import 'dart:convert';
import 'dart:typed_data';

import 'package:flutter/foundation.dart';
import 'asn1_identifier.dart';
import 'asn1_object.dart';

class ASN1DERDecoder {
  static List<ASN1Object> decode({@required List<int> data}) {
    var iterator = data.iterator;
    return parse(iterator: iterator);
  }

  static List<ASN1Object> parse({@required Iterator<int> iterator}) {
    var result = <ASN1Object>[];

    while (iterator.moveNext()) {
      var nextValue = iterator.current;

      var asn1obj = ASN1Object();
      asn1obj.identifier = ASN1Identifier(nextValue);

      if (asn1obj.identifier.isConstructed()) {
        var contentData = loadSubContent(iterator: iterator);

        if (contentData.isEmpty) {
          asn1obj.sub = parse(iterator: iterator);
        } else {
          var subIterator = contentData.iterator;
          asn1obj.sub = parse(iterator: subIterator);
        }

        asn1obj.value = null;

        asn1obj.encoded = Uint8List.fromList(contentData);

        for (var item in asn1obj.sub) {
          item.parent = asn1obj;
        }
      } else {
        if (asn1obj.identifier.typeClass() == ASN1IdentifierClass.UNIVERSAL) {
          var contentData = loadSubContent(iterator: iterator);

          asn1obj.encoded = Uint8List.fromList(contentData);

          // decode the content data with come more convenient format

          var tagNumber = asn1obj.identifier.tagNumber();

          if (tagNumber == ASN1IdentifierTagNumber.END_OF_CONTENT) {
            return result;
          } else if (tagNumber == ASN1IdentifierTagNumber.BOOLEAN) {
            var value = contentData.length > 0 ? contentData.first : null;
            if (value != null) {
              asn1obj.value = value > 0 ? true : false;
            }
          } else if (tagNumber == ASN1IdentifierTagNumber.INTEGER) {
            while (contentData.length > 0 && contentData.first == 0) {
              contentData.removeAt(0); // remove not significant digit
            }
            asn1obj.value = contentData;
          } else if (tagNumber == ASN1IdentifierTagNumber.NULL) {
            asn1obj.value = null;
          } else if (tagNumber == ASN1IdentifierTagNumber.OBJECT_IDENTIFIER) {
            asn1obj.value = decodeOid(contentData: contentData);
          } else if ([
            ASN1IdentifierTagNumber.UTF8_STRING,
            ASN1IdentifierTagNumber.PRINTABLE_STRING,
            ASN1IdentifierTagNumber.NUMERIC_STRING,
            ASN1IdentifierTagNumber.GENERAL_STRING,
            ASN1IdentifierTagNumber.UNIVERSAL_STRING,
            ASN1IdentifierTagNumber.CHARACTER_STRING,
            ASN1IdentifierTagNumber.T61_STRING
          ].contains(tagNumber)) {
            asn1obj.value = utf8.decode(contentData, allowMalformed: true);
          } else if (tagNumber == ASN1IdentifierTagNumber.BMP_STRING) {
            asn1obj.value = String.fromCharCodes(contentData);
          } else if ([
            ASN1IdentifierTagNumber.VISIBLE_STRING,
            ASN1IdentifierTagNumber.IA5_STRING
          ].contains(tagNumber)) {
            asn1obj.value = ascii.decode(contentData, allowInvalid: true);
          } else if (tagNumber == ASN1IdentifierTagNumber.UTC_TIME) {
            asn1obj.value = utcTimeToDate(contentData: contentData);
          } else if (tagNumber == ASN1IdentifierTagNumber.GENERALIZED_TIME) {
            asn1obj.value = generalizedTimeToDate(contentData: contentData);
          } else if (tagNumber == ASN1IdentifierTagNumber.BIT_STRING) {
            if (contentData.length > 0) {
              contentData.removeAt(0); // unused bits
            }
            asn1obj.value = contentData;
          } else if (tagNumber == ASN1IdentifierTagNumber.OCTET_STRING) {
            try {
              var subIterator = contentData.iterator;
              asn1obj.sub = parse(iterator: subIterator);
            } catch (e) {
              var str;
              try {
                str = utf8.decode(contentData);
              } catch (e) {}
              if (str != null) {
                asn1obj.value = str;
              } else {
                asn1obj.value = contentData;
              }
            }
          } else {
            // print("unsupported tag: ${asn1obj.identifier.tagNumber()}");
            asn1obj.value = contentData;
          }
        } else {
          // custom/private tag

