# frozen_string_literal: true

require "pg_query"
require "pg"

module PgOnlineSchemaChange
  class Query
    extend Helper

    INDEX_SUFFIX = "_pgosc"
    DROPPED_COLUMN_TYPE = :AT_DropColumn
    RENAMED_COLUMN_TYPE = :AT_RenameColumn
    LOCK_ATTEMPT = 4

    class << self
      def alter_statement?(query)
        PgQuery.parse(query).tree.stmts.all? do |statement|
          statement.stmt.alter_table_stmt.instance_of?(PgQuery::AlterTableStmt) || statement.stmt.rename_stmt.instance_of?(PgQuery::RenameStmt)
        end
      rescue PgQuery::ParseError
        false
      end

      def same_table?(query)
        tables = PgQuery.parse(query).tree.stmts.filter_map do |statement|
          if statement.stmt.alter_table_stmt.instance_of?(PgQuery::AlterTableStmt)
            statement.stmt.alter_table_stmt.relation.relname
          elsif statement.stmt.rename_stmt.instance_of?(PgQuery::RenameStmt)
            statement.stmt.rename_stmt.relation.relname
          end
        end

        tables.uniq.count == 1
      rescue PgQuery::ParseError
        false
      end

      def table(query)
        from_rename_statement = PgQuery.parse(query).tree.stmts.filter_map do |statement|
          statement.stmt.rename_stmt&.relation&.relname
        end[0]
        PgQuery.parse(query).tables[0] || from_rename_statement
      end

      def run(connection, query, reuse_trasaction = false, &block)
        connection.cancel if [PG::PQTRANS_INERROR, PG::PQTRANS_UNKNOWN].include?(connection.transaction_status)

        logger.debug("Running query", { query: query })

        connection.async_exec("BEGIN;")

        result = connection.async_exec(query, &block)
      rescue Exception # rubocop:disable Lint/RescueException
        connection.cancel if connection.transaction_status != PG::PQTRANS_IDLE
        connection.block
        logger.info("Exception raised, rolling back query", { rollback: true, query: query })
        connection.async_exec("ROLLBACK;")
        connection.async_exec("COMMIT;")
        raise
      else
        connection.async_exec("COMMIT;") unless reuse_trasaction
        result
      end

      def table_columns(client, table = nil, reuse_trasaction = false)
        sql = <<~SQL
          SELECT attname as column_name, format_type(atttypid, atttypmod) as type, attnum as column_position FROM   pg_attribute
          WHERE  attrelid = \'#{table || client.table}\'::regclass AND attnum > 0 AND NOT attisdropped
          ORDER  BY attnum;
        SQL
        mapped_columns = []

        run(client.connection, sql, reuse_trasaction) do |result|
          mapped_columns = result.map do |row|
            row["column_name_regular"] = row["column_name"]
            row["column_name"] = client.connection.quote_ident(row["column_name"])
            row["column_position"] = row["column_position"].to_i
            row
          end
        end

        mapped_columns
      end

      def alter_statement_for(client, shadow_table)
        parsed_query = PgQuery.parse(client.alter_statement)

        parsed_query.tree.stmts.each do |statement|
          statement.stmt.alter_table_stmt.relation.relname = shadow_table if statement.stmt.alter_table_stmt

          statement.stmt.rename_stmt.relation.relname = shadow_table if statement.stmt.rename_stmt
        end
        parsed_query.deparse
      end

      def get_indexes_for(client, table)
        query = <<~SQL
          SELECT indexdef, schemaname
          FROM pg_indexes
          WHERE schemaname = \'#{client.schema}\' AND tablename = \'#{table}\'
        SQL

        indexes = []
        run(client.connection, query) do |result|
          indexes = result.map { |row| row["indexdef"] }
        end

        indexes
      end

      def get_all_constraints_for(client)
        query = <<~SQL
          SELECT  conrelid::regclass AS table_on,
                  confrelid::regclass AS table_from,
                  contype as constraint_type,
                  conname AS constraint_name,
                  convalidated AS constraint_validated,
                  pg_get_constraintdef(oid) AS definition
          FROM   	pg_constraint
          WHERE  	contype IN ('f', 'p')
        SQL

        constraints = []
        run(client.connection, query) do |result|
          constraints = result.map { |row| row }
        end

        constraints
      end

      def get_primary_keys_for(client, table)
        get_all_constraints_for(client).select do |row|
          row["table_on"] == table && row["constraint_type"] == "p"
        end
      end

      def get_foreign_keys_for(client, table)
        get_all_constraints_for(client).select do |row|
          row["table_on"] == table && row["constraint_type"] == "f"
        end
      end

      def get_foreign_keys_to_refresh(client, table)
        references = get_all_constraints_for(client).select do |row|
          row["table_from"] == table && row["constraint_type"] == "f"
        end

        references.map do |row|
          add_statement = if row["definition"].end_with?("NOT VALID")
                            "ALTER TABLE #{row["table_on"]} ADD CONSTRAINT #{row["constraint_name"]} #{row["definition"]};"
                          else
                            "ALTER TABLE #{row["table_on"]} ADD CONSTRAINT #{row["constraint_name"]} #{row["definition"]} NOT VALID;"
                          end

          drop_statement = "ALTER TABLE #{row["table_on"]} DROP CONSTRAINT #{row["constraint_name"]};"

