Implement an escaping scheme that handles all non-URL-safe characters.

This is a change from the previous scheme that only addresses dots;
old installations must be migrated by listing every channel in
the "legacy_escaping_scheme" key in application.yml.

config/application.yml.example

@@ -9,4 +9,7 @@ realname: whitequark's logger bot
 nickname: logger_test
 channels:
   - "#irclogger-test"
+  - "##irclogger-test"
+legacy_escaping_scheme:
+  - ".irclogger-test"
 domain: example.com

lib/irclogger/viewer_helpers.rb

@@ -4,12 +4,43 @@ module IrcLogger
   module ViewerHelpers
     include Rack::Utils
 
+    CHANNEL_ESCAPE = {
+      '~' => '~~',
+      '#' => '~h~',
+      '/' => '~s~',
+      '%' => '~p~',
+      '\\' => '~r~',
+      '?' => '~q~',
+      '`' => '~a~',
+      '<' => '~l~',
+      '>' => '~g~',
+      '|' => '~b~',
+      '{' => '~o~',
+      '}' => '~c~',
+      '^' => '~x~',
+      '"' => '~d~'
+    }
+    CHANNEL_ESCAPE_INVERTED = CHANNEL_ESCAPE.invert
+
+    def escape_url(url)
+      url.gsub(/(.)/) { |m| CHANNEL_ESCAPE.key?(m) ? CHANNEL_ESCAPE[m] : m }
+    end
+
+    def unescape_url(url)
+      url.gsub(/~[^~]?~/) { |m| CHANNEL_ESCAPE_INVERTED.key?(m) ? CHANNEL_ESCAPE_INVERTED[m] : m }
+    end
+
     def channel_escape(channel)
-      channel[1..-1].gsub(/^#+/) { |m| '.' * m.length }
+      escape_url(channel[1..-1])
     end
 
     def channel_unescape(channel)
-      "##{channel.gsub(/^\.+/) { |m| '#' * m.length }}"
+      c = unescape_url(channel)
+      if (Config.key?('legacy_escaping_scheme') &&
+          Config['legacy_escaping_scheme'].include?(c))
+        "\##{c.gsub(/^\.+/) { |m| '#' * m.length }}"
+      end
+      "\##{c}"
     end
 
     def channel_url(channel, postfix=nil)