# The ChangesetController is the RESTful interface to Changeset objects

class ChangesetController < ApplicationController
  require 'xml/libxml'
  require 'diff_reader'

  before_filter :authorize, :only => [:create, :update, :delete, :upload, :include, :close]
  before_filter :check_write_availability, :only => [:create, :update, :delete, :upload, :include]
  before_filter :check_read_availability, :except => [:create, :update, :delete, :upload, :download, :query]
  after_filter :compress_output

  # Help methods for checking boundary sanity and area size
  include MapBoundary

  # Create a changeset from XML.
  def create
    if request.put?
      cs = Changeset.from_xml(request.raw_post, true)

      if cs
        cs.user_id = @user.id
        cs.save_with_tags!
        render :text => cs.id.to_s, :content_type => "text/plain"
      else
        render :nothing => true, :status => :bad_request
      end
    else
      render :nothing => true, :status => :method_not_allowed
    end
  end

  def read
    begin
      changeset = Changeset.find(params[:id])
      render :text => changeset.to_xml.to_s, :content_type => "text/xml"
    rescue ActiveRecord::RecordNotFound
      render :nothing => true, :status => :not_found
    end
  end
  
  ##
  # marks a changeset as closed. this may be called multiple times
  # on the same changeset, so is idempotent.
  def close 
    unless request.put?
      render :nothing => true, :status => :method_not_allowed
      return
    end
    
    changeset = Changeset.find(params[:id])
    
    unless @user.id == changeset.user_id 
      raise OSM::APIUserChangesetMismatchError 
    end
    
    changeset.open = false
    changeset.save!
    render :nothing => true
  rescue ActiveRecord::RecordNotFound
    render :nothing => true, :status => :not_found
  rescue OSM::APIError => ex
    render ex.render_opts
  end

  ##
  # insert a (set of) points into a changeset bounding box. this can only
  # increase the size of the bounding box. this is a hint that clients can
  # set either before uploading a large number of changes, or changes that
  # the client (but not the server) knows will affect areas further away.
  def include
    # only allow POST requests, because although this method is
    # idempotent, there is no "document" to PUT really...
    if request.post?
      cs = Changeset.find(params[:id])

      # check user credentials - only the user who opened a changeset
      # may alter it.
      unless @user.id == cs.user_id 
        raise OSM::APIUserChangesetMismatchError 
      end

      # keep an array of lons and lats
      lon = Array.new
      lat = Array.new

      # the request is in pseudo-osm format... this is kind-of an
      # abuse, maybe should change to some other format?
      doc = XML::Parser.string(request.raw_post).parse
      doc.find("//osm/node").each do |n|
        lon << n['lon'].to_f * GeoRecord::SCALE
        lat << n['lat'].to_f * GeoRecord::SCALE
      end

      # add the existing bounding box to the lon-lat array
      lon << cs.min_lon unless cs.min_lon.nil?
      lat << cs.min_lat unless cs.min_lat.nil?
      lon << cs.max_lon unless cs.max_lon.nil?
      lat << cs.max_lat unless cs.max_lat.nil?

      # collapse the arrays to minimum and maximum
      cs.min_lon, cs.min_lat, cs.max_lon, cs.max_lat = 
        lon.min, lat.min, lon.max, lat.max

      # save the larger bounding box and return the changeset, which
      # will include the bigger bounding box.
      cs.save!
      render :text => cs.to_xml.to_s, :content_type => "text/xml"

    else
      render :nothing => true, :status => :method_not_allowed
    end

  rescue ActiveRecord::RecordNotFound
    render :nothing => true, :status => :not_found
  rescue OSM::APIError => ex
    render ex.render_opts
  end

