above copyright
//       notice, this list of conditions and the following disclaimer.
//
//     - Redistributions in binary form must reproduce the above copyright
//       notice, this list of conditions and the following disclaimer in
//       the documentation and/or other materials provided with the
//       distribution.
//
//     - Neither the name of OpenAxiom nor the names of its contributors
//       may be used to endorse or promote products derived from this
//       software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
// IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
// TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
// PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
// OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
// EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#include <open-axiom/Lisp>
#include <typeinfo>
#include <ostream>
#include <sstream>

namespace OpenAxiom {
   namespace Lisp {
      // -- UnboundSymbol
      UnboundSymbol::UnboundSymbol(const std::string& s)
            : BasicError(s)
      { }

      static void unbound_symbol_error(const std::string& s) {
         throw UnboundSymbol(s + " has no value binding");
      }
         

      // -- UnboundFunctiom
      UnboundFunctionSymbol::UnboundFunctionSymbol(const std::string& s)
            : BasicError(s)
      { }

      static void unbound_function_symbol_error(const Symbol* sym) {
         std::string s { sym->name->begin(), sym->name->end() };
         throw UnboundFunctionSymbol(s + " has no function definition");
      }
      
      namespace {
         template<typename T>
         struct NamedConstant {
            const char* const name;
            const T value;
         };
      }

      constexpr NamedConstant<Value> value_constants[] = {
         { "NIL", Value::nil },
         { "T", Value::t },
         { "MOST-NEGATIVE-FIXNUM", to_value(Fixnum::minimum) },
         { "MOST-POSITIVE-FIXNUM", to_value(Fixnum::maximum) },
      };

      static void define_special_constants(Evaluator* ctx) {
         auto core = ctx->core_package();
         for (auto& x : value_constants) {
            auto sym = core->make_symbol(ctx->intern(x.name));
            sym->value = x.value;
            sym->attributes = SymbolAttribute::SpecialConstant;
         }
      }

      Unimplemented::Unimplemented(const std::string& s)
            : BasicError(s)
      { }

      IntegerOverflow::IntegerOverflow(const std::string& s)
            : BasicError(s)
      { }

      std::string
      show(Value v) {
         std::ostringstream os;
         format(v, os);
         return os.str();
      }

      Fixnum
      retract_to_fixnum(Value v) {
         if (not is<Fixnum>(v))
            throw Diagnostics::BasicError(show(v) + " is not a fixnum");
         return to_fixnum(v);
      }

      Pair
      retract_to_pair(Value v) {
         if (not is<Pair>(v))
            throw Diagnostics::BasicError(show(v) + " is not a pair");
         return to_pair(v);
      }


      static void
      unimplemented(const Sexpr::Syntax& x) {
         std::string s = "unimplemented eval for ";
         throw Unimplemented{ s + typeid(x).name() };
      }

      static void
      integer_too_large(const Sexpr::IntegerSyntax& x) {
         std::string s { x.lexeme().begin(), x.lexeme().end() };
         throw IntegerOverflow{ s + " is too large for Fixnum; max value is "
               + std::to_string(FixnumBits(Fixnum::maximum)) };
      }

      constexpr auto fixmax_by_ten = FixnumBits(Fixnum::maximum) / 10;
      constexpr auto fixmax_lsd = FixnumBits(Fixnum::maximum) % 10;

      static Value
      construct(Evaluator* ctx, const Sexpr::IntegerSyntax& x) {
         bool neg = false;
         auto cur = x.lexeme().begin();
         FixnumBits val = 0;
         switch (*cur) {
         case '-': neg = true;
         case '+': ++cur;
         default:
            for (; cur < x.lexeme().end(); ++cur) {
               auto d = *cur - '0';
               if (val < fixmax_by_ten)
                  val = 10 * val + d;
               else if (val > fixmax_by_ten or d > fixmax_lsd)
                  integer_too_large(x);
               else
                  val = 10 * val + d;
            }
            if (neg) {
               if (val > FixnumBits(Fixnum::maximum))
                  integer_too_large(x);
               val = -val;
            }
         }
         return VM::to_value(Fixnum(val));
      }

