/** Lazy Substitution Algorithms.
 *
 * See_Also: http://forum.dlang.org/post/pymxzazxximtgixzbnpq@forum.dlang.org
 */
module nxt.substitution;

import std.range.primitives : isInputRange, ElementType;
import core.internal.traits : Unqual;
import std.typecons : Tuple;
import std.traits : isExpressionTuple;
import std.algorithm.searching : startsWith;

import nxt.traits_ex : hasEvenLength, haveCommonType;

import std.stdio;

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

import std.traits : isExpressionTuple;
import nxt.traits_ex : haveCommonType;

/** Similar to $(D among) but for set of replacements/substitutions $(D substs).
 *
 * Time-Complexity: O(1) thanks to D's $(D switch) guaranteeing O(1).
 */
template substitute(substs...)
if ((substs.length & 1) == 0 && // need even number of elements (>= 1)
    substs.length >= 2 && // and at least one replacement pair
    isExpressionTuple!substs &&
    haveCommonType!(substs))
{
    Value substitute(Value)(Value value)
    if (haveCommonType!(Value, substs)) // TODO: need static map incorrect
    {
        switch (value)
        {
            static foreach (i; 0 .. substs.length / 2)
            {
            case substs[2*i]:
                return substs[2*i + 1];
            }
        default:
            return value;
        }
    }
}

@safe pure nothrow unittest
{
    auto xyz_abc__(T)(T value)
    {
        immutable a = "a";
        const b = "b";
        auto c = "c";
        return value.substitute!("x", a,
                                 "y", b,
                                 "z", c);
    }
    assert(xyz_abc__("x") == "a");
    assert(xyz_abc__("y") == "b");
    assert(xyz_abc__("z") == "c");
    assert(xyz_abc__("w") == "w");
}

/** Substitute in parallel all elements in $(D r) which equal (according to $(D
 * pred)) $(D ss[2*n]) with $(D ss[2*n + 1]) for $(D n) = 0, 1, 2, ....
 */
auto substitute(alias pred = (a, b) => a == b, R, Ss...)(R r, Ss ss)
if (isInputRange!(Unqual!R) &&
    Ss.length >= 2 &&
    hasEvenLength!Ss &&
    haveCommonType!(ElementType!R, Ss))
{
    import std.algorithm.iteration : map;
    import std.functional : binaryFun;
    enum n = Ss.length / 2;
    auto replaceElement(E)(E e)
    {
        static foreach (i; 0 .. n)
        {
            if (binaryFun!pred(e, ss[2*i]))
            {
                return ss[2*i + 1];
            }
        }
        return e;
    }
    return r.map!(a => replaceElement(a));
}

///
@safe pure unittest
{
    import std.conv : to;
    import std.algorithm : map;
    auto x = `42`.substitute('2', '3')
                 .substitute('3', '1');
    static assert(is(ElementType!(typeof(x)) == dchar));
    assert(equal(x, `41`));
}

///
@safe pure unittest
{
    assert(`do_it`.substitute('_', ' ')
                  .equal(`do it`));
    int[3] x = [1, 2, 3];
    auto y = x[].substitute(1, 0.1)
                .substitute(0.1, 0.2);
    static assert(is(typeof(y.front) == double));
    assert(y.equal([0.2, 2, 3]));
    assert(`do_it`.substitute('_', ' ',
                              'd', 'g',
                              'i', 't',
                              't', 'o')
                  .equal(`go to`));
    import std.range : retro;
    assert(equal([1, 2, 3].substitute(1, 0.1)
                          .retro,
                 [3, 2, 0.1]));
}

/** Substitute in parallel all elements in $(D r) which equal (according to $(D
    pred)) $(D ss[2*n]) with $(D ss[2*n + 1]) for $(D n) = 0, 1, 2, ....

