Implement IRC format to xhtml-im conversion

The generated XML is very verbose because each IRC formatting tag makes us
close a <span/> element and reopen it with the new style applied.  However,
this works quite well and is easy to implement.

src/bridge/colors.cpp

@@ -1,7 +1,169 @@
 #include <bridge/colors.hpp>
+#include <xmpp/xmpp_stanza.hpp>
+#include <utils/make_unique.hpp>
+
 #include <algorithm>
 
 #include <iostream>
 
+#include <string.h>
+
+static const char IRC_NUM_COLORS = 16;
+
+static const char* irc_colors_to_css[IRC_NUM_COLORS] = {
+  "white",
+  "black",
+  "blue",
+  "green",
+  "indianred",
+  "red",
+  "magenta",
+  "brown",
+  "yellow",
+  "lightgreen",
+  "cyan",
+  "lightcyan",
+  "lightblue",
+  "lightmagenta",
+  "gray",
+  "white",
+};
+
+#define XHTML_NS "http://www.w3.org/1999/xhtml"
+
+struct styles_t
 {
+  bool strong;
+  bool underline;
+  bool italic;
+  int fg;
+  int bg;
+};
+
+/** We keep the currently-applied CSS styles in a structure. Each time a tag
+ * is found, update this style list, then close the current span XML element
+ * (if it is open), then reopen it with all the new styles in it.  This is
+ * done this way because IRC formatting does not map well with XML
+ * (hierarchical tags), it’s a lot easier and cleaner to remove all styles
+ * and reapply them for each tag, instead of trying to keep a consistent
+ * hierarchy of span, strong, em etc tags.  The generated XML is one-level
+ * deep only.
+*/
+Xmpp::body irc_format_to_xhtmlim(const std::string& s)
+{
+  if (s.find_first_of(irc_format_char) == std::string::npos)
+    // there is no special formatting at all
+    return std::make_tuple(s, nullptr);
+
+  std::string cleaned;
+
+  styles_t styles = {false, false, false, -1, -1};
+
+  std::unique_ptr<XmlNode> result = std::make_unique<XmlNode>("body");
+  (*result)["xmlns"] = XHTML_NS;
+
+  XmlNode* current_node = result.get();
+  std::string::size_type pos_start = 0;
+  std::string::size_type pos_end;
+
+  while ((pos_end = s.find_first_of(irc_format_char, pos_start)) != std::string::npos)
+    {
+      const std::string txt = s.substr(pos_start, pos_end-pos_start);
+      cleaned += txt;
+      if (current_node->has_children())
+        current_node->get_last_child()->set_tail(txt);
+      else
+        current_node->set_inner(txt);
+
+      if (s[pos_end] == IRC_FORMAT_BOLD_CHAR)
+        styles.strong = !styles.strong;
+      else if (s[pos_end] == IRC_FORMAT_UNDERLINE_CHAR)
+        styles.underline = !styles.underline;
+      else if (s[pos_end] == IRC_FORMAT_ITALIC_CHAR)
+        styles.italic = !styles.italic;
+      else if (s[pos_end] == IRC_FORMAT_RESET_CHAR)
+        styles = {false, false, false, -1, -1};
+      else if (s[pos_end] == IRC_FORMAT_REVERSE_CHAR)
+        { }                      // TODO
+      else if (s[pos_end] == IRC_FORMAT_REVERSE2_CHAR)
+        { }                      // TODO
+      else if (s[pos_end] == IRC_FORMAT_FIXED_CHAR)
+        { }                      // TODO
+      else if (s[pos_end] == IRC_FORMAT_COLOR_CHAR)
+        {
+          size_t pos = pos_end + 1;
+          styles.fg = -1;
+          styles.bg = -1;
+          // get the first number following the format char
+          if (pos < s.size() && s[pos] >= '0' && s[pos] <= '9')
+            {                   // first digit
+              styles.fg = s[pos++] - '0';
+              if (pos < s.size() && s[pos] >= '0' && s[pos] <= '9')
+                // second digit
+                styles.fg = styles.fg * 10 + s[pos++] - '0';
+            }
+          if (pos < s.size() && s[pos] == ',')
+            {                   // get bg color after the comma
+              pos++;
+              if (pos < s.size() && s[pos] >= '0' && s[pos] <= '9')
+                {               // first digit
+                  styles.bg = s[pos++] - '0';
+                  if (pos < s.size() && s[pos] >= '0' && s[pos] <= '9')
+                    // second digit
+                    styles.bg = styles.bg * 10 + s[pos++] - '0';
+                }
+            }
+          pos_end = pos - 1;
+        }
+
+      // close opened span, if any
+      if (current_node != result.get())
+        {
+          current_node->close();
+          result->add_child(current_node);
+          current_node = result.get();
+        }
+      // Take all currently-applied style and create a new span with it
+      std::string styles_str;
+      if (styles.strong)
+        styles_str += "font-weight:bold;";
+      if (styles.underline)
+        styles_str += "text-decoration:underline;";
+      if (styles.italic)
+        styles_str += "font-style:italic;";
+      if (styles.fg != -1)
+        styles_str += std::string("color:") +
+          irc_colors_to_css[styles.fg % IRC_NUM_COLORS] + ";";
+      if (styles.bg != -1)
+        styles_str += std::string("background-color:") +
+          irc_colors_to_css[styles.bg % IRC_NUM_COLORS] + ";";
+      if (!styles_str.empty())
+        {
+          current_node = new XmlNode("span");
+          (*current_node)["style"] = styles_str;
+        }
+
+      pos_start = pos_end + 1;
+    }
+
+  // If some text remains, without any format char, just append that text at
+  // the end of the current node
+  const std::string txt = s.substr(pos_start, pos_end-pos_start);
+  cleaned += txt;
+  if (current_node->has_children())
+    current_node->get_last_child()->set_tail(txt);
+  else
+    current_node->set_inner(txt);
+
+  if (current_node != result.get())
+    {
+      current_node->close();
+      result->add_child(current_node);
+      current_node = result.get();
+    }
+
+
+  result->close();
+  Xmpp::body body_res = std::make_tuple(cleaned, std::move(result));
+  return body_res;
 }