// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "src/developer/debug/zxdb/expr/expr_tokenizer.h"

#include <ctype.h>

#include <type_traits>

#include "src/lib/fxl/logging.h"
#include "src/lib/fxl/strings/string_printf.h"

namespace zxdb {

namespace {

bool IsNameFirstChar(char c) {
  // Note that "@" is used to annotate some special things:
  //  - "PLT" breakpoints which are breakpoints set on ELF imports rather than
  //    DWARF symbols (for example, "__stack_chk_fail@plt"). So it needs to
  //    count as a name character. This
  //  - "@main" special location for the program entrypoint.
  //    can be changed in the future if we have a better way of identifying
  //    these.
  return (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') || c == '_' || c == '~' || c == '@';
}

bool IsNameContinuingChar(char c) { return IsNameFirstChar(c) || (c >= '0' && c <= '9'); }

bool IsIntegerFirstChar(char c) { return isdigit(c); }

// This allows all alphanumeric characters for simplicity. Integer literals
// aren't validated at the tokenizer level and will be checked later. Our job
// is to find the extent of the literal.
bool IsIntegerContinuingChar(char c) { return isalnum(c); }

// Returns a list of all tokens sharing the given first character.
const std::vector<const ExprTokenRecord*>& TokensWithFirstChar(char c) {
  // Lookup table for all 7-bit characters.
  constexpr unsigned char kMaxLookupChar = 0x80;
  static std::vector<const ExprTokenRecord*> mapping[kMaxLookupChar];
  static bool initialized = false;

  if (!initialized) {
    // Construct the lookup table.
    initialized = true;
    for (size_t i = 0; i < kNumExprTokenTypes; i++) {
      const ExprTokenRecord& record = RecordForTokenType(static_cast<ExprTokenType>(i));
      if (!record.static_value.empty())
        mapping[static_cast<size_t>(record.static_value[0])].push_back(&record);
    }
  }

  if (static_cast<unsigned char>(c) >= kMaxLookupChar) {
    static std::vector<const ExprTokenRecord*> empty_records;
    return empty_records;
  }
  return mapping[static_cast<size_t>(c)];
}

}  // namespace

ExprTokenizer::ExprTokenizer(const std::string& input, ExprLanguage lang)
    : input_(input), language_(lang) {}

bool ExprTokenizer::Tokenize() {
  while (!done()) {
    AdvanceToNextToken();
    if (done())
      break;

    const ExprTokenRecord& record = ClassifyCurrent();
    if (has_error())
      break;

    size_t token_begin = cur_;
    AdvanceToEndOfToken(record);
    if (has_error())
      break;

    size_t token_end = cur_;
    std::string token_value(&input_[token_begin], token_end - token_begin);
    tokens_.emplace_back(record.type, token_value, token_begin);
  }
  return !has_error();
}

// static
std::string ExprTokenizer::GetErrorContext(const std::string& input, size_t byte_offset) {
  // Index should be in range of the input string. Also allow indicating one
  // character past the end.
  FXL_DCHECK(byte_offset <= input.size());

  // Future enhancements:
  // - If we allow multiline expressions in the, the returned context should
  //   not cross newlines or it will be messed up.
  // - Input longer than 80 chars should be clipped to guarantee it doesn't
  //   wrap.

  std::string output;
  output = "  " + input + "\n  ";
  output.append(byte_offset, ' ');
  output.push_back('^');
  return output;
}

void ExprTokenizer::AdvanceChars(int n) { cur_ += n; }

void ExprTokenizer::AdvanceOneChar() { cur_++; }

void ExprTokenizer::AdvanceToNextToken() {
  while (!at_end() && IsCurrentWhitespace())
    AdvanceOneChar();
}

void ExprTokenizer::AdvanceToEndOfToken(const ExprTokenRecord& record) {
  if (!record.static_value.empty()) {
    // Known sizes. Because the token matched we should always have enough
    // characters.
    FXL_DCHECK(input_.size() >= cur_ + record.static_value.size());
    cur_ += record.static_value.size();
    return;
  }

  // Manually advance over variable-length tokens.
  switch (record.type) {
    case ExprTokenType::kInteger:
      do {
        AdvanceOneChar();
      } while (!at_end() && IsIntegerContinuingChar(cur_char()));
      break;

    case ExprTokenType::kName:
      do {
        AdvanceOneChar();
      } while (!at_end() && IsNameContinuingChar(cur_char()));
      break;

    default:
      FXL_NOTREACHED();
      err_ = Err("Internal parser error.");
      error_location_ = cur_;
      break;
  }
}

bool ExprTokenizer::CurrentMatchesTokenRecord(const ExprTokenRecord& record) const {
  // Non-statically-known tokens shouldn't use this code path.
  FXL_DCHECK(!record.static_value.empty());

  const size_t size = record.static_value.size();
  if (!can_advance(size))
    return false;  // Not enought room.

  if (!(record.languages & static_cast<unsigned>(language_)))
    return false;  // Doesn't apply to this language.

  if (std::string_view(&input_[cur_], size) != record.static_value)
    return false;  // Doesn't match the token static value.

  if (record.is_alphanum) {
    if (cur_ + size < input_.size() && isalnum(input_[cur_ + size]))
      return false;  // Alphanumeric character follows so won't match.
  }

  return true;
}

bool ExprTokenizer::IsCurrentWhitespace() const {
  FXL_DCHECK(!at_end());
  char c = input_[cur_];
  return c == 0x0A || c == 0x0D || c == 0x20;
}

const ExprTokenRecord& ExprTokenizer::ClassifyCurrent() {
  FXL_DCHECK(!at_end());
  char cur = cur_char();

  const ExprTokenRecord* longest = nullptr;
  for (const ExprTokenRecord* match : TokensWithFirstChar(cur)) {
    if (!CurrentMatchesTokenRecord(*match))
      continue;

    if (!longest || match->static_value.size() > longest->static_value.size())
      longest = match;
  }

  if (longest)
    return *longest;

  // Numbers.
  if (IsIntegerFirstChar(cur))
    return RecordForTokenType(ExprTokenType::kInteger);

  // Everything else is a general name.
  if (IsNameFirstChar(cur)) {
    return RecordForTokenType(ExprTokenType::kName);
  }

  error_location_ = cur_;
  err_ = Err(fxl::StringPrintf("Invalid character '%c' in expression.\n", cur) +
             GetErrorContext(input_, cur_));
  return RecordForTokenType(ExprTokenType::kInvalid);
}

}  // namespace zxdb