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//! Runtime features.
//!
//! Runtime features provide a mechanism for features to be simultaneously activated across the
//! network. Since validators may choose when to upgrade, features must remain dormant until a
//! sufficient majority of the network is running a version that would support a given feature.
//!
//! Feature activation is accomplished by:
//! 1. Activation is requested by the feature authority, who issues a transaction to create the
//!    feature account. The newly created feature account will have the value of
//!    `Feature::default()`
//! 2. When the next epoch is entered the runtime will check for new activation requests and
//!    active them.  When this occurs, the activation slot is recorded in the feature account

use crate::{
    account_info::AccountInfo, clock::Slot, instruction::Instruction, program_error::ProgramError,
    pubkey::Pubkey, rent::Rent, system_instruction,
};

crate::declare_id!("Feature111111111111111111111111111111111111");

#[derive(Default, Debug, Serialize, Deserialize, PartialEq, Eq)]
pub struct Feature {
    pub activated_at: Option<Slot>,
}

impl Feature {
    pub const fn size_of() -> usize {
        9 // see test_feature_size_of.
    }

    pub fn from_account_info(account_info: &AccountInfo) -> Result<Self, ProgramError> {
        if *account_info.owner != id() {
            return Err(ProgramError::InvalidArgument);
        }
        bincode::deserialize(&account_info.data.borrow()).map_err(|_| ProgramError::InvalidArgument)
    }
}

/// Activate a feature
pub fn activate(feature_id: &Pubkey, funding_address: &Pubkey, rent: &Rent) -> Vec<Instruction> {
    activate_with_lamports(
        feature_id,
        funding_address,
        rent.minimum_balance(Feature::size_of()),
    )
}

pub fn activate_with_lamports(
    feature_id: &Pubkey,
    funding_address: &Pubkey,
    lamports: u64,
) -> Vec<Instruction> {
    vec![
        system_instruction::transfer(funding_address, feature_id, lamports),
        system_instruction::allocate(feature_id, Feature::size_of() as u64),
        system_instruction::assign(feature_id, &id()),
    ]
}

#[cfg(test)]
mod test {
    use {super::*, solana_program::clock::Slot};

    #[test]
    fn test_feature_size_of() {
        assert_eq!(Feature::size_of() as u64, {
            let feature = Feature {
                activated_at: Some(0),
            };
            bincode::serialized_size(&feature).unwrap()
        });
        assert!(
            Feature::size_of() >= bincode::serialized_size(&Feature::default()).unwrap() as usize
        );
        assert_eq!(Feature::default(), Feature { activated_at: None });

        let features = [
            Feature {
                activated_at: Some(0),
            },
            Feature {
                activated_at: Some(Slot::MAX),
            },
        ];
        for feature in &features {
            assert_eq!(
                Feature::size_of(),
                bincode::serialized_size(feature).unwrap() as usize
            );
        }
    }
}