1 files changed, 82 insertions, 4 deletions
diff --git a/assets/js/map/choropleth.js b/assets/js/map/choropleth.js
index e7d5d3d..9316f29 100644
--- a/assets/js/map/choropleth.js
+++ b/assets/js/map/choropleth.js
@@ -1,4 +1,82 @@
-// Phase 2: choropleth map rendering, gradient coloring
-export function initMap(container, countries, isoLookup) {}
-export function applyGradient(metricKey) {}
-export function setClickHandler(fn) {}
+import * as d3 from "https://cdn.jsdelivr.net/npm/d3@7/+esm";
+import * as topojson from "https://cdn.jsdelivr.net/npm/topojson-client@3/+esm";
+
+const WIDTH = 960;
+const HEIGHT = 500;
+const DEFAULT_FILL = "rgba(36, 171, 72, 0.8)";
+const NO_DATA_FILL = "#444";
+
+// Module-level state shared across exported functions
+let svg, mapGroup, projection, pathGen, features;
+let _countries, _isoLookup;
+let _clickHandler = null;
+
+export async function initMap(container, countries, isoLookup) {
+	_countries = countries;
+	_isoLookup = isoLookup;
+
+	svg = d3.select(container)
+		.append("svg")
+		.attr("viewBox", `0 0 ${WIDTH} ${HEIGHT}`)
+		.attr("preserveAspectRatio", "xMidYMid meet")
+		.style("width", "100%")
+		.style("height", "100%");
+
+	mapGroup = svg.append("g").attr("id", "map-layer");
+
+	const world = await d3.json("./assets/data/world-110m.json");
+	const geojson = topojson.feature(world, world.objects.countries);
+	features = geojson.features;
+
+	projection = d3.geoNaturalEarth1().fitSize([WIDTH, HEIGHT], geojson);
+	pathGen = d3.geoPath().projection(projection);
+
+	mapGroup.selectAll("path")
+		.data(features)
+		.join("path")
+		.attr("class", "country")
+		.attr("d", pathGen)
+		.attr("fill", d => _fillForFeature(d, null, null))
+		.attr("stroke", "#111")
+		.attr("stroke-width", 0.5)
+		.on("click", (event, d) => {
+			if (_clickHandler) _clickHandler(event, d);
+		});
+
+	return { svg, mapGroup, projection };
+}
+
+export function applyGradient(metricKey) {
+	const values = Object.values(_countries)
+		.map(c => c[metricKey])
+		.filter(v => typeof v === "number" && !isNaN(v));
+
+	const [min, max] = d3.extent(values);
+	const colorScale = d3.scaleSequential()
+		.domain([min, max])
+		.interpolator(d3.interpolateYlOrRd);
+
+	mapGroup.selectAll("path.country")
+		.transition()
+		.duration(400)
+		.attr("fill", d => _fillForFeature(d, metricKey, colorScale));
+}
+
+export function resetGradient() {
+	mapGroup.selectAll("path.country")
+		.transition()
+		.duration(400)
+		.attr("fill", d => _fillForFeature(d, null, null));
+}
+
+export function setClickHandler(fn) {
+	_clickHandler = fn;
+}
+
+function _fillForFeature(d, metricKey, colorScale) {
+	const alpha3 = _isoLookup[+d.id];
+	if (!alpha3 || !_countries[alpha3]) return NO_DATA_FILL;
+	if (!metricKey) return DEFAULT_FILL;
+	const val = _countries[alpha3][metricKey];
+	return typeof val === "number" && !isNaN(val) ? colorScale(val) : NO_DATA_FILL;
+}