/* 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/. */

/**
 * This module defines primitives for working with ranges.
 *
 * Copyright: Eugen Wissner 2017-2026.
 * License: $(LINK2 https://www.mozilla.org/en-US/MPL/2.0/,
 *                  Mozilla Public License, v. 2.0).
 */
module tanya.range.primitive;

import std.algorithm.comparison;
import std.range : isInfinite, hasSlicing, hasLvalueElements, isInputRange, isBidirectionalRange;
import std.traits;
import tanya.memory.lifetime;
import tanya.meta;
import tanya.range.array;

/**
 * Returns the element type of the range $(D_PARAM R).
 *
 * Element type is the return type of such primitives like
 * $(D_INLINECODE R.front) and (D_INLINECODE R.back) or the array base type.
 * If $(D_PARAM R) is not a range, its element type is $(D_KEYWORD void).
 *
 * If $(D_PARAM R) is a string, $(D_PSYMBOL ElementType) doesn't distinguish
 * between narrow and wide strings, it just returns the base type of the
 * underlying array ($(D_KEYWORD char), $(D_KEYWORD wchar) or
 * $(D_KEYWORD dchar)).
 *
 * Params:
 *  R = Range type.
 *
 * Returns: Element type of the range $(D_PARAM R).
 */
template ElementType(R)
{
    static if (is(R U : U[]))
    {
        alias ElementType = U;
    }
    else static if (isInputRange!R)
    {
        alias ElementType = ReturnType!((R r) => r.front());
    }
    else
    {
        alias ElementType = void;
    }
}

/**
 * Detects whether $(D_PARAM R) has a length property.
 *
 * $(D_PARAM R) does not have to be a range to support the length.
 *
 * Length mustn't be a $(D_KEYWORD @property) or a function, it can be a member
 * variable or $(D_KEYWORD enum). But its type (or the type returned by the
 * appropriate function) should be $(D_KEYWORD size_t), otherwise
 * $(D_PSYMBOL hasLength) is $(D_KEYWORD false).
 *
 * All dynamic arrays except $(D_KEYWORD void)-arrays have length.
 *
 * Params:
 *  R = A type.
 *
 * Returns: $(D_KEYWORD true) if $(D_PARAM R) has a length property,
 *          $(D_KEYWORD false) otherwise.
 *
 * See_Also: $(D_PSYMBOL isInfinite).
 */
enum bool hasLength(R) = is(ReturnType!((R r) => r.length) == size_t);

///
@nogc nothrow pure @safe unittest
{
    static assert(hasLength!(char[]));
    static assert(hasLength!(int[]));
    static assert(hasLength!(const(int)[]));

    struct A
    {
        enum size_t length = 1;
    }
    static assert(hasLength!(A));

    struct B
    {
        @property size_t length() const @nogc nothrow pure @safe
        {
            return 0;
        }
    }
    static assert(hasLength!(B));

    struct C
    {
        @property const(size_t) length() const @nogc nothrow pure @safe
        {
            return 0;
        }
    }
    static assert(!hasLength!C);
}

private template isDynamicArrayRange(R)
{
    static if (is(R E : E[]))
    {
        enum bool isDynamicArrayRange = !is(E == void);
    }
    else
    {
        enum bool isDynamicArrayRange = false;
    }
}

private struct Primitive(Candidate, string primitive)
{
    auto ref returnType(ref Candidate candidate)
    {
        mixin("return candidate." ~ primitive ~ ";");
    }

    alias ReturnType = .ReturnType!returnType;
    static assert(!is(ReturnType == void));

    enum uint attributes = functionAttributes!returnType
                         & FunctionAttribute.ref_;

    bool opEquals(That)(That) const
    {
        return is(ReturnType == That.ReturnType)
            && attributes == That.attributes;
    }
}

/**
 * Returns the first element and advances the range.
 *
 * If $(D_PARAM range) has lvalue elements, then $(D_PSYMBOL getAndPopFront)
 * returns by reference, otherwise the returned element is copied.
 *
 * Params:
 *  R     = Input range type.
 *  range = Input range.
 *
 * Returns: Front range element.
 *
 * See_Also: $(D_PSYMBOL getAndPopBack).
 */
ElementType!R getAndPopFront(R)(ref R range)
if (isInputRange!R)
in
{
    assert(!range.empty);
}
do
{
    static if (hasLvalueElements!R)
    {
        if (false)
        {
            // This code is removed by the compiler but ensures that
            // this function isn't @safe if range.front isn't @safe.
            auto _ = range.front();
        }
        auto el = (() @trusted => &range.front())();
    }
    else
    {
        auto el = range.front;
    }
    range.popFront();
    static if (hasLvalueElements!R)
    {
        return *el;
    }
    else
    {
        return el;
    }
}

///
@nogc nothrow pure @safe unittest
{
    int[3] array = [1, 2, 3];
    auto slice = array[];

    assert(getAndPopFront(slice) == 1);
    assert(slice.length == 2);
}

/**
 * Returns the last element and removes it from the range.
 *
 * If $(D_PARAM range) has lvalue elements, then $(D_PSYMBOL getAndPopBack)
 * returns by reference, otherwise the returned element is copied.
 *
 * Params:
 *  R     = Bidirectional range type.
 *  range = Bidirectional range.
 *
 * Returns: Last range element.
 *
 * See_Also: $(D_PSYMBOL getAndPopFront).
 */
auto ref getAndPopBack(R)(ref R range)
if (isBidirectionalRange!R)
in
{
    assert(!range.empty);
}
do
{
    static if (hasLvalueElements!R)
    {
        if (false)
        {
            // This code is removed by the compiler but ensures that
            // this function isn't @safe if range.back isn't @safe.
            auto _ = range.back();
        }
        auto el = (() @trusted => &range.back())();
    }
    else
    {
        auto el = range.back;
    }
    range.popBack();
    static if (hasLvalueElements!R)
    {
        return *el;
    }
    else
    {
        return el;
    }
}

///
@nogc nothrow pure @trusted unittest
{
    int[3] array = [1, 2, 3];
    auto slice = array[];

    assert(getAndPopBack(slice) == 3);
    assert(slice.length == 2);
}