# Module providing an extract_ref method for controllers working with Git
# tree-ish + path params
#
# Given a string containing both a Git ref - such as a branch or tag - and a
# filesystem path joined by forward slashes, attempts to separate the two.
#
# Expects a @project instance variable to contain the active project. Used to
# check the input against a list of valid repository refs.
#
# Examples
#
#   # No @project available
#   extract_ref('master')
#   # => ['', '']
#
#   extract_ref('master')
#   # => ['master', '/']
#
#   extract_ref("f4b14494ef6abf3d144c28e4af0c20143383e062/CHANGELOG")
#   # => ['f4b14494ef6abf3d144c28e4af0c20143383e062', '/CHANGELOG']
#
#   extract_ref("v2.0.0/README.md")
#   # => ['v2.0.0', '/README.md']
#
#   extract_ref('issues/1234/app/models/project.rb')
#   # => ['issues/1234', '/app/models/project.rb']
#
#   # Given an invalid branch, we fall back to just splitting on the first slash
#   extract_ref('non/existent/branch/README.md')
#   # => ['non', '/existent/branch/README.md']
#
# Returns an Array where the first value is the tree-ish and the second is the
# path
module RefExtractor
  def extract_ref(input)
    pair = ['', '']

    return pair unless @project

    if input.match(/^([[:alnum:]]{40})(.+)/)
      # If the ref appears to be a SHA, we're done, just split the string
      pair = $~.captures
    else
      # Append a trailing slash if we only get a ref and no file path
      id = input
      id += '/' unless id.include?('/')

      # Otherwise, attempt to detect the ref using a list of the project's
      # branches and tags
      valid_refs = @project.branches + @project.tags
      valid_refs.select! { |v| id.start_with?("#{v}/") }

      if valid_refs.length != 1
        # No exact ref match, so just try our best
        pair = id.match(/([^\/]+)(.+)/).captures
      else
        # Partition the string into the ref and the path, ignoring the empty first value
        pair = id.partition(valid_refs.first)[1..-1]
      end
    end

    pair
  end
end