require "fuzzily/trigram"
require "ostruct"

module Fuzzily
  module Searchable

    def self.included(by)
      case ActiveRecord::VERSION::MAJOR
        when 5 then by.extend Rails5ClassMethods
        when 6 then by.extend Rails6ClassMethods
      end
    end

    private

    def _update_fuzzy!(_o)
      self.send(_o.trigram_association).delete_all
      String.new(self.send(_o.field)).scored_trigrams.each do |trigram, score|
        self.send(_o.trigram_association).build.tap do |record|
          record.score       = score
          record.trigram     = trigram
          record.fuzzy_field = _o.field.to_s
          record.save!
        end
      end
    end


    module ClassMethods
      # fuzzily_searchable <field> [, <field>...] [, <options>]
      def fuzzily_searchable(*fields)
        options = fields.last.kind_of?(Hash) ? fields.pop : {}

        fields.each do |field|
          make_field_fuzzily_searchable(field, options)
        end
      end

      private

      def _find_by_fuzzy(_o, pattern, options={})
        options[:limit] ||= 10 unless options.has_key? :limit
        options[:offset] ||= 0

        trigrams = _o.trigram_class_name.constantize.
          limit(options[:limit]).
          offset(options[:offset]).
          for_model(self.name).
          for_field(_o.field.to_s).
          matches_for(pattern)
        records = _load_for_ids(trigrams.map(&:owner_id))
        # order records as per trigram query (no portable way to do this in SQL)
        trigrams.map { |t| records[t.owner_id] }.compact
      end

      def _load_for_ids(ids)
        {}.tap do |result|
          results = if respond_to? :where
            where(id: ids)
          else
            find(:all, ids)
          end
          results.each { |_r| result[_r.id] = _r }
        end
      end

      def _bulk_update_fuzzy(_o)
        trigram_class = _o.trigram_class_name.constantize
        supports_bulk_inserts  =
          connection.class.name !~ /sqlite/i ||
          (
            defined?(SQLite3::SQLITE_VERSION) &&
            Gem::Version.new(SQLite3::SQLITE_VERSION) >= Gem::Version.new("3.7.11")
          )

        _with_included_trigrams(_o).find_in_batches(batch_size: 100) do |batch|
          inserts = []
          batch.each do |record|
            data = Fuzzily::String.new(record.send(_o.field))
            data.scored_trigrams.each do |trigram, score|
              inserts << sanitize_sql_array(["(?,?,?,?,?)", self.name, record.id, _o.field.to_s, score, trigram])
            end
          end

          # take care of quoting
          c = trigram_class.connection
          insert_sql = %Q{
            INSERT INTO %s (%s, %s, %s, %s, %s)
            VALUES
          } % [
            c.quote_table_name(trigram_class.table_name),
            c.quote_column_name("owner_type"),
            c.quote_column_name("owner_id"),
            c.quote_column_name("fuzzy_field"),
            c.quote_column_name("score"),
            c.quote_column_name("trigram")
          ]

          trigram_class.transaction do
            batch.each { |record| record.send(_o.trigram_association).delete_all }
            break if inserts.empty?

            if supports_bulk_inserts
              trigram_class.connection.insert(insert_sql + inserts.join(", "))
            else
              inserts.each do |insert|
                trigram_class.connection.insert(insert_sql + insert)
              end
            end
          end
        end
      end

      def make_field_fuzzily_searchable(field, options={})
        class_variable_defined?(:"@@fuzzily_searchable_#{field}") and return

        _o = OpenStruct.new(
          field:                  field,
          trigram_class_name:     options.fetch(:class_name, "Trigram"),
          trigram_association:    "trigrams_for_#{field}".to_sym,
          update_trigrams_method: "update_fuzzy_#{field}!".to_sym,
          async:                  options.fetch(:async, false)
        )

        _add_trigram_association(_o)

        singleton_class.send(:define_method, "find_by_fuzzy_#{field}".to_sym) do |*args|
          _find_by_fuzzy(_o, *args)
        end

        singleton_class.send(:define_method, "bulk_update_fuzzy_#{field}".to_sym) do
          _bulk_update_fuzzy(_o)
        end

        define_method _o.update_trigrams_method do
          if _o.async && self.respond_to?(:delay)
            self.delay._update_fuzzy!(_o)
          else
            _update_fuzzy!(_o)
          end
        end

        after_save do |record|
          next unless record.send("saved_change_to_#{field}?".to_sym)

          record.send(_o.update_trigrams_method)
        end

        class_variable_set(:"@@fuzzily_searchable_#{field}", true)
        self
      end
    end

    module Rails5ClassMethods
      include ClassMethods

      private

      def _add_trigram_association(_o)
        has_many _o.trigram_association,
          lambda { where(fuzzy_field: _o.field.to_s) },
          class_name: _o.trigram_class_name,
          as:         :owner,
          dependent:  :delete_all,
          autosave:   true
      end

      def _with_included_trigrams(_o)
        self.includes(_o.trigram_association)
      end
    end

    module Rails6ClassMethods
      include Rails5ClassMethods
    end
  end
end