Replace Filter class with expression structure

This is in order to be able to support UPPER() and LOWER() functions in
queries which are needed for case-insensitive search.

client/filter-component.js

@@ -2,7 +2,7 @@
 
 import m from "mithril";
 
-import * as filterParser from "../common/filter-parser";
+import * as expression from "../common/expression";
 
 const component = {
   view: vnode => {
@@ -15,16 +15,14 @@ const component = {
     if (vnode.attrs.filter !== vnode.state.filter) {
       vnode.state.filterList = [];
       vnode.state.filter = vnode.attrs.filter;
-      if (vnode.attrs.filter)
+      if (vnode.attrs.filter != null)
         if (vnode.attrs.filter[0] === "AND")
           for (let i = 1; i < vnode.attrs.filter.length; ++i)
             vnode.state.filterList.push(
-              filterParser.stringify(vnode.attrs.filter[i])
+              expression.stringify(vnode.attrs.filter[i])
             );
         else
-          vnode.state.filterList.push(
-            filterParser.stringify(vnode.attrs.filter)
-          );
+          vnode.state.filterList.push(expression.stringify(vnode.attrs.filter));
       vnode.state.filterList.push("");
     }
 
@@ -33,18 +31,18 @@ const component = {
       vnode.state.filterList = vnode.state.filterList.filter(
         f => f && f.trim()
       );
-      let filterAst = vnode.state.filterList.map((f, idx) => {
+      let filter = vnode.state.filterList.map((f, idx) => {
         try {
-          return filterParser.parse(f);
+          return expression.parse(f);
         } catch (err) {
           vnode.state.filterInvalid |= 1 << idx;
         }
       });
-      if (filterAst.length) filterAst = ["AND"].concat(filterAst);
-      else filterAst = null;
+      if (filter.length) filter = ["AND"].concat(filter);
+      else filter = null;
 
       vnode.state.filterList.push("");
-      if (!vnode.state.filterInvalid) vnode.attrs.onChange(filterAst);
+      if (!vnode.state.filterInvalid) vnode.attrs.onChange(filter);
     }
 
     return m(