using System;
using System.Collections;
using System.Diagnostics;

using Org.BouncyCastle.Asn1.X9;

using Org.BouncyCastle.Math.EC.Multiplier;

namespace Org.BouncyCastle.Math.EC
{
    /**
     * base class for points on elliptic curves.
     */
    public abstract class ECPoint
    {
        internal readonly ECCurve			curve;
        internal readonly ECFieldElement	x, y;
        internal readonly bool				withCompression;
        internal ECMultiplier				multiplier = null;
        internal PreCompInfo				preCompInfo = null;

        protected internal ECPoint(
            ECCurve			curve,
            ECFieldElement	x,
            ECFieldElement	y,
            bool			withCompression)
        {
            if (curve == null)
                throw new ArgumentNullException("curve");

            this.curve = curve;
            this.x = x;
            this.y = y;
            this.withCompression = withCompression;
        }

        public ECCurve Curve
        {
            get { return curve; }
        }

        public ECFieldElement X
        {
            get { return x; }
        }

        public ECFieldElement Y
        {
            get { return y; }
        }

        public bool IsInfinity
        {
            get { return x == null && y == null; }
        }

        public bool IsCompressed
        {
            get { return withCompression; }
        }

        public override bool Equals(
            object obj)
        {
            if (obj == this)
                return true;

            ECPoint o = obj as ECPoint;

            if (o == null)
                return false;

            if (this.IsInfinity)
                return o.IsInfinity;

            return x.Equals(o.x) && y.Equals(o.y);
        }

        public override int GetHashCode()
        {
            if (this.IsInfinity)
                return 0;

            return x.GetHashCode() ^ y.GetHashCode();
        }

//		/**
//		 * Mainly for testing. Explicitly set the <code>ECMultiplier</code>.
//		 * @param multiplier The <code>ECMultiplier</code> to be used to multiply
//		 * this <code>ECPoint</code>.
//		 */
//		internal void SetECMultiplier(
//			ECMultiplier multiplier)
//		{
//			this.multiplier = multiplier;
//		}

        /**
         * Sets the <code>PreCompInfo</code>. Used by <code>ECMultiplier</code>s
         * to save the precomputation for this <code>ECPoint</code> to store the
         * precomputation result for use by subsequent multiplication.
         * @param preCompInfo The values precomputed by the
         * <code>ECMultiplier</code>.
         */
        internal void SetPreCompInfo(
            PreCompInfo preCompInfo)
        {
            this.preCompInfo = preCompInfo;
        }

        public virtual byte[] GetEncoded()
        {
            return GetEncoded(withCompression);
        }

        public abstract byte[] GetEncoded(bool compressed);

        public abstract ECPoint Add(ECPoint b);
        public abstract ECPoint Subtract(ECPoint b);
        public abstract ECPoint Negate();
        public abstract ECPoint Twice();
        public abstract ECPoint Multiply(BigInteger b);

        /**
        * Sets the appropriate <code>ECMultiplier</code>, unless already set. 
        */
        internal virtual void AssertECMultiplier()
        {
            if (this.multiplier == null)
            {
                lock (this)
                {
                    if (this.multiplier == null)
                    {
                        this.multiplier = new FpNafMultiplier();
                    }
                }
            }
        }
    }

    public abstract class ECPointBase
        : ECPoint
    {
        protected internal ECPointBase(
            ECCurve			curve,
            ECFieldElement	x,
            ECFieldElement	y,
            bool			withCompression)
            : base(curve, x, y, withCompression)
        {
        }

        protected internal abstract bool YTilde { get; }

        /**
         * return the field element encoded with point compression. (S 4.3.6)
         */
        public override byte[] GetEncoded(bool compressed)
        {
            if (this.IsInfinity)
                return new byte[1];