    Because $(D ss) are known at compile time, time-complexity for each element
    substitution is O(1).
*/
template substitute(ss...)
if (isExpressionTuple!ss &&
    ss.length >= 2 &&
    hasEvenLength!ss)
{
    auto substitute(R)(R r)
        if (isInputRange!(Unqual!R) &&
            haveCommonType!(ElementType!R, ss))
    {
        import std.algorithm.iteration : map;
        enum n = ss.length / 2;
        auto replaceElement(E)(E e)
        {
            switch (e)
            {
                static foreach (i; 0 .. n)
                {
                case ss[2*i]: return ss[2*i + 1];
                }
            default: return e;
            }
        }
        return r.map!(a => replaceElement(a));
    }
}

///
@safe pure unittest
{
    assert(`do_it`.substitute!('_', ' ')
                  .equal(`do it`));
    int[3] x = [1, 2, 3];
    auto y = x[].substitute!(1, 0.1);
    assert(y.equal([0.1, 2, 3]));
    static assert(is(typeof(y.front) == double));
    assert(`do_it`.substitute!('_', ' ',
                               'd', 'g',
                               'i', 't',
                               't', 'o')
                  .equal(`go to`));
    import std.range : retro;
    assert(equal([1, 2, 3].substitute!(1, 0.1)
                          .retro,
                 [3, 2, 0.1]));
}

/** Helper range for subsequence overload of $(D substitute).
 */
private auto substituteSplitter(alias pred = `a == b`, R, Rs...)(R haystack, Rs needles)
if (Rs.length >= 1 &&
    is(typeof(startsWith!pred(haystack, needles))))
{
    static struct Result
    {
        alias Hit = size_t; // 0 iff no hit, otherwise hit in needles[index-1]
        alias E = Tuple!(R, Hit);
        this(R haystack, Rs needles)
        {
            this._rest = haystack;
            this._needles = needles;
            popFront();
        }

        @property auto ref front()
        {
            import std.range.primitives : empty;
            return !_skip.empty ? E(_skip, 0) : E(_hit, _hitNr);
        }

        import std.range.primitives : isInfinite;
        static if (isInfinite!R)
            enum empty = false; // propagate infiniteness
        else
            bool empty() const @property
            {
                import std.range.primitives : empty;
                return _skip.empty && _hit.empty && _rest.empty;
            }

        void popFront() @trusted
        {
            import std.range.primitives : empty;
            if (!_skip.empty)
            {
                _skip = R.init; // jump over _skip
            }
            else
            {
                import std.algorithm.searching : find;

                static if (_needles.length >= 2) // if variadic version
                {
                    auto match = _rest.find!pred(_needles);
                    auto hitValue = match[0];
                    _hitNr = match[1];
                }
                else
                {
                    auto match = _rest.find!pred(_needles);
                    auto hitValue = match;
                    _hitNr = !match.empty ? 1 : 0;
                }

                if (_hitNr == 0) // no more hits
                {
                    _skip = _rest;
                    _hit = R.init;
                    _rest = R.init;
                }
                else
                {
                    import std.traits : isSomeString;
                    static if (isSomeString!R)
                    {
                        size_t hitLength = size_t.max;
                        final switch (_hitNr - 1)
                        {
                            foreach (const i, Ri; Rs)
                            {
                            case i: hitLength = _needles[i].length; break;
                            }
                        }
                        assert(hitLength != size_t.max); // not needed if match returned bounded!int

                        if (_rest.ptr == hitValue.ptr) // match at start of _rest
                        {
                            _hit = hitValue[0 .. hitLength];
                            _rest = hitValue[hitLength .. $];
                        }
                        else
                        {
                            _skip = _rest[0 .. hitValue.ptr - _rest.ptr];
                            _hit = hitValue[0 .. hitLength];
                            _rest = hitValue[hitLength .. $];
                        }
                    }
                    else
                    {
                        static assert(0, `Handle R without slicing ` ~ R.stringof);
                    }
                }
            }
        }
    private:
        R _rest;
        Rs _needles;
        R _skip; // skip before next hit
        R _hit; // most recent (last) hit if any
        size_t _hitNr; // hit number: 0 means no hit, otherwise index+1 to needles that matched
    }
    return Result(haystack, needles);
}

@safe pure unittest
{
    auto h = `alpha.beta.gamma`;
    auto fs = h.substituteSplitter(`alpha`, `beta`, `gamma`);
    alias FS = typeof(fs);
    alias E = ElementType!FS;
    static assert(is(E == Tuple!(string, ulong)));
    assert(equal(fs, [E(`alpha`, 1),
                      E(`.`, 0),
                      E(`beta`, 2),
                      E(`.`, 0),
                      E(`gamma`, 3)]));
}