      static Value
      construct(Evaluator* ctx, const Sexpr::ListSyntax& x) {
         if (x.empty())
            return Value::nil;
         auto result = Value::nil;
         auto p = x.rbegin();
         if (x.dotted())
            result = ctx->make_value(*p++);
         while (p != x.rend())
            result = to_value(ctx->make_pair(ctx->make_value(*p++), result));
         return result;
      }

      static Value
      construct(Evaluator* ctx, const Sexpr::StringSyntax& x) {
         auto s = ctx->intern(x.lexeme().begin(), x.lexeme().size());
         return to_value(s);
      }

      static Value
      construct(Evaluator* ctx, const Sexpr::SymbolSyntax& x) {
         auto s = ctx->intern(x.lexeme().begin(), x.lexeme().size());
         switch (x.kind()) {
         case Sexpr::SymbolSyntax::uninterned:
            return to_value(ctx->homeless_package()->make_symbol(s));

         case Sexpr::SymbolSyntax::keyword:
            return to_value(ctx->make_keyword(s));

         default:
            return to_value(ctx->current_package()->make_symbol(s));
         }
      }

      VM::Value
      Evaluator::make_value(const Sexpr::Syntax* x) {
         using namespace Sexpr;
         struct V : Sexpr::Syntax::Visitor {
            Evaluator* ctx;
            Value result;
            V(Evaluator* e) : ctx(e), result(Value::nil) { }
            void visit(const IntegerSyntax& x) { result = construct(ctx, x); }
            void visit(const CharacterSyntax& x) { unimplemented(x); }
            void visit(const StringSyntax& x) { result = construct(ctx, x); }
            void visit(const SymbolSyntax& x) { result = construct(ctx, x); }
            void visit(const ReferenceSyntax& x) {
               auto p = ctx->anchor_map.find(x.tag());
               if (p == ctx->anchor_map.end())
                  throw Diagnostics::BasicError{ "undefined anchor "
                        + std::to_string(x.tag())
                        };
               result = p->second;
            }
            void visit(const AnchorSyntax& x) {
               auto& v = ctx->anchor_map[x.ref()];
               if (v != Value::nil)
                  throw Diagnostics::BasicError{
                     "duplicate anchor " + std::to_string(x.ref())
                        };
               result = v = ctx->make_value(x.value());
            }
            void visit(const QuoteSyntax& x) { unimplemented(x); }
            void visit(const AntiquoteSyntax& x) { unimplemented(x); }
            void visit(const Expand& x) { unimplemented(x); }
            void visit(const Eval& x) { unimplemented(x); }
            void visit(const Splice& x) { unimplemented(x); }
            void visit(const Function& x) { unimplemented(x); }
            void visit(const Include& x) { unimplemented(x); }
            void visit(const Exclude& x) { unimplemented(x); }
            void visit(const ListSyntax& x) { result = construct(ctx, x); }
            void visit(const VectorSyntax& x) { unimplemented(x); }
         };

         if (x == nullptr)
            return Value::nil;
         V v { this };
         x->accept(v);
         return v.result;
      }

      static std::string
      canonical_name(const Sexpr::SymbolSyntax& x) {
         if (x.kind() & Sexpr::SymbolSyntax::absolute)
            return { x.begin(), x.end() };
         const auto sz = x.size();
         std::string s(sz, char{ });
         for (std::size_t i = 0; i < sz; ++i)
            s[i] = toupper(x[i]);
         return s;
      }

      // Return the (global) symbol value
      static Symbol*
      retrieve_symbol(Evaluator* ctx, const Sexpr::SymbolSyntax& x) {
         const auto s = canonical_name(x);
         auto name = ctx->intern(s.c_str());
         if (x.kind() & Sexpr::SymbolSyntax::keyword)
            return ctx->make_keyword(name);
         // Note: Uninterned symbols are always distincts;
         else if (x.kind() & Sexpr::SymbolSyntax::uninterned)
            unbound_symbol_error(s);
         // FIXME: if this is a qualified symbol, lookup in its home.
         else if (auto symbol = ctx->current_package()->find_symbol(name))
            return symbol;
         unbound_symbol_error(s);
         return nullptr;
      }

