Fix network difficulty chart for hybrid coins

-Difficulty chart would fail to populate if the shared_pages.difficulty setting was 'Hybrid' and is now handled properly. The chart now supports 2 datasets: POW and POS
-NetworkHistory.difficulty field was renamed to difficulty_pow and a new difficulty_pos field was added
-The shared_pages.page_header.network_charts.difficulty_chart.line_color setting was renamed to pow_line_color
-The shared_pages.page_header.network_charts.difficulty_chart.fill_color setting was renamed to pow_fill_color

NOTE: If you have existing NetworkHistory data from before this update, it will be automatically assumed to be POW. If it was actualy POS, you will need to either manually fix the data in mongo or simply wait a couple hours while syncing to eventually push the old data out of the chart

lib/database.js

@@ -205,6 +205,22 @@ function check_add_db_field(model_obj, field_name, default_value, cb) {
   });
 }
 
+function check_rename_db_field(model_obj, old_field_name, new_field_name, cb) {
+  // determine if a particular field exists in a db collection
+  model_obj.findOne({[old_field_name]: {$exists: false}}, function(err, model_data) {
+    // check if old field exists
+    if (model_data) {
+      // rename field
+      model_obj.updateMany({}, {
+        $rename: { [old_field_name]: new_field_name }
+      }, { multi: true, strict: false }, function() {
+        return cb(true);
+      });
+    } else
+      return cb(false);
+  });
+}
+
 function hex_to_ascii(hex) {
     var str = '';
     for (var i = 0; i < hex.length; i += 2)
@@ -935,11 +951,28 @@ module.exports = {
         lib.get_hashrate(function(hashrate) {
           // lookup network difficulty
           lib.get_difficulty(function(difficulty) {
+            var difficultyPOW = 0;
+            var difficultyPOS = 0;
+
+            if (difficulty && difficulty['proof-of-work']) {
+              if (settings.shared_pages.difficulty == 'Hybrid') {
+                difficultyPOS = difficulty['proof-of-stake'];
+                difficultyPOW = difficulty['proof-of-work'];
+              } else if (settings.shared_pages.difficulty == 'POW')
+                difficultyPOW = difficulty['proof-of-work'];
+              else
+                difficultyPOS = difficulty['proof-of-stake'];
+            } else if (settings.shared_pages.difficulty == 'POW')
+              difficultyPOW = difficulty;
+            else
+              difficultyPOS = difficulty;
+
             // create a new network history record
             var newNetworkHistory = new NetworkHistory({
               blockindex: height,
               nethash: (hashrate == null || hashrate == '-' ? 0 : hashrate),
-              difficulty: difficulty
+              difficulty_pow: difficultyPOW,
+              difficulty_pos: difficultyPOS,
             });
 
             // save the new network history record
@@ -1541,6 +1574,22 @@ module.exports = {
     });
   },
 
+  check_networkhistory: function(cb) {
+    NetworkHistory.findOne({}, function(err, networkhistory) {
+      if (networkhistory) {
+        // collection has data
+        // determine if the difficulty field exists
+        check_rename_db_field(NetworkHistory, 'difficulty', 'difficulty_pow', function(renamed) {
+          // determine if difficulty_pos field exists
+          check_add_db_field(NetworkHistory, 'difficulty_pos', 0, function(exists) {
+            return cb(true);
+          });
+        });
+      } else
+        return cb(false);
+    });
+  },
+
   initialize_data_startup: function(cb) {
     console.log('Initializing database.. Please wait...');
 
@@ -1562,23 +1611,26 @@ module.exports = {
           module.exports.check_txes(function(txes_exists) {
             // add new field(s) to masternode collection if missing
             module.exports.check_masternodes(function(masternodes_exists) {
-              // check if richlist collection is initialized
-              module.exports.check_richlist(settings.coin.name, function(richlist_exists) {
-                skip = true;
+              // add new field(s) and/or rename old field(s) in networkhistory collection if applicable
+              module.exports.check_networkhistory(function(networkhistory_exists) {
+                // check if richlist collection is initialized
+                module.exports.check_richlist(settings.coin.name, function(richlist_exists) {
+                  skip = true;
 
-                // determine if richlist collection already exists
-                if (richlist_exists == false) {
-                  console.log('No richlist entry found. Creating new entry now..');
-                  skip = false;
-                }
+                  // determine if richlist collection already exists
+                  if (richlist_exists == false) {
+                    console.log('No richlist entry found. Creating new entry now..');
+                    skip = false;
+                  }
 
-                // initialize the richlist collection
-                module.exports.create_richlist(settings.coin.name, skip, function() {
-                  // check and initialize the heavycoin collection
-                  init_heavy(function() {
-                    // finished initializing startup data
-                    console.log('Database initialization complete');
-                    return cb();
+                  // initialize the richlist collection
+                  module.exports.create_richlist(settings.coin.name, skip, function() {
+                    // check and initialize the heavycoin collection
+                    init_heavy(function() {
+                      // finished initializing startup data
+                      console.log('Database initialization complete');
+                      return cb();
+                    });
                   });
                 });
               });