          var contentData = loadSubContent(iterator: iterator);

          var str;
          try {
            str = utf8.decode(contentData);
          } catch (e) {}
          if (str != null) {
            asn1obj.value = str;
          } else {
            asn1obj.value = contentData;
          }
        }
      }
      result.add(asn1obj);
    }

    return result;
  }

  static BigInt getContentLength({@required Iterator<int> iterator}) {
    if (iterator.moveNext()) {
      var first = iterator.current;
      if (first != null) {
        if ((first & 0x80) != 0) {
          // long

          var octetsToRead = first - 0x80;
          var data = <int>[];
          for (var i = 0; i < octetsToRead; i++) {
            if (iterator.moveNext()) {
              var n = iterator.current;
              if (n != null) {
                data.add(n);
              }
            }
          }

          return toIntValue(data) ?? BigInt.from(0);
        } else {
          // short
          return BigInt.from(first);
        }
      }
    }
    return BigInt.from(0);
  }

  static List<int> loadSubContent({@required Iterator<int> iterator}) {
    var len = getContentLength(iterator: iterator);
    int int64MaxValue = 9223372036854775807;

    if (len >= BigInt.from(int64MaxValue)) {
      return <int>[];
    }

    var byteArray = <int>[];

    for (var i = 0; i < len.toInt(); i++) {
      if (iterator.moveNext()) {
        var n = iterator.current;
        if (n != null) {
          byteArray.add(n);
        }
      } else {
        throw ASN1OutOfBufferError();
      }
    }

    return byteArray;
  }

  /// Decode DER OID bytes to String with dot notation
  static String decodeOid({@required List<int> contentData}) {
    if (contentData.isEmpty) {
      return "";
    }

    var oid = "";

    var first = contentData.removeAt(0);
    oid += "${(first / 40).truncate()}.${first % 40}";

    var t = 0;
    while (contentData.length > 0) {
      var n = contentData.removeAt(0);
      t = (t << 7) | (n & 0x7F);
      if ((n & 0x80) == 0) {
        oid += ".$t";
        t = 0;
      }
    }
    return oid;
  }

  ///Converts a UTCTime value to a date.
  ///
  ///Note: GeneralizedTime has 4 digits for the year and is used for X.509
  ///dates past 2049. Parsing that structure hasn't been implemented yet.
  ///
  ///[contentData] the UTCTime value to convert.
  static DateTime utcTimeToDate({@required List<int> contentData}) {
    /* The following formats can be used:
      YYMMDDhhmmZ
      YYMMDDhhmm+hh'mm'
      YYMMDDhhmm-hh'mm'
      YYMMDDhhmmssZ
      YYMMDDhhmmss+hh'mm'
      YYMMDDhhmmss-hh'mm'
      Where:
      YY is the least significant two digits of the year
      MM is the month (01 to 12)
      DD is the day (01 to 31)
      hh is the hour (00 to 23)
      mm are the minutes (00 to 59)
      ss are the seconds (00 to 59)
      Z indicates that local time is GMT, + indicates that local time is
      later than GMT, and - indicates that local time is earlier than GMT
      hh' is the absolute value of the offset from GMT in hours
      mm' is the absolute value of the offset from GMT in minutes */

    String utc;
    try {
      utc = utf8.decode(contentData);
    } catch (e) {}
    if (utc == null) {
      return null;
    }

    // if YY >= 50 use 19xx, if YY < 50 use 20xx
    var year = int.parse(utc.substring(0, 2), radix: 10);
    year = (year >= 50) ? 1900 + year : 2000 + year;
    var MM = int.parse(utc.substring(2, 4), radix: 10);
    var DD = int.parse(utc.substring(4, 6), radix: 10);
    var hh = int.parse(utc.substring(6, 8), radix: 10);
    var mm = int.parse(utc.substring(8, 10), radix: 10);
    var ss = 0;

    int end;
    String c;
    // not just YYMMDDhhmmZ
    if (utc.length > 11) {
      // get character after minutes
      c = utc[10];
      end = 10;

