From 98ce24f33b830a82cd5d380687d8af6d2db885e4 Mon Sep 17 00:00:00 2001
From: Marcin Rataj <lidel@lidel.org>
Date: Wed, 12 Nov 2014 00:38:55 +0100
Subject: Basic oneboxing with marker support.

---
 plugin.rb | 72 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 68 insertions(+), 4 deletions(-)

diff --git a/plugin.rb b/plugin.rb
index ff11c3c..cbe2019 100644
--- a/plugin.rb
+++ b/plugin.rb
@@ -2,16 +2,80 @@
 # version: 0.1
 # authors: Marcin Rataj
 
-# whitelist raw iframes
+# whitelist raw iframes posted by users
 register_asset('javascripts/iframe_whitelist.js', :server_side)
 
 class Onebox::Engine::OpenStreetMapOnebox
   include Onebox::Engine
 
-  # oneboxing canonical links into iframes
-  matches_regexp(/^https?:\/\/(?:www\.)?(?:openstreetmap\.org\/\?mlat)\/.+$/)
+  # current embed defaults from openstreetmap.org
+  @@width     = 425
+  @@height    = 350
+  @@tile_size = 256
+
+
+  # enable oneboxing permalinks (http://wiki.openstreetmap.org/wiki/Permalink) into iframes
+  matches_regexp(/^https?:\/\/(?:www\.)openstreetmap\.org/)
 
   def to_html
-    "<iframe src='#{@url}' style='border: 0' width='100%' height='350' frameborder='0' scrolling='no'></iframe>"
+    if match = @url.match(/#map=([\d\.]+)\/([\d\.]+)\/([\d\.]+)/)
+      zoom, lat, lon = match.captures
+      iframe_url = "//www.openstreetmap.org/export/embed.html?bbox=#{get_bbox(lat.to_f, lon.to_f, zoom.to_i)}"
+
+      if marker = @url.match(/mlat=([\d\.]+).+mlon=([\d\.]+)/)
+        mlat, mlon = marker.captures
+        iframe_url = "#{iframe_url}&amp;marker=#{mlat}%2C#{mlon}"
+      end
+
+      "<iframe src='#{iframe_url}' style='border: 0' width='#{@@width.to_i}' height='#{@@height.to_i}' frameborder='0' scrolling='no'></iframe>"
+    else
+      #"NOPE" #@url
+      @url
+    end
+  end
+
+  private
+
+  # http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames#Lon..2Flat._to_tile_numbers_3
+  # note: it is slightly modified as fractional part is not discarded (http://goo.gl/oNtQ5g)
+  def get_tile_number(lat_deg, lng_deg, zoom)
+    lat_rad = lat_deg/180 * Math::PI
+    n = 2.0 ** zoom
+    x = (lng_deg + 180.0) / 360.0 * n
+    y = (1.0 - Math::log(Math::tan(lat_rad) + (1 / Math::cos(lat_rad))) / Math::PI) / 2.0 * n
+    if !y.infinite?.nil?
+      y = x
+    end
+
+    [x, y]
   end
+
+  # http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames#Tile_numbers_to_lon..2Flat._3
+  def get_lat_lng_for_number(xtile, ytile, zoom)
+    n = 2.0 ** zoom
+    lon_deg = xtile / n * 360.0 - 180.0
+    lat_rad = Math::atan(Math::sinh(Math::PI * (1 - 2 * ytile / n)))
+    lat_deg = 180.0 * (lat_rad / Math::PI)
+
+    [lat_deg, lon_deg]
+  end
+
+  # http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames#Lon..2Flat._to_bbox
+  def get_bbox(lat, lon, zoom)
+
+    xtile, ytile = get_tile_number(lat, lon, zoom)
+
+    xtile_s = (xtile * @@tile_size - @@width/2.0)  / @@tile_size
+    ytile_s = (ytile * @@tile_size - @@height/2.0) / @@tile_size
+    xtile_e = (xtile * @@tile_size + @@width/2.0)  / @@tile_size
+    ytile_e = (ytile * @@tile_size + @@height/2.0) / @@tile_size
+
+    lat_s, lon_s = get_lat_lng_for_number(xtile_s, ytile_s, zoom)
+    lat_e, lon_e = get_lat_lng_for_number(xtile_e, ytile_e, zoom)
+
+    "#{lon_s}%2C#{lat_s}%2C#{lon_e}%2C#{lat_e}"
+  end
+
 end
+
+# vim:ts=2:sw=2:et:
-- 
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