#pragma once

#include <cctype>
#include <cstddef>
#include <ctime>
#include <iostream>
#include <string>
#include <unordered_map>
#include <utility>

#include <jvalidate/forward.h>

namespace jvalidate::format::detail {
inline bool is_leapyear(int y) { return (y % 400) == 0 || ((y % 4) == 0 && (y % 100) != 0); }

inline bool illegal_date(int y, int m, int d) {
  static constexpr int days[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
  if (is_leapyear(y) && m == 1) {
    --d;
  }
  return d > days[m];
}

inline auto date(std::string_view dt) {
  struct tm tm;
  if (auto end = strptime(dt.data(), "%Y-%m-%d", &tm); end) {
    if ((end - dt.data()) != 10 || illegal_date(tm.tm_year + 1900, tm.tm_mon, tm.tm_mday)) {
      return std::make_pair(0L, false);
    }
    return std::make_pair(end - dt.data(), true);
  }
  return std::make_pair(0L, false);
}
}

namespace jvalidate::format {
inline bool date(std::string_view dt) {
  auto [size, good] = detail::date(dt);
  return good && size == dt.size();
}

inline bool time(std::string_view dt) {
  struct tm tm;
  char const * end = strptime(dt.data(), "%T", &tm);
  if (end == nullptr || end == dt.end() || (end - dt.data()) < 8) {
    return false;
  }
  dt.remove_prefix(end - dt.begin());
  if (dt[0] == '.') {
    dt.remove_prefix(1);
    if (dt.empty() || not std::isdigit(dt[0])) {
      return false;
    }
    while (std::isdigit(dt[0])) {
      dt.remove_prefix(1);
    }
  }

  if (dt[0] == 'Z' || dt[0] == 'z') {
    return dt.size() == 1;
  }
  if (std::strchr("+-", dt[0])) {
    return strptime(dt.data() + 1, "%R", &tm) == dt.end();
  }
  return false;
}

inline bool date_time(std::string_view dt) {
  auto [size, good] = detail::date(dt);
  if (not good || std::strchr("Tt", dt[size]) == nullptr) {
    return false;
  }
  dt.remove_prefix(size + 1);
  return time(dt);
}

inline bool uuid(std::string_view id) {
  constexpr char const * g_hex_digits = "0123456789ABCDEFabcdef";
  constexpr size_t g_uuid_len = 36;
  constexpr size_t g_uuid_tokens = 5;
  char tok0[9], tok1[5], tok2[5], tok3[5], tok4[13];

  auto is_hex = [](std::string_view s) {
    return s.find_first_not_of(g_hex_digits) == std::string::npos;
  };
  return id.size() == g_uuid_len &&
         sscanf(id.data(), "%8s-%4s-%4s-%4s-%12s", tok0, tok1, tok2, tok3, tok4) == g_uuid_tokens &&
         is_hex(tok0) && is_hex(tok1) && is_hex(tok2) && is_hex(tok3) && is_hex(tok4);
}

inline bool duration(std::string_view dur) {
  auto eat = [&dur](std::string_view text) {
    char type;
    unsigned int rep;
    if (sscanf(dur.data(), "%u%c", &rep, &type) != 2 || text.find(type) == std::string::npos) {
      return std::string::npos;
    }
    dur.remove_prefix(dur.find(type) + 1);
    return text.find(type);
  };

  if (dur[0] != 'P' || dur.size() == 1) {
    return false;
  }
  dur.remove_prefix(1);

  if (dur[0] != 'T') {
    if (eat("W") != std::string::npos) {
      return dur.empty();
    }
    std::string_view ymd{"YMD"};
    while (not ymd.empty() && not dur.empty()) {
      if (size_t n = eat(ymd); n != std::string::npos) {
        ymd.remove_prefix(n + 1);
      } else {
        return false;
      }
    }
    if (dur.empty()) {
      return true;
    }
  }

  if (dur[0] != 'T' || dur.size() == 1) {
    return false;
  }
  dur.remove_prefix(1);

  std::string_view hms{"HMS"};
  while (not hms.empty() && not dur.empty()) {
    if (size_t n = eat(hms); n != std::string::npos) {
      hms.remove_prefix(n + 1);
    } else {
      return false;
    }
  }
  return dur.empty();
}

