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//
// Copyright 2021 Signal Messenger, LLC.
// SPDX-License-Identifier: AGPL-3.0-only
//

use curve25519_dalek_signal::scalar::Scalar;
use serde::{Deserialize, Serialize};

use crate::common::sho::Sho;
use crate::common::simple_types::{ReceiptLevel, ReceiptSerialBytes, Timestamp};

/// The full set of information known by the client after receiving the credential response from
/// the issuing server. It will all be shared with the credential presentation. Initially the
/// client only knows the receipt_serial_bytes which is randomly generated. receipt_serial_bytes
/// should never be shared with the issuing service in unencrypted form.
///
/// Clients must do validation on the returned receipt_expiration_time and receipt_level to ensure
/// no tagging has occurred.
#[derive(Copy, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct ReceiptStruct {
    pub(crate) receipt_serial_bytes: ReceiptSerialBytes,
    pub(crate) receipt_expiration_time: Timestamp,
    pub(crate) receipt_level: ReceiptLevel,
}

impl ReceiptStruct {
    pub fn new(
        receipt_serial_bytes: ReceiptSerialBytes,
        receipt_expiration_time: Timestamp,
        receipt_level: ReceiptLevel,
    ) -> Self {
        Self {
            receipt_serial_bytes,
            receipt_expiration_time,
            receipt_level,
        }
    }

    pub fn calc_m1(&self) -> Scalar {
        Self::calc_m1_from(self.receipt_expiration_time, self.receipt_level)
    }

    pub fn calc_m1_from(receipt_expiration_time: Timestamp, receipt_level: ReceiptLevel) -> Scalar {
        let mut bytes =
            [0u8; std::mem::size_of::<Timestamp>() + std::mem::size_of::<ReceiptLevel>()];
        bytes[..std::mem::size_of::<Timestamp>()]
            .copy_from_slice(&receipt_expiration_time.to_be_bytes());
        bytes[std::mem::size_of::<Timestamp>()..].copy_from_slice(&receipt_level.to_be_bytes());
        let mut sho = Sho::new(b"Signal_ZKGroup_20210919_Receipt_CalcM1", &bytes);
        sho.get_scalar()
    }
}