feat: implement dynamic server list loading from API

Add internal/api package to fetch server list from /api/servers.json endpoint

Replace hardcoded server list with dynamic API call

Implement loading states, error handling, and refresh capability

internal/api/server.go

@@ -0,0 +1,72 @@
+// package api handles launcher-specific API calls to the backend.
+package api
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"time"
+
+	"gitea.mrixs.me/Mrixs/MrixsCraft-launcher/internal/ui/screens"
+)
+
+// ServerResponse represents the JSON response from /api/servers.json endpoint.
+type ServerResponse struct {
+	Servers []ServerInfo `json:"servers"`
+}
+
+// ServerInfo represents a single server/modpack entry from the API.
+type ServerInfo struct {
+	Slug   string `json:"slug"`
+	Name   string `json:"name"`
+	Version string `json:"version"`
+	IP     string `json:"ip"`
+}
+
+// FetchServerList retrieves and parses the server list from the backend API.
+// Returns a slice of Modpack objects suitable for UI consumption.
+func FetchServerList(serverURL string) ([]screens.Modpack, error) {
+	// Create HTTP client with timeout
+	client := &http.Client{
+		Timeout: 10 * time.Second,
+	}
+
+	// Create request with context for cancellation
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+
+	req, err := http.NewRequestWithContext(ctx, "GET", fmt.Sprintf("%s/api/servers.json", serverURL), nil)
+	if err != nil {
+		return nil, fmt.Errorf("creating request: %w", err)
+	}
+
+	// Make the HTTP request
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("making request: %w", err)
+	}
+	defer resp.Body.Close()
+
+	// Check HTTP status code
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("unexpected status code: %d", resp.StatusCode)
+	}
+
+	// Decode JSON response
+	var serverResp ServerResponse
+	if err := json.NewDecoder(resp.Body).Decode(&serverResp); err != nil {
+		return nil, fmt.Errorf("decoding JSON: %w", err)
+	}
+
+	// Convert API server info to UI Modpack format
+	var modpacks []screens.Modpack
+	for _, server := range serverResp.Servers {
+		modpacks = append(modpacks, screens.Modpack{
+			Slug: server.Slug,
+			Name: server.Name,
+		})
+	}
+
+	return modpacks, nil
+}

internal/api/server_test.go

@@ -0,0 +1,133 @@
+// package api handles launcher-specific API calls to the backend.
+package api
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"gitea.mrixs.me/Mrixs/MrixsCraft-launcher/internal/ui/screens"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFetchServerList_Success(t *testing.T) {
+	// Arrange - create mock server response
+	serverResp := ServerResponse{
+		Servers: []ServerInfo{
+			{Slug: "hitech", Name: "HiTech 1.21", Version: "1.21", IP: "192.168.1.100"},
+			{Slug: "vanilla", Name: "Vanilla 1.20", Version: "1.20", IP: "192.168.1.101"},
+		},
+	}
+
+	// Create test server with mock response
+	testServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/servers.json" {
+			t.Errorf("unexpected path: %s", r.URL.Path)
+			w.WriteHeader(http.StatusNotFound)
+			return
+		}
+		if r.Method != http.MethodGet {
+			t.Errorf("unexpected method: %s", r.Method)
+			w.WriteHeader(http.StatusMethodNotAllowed)
+			return
+		}
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(serverResp)
+	}))
+	defer testServer.Close()
+
+	// Act - call FetchServerList with test server URL
+	modpacks, err := FetchServerList(testServer.URL)
+	require.NoError(t, err)
+
+	// Assert - check results
+	require.Len(t, modpacks, 2)
+	require.Equal(t, screens.Modpack{Slug: "hitech", Name: "HiTech 1.21"}, modpacks[0])
+	require.Equal(t, screens.Modpack{Slug: "vanilla", Name: "Vanilla 1.20"}, modpacks[1])
+}
+
+func TestFetchServerList_EmptyList(t *testing.T) {
+	// Arrange - create mock server with empty servers list
+	serverResp := ServerResponse{Servers: []ServerInfo{}}
+
+	// Create test server with mock response
+	testServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/servers.json" {
+			t.Errorf("unexpected path: %s", r.URL.Path)
+			w.WriteHeader(http.StatusNotFound)
+			return
+		}
+		if r.Method != http.MethodGet {
+			t.Errorf("unexpected method: %s", r.Method)
+			w.WriteHeader(http.StatusMethodNotAllowed)
+			return
+		}
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(serverResp)
+	}))
+	defer testServer.Close()
+
+	// Act - call FetchServerList with test server URL
+	modpacks, err := FetchServerList(testServer.URL)
+	require.NoError(t, err)
+
+	// Assert - should return empty slice
+	require.Empty(t, modpacks)
+}
+
+func TestFetchServerList_NetworkError(t *testing.T) {
+	// Act - call FetchServerList with invalid URL that will fail to connect
+	modpacks, err := FetchServerList("http://localhost:12345/api/servers.json") // Assuming no server on this port
+
+	// Assert - should return error
+	require.Error(t, err)
+	require.Nil(t, modpacks)
+	require.Contains(t, err.Error(), "making request")
+}
+
+func TestFetchServerList_HTTPError(t *testing.T) {
+	// Arrange - create test server that returns 500 error
+	testServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusInternalServerError)
+	}))
+	defer testServer.Close()
+
+	// Act - call FetchServerList with test server URL
+	modpacks, err := FetchServerList(testServer.URL)
+	require.Error(t, err)
+	require.Nil(t, modpacks)
+	require.Contains(t, err.Error(), "unexpected status code: 500")
+}
+
+func TestFetchServerList_InvalidJSON(t *testing.T) {
+	// Arrange - create test server that returns invalid JSON
+	testServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.Write([]byte(`{"invalid": json}`))
+	}))
+	defer testServer.Close()
+
+	// Act - call FetchServerList with test server URL
+	modpacks, err := FetchServerList(testServer.URL)
+	require.Error(t, err)
+	require.Nil(t, modpacks)
+	require.Contains(t, err.Error(), "decoding JSON")
+}
+
+func TestFetchServerList_Timeout(t *testing.T) {
+	// Arrange - create test server that delays response to trigger timeout
+	testServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Sleep longer than our timeout to trigger timeout error
+		time.Sleep(15 * time.Second)
+	}))
+	defer testServer.Close()
+
+	// Act - call FetchServerList with test server URL
+	modpacks, err := FetchServerList(testServer.URL)
+	require.Error(t, err)
+	require.Nil(t, modpacks)
+	require.Contains(t, err.Error(), "context deadline exceeded")
+	require.Contains(t, err.Error(), "making request")
+}

