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//! Arithmetic functions for the Fuel VM

use fuel_asm::{PanicReason, Word};

use crate::error::RuntimeError;

/// Add two unchecked words, returning an error if overflow
#[inline(always)]
pub fn checked_add_word(a: Word, b: Word) -> Result<Word, PanicReason> {
    a.checked_add(b).ok_or(PanicReason::ArithmeticOverflow)
}

/// Subtract two unchecked words, returning an error if overflow
#[inline(always)]
pub fn checked_sub_word(a: Word, b: Word) -> Result<Word, PanicReason> {
    a.checked_sub(b).ok_or(PanicReason::ArithmeticOverflow)
}

/// Add two unchecked numbers, returning an error if overflow
#[inline(always)]
pub fn checked_add_usize(a: usize, b: usize) -> Result<usize, PanicReason> {
    a.checked_add(b).ok_or(PanicReason::ArithmeticOverflow)
}

/// Subtract two unchecked numbers, returning an error if overflow
#[inline(always)]
pub fn checked_sub_usize(a: usize, b: usize) -> Result<usize, PanicReason> {
    a.checked_sub(b).ok_or(PanicReason::ArithmeticOverflow)
}

/// Add two checked words. Might wrap if overflow
///
/// The function is inlined so it will be optimized to `a + b` if `optimized` feature is enabled so
/// the operation is unchecked.
///
/// This should be used in contexts that are checked and guaranteed by the protocol to never
/// overflow, but then they might due to some bug in the code.
#[inline(always)]
pub fn add_word(a: Word, b: Word) -> Result<Word, RuntimeError> {
    #[cfg(feature = "optimized")]
    #[allow(clippy::integer_arithmetic)]
    return Ok(a + b);

    #[cfg(not(feature = "optimized"))]
    return a
        .checked_add(b)
        .ok_or_else(|| RuntimeError::unexpected_behavior("unexpected overflow"));
}

/// Subtract two checked words. Might wrap if overflow
///
/// The function is inlined so it will be optimized to `a + b` if `optimized` feature is enabled so
/// the operation is unchecked.
///
/// This should be used in contexts that are checked and guaranteed by the protocol to never
/// overflow, but then they might due to some bug in the code.
#[inline(always)]
pub fn sub_word(a: Word, b: Word) -> Result<Word, RuntimeError> {
    #[cfg(feature = "optimized")]
    #[allow(clippy::integer_arithmetic)]
    return Ok(a - b);

    #[cfg(not(feature = "optimized"))]
    return a
        .checked_sub(b)
        .ok_or_else(|| RuntimeError::unexpected_behavior("unexpected underflow"));
}

/// Add two numbers. Should be used only in compile-time evaluations so the code won't compile in
/// case of unexpected overflow.
#[inline(always)]
#[allow(clippy::integer_arithmetic)]
pub const fn add_usize(a: usize, b: usize) -> usize {
    a + b
}