const std = @import("std");
const typeVerify = @import("util.zig").typeVerify;

/// ```zig
/// (fn (fn (fn (a) bool, []a) []a)
/// ```
/// Filters a slice, only keeping items give `true` when passed into `func`
/// Type signature: `(a -> bool) -> [a] -> [a]`
/// `func` is of type `a -> bool`, where `items` is of type `[a]`
pub fn filterAlloc(
    allocator: std.mem.Allocator,
    func: anytype,
    items: []typeVerify(@TypeOf(func), .{ .@"fn" }).@"fn".params[0].type.?,
) ![]typeVerify(@TypeOf(func), .{ .@"fn" }).@"fn".params[0].type.? {
    var tmp = items;
    var i: u32 = 0;
    for (items) |it|
        if (func(it)) {
            tmp[i] = it;
            i = i + 1;
        };

    const output = try allocator.alloc(typeVerify(@TypeOf(func), .{ .@"fn" }).@"fn".params[0].type.?, i);
    for (0..i) |j|
        output[j] = tmp[i];
    return output;
}

pub fn filterBuff(
    func: anytype,
    items: []typeVerify(@TypeOf(func), .{ .@"fn" }).@"fn".params[0].type.?,
    buffer: *[]typeVerify(@TypeOf(func), .{ .@"fn" }).@"fn".params[0].type.?,
) void {
    var tmp = items;
    var i: u32 = 0;
    for (items) |it|
        if (func(it)) {
            tmp[i] = it;
            i = i + 1;
        };

    for (0..i) |j|
        buffer[j] = tmp[i];
}