// Written in the D programming language.

/** Module that will replace the built-in types $(D cfloat), $(D cdouble),
    $(D creal), $(D ifloat), $(D idouble), and $(D ireal).

    Authors:    Lars Tandle Kyllingstad
    Copyright:  Copyright (c) 2010, Lars T. Kyllingstad.
    License:    $(WEB boost.org/LICENSE_1_0.txt, Boost License 1.0)
*/
module std.complex;


import std.format;
import std.math;
import std.numeric;
import std.traits;




/** A complex number parametrised by a type T.

    Bugs:
    Some operators, such as opAssign and opOpAssign, should return by ref,
    but currently don't.  This will be implemented as soon as
    $(LINK2 http://d.puremagic.com/issues/show_bug.cgi?id=2460, DMD bug 2460)
    is fixed.
*/
struct Complex(T)  if (isFloatingPoint!T)
{
    /** The real part of the number. */
    T re;

    /** The imaginary part of the number. */
    T im;


    /** Calculate the absolute value (or modulus) of the number. */
    @property T abs() const
    {
        return hypot(re, im);
    }


    /** Calculate the argument (or phase) of the number. */
    @property T arg() const
    {
        return atan2(im, re);
    }


    /** Return the complex conjugate of the number. */
    @property Complex conj() const
    {
        return Complex(re, -im);
    }




    // ASSIGNMENT OPERATORS

    // TODO: Make operators return by ref when DMD bug 2460 is fixed.


    // this = complex
    Complex opAssign(R : T)(Complex!R z)
    {
        re = z.re;
        im = z.im;
        return this;
    }


    // this = numeric
    Complex opAssign(R : T)(R r)
    {
        re = r;
        im = 0;
        return this;
    }




    // COMPARISON OPERATORS


    // this == complex
    bool opEquals(R : T)(Complex!R z) const
    {
        return re == z.re && im == z.im;
    }


    // this == numeric
    bool opEquals(R : T)(R r) const
    {
        return re == r && im == 0;
    }



    // UNARY OPERATORS


    // +complex
    Complex opUnary(string op)() const
        if (op == "+")
    {
        return this;
    }


    // -complex
    Complex opUnary(string op)() const
        if (op == "-")
    {
        return Complex(-re, -im);
    }



    // BINARY OPERATORS


    // complex op complex
    Complex!(CommonType!(T,R)) opBinary(string op, R)(Complex!R z) const
    {
        alias typeof(return) C;
        auto w = C(this.re, this.im);
        return w.opOpAssign!(op)(z);
    }


    // complex op numeric
    Complex!(CommonType!(T,R)) opBinary(string op, R)(R r) const
        if (isNumeric!R)
    {
        alias typeof(return) C;
        auto w = C(this.re, this.im);
        return w.opOpAssign!(op)(r);
    }


    // numeric + complex,  numeric * complex
    Complex!(CommonType!(T, R)) opBinaryRight(string op, R)(R r) const
        if ((op == "+" || op == "*") && (isNumeric!R))
    {
        return opBinary!(op)(r);
    }


    // numeric - complex
    Complex!(CommonType!(T, R)) opBinaryRight(string op, R)(R r) const
        if (op == "-" && isNumeric!R)
    {
        return Complex(r - re, -im);
    }


    // numeric / complex
    Complex!(CommonType!(T, R)) opBinaryRight(string op, R)(R r) const
        if (op == "/" && isNumeric!R)
    {
        typeof(return) w;
        alias FPTemporary!(typeof(w.re)) Tmp;

        if (fabs(re) < fabs(im))
        {
            Tmp ratio = re/im;
            Tmp rdivd = r/(re*ratio + im);

            w.re = rdivd*ratio;
            w.im = -rdivd;
        }
        else
        {
            Tmp ratio = im/re;
            Tmp rdivd = r/(re + im*ratio);

            w.re = rdivd;
            w.im = -rdivd*ratio;
        }

        return w;
    }



    // OPASSIGN OPERATORS


    // complex += complex,  complex -= complex
    Complex opOpAssign(string op, C)(C z)
        if ((op == "+" || op == "-") && is(C R == Complex!R))
    {
        mixin ("re "~op~"= z.re;");
        mixin ("im "~op~"= z.im;");
        return this;
    }


    // complex *= complex
    Complex opOpAssign(string op, C)(C z)
        if (op == "*" && is(C R == Complex!R))
    {
        auto temp = re*z.re - im*z.im;
        im = im*z.re + re*z.im;
        re = temp;
        return this;
    }


