#!/usr/bin/ruby

require 'proj4'
require 'xml/libxml'
require 'set'
require 'postgres'

# projection object to go from latlon -> spherical mercator
PROJ = Proj4::Projection.new(["+proj=merc", "+a=6378137", "+b=6378137", 
                              "+lat_ts=0.0", "+lon_0=0.0", "+x_0=0.0",
                              "+y_0=0", "+k=1.0", "+units=m", 
                              "+nadgrids=@null", "+no_defs +over"])

# width/height of the spherical mercator projection
SIZE=40075016.6855784
# the size of the meta tile blocks
METATILE = 8
# the directory root for meta tiles
HASH_ROOT = "/var/www/tiles/direct/"
# lowest zoom that we want to expire
MIN_ZOOM=5
# highest zoom that we want to expire
MAX_ZOOM=18
# database parameters
DBNAME="gis"
DBHOST=""
DBPORT=5432
DBTABLE="planet_osm_nodes"

# turns a spherical mercator coord into a tile coord
def tile_from_merc(point, zoom)
  # renormalise into unit space [0,1]
  point.x = 0.5 + point.x / SIZE
  point.y = 0.5 - point.y / SIZE
  # transform into tile space
  point.x = point.x * 2 ** zoom
  point.y = point.y * 2 ** zoom
  # chop of the fractional parts
  [point.x.to_int, point.y.to_int, zoom]
end

# turns a latlon -> tile x,y given a zoom level
def tile_from_latlon(latlon, zoom)
  # first convert to spherical mercator
  point = PROJ.forward(latlon)
  tile_from_merc(point, zoom)
end

# this must match the definition of xyz_to_meta in mod_tile
def xyz_to_meta(root, x, y, z)
  # mask off the final few bits
  x &= ~(METATILE - 1)
  y &= ~(METATILE - 1)
  # generate the path
  hash_path = (0..4).collect { |i| 
    (((x >> 4*i) & 0xf) << 4) | ((y >> 4*i) & 0xf) 
  }.reverse.join('/')
  root + '/' + z.to_s + '/' + hash_path + ".meta"
end

# expire the meta tile by setting the modified time back to some
# very stupidly early time, before OSM started
def expire(meta)
  puts "Expiring #{meta}"
  `touch -t 200001010000 #{meta}`
end

# read in the osm change file
doc = XML::Document.file(ARGV[0])

# hash map to contain all the nodes
nodes = Hash.new

# we put all the nodes into the hash, as it doesn't matter whether the node was
# added, deleted or modified - the tile will need updating anyway.
doc.find('//node').each do |node|
  point = Proj4::Point.new(Math::PI * node['lon'].to_f / 180, 
                           Math::PI * node['lat'].to_f / 180)
  nodes[node['id'].to_i] = tile_from_latlon(point, MAX_ZOOM)
end

# now we look for all the ways that have changed and put all of their nodes into
# the hash too. this will add too many nodes, as it is possible a long way will be
# changed at only a portion of its length. however, due to the non-local way that
# mapnik does text placement, it may stil not be enough.
#
# also, we miss cases where nodes are deleted from ways where that node is not 
# itself deleted and the coverage of the point set isn't enough to encompass the
# change.
conn = PGconn.connect(DBHOST, DBPORT, "", "", DBNAME)
doc.find('//way/nd').each do |node|
  node_id = node['ref'].to_i
  unless nodes.include? node_id
    # this is a node referenced but not added, modified or deleted, so it should
    # still be in the postgis DB.
    res = conn.query("select lon, lat from #{DBTABLE} where id=#{node_id};")

    # bizarrely, sometimes we can't find the node. this seems to happen when the node is
    # created and deleted within the diff period and (i guess therefore) doesn't appear
    # in the diff, but may be referenced in a way. so... the way to deal with them is just
    # to ignore them and output a warning?
    if res.empty? 
      puts "Failed to look up node #{node_id} referenced in way #{node.parent['id']}."

    else
      point = Proj4::Point.new(res[0][0].to_f, res[0][1].to_f)
      nodes[node_id] = tile_from_merc(point, MAX_ZOOM)
    end
  end
end

# create a set of all the tiles at the maximum zoom level which are touched by 
# any of the nodes we've collected. we'll create the tiles at other zoom levels
# by a simple recursion.
set = Set.new nodes.values

# expire tiles and shrink to the set of parents
(MAX_ZOOM).downto(MIN_ZOOM) do |z|
  new_set = Set.new
  meta_set = Set.new

  # turn all the tiles into expires, putting them in the set
  # so that we don't expire things multiple times
  set.each do |xy|
    # this has to match the routine in mod_tile
    meta = xyz_to_meta(HASH_ROOT, xy[0], xy[1], xy[2])
    
    meta_set.add(meta) if File.exist? meta

    # add the parent into the set for the next round
    new_set.add([xy[0] / 2, xy[1] / 2, xy[2] - 1])
  end

  # expire all meta tiles
  meta_set.each do |meta|
    expire(meta)
  end

  # reset for the next round at a lower zoom level
  set = new_set
end