mastodon/app/lib/search_query_transformer.rb

# 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