            // Note: some of the tests rely on calculating byte length from the field element
            // (since the test cases use mismatching fields for curve/elements)
            int byteLength = X9IntegerConverter.GetByteLength(x);
            byte[] X = X9IntegerConverter.IntegerToBytes(this.X.ToBigInteger(), byteLength);
            byte[] PO;

            if (compressed)
            {
                PO = new byte[1 + X.Length];

                PO[0] = (byte)(YTilde ? 0x03 : 0x02);
            }
            else
            {
                byte[] Y = X9IntegerConverter.IntegerToBytes(this.Y.ToBigInteger(), byteLength);
                PO = new byte[1 + X.Length + Y.Length];

                PO[0] = 0x04;

                Y.CopyTo(PO, 1 + X.Length);
            }

            X.CopyTo(PO, 1);

            return PO;
        }

        /**
         * Multiplies this <code>ECPoint</code> by the given number.
         * @param k The multiplicator.
         * @return <code>k * this</code>.
         */
        public override ECPoint Multiply(
            BigInteger k)
        {
            if (k.SignValue < 0)
                throw new ArgumentException("The multiplicator cannot be negative", "k");

            if (this.IsInfinity)
                return this;

            if (k.SignValue == 0)
                return this.curve.Infinity;

            AssertECMultiplier();
            return this.multiplier.Multiply(this, k, preCompInfo);
        }
    }

    /**
     * Elliptic curve points over Fp
     */
    public class FpPoint
        : ECPointBase
    {
        /**
         * Create a point which encodes with point compression.
         *
         * @param curve the curve to use
         * @param x affine x co-ordinate
         * @param y affine y co-ordinate
         */
        public FpPoint(
            ECCurve			curve,
            ECFieldElement	x,
            ECFieldElement	y)
            : this(curve, x, y, false)
        {
        }

        /**
         * Create a point that encodes with or without point compresion.
         *
         * @param curve the curve to use
         * @param x affine x co-ordinate
         * @param y affine y co-ordinate
         * @param withCompression if true encode with point compression
         */
        public FpPoint(
            ECCurve			curve,
            ECFieldElement	x,
            ECFieldElement	y,
            bool			withCompression)
            : base(curve, x, y, withCompression)
        {
            if ((x == null) != (y == null))
                throw new ArgumentException("Exactly one of the field elements is null");
        }

        protected internal override bool YTilde
        {
            get
            {
                return this.Y.ToBigInteger().TestBit(0);
            }
        }

        // B.3 pg 62
        public override ECPoint Add(
            ECPoint b)
        {
            if (this.IsInfinity)
                return b;

            if (b.IsInfinity)
                return this;

            // Check if b = this or b = -this
            if (this.x.Equals(b.x))
            {
                if (this.y.Equals(b.y))
                {
                    // this = b, i.e. this must be doubled
                    return this.Twice();
                }

                Debug.Assert(this.y.Equals(b.y.Negate()));

                // this = -b, i.e. the result is the point at infinity
                return this.curve.Infinity;
            }

            ECFieldElement gamma = b.y.Subtract(this.y).Divide(b.x.Subtract(this.x));

            ECFieldElement x3 = gamma.Square().Subtract(this.x).Subtract(b.x);
            ECFieldElement y3 = gamma.Multiply(this.x.Subtract(x3)).Subtract(this.y);

            return new FpPoint(curve, x3, y3, withCompression);
        }

        // B.3 pg 62
        public override ECPoint Twice()
        {
            // Twice identity element (point at infinity) is identity
            if (this.IsInfinity)
                return this;

            // if y1 == 0, then (x1, y1) == (x1, -y1)
            // and hence this = -this and thus 2(x1, y1) == infinity
            if (this.y.ToBigInteger().SignValue == 0)
                return this.curve.Infinity;

            ECFieldElement TWO = this.curve.FromBigInteger(BigInteger.Two);
            ECFieldElement THREE = this.curve.FromBigInteger(BigInteger.Three);
            ECFieldElement gamma = this.x.Square().Multiply(THREE).Add(curve.a).Divide(y.Multiply(TWO));

