require "open3"

module Api
  module V1
    module Admin
      class DatabaseController < BaseController
        MAX_UPLOAD_SIZE = 250.megabytes

        def backup
          Dir.mktmpdir("praktikum-backup") do |directory|
            sql_path = File.join(directory, "praktikum-#{Time.current.strftime('%Y%m%d-%H%M%S')}.sql")
            run_database_command!(pg_dump_command(sql_path))
            zip_path = "#{sql_path}.zip"
            stdout, stderr, status = Open3.capture3("zip", "-j", zip_path, sql_path)
            raise "ZIP-Erstellung fehlgeschlagen: #{stderr.presence || stdout}" unless status.success?
            send_data File.binread(zip_path), filename: File.basename(zip_path), type: "application/zip"
          end
        rescue StandardError => error
          Rails.logger.error("Backup failed: #{error.class}: #{error.message}")
          render json: { error: "Datenbanksicherung konnte nicht erstellt werden" }, status: :internal_server_error
        end

        def restore
          upload = params[:file]
          return render json: { error: "Keine Datei ausgewählt" }, status: :bad_request unless upload
          return render json: { error: "Datei ist größer als 250 MB" }, status: :payload_too_large if upload.size.to_i > MAX_UPLOAD_SIZE

          Dir.mktmpdir("praktikum-restore") do |directory|
            uploaded_path = File.join(directory, File.basename(upload.original_filename.to_s))
            File.binwrite(uploaded_path, upload.read)
            sql_path = extract_sql(uploaded_path, directory)
            restore_path = build_atomic_restore_file(sql_path, directory)
            Rails.logger.info("Atomic database restore v2026.08.16.8 using #{File.basename(restore_path)}")
            run_database_command!(psql_command(restore_path))
            # The restored schema invalidates prepared statements and the schema
            # cache of already open Rails connections. Reconnect cleanly before
            # the next request uses the restored database.
            ActiveRecord::Base.connection_handler.clear_all_connections!
            run_pending_migrations!
            ActiveRecord::Base.connection_handler.clear_all_connections!
          end
          render json: { message: "Datenbank wurde erfolgreich wiederhergestellt" }
        rescue StandardError => error
          Rails.logger.error("Restore failed: #{error.class}: #{error.message}")
          render json: { error: "Wiederherstellung fehlgeschlagen: #{error.message}" }, status: :unprocessable_content
        end

        private

        def extract_sql(uploaded_path, directory)
          return uploaded_path if File.extname(uploaded_path).downcase == ".sql"
          raise "Erlaubt sind nur .zip- oder .sql-Dateien" unless File.extname(uploaded_path).downcase == ".zip"
          list, stderr, status = Open3.capture3("unzip", "-Z1", uploaded_path)
          raise "ZIP-Datei ist ungültig: #{stderr}" unless status.success?
          entries = list.lines.map(&:strip).reject(&:blank?)
          sql_entries = entries.select { |entry| File.extname(entry).downcase == ".sql" && !entry.include?("..") && !entry.start_with?("/") }
          raise "ZIP muss genau eine SQL-Datei enthalten" unless sql_entries.one?
          sql_path = File.join(directory, "restore.sql")
          File.binwrite(sql_path, Open3.capture3("unzip", "-p", uploaded_path, sql_entries.first).then { |out, err, result| raise("SQL konnte nicht entpackt werden: #{err}") unless result.success?; out })
          sql_path
        end

        def database_config = ActiveRecord::Base.connection_db_config.configuration_hash

        # Use one physical SQL input so resetting the existing schema always
        # happens before the first CREATE TABLE from legacy plain-text dumps.
        # psql --single-transaction rolls the reset back as well when any
        # statement from the uploaded dump fails.
        def build_atomic_restore_file(sql_path, directory)
          restore_path = File.join(directory, "atomic_restore.sql")
          File.open(restore_path, "wb") do |restore|
            restore.write("DROP SCHEMA IF EXISTS public CASCADE;\n")
            restore.write("CREATE SCHEMA public;\n")
            File.open(sql_path, "rb") { |source| IO.copy_stream(source, restore) }
          end
          restore_path
        end

        def pg_dump_command(path)
          config = database_config
          ["pg_dump", "-U", config[:username].to_s, "-h", (config[:host] || "localhost").to_s, "-p", (config[:port] || 5432).to_s, "-d", config[:database].to_s, "--clean", "--if-exists", "--no-owner", "--no-privileges", "-f", path]
        end

        def psql_command(path)
          config = database_config
          [
            "psql",
            "-v", "ON_ERROR_STOP=1",
            "--single-transaction",
            "-U", config[:username].to_s,
            "-h", (config[:host] || "localhost").to_s,
            "-p", (config[:port] || 5432).to_s,
            "-d", config[:database].to_s,
            "-f", path
          ]
        end

        def run_database_command!(command)
          _stdout, stderr, status = Open3.capture3({ "PGPASSWORD" => database_config[:password].to_s }, *command)
          raise stderr.presence || "Datenbankbefehl fehlgeschlagen" unless status.success?
        end

        def run_pending_migrations!
          stdout, stderr, status = Open3.capture3(
            "bundle", "exec", "rails", "db:migrate",
            chdir: Rails.root.to_s
          )
          Rails.logger.info("Post-restore migrations completed: #{stdout.lines.last.to_s.strip}") if status.success?
          raise "Migrationen nach dem Restore fehlgeschlagen: #{stderr.presence || stdout}" unless status.success?
        end
      end
    end
  end
end