require 'yaml'
require 'longleaf/models/metadata_record'
require 'longleaf/models/md_fields'
require 'longleaf/services/metadata_validator'
require 'longleaf/errors'
require 'longleaf/logging'

module Longleaf
  # Service which deserializes metadata files into MetadataRecord objects
  class MetadataDeserializer
    extend Longleaf::Logging
    MDF ||= MDFields

    # Deserialize a file into a MetadataRecord object
    #
    # @param file_path [String] path of the file to read. Required.
    # @param format [String] format the file is stored in. Default is 'yaml'.
    def self.deserialize(file_path:, format: 'yaml', digest_algs: [])
      file_path = file_path.path if file_path.is_a?(File)

      case format
      when 'yaml'
        md = from_yaml(file_path, digest_algs)
      else
        raise ArgumentError.new("Invalid deserialization format #{format} specified")
      end

      data = Hash.new.merge(md[MDF::DATA])
      # Extract reserved properties for submission as separate parameters
      registered = data.delete(MDFields::REGISTERED_TIMESTAMP)
      deregistered = data.delete(MDFields::DEREGISTERED_TIMESTAMP)
      checksums = data.delete(MDFields::CHECKSUMS)
      file_size = data.delete(MDFields::FILE_SIZE)
      last_modified = data.delete(MDFields::LAST_MODIFIED)

      services = md[MDF::SERVICES]
      service_records = Hash.new
      services&.each do |name, props|
        raise MetadataError.new("Value of service #{name} must be a hash") unless props.class == Hash

        service_props = Hash.new.merge(props)

        stale_replicas = service_props.delete(MDFields::STALE_REPLICAS)
        timestamp = service_props.delete(MDFields::SERVICE_TIMESTAMP)
        run_needed = service_props.delete(MDFields::RUN_NEEDED)

        service_records[name] = ServiceRecord.new(
          properties: service_props,
          stale_replicas: stale_replicas,
          timestamp: timestamp,
          run_needed: run_needed)
      end

      MetadataRecord.new(properties: data,
                         services: service_records,
                         registered: registered,
                         deregistered: deregistered,
                         checksums: checksums,
                         file_size: file_size,
                         last_modified: last_modified)
    end

    # Load configuration a yaml encoded configuration file
    def self.from_yaml(file_path, digest_algs)
      File.open(file_path, 'r:bom|utf-8') do |f|
        contents = f.read

        checksum_error = nil
        begin
          verify_digests(file_path, contents, digest_algs)
        rescue ChecksumMismatchError => err
          # Hold onto the checksum error, in case we can identify the underlying cause
          checksum_error = err
        end

        begin
          md = nil
          begin
            md = YAML.safe_load(contents, [], [], true)
          rescue => err
            raise MetadataError.new("Failed to parse metadata file #{file_path}: #{err.message}")
          end

          validation_result = MetadataValidator.new(md).validate_config
          if !validation_result.valid?
            if checksum_error.nil?
              raise MetadataError.new("Invalid metadata file #{file_path.to_s}:\n#{validation_result.errors.join("\n")}")
            else
              raise MetadataError.new(validation_result.errors.join("\n"))
            end
          end

          # Either return the valid metadata, or raise the checksum error as is
          if checksum_error.nil?
            md
          else
            raise checksum_error
          end
        rescue MetadataError => err
          if checksum_error.nil?
            raise err
          else
            # Add underlying cause from the metadata error to the checksum mismatch error
            msg = checksum_error.message + "\nWith related issue(s):\n#{err.message}"
            raise ChecksumMismatchError.new(msg)
          end
        end
      end
    end

    def self.verify_digests(file_path, contents, digest_algs)
      return if digest_algs.nil? || digest_algs.empty?

      digest_algs.each do |alg|
        if file_path.respond_to?(:path)
          path = file_path.path
        else
          path = file_path
        end
        digest_path = "#{path}.#{alg}"
        unless File.exist?(digest_path)
          logger.warn("Missing expected #{alg} digest for #{path}")
          next
        end

        digest = DigestHelper::start_digest(alg)
        result = digest.hexdigest(contents)
        existing_digest = IO.read(digest_path)

        if result == existing_digest
          logger.info("Metadata fixity check using algorithm '#{alg}' succeeded for file #{path}")
        else
          raise ChecksumMismatchError.new("Metadata digest of type #{alg} did not match the contents of #{path}:" \
                                          + " expected #{existing_digest}, calculated #{result}")
        end
      end
    end
  end
end