const std = @import("std");
const common = @import("common.zig");
const builtin = @import("builtin");
const div_t = std.c.div_t;
const ldiv_t = std.c.ldiv_t;
const lldiv_t = std.c.lldiv_t;

comptime {
    if (builtin.target.isMuslLibC() or builtin.target.isWasiLibC()) {
        // Functions specific to musl and wasi-libc.
        @export(&abs, .{ .name = "abs", .linkage = common.linkage, .visibility = common.visibility });
        @export(&labs, .{ .name = "labs", .linkage = common.linkage, .visibility = common.visibility });
        @export(&llabs, .{ .name = "llabs", .linkage = common.linkage, .visibility = common.visibility });

        @export(&div, .{ .name = "div", .linkage = common.linkage, .visibility = common.visibility });
        @export(&ldiv, .{ .name = "ldiv", .linkage = common.linkage, .visibility = common.visibility });
        @export(&lldiv, .{ .name = "lldiv", .linkage = common.linkage, .visibility = common.visibility });

        @export(&qsort_r, .{ .name = "qsort_r", .linkage = common.linkage, .visibility = common.visibility });
        @export(&qsort, .{ .name = "qsort", .linkage = common.linkage, .visibility = common.visibility });

        @export(&bsearch, .{ .name = "bsearch", .linkage = common.linkage, .visibility = common.visibility });
    }
}

fn abs(a: c_int) callconv(.c) c_int {
    return @intCast(@abs(a));
}

fn labs(a: c_long) callconv(.c) c_long {
    return @intCast(@abs(a));
}

fn llabs(a: c_longlong) callconv(.c) c_longlong {
    return @intCast(@abs(a));
}

fn div(a: c_int, b: c_int) callconv(.c) div_t {
    return .{
        .quot = @divTrunc(a, b),
        .rem = @rem(a, b),
    };
}

fn ldiv(a: c_long, b: c_long) callconv(.c) ldiv_t {
    return .{
        .quot = @divTrunc(a, b),
        .rem = @rem(a, b),
    };
}

fn lldiv(a: c_longlong, b: c_longlong) callconv(.c) lldiv_t {
    return .{
        .quot = @divTrunc(a, b),
        .rem = @rem(a, b),
    };
}

// NOTE: Despite its name, `qsort` doesn't have to use quicksort or make any complexity or stability guarantee.
fn qsort_r(base: *anyopaque, n: usize, size: usize, compare: *const fn (a: *const anyopaque, b: *const anyopaque, arg: ?*anyopaque) callconv(.c) c_int, arg: ?*anyopaque) callconv(.c) void {
    const Context = struct {
        base: [*]u8,
        size: usize,
        compare: *const fn (a: *const anyopaque, b: *const anyopaque, arg: ?*anyopaque) callconv(.c) c_int,
        arg: ?*anyopaque,

        pub fn lessThan(ctx: @This(), a: usize, b: usize) bool {
            return ctx.compare(&ctx.base[a * ctx.size], &ctx.base[b * ctx.size], ctx.arg) < 0;
        }

        pub fn swap(ctx: @This(), a: usize, b: usize) void {
            const a_bytes: []u8 = ctx.base[a * ctx.size ..][0..ctx.size];
            const b_bytes: []u8 = ctx.base[b * ctx.size ..][0..ctx.size];

            for (a_bytes, b_bytes) |*ab, *bb| {
                const tmp = ab.*;
                ab.* = bb.*;
                bb.* = tmp;
            }
        }
    };

    std.mem.sortUnstableContext(0, n, Context{
        .base = @ptrCast(base),
        .size = size,
        .compare = compare,
        .arg = arg,
    });
}

fn qsort(base: *anyopaque, n: usize, size: usize, compare: *const fn (a: *const anyopaque, b: *const anyopaque) callconv(.c) c_int) callconv(.c) void {
    return qsort_r(base, n, size, (struct {
        fn wrap(a: *const anyopaque, b: *const anyopaque, arg: ?*anyopaque) callconv(.c) c_int {
            const cmp: *const fn (a: *const anyopaque, b: *const anyopaque) callconv(.c) c_int = @ptrCast(@alignCast(arg.?));
            return cmp(a, b);
        }
    }).wrap, @constCast(compare));
}

// NOTE: Despite its name, `bsearch` doesn't need to be implemented using binary search or make any complexity guarantee.
fn bsearch(key: *const anyopaque, base: *const anyopaque, n: usize, size: usize, compare: *const fn (a: *const anyopaque, b: *const anyopaque) callconv(.c) c_int) callconv(.c) ?*anyopaque {
    const base_bytes: [*]const u8 = @ptrCast(base);
    var low: usize = 0;
    var high: usize = n;

    while (low < high) {
        // Avoid overflowing in the midpoint calculation
        const mid = low + (high - low) / 2;
        const elem = &base_bytes[mid * size];

        switch (std.math.order(compare(key, elem), 0)) {
            .eq => return @constCast(elem),
            .gt => low = mid + 1,
            .lt => high = mid,
        }
    }
    return null;
}

test abs {
    const val: c_int = -10;
    try std.testing.expectEqual(10, abs(val));
}

test labs {
    const val: c_long = -10;
    try std.testing.expectEqual(10, labs(val));
}

test llabs {
    const val: c_longlong = -10;
    try std.testing.expectEqual(10, llabs(val));
}

test div {
    const expected: div_t = .{ .quot = 5, .rem = 5 };
    try std.testing.expectEqual(expected, div(55, 10));
}

test ldiv {
    const expected: ldiv_t = .{ .quot = -6, .rem = 2 };
    try std.testing.expectEqual(expected, ldiv(38, -6));
}

test lldiv {
    const expected: lldiv_t = .{ .quot = 1, .rem = 2 };
    try std.testing.expectEqual(expected, lldiv(5, 3));
}

test bsearch {
    const Comparison = struct {
        pub fn compare(a: *const anyopaque, b: *const anyopaque) callconv(.c) c_int {
            const a_u16: *const u16 = @ptrCast(@alignCast(a));
            const b_u16: *const u16 = @ptrCast(@alignCast(b));

            return switch (std.math.order(a_u16.*, b_u16.*)) {
                .gt => 1,
                .eq => 0,
                .lt => -1,
            };
        }
    };

    const items: []const u16 = &.{ 0, 5, 7, 9, 10, 200, 512, 768 };

    try std.testing.expectEqual(@as(?*anyopaque, null), bsearch(&@as(u16, 2000), items.ptr, items.len, @sizeOf(u16), Comparison.compare));

    for (items) |*value| {
        try std.testing.expectEqual(@as(*const anyopaque, value), bsearch(value, items.ptr, items.len, @sizeOf(u16), Comparison.compare));
    }
}