feat: key wallet manager (step 2) (#103)

* work

* key wallet tests

* key wallet manager

* fixes

* fixes

* fixes

* more work

* refactoring

* fixes

Author: QuantumExplorer

dash/src/blockdata/transaction/mod.rs

@@ -43,7 +43,7 @@ use crate::blockdata::constants::WITNESS_SCALE_FACTOR;
 use crate::blockdata::script;
 use crate::blockdata::script::Script;
 use crate::blockdata::transaction::hash_type::EcdsaSighashType;
-use crate::blockdata::transaction::special_transaction::{TransactionPayload, TransactionType};
+pub use crate::blockdata::transaction::special_transaction::{TransactionPayload, TransactionType};
 use crate::blockdata::transaction::txin::TxIn;
 use crate::blockdata::transaction::txout::TxOut;
 use crate::blockdata::witness::Witness;

dash/src/types/mod.rs

@@ -0,0 +1,231 @@
+# SPV Wallet with Compact Filters (BIP 157/158)
+
+This guide explains how the filter-based SPV wallet implementation works and how to use it.
+
+## Overview
+
+The system implements a lightweight SPV (Simplified Payment Verification) wallet using compact block filters as specified in BIP 157 and BIP 158. This approach provides:
+
+- **95% bandwidth savings** compared to downloading full blocks
+- **Privacy**: Servers don't learn which addresses belong to the wallet
+- **Efficiency**: Only download blocks containing relevant transactions
+- **Security**: Full SPV validation with merkle proofs
+
+## Architecture
+
+```
+┌─────────────────────────────────────────────────────┐
+│                   FilterSPVClient                    │
+│                                                      │
+│  ┌─────────────────┐       ┌──────────────────┐    │
+│  │  FilterClient   │◄──────►│  WalletManager   │    │
+│  │                 │       │                   │    │
+│  │ - Check filters │       │ - Manage wallets  │    │
+│  │ - Fetch blocks  │       │ - Track UTXOs     │    │
+│  │ - Process txs   │       │ - Update balances │    │
+│  └────────┬────────┘       └──────────────────┘    │
+│           │                                         │
+│           ▼                                         │
+│  ┌─────────────────┐                               │
+│  │ Network Layer   │                               │
+│  │                 │                               │
+│  │ - P2P Protocol  │                               │
+│  │ - Fetch filters │                               │
+│  │ - Fetch blocks  │                               │
+│  └─────────────────┘                               │
+└─────────────────────────────────────────────────────┘
+```
+
+## Workflow
+
+### 1. Initial Setup
+
+```rust
+use key_wallet_manager::{FilterSPVClient, Network};
+
+// Create SPV client
+let mut spv_client = FilterSPVClient::new(Network::Testnet);
+
+// Add wallet from mnemonic
+spv_client.add_wallet(
+    "main_wallet".to_string(),
+    "My Wallet".to_string(),
+    mnemonic,
+    passphrase,
+    Some(birth_height), // Start scanning from this height
+)?;
+```
+
+### 2. Filter Processing Flow
+
+```
+For each new block:
+    1. Receive compact filter from network
+    2. Check if filter matches any of:
+       - Our addresses (watched scripts)
+       - Our UTXOs (watched outpoints)
+    3. If match found:
+       - Fetch full block
+       - Process transactions
+       - Update wallet state
+    4. If no match:
+       - Skip block (save bandwidth)
+```
+
+### 3. Filter Matching
+
+The system watches two types of data:
+
+#### Watched Scripts (Addresses)
+- All addresses generated for the wallet
+- Automatically updated when new addresses are created
+- Matched against transaction outputs
+
+#### Watched Outpoints (UTXOs)
+- All unspent transaction outputs owned by the wallet
+- Automatically updated when receiving/spending
+- Matched against transaction inputs (spending detection)
+
+### 4. Processing Matched Blocks
+
+When a filter matches, the system:
+
+1. **Fetches the full block** from the network
