using System;
using System.IO;
using System.Text;

namespace Unosquare.Swan.Networking.Ldap {
  /// <summary>
  /// The Asn1Set class can hold an unordered collection of components with
  /// identical type. This class inherits from the Asn1Structured class
  /// which already provides functionality to hold multiple Asn1 components.
  /// </summary>
  /// <seealso cref="Asn1Structured" />
  internal class Asn1SetOf
      : Asn1Structured {
    public const Int32 Tag = 0x11;

    public static readonly Asn1Identifier Id = new Asn1Identifier(Asn1IdentifierTag.Universal, true, Tag);

    public Asn1SetOf(Int32 size = 10)
        : base(Id, size) {
    }

    public override String ToString() => this.ToString("SET OF: { ");
  }

  /// <summary>
  /// The Asn1Choice object represents the choice of any Asn1Object. All
  /// Asn1Object methods are delegated to the object this Asn1Choice contains.
  /// </summary>
  /// <seealso cref="Asn1Object" />
  internal class Asn1Choice
      : Asn1Object {
    private Asn1Object _content;

    public Asn1Choice(Asn1Object content = null) => this._content = content;

    protected internal virtual Asn1Object ChoiceValue {
      get => this._content;
      set => this._content = value;
    }

    public override Asn1Identifier GetIdentifier() => this._content.GetIdentifier();

    public override void SetIdentifier(Asn1Identifier id) => this._content.SetIdentifier(id);

    public override String ToString() => this._content.ToString();
  }

  /// <summary>
  /// This class is used to encapsulate an ASN.1 Identifier.
  /// An Asn1Identifier is composed of three parts:
  /// <li> a class type,</li><li> a form, and</li><li> a tag.</li>
  /// The class type is defined as:
  /// <pre>
  /// bit 8 7 TAG CLASS
  /// ------- -----------
  /// 0 0 UNIVERSAL
  /// 0 1 APPLICATION
  /// 1 0 CONTEXT
  /// 1 1 PRIVATE
  /// </pre>
  /// The form is defined as:
  /// <pre>
  /// bit 6 FORM
  /// ----- --------
  /// 0 PRIMITIVE
  /// 1 CONSTRUCTED
  /// </pre>
  /// Note: CONSTRUCTED types are made up of other CONSTRUCTED or PRIMITIVE
  /// types.
  /// The tag is defined as:.
  /// <pre>
  /// bit 5 4 3 2 1 TAG
  /// ------------- ---------------------------------------------
  /// 0 0 0 0 0
  /// . . . . .
  /// 1 1 1 1 0 (0-30) single octet tag
  /// 1 1 1 1 1 (&gt; 30) multiple octet tag, more octets follow
  /// </pre></summary>
  internal sealed class Asn1Identifier {
    public Asn1Identifier(Asn1IdentifierTag tagClass, Boolean constructed, Int32 tag) {
      this.Asn1Class = tagClass;
      this.Constructed = constructed;
      this.Tag = tag;
    }

    public Asn1Identifier(LdapOperation tag)
        : this(Asn1IdentifierTag.Application, true, (Int32)tag) {
    }

    public Asn1Identifier(Int32 contextTag, Boolean constructed = false)
        : this(Asn1IdentifierTag.Context, constructed, contextTag) {
    }

    public Asn1Identifier(Stream stream) {
      Int32 r = stream.ReadByte();
      this.EncodedLength++;

      if(r < 0) {
        throw new EndOfStreamException("BERDecoder: decode: EOF in Identifier");
      }

      this.Asn1Class = (Asn1IdentifierTag)(r >> 6);
      this.Constructed = (r & 0x20) != 0;
      this.Tag = r & 0x1F; // if tag < 30 then its a single octet identifier.

      if(this.Tag == 0x1F) {
        // if true, its a multiple octet identifier.
        this.Tag = this.DecodeTagNumber(stream);
      }
    }

    public Asn1IdentifierTag Asn1Class {
      get;
    }

    public Boolean Constructed {
      get;
    }

    public Int32 Tag {
      get;
    }

    public Int32 EncodedLength {
      get; private set;
    }

    public Boolean Universal => this.Asn1Class == Asn1IdentifierTag.Universal;

    public Object Clone() => this.MemberwiseClone();

    private Int32 DecodeTagNumber(Stream stream) {
      Int32 n = 0;
      while(true) {
        Int32 r = stream.ReadByte();
        this.EncodedLength++;
        if(r < 0) {
          throw new EndOfStreamException("BERDecoder: decode: EOF in tag number");
        }

