#pragma once

#include <concepts>
#include <cstdint>
#include <cstring>
#include <iostream>

#include "arena.hpp"
#include "pod.hpp"

// Forward declarations

class Value;

class Object {
 public:
  virtual Tag tag() = 0;
  virtual Result<Value> copy(Arena& arena) = 0;
  virtual PodObject* pod() = 0;
};

class Nil : public Object {
 public:
  Nil() {}
  Nil(GcRoot<PodNil>&& val) : _value(std::move(val)) {}

  virtual Tag tag() final { return Tag::Nil; }
  virtual PodObject* pod() final { return _value.get(); }

  static Result<Nil> create(Arena& arena, PodNil* obj) {
    return Nil(TRY(MkGcRoot(obj, arena)));
  }

  static Result<Nil> create(Arena& arena) {
    auto pod = TRY(arena.alloc<PodNil>());

    return Nil(TRY(MkGcRoot(pod, arena)));
  }

  virtual Result<Value> copy(Arena& arena) final;

 private:
  GcRoot<PodNil> _value;
};

class String : public Object {
 public:
  String() {}
  String(GcRoot<PodString>&& val) : _value(std::move(val)) {}
  virtual Tag tag() final { return Tag::String; }
  virtual PodObject* pod() final { return _value.get(); }

  static Result<String> create(Arena& arena, PodString* obj) {
    return String(TRY(MkGcRoot(obj, arena)));
  }
  static Result<String> create(Arena& arena, char32_t* chars, int64_t size) {
    auto pod_string = TRY(arena.alloc<PodString>(size * sizeof(char32_t)));

    memcpy(pod_string->data, chars, size * sizeof(char32_t));
    pod_string->size = size;

    return String(TRY(MkGcRoot(pod_string, arena)));
  }

  static Result<String> create(Arena& arena, const char* str) {
    uint64_t size = strlen(str);
    auto pod_string = TRY(arena.alloc<PodString>(size * sizeof(char32_t)));

    for (uint64_t i = 0; i < size; i++) pod_string->data[i] = str[i];
    pod_string->size = size;

    return String(TRY(MkGcRoot(pod_string, arena)));
  }

  uint64_t size() { return _value->size; }

  Result<char32_t> operator[](uint64_t idx) {
    if (idx >= _value->size) return ErrorCode::IndexOutOfRange;
    return _value->data[idx];
  }

  virtual Result<Value> copy(Arena& arena) final;

 private:
  GcRoot<PodString> _value;
};

class Symbol : public Object {
 public:
  Symbol() {}
  Symbol(GcRoot<PodSymbol>&& val) : _value(std::move(val)) {}
  virtual Tag tag() final { return Tag::Symbol; }
  virtual PodObject* pod() final { return _value.get(); }

  static Result<Symbol> create(Arena& arena, PodSymbol* obj) {
    return Symbol(TRY(MkGcRoot(obj, arena)));
  }

  static Result<Symbol> create(Arena& arena, char32_t* chars, int64_t size) {
    auto pod_symbol = TRY(arena.alloc<PodSymbol>(size * sizeof(char32_t)));

    memcpy(pod_symbol->data, chars, size * sizeof(char32_t));

    return Symbol(TRY(MkGcRoot(pod_symbol, arena)));
  }

  virtual Result<Value> copy(Arena& arena) final;

 private:
  GcRoot<PodSymbol> _value;
};

class Syntax : public Object {
 public:
  Syntax() {}
  Syntax(GcRoot<PodSyntax>&& val) : _value(std::move(val)) {}
  Syntax(String filename, String modulename, Value expression);
  virtual Tag tag() final { return Tag::Syntax; }
  virtual PodObject* pod() final { return _value.get(); }

  static Result<Syntax> create(Arena& arena, PodSyntax* obj) {
    return Syntax(TRY(MkGcRoot(obj, arena)));
  }

  Result<Value> get_value(Arena& arena);

  virtual Result<Value> copy(Arena& arena) final;

 private:
  GcRoot<PodSyntax> _value;
};

class Pair : public Object {
 public:
  Pair() {}
  Pair(GcRoot<PodPair>&& val) : _value(std::move(val)) {}
  virtual Tag tag() final { return Tag::Pair; }
  virtual PodObject* pod() final { return _value.get(); }

  static Result<Pair> create(Arena& arena, PodPair* obj) {
    return Pair(TRY(MkGcRoot(obj, arena)));
  }
  static Result<Pair> create(Arena& arena, Value& first, Value& rest);

  Result<Value> first(Arena& arena);
  Result<Value> rest(Arena& arena);

  virtual Result<Value> copy(Arena& arena) final;

 private:
  GcRoot<PodPair> _value;
};

class Int64 : public Object {
 public:
  Int64() {}
  Int64(GcRoot<PodInt64>&& val) : _value(std::move(val)) {}
  virtual Tag tag() final { return Tag::Int64; }
  virtual PodObject* pod() final { return _value.get(); }

  static Result<Int64> create(Arena& arena, PodInt64* obj) {
    return Int64(TRY(MkGcRoot(obj, arena)));
  }

  static Result<Int64> create(Arena& arena, double val) {
    auto pod = TRY(arena.alloc<PodInt64>());
    pod->value = val;

    return Int64(TRY(MkGcRoot(pod, arena)));
  }

  int64_t value() { return _value->value; }

  virtual Result<Value> copy(Arena& arena) final;

 private:
  GcRoot<PodInt64> _value;
};

class Float : public Object {
 public:
  Float() {}
  Float(GcRoot<PodFloat>&& val) : _value(std::move(val)) {}
  virtual Tag tag() final { return Tag::Float; }
  virtual PodObject* pod() final { return _value.get(); }

  static Result<Float> create(Arena& arena, PodFloat* obj) {
    return Float(TRY(MkGcRoot(obj, arena)));
  }

  static Result<Float> create(Arena& arena, double val) {
    auto pod = TRY(arena.alloc<PodFloat>());
    pod->value = val;

    return Float(TRY(MkGcRoot(pod, arena)));
  }

  double value() { return _value->value; }

  virtual Result<Value> copy(Arena& arena) final;

 private:
  GcRoot<PodFloat> _value;
};

// note: this class doesn't perform proper destruction of objects in some cases
class Value {
 public:
  Value() { new (buf) Nil(); }
  ~Value() { ((Object*)buf)->~Object(); }
  Value(Value&& val) {
    memcpy(buf, val.buf, 24);
    new (val.buf) Nil();
  }
  Value(const Value&) = delete;

  template <class T>
  Value(T&& obj)
    requires std::derived_from<T, Object>
  {
    new (buf) T(std::move(obj));
  }

  Value& operator=(Value&& val) {
    memcpy(buf, val.buf, 24);
    new (val.buf) Nil();
    return *this;
  }

  static Result<Value> create(Arena& arena, PodObject* obj);

  template <class T>
  bool is() {
    return dynamic_cast<T*>((Object*)buf) != nullptr;
  }

  template <class T>
  T* to() {
    return dynamic_cast<T*>((Object*)buf);
  }

  PodObject* pod() { return ((Object*)buf)->pod(); }

  Object& operator*() { return *(Object*)(buf); }
  Object* operator->() { return (Object*)(buf); }

  Result<Value> copy(Arena& arena) { return ((Object*)buf)->copy(arena); }

 private:
  uint8_t buf[24];
};

Result<Value> syntax_unwrap(Value& val);

Result<Value> reverse(Arena& arena, Value& val);