add registration via cpi doc

sns-book/src/domain-name/registration.md

@@ -67,3 +67,93 @@ GET https://sns-sdk-proxy.bonfida.workers.dev/register?buyer={buyer}&domain={dom
 This endpoint can be used to register domain for buyer. Additionaly, the buyer dans specify the space it wants to allocate for the domain account. In the case where serialize is true the endpoint will return the transaction serialized in the wire format base64 encoded. Otherwise it will return the instruction in the following format: `{ programId: string, keys: {isWritable: boolean, isSigner: boolean, pubkey: string}[], data: string }` where `data` is base64 encoded.
 
 This endpoint also supports the optional mint parameter to change the mint of the token used for registration (currently supports USDC, USDT, FIDA and wSOL), if mint is omitted it defaults to USDC.
+
+## Registration via CPI
+
+Add the `sns-registrar` dependency to your `Cargo.toml`:
+
+```toml
+[dependencies]
+sns-registrar = { git = "ssh://[email protected]/Bonfida/sns-registrar.git", features = ["no-entrypoint"] }
+```
+
+In your code make sure to import the required functions
+
+```rust
+use sns_registrar::{instruction_auto::create_split_v2, processor::create_split_v2};
+```
+
+The main function for domain registration is `create_split_v2`. Here's how to use it:
+
+```rust
+let registration_instruction = create_split_v2(
+    sns_registrar::ID,
+    create_split_v2::Accounts {
+        naming_service_program: accounts.spl_name_service.key,
+        root_domain: accounts.root_domain.key,
+        name: accounts.name_account.key,
+        reverse_lookup: accounts.reverse_lookup.key,
+        system_program: accounts.system_program.key,
+        central_state: accounts.sns_registrar_central_state.key,
+        buyer: accounts.buyer.key,
+        domain_owner: accounts.new_domain_owner.key,
+        buyer_token_source: accounts.buyer_token_source.key,
+        pyth_feed_account: accounts.pyth_feed_account.key,
+        vault: accounts.bonfida_fee_vault.key,
+        spl_token_program: accounts.spl_token_program.key,
+        rent_sysvar: accounts.rent_sysvar.key,
+        state: accounts.sns_registrar_state.key,
+        referrer_account_opt: None,
+        fee_payer: accounts.fee_payer.key,
+    },
+    create_split_v2::Params {
+        name: domain_name,
+        space: 0,
+        referrer_idx_opt: None,
+    },
+);
+```
+
+Important Account Keys:
+
+- `sns_registrar`: Constant key `jCebN34bUfdeUYJT13J1yG16XWQpt5PDx6Mse9GUqhR`
+- `naming_service_program`: Constant key `namesLPneVptA9Z5rqUDD9tMTWEJwofgaYwp8cawRkX`
+- `root_domain`: Constant key `58PwtjSDuFHuUkYjH9BYnnQKHfwo9reZhC2zMJv9JPkx`
+- `central_state`: Constant key `33m47vH6Eav6jr5Ry86XjhRft2jRBLDnDgPSHoquXi2Z`
+- `name`: Computed using `sns_registrar::utils::get_name_key("something", None)?;` for registering `something.sol`
+- `reverse_lookup`: Computed using `sns_registrar::utils::get_reverse_key(accounts.name_account.key, None)?;`
+- `pyth_feed_account`: Derived based on the mint used for registration. See Pyth price feed derivation and token utilities
+- `vault`: ATA of `5D2zKog251d6KPCyFyLMt3KroWwXXPWSgTPyhV22K2gR` for the mint used in registration
+- `state`: PDA derived as: `Pubkey::find_program_address(&[&accounts.name_account.key.to_bytes()], accounts.sns_registrar.key).0`
+- `domain_owner` and `buyer` can be different this flexibility enables scenarios where one account pays for the registration while another becomes the owner of the domain.
+- `buyer_token_source` is the associated token account of `buyer` for the mint used for the registration and used to pay the registration
+
+After creating the instruction, invoke it like this:
+
+```rust
+invoke_signed(
+    &registration_instruction,
+    &[
+        accounts.sns_registrar.clone(),
+        accounts.spl_name_service.clone(),
+        accounts.root_domain.clone(),
+        accounts.name_account.clone(),
+        accounts.reverse_lookup.clone(),
+        accounts.system_program.clone(),
+        accounts.sns_registrar_central_state.clone(),
+        accounts.central_state.clone(),
+        accounts.fee_payer.clone(),
+        accounts.destination_token_vault.clone(),
+        accounts.pyth_feed_account.clone(),
+        accounts.bonfida_fee_vault.clone(),
+        accounts.spl_token_program.clone(),
+        accounts.rent_sysvar.clone(),
+        accounts.sns_registrar_state.clone(),
+        accounts.new_domain_owner.clone(),
+    ],
+    &[&signer_seeds],
+)?;
+```
+
+- The `space` parameter in `create_split_v2::Params` is set to `0` in this example.
+- The `referrer_account_opt` and `referrer_idx_opt` are set to `None` here. Use these for referral functionality if required.