        n = (n << 7) + (r & 0x7F);
        if((r & 0x80) == 0) {
          break;
        }
      }

      return n;
    }
  }

  /// <summary>
  /// This is the base class for all other Asn1 types.
  /// </summary>
  internal abstract class Asn1Object {
    private static readonly String[] ClassTypes = { "[UNIVERSAL ", "[APPLICATION ", "[", "[PRIVATE " };

    private Asn1Identifier _id;

    protected Asn1Object(Asn1Identifier id = null) => this._id = id;

    public virtual Asn1Identifier GetIdentifier() => this._id;

    public virtual void SetIdentifier(Asn1Identifier identifier) => this._id = identifier;

    public override String ToString() {
      Asn1Identifier identifier = this.GetIdentifier();

      return $"{ClassTypes[(Int32)identifier.Asn1Class]}{identifier.Tag}]";
    }
  }

  /// <summary>
  /// This class encapsulates the OCTET STRING type.
  /// </summary>
  /// <seealso cref="Asn1Object" />
  internal sealed class Asn1OctetString
      : Asn1Object {
    public const Int32 Tag = 0x04;

    private static readonly Asn1Identifier Id = new Asn1Identifier(Asn1IdentifierTag.Universal, false, Tag);

    private readonly SByte[] _content;

    public Asn1OctetString(SByte[] content)
        : base(Id) => this._content = content;

    public Asn1OctetString(String content)
        : base(Id) => this._content = Encoding.UTF8.GetSBytes(content);

    public Asn1OctetString(Stream stream, Int32 len)
        : base(Id) => this._content = len > 0 ? (SByte[])LberDecoder.DecodeOctetString(stream, len) : new SByte[0];

    public SByte[] ByteValue() => this._content;

    public String StringValue() => Encoding.UTF8.GetString(this._content);

    public override String ToString() => base.ToString() + "OCTET STRING: " + this.StringValue();
  }

  /// <summary>
  /// The Asn1Tagged class can hold a base Asn1Object with a distinctive tag
  /// describing the type of that base object. It also maintains a boolean value
  /// indicating whether the value should be encoded by EXPLICIT or IMPLICIT
  /// means. (Explicit is true by default.)
  /// If the type is encoded IMPLICITLY, the base types form, length and content
  /// will be encoded as usual along with the class type and tag specified in
  /// the constructor of this Asn1Tagged class.
  /// If the type is to be encoded EXPLICITLY, the base type will be encoded as
  /// usual after the Asn1Tagged identifier has been encoded.
  /// </summary>
  /// <seealso cref="Asn1Object" />
  internal class Asn1Tagged : Asn1Object {
    private Asn1Object _content;

    public Asn1Tagged(Asn1Identifier identifier, Asn1Object obj = null, Boolean isExplicit = true)
        : base(identifier) {
      this._content = obj;
      this.Explicit = isExplicit;

      if(!isExplicit) {
        // replace object's id with new tag.
        this._content?.SetIdentifier(identifier);
      }
    }

    public Asn1Tagged(Asn1Identifier identifier, SByte[] vals)
        : base(identifier) {
      this._content = new Asn1OctetString(vals);
      this.Explicit = false;
    }

    public Asn1Tagged(Stream stream, Int32 len, Asn1Identifier identifier)
        : base(identifier) =>
      // If we are decoding an implicit tag, there is no way to know at this
      // low level what the base type really is. We can place the content
      // into an Asn1OctetString type and pass it back to the application who
      // will be able to create the appropriate ASN.1 type for this tag.
      this._content = new Asn1OctetString(stream, len);

    public Asn1Object TaggedValue {
      get => this._content;

      set {
        this._content = value;
        if(!this.Explicit) {
          // replace object's id with new tag.
          value?.SetIdentifier(this.GetIdentifier());
        }
      }
    }

    public Boolean Explicit {
      get;
    }

    public override String ToString() => this.Explicit ? base.ToString() + this._content : this._content.ToString();
  }