  ##
  # Upload a diff in a single transaction.
  #
  # This means that each change within the diff must succeed, i.e: that
  # each version number mentioned is still current. Otherwise the entire
  # transaction *must* be rolled back.
  #
  # Furthermore, each element in the diff can only reference the current
  # changeset.
  #
  # Returns: a diffResult document, as described in 
  # http://wiki.openstreetmap.org/index.php/OSM_Protocol_Version_0.6
  def upload
    # only allow POST requests, as the upload method is most definitely
    # not idempotent, as several uploads with placeholder IDs will have
    # different side-effects.
    # see http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.2
    unless request.post?
      render :nothing => true, :status => :method_not_allowed
      return
    end

    changeset = Changeset.find(params[:id])

    # access control - only the user who created a changeset may
    # upload to it.
    unless @user.id == changeset.user_id 
      raise OSM::APIUserChangesetMismatchError 
    end
    
    diff_reader = DiffReader.new(request.raw_post, changeset)
    Changeset.transaction do
      result = diff_reader.commit
      render :text => result.to_s, :content_type => "text/xml"
    end
    
  rescue ActiveRecord::RecordNotFound
    render :nothing => true, :status => :not_found
  rescue OSM::APIError => ex
    render ex.render_opts
  end

  ##
  # download the changeset as an osmChange document.
  #
  # to make it easier to revert diffs it would be better if the osmChange
  # format were reversible, i.e: contained both old and new versions of 
  # modified elements. but it doesn't at the moment...
  #
  # this method cannot order the database changes fully (i.e: timestamp and
  # version number may be too coarse) so the resulting diff may not apply
  # to a different database. however since changesets are not atomic this 
  # behaviour cannot be guaranteed anyway and is the result of a design
  # choice.
  def download
    changeset = Changeset.find(params[:id])
    
    # get all the elements in the changeset and stick them in a big array.
    elements = [changeset.old_nodes, 
                changeset.old_ways, 
                changeset.old_relations].flatten
    
    # sort the elements by timestamp and version number, as this is the 
    # almost sensible ordering available. this would be much nicer if 
    # global (SVN-style) versioning were used - then that would be 
    # unambiguous.
    elements.sort! do |a, b| 
      if (a.timestamp == b.timestamp)
        a.version <=> b.version
      else
        a.timestamp <=> b.timestamp 
      end
    end
    
    # create an osmChange document for the output
    result = OSM::API.new.get_xml_doc
    result.root.name = "osmChange"

    # generate an output element for each operation. note: we avoid looking
    # at the history because it is simpler - but it would be more correct to 
    # check these assertions.
    elements.each do |elt|
      result.root <<
        if (elt.version == 1) 
          # first version, so it must be newly-created.
          created = XML::Node.new "create"
          created << elt.to_xml_node
        else
          # get the previous version from the element history
          prev_elt = elt.class.find(:first, :conditions => 
                                    ['id = ? and version = ?',
                                     elt.id, elt.version])
          unless elt.visible
            # if the element isn't visible then it must have been deleted, so
            # output the *previous* XML
            deleted = XML::Node.new "delete"
            deleted << prev_elt.to_xml_node
          else
            # must be a modify, for which we don't need the previous version
            # yet...
            modified = XML::Node.new "modify"
            modified << elt.to_xml_node
          end
        end
    end

    render :text => result.to_s, :content_type => "text/xml"
            
  rescue ActiveRecord::RecordNotFound
    render :nothing => true, :status => :not_found
  rescue OSM::APIError => ex
    render ex.render_opts
  end

  ##
  # query changesets by bounding box, time, user or open/closed status.
  def query
    # create the conditions that the user asked for. some or all of
    # these may be nil.
    conditions = conditions_bbox(params['bbox'])
    conditions = cond_merge conditions, conditions_user(params['user'])
    conditions = cond_merge conditions, conditions_time(params['time'])
    conditions = cond_merge conditions, conditions_open(params['open'])

