planning

node_modules/@mapbox/mapbox-gl-style-spec/group_by_layout.js

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+// @flow
+
+import type {LayerSpecification} from './types.js';
+
+import refProperties from './util/ref_properties.js';
+
+function stringify(obj) {
+    if (typeof obj === 'number' || typeof obj === 'boolean' || typeof obj === 'string' || obj === undefined || obj === null)
+        return JSON.stringify(obj);
+
+    if (Array.isArray(obj)) {
+        let str = '[';
+        for (const val of obj) {
+            str += `${stringify(val)},`;
+        }
+        return `${str}]`;
+    }
+
+    let str = '{';
+    for (const key of Object.keys(obj).sort()) {
+        str += `${key}:${stringify((obj: any)[key])},`;
+    }
+    return `${str}}`;
+}
+
+function getKey(layer) {
+    let key = '';
+    for (const k of refProperties) {
+        key += `/${stringify((layer: any)[k])}`;
+    }
+    return key;
+}
+
+/**
+ * Given an array of layers, return an array of arrays of layers where all
+ * layers in each group have identical layout-affecting properties. These
+ * are the properties that were formerly used by explicit `ref` mechanism
+ * for layers: 'type', 'source', 'source-layer', 'minzoom', 'maxzoom',
+ * 'filter', and 'layout'.
+ *
+ * The input is not modified. The output layers are references to the
+ * input layers.
+ *
+ * @private
+ * @param {Array<Layer>} layers
+ * @param {Object} [cachedKeys] - an object to keep already calculated keys.
+ * @returns {Array<Array<Layer>>}
+ */
+export default function groupByLayout(layers: Array<LayerSpecification>, cachedKeys: {[id: string]: string}): Array<Array<LayerSpecification>> {
+    const groups = {};
+
+    for (let i = 0; i < layers.length; i++) {
+
+        const k = (cachedKeys && cachedKeys[layers[i].id]) || getKey(layers[i]);
+        // update the cache if there is one
+        if (cachedKeys)
+            cachedKeys[layers[i].id] = k;
+
+        let group = groups[k];
+        if (!group) {
+            group = groups[k] = [];
+        }
+        group.push(layers[i]);
+    }
+
+    const result = [];
+
+    for (const k in groups) {
+        result.push(groups[k]);
+    }
+
+    return result;
+}