internal/ui/screens/screens.go

@@ -28,27 +28,54 @@ func MainScreen(
 	serverList []Modpack,
 	onPlay func(),
 	onSettings func(),
+	onServerListRefresh func(),
+	isServerListLoading bool,
+	serverListError error,
 ) fyne.CanvasObject {
 
 	// ── Sidebar (Left) ──────────────────────────────────────
-	serverLabels := make([]*widget.Label, len(serverList))
-	serverContainer := container.NewVBox()
+	var sidebar fyne.CanvasObject
+	if isServerListLoading {
+		// Show loading state
+		loadingLabel := widget.NewLabelWithStyle("Loading server list...", fyne.TextAlignCenter, fyne.TextStyle{})
+		sidebar = container.NewVScroll(container.NewVBox(loadingLabel))
+	} else if len(serverList) == 0 && serverListError == nil {
+		// Show empty state (no error, just empty list)
+		emptyLabel := widget.NewLabelWithStyle("No servers available", fyne.TextAlignCenter, fyne.TextStyle{})
+		sidebar = container.NewVScroll(container.NewVBox(emptyLabel))
+	} else if serverListError != nil {
+		// Show error state
+		errorLabel := widget.NewLabelWithStyle("Failed to load server list", fyne.TextAlignCenter, fyne.TextStyle{})
+		detailLabel := widget.NewLabel(serverListError.Error())
+		detailLabel.Wrapping = fyne.TextWrapWord
+		retryBtn := components.SettingsButton(onServerListRefresh)
+		retryBtn.Text = "Retry"
+		sidebar = container.NewVScroll(container.NewVBox(
+			errorLabel,
+			detailLabel,
+			retryBtn,
+		))
+	} else {
+		// Show normal server list
+		serverLabels := make([]*widget.Label, len(serverList))
+		serverContainer := container.NewVBox()
 
-	for i, sp := range serverList {
-		label := widget.NewLabel(sp.Name)
-		serverLabels[i] = label
-		index := i
-		card := components.ServerCard(sp.Name, index == 0, func() {
-			for j, l := range serverLabels {
-				l.TextStyle.Bold = (j == index)
-				l.Refresh()
-			}
-		})
-		serverContainer.Add(card)
+		for i, sp := range serverList {
+			label := widget.NewLabel(sp.Name)
+			serverLabels[i] = label
+			index := i
+			card := components.ServerCard(sp.Name, index == 0, func() {
+				for j, l := range serverLabels {
+					l.TextStyle.Bold = (j == index)
+					l.Refresh()
+				}
+			})
+			serverContainer.Add(card)
+		}
+
+		sidebar = container.NewVScroll(serverContainer)
 	}
 
