require_relative 'parser'

class TextToSqlQuery
  def initialize(text, fields, default_field, fields_mappings = {})
    @text = text.to_s.strip
    @fields = fields.map(&:to_sym)
    @default_field = default_field.to_sym
    @fields_mappings = fields_mappings.merge(@fields.reduce({}) do |mappings, field|
      _table_name, field_name = field.to_s.split('.')
      mappings[field_name.to_sym] = field
      mappings
    end)
    fields_mappings.each do |field, value|
      @fields_mappings[field] = value if @fields_mappings[field]
    end
  end

  def where_clause
    @parser = Query.new
    @parsed_tree = @parser.parse(@text)
    generate_sql @parsed_tree
  end

  private

  def generate_sql(tree)
    first_key = tree.keys.first
    node_value = tree[first_key]
    case first_key
    when :DEFAULT_COLUMN
      escaped_node_value = handle_special_chars node_value
      ["#{@default_field.to_s} ILIKE ?", "%#{escaped_node_value}%"]
    when :OPERATOR_OR
      generate_expression_for_logical_operator(:OR, node_value)
    when :OPERATOR_AND
      generate_expression_for_logical_operator(:AND, node_value)
    when :OPERATOR_NOT
      not_array = generate_sql node_value

      if not_array.length < 2
        raise "There should be more than 1 element for expression following NOT operator"
      end

      not_expression = not_array.shift
      not_params = not_array
      
      ["NOT #{not_expression}"] + not_params

    else
      # key is column name
      escaped_node_value = handle_special_chars node_value
      mapping = @fields_mappings[first_key.to_sym]
      if mapping.nil?
        raise "Unknown field '#{first_key.to_s}'"
      else
        ["#{mapping.to_s} ILIKE ?", "%#{escaped_node_value}%"]
      end
    end
  end

  def generate_expression_for_logical_operator(operator, operator_array)
    if operator_array.length != 2
      raise "There should be two array elements for #{operator.to_s} operator"
    end

    first_operand = generate_sql operator_array.first
    second_operand = generate_sql operator_array.last

    if first_operand.length < 2
      raise 'There should be more than 1 element in first operand array'
    end

    if second_operand.length < 2
      raise 'There should be more than 1 element in second operand array'
    end

    first_operand_expression = first_operand.shift
    first_operand_params = first_operand

    second_operand_expression = second_operand.shift
    second_operand_params = second_operand

    ["(#{first_operand_expression} #{operator.to_s} #{second_operand_expression})"] + first_operand_params + second_operand_params
  end

  def handle_special_chars(text)
    result = text.gsub(/\"/, '')
    result.gsub!(/\_/, '\_')
    result.tr!('\\', '\\')
    result.gsub!(/%/, '\%')
    result
  end
end