Added relative date handling

closes: https://github.com/NexesJS/NQL-Lang/issues/9

This adds relative date expressions in the form now-1d.
These are translated into absolute dates inside the NQL parser
The output format then contains a standard gt/lt type date expression

This is because mongo queries don't support relative dates without using $expr and knex doesn't support them at all.
We'd have to change a lot of stuff to support relative queries to the DB / to JSON but this solves the immediate problem simply.

This has meant introducing state into the lexer, which is new to me. This done so that we can correctly interpret the -/+ symbols
in two different "states". This could be used to improve the lexer further.

This is quite a complex addition to the language, but it reduces complexity everywhere else.

lib/scope.js

@@ -1,4 +1,19 @@
 const util = require('util');
+const ops = {
+    add: require('date-fns/add'),
+    sub: require('date-fns/sub')
+};
+const format = require('date-fns/formatRFC3339');
+
+const intervals = {
+    d: 'days',
+    w: 'weeks',
+    M: 'months',
+    y: 'years',
+    h: 'hours',
+    m: 'minutes',
+    s: 'seconds'
+};
 
 module.exports = {
     ungroup(value) {
@@ -10,6 +25,13 @@ module.exports = {
         return value.replace(re, '$1');
     },
 
+    relDateToAbsolute(op, amount, duration) {
+        const now = new Date();
+        const finalDate = ops[op](now, {[intervals[duration]]: amount});
+
+        return format(finalDate);
+    },
+
     debug() {
         if (!process.env.DEBUG || !/nql/.test(process.env.DEBUG)) {
             return;

package.json

@@ -18,11 +18,13 @@
     "ship": "STATUS=$(git status --porcelain); echo $STATUS; if [ -z \"$STATUS\" ]; then yarn publish && git push --follow-tags; fi"
   },
   "devDependencies": {
+    "date-fns": "2.28.0",
     "eslint": "4.19.1",
     "eslint-plugin-ghost": "0.0.25",
     "jison": "0.4.18",
     "mocha": "5.2.0",
-    "should": "13.2.1"
+    "should": "13.2.1",
+    "sinon": "13.0.1"
   },
   "dependencies": {}
 }

src/nql.l

@@ -5,7 +5,9 @@
 omitops                      [^\s'"\+\,\(\)\>\<=\[\]\-]
 omitopsbarnot                [^\s'"\+\,\(\)\>\<=\[\]]
 escapable                    ['"\+\,\(\)\>\<=\[\]]
+final                        [\+\,\(\)\[\]]
 
+%s reldate
 
 %%
 
@@ -17,6 +19,16 @@ escapable                    ['"\+\,\(\)\>\<=\[\]]
 [0-9]+(\.[0-9]+)?\b(?![\-])                                 return 'NUMBER';
 '['                                                         return 'LBRACKET';
 ']'                                                         return 'RBRACKET';
+
+/* relative date handling */
+now(?=[-+]\d+[dwMyhms](?:{final}|$))                        { this.pushState('reldate');
+                                                            return 'NOW'; }
+<reldate>'-'                                                return 'SUB';
+<reldate>'+'                                                return 'ADD';
+<reldate>\d+                                                return 'AMOUNT'
+<reldate>[dwMyhms]                                          { this.popState();
+                                                            return 'INTERVAL' }
+
 {omitops}(\\{escapable}|{omitopsbarnot})+                   return 'LITERAL';
 ['](\\['"]|[^'"])+?[']                                      return 'STRING';
 '('                                                         return 'LPAREN';

src/nql.y

@@ -66,10 +66,16 @@ VALUE
     | TRUE { $$ = true }
     | FALSE { $$ = false }
     | NUMBER { $$ = parseInt(yytext); }
+    | NOW DATEOP AMOUNT INTERVAL { $$ = yy.relDateToAbsolute($2, $3, $4) }
     | LITERAL { $$ = yy.unescape($1); }
     | STRING  { $1 = $1.replace(/^'|'$/g, ''); $$ = yy.unescape($1); }
     ;
 
+DATEOP
+   : ADD      { $$ = "add"; }
+   | SUB      { $$ = "sub"; }
+   ;
+
 OP
     : NOT { $$ = "$ne"; }
     | GT { $$ = "$gt"; }