    // complex /= complex
    Complex opOpAssign(string op, C)(C z)
        if (op == "/" && is(C R == Complex!R))
    {
        if (fabs(z.re) < fabs(z.im))
        {
            FPTemporary!T ratio = z.re/z.im;
            FPTemporary!T denom = z.re*ratio + z.im;

            auto temp = (re*ratio + im)/denom;
            im = (im*ratio - re)/denom;
            re = temp;
        }
        else
        {
            FPTemporary!T ratio = z.im/z.re;
            FPTemporary!T denom = z.re + z.im*ratio;

            auto temp = (re + im*ratio)/denom;
            im = (im - re*ratio)/denom;
            re = temp;
        }
        return this;
    }


    // complex ^^= complex
    Complex opOpAssign(string op, C)(C z)
        if (op == "^^" && is(C R == Complex!R))
    {
        FPTemporary!T r = abs;
        FPTemporary!T t = arg;
        FPTemporary!T ab = r^^z.re * exp(-t*z.im);
        FPTemporary!T ar = t*z.re + log(r)*z.im;

        re = ab*cos(ar);
        im = ab*sin(ar);
        return this;
    }


    // complex += numeric,  complex -= numeric
    Complex opOpAssign(string op, U : T)(U a)  if (op == "+" || op == "-")
    {
        mixin ("re "~op~"= a;");
        return this;
    }


    // complex *= numeric,  complex /= numeric
    Complex opOpAssign(string op, U : T)(U a)  if (op == "*" || op == "/")
    {
        mixin ("re "~op~"= a;");
        mixin ("im "~op~"= a;");
        return this;
    }


    // complex ^^= real
    Complex opOpAssign(string op, R)(R r)
        if (op == "^^" && isFloatingPoint!R)
    {
        FPTemporary!T ab = abs^^r;
        FPTemporary!T ar = arg*r;
        re = ab*cos(ar);
        im = ab*sin(ar);
        return this;
    }


    // complex ^^= int
    Complex opOpAssign(string op, U)(U i)
        if (op == "^^" && isIntegral!U)
    {
        switch (i)
        {
        case 0:
            re = 1.0;
            im = 0.0;
            break;
        case 1:
            // identity; do nothing
            break;
        case 2:
            this *= this;
            break;
        case 3:
            auto z = this;
            this *= z;
            this *= z;
            break;
        default:
            this ^^= cast(real) i;
        }
        return this;
    }




    /** Convert the complex number to a string representation.
    
        If a $(D sink) delegate is specified, the string is passed to it
        and this function returns $(D null).  Otherwise, this function
        returns the string representation directly.

        The output format is controlled via $(D formatSpec), which should consist
        of a single POSIX format specifier, including the percent (%) character.
        Note that complex numbers are floating point numbers, so the only
        valid format characters are 'e', 'f', 'g', 'a', and 's', where 's'
        gives the default behaviour. Positional parameters are not valid
        in this context.

        See the $(LINK2 std_format.html, std.format documentation) for
        more information.
    */
    string toString
        (void delegate(const(char)[]) sink = null, string formatSpec = "%s")
        const
    {
        if (sink == null)
        {
            char[] buf;
            buf.reserve(100);
            toString((const(char)[] s) { buf ~= s; }, formatSpec);
            return cast(string) buf;
        }

        formattedWrite(sink, formatSpec, re);
        if (signbit(im) == 0)  sink("+");
        formattedWrite(sink, formatSpec, im);
        sink("i");
        return null;
    }
}


unittest
{
    enum EPS = double.epsilon;

    // Check abs() and arg()
    auto c1 = Complex!double(1.0, 1.0);
    assert (approxEqual(c1.abs, sqrt(2.0), EPS));
    assert (approxEqual(c1.arg, PI_4, EPS));

    auto c1c = c1.conj;
    assert (c1c.re == 1.0 && c1c.im == -1.0);


    // Check unary operations.
    auto c2 = Complex!double(0.5, 2.0);

    assert (c2 == +c2);

    assert ((-c2).re == -(c2.re));
    assert ((-c2).im == -(c2.im));
    assert (c2 == -(-c2));


    // Check complex-complex operations.
    auto cpc = c1 + c2;
    assert (cpc.re == c1.re + c2.re);
    assert (cpc.im == c1.im + c2.im);

    auto cmc = c1 - c2;
    assert (cmc.re == c1.re - c2.re);
    assert (cmc.im == c1.im - c2.im);

    auto ctc = c1 * c2;
    assert (approxEqual(ctc.abs, c1.abs*c2.abs, EPS));
    assert (approxEqual(ctc.arg, c1.arg+c2.arg, EPS));

    auto cdc = c1 / c2;
    assert (approxEqual(cdc.abs, c1.abs/c2.abs, EPS));
    assert (approxEqual(cdc.arg, c1.arg-c2.arg, EPS));

    auto cec = c1^^c2;
    assert (approxEqual(cec.re, 0.11524131979943839881, EPS));
    assert (approxEqual(cec.im, 0.21870790452746026696, EPS));