// Limitation - does not inspect graphemes, so it cannot check idn-hostname
// to fix this - we'd need to
inline bool hostname(std::string_view name) {
  auto hostname_part = [&name](size_t end) {
    if (end == 0 || end >= 64 || name[0] == '-' || name[end - 1] == '-') {
      return false;
    }
    for (size_t i = 0; i < end; ++i) {
      if (name[i] != '-' && not std::isalnum(name[i])) {
        return false;
      }
    }
    return true;
  };

  if (name.size() > (name.back() == '.' ? 254 : 253)) {
    return false;
  }
  for (size_t n = name.find('.'); n != std::string::npos;
       name.remove_prefix(n + 1), n = name.find('.')) {
    if (not hostname_part(n)) {
      return false;
    }
  }
  return name.empty() || hostname_part(name.size());
}

inline bool ipv4(std::string_view ip) {
  unsigned int ip0, ip1, ip2, ip3;
  char eof;
  if (ip.find_first_not_of("0123456789.") != std::string::npos) {
    return false;
  }
  if (ip[0] == '0' && std::isdigit(ip[1])) {
    return false;
  }
  if (size_t n = ip.find(".0"); n != std::string::npos && std::isdigit(ip[n + 2])) {
    return false;
  }
  if (sscanf(ip.data(), "%3u.%3u.%3u.%3u%c", &ip0, &ip1, &ip2, &ip3, &eof) != 4) {
    return false;
  }
  return ip0 <= 0xFF && ip1 <= 0xFF && ip2 <= 0xFF && ip3 <= 0xFF;
}

inline bool ipv6(std::string_view ip) {
  int expected_spans = 8;

  if (size_t n = ip.find('.'); n != std::string::npos) {
    if (not ipv4(ip.substr(ip.find_last_of(':') + 1))) {
      return false;
    }
    // This is a cheat to allow e.g. ::127.0.0.1 to validate
    expected_spans = 7;
    ip = ip.substr(0, n);
  }

  if (ip.find_first_not_of("0123456789ABCDEFabcdef:") != std::string::npos) {
    return false;
  }
  if (ip.size() >= 40) {
    return false;
  }

  bool has_compressed = false;
  int groups = 0;

  if (ip.starts_with("::")) {
    has_compressed = true;
    ip.remove_prefix(2);
  }
  while (!ip.empty()) {
    int data;
    if (sscanf(ip.data(), "%4x", &data) != 1) {
      return false;
    }
    if (size_t n = ip.find(':'); std::min(n, ip.size()) > 4) {
      return false;
    } else if (n != std::string::npos) {
      ip.remove_prefix(n + 1);
    } else {
      ip = "";
    }
    ++groups;
    if (ip[0] == ':') {
      if (std::exchange(has_compressed, true)) {
        return false;
      }
      ip.remove_prefix(1);
    }
  }

  return groups == expected_spans || (has_compressed && groups < expected_spans);
}

// Let's be honest - no matter what RFC 5321 §4.1.2 or RFC 6531 say, the only
// way to know if an email address is valid is to try and send a message to it.
// Therefore, there's no point in trying to validate things according to a
// complex grammar - as long as it has an '@' sign with at least one character
// on each side, we ought to call it an email.
inline bool email(std::string_view em) {
  size_t n = em.find_last_of('@');
  if (n == 0 || n >= em.size() - 1) {
    return false;
  }

  if (em[0] == '"' && em[n - 1] == '"') {
    // No validation
  } else if (em.substr(0, n).find("..") != std::string::npos || em[n - 1] == '.' || em[0] == '.') {
    return false;
  }

  em.remove_prefix(n + 1);
  if (em.front() == '[' && em.back() == ']') {
    em.remove_prefix(1);
    em.remove_suffix(1);
    if (em.starts_with("IPv6:")) {
      return ipv6(std::string(em.substr(5)));
    }
    return ipv4(std::string(em)); // Re-acquire NULL-term
  }
  return hostname(em);
}
}

namespace jvalidate {
class FormatValidator {
public:
  using Predicate = bool (*)(std::string_view);
  enum class Status { Unknown, Unimplemented, Valid, Invalid };

private:
  std::unordered_map<std::string, Predicate> supported_formats_{
      {"date", &format::date},
      {"date-time", &format::date_time},
      {"duration", &format::duration},
      {"email", &format::email},
      {"hostname", &format::hostname},
      {"idn-email", nullptr},
      {"idn-hostname", nullptr},
      {"ipv4", &format::ipv4},
      {"ipv6", &format::ipv6},
      {"iri", nullptr},
      {"iri-reference", nullptr},
      {"json-pointer", nullptr},
      {"relative-json-pointer", nullptr},
      /* {"regex", &detail::StdRegexEngine::is_valid}, */
      {"time", &format::time},
      {"uri", nullptr},
      {"uri-reference", nullptr},
      {"uri-template", nullptr},
      {"uuid", &format::uuid},
  };

public:
  FormatValidator() = default;

  Status operator()(std::string const & format, std::string_view text) const {
    if (auto it = supported_formats_.find(format); it != supported_formats_.end() && it->second) {
      if (not it->second) {
        return Status::Unimplemented;
      }
      return it->second(text) ? Status::Valid : Status::Invalid;
    }
    return Status::Unknown;
  }
};
}