module nxt.owned;

/** Return wrapper around container `Container` that can be safely sliced, by
    tracking number of read borrowed ranges and whether it's currently write
    borrowed.

    Only relevant when `Container` implements referenced access over
    <ul>
    <li> `opSlice` and
    <li> `opIndex`
    </ul>

    TODO: Iterate and wrap all @unsafe accessors () and wrapped borrow
    checks for all modifying members of `Container`?
*/
struct Owned(Container)
    if (needsOwnership!Container)
{
    import std.range.primitives : hasSlicing;
    import std.traits : isMutable;

    /// Type of range of `Container`.
    alias Range = typeof(Container.init[]);

pragma(inline):

    ~this() nothrow @nogc
    {
        assert(!_writeBorrowed, "This is still write-borrowed, cannot release!");
        assert(_readBorrowCount == 0, "This is still read-borrowed, cannot release!");
    }

    /// Move `this` into a returned r-value.
    typeof(this) move()
    {
        assert(!_writeBorrowed, "This is still write-borrowed, cannot move!");
        assert(_readBorrowCount == 0, "This is still read-borrowed, cannot move!");
        import core.lifetime : move;
        return move(this);
    }

    /** Checked overload for `std.algorithm.mutation.move`. */
    void move(ref typeof(this) dst) pure nothrow @nogc
    {
        assert(!_writeBorrowed, "Source is still write-borrowed, cannot move!");
        assert(_readBorrowCount == 0, "Source is still read-borrowed, cannot move!");

        assert(!dst._writeBorrowed, "Destination is still write-borrowed, cannot move!");
        assert(dst._readBorrowCount == 0, "Destination is still read-borrowed, cannot move!");

        import core.lifetime : move;
        move(this, dst);
    }

    /** Checked overload for `std.algorithm.mutation.moveEmplace`. */
    void moveEmplace(ref typeof(this) dst) pure nothrow @nogc
    {
        assert(!_writeBorrowed, "Source is still write-borrowed, cannot moveEmplace!");
        assert(_readBorrowCount == 0, "Source is still read-borrowed, cannot moveEmplace!");

        import core.lifetime : moveEmplace;
        moveEmplace(this, dst);
    }

    static if (true/*TODO: hasUnsafeSlicing!Container*/)
    {
        import nxt.borrowed : ReadBorrowed, WriteBorrowed;

        // TODO: can all these definitions be reduce somehow?

        /// Get full read-only slice.
        ReadBorrowed!(Range, Owned) sliceRO() const @trusted
        {
            import core.internal.traits : Unqual;
            assert(!_writeBorrowed, "This is already write-borrowed");
            return typeof(return)(_container.opSlice,
                                  cast(Unqual!(typeof(this))*)(&this)); // trusted unconst casta
        }

        /// Get read-only slice in range `i` .. `j`.
        ReadBorrowed!(Range, Owned) sliceRO(size_t i, size_t j) const @trusted
        {
            import core.internal.traits : Unqual;
            assert(!_writeBorrowed, "This is already write-borrowed");
            return typeof(return)(_container.opSlice[i .. j],
                                  cast(Unqual!(typeof(this))*)(&this)); // trusted unconst cast
        }

        /// Get full read-write slice.
        WriteBorrowed!(Range, Owned) sliceRW() @trusted
        {
            assert(!_writeBorrowed, "This is already write-borrowed");
            assert(_readBorrowCount == 0, "This is already read-borrowed");
            return typeof(return)(_container.opSlice, &this);
        }

        /// Get read-write slice in range `i` .. `j`.
        WriteBorrowed!(Range, Owned) sliceRW(size_t i, size_t j) @trusted
        {
            assert(!_writeBorrowed, "This is already write-borrowed");
            assert(_readBorrowCount == 0, "This is already read-borrowed");
            return typeof(return)(_container.opSlice[i .. j], &this);
        }

        /// Get read-only slice in range `i` .. `j`.
        auto opSlice(size_t i, size_t j) const
        {
            return sliceRO(i, j);
        }
        /// Get read-write slice in range `i` .. `j`.
        auto opSlice(size_t i, size_t j)
        {
            return sliceRW(i, j);
        }

        /// Get read-only full slice.
        auto opSlice() const
        {
            return sliceRO();
        }
        /// Get read-write full slice.
        auto opSlice()
        {
            return sliceRW();
        }
    }

    @safe pure nothrow @nogc:

    @property:

    /// Returns: `true` iff `this` is either write or read borrowed.
    bool isBorrowed() const { return _writeBorrowed || _readBorrowCount >= 1; }

