# Instructions

Instructions are used to communicate with networks connected to Serai, and they
come in two forms:

  - In Instructions are programmable specifications paired with incoming coins,
encoded into transactions on connected networks. Serai will parse included
instructions when it receives coins, executing the included specs.

  - Out Instructions detail how to transfer coins, either to a Serai address or
an address native to the network of the coins in question.

A transaction containing an In Instruction and an Out Instruction (to a native
address) will receive coins to Serai and send coins from Serai, without
requiring directly performing any transactions on Serai itself.

All instructions are encoded under [Shorthand](#shorthand). Shorthand provides
frequent use cases to create minimal data representations on connected networks.

Instructions are interpreted according to their non-Serai network. Addresses
have no validation performed unless otherwise noted. If the processor is
instructed to act on invalid data, it will drop the entire instruction.

### Serialization

Instructions are SCALE encoded.

### In Instruction

InInstruction is an enum of:

  - `Transfer`
  - `Dex(Data)`

The specified target will be minted an appropriate amount of the respective
Serai token. If `Dex`, the encoded call will be executed.

### Refundable In Instruction

  - `origin`      (Option\<ExternalAddress>): Address, from the network of
origin, which sent coins in.
  - `instruction` (InInstruction):            The action to perform with the
incoming coins.

Networks may automatically provide `origin`. If they do, the instruction may
still provide `origin`, overriding the automatically provided value.

If the instruction fails, coins are scheduled to be returned to `origin`,
if provided.

### Out Instruction

  - `address` (ExternalAddress): Address to transfer the coins included with
this instruction to.
  - `data`    (Option<Data>):    Data to include when transferring coins.

No validation of external addresses/data is performed on-chain. If data is
specified for a chain not supporting data, it is silently dropped.

### Destination

Destination is an enum of SeraiAddress and OutInstruction.

### Shorthand

Shorthand is an enum which expands to an Refundable In Instruction.

##### Raw

Raw Shorthand contains a Refundable In Instruction directly. This is a verbose
fallback option for infrequent use cases not covered by Shorthand.

##### Swap

  - `origin`  (Option\<ExternalAddress>): Refundable In Instruction's `origin`.
  - `coin`    (Coin):                     Coin to swap funds for.
  - `minimum` (Amount):                   Minimum amount of `coin` to receive.
  - `out`     (Destination):              Final destination for funds.

which expands to:

```
RefundableInInstruction {
  origin,
  instruction: InInstruction::Dex(swap(Incoming Asset, coin, minimum, out)),
}
```

where `swap` is a function which:

  1) Swaps the incoming funds for SRI.
  2) Swaps the SRI for `coin`.
  3) Checks the amount of `coin` received is greater than `minimum`.
  4) Executes `out` with the amount of `coin` received.

##### Add Liquidity

  - `origin`  (Option\<ExternalAddress>): Refundable In Instruction's `origin`.
  - `minimum` (Amount):                   Minimum amount of SRI tokens to swap
half for.
  - `gas`     (Amount):                   Amount of SRI to send to `address` to
cover gas in the future.
  - `address` (Address):                  Account to send the created liquidity
tokens.

which expands to:

```
RefundableInInstruction {
  origin,
  instruction: InInstruction::Dex(
    swap_and_add_liquidity(Incoming Asset, minimum, gas, address)
  ),
}
```

where `swap_and_add_liquidity` is a function which:

  1) Swaps half of the incoming funds for SRI.
  2) Checks the amount of SRI received is greater than `minimum`.
  3) Calls `swap_and_add_liquidity` with the amount of SRI received - `gas`, and
a matching amount of the incoming coin.
  4) Transfers any leftover funds to `address`.