    # create the results document
    results = OSM::API.new.get_xml_doc

    # add all matching changesets to the XML results document
    Changeset.find(:all, 
                   :conditions => conditions, 
                   :limit => 100,
                   :order => 'created_at desc').each do |cs|
      results.root << cs.to_xml_node
    end

    render :text => results.to_s, :content_type => "text/xml"

  rescue ActiveRecord::RecordNotFound
    render :nothing => true, :status => :not_found
  rescue OSM::APIError => ex
    render ex.render_opts
  rescue String => s
    render :text => s, :content_type => "text/plain", :status => :bad_request
  end
  
  ##
  # updates a changeset's tags. none of the changeset's attributes are
  # user-modifiable, so they will be ignored.
  #
  # changesets are not (yet?) versioned, so we don't have to deal with
  # history tables here. changesets are locked to a single user, however.
  #
  # after succesful update, returns the XML of the changeset.
  def update
    # request *must* be a PUT.
    unless request.put?
      render :nothing => true, :status => :method_not_allowed
      return
    end
    
    changeset = Changeset.find(params[:id])
    new_changeset = Changeset.from_xml(request.raw_post)

    unless new_changeset.nil?
      changeset.update_from(new_changeset, @user)
      render :text => changeset.to_xml, :mime_type => "text/xml"
    else
      
      render :nothing => true, :status => :bad_request
    end
      
  rescue ActiveRecord::RecordNotFound
    render :nothing => true, :status => :not_found
  rescue OSM::APIError => ex
    render ex.render_opts
  end

  #------------------------------------------------------------
  # utility functions below.
  #------------------------------------------------------------  

  ##
  # merge two conditions
  def cond_merge(a, b)
    if a and b
      a_str = a.shift
      b_str = b.shift
      return [ a_str + " and " + b_str ] + a + b
    elsif a 
      return a
    else b
      return b
    end
  end

  ##
  # if a bounding box was specified then parse it and do some sanity 
  # checks. this is mostly the same as the map call, but without the 
  # area restriction.
  def conditions_bbox(bbox)
    unless bbox.nil?
      raise "Bounding box should be min_lon,min_lat,max_lon,max_lat" unless bbox.count(',') == 3
      bbox = sanitise_boundaries(bbox.split(/,/))
      raise "Minimum longitude should be less than maximum." unless bbox[0] <= bbox[2]
      raise "Minimum latitude should be less than maximum." unless bbox[1] <= bbox[3]
      return ['min_lon < ? and max_lon > ? and min_lat < ? and max_lat > ?',
              bbox[2] * GeoRecord::SCALE, bbox[0] * GeoRecord::SCALE, bbox[3]* GeoRecord::SCALE, bbox[1] * GeoRecord::SCALE]
    else
      return nil
    end
  end

  ##
  # restrict changesets to those by a particular user
  def conditions_user(user)
    unless user.nil?
      u = User.find(user.to_i)
      # should be able to get changesets of public users only, or 
      # our own changesets regardless of public-ness.
      unless u.data_public?
        # get optional user auth stuff so that users can see their own
        # changesets if they're non-public
        setup_user_auth
        
        raise OSM::APINotFoundError if @user.nil? or @user.id != u.id
      end
      return ['user_id = ?', u.id]
    else
      return nil
    end
  end

  ##
  # restrict changes to those during a particular time period
  def conditions_time(time) 
    unless time.nil?
      # if there is a range, i.e: comma separated, then the first is 
      # low, second is high - same as with bounding boxes.
      if time.count(',') == 1
        from, to = time.split(/,/).collect { |t| DateTime.parse(t) }
        return ['created_at > ? and created_at < ?', from, to]
      else
        # if there is no comma, assume its a lower limit on time
        return ['created_at > ?', DateTime.parse(time)]
      end
    else
      return nil
    end
  rescue ArgumentError => ex
    raise ex.message.to_s
  end

  ##
  # restrict changes to those which are open
  def conditions_open(open)
    return open.nil? ? nil : ['open = ?', true]
  end

end