gear-common 2.0.0-pre.1

// Copyright (C) Gear Technologies Inc.
// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0

//! Module for counter implementation.
//!
//! Counter provides API for step-by-step changing of the value.
//! Could be used to count amount of some parameter.

use crate::storage::ValueStorage;
use core::marker::PhantomData;

/// Represents logic of managing step-by-step changeable value.
pub trait Counter {
    /// Counter stored type.
    type Value;

    /// Decreases stored value.
    ///
    /// Should be safe from overflow.
    fn decrease();

    /// Returns stored value, if present, or default/starting value.
    fn get() -> Self::Value;

    /// Increases stored value.
    ///
    /// Should be safe from overflow.
    fn increase();

    /// Resets stored value by setting default/starting value.
    fn reset();
}

/// `Counter` implementation based on `ValueStorage`.
///
/// Generic parameter `T` presents inner storing type.
pub struct CounterImpl<T, VS: ValueStorage<Value = T>>(PhantomData<VS>);

/// Crate local macro for repeating `Counter` implementation
/// over `ValueStorage` with Rust's numeric types.
macro_rules! impl_counter {
    ($($t: ty), +) => { $(
        impl<VS: ValueStorage<Value = $t>> Counter for CounterImpl<$t, VS> {
            type Value = VS::Value;

            fn decrease() {
                VS::mutate(|opt_val| {
                    if let Some(val) = opt_val {
                        *val = val.saturating_sub(1);
                    }
                });
            }

            fn get() -> Self::Value {
                VS::get().unwrap_or(0)
            }

            fn increase() {
                VS::mutate(|opt_val| {
                    if let Some(val) = opt_val {
                        *val = val.saturating_add(1);
                    } else {
                        *opt_val = Some(1)
                    }
                });
            }

            fn reset() {
                VS::put(0);
            }
        }
    ) + };
}

// Implementation for unsigned integers.
impl_counter!(u8, u16, u32, u64, u128);

// Implementation for signed integers.
impl_counter!(i8, i16, i32, i64, i128);