+2. **Processes each transaction**:
+   - Check outputs for payments to our addresses
+   - Check inputs for spending of our UTXOs
+3. **Updates wallet state**:
+   - Add new UTXOs
+   - Remove spent UTXOs
+   - Update balances
+   - Record transaction history
+
+## Implementation Details
+
+### Compact Filters (BIP 158)
+
+Compact filters use Golomb-Rice coding to create a probabilistic data structure:
+
+- **Size**: ~1/20th of the full block
+- **False positive rate**: 1 in 784,931
+- **No false negatives**: If your transaction is in the block, the filter will match
+
+### Filter Chain Validation
+
+The system maintains a chain of filter headers for validation:
+
+```rust
+FilterHeader {
+    filter_type: FilterType::Basic,
+    block_hash: [u8; 32],
+    prev_header: [u8; 32],  // Hash of previous filter header
+    filter_hash: [u8; 32],   // Hash of this block's filter
+}
+```
+
+### Address Gap Limit
+
+The wallet implements BIP 44 gap limit handling:
+
+- Default gap limit: 20 addresses
+- Automatically generates new addresses when used
+- Tracks both receive and change addresses separately
+
+## Usage Example
+
+```rust
+// Process incoming filter
+let filter = receive_filter_from_network();
+let block_hash = BlockHash::from_slice(&filter.block_hash)?;
+
+// Check if we need this block
+match spv_client.process_new_filter(height, block_hash, filter)? {
+    Some(result) => {
+        println!("Found {} relevant transactions", result.relevant_txs.len());
+        println!("New UTXOs: {}", result.new_outpoints.len());
+        println!("Spent UTXOs: {}", result.spent_outpoints.len());
+    }
+    None => {
+        println!("Block not relevant, skipping");
+    }
+}
+
+// Check balance
+let (confirmed, unconfirmed) = spv_client.get_balance("main_wallet")?;
+println!("Balance: {} confirmed, {} unconfirmed", confirmed, unconfirmed);
+```
+
+## Network Integration
+
+To integrate with a P2P network, implement the trait interfaces:
+
+```rust
+impl BlockFetcher for YourNetworkClient {
+    fn fetch_block(&mut self, block_hash: &BlockHash) -> Result<Block, FetchError> {
+        // Send getdata message
+        // Wait for block response
+        // Return parsed block
+    }
+}
+
+impl FilterFetcher for YourNetworkClient {
+    fn fetch_filter(&mut self, block_hash: &BlockHash) -> Result<CompactFilter, FetchError> {
+        // Send getcfilters message
+        // Wait for cfilter response
+        // Return parsed filter
+    }
+}
+```
+
+## Performance Characteristics
+
+### Bandwidth Usage
+
+| Method | Data Downloaded | Privacy | Speed |
+|--------|----------------|---------|-------|
+| Full Node | 100% of blocks | Full | Slow |
+| Traditional SPV | 100% of blocks with txs | Low | Medium |
+| **Compact Filters** | ~5% of blocks | High | Fast |
+
+### Storage Requirements
+
+- **Headers**: ~4 MB per year
+- **Filters**: ~50 MB per year
+- **Relevant blocks**: Only blocks with your transactions
+- **Total**: <100 MB for typical wallet
+
+## Security Considerations
+
+1. **SPV Security**: Validates proof-of-work and merkle proofs
+2. **Privacy**: Server doesn't know which addresses are yours
+3. **Filter Validation**: Validates filter chain to prevent omission attacks
+4. **Multiple Peers**: Should connect to multiple peers for security
+
+## Testing
+
+Run the example:
+
+```bash
+cargo run --example spv_wallet
+```
+
+Run tests:
+
+```bash
+cargo test -p key-wallet-manager
+```
+
+## Future Enhancements
+
+- [ ] Batch filter requests for efficiency
+- [ ] Filter caching and persistence
+- [ ] Peer rotation for privacy
+- [ ] Tor/proxy support
+- [ ] Lightning Network integration
+- [ ] Hardware wallet support
+
+## References
+
+- [BIP 157: Client Side Block Filtering](https://github.com/bitcoin/bips/blob/master/bip-0157.mediawiki)
+- [BIP 158: Compact Block Filters](https://github.com/bitcoin/bips/blob/master/bip-0158.mediawiki)
+- [Neutrino Protocol](https://github.com/lightninglabs/neutrino)