voter-stake-registry/programs/voter-stake-registry/src/instructions/configure_voting_mint.rs

use crate::error::*;
use crate::state::*;
use anchor_lang::prelude::*;
use anchor_spl::token::Mint;

// Remaining accounts must be all the token mints that have registered
// as voting mints, including the newly registered one.
#[derive(Accounts)]
pub struct ConfigureVotingMint<'info> {
    #[account(mut, has_one = realm_authority)]
    pub registrar: AccountLoader<'info, Registrar>,
    pub realm_authority: Signer<'info>,

    /// Tokens of this mint will produce vote weight
    pub mint: Account<'info, Mint>,
    // This instruction expects that all voting mint addresses, including a
    // newly registered one, are passed in ctx.remainingAccounts.
}

/// Creates a new exchange rate for a given mint. This allows a voter to
/// deposit the mint in exchange for vote weight. There can only be a single
/// exchange rate per mint.
///
/// * `idx`: index of the rate to be set
/// * `digit_shift`: how many digits to shift the native token amount, see below
/// * `baseline_vote_weight_scaled_factor`: vote weight factor for all funds in vault, in 1/1e9 units
/// * `max_extra_lockup_vote_weight_scaled_factor`: max extra weight for lockups, in 1/1e9 units
/// * `lockup_saturation_secs`: lockup duration at which the full vote weight
///   bonus is given to locked up deposits
///
/// This instruction can be called several times for the same mint and index to
/// change the voting mint configuration.
///
/// The vote weight for `amount` of native tokens will be
/// ```
/// vote_weight =
///     amount * 10^(digit_shift)
///            * (baseline_vote_weight_scaled_factor/1e9
///               + lockup_duration_factor * max_extra_lockup_vote_weight_scaled_factor/1e9)
/// ```
/// where lockup_duration_factor is a value between 0 and 1, depending on how long
/// the amount is locked up. It is 1 when the lockup duration is greater or equal
/// lockup_saturation_secs.
///
/// Warning: Choose values that ensure that the vote weight will not overflow the
/// u64 limit! There is a check based on the supply of all configured mints, but
/// do your own checking too.
///
/// If you use a single mint, prefer digit_shift=0 and baseline_vote_weight_scaled_factor +
/// max_extra_lockup_vote_weight_scaled_factor <= 1e9. That way you won't have issues with overflow no
/// matter the size of the mint's supply.
///
/// Digit shifting is particularly useful when using several voting token mints
/// that have a different number of decimals. It can be used to align them to
/// a common number of decimals.
///
/// Example: If you have token A with 6 decimals and token B with 9 decimals, you
/// could set up:
///    * A with digit_shift=0,  baseline_vote_weight_scaled_factor=2e9, max_extra_lockup_vote_weight_scaled_factor=0
///    * B with digit_shift=-3, baseline_vote_weight_scaled_factor=1e9, max_extra_lockup_vote_weight_scaled_factor=1e9
///
/// That would make 1.0 decimaled tokens of A as valuable as 2.0 decimaled tokens
/// of B when unlocked. B tokens could be locked up to double their vote weight. As
/// long as A's and B's supplies are below 2^63, there could be no overflow.
///
/// Note that in this example, you need 1000 native B tokens before receiving 1
/// unit of vote weight. If the supplies were significantly lower, you could use
///    * A with digit_shift=3, baseline_vote_weight_scaled_factor=2e9, max_extra_lockup_vote_weight_scaled_factor=0
///    * B with digit_shift=0, baseline_vote_weight_scaled_factor=1e9, max_extra_lockup_vote_weight_scaled_factor=1e9
/// to not lose precision on B tokens.
///
pub fn configure_voting_mint(
    ctx: Context<ConfigureVotingMint>,
    idx: u16,
    digit_shift: i8,
    baseline_vote_weight_scaled_factor: u64,
    max_extra_lockup_vote_weight_scaled_factor: u64,
    lockup_saturation_secs: u64,
    grant_authority: Option<Pubkey>,
) -> Result<()> {
    require_gt!(
        lockup_saturation_secs,
        0,
        VsrError::LockupSaturationMustBePositive
    );
    let registrar = &mut ctx.accounts.registrar.load_mut()?;
    let mint = ctx.accounts.mint.key();
    let idx = idx as usize;
    require_gt!(
        registrar.voting_mints.len(),
        idx,
        VsrError::OutOfBoundsVotingMintConfigIndex
    );

    // Either it's reconfiguring an existing mint with the correct index,
    // or configuring a new mint on an unused index.
    match registrar.voting_mint_config_index(mint) {
        Ok(existing_idx) => require_eq!(
            existing_idx,
            idx,
            VsrError::VotingMintConfiguredWithDifferentIndex
        ),
        Err(_) => require!(
            !registrar.voting_mints[idx].in_use(),
            VsrError::VotingMintConfigIndexAlreadyInUse
        ),
    };

    registrar.voting_mints[idx] = VotingMintConfig {
        mint,
        digit_shift,
        baseline_vote_weight_scaled_factor,
        max_extra_lockup_vote_weight_scaled_factor,
        lockup_saturation_secs,
        grant_authority: grant_authority.unwrap_or_default(),
        reserved1: [0; 7],
        reserved2: [0; 7],
    };

    // Check for overflow in vote weight
    registrar.max_vote_weight(ctx.remaining_accounts)?;

    Ok(())
}