/*
 * Copyright 2019 WebAssembly Community Group participants
 *
 * 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.
 */

#include "wasm-debug.h"
#include "wasm.h"

#ifdef BUILD_LLVM_DWARF
#include "llvm/ObjectYAML/DWARFEmitter.h"
#include "llvm/ObjectYAML/DWARFYAML.h"
#include "llvm/include/llvm/DebugInfo/DWARFContext.h"

std::error_code dwarf2yaml(llvm::DWARFContext& DCtx, llvm::DWARFYAML::Data& Y);
#endif

namespace wasm {

namespace Debug {

bool isDWARFSection(Name name) { return name.startsWith(".debug_"); }

bool hasDWARFSections(const Module& wasm) {
  for (auto& section : wasm.userSections) {
    if (isDWARFSection(section.name)) {
      return true;
    }
  }
  return false;
}

#ifdef BUILD_LLVM_DWARF

struct BinaryenDWARFInfo {
  llvm::StringMap<std::unique_ptr<llvm::MemoryBuffer>> sections;
  std::unique_ptr<llvm::DWARFContext> context;

  BinaryenDWARFInfo(const Module& wasm) {
    // Get debug sections from the wasm.
    for (auto& section : wasm.userSections) {
      if (Name(section.name).startsWith(".debug_")) {
        // TODO: efficiency
        sections[section.name.substr(1)] = llvm::MemoryBuffer::getMemBufferCopy(
          llvm::StringRef(section.data.data(), section.data.size()));
      }
    }
    // Parse debug sections.
    uint8_t addrSize = 4;
    context = llvm::DWARFContext::create(sections, addrSize);
  }
};

void dumpDWARF(const Module& wasm) {
  BinaryenDWARFInfo info(wasm);
  std::cout << "DWARF debug info\n";
  std::cout << "================\n\n";
  for (auto& section : wasm.userSections) {
    if (Name(section.name).startsWith(".debug_")) {
      std::cout << "Contains section " << section.name << " ("
                << section.data.size() << " bytes)\n";
    }
  }
  llvm::DIDumpOptions options;
  options.Verbose = true;
  info.context->dump(llvm::outs(), options);
}

//
// Big picture: We use a DWARFContext to read data, then DWARFYAML support
// code to write it. That is not the main LLVM Dwarf code used for writing
// object files, but it avoids us create a "fake" MC layer, and provides a
// simple way to write out the debug info. Likely the level of info represented
// in the DWARFYAML::Data object is sufficient for Binaryen's needs, but if not,
// we may need a different approach.
//
// In more detail:
//
// 1. Binary sections => DWARFContext:
//
//     llvm::DWARFContext::create(sections..)
//
// 2. DWARFContext => DWARFYAML::Data
//
//     std::error_code dwarf2yaml(DWARFContext &DCtx, DWARFYAML::Data &Y) {
//
// 3. DWARFYAML::Data => binary sections
//
//     StringMap<std::unique_ptr<MemoryBuffer>>
//     EmitDebugSections(llvm::DWARFYAML::Data &DI, bool ApplyFixups);
//
// For modifying data, like line numberes, we can in theory do that either on
// the DWARFContext or DWARFYAML::Data; unclear which is best, but modifying
// the DWARFContext may save us doing fixups in EmitDebugSections.
//

void writeDWARFSections(Module& wasm) {
  BinaryenDWARFInfo info(wasm);

  // Convert to Data representation, which YAML can use to write.
  llvm::DWARFYAML::Data Data;
  if (dwarf2yaml(*info.context, Data)) {
    Fatal() << "Failed to parse DWARF to YAML";
  }

  // TODO: Actually update, and remove sections we don't know how to update yet?

  // Convert to binary sections.
  auto newSections = EmitDebugSections(
    Data,
    false /* ApplyFixups, should be true if we modify Data, presumably? */);

  // Update the custom sections in the wasm.
  // TODO: efficiency
  for (auto& section : wasm.userSections) {
    if (Name(section.name).startsWith(".debug_")) {
      auto llvmName = section.name.substr(1);
      if (newSections.count(llvmName)) {
        auto llvmData = newSections[llvmName]->getBuffer();
        section.data.resize(llvmData.size());
        std::copy(llvmData.begin(), llvmData.end(), section.data.data());
      }
    }
  }
}

#else // BUILD_LLVM_DWARF

void dumpDWARF(const Module& wasm) {
  std::cerr << "warning: no DWARF dumping support present\n";
}

void writeDWARFSections(Module& wasm) {
  std::cerr << "warning: no DWARF updating support present\n";
}

#endif // BUILD_LLVM_DWARF

} // namespace Debug

} // namespace wasm