Add constant time fee calculation function

Change-Id: Ifc6dcfce4066d6767bf03f79133920daea112697

solana/anchor-bridge/programs/anchor-bridge/src/api/publish_message.rs

@@ -6,8 +6,50 @@ use crate::{
     types::{BridgeConfig, Index},
     PublishMessage,
     Result,
+    MAX_LEN_GUARDIAN_KEYS,
 };
 
+// Constant fee for VAA transactions, measured in lamports.
+const VAA_TX_FEE: u64 = 18 * 10000;
+
 pub fn publish_message(bridge: &mut Bridge, ctx: Context<PublishMessage>) -> Result<()> {
     Ok(())
 }
+
+// A const time calculation of the fee required to publish a message.
+//
+// Cost breakdown:
+// - 2 Signatures
+// - 1 Claimed VAA Rent
+// - 2x Guardian Fees
+const fn calculate_transfer_fee() -> u64 {
+    use std::mem::size_of;
+    const SIGNATURE_COST: u64 = size_of::<SignatureState>() as u64;
+    const VAA_COST: u64 = size_of::<ClaimedVAA>() as u64;
+    const VAA_FEE: u64 = VAA_TX_FEE;
+    SIGNATURE_COST + VAA_COST + VAA_FEE
+}
+
+/// Signature state
+#[repr(C)]
+#[derive(Clone, Copy)]
+pub struct SignatureState {
+    /// signatures of validators
+    pub signatures: [[u8; 65]; MAX_LEN_GUARDIAN_KEYS],
+
+    /// hash of the data
+    pub hash: [u8; 32],
+
+    /// index of the guardian set
+    pub guardian_set_index: u32,
+}
+
+/// Record of a claimed VAA
+#[repr(C)]
+#[derive(Clone, Copy, Debug, Default, PartialEq)]
+pub struct ClaimedVAA {
+    /// hash of the vaa
+    pub hash: [u8; 32],
+    /// time the vaa was submitted
+    pub vaa_time: u32,
+}