// Copyright 2021 Benjamin Barenblat
//
// 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
//
//     https://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 "goldfishterm/terminfo.h"

#include <byteswap.h>
#include <stdint.h>
#include <stdlib.h>

#include <fstream>
#include <istream>
#include <stdexcept>
#include <string>
#include <vector>

#include "third_party/abseil/absl/base/config.h"
#include "third_party/abseil/absl/meta/type_traits.h"
#include "third_party/abseil/absl/strings/str_cat.h"
#include "third_party/abseil/absl/strings/str_format.h"
#include "third_party/abseil/absl/strings/str_split.h"
#include "third_party/abseil/absl/types/optional.h"

namespace goldfishterm {

namespace {

constexpr int16_t kTerminfoMagic = 0432;
constexpr int16_t kTerminfoExtendedNumberFormatMagic = 01036;
constexpr char kSystemTerminfoDirectory[] = "/etc/terminfo";

template <typename T>
constexpr absl::underlying_type_t<T> FromEnum(T x) {
  return static_cast<absl::underlying_type_t<T>>(x);
}

std::string GetEnv(const char* var) noexcept {
  const char* val = getenv(var);
  if (val == nullptr) {
    return "";
  }
  return val;
}

// Reads a potentially unaligned little-endian int16_t.
int16_t ReadShort(std::istream& in) {
  // TODO(bbarenblat@gmail.com): Do we need to support anything else here (maybe
  // PDP-11-endian)?
#if !defined(ABSL_IS_LITTLE_ENDIAN) && !defined(ABSL_IS_BIG_ENDIAN)
#error Neither ABSL_IS_LITTLE_ENDIAN nor ABSL_IS_BIG_ENDIAN is defined
#endif

  int16_t n;
  in.read(reinterpret_cast<char*>(&n), sizeof(int16_t));
#ifdef ABSL_IS_BIG_ENDIAN
  n = bswap_16(n);
#endif
  return n;
}

// Reads a potentially unaligned little-endian int32_t.
int32_t ReadInt(std::istream& in) {
  // TODO(bbarenblat@gmail.com): Do we need to support anything else here (maybe
  // PDP-11-endian)?
#if !defined(ABSL_IS_LITTLE_ENDIAN) && !defined(ABSL_IS_BIG_ENDIAN)
#error Neither ABSL_IS_LITTLE_ENDIAN nor ABSL_IS_BIG_ENDIAN is defined
#endif

  int32_t n;
  in.read(reinterpret_cast<char*>(&n), sizeof(int32_t));
#ifdef ABSL_IS_BIG_ENDIAN
  n = bswap_32(n);
#endif
  return n;
}

int16_t ReadNonnegativeShort(const char* error_message, std::istream& in) {
  int16_t n = ReadShort(in);
  if (n < 0) {
    throw std::runtime_error(error_message);
  }
  return n;
}

void RequireValidNumber(const char* error_message, int n) {
  // -1 and -2 are reserved to mean "not present" and "canceled", respectively.
  if (n < -2) {
    throw std::runtime_error(absl::StrCat(error_message, " ", n));
  }
}

struct Header final {
  bool extended_number_format;
  int names_bytes;
  int booleans_bytes;
  int numbers_count;
  int strings_offsets_count;
  int strings_bytes;

  Header(std::istream& description) {
    switch (ReadShort(description)) {
      case kTerminfoMagic:
        extended_number_format = false;
        break;
      case kTerminfoExtendedNumberFormatMagic:
        extended_number_format = true;
        break;
      default:
        throw std::runtime_error("bad magic");
    }
    names_bytes = ReadNonnegativeShort(
        "terminal names section cannot have negative length", description);
    booleans_bytes = ReadNonnegativeShort(
        "boolean flags section cannot have negative length", description);
    numbers_count = ReadNonnegativeShort(
        "numbers section cannot have negative length", description);
    strings_offsets_count = ReadNonnegativeShort(
        "strings section cannot have negative numbers of entries", description);
    strings_bytes = ReadNonnegativeShort(
        "strings table cannot have negative length", description);
  }
};

std::vector<std::string> ReadTerminalNames(int bytes, std::istream& in) {
  assert(bytes > 0);
  std::string names(bytes - 1, '\0');
  in.read(names.data(), names.size());
  // Discard the null at the end of the names list.
  if (in.get() != '\0') {
    throw std::runtime_error("terminal names were not null-terminated");
  }
  return absl::StrSplit(names, '|');
}

std::vector<int8_t> ReadBooleanFlags(int bytes, std::istream& in) {
  std::vector<int8_t> booleans(bytes);
  in.read(reinterpret_cast<char*>(booleans.data()), booleans.size());
  for (int8_t b : booleans) {
    RequireValidNumber("invalid boolean capability", b);
  }
  return booleans;
}

std::vector<int32_t> ReadNumbers(bool extended_number_format, int count,
                                 std::istream& in) {
  std::vector<int32_t> numbers;
  numbers.reserve(count);
  for (int i = 0; i < count; ++i) {
    int32_t n;
    if (extended_number_format) {
      n = ReadInt(in);
    } else {
      n = ReadShort(in);
    }
    RequireValidNumber("invalid numeric capability", n);
    numbers.push_back(n);
  }
  return numbers;
}

std::vector<absl::optional<std::string>> ReadStrings(int offsets_count,
                                                     int bytes,
                                                     std::istream& in) {
  std::vector<int16_t> offsets;
  offsets.reserve(offsets_count);
  for (int i = 0; i < offsets_count; ++i) {
    int16_t n = ReadShort(in);
    RequireValidNumber("invalid string offset", n);
    offsets.push_back(n);
  }

