Ignore unknown bases ('N's) when detecting DB type

Some FASTAs might have a lot of unknown bases before meaningful data
starts e.g. https://www.ncbi.nlm.nih.gov/nuccore/CM000994.3
Keep scanning the file until we reach meaningful bases to run the
determination algorithm against.

Closes #727

Author: tadast

lib/sequenceserver/makeblastdb.rb

@@ -13,6 +13,7 @@ module SequenceServer
   #
   class MAKEBLASTDB
     extend Forwardable
+    GUESS_SAMPLE_SIZE = 1_048_576
 
     def_delegators SequenceServer, :config, :sys
 
@@ -333,8 +334,21 @@ def guess_sequence_type_in_fasta(file)
     # If the given file is FASTA, returns Array of as many different
     # sequences in the portion of the file read. Returns the portion
     # of the file read wrapped in an Array otherwise.
-    def sample_sequences(file)
-      File.read(file, 1_048_576).split(/^>.+$/).delete_if(&:empty?)
+    def sample_sequences(file, offset = 0)
+      sample = File.read(file, GUESS_SAMPLE_SIZE, offset)
+
+      return [] if sample.nil?
+
+      # remove all unknown bases (indicated by 'N') before sampling
+      sample.gsub!(/N/, '')
+      meaningful_samples = sample.split(/^>.+$/).map { |line| line.gsub(/^\n+$/, '') }.delete_if(&:empty?)
+
+      if meaningful_samples.empty?
+        offset += GUESS_SAMPLE_SIZE
+        sample_sequences(file, offset)
+      else
+        meaningful_samples
+      end
     end
   end
 end

spec/makeblastdb_spec.rb

@@ -42,6 +42,23 @@ module SequenceServer
                 'Sinvicta2-2-3.prot.subset.fasta')
     end
 
+    let 'fasta_file_prot_with_unknown_bases_seq' do
+      dir_path = File.join(root_database_dir, 'with_unknown_bases')
+      FileUtils.mkdir_p(dir_path)
+      file_path = File.join(dir_path, 'with_unknown_bases.fasta')
+      # Write a file with unknown bases that is GUESS_SAMPLE_SIZE 'N's long.
+      File.open(file_path, 'w') do |f|
+        f.puts ">seq1"
+        f.puts (("N" * 70) + "\n") * (SequenceServer::MAKEBLASTDB::GUESS_SAMPLE_SIZE / 70).to_i
+        f.puts "VSDTAKVLVTEVLEKVSVNRVATFTIEADASLGTPVVEVLSPTRESLSVHVKQNSQGTYTV"
+        f.puts ">seq2"
+        f.puts "VSDTAKVLVTEVLEKVSVNRVATFTIEADASLGTPVVEVLSPTRESLSVHVKQNSQGTYTV"
+        f.puts "VSDTAKVLVTEVLEKVSVNRVATFTIEADASLGTPVVEVLSPTRESLSVHVKQNSQGTYTV"
+      end
+
+      file_path
+    end
+
     let 'fasta_file_nucl_seqs' do
       File.join(database_dir_v5, 'transcripts', 'Solenopsis_invicta',
                 'Sinvicta2-2-3.cdna.subset.fasta')
@@ -72,6 +89,10 @@ module SequenceServer
       expect(makeblastdb.send(:guess_sequence_type_in_fasta, fasta_file_nucl_seqs)).to eq :nucleotide
     end
 
+    it 'can ignore unknown bases when detecting the sequence type' do
+      expect(makeblastdb.send(:guess_sequence_type_in_fasta, fasta_file_prot_with_unknown_bases_seq)).to eq :protein
+    end
+
     it 'can tell FASTA files that are yet to be made into a BLAST+ database' do
       makeblastdb = SequenceServer::MAKEBLASTDB.new(database_dir_unformatted)
       expect(makeblastdb.any_to_format_or_reformat?).to be_truthy