// Copyright (c) 2024 PaddlePaddle Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#pragma once
#include <atomic>
#include <map>
#include "paddle/ap/include/axpr/anf_expr_builder.h"
#include "paddle/ap/include/axpr/core_expr.h"
#include "paddle/common/enforce.h"

namespace ap::axpr {

class LetContext;

class LetVar {
 public:
  LetVar(const LetVar&) = default;
  LetVar(LetVar&&) = default;

  LetVar& operator=(const LetVar& let_var);
  LetVar& operator=(const AnfExpr& anf_val);

  const std::string& name() const { return name_; }

  operator Atomic<AnfExpr>() const { return tVar<std::string>{name()}; }

  LetVar& Attr(const std::string& attr_name) {
    return AttrImpl(Atomic<AnfExpr>{attr_name});
  }
  LetVar& Attr(const LetVar& attr_name) {
    return AttrImpl(static_cast<Atomic<AnfExpr>>(attr_name));
  }
  void SetAttr(const std::string& attr_name, const AnfExpr& anf_expr) {
    return SetAttrImpl(Atomic<AnfExpr>{attr_name}, anf_expr);
  }
  void SetAttr(const LetVar& attr_name, const AnfExpr& anf_expr) {
    return SetAttrImpl(static_cast<Atomic<AnfExpr>>(attr_name), anf_expr);
  }
  void SetAttrImpl(const Atomic<AnfExpr>& attr_name, const AnfExpr& anf_expr);
  LetVar& At(int64_t idx);
  LetVar& At(const Atomic<AnfExpr>& idx);

  template <typename... Args>
  LetVar& Call(Args&&... args);

  template <typename... Args>
  LetVar& Apply(Args&&... args);

  LetContext* ctx() const { return let_ctx_; }

 private:
  friend class LetContext;
  LetVar(LetContext* let_ctx, const std::string& name)
      : let_ctx_(let_ctx), name_(name) {}

  LetVar& AttrImpl(const Atomic<AnfExpr>& attr_name);

  LetContext* let_ctx_;
  std::string name_;
};

class LetContext : public AtomicExprBuilder<AnfExpr> {
 public:
  explicit LetContext(const std::function<size_t()>& SeqNoGenerator)
      : SeqNoGenerator_(SeqNoGenerator) {}
  LetContext(const LetContext&) = delete;
  LetContext(LetContext&&) = delete;

  using var_type = LetVar;

  LetVar& Var(const std::string& name) {
    auto iter = let_var_storage_.find(name);
    if (iter == let_var_storage_.end()) {
      auto var = std::unique_ptr<LetVar>(new LetVar(this, name));
      iter = let_var_storage_.emplace(name, std::move(var)).first;
    }
    return *iter->second;
  }

  template <typename Arg0, typename... Args>
  AnfExpr Call(const LetVar& f, Arg0 arg0, Args&&... args) {
    return ApplyImpl(f.name(),
                     std::vector<AnfExpr>{std::forward<Arg0>(arg0),
                                          std::forward<Args>(args)...});
  }

  template <typename Arg0, typename... Args>
  AnfExpr Call(const std::string& f, Arg0 arg0, Args&&... args) {
    return ApplyImpl(f,
                     std::vector<AnfExpr>{std::forward<Arg0>(arg0),
                                          std::forward<Args>(args)...});
  }

  AnfExpr Call(const LetVar& f) {
    return ApplyImpl(f.name(), std::vector<AnfExpr>{});
  }

  AnfExpr Call(const std::string& f) {
    return ApplyImpl(f, std::vector<AnfExpr>{});
  }

  AnfExpr Apply(const LetVar& f, const std::vector<LetVar>& vars) {
    return Apply(f.name(), vars);
  }

  AnfExpr Apply(const std::string& f, const std::vector<LetVar>& vars) {
    std::vector<AnfExpr> args;
    args.reserve(vars.size());
    for (const auto& var : vars) {
      args.emplace_back(var);
    }
    return ApplyImpl(f, args);
  }

  AnfExpr Apply(const LetVar& f, const std::vector<AnfExpr>& args) {
    return ApplyImpl(f.name(), args);
  }

  AnfExpr Apply(const std::string& f, const std::vector<AnfExpr>& args) {
    return ApplyImpl(f, args);
  }

  AnfExpr Apply(const LetVar& f,
                const std::vector<AnfExpr>& args,
                const std::map<std::string, AnfExpr>& kwargs) {
    return Apply(f.name(), args, kwargs);
  }

