feat(.well-known): add .well-known/immich to reference API endpoint

mobile/lib/shared/services/api.service.dart

@@ -1,4 +1,8 @@
+import 'dart:convert';
+
+import 'package:flutter/material.dart';
 import 'package:openapi/api.dart';
+import 'package:http/http.dart';
 
 class ApiService {
   late ApiClient _apiClient;
@@ -22,6 +26,47 @@ class ApiService {
     deviceInfoApi = DeviceInfoApi(_apiClient);
   }
 
+  resolveEndpoint(String serverUrl) async {
+    // Sanitize URL to only include origin+path
+    final url = Uri.parse(serverUrl);
+    final baseUrl = "${url.origin}${url.path}";
+
+    // Remove trailing slash, if exists
+    final endpoint = baseUrl[baseUrl.length - 1] == "/"
+        ? baseUrl.substring(0, baseUrl.length - 1)
+        : baseUrl;
+
+    // Check for .well-known definition, otherwise assume endpoint is full API address
+    final apiEndpoint = await getWellKnownEndpoint(endpoint) ?? endpoint;
+    return apiEndpoint;
+  }
+
+  getWellKnownEndpoint(String baseUrl) async {
+    final Client client = Client();
+
+    try {
+      final res = await client.get(
+        Uri.parse("$baseUrl/.well-known/immich"),
+        headers: {"Accept": "application/json"},
+      );
+
+      if (res.statusCode == 200) {
+        final data = jsonDecode(res.body);
+        final endpoint = data['api']['endpoint'] as String;
+
+        if (endpoint.startsWith('/')) {
+          // Full URL is relative to base
+          return "$baseUrl$endpoint";
+        }
+        return endpoint;
+      }
+    } catch (e) {
+      debugPrint("Could not locate .well-known at $baseUrl: $e");
+    }
+
+    return null;
+  }
+
   setAccessToken(String accessToken) {
     _apiClient.addDefaultHeader('Authorization', 'Bearer $accessToken');
   }