    /// Returns: `true` iff owned container is write borrowed.
    bool isWriteBorrowed() const { return _writeBorrowed; }

    /// Returns: number of read-only borrowers of owned container.
    uint readBorrowCount() const { return _readBorrowCount; }

    Container _container;            /// wrapped container
    alias _container this;

public:
    bool _writeBorrowed = false; /// `true` iff `_container` is currently referred to
    uint _readBorrowCount = 0; /// number of readable borrowers. TODO: use `size_t` minus one bit instead in `size_t _stats`
    enum readBorrowCountMax = typeof(_readBorrowCount).max;
}

/** Checked overload for `std.algorithm.mutation.move`.

    TODO: Can we somehow prevent users of Owned from accidentally using
    `std.algorithm.mutation.move` instead of this wrapper?
 */
void move(Owner)(ref Owner src, ref Owner dst) @safe pure nothrow @nogc
    if (isInstanceOf!(Owned, Owner))
{
    src.move(dst);              // reuse member function
}

/** Checked overload for `std.algorithm.mutation.moveEmplace`.

    TODO: Can we somehow prevent users of Owned from accidentally using
    `std.algorithm.mutation.moveEmplace` instead of this wrapper?
*/
void moveEmplace(Owner)(ref Owner src, ref Owner dst) @safe pure nothrow @nogc
    if (isInstanceOf!(Owned, Owner))
{
    src.moveEmplace(dst);   // reuse member function
}

template needsOwnership(Container)
{
    import std.range.primitives : hasSlicing;
    // TODO: activate when array_ex : UniqueArray
    // enum needsOwnership = hasSlicing!Container; // TODO: extend to check if it's not @safe
    enum needsOwnership = is(Container == struct);
}

pure unittest
{
    alias A = UniqueArray!int;
    const Owned!A co;          // const owner

    import std.traits : isMutable;
    static assert(!isMutable!(typeof(co)));

    const cos = co[];
}

@safe pure unittest
{
    alias A = UniqueArray!int;
    A a = A.init;
    a = A.init;
    // TODO: a ~= A.init;
}

pure unittest
{
    import std.traits : isInstanceOf;
    import std.exception: assertThrown;
    import core.exception : AssertError;

    import nxt.borrowed : ReadBorrowed, WriteBorrowed;

    alias A = UniqueArray!int;

    Owned!A oa;

    Owned!A ob;
    oa.move(ob);                // ok to move unborrowed

    Owned!A od = void;
    oa.moveEmplace(od);         // ok to moveEmplace unborrowed

    oa ~= 1;
    oa ~= 2;
    assert(oa[] == [1, 2]);
    assert(oa[0 .. 1] == [1]);
    assert(oa[1 .. 2] == [2]);
    assert(oa[0 .. 2] == [1, 2]);
    assert(!oa.isWriteBorrowed);
    assert(!oa.isBorrowed);
    assert(oa.readBorrowCount == 0);

    {
        const wb = oa.sliceRW;

        Owned!A oc;
        assertThrown!AssertError(oa.move()); // cannot move write borrowed

        assert(wb.length == 2);
        static assert(!__traits(compiles, { auto wc = wb; })); // write borrows cannot be copied
        assert(oa.isBorrowed);
        assert(oa.isWriteBorrowed);
        assert(oa.readBorrowCount == 0);
        assertThrown!AssertError(oa.opSlice); // one more write borrow is not allowed
    }

    // ok to write borrow again in separate scope
    {
        const wb = oa.sliceRW;

        assert(wb.length == 2);
        assert(oa.isBorrowed);
        assert(oa.isWriteBorrowed);
        assert(oa.readBorrowCount == 0);
    }

    // ok to write borrow again in separate scope
    {
        const wb = oa.sliceRW(0, 2);
        assert(wb.length == 2);
        assert(oa.isBorrowed);
        assert(oa.isWriteBorrowed);
        assert(oa.readBorrowCount == 0);
    }

    // multiple read-only borrows are allowed
    {
        const rb1 = oa.sliceRO;

        Owned!A oc;
        assertThrown!AssertError(oa.move(oc)); // cannot move read borrowed

        assert(rb1.length == oa.length);
        assert(oa.readBorrowCount == 1);

        const rb2 = oa.sliceRO;
        assert(rb2.length == oa.length);
        assert(oa.readBorrowCount == 2);

        const rb3 = oa.sliceRO;
        assert(rb3.length == oa.length);
        assert(oa.readBorrowCount == 3);

        const rb_ = rb3;
        assert(rb_.length == oa.length);
        assert(oa.readBorrowCount == 4);
        assertThrown!AssertError(oa.sliceRW); // single write borrow is not allowed
    }

