[Junie]: feat: add location input form with autocomplete suggestions (#6)

* feat: add location input form with autocomplete suggestions
 A form for user location input with autocomplete suggestions was added, linking to a new Java backend city search endpoint. The endpoint returns the top 10 city suggestions, and a submit button is included but currently does nothing.

* add cities.json, remove reference to other repo

---------

Co-authored-by: jetbrains-junie[bot] <201638009+jetbrains-junie[bot]@users.noreply.github.com>
Co-authored-by: Ivan Šarić <invoices@path-variable.com>

Author: jetbrains-junie[bot]

src/main/java/com/example/weatherapp/city/City.java

@@ -0,0 +1,52 @@
+package com.example.weatherapp.city;
+
+import com.fasterxml.jackson.annotation.JsonAlias;
+import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+@JsonIgnoreProperties(ignoreUnknown = true)
+public class City {
+
+    private String name;
+    // two-letter country code expected
+    private String country;
+
+    private Double lat;
+
+    @JsonAlias({"lng", "lon"})
+    @JsonProperty("lon")
+    private Double lon;
+
+    // Optional field in some datasets (ignored for formatting)
+    private String state;
+
+    public City() {}
+
+    public String getName() { return name; }
+    public void setName(String name) { this.name = name; }
+
+    public String getCountry() { return country; }
+    public void setCountry(String country) { this.country = country; }
+
+    public Double getLat() { return lat; }
+    public void setLat(Double lat) { this.lat = lat; }
+
+    public Double getLon() { return lon; }
+    public void setLon(Double lon) { this.lon = lon; }
+
+    public String getState() { return state; }
+    public void setState(String state) { this.state = state; }
+
+    public String toSuggestionString() {
+        String n = name != null ? name : "";
+        String c = country != null ? country : "";
+        String la = lat != null ? String.valueOf(trimDouble(lat)) : "";
+        String lo = lon != null ? String.valueOf(trimDouble(lon)) : "";
+        return String.format("%s %s (%s,%s)", n, c, la, lo).trim();
+    }
+
+    private static double trimDouble(Double d) {
+        // limit to 6 decimal places in string form
+        return Math.round(d * 1_000_000d) / 1_000_000d;
+    }
+}

src/main/java/com/example/weatherapp/city/CitySearchService.java

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+package com.example.weatherapp.city;
+
+import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.springframework.core.io.ClassPathResource;
+import org.springframework.stereotype.Service;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Collections;
+import java.util.List;
+import java.util.Locale;
+import java.util.Objects;
+import java.util.stream.Collectors;
+
+@Service
+public class CitySearchService {
+
+    private static final String CLASSPATH_JSON = "cities.json";
+
+    private final Object lock = new Object();
+    private volatile List<City> cached;
+
+    private final ObjectMapper mapper = new ObjectMapper();
+
+    public List<String> searchSuggestions(String query, int limit) {
+        if (query == null) return Collections.emptyList();
+        String q = query.trim().toLowerCase(Locale.ROOT);
+        if (q.isEmpty()) return Collections.emptyList();
+
+        List<City> all = loadAllCities();
+        if (all.isEmpty()) return Collections.emptyList();
+
+        // Simple case-insensitive substring match against name and optionally state
+        List<City> matched = all.stream()
+                .filter(c -> {
+                    String name = safeLower(c.getName());
+                    String state = safeLower(c.getState());
+                    return (name != null && name.contains(q)) || (state != null && state.contains(q));
+                })
+                .limit(Math.max(limit, 10) * 10L) // scan a bit more then trim to allow for simple ordering
+                .collect(Collectors.toList());
+
+        // Basic ordering: starts-with first, then by name length, then lexicographically
+        matched.sort((a, b) -> {
+            String an = safeLower(a.getName());
+            String bn = safeLower(b.getName());
+            int as = startsWithScore(an, q) - startsWithScore(bn, q);
+            if (as != 0) return -as; // higher score first
+            int al = an != null ? an.length() : Integer.MAX_VALUE;
+            int bl = bn != null ? bn.length() : Integer.MAX_VALUE;
+            int cmp = Integer.compare(al, bl);
+            if (cmp != 0) return cmp;
+            return Objects.compare(an, bn, String::compareTo);
+        });
+
+        return matched.stream()
+                .map(City::toSuggestionString)
+                .distinct()
+                .limit(limit)
+                .collect(Collectors.toList());
+    }
+
+    private static int startsWithScore(String s, String q) {
+        if (s == null) return 0;
+        return s.startsWith(q) ? 1 : 0;
+    }
+
+    private static String safeLower(String s) {
+        return s == null ? null : s.toLowerCase(Locale.ROOT);
+    }
+
+    private List<City> loadAllCities() {
+        List<City> local = cached;
+        if (local != null) return local;
+        synchronized (lock) {
+            if (cached != null) return cached;
+            List<City> loaded = tryLoadFromClasspath();
+            cached = loaded;
+            return cached;
+        }
+    }
+
+    private List<City> tryLoadFromClasspath() {
+        try {
+            ClassPathResource resource = new ClassPathResource(CLASSPATH_JSON);
+            if (!resource.exists()) return Collections.emptyList();
+            try (InputStream is = resource.getInputStream()) {
+                return mapper.readValue(is, new TypeReference<List<City>>() {});
+            }
+        } catch (IOException e) {
+            return Collections.emptyList();
+        }
+    }
+}

src/main/java/com/example/weatherapp/web/CitySearchController.java

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+package com.example.weatherapp.web;
+
+import com.example.weatherapp.city.CitySearchService;
+import org.springframework.http.MediaType;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestParam;
+import org.springframework.web.bind.annotation.RestController;
+
+import java.util.List;
+
+@RestController
+public class CitySearchController {
+
+    private final CitySearchService service;
+
+    public CitySearchController(CitySearchService service) {
+        this.service = service;
+    }
+
+    @GetMapping(value = "/api/cities/search", produces = MediaType.APPLICATION_JSON_VALUE)
+    public List<String> search(@RequestParam(name = "q", required = false) String query,
+                               @RequestParam(name = "limit", required = false, defaultValue = "10") int limit) {
+        int safeLimit = Math.max(1, Math.min(limit, 50));
+        return service.searchSuggestions(query, safeLimit);
+    }
+}