@safe pure unittest
{
    auto h = `.alpha.beta.gamma`;
    auto fs = h.substituteSplitter(`alpha`, `beta`, `gamma`);
    alias FS = typeof(fs);
    alias E = ElementType!FS;
    static assert(is(E == Tuple!(string, ulong)));
    assert(equal(fs, [E(`.`, 0),
                      E(`alpha`, 1),
                      E(`.`, 0),
                      E(`beta`, 2),
                      E(`.`, 0),
                      E(`gamma`, 3)]));
}

@safe pure unittest
{
    auto h = `alpha.beta.gamma.`;
    auto fs = h.substituteSplitter(`alpha`, `beta`, `gamma`);
    alias FS = typeof(fs);
    alias E = ElementType!FS;
    static assert(is(E == Tuple!(string, ulong)));
    assert(equal(fs, [E(`alpha`, 1),
                      E(`.`, 0),
                      E(`beta`, 2),
                      E(`.`, 0),
                      E(`gamma`, 3),
                      E(`.`, 0)]));
}

@safe pure unittest
{
    auto h = `alpha.alpha.alpha.`;
    auto fs = h.substituteSplitter(`alpha`);
    alias FS = typeof(fs);
    alias E = ElementType!FS;
    static assert(is(E == Tuple!(string, ulong)));
    assert(equal(fs, [E(`alpha`, 1),
                      E(`.`, 0),
                      E(`alpha`, 1),
                      E(`.`, 0),
                      E(`alpha`, 1),
                      E(`.`, 0)]));
}

template Stride(size_t stride, size_t offset, Args...)
if (stride > 0)
{
    import std.meta : AliasSeq;
    static if (offset >= Args.length)
    {
        alias Stride = AliasSeq!();
    }
    else static if (stride >= Args.length)
    {
        alias Stride = AliasSeq!(Args[offset]);
    }
    else
    {
        alias Stride = AliasSeq!(Args[offset],
                                 Stride!(stride, offset, Args[stride .. $]));
    }
}

/** Substitute in parallel all subsequences in $(D r) which equal (according to
    $(D pred)) $(D ss[2*n]) with $(D ss[2*n + 1]) for $(D n) = 0, 1, 2, ....
*/
auto substitute(alias pred = (a, b) => a == b, R, Ss...)(R r, Ss ss)
if (isInputRange!(Unqual!R) &&
    Ss.length >= 2 &&
    hasEvenLength!Ss &&
    haveCommonType!(ElementType!R,
                    ElementType!(Ss[0])))
{
    import std.algorithm.iteration : map;
    import std.functional : binaryFun;

    enum n = Ss.length / 2;

    auto replaceElement(E)(E e)
    {
        auto value = e[0];
        const hitNr = e[1];
        if (hitNr == 0) // not hit
        {
            return value;
        }
        else
        {
            static foreach (i; 0 .. n)
            {
                if (hitNr == i + 1)
                {
                    return ss[2*i + 1]; // replacement
                }
            }
            assert(false);
        }
    }

    // extract inputs
    alias Ins = Stride!(2, 0, Ss);
    Ins ins;
    static foreach (i; 0 .. n)
    {
        ins[i] = ss[2*i];
    }

    import std.algorithm.iteration : map, joiner;
    return r.substituteSplitter!pred(ins)
            .map!(a => replaceElement(a))
            .joiner;
}

@safe pure unittest
{
    assert(`do_it now, sir`.substitute(`_`, ` `,
                                       `d`, `g`,
                                       `i`, `t`,
                                       `t`, `o`,
                                       `now`, `work`,
                                       `sir`, `please`)
                  .equal(`go to work, please`));
}

@safe pure unittest
{
    assert((`abcDe`.substitute(`a`, `AA`,
                               `b`, `DD`)
                   .substitute('A', 'y',
                               'D', 'x',
                               'e', '1'))
           .equal(`yyxxcx1`));
}