-	sidebar := container.NewVScroll(serverContainer)
-
 	// ── Center (background + info) ──────────────────────────
 	bg := widget.NewRichTextFromMarkdown(
 		"# Welcome to MrixsCraft\n\n" +
@@ -93,9 +120,14 @@ func MainScreen(
 	playBtn := components.PlayButton(onPlay)
 	settingsBtn := components.SettingsButton(onSettings)
 
+	// Refresh button for server list
+	refreshBtn := components.SettingsButton(onServerListRefresh)
+
 	bottomRight := container.NewHBox(
 		settingsBtn,
 		widget.NewSeparator(),
+		refreshBtn,
+		widget.NewSeparator(),
 		playBtn,
 	)
 

internal/ui/screens/screens_test.go

@@ -0,0 +1,10 @@
+// package screens implements application screens (login, main menu, settings).
+package screens
+
+import "testing"
+
+// Dummy test to ensure package compiles
+func TestScreensPackage_Compiles(t *testing.T) {
+	// This test ensures the screens package compiles without errors
+	// We're not testing the actual UI output as that requires a GUI environment
+}

internal/ui/ui.go

@@ -5,6 +5,7 @@ import (
 	"fyne.io/fyne/v2"
 	"fyne.io/fyne/v2/app"
 
+	"gitea.mrixs.me/Mrixs/MrixsCraft-launcher/internal/api"
 	"gitea.mrixs.me/Mrixs/MrixsCraft-launcher/internal/auth"
 	"gitea.mrixs.me/Mrixs/MrixsCraft-launcher/internal/config"
 	"gitea.mrixs.me/Mrixs/MrixsCraft-launcher/internal/ui/screens"
@@ -20,12 +21,13 @@ func Launch(client *auth.Client, session *auth.Session, settings config.Settings
 	w.Resize(fyne.NewSize(float32(settings.Width), float32(settings.Height)))
 	w.CenterOnScreen()
 
-	// TODO: fetch from /api/servers.json
-	serverList := []screens.Modpack{
-		{Slug: "hitech", Name: "HiTech 1.21"},
-		{Slug: "vanilla", Name: "Vanilla 1.20"},
-	}
+					// State for server list loading
+	var serverList []screens.Modpack
+	var isServerListLoading bool
+	var serverListError error
+	_ = serverListError // Use variable to prevent "declared and not used" error
 
+	// Callback functions
 	onPlay := func() {
 		// TODO: launch selected modpack
 	}
@@ -38,15 +40,38 @@ func Launch(client *auth.Client, session *auth.Session, settings config.Settings
 		})
 	}
 
-	content := screens.MainScreen(w, client, session, serverList, onPlay, onSettings)
+	// Function to refresh server list
+	var refreshServerList func()
+	refreshServerList = func() {
+		isServerListLoading = true
+		serverListError = nil
+		// Update UI to show loading state
+		content := screens.MainScreen(w, client, session, serverList, onPlay, onSettings, refreshServerList, isServerListLoading, serverListError)
+		w.SetContent(content)
+
+		// Fetch server list in goroutine to avoid blocking UI
+		go func() {
+			serverList, serverListError = api.FetchServerList(settings.ServerURL)
+			isServerListLoading = false
+			// Update UI with result
+			content := screens.MainScreen(w, client, session, serverList, onPlay, onSettings, refreshServerList, isServerListLoading, serverListError)
+			w.SetContent(content)
+		}()
+	}
+
+	// Initial load of server list
+	content := screens.MainScreen(w, client, session, serverList, onPlay, onSettings, refreshServerList, isServerListLoading, serverListError)
 	w.SetContent(content)
 
+	// Start fetching server list in background
+	go refreshServerList()
+
 	// If no session, show login modal after the window is rendered.
 	if session == nil {
 		w.Show()
 		screens.LoginScreen(w, client, func(sess *auth.Session) {
 			// Refresh UI with logged-in state.
-			content := screens.MainScreen(w, client, sess, serverList, onPlay, onSettings)
+			content := screens.MainScreen(w, client, sess, serverList, onPlay, onSettings, refreshServerList, isServerListLoading, serverListError)
 			w.SetContent(content)
 		})
 	}

internal/ui/ui_test.go

@@ -0,0 +1,9 @@
+// package ui contains the Fyne GUI bootstrap and wiring.
+package ui
+
+import "testing"
+
+// Dummy test to ensure package compiles
+func TestUIPackage_Compiles(t *testing.T) {
+	// This test ensures the ui package compiles without errors
+}