# frozen_string_literal: true

require 'digest'

module AceOfBase
  # Implements our database.
  class Storage
    include Enumerable

    STORAGE_DIR = File.expand_path('../../data/', __dir__)

    Error = Class.new(AceOfBase::Error)

    def initialize(storage_dir = STORAGE_DIR)
      @storage_dir = storage_dir
      ensure_data_dir_exists_and_is_writable!
    end

    def store(record)
      with_write_locked_file_for_record(record) do |file|
        file.write(RecordSerialiser.encode(record))
      end
    end

    def retrieve(project, shot, version)
      with_read_locked_file(hash_for(project, shot, version)) do |file|
        RecordSerialiser.decode(file.read)
      end
    end

    def each
      Dir['*', base: storage_dir].each do |path|
        with_read_locked_file(path) do |file|
          yield RecordSerialiser.decode(file.read)
        end
      end
    end

    private

    attr_reader :storage_dir

    def ensure_data_dir_exists_and_is_writable!
      raise Error, format('Storage directory (%p) does not exist.', storage_dir) unless File.directory?(storage_dir)
      raise Error, format('Storage directory (%p) is not writable.', storage_dir) unless File.writable?(storage_dir)
    end

    def with_write_locked_file_for_record(record)
      target = File.join(storage_dir, hash_for(record.project, record.shot, record.version))
      File.open(target, File::CREAT | File::WRONLY, 0o600) do |file|
        raise Error, 'Unable to acquire exclusive lock.' unless file.flock(File::LOCK_EX | File::LOCK_NB)

        result = yield file
        file.flock(File::LOCK_UN)
        result
      end
    end

    def with_read_locked_file(path)
      target = File.join(storage_dir, path)
      File.open(target, File::RDONLY) do |file|
        file.flock(File::LOCK_SH)
        result = yield file
        file.flock(File::LOCK_UN)
        result
      end
    rescue Errno::ENOENT
      raise Error, 'Record not found'
    end

    def hash_for(project, shot, version)
      Digest::SHA1.hexdigest("#{project}|#{shot}|#{version}")
    end
  end
end