          "#{drop_statement} #{add_statement}"
        end.join
      end

      def get_foreign_keys_to_validate(client, table)
        references = get_all_constraints_for(client).select do |row|
          row["table_from"] == table && row["constraint_type"] == "f"
        end

        references.map do |row|
          "ALTER TABLE #{row["table_on"]} VALIDATE CONSTRAINT #{row["constraint_name"]};"
        end.join
      end

      def dropped_columns(client)
        PgQuery.parse(client.alter_statement).tree.stmts.map do |statement|
          next if statement.stmt.alter_table_stmt.nil?

          statement.stmt.alter_table_stmt.cmds.map do |cmd|
            cmd.alter_table_cmd.name if cmd.alter_table_cmd.subtype == DROPPED_COLUMN_TYPE
          end
        end.flatten.compact
      end

      def renamed_columns(client)
        PgQuery.parse(client.alter_statement).tree.stmts.map do |statement|
          next if statement.stmt.rename_stmt.nil?

          {
            old_name: statement.stmt.rename_stmt.subname,
            new_name: statement.stmt.rename_stmt.newname,
          }
        end.flatten.compact
      end

      def primary_key_for(client, table)
        query = <<~SQL
          SELECT
            pg_attribute.attname as column_name
          FROM pg_index, pg_class, pg_attribute, pg_namespace
          WHERE
            pg_class.oid = \'#{table}\'::regclass AND
            indrelid = pg_class.oid AND
            nspname = \'#{client.schema}\' AND
            pg_class.relnamespace = pg_namespace.oid AND
            pg_attribute.attrelid = pg_class.oid AND
            pg_attribute.attnum = any(pg_index.indkey)
          AND indisprimary
        SQL

        columns = []
        run(client.connection, query) do |result|
          columns = result.map { |row| row["column_name"] }
        end

        columns.first
      end

      def storage_parameters_for(client, table, reuse_trasaction = false)
        query = <<~SQL
          SELECT array_to_string(reloptions, ',') as params FROM pg_class WHERE relname=\'#{table}\';
        SQL

        columns = []
        run(client.connection, query, reuse_trasaction) do |result|
          columns = result.map { |row| row["params"] }
        end

        columns.first
      end

      # This function acquires the lock and keeps the transaction
      # open. If a lock is acquired, its upon the caller
      # to call COMMIT to end the transaction. If a lock
      # is not acquired, transaction is closed and a new transaction
      # is started to acquire lock again
      def open_lock_exclusive(client, table)
        attempts ||= 1

        query = <<~SQL
          SET lock_timeout = '#{client.wait_time_for_lock}s';
          LOCK TABLE #{client.table} IN ACCESS EXCLUSIVE MODE;
        SQL
        run(client.connection, query, true)

        true
      rescue PG::LockNotAvailable, PG::InFailedSqlTransaction
        if (attempts += 1) < LOCK_ATTEMPT
          logger.info("Couldn't acquire lock, attempt: #{attempts}")

          run(client.connection, "RESET lock_timeout;")
          kill_backends(client, table)

          retry
        end

        logger.info("Lock acquire failed")
        run(client.connection, "RESET lock_timeout;")

        false
      end

      def kill_backends(client, table)
        return unless client.kill_backends

        logger.info("Terminating other backends")

        query = <<~SQL
          SELECT pg_terminate_backend(pid) FROM pg_locks WHERE locktype = 'relation' AND relation = \'#{table}\'::regclass::oid AND pid <> pg_backend_pid()
        SQL

        run(client.connection, query, true)
      end

      def copy_data_statement(client, shadow_table, reuse_trasaction = false)
        select_columns = table_columns(client, client.table, reuse_trasaction).map do |entry|
          entry["column_name_regular"]
        end

        select_columns -= dropped_columns_list if dropped_columns_list.any?

        insert_into_columns = select_columns.dup

        if renamed_columns_list.any?
          renamed_columns_list.each do |obj|
            insert_into_columns.each_with_index do |insert_into_column, index|
              insert_into_columns[index] = obj[:new_name] if insert_into_column == obj[:old_name]
            end
          end
        end

        insert_into_columns.map! do |insert_into_column|
          client.connection.quote_ident(insert_into_column)
        end

        select_columns.map! do |select_column|
          client.connection.quote_ident(select_column)
        end

        <<~SQL
          INSERT INTO #{shadow_table}(#{insert_into_columns.join(", ")})
          SELECT #{select_columns.join(", ")}
          FROM ONLY #{client.table}
        SQL
      end
    end
  end
end