  // Read the string table, including the trailing null (so we can easily find
  // the end of each capability).
  std::string data(bytes, '\0');
  in.read(data.data(), data.size());

  std::vector<absl::optional<std::string>> result;
  for (int16_t offset : offsets) {
    if (offset < 0) {
      result.push_back(absl::nullopt);
    } else {
      result.push_back(std::string(data.data() + offset));
    }
  }
  return result;
}

std::vector<std::string> DatabasePaths() noexcept {
  // If TERMINFO is set, only look there.
  if (std::string terminfo = GetEnv("TERMINFO"); !terminfo.empty()) {
    return {terminfo};
  }

  std::vector<std::string> paths;

  // Start by looking in HOME.
  if (std::string home = GetEnv("HOME"); !home.empty()) {
    paths.push_back(absl::StrCat(home, "/.terminfo"));
  }

  // Next, look in TERMINFO_DIRS.
  if (std::string terminfo_dirs = GetEnv("TERMINFO_DIRS");
      !terminfo_dirs.empty()) {
    for (absl::string_view dir : absl::StrSplit(terminfo_dirs, ':')) {
      if (dir.empty()) {
        paths.push_back(kSystemTerminfoDirectory);
      } else {
        paths.push_back(std::string(dir));
      }
    }
  }

  // Finally, look in system locations.
  paths.push_back(kSystemTerminfoDirectory);
  paths.push_back("/lib/terminfo");
  paths.push_back("/usr/share/terminfo");

  return paths;
}

std::ifstream OpenDescriptionForTerminal(absl::string_view db_path,
                                         absl::string_view name) {
  // The path to the terminal entry inside the database takes the general form
  // `c/name`, where c is the first character of the name (on file systems that
  // are case-sensitive) and the hex encoding of the name (on file systems that
  // are not).

  if (name.empty()) {
    throw std::invalid_argument("empty terminal name");
  }

  std::ifstream entry(absl::StrFormat("%s/%02x/%s", db_path, name[0], name));
  if (!entry.fail()) {
    return entry;
  }

  entry = std::ifstream(absl::StrFormat("%s/%c/%s", db_path, name[0], name));
  if (!entry.fail()) {
    return entry;
  }

  throw std::runtime_error("terminfo entry not found");
}

}  // namespace

TerminfoEntry TerminfoEntry::FromSystemDatabase(
    absl::string_view terminal_name) {
  for (const auto& path : DatabasePaths()) {
    try {
      std::ifstream binary = OpenDescriptionForTerminal(path, terminal_name);
      return TerminfoEntry(binary);
    } catch (const std::runtime_error&) {
      continue;
    }
  }
  throw std::runtime_error("no valid system entry by that name");
}

TerminfoEntry::TerminfoEntry(std::istream& description) {
  description.exceptions(std::istream::badbit | std::istream::failbit);

  Header header(description);
  if (header.names_bytes > 0) {
    names_ = ReadTerminalNames(header.names_bytes, description);
  }
  booleans_ = ReadBooleanFlags(header.booleans_bytes, description);

  // Discard the padding byte between the boolean flags section and the number
  // section, if it exists.
  if ((header.names_bytes + header.booleans_bytes) % 2 == 1 &&
      (header.numbers_count != 0 || header.strings_offsets_count != 0 ||
       header.strings_bytes != 0) &&
      description.get() != '\0') {
    throw std::runtime_error("padding byte was nonnull");
  }

  numbers_ = ReadNumbers(header.extended_number_format, header.numbers_count,
                         description);
  strings_ = ReadStrings(header.strings_offsets_count, header.strings_bytes,
                         description);
}

bool TerminfoEntry::get(BooleanCapability cap) const noexcept {
  try {
    return booleans_.at(FromEnum(cap)) > 0;
  } catch (const std::out_of_range&) {
    return false;
  }
}

absl::optional<int> TerminfoEntry::get(NumericCapability cap) const noexcept {
  try {
    int r = numbers_.at(FromEnum(cap));
    if (r >= 0) {
      return r;
    } else {
      return absl::nullopt;
    }
  } catch (const std::out_of_range&) {
    return absl::nullopt;
  }
}

const absl::optional<std::string>& TerminfoEntry::get(
    StringCapability cap) const noexcept {
  try {
    return strings_.at(FromEnum(cap));
  } catch (const std::out_of_range&) {
    static const absl::optional<std::string> kNone = absl::nullopt;
    return kNone;
  }
}

}  // namespace goldfishterm