  /// <summary>
  /// This class serves as the base type for all ASN.1
  /// structured types.
  /// </summary>
  /// <seealso cref="Asn1Object" />
  internal abstract class Asn1Structured : Asn1Object {
    private Asn1Object[] _content;
    private Int32 _contentIndex;

    protected internal Asn1Structured(Asn1Identifier id, Int32 size = 10)
        : base(id) => this._content = new Asn1Object[size];

    public Asn1Object[] ToArray() {
      Asn1Object[] cloneArray = new Asn1Object[this._contentIndex];
      Array.Copy(this._content, 0, cloneArray, 0, this._contentIndex);
      return cloneArray;
    }

    public void Add(String s) => this.Add(new Asn1OctetString(s));

    public void Add(Asn1Object obj) {
      if(this._contentIndex == this._content.Length) {
        // Array too small, need to expand it, double length
        Asn1Object[] newArray = new Asn1Object[this._contentIndex + this._contentIndex];
        Array.Copy(this._content, 0, newArray, 0, this._contentIndex);
        this._content = newArray;
      }

      this._content[this._contentIndex++] = obj;
    }

    public void Set(Int32 index, Asn1Object value) {
      if(index >= this._contentIndex || index < 0) {
        throw new IndexOutOfRangeException($"Asn1Structured: get: index {index}, size {this._contentIndex}");
      }

      this._content[index] = value;
    }

    public Asn1Object Get(Int32 index) {
      if(index >= this._contentIndex || index < 0) {
        throw new IndexOutOfRangeException($"Asn1Structured: set: index {index}, size {this._contentIndex}");
      }

      return this._content[index];
    }

    public Int32 Size() => this._contentIndex;

    public String ToString(String type) {
      StringBuilder sb = new StringBuilder().Append(type);

      for(Int32 i = 0; i < this._contentIndex; i++) {
        _ = sb.Append(this._content[i]);
        if(i != this._contentIndex - 1) {
          _ = sb.Append(", ");
        }
      }

      _ = sb.Append(" }");

      return base.ToString() + sb;
    }

    protected internal void DecodeStructured(Stream stream, Int32 len) {
      Int32[] componentLen = new Int32[1]; // collects length of component

      while(len > 0) {
        this.Add(LberDecoder.Decode(stream, componentLen));
        len -= componentLen[0];
      }
    }
  }

  /// <summary>
  /// This class encapsulates the ASN.1 BOOLEAN type.
  /// </summary>
  /// <seealso cref="Asn1Object" />
  internal class Asn1Boolean
      : Asn1Object {
    public const Int32 Tag = 0x01;

    public static readonly Asn1Identifier Id = new Asn1Identifier(Asn1IdentifierTag.Universal, false, Tag);

    private readonly Boolean _content;

    public Asn1Boolean(Boolean content)
        : base(Id) => this._content = content;

    public Asn1Boolean(Stream stream, Int32 len)
        : base(Id) => this._content = LberDecoder.DecodeBoolean(stream, len);

    public Boolean BooleanValue() => this._content;

    public override String ToString() => $"{base.ToString()}BOOLEAN: {this._content}";
  }

  /// <summary>
  /// This class represents the ASN.1 NULL type.
  /// </summary>
  /// <seealso cref="Asn1Object" />
  internal sealed class Asn1Null
      : Asn1Object {
    public const Int32 Tag = 0x05;

    public static readonly Asn1Identifier Id = new Asn1Identifier(Asn1IdentifierTag.Universal, false, Tag);

    public Asn1Null()
        : base(Id) {
    }

    public override String ToString() => $"{base.ToString()}NULL: \"\"";
  }

  /// <summary>
  /// This abstract class is the base class
  /// for all Asn1 numeric (integral) types. These include
  /// Asn1Integer and Asn1Enumerated.
  /// </summary>
  /// <seealso cref="Asn1Object" />
  internal abstract class Asn1Numeric : Asn1Object {
    private readonly Int64 _content;

    internal Asn1Numeric(Asn1Identifier id, Int32 numericValue)
        : base(id) => this._content = numericValue;

    internal Asn1Numeric(Asn1Identifier id, Int64 numericValue)
        : base(id) => this._content = numericValue;

    public Int32 IntValue() => (Int32)this._content;

    public Int64 LongValue() => this._content;
  }

  /// <summary>
  /// This class provides a means to manipulate ASN.1 Length's. It will
  /// be used by Asn1Encoder's and Asn1Decoder's by composition.
  /// </summary>
  internal sealed class Asn1Length {
    public Asn1Length(Stream stream) {
      Int32 r = stream.ReadByte();
      this.EncodedLength++;
      if(r == 0x80) {
        this.Length = -1;
      } else if(r < 0x80) {
        this.Length = r;
      } else {
        this.Length = 0;
        for(r &= 0x7F; r > 0; r--) {
          Int32 part = stream.ReadByte();
          this.EncodedLength++;
          if(part < 0) {
            throw new EndOfStreamException("BERDecoder: decode: EOF in Asn1Length");
          }

