ota42y/openapi_parser

class OpenAPIParser::PathItemFinder
  # @param [OpenAPIParser::Schemas::Paths] paths
  def initialize(paths)
    @paths = paths
  end

  # find operation object and if not exist return nil
  # @param [String, Symbol] http_method like (get, post .... allow symbol)
  # @param [String] request_path
  # @return [Result, nil]
  def operation_object(http_method, request_path)
    if (path_item_object = @paths.path[request_path])
      if (op = path_item_object.operation(http_method))
        return Result.new(path_item_object, op, request_path, {}) # find no path_params path
      end
    end

    # check with path_params
    parse_request_path(http_method, request_path)
  end

  class Result
    attr_reader :path_item_object, :operation_object, :original_path, :path_params
    # @!attribute [r] path_item_object
    #   @return [OpenAPIParser::Schemas::PathItem]
    # @!attribute [r] operation_object
    #   @return [OpenAPIParser::Schemas::Operation]
    # @!attribute [r] path_params
    #   @return [Hash{String => String}]
    # @!attribute [r] original_path
    #   @return [String]

    def initialize(path_item_object, operation_object, original_path, path_params)
      @path_item_object = path_item_object
      @operation_object = operation_object
      @original_path = original_path
      @path_params = path_params
    end
  end

  def parse_path_parameters(schema_path, request_path)
    parameters = path_parameters(schema_path)
    return nil if parameters.empty?

    # If there are regex special characters in the path, the regex will
    # be too permissive, so escape the non-parameter parts.
    components = []
    unprocessed = schema_path.dup
    parameters.each do |parameter|
      parts = unprocessed.partition(parameter)
      components << Regexp.escape(parts[0]) unless parts[0] == ''
      components << "(?<#{param_name(parameter)}>.+)"
      unprocessed = parts[2]
    end
    components << Regexp.escape(unprocessed) unless unprocessed == ''

    regex = components.join('')
    matches = request_path.match(regex)
    return nil unless matches

    # Match up the captured names with the captured values as a hash
    matches.names.zip(matches.captures).to_h
  end

  private
    def path_parameters(schema_path)
      # OAS3 follows a RFC6570 subset for URL templates
      # https://swagger.io/docs/specification/serialization/#uri-templates
      # A URL template param can be preceded optionally by a "." or ";", and can be succeeded optionally by a "*";
      # this regex returns a match of the full parameter name with all of these modifiers. Ex: {;id*}
      parameters = schema_path.scan(/(\{[\.;]*[^\{\*\}]+\**\})/)
      # The `String#scan` method returns an array of arrays; we want an array of strings
      parameters.collect { |param| param[0] }
    end

    # check if there is a identical path in the schema (without any param)
    def matches_directly?(request_path, http_method)
      @paths.path[request_path]&.operation(http_method)
    end

    # used to filter paths with different depth or without given http method
    def different_depth_or_method?(splitted_schema_path, splitted_request_path, path_item, http_method)
      splitted_schema_path.size != splitted_request_path.size || !path_item.operation(http_method)
    end

    # check if the path item is a template
    # EXAMPLE: path_template?('{id}') => true
    def path_template?(schema_path_item)
      schema_path_item.start_with?('{') && schema_path_item.end_with?('}')
    end

    # get the parameter name from the schema path item
    # EXAMPLE: param_name('{id}') => 'id'
    def param_name(schema_path_item)
      schema_path_item[1..(schema_path_item.length - 2)]
    end

    # extract params by comparing the request path and the path from schema
    # EXAMPLE:
    # extract_params(['org', '1', 'user', '2', 'edit'], ['org', '{org_id}', 'user', '{user_id}'])
    # => { 'org_id' => 1, 'user_id' => 2 }
    # return nil if the schema does not match
    def extract_params(splitted_request_path, splitted_schema_path)
      splitted_request_path.zip(splitted_schema_path).reduce({}) do |result, zip_item|
        request_path_item, schema_path_item = zip_item

        params = parse_path_parameters(schema_path_item, request_path_item)
        if params
          result.merge!(params)
        else
          return if schema_path_item != request_path_item
        end

        result
      end
    end

    # find all matching paths with parameters extracted
    # EXAMPLE:
    # [
    #    ['/user/{id}/edit', { 'id' => 1 }],
    #    ['/user/{id}/{action}', { 'id' => 1, 'action' => 'edit' }],
    #  ]
    def matching_paths_with_params(request_path, http_method)
      splitted_request_path = request_path.split('/')

      @paths.path.reduce([]) do |result, item|
        path, path_item = item
        splitted_schema_path = path.split('/')

        next result if different_depth_or_method?(splitted_schema_path, splitted_request_path, path_item, http_method)

        extracted_params = extract_params(splitted_request_path, splitted_schema_path)
        result << [path, extracted_params] if extracted_params
        result
      end
    end

    # find matching path and extract params
    # EXAMPLE: find_path_and_params('get', '/user/1') => ['/user/{id}', { 'id' => 1 }]
    def find_path_and_params(http_method, request_path)
      return [request_path, {}] if matches_directly?(request_path, http_method)

      matching = matching_paths_with_params(request_path, http_method)

      # if there are many matching paths, return the one with the smallest number of params
      # (prefer /user/{id}/action over /user/{param_1}/{param_2} )
      matching.min_by { |match| match[1].size }
    end

    def parse_request_path(http_method, request_path)
      original_path, path_params = find_path_and_params(http_method, request_path)
      return nil unless original_path # # can't find

      path_item_object = @paths.path[original_path]
      obj = path_item_object.operation(http_method.to_s)
      return nil unless obj

      Result.new(path_item_object, obj, original_path, path_params)
    end
end