Drop MOBI support (#458)

Amazon is slowly killing it, it's just a question of time when it fully dies.

References:

* https://kdp.amazon.com/en_US/help/topic/GULSQMHU5MNH4EZM

> Starting August 1, 2021, we will no longer support MOBI files for reflowable eBooks. Use EPUB, DOCX or KPF to publish new or update reflowable eBooks.

* https://www.amazon.com/gp/help/customer/display.html?nodeId=G5WYD9SAF7PGXRNA

> Beginning in late 2022, you'll no longer be able to send MOBI (.AZW, .MOBI) files to your Kindle library using Send to Kindle. This change won't affect any MOBI files already in your Kindle library. You can still read them with Kindle. MOBI is an older file format and won't support the newest Kindle features for documents.

* https://www.reddit.com/r/kindle/comments/16rw6e3/amazon_announcement_about_mobi_support_timeline/

> We will end all Send to Kindle support for MOBI files by December 20, 2023.

* https://www.mobileread.com/forums/showthread.php?t=336365

> Does anyone still have Kindle Previewer installer older than 3.49 that you could share? The reason I am looking for it is because newer versions no longer open .mobi files.

3 files changed, 0 insertions, 41 deletions

diff --git a/spec/cli_spec.rb b/spec/cli_spec.rb
index fd790a3..032dc29 100644
--- a/spec/cli_spec.rb
+++ b/spec/cli_spec.rb
@@ -37,17 +37,6 @@ describe 'asciidoctor-epub3' do
     expect(File).to exist(out_file)
   end
 
-  it 'converts sample book to mobi' do
-    in_file = example_file 'sample-book.adoc'
-    out_file = temp_file 'sample-book.mobi'
-
-    _, err, res = to_mobi in_file, out_file
-    expect(res.exitstatus).to eq(0)
-    expect(err).not_to include 'ERROR'
-    expect(err).not_to include 'invalid reference'
-    expect(File).to exist(out_file)
-  end
-
   it 'prints errors to stderr when converts invalid book to epub' do
     _, err, res = to_epub fixture_file('invalid.adoc'), temp_file('invalid.epub')
     expect(res.exitstatus).to eq(0)
@@ -57,17 +46,6 @@ describe 'asciidoctor-epub3' do
     expect(err).to include 'EPUB validation failed'
   end
 
-  it 'prints errors to stderr when converts invalid book to mobi' do
-    _, err, res = to_mobi fixture_file('invalid.adoc'), temp_file('invalid.mobi')
-    expect(err).to include 'ERROR'
-    expect(res.exitstatus).to eq(0)
-  end
-
-  def to_mobi(in_file, out_file)
-    skip_unless_has_kindlegen
-    run_command asciidoctor_epub3_bin, '-a', 'ebook-format=mobi', in_file.to_s, '-o', out_file.to_s
-  end
-
   def to_epub(in_file, out_file = nil)
     argv = asciidoctor_epub3_bin + ['-a', 'ebook-validate', in_file.to_s]
     argv += ['-o', out_file.to_s] unless out_file.nil?
diff --git a/spec/converter_spec.rb b/spec/converter_spec.rb
index 273cbd9..454f6f1 100644
--- a/spec/converter_spec.rb
+++ b/spec/converter_spec.rb
@@ -8,10 +8,6 @@ describe Asciidoctor::Epub3::Converter do
       expect(to_epub(fixture_file('empty.adoc'))).not_to be_nil
     end
 
-    it 'converts empty file to mobi without exceptions' do
-      expect(to_mobi(fixture_file('empty.adoc'))).not_to be_nil
-    end
-
     it 'converts empty heredoc document to epub without exceptions' do
       expect(to_epub('')).not_to be_nil
     end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 941c643..4d61d2f 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -61,12 +61,6 @@ RSpec.configure do |config|
     examples_dir.join(*path)
   end
 
-  def skip_unless_has_kindlegen
-    require 'kindlegen'
-  rescue LoadError
-    skip 'kindlegen gem is unavailable'
-  end
-
   def convert(input, opts = {})
     opts[:backend] = 'epub3'
     opts[:header_footer] = true
@@ -89,15 +83,6 @@ RSpec.configure do |config|
     book = GEPUB::Book.parse output
     [book, output]
   end
-
-  def to_mobi(input, opts = {})
-    skip_unless_has_kindlegen
-    (opts[:attributes] ||= {})['ebook-format'] = 'mobi'
-    doc = convert input, opts
-    output = Pathname.new(doc.attr('outfile')).sub_ext '.mobi'
-    expect(output).to exist
-    output
-  end
 end
 
 RSpec::Matchers.define :have_size do |expected|