# EVM Client Architecture & Implementation Plan

## Project Goal
Build a cross-platform (native + WASM) EVM client that can:
- Interact with multiple EVM-compatible networks/providers
- Use pluggable signing backends (e.g., SessionManager, hardware wallets, mocks)
- Integrate seamlessly with Rhai scripting and the rest of the modular Rust workspace

---

## Requirements & Principles
- **Async, modular, and testable**: All APIs are async and trait-based
- **Cross-platform**: Native (Rust) and WASM (browser) support
- **Multi-network**: Support for multiple EVM networks/providers, switchable at runtime
- **Pluggable signing**: No direct dependency on vault/session; uses a generic Signer trait
- **Consistency**: Follows conventions in architecture.md and other project docs
- **Scripting**: Exposes ergonomic API for both Rust and Rhai scripting

---

## Recommended File Structure

```
evm_client/
├── Cargo.toml
└── src/
    ├── lib.rs           # Public API
    ├── provider.rs      # EvmProvider abstraction
    ├── client.rs        # EvmClient struct
    ├── signer.rs        # Signer trait
    └── utils.rs         # Helpers (e.g., HTTP, WASM glue)
```

---

## 1. Pluggable Signer Trait

```rust
// signer.rs
#[async_trait::async_trait]
pub trait Signer {
    async fn sign(&self, message: &[u8]) -> Result<Vec<u8>, EvmError>;
    fn address(&self) -> String;
}
```

- `SessionManager` in vault implements this trait.
- Any other backend (mock, hardware wallet, etc.) can implement it.

---

## 2. EvmProvider Abstraction

```rust
// provider.rs
pub enum EvmProvider {
    Http { name: String, url: String, chain_id: u64 },
    // Future: WebSocket, Infura, etc.
}

impl EvmProvider {
    pub async fn send_raw_transaction<S: Signer>(&self, tx: &Transaction, signer: &S) -> Result<TxHash, EvmError> {
        let raw_tx = tx.sign(signer).await?;
        let body = format!("{{\"raw\":\"{}\"}}", hex::encode(&raw_tx));
        match self {
            EvmProvider::Http { url, .. } => {
                http_post(url, &body).await
            }
        }
    }
}
```

---

## 3. EvmClient Struct & API

```rust
// client.rs
use std::collections::HashMap;

pub struct EvmClient<S: Signer> {
    providers: HashMap<String, EvmProvider>,
    current: String,
    signer: S,
}

impl<S: Signer> EvmClient<S> {
    pub fn new(signer: S) -> Self {
        Self {
            providers: HashMap::new(),
            current: String::new(),
            signer,
        }
    }
    pub fn add_provider(&mut self, key: String, provider: EvmProvider) {
        self.providers.insert(key, provider);
    }
    pub fn set_current(&mut self, key: &str) -> Result<(), EvmError> {
        if self.providers.contains_key(key) {
            self.current = key.to_string();
            Ok(())
        } else {
            Err(EvmError::UnknownNetwork)
        }
    }
    pub fn current_provider(&self) -> Option<&EvmProvider> {
        self.providers.get(&self.current)
    }
    pub async fn send_transaction(&self, tx: Transaction) -> Result<TxHash, EvmError> {
        let provider = self.current_provider().ok_or(EvmError::NoNetwork)?;
        provider.send_raw_transaction(&tx, &self.signer).await
    }
}
```

---

## 4. Cross-Platform Networking (Native + WASM)

```rust
// utils.rs
pub async fn http_post(url: &str, body: &str) -> Result<TxHash, EvmError> {
    #[cfg(not(target_arch = "wasm32"))]
    {
        let resp = reqwest::Client::new().post(url).body(body.to_owned()).send().await?;
        // parse response...
        Ok(parse_tx_hash(resp.text().await?))
    }
    #[cfg(target_arch = "wasm32")]
    {
        let resp = gloo_net::http::Request::post(url).body(body).send().await?;
        // parse response...
        Ok(parse_tx_hash(resp.text().await?))
    }
}
```

---

## 5. Rhai Scripting Integration

```rust
// rhai_bindings.rs
pub fn register_rhai_api(engine: &mut Engine) {
    engine.register_type::<EvmClient<MySigner>>();
    engine.register_fn("add_network", EvmClient::add_provider);
    engine.register_fn("switch_network", EvmClient::set_current);
    engine.register_fn("send_tx", EvmClient::send_transaction);
}
```

---

## 6. Usage Example

```rust
use evm_client::{EvmClient, EvmProvider, Signer};
use vault::SessionManager;

let mut client = EvmClient::new(session_manager);
client.add_provider("mainnet".into(), EvmProvider::Http { name: "Ethereum Mainnet".into(), url: "...".into(), chain_id: 1 });
client.add_provider("polygon".into(), EvmProvider::Http { name: "Polygon".into(), url: "...".into(), chain_id: 137 });
client.set_current("polygon")?;
let tx_hash = client.send_transaction(tx).await?;
```

---

## 7. Compliance & Consistency
- **Async/trait-based**: Like kvstore/vault, all APIs are async and trait-based
- **No direct dependencies**: Uses generic Signer, not vault/session directly
- **Cross-platform**: Uses conditional networking for native/WASM
- **Modular/testable**: Clear separation of provider, client, and signer logic
- **Rhai scripting**: Exposes ergonomic scripting API
- **Follows architecture.md**: Modular, layered, reusable, and extensible

---

## 8. Open Questions / TODOs
- How to handle provider-specific errors and retries?
- Should we support WebSocket providers in v1?
- What subset of EVM JSON-RPC should be exposed to Rhai?
- How to best test WASM networking in CI?

---

*Last updated: 2025-05-16*