    // Check complex-real operations.
    double a = 123.456;

    auto cpr = c1 + a;
    assert (cpr.re == c1.re + a);
    assert (cpr.im == c1.im);

    auto cmr = c1 - a;
    assert (cmr.re == c1.re - a);
    assert (cmr.im == c1.im);

    auto ctr = c1 * a;
    assert (ctr.re == c1.re*a);
    assert (ctr.im == c1.im*a);

    auto cdr = c1 / a;
    assert (approxEqual(cdr.abs, c1.abs/a, EPS));
    assert (approxEqual(cdr.arg, c1.arg, EPS));

    auto rpc = a + c1;
    assert (rpc == cpr);

    auto rmc = a - c1;
    assert (rmc.re == a-c1.re);
    assert (rmc.im == -c1.im);

    auto rtc = a * c1;
    assert (rtc == ctr);

    auto rdc = a / c1;
    assert (approxEqual(rdc.abs, a/c1.abs, EPS));
    assert (approxEqual(rdc.arg, -c1.arg, EPS));

    auto cer = c1^^3.0;
    assert (approxEqual(cer.abs, c1.abs^^3, EPS));
    assert (approxEqual(cer.arg, c1.arg*3, EPS));


    // Check Complex-int operations.
    foreach (i; 0..6)
    {
        auto cei = c1^^i;
        assert (approxEqual(cei.abs, c1.abs^^i, EPS));
        // Use cos() here to deal with arguments that go outside
        // the (-pi,pi] interval (only an issue for i>3).
        assert (approxEqual(cos(cei.arg), cos(c1.arg*i), EPS));
    }


    // Check operations between different complex types.
    auto cf = Complex!float(1.0, 1.0);
    auto cr = Complex!real(1.0, 1.0);
    auto c1pcf = c1 + cf;
    auto c1pcr = c1 + cr;
    static assert (is(typeof(c1pcf) == Complex!double));
    static assert (is(typeof(c1pcr) == Complex!real));
    assert (c1pcf.re == c1pcr.re);
    assert (c1pcf.im == c1pcr.im);
}

unittest
{
    // Assignments and comparisons
    Complex!double z;

    z = 1;
    assert (z == 1);
    assert (z.re == 1.0  &&  z.im == 0.0);

    z = 2.0;
    assert (z == 2.0);
    assert (z.re == 2.0  &&  z.im == 0.0);

    z = 1.0L;
    assert (z == 1.0L);
    assert (z.re == 1.0  &&  z.im == 0.0);


    auto w = Complex!real(1.0, 1.0);
    z = w;
    assert (z == w);
    assert (z.re == 1.0  &&  z.im == 1.0);

    auto c = Complex!float(2.0, 2.0);
    z = c;
    assert (z == c);
    assert (z.re == 2.0  &&  z.im == 2.0);
}

unittest
{
    // Convert to string.

    // Using default format specifier
    auto z1 = Complex!real(0.123456789, 0.123456789);
    char[] s1;
    z1.toString((const(char)[] c) { s1 ~= c; });
    assert (s1 == "0.123457+0.123457i");
    assert (s1 == z1.toString());

    // Using custom format specifier
    auto z2 = z1.conj;
    char[] s2;
    z2.toString((const(char)[] c) { s2 ~= c; }, "%.8e");
    assert (s2 == "1.23456789e-01-1.23456789e-01i");
    assert (s2 == z2.toString(null, "%.8e"));
}




/*  Fold Complex!(Complex!T) to Complex!T.

    The rationale for this is that just like the real line is a
    subspace of the complex plane, the complex plane is a subspace
    of itself.  Example of usage:
    ---
    Complex!T addI(T)(T x)
    {
        return x + Complex!T(0.0, 1.0);
    }
    ---
    The above will work if T is both real and complex.
*/
template Complex(T) if (is(T R == Complex!R))
{
    alias T Complex;
}

unittest
{
    static assert (is(Complex!(Complex!real) == Complex!real));

    Complex!T addI(T)(T x)
    {
        return x + Complex!T(0.0, 1.0);
    }

    auto z1 = addI(1.0);
    assert (z1.re == 1.0 && z1.im == 1.0);

    enum one = Complex!double(1.0, 0.0);
    auto z2 = addI(one);
    assert (z1 == z2);
}




/** Construct a complex number given its absolute value and argument. */
Complex!(CommonType!(T, U)) fromPolar(T, U)(T modulus, U argument)
{
    return Complex!(CommonType!(T,U))
        (modulus*cos(argument), modulus*sin(argument));
}


unittest
{
    auto z = fromPolar(sqrt(2.0), PI_4);
    assert (approxEqual(z.re, 1.0L, real.epsilon));
    assert (approxEqual(z.im, 1.0L, real.epsilon));
}