          this.Length = (this.Length << 8) + part;
        }
      }
    }

    public Int32 Length {
      get;
    }

    public Int32 EncodedLength {
      get;
    }
  }

  /// <summary>
  /// The Asn1Sequence class can hold an ordered collection of components with
  /// distinct type.
  /// This class inherits from the Asn1Structured class which
  /// provides functionality to hold multiple Asn1 components.
  /// </summary>
  /// <seealso cref="Asn1Structured" />
  internal class Asn1Sequence
      : Asn1Structured {
    public const Int32 Tag = 0x10;

    private static readonly Asn1Identifier Id = new Asn1Identifier(Asn1IdentifierTag.Universal, true, Tag);

    public Asn1Sequence(Int32 size)
        : base(Id, size) {
    }

    public Asn1Sequence(Stream stream, Int32 len)
        : base(Id) => this.DecodeStructured(stream, len);

    public override String ToString() => this.ToString("SEQUENCE: { ");
  }

  /// <summary>
  /// The Asn1Set class can hold an unordered collection of components with
  /// distinct type. This class inherits from the Asn1Structured class
  /// which already provides functionality to hold multiple Asn1 components.
  /// </summary>
  /// <seealso cref="Asn1Structured" />
  internal sealed class Asn1Set
      : Asn1Structured {
    public const Int32 Tag = 0x11;

    public static readonly Asn1Identifier Id = new Asn1Identifier(Asn1IdentifierTag.Universal, true, Tag);

    public Asn1Set(Stream stream, Int32 len)
        : base(Id) => this.DecodeStructured(stream, len);

    public override String ToString() => this.ToString("SET: { ");
  }

  /// <summary>
  /// This class encapsulates the ASN.1 INTEGER type.
  /// </summary>
  /// <seealso cref="Asn1Numeric" />
  internal class Asn1Integer
      : Asn1Numeric {
    public const Int32 Tag = 0x02;

    public static readonly Asn1Identifier Id = new Asn1Identifier(Asn1IdentifierTag.Universal, false, Tag);

    public Asn1Integer(Int32 content)
        : base(Id, content) {
    }

    public Asn1Integer(Stream stream, Int32 len)
        : base(Id, LberDecoder.DecodeNumeric(stream, len)) {
    }

    public override String ToString() => base.ToString() + "INTEGER: " + this.LongValue();
  }

  /// <summary>
  /// This class encapsulates the ASN.1 ENUMERATED type.
  /// </summary>
  /// <seealso cref="Asn1Numeric" />
  internal sealed class Asn1Enumerated : Asn1Numeric {
    public const Int32 Tag = 0x0a;

    public static readonly Asn1Identifier Id = new Asn1Identifier(Asn1IdentifierTag.Universal, false, Tag);

    public Asn1Enumerated(LdapScope content)
        : base(Id, (Int32)content) {
    }

    public Asn1Enumerated(Int32 content)
        : base(Id, content) {
    }

    /// <summary>
    /// Initializes a new instance of the <see cref="Asn1Enumerated"/> class.
    /// Constructs an Asn1Enumerated object by decoding data from an
    /// input stream.
    /// </summary>
    /// <param name="stream">The stream.</param>
    /// <param name="len">The length.</param>
    public Asn1Enumerated(Stream stream, Int32 len)
        : base(Id, LberDecoder.DecodeNumeric(stream, len)) {
    }

    public override String ToString() => base.ToString() + "ENUMERATED: " + this.LongValue();
  }

  /// <summary>
  /// The Asn1SequenceOf class is used to hold an ordered collection
  /// of components with identical type.  This class inherits
  /// from the Asn1Structured class which already provides
  /// functionality to hold multiple Asn1 components.
  /// </summary>
  /// <seealso cref="Asn1Structured" />
  internal class Asn1SequenceOf : Asn1Structured {
    public const Int32 Tag = 0x10;

    public static readonly Asn1Identifier Id = new Asn1Identifier(Asn1IdentifierTag.Universal, true, Tag);

    public Asn1SequenceOf(Int32 size)
        : base(Id, size) {
    }

    public Asn1SequenceOf(Stream stream, Int32 len)
        : base(Id) => this.DecodeStructured(stream, len);

    public override String ToString() => this.ToString("SEQUENCE OF: { ");
  }
}