2 files changed, 100 insertions, 0 deletions
diff --git a/app/lib/search_query_parser.rb b/app/lib/search_query_parser.rb
new file mode 100644
index 000000000..405ad15b8
--- /dev/null
+++ b/app/lib/search_query_parser.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+class SearchQueryParser < Parslet::Parser
+  rule(:term)     { match('[^\s":]').repeat(1).as(:term) }
+  rule(:quote)    { str('"') }
+  rule(:colon)    { str(':') }
+  rule(:space)    { match('\s').repeat(1) }
+  rule(:operator) { (str('+') | str('-')).as(:operator) }
+  rule(:prefix)   { (term >> colon).as(:prefix) }
+  rule(:phrase)   { (quote >> (term >> space.maybe).repeat >> quote).as(:phrase) }
+  rule(:clause)   { (prefix.maybe >> operator.maybe >> (phrase | term)).as(:clause) }
+  rule(:query)    { (clause >> space.maybe).repeat.as(:query) }
+  root(:query)
+end
diff --git a/app/lib/search_query_transformer.rb b/app/lib/search_query_transformer.rb
new file mode 100644
index 000000000..2c4144790
--- /dev/null
+++ b/app/lib/search_query_transformer.rb
@@ -0,0 +1,86 @@
+# frozen_string_literal: true
+
+class SearchQueryTransformer < Parslet::Transform
+  class Query
+    attr_reader :should_clauses, :must_not_clauses, :must_clauses
+
+    def initialize(clauses)
+      grouped = clauses.chunk(&:operator).to_h
+      @should_clauses = grouped.fetch(:should, [])
+      @must_not_clauses = grouped.fetch(:must_not, [])
+      @must_clauses = grouped.fetch(:must, [])
+    end
+
+    def apply(search)
+      should_clauses.each { |clause| search = search.query.should(clause_to_query(clause)) }
+      must_clauses.each { |clause| search = search.query.must(clause_to_query(clause)) }
+      must_not_clauses.each { |clause| search = search.query.must_not(clause_to_query(clause)) }
+      search.query.minimum_should_match(1)
+    end
+
+    private
+
+    def clause_to_query(clause)
+      case clause
+      when TermClause
+        { multi_match: { type: 'most_fields', query: clause.term, fields: ['text', 'text.stemmed'] } }
+      when PhraseClause
+        { match_phrase: { text: { query: clause.phrase } } }
+      else
+        raise "Unexpected clause type: #{clause}"
+      end
+    end
+  end
+
+  class Operator
+    class << self
+      def symbol(str)
+        case str
+        when '+'
+          :must
+        when '-'
+          :must_not
+        when nil
+          :should
+        else
+          raise "Unknown operator: #{str}"
+        end
+      end
+    end
+  end
+
+  class TermClause
+    attr_reader :prefix, :operator, :term
+
+    def initialize(prefix, operator, term)
+      @prefix = prefix
+      @operator = Operator.symbol(operator)
+      @term = term
+    end
+  end
+
+  class PhraseClause
+    attr_reader :prefix, :operator, :phrase
+
+    def initialize(prefix, operator, phrase)
+      @prefix = prefix
+      @operator = Operator.symbol(operator)
+      @phrase = phrase
+    end
+  end
+
+  rule(clause: subtree(:clause)) do
+    prefix   = clause[:prefix][:term].to_s if clause[:prefix]
+    operator = clause[:operator]&.to_s
+
+    if clause[:term]
+      TermClause.new(prefix, operator, clause[:term].to_s)
+    elsif clause[:phrase]
+      PhraseClause.new(prefix, operator, clause[:phrase].map { |p| p[:term].to_s }.join(' '))
+    else
+      raise "Unexpected clause type: #{clause}"
+    end
+  end
+
+  rule(query: sequence(:clauses)) { Query.new(clauses) }
+end