    // test modification via write borrow
    {
        auto wb = oa.sliceRW;
        wb[0] = 11;
        wb[1] = 12;
        assert(wb.length == oa.length);
        assert(oa.isWriteBorrowed);
        assert(oa.readBorrowCount == 0);
        assertThrown!AssertError(oa.sliceRO);
    }
    assert(oa[] == [11, 12]);
    assert(oa.sliceRO(0, 2) == [11, 12]);

    // test mutable slice
    static assert(isInstanceOf!(WriteBorrowed, typeof(oa.sliceRW())));
    static assert(isInstanceOf!(WriteBorrowed, typeof(oa[])));
    foreach (ref e; oa.sliceRW)
    {
        assertThrown!AssertError(oa.sliceRO); // one more write borrow is not allowed
        assertThrown!AssertError(oa.sliceRW); // one more write borrow is not allowed
        assertThrown!AssertError(oa[]); // one more write borrow is not allowed
    }

    // test readable slice
    static assert(isInstanceOf!(ReadBorrowed, typeof(oa.sliceRO())));
    foreach (const ref e; oa.sliceRO)
    {
        assert(oa.sliceRO.length == oa.length);
        assert(oa.sliceRO[0 .. 0].length == 0);
        assert(oa.sliceRO[0 .. 1].length == 1);
        assert(oa.sliceRO[0 .. 2].length == oa.length);
        assertThrown!AssertError(oa.sliceRW); // write borrow during iteration is not allowed
        assertThrown!AssertError(oa.move());  // move not allowed when borrowed
    }

    // move semantics
    auto oaMove1 = oa.move();
    auto oaMove2 = oaMove1.move();
    assert(oaMove2[] == [11, 12]);

    // constness propagation from owner to borrower
    Owned!A mo;          // mutable owner
    assert(mo.sliceRO.ptr == mo.ptr);
    assert(mo.sliceRO(0, 0).ptr == mo.ptr);
    static assert(isInstanceOf!(ReadBorrowed, typeof(mo.sliceRO())));

    const Owned!A co;          // const owner
    assert(co.sliceRO.ptr == co.ptr);
    static assert(isInstanceOf!(ReadBorrowed, typeof(co.sliceRO())));
}

nothrow unittest
{
    import std.algorithm.sorting : sort;
    alias E = int;
    alias A = UniqueArray!E;
    A a;
    sort(a[]);         // TODO: make this work
}

// y = sort(x.move()), where x and y are instances of unsorted Array
@safe nothrow unittest
{
    import std.algorithm.sorting : sort;
    import std.range.primitives : isInputRange, isForwardRange, isRandomAccessRange, hasSlicing;

    alias E = int;
    alias A = UniqueArray!E;
    alias O = Owned!A;

    O o;
    o ~= [42, 43];

    assert(o.length == 2);

    scope os = o.sliceRO;

    alias OS = typeof(os);
    static assert(isInputRange!(OS));
    static assert(isForwardRange!(OS));
    static assert(hasSlicing!(OS));
    static assert(isRandomAccessRange!OS);

    assert(!os.empty);
    assert(os.length == 2);
    os.popFront();
    assert(!os.empty);
    assert(os.length == 1);
    os.popFront();
    assert(os.empty);

    // TODO: scope oss = os[];            // no op
    // TODO: assert(oss.empty);
}

// check write-borrow
@safe nothrow unittest
{
    import std.algorithm.sorting : sort;
    import std.range.primitives : isInputRange, isForwardRange, isRandomAccessRange, hasSlicing;

    alias E = int;
    alias A = UniqueArray!E;
    alias O = Owned!A;

    const O co;
    auto cos = co[0 .. 0];
    const ccos = co[0 .. 0];

    // TODO: const coc = co[].save();

    O o;
    o ~= [42, 43];
    auto os = o.sliceRW;
    alias OS = typeof(os);
    static assert(isInputRange!(OS));

    // static assert(isForwardRange!(OS));
    // static assert(hasSlicing!(OS));
    // static assert(isRandomAccessRange!OS);
    // import std.algorithm.sorting : sort;
    // sort(o[]);
}

version(unittest)
{
    import nxt.container.dynamic_array : UniqueArray = DynamicArray;
    import nxt.dbgio;
}