  AnfExpr Apply(const LetVar& f, const std::map<std::string, AnfExpr>& kwargs) {
    return Apply(f.name(), std::vector<AnfExpr>{}, kwargs);
  }

  AnfExpr Apply(const std::string& f,
                const std::vector<AnfExpr>& args,
                const std::map<std::string, AnfExpr>& kwargs) {
    std::vector<AnfExpr> kwarg_list;
    for (const auto& [keyword, val] : kwargs) {
      const AnfExpr& item =
          this->Call(ap::axpr::kBuiltinList(), this->String(keyword), val);
      kwarg_list.emplace_back(item);
    }
    const AnfExpr& packed_args =
        this->Call(this->Var("__builtin_PackedArgs__"),
                   this->Apply(ap::axpr::kBuiltinList(), args),
                   this->Apply(ap::axpr::kBuiltinList(), kwarg_list));
    return this->Call(f, packed_args);
  }

  LetVar& Attr(const AnfExpr& self, const std::string& attr_name) {
    const auto& var_name = NewTmpVarName();
    Var(var_name) = self;
    return Var(var_name).Attr(attr_name);
  }

  const std::vector<Bind<AnfExpr>>& bindings() { return bindings_; }

  std::string NewTmpVarName() {
    static const std::string prefix = "___";
    return prefix + std::to_string(SeqNoGenerator_());
  }

 private:
  friend class LetVar;

  AnfExpr ApplyImpl(const std::string& f, const std::vector<AnfExpr>& args) {
    std::vector<Atomic<AnfExpr>> atomic_args;
    atomic_args.reserve(args.size());
    for (const auto& anf_expr : args) {
      anf_expr.Match(
          [&](const Atomic<AnfExpr>& atomic) { atomic_args.push_back(atomic); },
          [&](const auto&) { atomic_args.push_back(BindToTmpVar(anf_expr)); });
    }
    return AnfExprBuilder().Call(tVar<std::string>{f}, atomic_args);
  }

  tVar<std::string> BindToTmpVar(const AnfExpr& anf_val) {
    const tVar<std::string> tmp_var_name{NewTmpVarName()};
    AddBinding(tmp_var_name.value(), anf_val);
    return tmp_var_name;
  }

  void AddBinding(const std::string& name, const AnfExpr& anf_val) {
    AnfExprBuilder anf;
    anf_val.Match(
        [&](const Atomic<AnfExpr>& atomic) {
          const auto& combined =
              anf.Call(tVar<std::string>{kBuiltinIdentity()}, {atomic});
          bindings_.push_back(anf.Bind(name, combined));
        },
        [&](const Combined<AnfExpr>& combined) {
          bindings_.push_back(anf.Bind(name, combined));
        },
        [&](const Let<AnfExpr>& let) {
          const auto& lambda = anf.Lambda({}, let);
          const auto& combined = anf.Call(lambda, {});
          bindings_.push_back(anf.Bind(name, combined));
        });
  }

  std::unordered_map<std::string, std::unique_ptr<LetVar>> let_var_storage_;
  std::vector<Bind<AnfExpr>> bindings_;
  std::function<size_t()> SeqNoGenerator_;
};

inline LetVar& LetVar::operator=(const LetVar& let_var) {
  AnfExprBuilder anf{};
  return *this = anf.Call(tVar<std::string>{kBuiltinIdentity()},
                          {tVar<std::string>{let_var.name()}});
}

inline LetVar& LetVar::operator=(const AnfExpr& anf_val) {
  let_ctx_->AddBinding(name_, anf_val);
  return *this;
}

inline LetVar& LetVar::AttrImpl(const Atomic<AnfExpr>& attr_name) {
  AnfExprBuilder anf{};
  AnfExpr anf_expr = anf.Call(tVar<std::string>{kBuiltinGetAttr()},
                              {tVar<std::string>{name()}, attr_name});
  return let_ctx_->Var(let_ctx_->BindToTmpVar(anf_expr).value());
}

inline void LetVar::SetAttrImpl(const Atomic<AnfExpr>& attr_name,
                                const AnfExpr& val) {
  const auto& atomic = val.Match(
      [&](const Atomic<AnfExpr>& atomic_val) -> Atomic<AnfExpr> {
        return atomic_val;
      },
      [&](const auto& impl) -> Atomic<AnfExpr> {
        return let_ctx_->BindToTmpVar(val);
      });
  AnfExprBuilder anf{};
  const auto& method_anf_expr =
      anf.Call(tVar<std::string>{kBuiltinSetAttr()},
               {tVar<std::string>{name()}, attr_name});
  const auto& method = let_ctx_->BindToTmpVar(method_anf_expr);
  AnfExpr anf_expr = anf.Call(method, {attr_name, atomic});
  let_ctx_->BindToTmpVar(anf_expr);
}

