exw3/README.md

<p align="center">
  <img src="./exw3_logo.jpg"/>
</p>

## Installation

        def deps do
          [{:exw3, "~> 0.1.3"}]
        end

## Overview

ExW3 is a wrapper around ethereumex to provide a high level, user friendly json rpc api. It currently only supports Http. The primary feature it provides is a handy abstraction for working with smart contracts.

## Usage

Ensure you have an ethereum node to connect to at the specified url in your config. An easy local testnet to use is ganache-cli:
```
ganache-cli
```

Make sure your config includes:
```elixir
config :ethereumex,
  url: "http://localhost:8545"
```

Currently, ExW3 supports a handful of json rpc commands. Mostly just the useful ones. If it doesn't support a specific commands you can always use the [Ethereumex](https://github.com/exthereum/ethereumex) commands.

Check out the [documentation](https://hexdocs.pm/exw3/ExW3.html)

```elixir
iex(1)> accounts = ExW3.accounts()
["0xb5c17637ccc1a5d91715429de76949fbe49d36f0",
 "0xecf00f60a29acf81d7fdf696fd2ca1fa82b623b0",
 "0xbf11365685e07ad86387098f27204700d7568ee2",
 "0xba76d611c29fb25158e5a7409cb627cf1bd220cf",
 "0xbb209f51ef097cc5ca320264b5373a48f7ee0fba",
 "0x31b7a2c8b2f82a92bf4cb5fd13971849c6c956fc",
 "0xeb943cee8ec3723ab3a06e45dc2a75a3caa04288",
 "0x59315d9706ac567d01860d7ede03720876972162",
 "0x4dbd23f361a4df1ef5e517b68e099bf2fcc77b10",
 "0x150eb320428b9bc93453b850b4ea454a35308f17"]
iex(2)> ExW3.balance(Enum.at(accounts, 0))
99999999999962720359
iex(3)> ExW3.block_number()
835
iex(4)> simple_storage_abi = ExW3.load_abi("test/examples/build/SimpleStorage.abi")
%{
  "get" => %{
    "constant" => true,
    "inputs" => [],
    "name" => "get",
    "outputs" => [%{"name" => "", "type" => "uint256"}],
    "payable" => false,
    "stateMutability" => "view",
    "type" => "function"
  },
  "set" => %{
    "constant" => false,
    "inputs" => [%{"name" => "_data", "type" => "uint256"}],
    "name" => "set",
    "outputs" => [],
    "payable" => false,
    "stateMutability" => "nonpayable",
    "type" => "function"
  }
}
iex(5)> ExW3.Contract.start_link(SimpleStorage, abi: simple_storage_abi)
{:ok, #PID<0.239.0>}
iex(6)> {:ok, address} = ExW3.Contract.deploy(SimpleStorage, bin: ExW3.load_bin("test/examples/build/SimpleStorage.bin"), options: %{gas: 300000, from: Enum.at(accounts, 0)})
{:ok, "0xd99306b81bd61cb0ecdd3f2c946af513b3395088"}
iex(7)> ExW3.Contract.at(SimpleStorage, address)
:ok
iex(8)> ExW3.Contract.call(SimpleStorage, :get)
{:ok, 0}
iex(9)> ExW3.Contract.send(SimpleStorage, :set, [1], %{from: Enum.at(accounts, 0)})
{:ok, "0xb7e9cbdd2cec8ca017e675059a3af063d754496c960f156e1a41fe51ea82f3b8"}
iex(10)> ExW3.Contract.call(SimpleStorage, :get)                                
{:ok, 1}
```

## Listening for Events

Elixir doesn't have event listeners like say JS. However, we can simulate that behavior with message passing. The way ExW3 handles event filters, is that it starts a background process that will call eth_getFilterChanges every cycle. Whenever a change is detected it will send a message to the listener.

```
# Start the background listener
ExW3.EventListener.start_link

# Assuming we have already setup our contract called EventTester
# We can then add a filter for the event listener to look out for
# by passing in the event name, and the process we want to receive the messages when an event is triggered.
# For now we are going to use the main process, however, we could pass in a pid of a different process.

filter_id = ExW3.Contract.filter(EventTester, "Simple", self())

# We can then wait for the event. Using the typical receive will wait for the first instance of the event, and then continue.
# This is useful for testing.
receive do
  {:event, {filter_id, data}} -> IO.inspect data
end

# We can then uninstall the filter after we are done using it
ExW3.uninstall_filter(filter_id)

# ExW3 also provides a helper method to continuously listen for events. One use is to combine all of our filters and using pattern matching
ExW3.EventListener.listen(fn result ->
  case result do
    {filter_id, data} -> IO.inspect data
    {filter_id2, data} -> IO.inspect data
  end
end

# The listen method is a simple receive loop waiting for `{:event, _}` messages.
# It looks like this:
    def listen(callback) do
      receive do
	{:event, result} -> apply callback, [result]
      end
      listen(callback)
    end
```

# You could do something similar with your own process, whether it is a simple Task or a more involved GenServer.

# Compiling Soldity

To compile the test solidity contracts after making a change run this command:
```
solc --abi --bin --overwrite -o test/examples/build test/examples/contracts/*.sol
```