      // see if seconds are present
      if (c != '+' && c != '-') {
        // get seconds
        ss = int.parse(utc.substring(10, 12), radix: 10);
        end += 2;
      }
    }

    var date = DateTime.utc(year, MM, DD, hh, mm, ss, 0);

    if (end != null) {
      // get +/- after end of time
      c = utc[end];
      if (c == '+' || c == '-') {
        // get hours+minutes offset
        var hhoffset =
            int.parse(utc.substring(end + 1, end + 1 + 2), radix: 10);
        var mmoffset =
            int.parse(utc.substring(end + 4, end + 4 + 2), radix: 10);

        // calculate offset in milliseconds
        var offset = hhoffset * 60 + mmoffset;
        offset *= 60000;

        var offsetDuration = Duration(milliseconds: offset);
        // apply offset
        if (c == '+') {
          date.subtract(offsetDuration);
        } else {
          date.add(offsetDuration);
        }
      }
    }

    return date;
  }

  ///Converts a GeneralizedTime value to a date.
  ///
  ///[contentData] the GeneralizedTime value to convert.
  static DateTime generalizedTimeToDate({@required List<int> contentData}) {
    /* The following formats can be used:
      YYYYMMDDHHMMSS
      YYYYMMDDHHMMSS.fff
      YYYYMMDDHHMMSSZ
      YYYYMMDDHHMMSS.fffZ
      YYYYMMDDHHMMSS+hh'mm'
      YYYYMMDDHHMMSS.fff+hh'mm'
      YYYYMMDDHHMMSS-hh'mm'
      YYYYMMDDHHMMSS.fff-hh'mm'
      Where:
      YYYY is the year
      MM is the month (01 to 12)
      DD is the day (01 to 31)
      hh is the hour (00 to 23)
      mm are the minutes (00 to 59)
      ss are the seconds (00 to 59)
      .fff is the second fraction, accurate to three decimal places
      Z indicates that local time is GMT, + indicates that local time is
      later than GMT, and - indicates that local time is earlier than GMT
      hh' is the absolute value of the offset from GMT in hours
      mm' is the absolute value of the offset from GMT in minutes */

    String gentime;
    try {
      gentime = utf8.decode(contentData);
    } catch (e) {}
    if (gentime == null) {
      return null;
    }

    // if YY >= 50 use 19xx, if YY < 50 use 20xx
    var YYYY = int.parse(gentime.substring(0, 4), radix: 10);
    var MM = int.parse(gentime.substring(4, 6), radix: 10);
    var DD = int.parse(gentime.substring(6, 8), radix: 10);
    var hh = int.parse(gentime.substring(8, 10), radix: 10);
    var mm = int.parse(gentime.substring(10, 12), radix: 10);
    var ss = int.parse(gentime.substring(12, 14), radix: 10);

    double fff = 0.0;
    var offset = 0;
    var isUTC = false;

    if (gentime[gentime.length - 1] == 'Z') {
      isUTC = true;
    }

    var end = gentime.length - 5;
    var c = gentime[end];
    if (c == '+' || c == '-') {
      // get hours+minutes offset
      var hhoffset =
          int.parse(gentime.substring(end + 1, end + 1 + 2), radix: 10);
      var mmoffset =
          int.parse(gentime.substring(end + 4, end + 4 + 2), radix: 10);

      // calculate offset in milliseconds
      offset = hhoffset * 60 + mmoffset;
      offset *= 60000;

      // apply offset
      if (c == '+') {
        offset *= -1;
      }

      isUTC = true;
    }

    // check for second fraction
    if (gentime[14] == '.') {
      fff = double.parse(gentime.substring(14)) * 1000;
    }

    var date = DateTime.utc(YYYY, MM, DD, hh, mm, ss, fff.toInt());

    if (isUTC) {
      var offsetDuration = Duration(milliseconds: offset);
      date.add(offsetDuration);
    }

    return date;
  }
}

BigInt toIntValue(List<int> data) {
  if (data.length > 8) {
    return null;
  }

  BigInt value = BigInt.from(0);
  for (var index = 0; index < data.length; index++) {
    var byte = data[index];
    value += BigInt.from(byte << 8 * (data.length - index - 1));
  }
  return value;
}

class ASN1OutOfBufferError extends Error {}

class ASN1ParseError extends Error {}