      // Return the value designated by this symbol.
      static Value
      evaluate(Evaluator* ctx, const Sexpr::SymbolSyntax& x) {
         const auto s = canonical_name(x);
         auto name = ctx->intern(s.c_str());
         if (x.kind() & Sexpr::SymbolSyntax::keyword)
            return to_value(ctx->make_keyword(name));
         else if (x.kind() & Sexpr::SymbolSyntax::uninterned)
            unbound_symbol_error(s);
         else if (auto p = ctx->lexical_binding(name))
            return *p;
         auto symbol = ctx->current_package()->find_symbol(name);
         if (symbol == nullptr or not symbol->has(SymbolAttribute::Special))
            unbound_symbol_error(s);
         return symbol->value;
      }

      // Return the denotation of a sharp-apostrophe syntax.

      static const Callable*
      symbol_function(Evaluator* ctx, const Sexpr::SymbolSyntax& s) {
         auto sym = retrieve_symbol(ctx, s);
         if (sym->function == nullptr)
            unbound_function_symbol_error(sym);
         return sym->function;
      }
      
      static Value
      evaluate(Evaluator* ctx, const Sexpr::Function& x) {
         auto s = dynamic_cast<const Sexpr::SymbolSyntax*>(x.body());
         if (s == nullptr)
            throw Unimplemented("FUNCTION of non-symbol expression");
         return to_value(symbol_function(ctx, *s));
      }

      static Value
      evaluate(Evaluator* ctx, const Sexpr::QuoteSyntax& x) {
         return ctx->make_value(x.body());
      }

      // -- special operators
      using SpecialOperator = Value (*)(Evaluator*, const Sexpr::Syntax&);
      const NamedConstant<SpecialOperator> special_ops[] = {
      };      

      static SpecialOperator
      special_operator(const Sexpr::SymbolSyntax& s) {
         auto name = canonical_name(s);
         for (auto& x : special_ops) {
            if (x.name == name)
               return x.value;
         }
         return nullptr;
      }

      static Value
      evaluate(Evaluator* ctx, const Sexpr::ListSyntax& x) {
         if (x.empty())
            return Value::nil;
         auto s = dynamic_cast<const Sexpr::SymbolSyntax*>(x.front());
         if (s == nullptr)
            // FIXME: real error
            unimplemented(x);
         if (auto op = special_operator(*s))
            return op(ctx, x);
         auto fun = symbol_function(ctx, *s);
      }

      Value
      Evaluator::eval(const Sexpr::Syntax* x) {
         using namespace Sexpr;
         struct V : Syntax::Visitor {
            Evaluator* ctx;
            Value result;
            V(Evaluator* e) : ctx(e), result(Value::nil) { }
            void visit(const IntegerSyntax& x) { result = construct(ctx, x); }
            void visit(const CharacterSyntax& x) { unimplemented(x); }
            void visit(const StringSyntax& x) { result = construct(ctx, x); }
            void visit(const SymbolSyntax& x) { result = evaluate(ctx, x); }
            void visit(const ReferenceSyntax& x) { unimplemented(x); }
            void visit(const AnchorSyntax& x) { unimplemented(x); }
            void visit(const QuoteSyntax& x) { result = evaluate(ctx, x); }
            void visit(const AntiquoteSyntax& x) { unimplemented(x); }
            void visit(const Expand& x) { unimplemented(x); }
            void visit(const Eval& x) { unimplemented(x); }
            void visit(const Splice& x) { unimplemented(x); }
            void visit(const Function& x) { result = evaluate(ctx, x); }
            void visit(const Include& x) { unimplemented(x); }
            void visit(const Exclude& x) { unimplemented(x); }
            void visit(const ListSyntax& x) { result = evaluate(ctx, x); }
            void visit(const VectorSyntax& x) { unimplemented(x); }
         };
         
         if (x == nullptr)
            return Value::nil;
         V v { this };
         x->accept(v);
         return v.result;
      }

      Value*
      Evaluator::lexical_binding(String name) {
         if (env_stack.empty())
            return nullptr;
         else if (auto b = env_stack.back().lookup(name))
            return &b->value;
         return nullptr;
      }

