require "pairtree/identifier"
require "pairtree/path"
require "pairtree/obj"
require "pairtree/root"

require "fileutils"

module Pairtree
  class IdentifierError < RuntimeError; end

  class PathError < RuntimeError; end

  class VersionMismatch < RuntimeError; end

  SPEC_VERSION = 0.1

  ##
  # Instantiate a pairtree at a given path location
  # @param [String] path The path in which the pairtree resides
  # @param [Hash] args Pairtree options
  # @option args [String] :prefix (nil) the identifier prefix used throughout the pairtree
  # @option args [String] :version (Pairtree::SPEC_VERSION) the version of the pairtree spec that this tree conforms to
  # @option args [Boolean] :create (false) if true, create the pairtree and its directory structure if it doesn't already exist
  def self.at path, args = {}
    args = {prefix: nil, version: nil, create: false}.merge(args)
    args[:version] ||= SPEC_VERSION
    args[:version] = args[:version].to_f

    root_path = File.join(path, "pairtree_root")
    prefix_file = File.join(path, "pairtree_prefix")
    version_file = File.join(path, pairtree_version_filename(args[:version]))
    existing_version_file = Dir[File.join(path, "pairtree_version*")].max

    if args.delete(:create)
      if File.exist?(path) && !File.directory?(path)
        raise PathError, "#{path} exists, but is not a valid pairtree root"
      end
      FileUtils.mkdir_p(root_path)

      unless File.exist? prefix_file
        File.write(prefix_file, args[:prefix].to_s)
      end

      if existing_version_file
        if existing_version_file != version_file
          stored_version = existing_version_file.scan(/([0-9]+)_([0-9]+)/).flatten.join(".").to_f
          raise VersionMismatch, "Version #{args[:version]} specified, but #{stored_version} found."
        end
      else
        args[:version] ||= SPEC_VERSION
        version_file = File.join(path, pairtree_version_filename(args[:version]))
        File.write(version_file, %(This directory conforms to Pairtree Version #{args[:version]}. Updated spec: http://www.cdlib.org/inside/diglib/pairtree/pairtreespec.html))
        existing_version_file = version_file
      end
    else
      unless File.directory? root_path
        raise PathError, "#{path} does not point to an existing pairtree"
      end
    end

    stored_prefix = File.read(prefix_file)
    unless args[:prefix].nil? || (args[:prefix].to_s == stored_prefix)
      raise IdentifierError, "Specified prefix #{args[:prefix].inspect} does not match stored prefix #{stored_prefix.inspect}"
    end
    args[:prefix] = stored_prefix

    stored_version = existing_version_file.scan(/([0-9]+)_([0-9]+)/).flatten.join(".").to_f
    args[:version] ||= stored_version
    unless args[:version] == stored_version
      raise VersionMismatch, "Version #{args[:version]} specified, but #{stored_version} found."
    end

    Pairtree::Root.new(File.join(path, "pairtree_root"), args)
  end

  class << self
    private

    def pairtree_version_filename(version)
      "pairtree_version#{version.to_s.tr(".", "_")}"
    end
  end
end