/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/**
 * Algorithms that modify its arguments.
 *
 * Copyright: Eugene Wissner 2017-2018.
 * License: $(LINK2 https://www.mozilla.org/en-US/MPL/2.0/,
 *                  Mozilla Public License, v. 2.0).
 * Authors: $(LINK2 mailto:info@caraus.de, Eugene Wissner)
 * Source: $(LINK2 https://github.com/caraus-ecms/tanya/blob/master/source/tanya/algorithm/mutation.d,
 *                 tanya/algorithm/mutation.d)
 */
module tanya.algorithm.mutation;

static import tanya.memory.op;
import tanya.meta.trait;
import tanya.meta.transform;
import tanya.range;

private void deinitialize(bool zero, T)(ref T value)
{
    static if (is(T == U[S], U, size_t S))
    {
        foreach (ref e; value)
        {
            deinitialize!zero(e);
        }
    }
    else
    {
        static if (isNested!T)
        {
            // Don't override the context pointer.
            enum size_t size = T.sizeof - (void*).sizeof;
        }
        else
        {
            enum size_t size = T.sizeof;
        }
        static if (zero)
        {
            tanya.memory.op.fill!0((cast(void*) &value)[0 .. size]);
        }
        else
        {
            tanya.memory.op.copy(typeid(T).initializer()[0 .. size],
                                 (&value)[0 .. 1]);
        }
    }
}

/**
 * Moves $(D_PARAM source) into $(D_PARAM target) assuming that
 * $(D_PARAM target) isn't initialized.
 *
 * Moving the $(D_PARAM source) copies it into the $(D_PARAM target) and places
 * the $(D_PARAM source) into a valid but unspecified state, which means that
 * after moving $(D_PARAM source) can be destroyed or assigned a new value, but
 * accessing it yields an unspecified value. No postblits or destructors are
 * called. If the $(D_PARAM target) should be destroyed before, use
 * $(D_PSYMBOL move).
 *
 * $(D_PARAM source) and $(D_PARAM target) must be different objects.
 *
 * Params:
 *  T      = Object type.
 *  source = Source object.
 *  target = Target object.
 *
 * See_Also: $(D_PSYMBOL move),
 *           $(D_PSYMBOL hasElaborateCopyConstructor),
 *           $(D_PSYMBOL hasElaborateDestructor).
 *
 * Precondition: `&source !is &target`.
 */
void moveEmplace(T)(ref T source, ref T target) @system
in
{
    assert(&source !is &target, "Source and target must be different");
}
do
{
    static if (is(T == struct) || isStaticArray!T)
    {
        tanya.memory.op.copy((&source)[0 .. 1], (&target)[0 .. 1]);

        static if (hasElaborateCopyConstructor!T || hasElaborateDestructor!T)
        {
            if (typeid(T).initializer().ptr is null)
            {
                deinitialize!true(source);
            }
            else
            {
                deinitialize!false(source);
            }
        }
    }
    else
    {
        target = source;
    }
}

///
@nogc nothrow pure @system unittest
{
    static struct S
    {
        int member = 5;

        this(this) @nogc nothrow pure @safe
        {
            assert(false);
        }
    }
    S source, target = void;
    moveEmplace(source, target);
    assert(target.member == 5);

    int x1 = 5, x2;
    moveEmplace(x1, x2);
    assert(x2 == 5);
}

// Is pure.
@nogc nothrow pure @system unittest
{
    struct S
    {
        this(this)
        {
        }
    }
    S source, target = void;
    static assert(is(typeof({ moveEmplace(source, target); })));
}

// Moves nested.
@nogc nothrow pure @system unittest
{
    struct Nested
    {
        void method() @nogc nothrow pure @safe
        {
        }
    }
    Nested source, target = void;
    moveEmplace(source, target);
    assert(source == target);
}

// Emplaces static arrays.
@nogc nothrow pure @system unittest
{
    static struct S
    {
        size_t member;
        this(size_t i) @nogc nothrow pure @safe
        {
            this.member = i;
        }
        ~this() @nogc nothrow pure @safe
        {
        }
    }
    S[2] source = [ S(5), S(5) ], target = void;
    moveEmplace(source, target);
    assert(source[0].member == 0);
    assert(target[0].member == 5);
    assert(source[1].member == 0);
    assert(target[1].member == 5);
}

