Plugin: Math - Support European-style decimal separator (#268)

* Plugin: Math

* Autodetect input mode - UK-style decimal separator "." (current) or European-style decimal separator "," (new) - and ensure the calculation and output matches what the user expects.

Follows the suggested implementation from the MathJS library documentation: http://mathjs.org/examples/browser/custom_separators.html.html

* * Run eslint

app/main/plugins/hain-plugin-math/index.js

@@ -7,6 +7,9 @@ const lo_has = require('lodash.has');
 
 const math = require('mathjs');
 
+const DECIMAL_SEPARATOR_UK = '.';
+const DECIMAL_SEPARATOR_EUROPE = ',';
+
 module.exports = (context) => {
   const app = context.app;
   const clipboard = context.clipboard;
@@ -29,22 +32,50 @@ module.exports = (context) => {
 
   function makeResultItem(titleKey, query, answer) {
     const result = {};
-    result[titleKey] = `${query.trim()} = ${answer}`;
+    result[titleKey] = `${query.trim()} = <b>${answer}</b>`;
     result.group = 'Math';
     result.payload = answer;
     return result;
   }
 
-  function calculate(query, showRedundantResult) {
+  function calculate(rawQuery, showRedundantResult) {
     try {
+      let query = rawQuery;
+
+      // determine input mode by the presence of European-style decimal separators
+      let inputMode = DECIMAL_SEPARATOR_UK;
+
+      if (query.includes(DECIMAL_SEPARATOR_EUROPE)) {
+        inputMode = DECIMAL_SEPARATOR_EUROPE;
+
+        // replace European-style decimal separators with UK-style decimal separators as required by the MathJS library:
+        // http://mathjs.org/examples/browser/custom_separators.html.html
+        query = query.replace(
+          new RegExp(DECIMAL_SEPARATOR_EUROPE, 'g'),
+          DECIMAL_SEPARATOR_UK
+        );
+      }
+
+      // calculate value by passing the query into MathJS
       const ans = math.eval(query);
+
       if (
         lo_isNumber(ans) ||
         lo_isString(ans) ||
         (lo_isObject(ans) && lo_has(ans, 'value'))
       ) {
-        const ansString = Number.parseFloat(ans.toPrecision(10)).toString();
+        let ansString = Number.parseFloat(ans.toPrecision(10)).toString();
         const isResultMeaningful = ansString.trim() !== query.trim();
+
+        // if the input mode is the non-standard European-style, take the UK-style output of MathJS and transform it
+        // back into the European-style that the user expects
+        if (inputMode === DECIMAL_SEPARATOR_EUROPE && ansString.includes('.')) {
+          ansString = ansString.replace(
+            new RegExp(`\\${DECIMAL_SEPARATOR_UK}`, 'g'),
+            DECIMAL_SEPARATOR_EUROPE
+          );
+        }
+
         if (isResultMeaningful || showRedundantResult) return ansString;
       }
     } catch (e) {}