src/fee_program.rs

use crate::error::{AppError, ErrorCode};
use borsh::{to_vec, BorshSerialize};
use sha2::{Digest, Sha256};
use solana_sdk::instruction::{AccountMeta, Instruction};
use solana_sdk::pubkey::Pubkey;

pub const CARDCLI_FEE_VAULT_PROGRAM_ID: &str = "EpB6hUZUf1vvvTVAYvEN57pjUWfYswaAuKGGQDHP5iH";
pub const DEFAULT_FIXED_FEE_CENTS: u64 = 10;
pub const DEFAULT_VARIABLE_FEE_BPS: u16 = 20;
const FEE_VAULT_SEED: &[u8] = b"fee_vault";

#[derive(BorshSerialize)]
struct InitializeArgs {
    fee_bps: u16,
    fixed_fee_usd_cents: u16,
}

#[derive(BorshSerialize)]
struct CollectFeeArgs {
    card_amount_usd_cents: u64,
    fee_usd_cents: u64,
    fee_lamports: u64,
    fee_reference: [u8; 16],
}

pub fn card_fee_cents(card_amount_cents: u64, fixed_fee_cents: u64, fee_bps: u16) -> u64 {
    let variable_fee = (card_amount_cents * fee_bps as u64).div_ceil(10_000);
    fixed_fee_cents + variable_fee
}

pub fn usd_cents_to_lamports(fee_usd_cents: u64, sol_price_usd: &str) -> Result<u64, AppError> {
    let price_cents = parse_money_to_cents(sol_price_usd)? as u128;
    if price_cents == 0 {
        return Err(AppError::new(
            ErrorCode::Usage,
            "SOL spot price must be greater than zero",
        ));
    }
    let lamports = (fee_usd_cents as u128 * 1_000_000_000u128).div_ceil(price_cents) as u64;
    Ok(lamports.max(1))
}

pub fn derive_treasury_vault_pda(program_id: &Pubkey) -> (Pubkey, u8) {
    Pubkey::find_program_address(&[FEE_VAULT_SEED], program_id)
}

pub fn initialize_fee_vault_instruction(
    program_id: &Pubkey,
    authority: &Pubkey,
    fee_bps: u16,
    fixed_fee_cents: u64,
) -> Result<(Instruction, Pubkey), AppError> {
    let (fee_vault, _bump) = derive_treasury_vault_pda(program_id);
    let fixed_fee_usd_cents = u16::try_from(fixed_fee_cents).map_err(|_| {
        AppError::new(
            ErrorCode::Usage,
            "fixed_fee_cents must fit into a u16 for Anchor initialization",
        )
    })?;
    let args = InitializeArgs {
        fee_bps,
        fixed_fee_usd_cents,
    };
    let mut data = anchor_discriminator("initialize").to_vec();
    data.extend(to_vec(&args).map_err(|e| AppError::new(ErrorCode::General, e.to_string()))?);
    Ok((
        Instruction {
            program_id: *program_id,
            accounts: vec![
                AccountMeta::new(fee_vault, false),
                AccountMeta::new(*authority, true),
                AccountMeta::new_readonly(
                    "11111111111111111111111111111111"
                        .parse::<Pubkey>()
                        .expect("valid system program id"),
                    false,
                ),
            ],
            data,
        },
        fee_vault,
    ))
}

pub fn collect_fee_instruction(
    program_id: &Pubkey,
    payer: &Pubkey,
    card_amount_usd_cents: u64,
    fee_usd_cents: u64,
    fee_lamports: u64,
    fee_reference: [u8; 16],
) -> Result<(Instruction, Pubkey), AppError> {
    let (fee_vault, _bump) = derive_treasury_vault_pda(program_id);
    let args = CollectFeeArgs {
        card_amount_usd_cents,
        fee_usd_cents,
        fee_lamports,
        fee_reference,
    };
    let mut data = anchor_discriminator("collect_fee").to_vec();
    data.extend(to_vec(&args).map_err(|e| AppError::new(ErrorCode::General, e.to_string()))?);
    Ok((
        Instruction {
            program_id: *program_id,
            accounts: vec![
                AccountMeta::new(fee_vault, false),
                AccountMeta::new(*payer, true),
                AccountMeta::new_readonly(
                    "11111111111111111111111111111111"
                        .parse::<Pubkey>()
                        .expect("valid system program id"),
                    false,
                ),
            ],
            data,
        },
        fee_vault,
    ))
}

fn anchor_discriminator(name: &str) -> [u8; 8] {
    let mut hasher = Sha256::new();
    hasher.update(format!("global:{name}").as_bytes());
    let hash = hasher.finalize();
    let mut out = [0u8; 8];
    out.copy_from_slice(&hash[..8]);
    out
}

fn parse_money_to_cents(value: &str) -> Result<i64, AppError> {
    let parsed = value.trim().parse::<f64>().map_err(|_| {
        AppError::new(
            ErrorCode::Usage,
            format!("Invalid money value for SOL price: {value}"),
        )
    })?;
    Ok((parsed * 100.0).round() as i64)
}

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

    #[test]
    fn hybrid_fee_formula_is_stable() {
        assert_eq!(
            card_fee_cents(1_000, DEFAULT_FIXED_FEE_CENTS, DEFAULT_VARIABLE_FEE_BPS),
            12
        );
    }

    #[test]
    fn fee_lamports_rounds_up() {
        assert_eq!(usd_cents_to_lamports(12, "80.00").unwrap(), 1_500_000);
    }

    #[test]
    fn fee_vault_space_matches_anchor_account() {
        assert_eq!(8 + 61, 69);
    }

    #[test]
    fn collect_fee_discriminator_is_stable() {
        assert_eq!(
            anchor_discriminator("collect_fee"),
            [60, 173, 247, 103, 4, 93, 130, 48]
        );
    }

    #[test]
    fn initialize_discriminator_is_stable() {
        assert_eq!(
            anchor_discriminator("initialize"),
            [175, 175, 109, 31, 13, 152, 155, 237]
        );
    }
}