module nxt.slicing;

/** Slice at all positions where $(D isTerminator) is $(D false) before current
    element and $(D true) at current.

    TODO: Can this be replaced by chunkBy
    See_Also: http://dlang.org/library/std/algorithm/splitter.html.
    See_Also: http://forum.dlang.org/post/cwqeywykubsuynkidlux@forum.dlang.org
*/
auto preSlicer(alias isTerminator, R)(R input)
/* if (((isRandomAccessRange!R && */
/*       hasSlicing!R) || */
/*      isSomeString!R) && */
/*     is(typeof(unaryFun!isTerminator(input.front)))) */
{
    import std.functional : unaryFun;
    return PreSlicer!(unaryFun!isTerminator, R)(input);
}

private struct PreSlicer(alias isTerminator, R)
{
    this(R input)
    {
        _input = input;
        import std.range.primitives : empty;
        if (_input.empty)
            _end = size_t.max;
        else
            skipTerminatorsAndSetEnd();
    }

    import std.range.primitives : isInfinite;

    static if (isInfinite!R)
        enum bool empty = false;  // propagate infiniteness
    else
        @property bool empty() => _end == size_t.max;

    @property auto front() => _input[0 .. _end];

    void popFront()
    {
        _input = _input[_end .. $];
        import std.range.primitives : empty;
        if (_input.empty)
        {
            _end = size_t.max;
            return;
        }
        skipTerminatorsAndSetEnd();
    }

    @property PreSlicer save()
    {
        auto ret = this;
        import std.range.primitives : save;
        ret._input = _input.save;
        return ret;
    }

    private void skipTerminatorsAndSetEnd()
    {
        // `_end` is now invalid in relation to `_input`
        alias ElementEncodingType = typeof(_input[0]);
        static if (is(ElementEncodingType : char) ||
                   is(ElementEncodingType : wchar))
        {
            size_t offset = 0;
            while (offset != _input.length)
            {
                auto slice = _input[offset .. $];
                import std.utf : decodeFront;
                size_t numCodeUnits;
                const dchar dch = decodeFront(slice, numCodeUnits);
                if (offset != 0 && // ignore terminator at offset 0
                    isTerminator(dch))
                    break;
                offset += numCodeUnits; // skip over
            }
            _end = offset;
        }
        else
        {
            size_t offset = 0;
            if (isTerminator(_input[0]))
                offset += 1;        // skip over it
            import std.algorithm : countUntil;
            const count = _input[offset .. $].countUntil!isTerminator();
            if (count == -1)        // end reached
                _end = _input.length;
            else
                _end = offset + count;
        }
    }

    private R _input;
    private size_t _end = 0;    // _input[0 .. _end] is current front
}
alias preSplitter = preSlicer;

unittest
{
    import std.uni : isUpper, isWhite;
    alias sepPred = ch => (ch == '-' || ch.isWhite);
    assert(equal("doThis or doThat do-stuff".preSlicer!(_ => (_.isUpper ||
                                                              sepPred(_)))
                                   .map!(word => (word.length >= 1 &&
                                                  sepPred(word[0]) ?
                                                  word[1 .. $] :
                                                  word)),
                 ["do", "This", "or", "do", "That", "do", "stuff"]));

    assert(equal("isAKindOf".preSlicer!isUpper, ["is", "A", "Kind", "Of"]));

    assert(equal("doThis".preSlicer!isUpper, ["do", "This"]));

    assert(equal("doThisIf".preSlicer!isUpper, ["do", "This", "If"]));

    assert(equal("utcOffset".preSlicer!isUpper, ["utc", "Offset"]));
    assert(equal("isUri".preSlicer!isUpper, ["is", "Uri"]));
    // TODO: assert(equal("baseSIUnit".preSlicer!isUpper, ["base", "SI", "Unit"]));

    assert(equal("SomeGreatVariableName".preSlicer!isUpper, ["Some", "Great", "Variable", "Name"]));
    assert(equal("someGGGreatVariableName".preSlicer!isUpper, ["some", "G", "G", "Great", "Variable", "Name"]));

    string[] e;
    assert(equal("".preSlicer!isUpper, e));
    assert(equal("a".preSlicer!isUpper, ["a"]));
    assert(equal("A".preSlicer!isUpper, ["A"]));
    assert(equal("A".preSlicer!isUpper, ["A"]));
    assert(equal("ö".preSlicer!isUpper, ["ö"]));
    assert(equal("åa".preSlicer!isUpper, ["åa"]));
    assert(equal("aå".preSlicer!isUpper, ["aå"]));
    assert(equal("åäö".preSlicer!isUpper, ["åäö"]));
    assert(equal("aB".preSlicer!isUpper, ["a", "B"]));
    assert(equal("äB".preSlicer!isUpper, ["ä", "B"]));
    assert(equal("aäB".preSlicer!isUpper, ["aä", "B"]));
    assert(equal("äaB".preSlicer!isUpper, ["äa", "B"]));
    assert(equal("äaÖ".preSlicer!isUpper, ["äa", "Ö"]));

    assert(equal([1, -1, 1, -1].preSlicer!(a => a > 0), [[1, -1], [1, -1]]));

    /* TODO: Add bidir support */
    /* import std.range : retro; */
    /* assert(equal([-1, 1, -1, 1].retro.preSlicer!(a => a > 0), [[1, -1], [1, -1]])); */
}

version(none)                   // TODO: enable
auto wordByMixedCaseSubWord(Range)(Range r)
{
    static struct Result
    {
        this(Range input)
        {
            _input = input;
            import std.range.primitives : empty;
            if (_input.empty)
                _end = size_t.max;
            else
                skipTerminatorsAndSetEnd();
        }

        @property bool empty() => _end == size_t.max;

        @property auto front() => _input[0 .. _end];

        void popFront()
        {
            _input = _input[_end .. $];
            import std.range.primitives : empty;
            if (_input.empty)
            {
                _end = size_t.max;
                return;
            }
            skipTerminatorsAndSetEnd();
        }

        private void skipTerminatorsAndSetEnd()
        {
            // `_end` is now invalid in relation to `_input`
            size_t offset = 0;
            while (offset != _input.length)
            {
                auto slice = _input[offset .. $];
                import std.utf : decodeFront;
                size_t numCodeUnits;
                const dchar dch = decodeFront(slice, numCodeUnits);
                if (offset != 0 && // ignore terminator at offset 0
                    isTerminator(dch))
                    break;
                offset += numCodeUnits; // skip over
            }
            _end = offset;
        }

        private Range _input;
        private size_t _end = 0;    // _input[0 .. _end] is current front
    }
    return Result(r);
}

version(none)                   // TODO: enable
@safe pure unittest
{
    assert(equal("äaÖ".wordByMixedCaseSubWord, ["äa", "Ö"]));
}

version(unittest)
{
     import std.algorithm.comparison : equal;
     import std.algorithm.iteration : map;
}