inline LetVar& LetVar::At(int64_t idx) {
  AnfExprBuilder anf{};
  AnfExpr anf_expr = anf.Call(tVar<std::string>{kBuiltinGetItem()},
                              {tVar<std::string>{name()}, anf.Int64(idx)});
  return let_ctx_->Var(let_ctx_->BindToTmpVar(anf_expr).value());
}

inline LetVar& LetVar::At(const Atomic<AnfExpr>& idx) {
  AnfExprBuilder anf{};
  AnfExpr anf_expr = anf.Call(tVar<std::string>{kBuiltinGetItem()},
                              {tVar<std::string>{name()}, idx});
  return let_ctx_->Var(let_ctx_->BindToTmpVar(anf_expr).value());
}

template <typename... Args>
inline LetVar& LetVar::Call(Args&&... args) {
  const auto& anf_expr = let_ctx_->Call(*this, std::forward<Args>(args)...);
  return let_ctx_->Var(let_ctx_->BindToTmpVar(anf_expr).value());
}

template <typename... Args>
inline LetVar& LetVar::Apply(Args&&... args) {
  const auto& anf_expr = let_ctx_->Apply(*this, std::forward<Args>(args)...);
  return let_ctx_->Var(let_ctx_->BindToTmpVar(anf_expr).value());
}

class LambdaExprBuilder {
 public:
  LambdaExprBuilder() : SeqNoGenerator_(&LambdaExprBuilder::GenSeqNo) {}
  explicit LambdaExprBuilder(const std::function<size_t()>& SeqNoGenerator)
      : SeqNoGenerator_(SeqNoGenerator) {}
  LambdaExprBuilder(const LambdaExprBuilder&) = delete;
  LambdaExprBuilder(LambdaExprBuilder&&) = delete;

  AnfExpr Lambda(const std::vector<std::string>& args,
                 const std::function<AnfExpr(LetContext&)>& GetBody) {
    AnfExpr anf_expr = Let(GetBody);
    AnfExpr lambda_or_body = anf_expr.Match(
        [&](const ap::axpr::Let<AnfExpr>& let) {
          if (let->bindings.empty()) {
            return let->body;
          } else {
            return anf_expr;
          }
        },
        [&](const auto&) { return anf_expr; });
    return anf_.Lambda(MakeLambdaArgs(args), lambda_or_body);
  }

  AnfExpr Let(const std::function<AnfExpr(LetContext&)>& GetBody) {
    LetContext let_ctx{SeqNoGenerator_};
    AnfExpr ret = GetBody(let_ctx);
    return anf_.Let(let_ctx.bindings(), ret);
  }

  adt::Result<AnfExpr> TryLambda(
      const std::vector<std::string>& args,
      const std::function<adt::Result<AnfExpr>(LetContext&)>& GetBody) {
    ADT_LET_CONST_REF(anf_expr, TryLet(GetBody));
    AnfExpr lambda_or_body = anf_expr.Match(
        [&](const ap::axpr::Let<AnfExpr>& let) {
          if (let->bindings.empty()) {
            return let->body;
          } else {
            return anf_expr;
          }
        },
        [&](const auto&) { return anf_expr; });
    return anf_.Lambda(MakeLambdaArgs(args), lambda_or_body);
  }

  adt::Result<AnfExpr> TryLet(
      const std::function<adt::Result<AnfExpr>(LetContext&)>& GetBody) {
    LetContext let_ctx{SeqNoGenerator_};
    ADT_LET_CONST_REF(ret, GetBody(let_ctx));
    return anf_.Let(let_ctx.bindings(), ret);
  }

  std::vector<tVar<std::string>> MakeLambdaArgs(
      const std::vector<std::string>& args) {
    std::vector<tVar<std::string>> lambda_args;
    lambda_args.reserve(args.size());
    for (const auto& arg : args) {
      lambda_args.emplace_back(arg);
    }
    return lambda_args;
  }

 private:
  static size_t GenSeqNo() {
    static std::atomic<int64_t> seq_no(0);
    return seq_no++;
  }

  std::function<size_t()> SeqNoGenerator_;
  AnfExprBuilder anf_;
};

}  // namespace ap::axpr