Add notes on events

chapters/05_events.md

@@ -6,4 +6,155 @@
 
 <br>
 
+* Events in Archor provide a mechanism for notifying and communicating between different components of a Solana dapp.
 
+* Events are structured pieces of data holding information about a specific occurrence in a program.
+
+* Since there is no native support for events in Solana, Anchor events depend on logging to emit events.
+    - Programs log `base64` encoded event data and clients parse the logs of the transaction to interpret the events.
+
+
+
+
+<br>
+
+---
+
+### Defining Events
+
+<br>
+
+
+* Events are defined using `#[event]` attribute macro, which allows the specification of fields that an event should contain:
+
+<br>
+
+```rust
+#[event]
+pub struct TransferEvent {
+    from: Pubkey,
+    to: Pubkey,
+    amount: u64,
+}
+```
+
+<br>
+
+---
+
+### Emitting Events
+
+<br>
+
+* To emit an event, you can use the `emit!` macro:
+
+<br>
+
+```rust
+emit!(TransferEvent {
+    from: *ctx.accounts.from.key,
+    to: *ctx.accounts.to.key,
+    amount,
+});
+```
+
+<br>
+
+---
+
+### Subscribing to Events
+
+<br>
+
+* Anyone can subscribe to events emitted by your program, through the [@coral-xyz/archor](@coral-xyz/anchor) library:
+
+<br>
+
+```rust
+const subscriptionId = program.addEventListener("TransferEvent", (event) => {
+  // Handle event...
+});
+```
+
+<br>
+
+* The event listener should be removed once it's no longer needed:
+
+<br>
+
+```rust
+program.removeEventListener(subscriptionId);
+```
+
+<br>
+
+---
+
+### CPI Events
+
+<br>
+
+* Solana nodes truncate logs larger than 10KB, which makes regular events emitted via `emit!` unreliable.
+
+* Unlike logs, RPC providers store instruction data without truncation.
+    - CPI events make use of this by executing a self-invoke with the event data to store the event(s) in the instruction.
+
+* To use CPI vents, you can enable `event-cpi`:
+
+<br>
+
+```
+anchor-lang = { version = "0.29.0", features = ["event-cpi"] }
+```
+
+<br>
+
+* Then, add `#[event_cpi]` to accounts struct:
+
+<br>
+
+```rust
+#[event_cpi]
+#[derive(Accounts)]
+pub struct TransferContext {}
+```
+
+<br>
+
+* And the instruction handler:
+
+<br>
+
+```rust
+
+#![allow(unused)]
+fn main() {
+#[program]
+pub mod my_program {
+    use super::*;
+
+    pub fn transfer(ctx: Context<TransferContext>, amount: u64) -> Result<()>  {
+        // Perform transfer logic
+
+        // Emit the TransferEvent
+        emit_cpi!(TransferEvent {
+            from: *ctx.accounts.from.key,
+            to: *ctx.accounts.to.key,
+            amount,
+        });
+
+        Ok(())
+    }
+}
+}
+```
+
+<br>
+
+---
+
+### Resources
+
+<br>
+
+* [Events on The Anchor Book](https://book.anchor-lang.com/anchor_in_depth/events.html)