module nxt.splitter_ex;

import std.traits : isExpressions;

/** Non-decoding ASCII-separator-only variant of Phobos' `splitter`. */
auto splitterASCII(alias separatorPred, Range)(return Range r) @trusted
if (is(typeof(Range.init[0 .. 0])) && // can be sliced
    is(typeof(Range.init[0]) : char) &&
    is(typeof(separatorPred(char.init)) : bool)) // TODO: check that first parameter is bool
{
    static struct Result
    {
        private Range _input; // original copy of r
        private size_t _offset = 0; // hit offset if any, or `_haystack.length` if miss

        this(Range input)
        {
            // dbg("input:", input);
            _input = input;
            tryFindNextFront();  // find first hit if any
        }

        bool empty() const @property
        	=> _input.length == 0; // dbg("input:", _input, " ", " offset:", _offset);

        @property Range front() return @trusted
		in(!empty, "Attempting to fetch the front of an empty splitter.")
			=> _input.ptr[0 .. _offset]; // dbg("input:", _input, " ", " offset:", _offset);

        /** Skip any separators. */
        void skipSeparators() @trusted
        {
            while (_offset < _input.length &&
                   separatorPred(_input.ptr[_offset]))
            {
                /* predicate `separatorPred` must only filter out ASCII, or
                 * incorrect UTF-8 decoding will follow */
                assert(isASCII(_input.ptr[_offset]));
                _offset += 1;
            }
            _input = _input[_offset .. $]; // skip leading separators
            _offset = 0;
        }

        /** Skip any separators try finding the next front. */
        void tryFindNextFront() @trusted
        {
            skipSeparators(); // skip leading separators
            while (_offset < _input.length &&
                   !separatorPred(_input.ptr[_offset]))
                _offset += 1;
            // dbg("input:", _input, " ", " offset:", _offset);
        }

        void popFront() nothrow
		in(!empty, "Attempting to pop the front of an empty splitter.")
		  	=> tryFindNextFront();

		pragma(inline, true)
        static private bool isASCII(char x) @safe pure nothrow @nogc
			=> x < 128;
    }

    return Result(r);
}

///
@safe pure nothrow @nogc unittest
{
    import std.algorithm.comparison : equal;
    import std.algorithm.comparison : among;
    import nxt.array_help : s;

    assert(``.splitterASCII!(_ => _ == ' ')
             .empty);

    assert(` `.splitterASCII!(_ => _ == ' ')
              .empty);

    assert(`   `.splitterASCII!(_ => _ == ' ')
                .empty);

    assert(` - `.splitterASCII!(_ => _ == ' ')
                .equal([`-`].s[]));

    assert(`a`.splitterASCII!(_ => _ == ' ')
              .equal([`a`].s[]));

    assert(` a `.splitterASCII!(_ => _ == ' ')
                .equal([`a`].s[]));

    assert(` a b `.splitterASCII!(_ => _ == ' ')
                  .equal([`a`, `b`].s[]));

    assert(` a_b `.splitterASCII!(_ => _ == ' ')
                  .equal([`a_b`].s[]));

    assert(` - aa   bb--c-_d--_e`.splitterASCII!(_ => _.among!(' ', '-', '_') != 0)
                                 .equal([`aa`, `bb`, `c`, `d`, `e`].s[]));
}

/// DIP-1000 return ref escape analysis
@safe pure nothrow unittest
{
    import nxt.dip_traits : hasPreviewDIP1000;

    static if (hasPreviewDIP1000)
    {
        // See_Also: https://forum.dlang.org/post/pzddsrwhfvcopfaamvak@forum.dlang.org
        static assert(!__traits(compiles, {
                    char[] f()
                    {
                        char[2] x;
                        return x[].splitterASCII!(_ => _ == ' ').front;
                    }
                }));
    }
}

/** Non-decoding ASCII-separator-only variant of Phobos' `splitter` that .
 *
 * TODO: generalize to separators being either chars or strings.
 */
template splitterASCIIAmong(separators...)
if (separators.length != 0 &&
    isExpressions!separators)
{
    import std.meta : allSatisfy;
    import nxt.char_traits : isASCII;

    auto splitterASCIIAmong(Range)(return Range r)
    if (is(typeof(Range.init[0 .. 0])) && // can be sliced
        is(typeof(Range.init[0]) : char) &&
        allSatisfy!(isASCII, separators))
    {
        static if (separators.length == 1)
        {
            // reuse common instatiation of `splitterASCII` for predicate `pred`:
            alias pred = (char _) => (_ == separators[0]);
        }
        else static if (separators.length == 2)
        {
            // reuse common instatiation of `splitterASCII` for predicate `pred`:
            alias pred = (char _) => (_ == separators[0] ||
                                      _ == separators[1]);
        }
        else static if (separators.length == 3)
        {
            // reuse common instatiation of `splitterASCII` for predicate `pred`:
            alias pred = (char _) => (_ == separators[0] ||
                                      _ == separators[1] ||
                                      _ == separators[2]);
        }
        else
        {
            import std.algorithm.comparison : among;
            alias pred = (char _) => (_.among!(separators) != 0);
        }
        return splitterASCII!(pred)(r);
    }
}

///
@safe pure nothrow @nogc unittest
{
    import std.algorithm.comparison : equal;
    import nxt.array_help : s;

    assert(``.splitterASCIIAmong!(' ')
             .empty);

    assert(` `.splitterASCIIAmong!(' ')
              .empty);

    assert(`   `.splitterASCIIAmong!(' ')
                .empty);

    assert(` - `.splitterASCIIAmong!(' ')
                .equal([`-`].s[]));

    assert(`a`.splitterASCIIAmong!(' ')
              .equal([`a`].s[]));

    assert(` a `.splitterASCIIAmong!(' ')
                .equal([`a`].s[]));

    assert(` a b `.splitterASCIIAmong!(' ')
                  .equal([`a`, `b`].s[]));

    assert(` a_b `.splitterASCIIAmong!(' ')
                  .equal([`a_b`].s[]));

    assert(` - aa   bb--c-d--e`.splitterASCIIAmong!(' ', '-')
                                 .equal([`aa`, `bb`, `c`, `d`, `e`].s[]));

    assert(` - aa   bb--c-_d--_e`.splitterASCIIAmong!(' ', '-', '_')
                                 .equal([`aa`, `bb`, `c`, `d`, `e`].s[]));

    assert(` - aa ///  bb--c-_d--_e`.splitterASCIIAmong!(' ', '-', '_', '/')
                                    .equal([`aa`, `bb`, `c`, `d`, `e`].s[]));
}