            ECFieldElement x3 = gamma.Square().Subtract(this.x.Multiply(TWO));
            ECFieldElement y3 = gamma.Multiply(this.x.Subtract(x3)).Subtract(this.y);

            return new FpPoint(curve, x3, y3, this.withCompression);
        }

        // D.3.2 pg 102 (see Note:)
        public override ECPoint Subtract(
            ECPoint b)
        {
            if (b.IsInfinity)
                return this;

            // Add -b
            return Add(b.Negate());
        }

        public override ECPoint Negate()
        {
            return new FpPoint(this.curve, this.x, this.y.Negate(), this.withCompression);
        }

        /**
         * Sets the default <code>ECMultiplier</code>, unless already set. 
         */
        internal override void AssertECMultiplier()
        {
            if (this.multiplier == null)
            {
                lock (this)
                {
                    if (this.multiplier == null)
                    {
                        this.multiplier = new WNafMultiplier();
                    }
                }
            }
        }
    }

    /**
     * Elliptic curve points over F2m
     */
    public class F2mPoint
        : ECPointBase
    {
        /**
         * @param curve base curve
         * @param x x point
         * @param y y point
         */
        public F2mPoint(
            ECCurve			curve,
            ECFieldElement	x,
            ECFieldElement	y)
            :  this(curve, x, y, false)
        {
        }

        /**
         * @param curve base curve
         * @param x x point
         * @param y y point
         * @param withCompression true if encode with point compression.
         */
        public F2mPoint(
            ECCurve			curve,
            ECFieldElement	x,
            ECFieldElement	y,
            bool			withCompression)
            : base(curve, x, y, withCompression)
        {
            if ((x != null && y == null) || (x == null && y != null))
            {
                throw new ArgumentException("Exactly one of the field elements is null");
            }

            if (x != null)
            {
                // Check if x and y are elements of the same field
                F2mFieldElement.CheckFieldElements(this.x, this.y);

                // Check if x and a are elements of the same field
                F2mFieldElement.CheckFieldElements(this.x, this.curve.A);
            }
        }

        /**
         * Constructor for point at infinity
         */
        [Obsolete("Use ECCurve.Infinity property")]
        public F2mPoint(
            ECCurve curve)
            : this(curve, null, null)
        {
        }

        protected internal override bool YTilde
        {
            get
            {
                // X9.62 4.2.2 and 4.3.6:
                // if x = 0 then ypTilde := 0, else ypTilde is the rightmost
                // bit of y * x^(-1)
                return this.X.ToBigInteger().SignValue != 0
                    && this.Y.Multiply(this.X.Invert()).ToBigInteger().TestBit(0);
            }
        }

        /**
         * Check, if two <code>ECPoint</code>s can be added or subtracted.
         * @param a The first <code>ECPoint</code> to check.
         * @param b The second <code>ECPoint</code> to check.
         * @throws IllegalArgumentException if <code>a</code> and <code>b</code>
         * cannot be added.
         */
        private static void CheckPoints(
            ECPoint	a,
            ECPoint	b)
        {
            // Check, if points are on the same curve
            if (!a.curve.Equals(b.curve))
                throw new ArgumentException("Only points on the same curve can be added or subtracted");

//			F2mFieldElement.CheckFieldElements(a.x, b.x);
        }

        /* (non-Javadoc)
         * @see org.bouncycastle.math.ec.ECPoint#add(org.bouncycastle.math.ec.ECPoint)
         */
        public override ECPoint Add(ECPoint b)
        {
            CheckPoints(this, b);
            return AddSimple((F2mPoint) b);
        }

