//! The accounts data space has a maximum size it is permitted to grow to.  This module contains
//! the constants and types for tracking and metering the accounts data space during program
//! runtime.
use solana_sdk::instruction::InstructionError;

/// The maximum allowed size, in bytes, of the accounts data
/// 128 GB was chosen because it is the RAM amount listed under Hardware Recommendations on
/// [Validator Requirements](https://docs.solana.com/running-validator/validator-reqs), and
/// validators often put the ledger on a RAM disk (i.e. tmpfs).
pub const MAX_ACCOUNTS_DATA_LEN: u64 = 128_000_000_000;

/// Meter and track the amount of available accounts data space
#[derive(Debug, Default, Clone, Copy, Eq, PartialEq)]
pub struct AccountsDataMeter {
    /// The maximum amount of accounts data space that can be used (in bytes)
    maximum: u64,

    /// The initial amount of accounts data space used (in bytes)
    initial: u64,

    /// The amount of accounts data space that has changed since `initial` (in bytes)
    delta: i64,
}

impl AccountsDataMeter {
    /// Make a new AccountsDataMeter
    #[must_use]
    pub fn new(initial_accounts_data_len: u64) -> Self {
        let accounts_data_meter = Self {
            maximum: MAX_ACCOUNTS_DATA_LEN,
            initial: initial_accounts_data_len,
            delta: 0,
        };
        debug_assert!(accounts_data_meter.initial <= accounts_data_meter.maximum);
        accounts_data_meter
    }

    /// Return the maximum amount of accounts data space that can be used (in bytes)
    pub fn maximum(&self) -> u64 {
        self.maximum
    }

    /// Return the initial amount of accounts data space used (in bytes)
    pub fn initial(&self) -> u64 {
        self.initial
    }

    /// Return the amount of accounts data space that has changed (in bytes)
    pub fn delta(&self) -> i64 {
        self.delta
    }

    /// Return the current amount of accounts data space used (in bytes)
    pub fn current(&self) -> u64 {
        /// NOTE: Mixed integer ops currently not stable, so copying the impl.
        /// * https://github.com/rust-lang/rust/issues/87840
        /// * https://github.com/a1phyr/rust/blob/47edde1086412b36e9efd6098b191ec15a2a760a/library/core/src/num/uint_macros.rs#L1039-L1048
        const fn saturating_add_signed(lhs: u64, rhs: i64) -> u64 {
            let (res, overflow) = lhs.overflowing_add(rhs as u64);
            if overflow == (rhs < 0) {
                res
            } else if overflow {
                u64::MAX
            } else {
                u64::MIN
            }
        }
        saturating_add_signed(self.initial, self.delta)
    }

    /// Get the remaining amount of accounts data space (in bytes)
    pub fn remaining(&self) -> u64 {
        self.maximum.saturating_sub(self.current())
    }

    /// Consume accounts data space, in bytes.  If `amount` is positive, we are *increasing* the
    /// amount of accounts data space used.  If `amount` is negative, we are *decreasing* the
    /// amount of accounts data space used.  If `amount` is greater than the remaining space,
    /// return an error and *do not* consume more accounts data space.
    pub fn consume(&mut self, amount: i64) -> Result<(), InstructionError> {
        if amount > self.remaining() as i64 {
            return Err(InstructionError::MaxAccountsDataSizeExceeded);
        }
        self.consume_unchecked(amount);
        Ok(())
    }

    /// Unconditionally consume accounts data space.  Refer to `consume()` for more documentation.
    pub fn consume_unchecked(&mut self, amount: i64) {
        self.delta = self.delta.saturating_add(amount);
    }
}

#[cfg(test)]
impl AccountsDataMeter {
    pub fn set_maximum(&mut self, maximum: u64) {
        self.maximum = maximum;
    }
    pub fn set_initial(&mut self, initial: u64) {
        self.initial = initial;
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_new() {
        let initial = 1234;
        let accounts_data_meter = AccountsDataMeter::new(initial);
        assert_eq!(accounts_data_meter.maximum, MAX_ACCOUNTS_DATA_LEN);
        assert_eq!(accounts_data_meter.initial, initial);
    }

    #[test]
    fn test_new_can_use_max_len() {
        let _ = AccountsDataMeter::new(MAX_ACCOUNTS_DATA_LEN);
    }

    #[test]
    #[should_panic]
    fn test_new_panics_if_initial_len_too_big() {
        let _ = AccountsDataMeter::new(MAX_ACCOUNTS_DATA_LEN + 1);
    }

    #[test]
    fn test_remaining() {
        let initial_accounts_data_len = 0;
        let accounts_data_meter = AccountsDataMeter::new(initial_accounts_data_len);
        assert_eq!(accounts_data_meter.remaining(), MAX_ACCOUNTS_DATA_LEN);
    }

    #[test]
    fn test_remaining_saturates() {
        let initial_accounts_data_len = 0;
        let mut accounts_data_meter = AccountsDataMeter::new(initial_accounts_data_len);
        // To test that remaining() saturates, need to break the invariant that initial <= maximum
        accounts_data_meter.initial = MAX_ACCOUNTS_DATA_LEN + 1;
        assert_eq!(accounts_data_meter.remaining(), 0);
    }

    #[test]
    fn test_consume() {
        let initial_accounts_data_len = 0;
        let mut accounts_data_meter = AccountsDataMeter::new(initial_accounts_data_len);

        // Test: simple, positive numbers
        let result = accounts_data_meter.consume(0);
        assert!(result.is_ok());
        let result = accounts_data_meter.consume(1);
        assert!(result.is_ok());
        let result = accounts_data_meter.consume(4);
        assert!(result.is_ok());
        let result = accounts_data_meter.consume(9);
        assert!(result.is_ok());

        // Test: can consume the remaining amount
        let remaining = accounts_data_meter.remaining() as i64;
        let result = accounts_data_meter.consume(remaining);
        assert!(result.is_ok());
        assert_eq!(accounts_data_meter.remaining(), 0);
    }

    #[test]
    fn test_consume_deallocate() {
        let initial_accounts_data_len = 10_000;
        let mut accounts_data_meter = AccountsDataMeter::new(initial_accounts_data_len);
        let remaining_before = accounts_data_meter.remaining();

        let amount = (initial_accounts_data_len / 2) as i64;
        let amount = -amount;
        let result = accounts_data_meter.consume(amount);
        assert!(result.is_ok());
        let remaining_after = accounts_data_meter.remaining();
        assert_eq!(remaining_after, remaining_before + amount.abs() as u64);
    }

    #[test]
    fn test_consume_too_much() {
        let initial_accounts_data_len = 0;
        let mut accounts_data_meter = AccountsDataMeter::new(initial_accounts_data_len);

        // Test: consuming more than what's available (1) returns an error, (2) does not consume
        let remaining = accounts_data_meter.remaining();
        let result = accounts_data_meter.consume(remaining as i64 + 1);
        assert!(result.is_err());
        assert_eq!(accounts_data_meter.remaining(), remaining);
    }

    #[test]
    fn test_consume_zero() {
        // Pre-condition: set up the accounts data meter such that there is no remaining space
        let initial_accounts_data_len = 1234;
        let mut accounts_data_meter = AccountsDataMeter::new(initial_accounts_data_len);
        accounts_data_meter.maximum = initial_accounts_data_len;
        assert_eq!(accounts_data_meter.remaining(), 0);

        // Test: can always consume zero, even if there is no remaining space
        let result = accounts_data_meter.consume(0);
        assert!(result.is_ok());
    }
}