      Value
      Evaluator::toplevel_form(const Sexpr::Syntax* x) {
         auto anchors = std::move(anchor_map);
         anchor_map = AnchorTable{ };
         auto v = make_value(x);
         anchor_map = std::move(anchors);
         return v;
      }

      template<typename... Ts>
      using Operation = Value (*)(Ts...);

      template<Operation<Value> fun>
      RuntimeOperation<Value> runtime() {
         return [](BasicContext*, Value x) { return fun(x); };
      }

      const NamedConstant<UnaryCode> unary_builtins[] = {
         { "CONSP", runtime<consp>() },
         { "ATOM", runtime<atom>() },
         { "SYMBOLP", runtime<symbolp>() },
         { "KEYWORDP", runtime<keywordp>() },
      };

      template<typename T>
      static void
      define_builtin_operator(Evaluator* ctx, const char* s, T t) {
         auto name = ctx->intern(s);
         auto sym = ctx->current_package()->make_symbol(name);
         sym->function = ctx->make_operator(sym, t);
      }

      static void
      define_builtin_operators(Evaluator* ctx) {
         for (auto& x : unary_builtins)
            define_builtin_operator(ctx, x.name, x.value);
      }

      static Symbol*
      make_special_symbol(Evaluator* ctx, const char* s) {
         auto name = ctx->intern(s);
         auto sym = ctx->current_package()->make_symbol(name);
         sym->attributes = SymbolAttribute::Special;
         return sym;
      }

      static Symbol*
      define_features(Evaluator* ctx) {
         auto sym = make_special_symbol(ctx, "*FEATURES*");
         sym->value = Value::nil;
         return sym;
      }

      static void
      define_current_package(Evaluator* ctx) {
         auto sym = make_special_symbol(ctx, "*PACKAGE*");
         sym->value = to_value(ctx->current_package());
      }

      Evaluator::Evaluator()
            : core(make_package(intern("AxiomCore"))),
              ns(core),
              feature_list(define_features(this))
      {
         define_special_constants(this);
         define_builtin_operators(this);
         define_current_package(this);
         env_stack.push_back(Environment{ });
      }

      Environment*
      Evaluator::global_environment() {
         return &env_stack.front();
      }


      // -- Formatting

      static void format(Pair p, std::ostream& os) {
         os << '(';
         while (true) {
            format(p->head, os);
            auto v = p->tail;
            if (v == Value::nil)
               break;
            os << ' ';
            if (auto q = if_pair(v)) {
               p = q;
               continue;
            }
            os << '.' << ' ';
            format(v, os);
            break;
         }
         os << ')';
      }

      static void format(String s, std::ostream& os) {
         os << '"';
         for (auto c : *s) {
            if (c == '"')
               os << '\\';
            os << char(c);
         }
         os << '"';
      }

      static void format(const Boxed*, std::ostream&);

      void format(Value v, std::ostream& os) {
         if (v == Value::nil)
            os << "NIL";
         else if (v == Value::t)
            os << "T";
         else if (is<Fixnum>(v))
            os << FixnumBits(to_fixnum(v));
         else if (is<Pair>(v))
            format(to_pair(v), os);
         else if (is<String>(v))
            format(to_string(v), os);
         else if (is<Boxed>(v))
            format(to_boxed(v), os);
         else
            os << "#<unprintable>";
      }

      static void format(const Boxed* x, std::ostream& os) {
         struct V : Boxed::Visitor {
            std::ostream& os;
            V(std::ostream& s) : os(s) { }
            void visit(const Symbol& s) {
               // FIXME: handle escapes.
               std::copy(s.name->begin(), s.name->end(),
                         std::ostream_iterator<char>(os));
            }
            void visit(const Package& p) {
               os << "#<PACKAGE ";
               std::copy(p.name->begin(), p.name->end(),
                         std::ostream_iterator<char>(os));
               os << '>';
            }
            void visit(const FunctionBase& f) {
               os << "#<FUNCTION ";
               visit(*f.name);
               os << '>';
            }
            void visit(const Binding& b) {
               os << '(';
               visit(*b.symbol);
               os << ' ';
               format(b.value, os);
               os << ')';
            }
         };
         
         V v { os };
         x->accept(v);
      }
      
      // -- assoc: (T, List Pair(T, S)) -> S
      Value assoc(Value key, Pair al) {
         while (al != nullptr) {
            auto entry = retract_to_pair(al->head);
            if (entry->head == key)
               return entry->tail;
            else if (al->tail == Value::nil)
               return Value::nil;
            al = retract_to_pair(al->tail);
         }
         return Value::nil;
      }
   }
}