use super::funejson::Value;

const MAX_SAFE: i64 = 9_007_199_254_740_991;

fn check_safe(name: &str, value: i64) {
    // i64 could go further, but TypeScript cannot, and the three languages
    // must give the same answer or the same error.
    if !(-MAX_SAFE..=MAX_SAFE).contains(&value) {
        panic!("{} is outside the safe integer range (±9007199254740991)", name);
    }
}

/// Euclid's algorithm on wide integers. Never negative; `gcd_wide(0, 0)` is 0.
/// Exported for fraction arithmetic (math.rational), which reduces products
/// that are already past 2^53 before it checks them.
pub fn gcd_wide(a: i128, b: i128) -> i128 {
    let mut x = a.abs();
    let mut y = b.abs();
    while y != 0 {
        let r = x % y;
        x = y;
        y = r;
    }
    x
}

/// Greatest common divisor, never negative; `gcd(0, n)` is `|n|` and
/// `gcd(0, 0)` is 0.
///
/// # Panics
/// Panics if either input is outside ±(2^53 - 1).
pub fn gcd(a: i64, b: i64) -> i64 {
    check_safe("a", a);
    check_safe("b", b);
    gcd_wide(a as i128, b as i128) as i64
}

// Refuse what the typed signature cannot hold, with the wording TypeScript
// and Python use, rather than let the conversion quietly truncate it.
fn int_arg(v: &Value, name: &str) -> i64 {
    if let Value::Float(f) = v {
        if f.fract() != 0.0 {
            panic!("{} must be an integer, received {}", name, f);
        }
    }
    v.as_i64()
}

pub fn fune_vector(args: &[Value]) -> Value {
    Value::Int(gcd(int_arg(&args[0], "a"), int_arg(&args[1], "b")))
}