Add the utilOldestID() function

modules/util/index.js

@@ -35,6 +35,7 @@ export { utilHighlightEntities } from './util';
 export { utilKeybinding } from './keybinding';
 export { utilNoAuto } from './util';
 export { utilObjectOmit } from './object';
+export { utilOldestID } from './util';
 export { utilPrefixCSSProperty } from './util';
 export { utilPrefixDOMProperty } from './util';
 export { utilQsString } from './util';

modules/util/util.js

@@ -581,3 +581,53 @@ export function utilUnicodeCharsCount(str) {
 export function utilUnicodeCharsTruncated(str, limit) {
     return Array.from(str).slice(0, limit).join('');
 }
+
+
+// Returns the chronologically oldest ID in the list.
+// Database IDs (with positive numbers) before editor ones (with negative numbers).
+// Among each category, the closest number to 0 is the oldest.
+// Test IDs (any string that does not conform to OSM's ID scheme) are taken last.
+export function utilOldestID(ids) {
+    if (ids.length === 0) {
+        return undefined;
+    }
+
+    var idPattern = /^[cnwr](-?)(\d+)$/;
+    var decomposeID = (id) => {
+        var res = {
+            id: id,
+            num: NaN
+        };
+
+        var match = id.match(idPattern);
+        if (match) {
+            res.num = parseInt(match[2], 10);
+            res.isNew = !!match[1];
+        }
+
+        return res;
+    };
+
+    var compareDecomposed = (left, right) => {
+        if (isNaN(left.num) && isNaN(right.num)) return -1;
+        if (isNaN(left.num)) return 1;
+        if (isNaN(right.num)) return -1;
+        if (left.isNew && !right.isNew) return 1;
+        if (!left.isNew && right.isNew) return -1;
+        return Math.sign(left.num - right.num);
+    };
+
+    var oldestIDIndex = 0;
+    var oldestID = decomposeID(ids[0]);
+
+    for (var i = 1; i < ids.length; i++) {
+        var decomposed = decomposeID(ids[i]);
+
+        if (compareDecomposed(oldestID, decomposed) === 1) {
+            oldestIDIndex = i;
+            oldestID = decomposed;
+        }
+    }
+
+    return ids[oldestIDIndex];
+}

test/spec/spec_helpers.js

@@ -131,6 +131,14 @@ if (typeof ArrayBuffer.isView === 'undefined') {
     ArrayBuffer.isView = function() { return false; };
 }
 
+// Polyfill for `Math.sign()` in PhantomJS
+// From https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/sign#Polyfill
+if (!Math.sign) {
+    Math.sign = function(x) {
+        return ((x > 0) - (x < 0)) || +x;
+    };
+}
+
 // Add support for sinon-stubbing `fetch` API
 // (sinon fakeServer works only on `XMLHttpRequest`)
 // see https://github.com/sinonjs/nise/issues/7

test/spec/util/util.js

@@ -252,4 +252,25 @@ describe('iD.util', function() {
             expect(iD.utilDisplayName({tags: {network: 'BART', ref: 'Yellow', from: 'Antioch', to: 'Millbrae', via: 'Pittsburg/Bay Point;San Francisco International Airport', route: 'subway'}})).to.eql('BART Yellow from Antioch to Millbrae via Pittsburg/Bay Point;San Francisco International Airport');
         });
     });
+
+    describe('utilOldestID', function() {
+        it('returns the oldest database ID', function() {
+            expect(iD.utilOldestID(['w3', 'w1', 'w2'])).to.eql('w1');
+        });
+        it('returns the oldest editor ID', function() {
+            expect(iD.utilOldestID(['w-3', 'w-2', 'w-1'])).to.eql('w-1');
+        });
+        it('returns the oldest IDs among database and editor IDs', function() {
+            expect(iD.utilOldestID(['w-1', 'w1', 'w-2'])).to.eql('w1');
+        });
+        it('returns the oldest database ID', function() {
+            expect(iD.utilOldestID(['w100', 'w-1', 'a', 'w-300', 'w2'])).to.eql('w2');
+        });
+        it('returns the oldest editor ID if no database IDs', function() {
+            expect(iD.utilOldestID(['w-100', 'w-1', 'a', 'w-300', 'w-2'])).to.eql('w-1');
+        });
+        it('returns the first ID in the list otherwise', function() {
+            expect(iD.utilOldestID(['z', 'a', 'A', 'Z'])).to.eql('z');
+        });
+    });
 });