require_relative 'Table.rb'

require 'time'
require 'json'

module Timeseries
	module Hoarder
		class CachingTable < Table
			def initialize(db, name, content_name = 'tags', tag_access_update_delay: 60)
				@content_name = content_name
				@id_column = content_name + '_id'

				super(db, name, 'ts_hoarder')

				@known_tags = {}
				@tag_access_times = {}
				@tag_access_updates = {}

				@tag_access_update_delay = tag_access_update_delay
			end

			def table_creation
				@pg.exec("CREATE TABLE ts_hoarder.#{@table_name} ( #{@id_column} SERIAL PRIMARY KEY, #{@content_name} JSONB, created_at TIMESTAMPTZ, last_used TIMESTAMPTZ )")

				@pg.exec("CREATE INDEX ON ts_hoarder.#{@table_name} USING GIN ( #{@content_name} )")
			end

			def load_cache_content
				@pg.exec("SELECT * FROM ts_hoarder.#{@table_name}") do |results|
					results.each do |tuple|

						tags = JSON.parse(tuple[@content_name])

						@known_tags[tags] = tuple[@id_column]
						@tag_access_times[tags] = Time.parse(tuple['last_used'])
					end
				end

				true
			end

			def create_entry(tags)
				return @known_tags[tags] if @known_tags.include? tags

				returned_id = nil

				@pg.transaction do 
					@pg.exec("LOCK TABLE ts_hoarder.#{@table_name}")
					
					res = @pg.exec_params("SELECT * FROM ts_hoarder.#{@table_name} WHERE #{@content_name} = $1::jsonb", [tags.to_json])

					if(res.num_tuples >= 1)
						returned_id = res[0][@id_column]
						@known_tags[tags] = returned_id
						@tag_access_times[tags] = Time.parse(res[0]['last_used'])
					else
						res = @pg.exec_params("INSERT INTO ts_hoarder.#{@table_name} (#{@content_name}, created_at, last_used) VALUES ($1::jsonb, NOW(), NOW()) RETURNING #{@id_column}", [tags.to_json])
					
						returned_id = res[0][@id_column]
						@known_tags[tags] = returned_id
						@tag_access_times[tags] = Time.now()
					end
				end
				
				returned_id
			end

			def [](tags)
				access_time = Time.now()
				if(((@tag_access_times[tags] || Time.at(0)) - Time.now()) > @tag_access_update_delay)
					@tag_access_times[tags] = access_time
					@tag_access_updates[tags] = true
				end

				known_id = @known_tags[tags]
				return known_id unless known_id.nil?

				return create_entry(tags)
			end
		end
	end
end