require 'spec_helper'

module Flydata
  module Util
    describe FileUtil do
      subject { Class.new { include FileUtil }.new }

      let(:file_path) { Tempfile.new('helper_rspec_one_line_file').path }
      let(:dummy_content) { 'dummy_content' }

      before do
        FileUtils.rm(file_path) if File.exists?(file_path)
      end

      describe "#tail" do
        shared_examples 'tail and retrieves correct number of lines' do
          before do
            File.open(file_path,'w') do |io|
              1.upto(total_line_count) do |i|
                io.write("line#{i}\n")
              end
            end
          end
          it "returns expected lines" do
            tailed_lines = subject.tail(file_path, tailed_line_count)
            expect(tailed_lines.count("\n")).to eq(expected_line_range.size)
            expected_line_range.each do |i|
              expect(tailed_lines).to include("line#{i}\n")
            end
          end
        end

        context "when the tailed file has less lines than the passed parameter" do
          let(:total_line_count) { 10 }
          let(:tailed_line_count) { 100 }
          let(:expected_line_range) { 1..10 }
          include_examples 'tail and retrieves correct number of lines'
        end

        context "when the tailed file has equal number of lines as the passed parameter" do
          let(:total_line_count) { 10 }
          let(:tailed_line_count) { 10 }
          let(:expected_line_range) { 1..10 }
          include_examples 'tail and retrieves correct number of lines'
        end

        context "when the tailed file has greater number of lines than the passed parameter" do
          let(:total_line_count) { 100 }
          let(:tailed_line_count) { 10 }
          let(:expected_line_range) { 91..100 }
          include_examples 'tail and retrieves correct number of lines'
        end

        context "when the tailed file is empty" do
          before do
            File.open(file_path,'w').write("")
          end
          it "returns an empty string" do
            expect(subject.tail(file_path, 10)).to eq("")
          end
        end
      end

      describe "#write_line" do
        context 'when file does not exist' do
          it 'creates the file' do
            subject.write_line(file_path, dummy_content)
            expect(IO.read(file_path)).to eq(dummy_content)
          end
        end

        context 'when the file exists' do
          it 'overwrites file' do
            IO.write(file_path, "aaaa\nbbbb\nccc\n")
            subject.write_line(file_path, dummy_content)
            expect(IO.read(file_path)).to eq(dummy_content)
          end
        end
      end

      describe "#read_line" do
        let(:default_value) { nil }

        context 'when file does not exist' do
          it 'return nil' do
            expect(subject.read_line(file_path, nil)).to be_nil
          end
        end

        context 'when file exists' do
          before do
            subject.write_line(file_path, dummy_content)
          end
          it 'return first line of content' do
            expect(subject.read_line(file_path, nil)).to eq(dummy_content)
          end
        end

        context 'when file is empty' do
          before do
            subject.write_line(file_path, '')
          end
          it 'return empty string' do
            expect(subject.read_line(file_path, nil)).to eq('')
          end
        end
      end
    end
  end
end