feat: Initial implementation of GymFlow fitness tracking application with workout, plan, and exercise management, stats, and AI coach features.

App.tsx

@@ -0,0 +1,177 @@
+
+import React, { useState, useEffect } from 'react';
+import Navbar from './components/Navbar';
+import Tracker from './components/Tracker';
+import History from './components/History';
+import Stats from './components/Stats';
+import AICoach from './components/AICoach';
+import Plans from './components/Plans';
+import Login from './components/Login';
+import Profile from './components/Profile';
+import { TabView, WorkoutSession, WorkoutSet, WorkoutPlan, User, Language } from './types';
+import { getSessions, saveSession, deleteSession } from './services/storage';
+import { getCurrentUserProfile } from './services/auth';
+import { getSystemLanguage } from './services/i18n';
+
+function App() {
+  const [currentUser, setCurrentUser] = useState<User | null>(null);
+  const [currentTab, setCurrentTab] = useState<TabView>('TRACK');
+  const [language, setLanguage] = useState<Language>('en');
+  
+  const [sessions, setSessions] = useState<WorkoutSession[]>([]);
+  const [activeSession, setActiveSession] = useState<WorkoutSession | null>(null);
+  const [activePlan, setActivePlan] = useState<WorkoutPlan | null>(null);
+
+  useEffect(() => {
+    // Set initial language
+    setLanguage(getSystemLanguage());
+  }, []);
+
+  useEffect(() => {
+    if (currentUser) {
+        setSessions(getSessions(currentUser.id));
+        const profile = getCurrentUserProfile(currentUser.id);
+        if (profile?.language) {
+            setLanguage(profile.language);
+        }
+    } else {
+        setSessions([]);
+    }
+  }, [currentUser]);
+
+  const handleLogin = (user: User) => {
+      setCurrentUser(user);
+      setCurrentTab('TRACK');
+  };
+
+  const handleLogout = () => {
+      setCurrentUser(null);
+      setActiveSession(null);
+      setActivePlan(null);
+  };
+
+  const handleLanguageChange = (lang: Language) => {
+      setLanguage(lang);
+  };
+
+  const handleStartSession = (plan?: WorkoutPlan) => {
+    if (!currentUser) return;
+
+    // Get latest weight from profile or default
+    const profile = getCurrentUserProfile(currentUser.id);
+    const currentWeight = profile?.weight || 70;
+
+    const newSession: WorkoutSession = {
+      id: crypto.randomUUID(),
+      startTime: Date.now(),
+      userBodyWeight: currentWeight,
+      sets: [],
+      planId: plan?.id,
+      planName: plan?.name
+    };
+    setActivePlan(plan || null);
+    setActiveSession(newSession);
+    setCurrentTab('TRACK'); 
+  };
+
+  const handleEndSession = () => {
+    if (activeSession && currentUser) {
+      const finishedSession = { ...activeSession, endTime: Date.now() };
+      saveSession(currentUser.id, finishedSession);
+      setSessions(prev => [finishedSession, ...prev]); 
+      setActiveSession(null);
+      setActivePlan(null);
+    }
+  };
+
+  const handleAddSet = (set: WorkoutSet) => {
+    if (activeSession) {
+      setActiveSession(prev => {
+        if (!prev) return null;
+        return {
+          ...prev,
+          sets: [...prev.sets, set]
+        };
+      });
+    }
+  };
+
+  const handleRemoveSetFromActive = (setId: string) => {
+    if (activeSession) {
+      setActiveSession(prev => {
+        if (!prev) return null;
+        return {
+          ...prev,
+          sets: prev.sets.filter(s => s.id !== setId)
+        };
+      });
+    }
+  };
+
+  const handleUpdateSession = (updatedSession: WorkoutSession) => {
+      if (!currentUser) return;
+      saveSession(currentUser.id, updatedSession);
+      setSessions(prev => prev.map(s => s.id === updatedSession.id ? updatedSession : s));
+  };
+
+  const handleDeleteSession = (sessionId: string) => {
+      if (!currentUser) return;
+      deleteSession(currentUser.id, sessionId);
+      setSessions(prev => prev.filter(s => s.id !== sessionId));
+  };
+
+  if (!currentUser) {
+      return <Login onLogin={handleLogin} language={language} onLanguageChange={handleLanguageChange} />;
+  }
+
+  return (
+    <div className="h-screen w-screen bg-surface text-on-surface font-sans flex flex-col md:flex-row overflow-hidden">
+      
+      {/* Desktop Navigation Rail (Left) */}
+      <Navbar currentTab={currentTab} onTabChange={setCurrentTab} lang={language} />
+
+      {/* Main Content Area */}
+      <main className="flex-1 h-full relative w-full max-w-5xl mx-auto md:px-4">
+        <div className="h-full w-full pb-20 md:pb-0 bg-surface">
+            {currentTab === 'TRACK' && (
+            <Tracker 
+                userId={currentUser.id}
+                activeSession={activeSession}
+                activePlan={activePlan}
+                onSessionStart={handleStartSession}
+                onSessionEnd={handleEndSession}
+                onSetAdded={handleAddSet}
+                onRemoveSet={handleRemoveSetFromActive}
+                lang={language}
+            />
+            )}
+            {currentTab === 'PLANS' && (
+            <Plans userId={currentUser.id} onStartPlan={handleStartSession} lang={language} />
+            )}
+            {currentTab === 'HISTORY' && (
+                <History 
+                    sessions={sessions} 
+                    onUpdateSession={handleUpdateSession}
+                    onDeleteSession={handleDeleteSession}
+                    lang={language}
+                />
+            )}
+            {currentTab === 'STATS' && <Stats sessions={sessions} lang={language} />}
+            {currentTab === 'AI_COACH' && <AICoach history={sessions} lang={language} />}
+            {currentTab === 'PROFILE' && (
+                <Profile 
+                    user={currentUser} 
+                    onLogout={handleLogout} 
+                    lang={language} 
+                    onLanguageChange={handleLanguageChange} 
+                />
+            )}
+        </div>
+      </main>
+
+      {/* Mobile Navigation (rendered inside Navbar component, fixed to bottom) */}
+    </div>
+  );
+}
+
+export default App;