const std = @import("std");
const TypeId = @import("builtin").TypeId;

fn is_signed(comptime N: type) bool {
    switch (@typeInfo(N)) {
        TypeId.Int => |int| {
            return int.is_signed;
        },
        else => {
            @compileError("Is_signed is only available on integer types. Found `" ++ @typeName(N) ++ "`.");
        }
    }
}

fn bitcount(comptime N: type) u32 {
    switch (@typeInfo(N)) {
        TypeId.Int => |int| {
            return @intCast(u32, int.bits);
        },
        else => {
            @compileError("Bitcount only available on integer types. Found `" ++ @typeName(N) ++ "`.");
        }
    }
}

fn is_negative(comptime N: type, num: N) bool {
    return num < 0;
}

fn digits10(comptime N: type, n: N, comptime unroll: ?u8) usize {
    if (comptime is_signed(N)) {

        const nbits = comptime bitcount(N);

        const unsigned_friend = @IntType(false, nbits);

        if (is_negative(N, n)) {
            return digits10(unsigned_friend, @intCast(unsigned_friend, n * -1), unroll);
        }
        else {
            return digits10(unsigned_friend, @intCast(unsigned_friend, n), unroll);
        }
    }

    comptime var digits: usize = 1;
    comptime var check: usize = 10;

    if (comptime unroll) |unroll_count| {
        var num: usize = n;
        var result: usize = 0;
        comptime var counter: usize = 0;

        while (true) {
            inline while (counter != unroll_count) : ({counter += 1; check *= 10; digits += 1;}) {
                if (num < check) {
                    return result + digits;
                }
            }

            result += unroll_count;
            num /= comptime (check / 10);
        }
    } else {
        comptime var overflowed = false;
        inline while (check <= @maxValue(N) and !overflowed) : ({overflowed = @mulWithOverflow(usize, check, 10, &check); digits += 1;}) {
            if (n < check) {
                return digits;
            }
        }

        return digits;
    }
}

test "testimpl" {

    var n: usize = digits10(isize, -12345, null);
    std.debug.warn("{}\n", n);
    std.debug.assert(n == 5);
}