/**
 * Moves $(D_PARAM source) into $(D_PARAM target) assuming that
 * $(D_PARAM target) isn't initialized.
 *
 * Moving the $(D_PARAM source) copies it into the $(D_PARAM target) and places
 * the $(D_PARAM source) into a valid but unspecified state, which means that
 * after moving $(D_PARAM source) can be destroyed or assigned a new value, but
 * accessing it yields an unspecified value. $(D_PARAM target) is destroyed before
 * the new value is assigned. If $(D_PARAM target) isn't initialized and
 * therefore shouldn't be destroyed, $(D_PSYMBOL moveEmplace) can be used.
 *
 * If $(D_PARAM target) isn't specified, $(D_PSYMBOL move) returns the source
 * as rvalue without calling its copy constructor or destructor.
 *
 * $(D_PARAM source) and $(D_PARAM target) are the same object,
 * $(D_PSYMBOL move) does nothing.
 *
 * Params:
 *  T      = Object type.
 *  source = Source object.
 *  target = Target object.
 *
 * See_Also: $(D_PSYMBOL moveEmplace).
 */
void move(T)(ref T source, ref T target)
{
    if ((() @trusted => &source is &target)())
    {
        return;
    }
    static if (hasElaborateDestructor!T)
    {
        target.__xdtor();
    }
    (() @trusted => moveEmplace(source, target))();
}

/// ditto
T move(T)(ref T source) @trusted
{
    T target = void;
    moveEmplace(source, target);
    return target;
}

///
@nogc nothrow pure @safe unittest
{
    static struct S
    {
        int member = 5;

        this(this) @nogc nothrow pure @safe
        {
            assert(false);
        }
    }
    S source, target = void;
    move(source, target);
    assert(target.member == 5);
    assert(move(target).member == 5);

    int x1 = 5, x2;
    move(x1, x2);
    assert(x2 == 5);
    assert(move(x2) == 5);
}

// Moves if source is target.
@nogc nothrow pure @safe unittest
{
    int x = 5;
    move(x, x);
    assert(x == 5);
}

/**
 * Exchanges the values of $(D_PARAM a) and $(D_PARAM b).
 *
 * $(D_PSYMBOL swap) moves the contents of $(D_PARAM a) and $(D_PARAM b)
 * without calling its postblits or destructors.
 *
 * Params:
 *  a = The first object.
 *  b = The second object.
 */
void swap(T)(ref T a, ref T b) @trusted
{
    T tmp = void;
    moveEmplace(a, tmp);
    moveEmplace(b, a);
    moveEmplace(tmp, b);
}

///
@nogc nothrow pure @safe unittest
{
    int a = 3, b = 5;
    swap(a, b);
    assert(a == 5);
    assert(b == 3);
}

/**
 * Copies the $(D_PARAM source) range into the $(D_PARAM target) range.
 *
 * Params:
 *  Source = Input range type.
 *  Target = Output range type.
 *  source = Source input range.
 *  target = Target output range.
 *
 * Returns: $(D_PARAM target) range, whose front element is the one past the
 *          last element copied.
 *
 * Precondition: $(D_PARAM target) should be large enough to accept all
 *               $(D_PARAM source) elements.
 */
Target copy(Source, Target)(Source source, Target target)
if (isInputRange!Source && isOutputRange!(Target, Source))
in
{
    static if (hasLength!Source && hasLength!Target)
    {
        assert(target.length >= source.length);
    }
}
do
{
    alias E = ElementType!Source;
    static if (isDynamicArray!Source
            && is(Unqual!E == ElementType!Target)
            && !hasElaborateCopyConstructor!E
            && !hasElaborateAssign!E
            && !hasElaborateDestructor!E)
    {
        if (source.ptr < target.ptr
         && (() @trusted => (target.ptr - source.ptr) < source.length)())
        {
            tanya.memory.op.copyBackward(source, target);
        }
        else if (source.ptr !is target.ptr)
        {
            tanya.memory.op.copy(source, target);
        }
        return target[source.length .. $];
    }
    else
    {
        for (; !source.empty; source.popFront())
        {
            put(target, source.front);
        }
        return target;
    }
}

///
@nogc nothrow pure @safe unittest
{
    import tanya.algorithm.comparison : equal;

    const int[2] source = [1, 2];
    int[2] target = [3, 4];

    copy(source[], target[]);
    assert(equal(source[], target[]));
}

// Returns advanced target
@nogc nothrow pure @safe unittest
{
    int[5] input = [1, 2, 3, 4, 5];
    assert(copy(input[3 .. 5], input[]).front == 3);
}

// Copies overlapping arrays
@nogc nothrow pure @safe unittest
{
    import tanya.algorithm.comparison : equal;

    int[6] actual = [1, 2, 3, 4, 5, 6];
    const int[6] expected = [1, 2, 1, 2, 3, 4];

    copy(actual[0 .. 4], actual[2 .. 6]);
    assert(equal(actual[], expected[]));
}

@nogc nothrow pure @safe unittest
{
    static assert(is(typeof(copy((ubyte[]).init, (ushort[]).init))));
    static assert(!is(typeof(copy((ushort[]).init, (ubyte[]).init))));
}

@nogc nothrow pure @safe unittest
{
    static struct OutPutRange
    {
        int value;
        void put(int value) @nogc nothrow pure @safe
        in
        {
            assert(this.value == 0);
        }
        do
        {
            this.value = value;
        }
    }
    int[1] source = [5];
    OutPutRange target;

    assert(copy(source[], target).value == 5);
}