# NodeMutation

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NodeMutation provides a set of APIs to rewrite node source code.

## Installation

Add this line to your application's Gemfile:

```ruby
gem 'node_mutation'
```

And then execute:

    $ bundle install

Or install it yourself as:

    $ gem install node_mutation

## Usage

1. initialize the NodeMutation instance:

```ruby
require 'node_mutation'

mutation = NodeMutation.new(source, adapter: :parser)
```

2. call the rewrite apis:

```ruby
# append the code to the current node.
mutation.append node, 'include FactoryGirl::Syntax::Methods'
# delete source code of the child ast node
mutation.delete node, :dot, :message, and_comma: true
# indent code
mutation.indent node, tab_size: 1
# insert code to the ast node.
mutation.insert node, 'URI.', at: 'beginning'
# prepend code to the ast node.
mutation.prepend node, '{{arguments.first}}.include FactoryGirl::Syntax::Methods'
# remove source code of the ast node
mutation.remove node, and_comma: true
# replace child node of the ast node with new code
mutation.replace node, :message, with: 'test'
# replace the ast node with new code
mutation.replace_with node, 'create {{arguments}}'
# wrap node with prefix and suffix code
mutation.wrap node, prefix: 'module Foo', suffix: 'end', newline: true
# no operation
mutation.noop
# group actions
mutation.group do
  mutation.delete node, :message, :dot
  mutation.replace node, 'receiver.caller.message', with: 'flat_map'
end
```

3. process actions and write the new source code to file:

```ruby
result = mutation.process
# if it makes any change to the source
result.affected?
# if any action is conflicted
result.conflicted
# return the new source if it is affected
result.new_source
```

## Evaluated Value

NodeMutation supports to evaluate the value of the node, and use the evaluated value to rewrite the source code.

```ruby
source = 'after_commit :do_index, on: :create, if: :indexable?'
node = Parser::CurrentRuby.parse(source)
mutation.replace node, '{{arguments.-1.on_value}}', with: ':update'
source # after_commit :do_index, on: :update, if: :indexable?
```

See more in [PrismAdapter](https://synvert-hq.github.io/node-mutation-ruby/NodeMutation/PrismAdapter.html)
and [ParserAdapter](https://synvert-hq.github.io/node-mutation-ruby/NodeMutation/ParserAdapter.html)
and [SyntaxTreeAdapter](https://synvert-hq.github.io/node-mutation-ruby/NodeMutation/SyntaxTreeAdapter.html)

## Configuration

### adapter

Different parsers, like prism, parse and syntax_tree, will generate different AST nodes, to make NodeMutation work for them all,
we define an [Adapter](https://github.com/synvert-hq/node-mutation-ruby/blob/main/lib/node_mutation/adapter.rb) interface,
if you implement the Adapter interface, you can set it as NodeMutation's adapter.

It provides 3 adapters

1. `PrismAdapter`
2. `ParserAdapter`
3. `SyntaxTreeAdapter`

### strategy

It provides 3 strategies to handle conflicts when processing actions:

1. `Strategy.KEEP_RUNNING`: keep running and ignore the conflict action.
2. `Strategy.THROW_ERROR`: throw error when conflict action is found.

```ruby
NodeMutation.configure(strategy: Strategy.KEEP_RUNNING); // default is Strategy.THROW_ERROR
```

### tab_width

```ruby
NodeMutation.configure(tab_width: 4); // default is 2
```

## Development

After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and the created tag, and push the `.gem` file to [rubygems.org](https://rubygems.org).

## Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/synvert-hq/node_mutation.