# Mutual-credit implementation

## Entries

### Private entries:

struct Transaction {
    debtor_address: Address,
    creditor_address: Address,
    amount: f64,
    timestamp: u64
}

#[derive(Serialize, Deserialize, Debug, DefaultJson, Clone)]
pub enum OfferState {
    Pending,
    Canceled,
    Approved {
        approved_header_address: Option<Address>
    },
    Completed { attestation_address: Address },
}

struct Offer {
    transaction: Transaction,
    state: OfferState
}

### Public entry

struct Attestation {
    header_addresses: Vec<Address>
}

Link: "agent->attestation"

Create: only valid if
- It's signed by all the header's agents
- I can get all the headers from the DHT
- The headers' entry addresses are equal

## Create offer

sequenceDiagram
    DebtorUI->>DebtorCell: offer_credits(amount, receiver, timestamp)
    DebtorCell->>CreditorCell: send_offer(offer)
    CreditorCell-->>CreditorCell: create_offer(offer)
    CreditorCell-->>CreditorUI: signal_offer(offer)
    CreditorCell-->>DebtorCell: created
    DebtorCell-->>DebtorCell: create_offer(offer)

## Get counterparty balance

sequenceDiagram
    participant DebtorCell
    participant CreditorCell
    participant DHT
    participant CreditorUI

    ReceiverUI->>CreditorCell: get_balance(offer_address)
    CreditorCell->>DebtorCell: get_chain_snapshot(offer_address)
    DebtorCell-->>DebtorCell: check_offer(offer_address)
    DebtorCell-->>CreditorCell: chain_snapshot
    CreditorCell->>DHT: get_last_attestation(sender_address)
    DHT-->>CreditorCell: last_attestation
    CreditorCell-->>CreditorCell: check attestation & compute balance
    CreditorCell-->>CreditorUI: (last_header_address, balance)

## Accept offer

sequenceDiagram
    participant DebtorCell
    participant CreditorCell
    participant CreditorUI
    CreditorUI->>CreditorCell: accept_offer(transaction_address, last_header_address)
    CreditorCell->>DebtorCell: accept_offer(transaction_address, last_header_address)
    DebtorCell-->>DebtorCell: check_offer(transaction_address)
    DebtorCell-->>DebtorCell: check_last_header(last_header_address)
    DebtorCell-->>DebtorCell: create_transaction(transaction_address)
    DebtorCell->>CreditorCell: complete_tx(transaction_header)
    CreditorCell-->>CreditorCell: check_last_header
    CreditorCell-->>CreditorCell: check_offer(transaction_address)
    CreditorCell-->>CreditorCell: create_transaction(transaction_address)
    CreditorCell-->>CreditorCell: build_atestation(headers)
    CreditorCell->>DebtorCell: sign_attestation(headers)
    DebtorCell-->>DebtorCell: check_offer(transaction_address)
    DebtorCell-->>DebtorCell: check_last_header(last_header_address)
    DebtorCell-->>DebtorCell: sign_attestation(attestation)
    DebtorCell-->>CreditorCell: singature
    CreditorCell-->>CreditorCell: create_attestation
    CreditorCell-->>CreditorCell: complete_offer
    CreditorCell-->>DebtorCell: (headers, attestation_signature)
    DebtorCell-->>DebtorCell: create_attestation
    DebtorCell-->>DebtorCell: complete_offer