Address initial PR commits

src/lib/browse/InterventionColorSelector.svelte

@@ -1,5 +1,5 @@
 <script lang="ts">
-  import { get   return x as DataDrivenPropertyValueSpecification } from "../../maplibre_helpers";
+  import { constructMatchExpression } from "../../maplibre_helpers";
   import { colorInterventionsBySchema, schemaLegend } from "../../schemas";
   import { map } from "../../stores";
   import { Legend } from "../common";
@@ -15,7 +15,7 @@
       color = colorInterventionsBySchema("v1");
       legendRows = schemaLegend("v1");
     } else {
-      color = get   return x as DataDrivenPropertyValueSpecification(
+      color = constructMatchExpression(
         ["get", "funding_programme"],
         { ATF2: colors.atf2, ATF3: colors.atf3, ATF4: colors.atf4 },
         "grey"

src/lib/draw/route/route_tool.ts

@@ -6,7 +6,7 @@ import {
   isLine,
   isPoint,
   isPolygon,
-  getDataDrivenPropertyValueSpecification,
+  constructMatchExpression,
   overwriteCircleLayer,
   overwriteLineLayer,
   overwritePolygonLayer,
@@ -53,15 +53,15 @@ export class RouteTool {
       id: "route-points",
       source,
       filter: isPoint,
-      color: getDataDrivenPropertyValueSpecification(
+      color: constructMatchExpression(
         ["get", "type"],
         {
           hovered: "green",
           important: "red",
         },
         "black"
       ),
-      radius: getDataDrivenPropertyValueSpecification(
+      radius: constructMatchExpression(
         ["get", "type"],
         { unimportant: circleRadiusPixels / 2.0 },
         circleRadiusPixels

src/lib/layers/lane_details/IntersectionMarkings.svelte

@@ -1,14 +1,14 @@
 <script lang="ts">
   import type { GeoJSON } from "geojson";
-  import { get   return x as DataDrivenPropertyValueSpecification } from "../../../maplibre_helpers";
+  import { constructMatchExpression } from "../../../maplibre_helpers";
   import Layer from "./Layer.svelte";
 
   export let gj: GeoJSON;
 
   let style = {
     type: "fill",
     paint: {
-      "fill-color": get   return x as DataDrivenPropertyValueSpecification(
+      "fill-color": constructMatchExpression(
         ["get", "type"],
         {
           "sidewalk corner": "#CCCCCC",

src/lib/layers/lane_details/IntersectionPolygons.svelte

@@ -1,6 +1,6 @@
 <script lang="ts">
   import type { GeoJSON } from "geojson";
-  import { get   return x as DataDrivenPropertyValueSpecification } from "../../../maplibre_helpers";
+  import { constructMatchExpression } from "../../../maplibre_helpers";
   import Layer from "./Layer.svelte";
 
   export let gj: GeoJSON;
@@ -9,7 +9,7 @@
     type: "fill",
     filter: ["==", ["get", "type"], "intersection"],
     paint: {
-      "fill-color": get   return x as DataDrivenPropertyValueSpecification(
+      "fill-color": constructMatchExpression(
         ["get", "intersection_kind"],
         {
           MapEdge: "#696",

src/lib/layers/lane_details/LaneMarkings.svelte

@@ -1,14 +1,14 @@
 <script lang="ts">
   import type { GeoJSON } from "geojson";
-  import { get   return x as DataDrivenPropertyValueSpecification } from "../../../maplibre_helpers";
+  import { constructMatchExpression } from "../../../maplibre_helpers";
   import Layer from "./Layer.svelte";
 
   export let gj: GeoJSON;
 
   let style = {
     type: "fill",
     paint: {
-      "fill-color": get   return x as DataDrivenPropertyValueSpecification(
+      "fill-color": constructMatchExpression(
         ["get", "type"],
         {
           "center line": "white",

src/lib/layers/lane_details/LanePolygons.svelte

@@ -1,14 +1,14 @@
 <script lang="ts">
   import type { GeoJSON } from "geojson";
-  import { get   return x as DataDrivenPropertyValueSpecification } from "../../../maplibre_helpers";
+  import { constructMatchExpression } from "../../../maplibre_helpers";
   import Layer from "./Layer.svelte";
 
   export let gj: GeoJSON;
 
   let style = {
     type: "fill",
     paint: {
-      "fill-color": get   return x as DataDrivenPropertyValueSpecification(
+      "fill-color": constructMatchExpression(
         ["get", "type"],
         // TODO Generate TS types from osm2streets
         {

src/maplibre_helpers.ts

@@ -229,19 +229,11 @@ export function setPrecision(pt: Position): Position {
 //  Helper for https://maplibre.org/maplibre-style-spec/expressions/#match.
 //  Gets one feature property, uses a map to match a key to a value, and
 //  includes a fallback if no keys match.
-export function getDataDrivenPropertyValueSpecification<OutputType>(
+export function constructMatchExpression<OutputType>(
   getter: any[],
   map: { [name: string]: OutputType },
   fallback: OutputType
 ): DataDrivenPropertyValueSpecification<OutputType> {
-  // This looks weird because it is weird. I hate to add a comment but here we are.
-  // MapLibre's DataDrivenPropertyValueSpecification allows you to have a value which depends on properties
-  // of an object you are drawing, so you could see for a route which funding round it belonged to, for an
-  // ATIP example. Their specification is an array containing ordered elements of any kind. The first is how
-  // you want to match, then, an array defining the route to property you want to look at in your object.
-  // Key, value pairs are added directly to the array, where key is what you want the property in the object being tested
-  // to equal or not, and value is what you want to return. So in our case it might be ATF3 (a funding round)
-  // and red (a color to use for drawing the object). Finally there is a fallback value (e.g. grey) if nothing matches. Nonsense. 
   let x: any[] = ["match", getter];
   for (let [key, value] of Object.entries(map)) {
     x.push(key);

src/schemas.ts

@@ -1,6 +1,6 @@
 import type { DataDrivenPropertyValueSpecification } from "maplibre-gl";
 import { colors } from "./colors";
-import { getDataDrivenPropertyValueSpecification } from "./maplibre_helpers";
+import { constructMatchExpression } from "./maplibre_helpers";
 import type { Schema } from "./types";
 
 export function schemaTitle(schema: Schema): string {
@@ -39,7 +39,7 @@ export function colorInterventionsBySchema(
   schema: Schema
 ): DataDrivenPropertyValueSpecification<string> {
   if (schema == "planning") {
-    return getDataDrivenPropertyValueSpecification(
+    return constructMatchExpression(
       ["get", "reference_type", ["get", "planning"]],
       {
         preapp: colors.preapp,
@@ -53,7 +53,7 @@ export function colorInterventionsBySchema(
   }
 
   // All other schemas go by intervention type
-  return getDataDrivenPropertyValueSpecification(
+  return constructMatchExpression(
     ["get", "intervention_type"],
     {
       area: colors.area,