        /**
         * Adds another <code>ECPoints.F2m</code> to <code>this</code> without
         * checking if both points are on the same curve. Used by multiplication
         * algorithms, because there all points are a multiple of the same point
         * and hence the checks can be omitted.
         * @param b The other <code>ECPoints.F2m</code> to add to
         * <code>this</code>.
         * @return <code>this + b</code>
         */
        internal F2mPoint AddSimple(F2mPoint b)
        {
            if (this.IsInfinity)
                return b;

            if (b.IsInfinity)
                return this;

            F2mFieldElement x2 = (F2mFieldElement) b.X;
            F2mFieldElement y2 = (F2mFieldElement) b.Y;

            // Check if b == this or b == -this
            if (this.x.Equals(x2))
            {
                // this == b, i.e. this must be doubled
                if (this.y.Equals(y2))
                    return (F2mPoint) this.Twice();

                // this = -other, i.e. the result is the point at infinity
                return (F2mPoint) this.curve.Infinity;
            }

            ECFieldElement xSum = this.x.Add(x2);

            F2mFieldElement lambda
                = (F2mFieldElement)(this.y.Add(y2)).Divide(xSum);

            F2mFieldElement x3
                = (F2mFieldElement)lambda.Square().Add(lambda).Add(xSum).Add(this.curve.A);

            F2mFieldElement y3
                = (F2mFieldElement)lambda.Multiply(this.x.Add(x3)).Add(x3).Add(this.y);

            return new F2mPoint(curve, x3, y3, withCompression);
        }

        /* (non-Javadoc)
         * @see org.bouncycastle.math.ec.ECPoint#subtract(org.bouncycastle.math.ec.ECPoint)
         */
        public override ECPoint Subtract(
            ECPoint b)
        {
            CheckPoints(this, b);
            return SubtractSimple((F2mPoint) b);
        }

        /**
         * Subtracts another <code>ECPoints.F2m</code> from <code>this</code>
         * without checking if both points are on the same curve. Used by
         * multiplication algorithms, because there all points are a multiple
         * of the same point and hence the checks can be omitted.
         * @param b The other <code>ECPoints.F2m</code> to subtract from
         * <code>this</code>.
         * @return <code>this - b</code>
         */
        internal F2mPoint SubtractSimple(
            F2mPoint b)
        {
            if (b.IsInfinity)
                return this;

            // Add -b
            return AddSimple((F2mPoint) b.Negate());
        }

        /* (non-Javadoc)
         * @see Org.BouncyCastle.Math.EC.ECPoint#twice()
         */
        public override ECPoint Twice()
        {
            // Twice identity element (point at infinity) is identity
            if (this.IsInfinity)
                return this;

            // if x1 == 0, then (x1, y1) == (x1, x1 + y1)
            // and hence this = -this and thus 2(x1, y1) == infinity
            if (this.x.ToBigInteger().SignValue == 0)
                return this.curve.Infinity;

            F2mFieldElement lambda = (F2mFieldElement) this.x.Add(this.y.Divide(this.x));
            F2mFieldElement x2 = (F2mFieldElement)lambda.Square().Add(lambda).Add(this.curve.A);
            ECFieldElement ONE = this.curve.FromBigInteger(BigInteger.One);
            F2mFieldElement y2 = (F2mFieldElement)this.x.Square().Add(
                x2.Multiply(lambda.Add(ONE)));

            return new F2mPoint(this.curve, x2, y2, withCompression);
        }

        public override ECPoint Negate()
        {
            return new F2mPoint(curve, this.x, this.x.Add(this.y), withCompression);
        }

        /**
         * Sets the appropriate <code>ECMultiplier</code>, unless already set. 
         */
        internal override void AssertECMultiplier()
        {
            if (this.multiplier == null)
            {
                lock (this)
                {
                    if (this.multiplier == null)
                    {
                        if (((F2mCurve) this.curve).IsKoblitz)
                        {
                            this.multiplier = new WTauNafMultiplier();
                        }
                        else
                        {
                            this.multiplier = new WNafMultiplier();
                        }
                    }
                }
            }
        }
    }
}