diff --git a/src/App.tsx b/src/App.tsx
index 0297334..e1c9279 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -6,12 +6,20 @@ import { Sidebar } from './components/Sidebar';
 import { useHabits } from './hooks/useHabits';
 import { useWeek } from './hooks/useWeek';
 import { ThemeProvider, useThemeContext } from './contexts/ThemeContext';
+import { AuthProvider, useAuth } from './contexts/AuthContext';
+import { Login } from './components/Login';
+import { SignUp } from './components/SignUp';
+import { SettingsView } from './components/SettingsView';
+
+const DAYS_OF_WEEK = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'];
 
 function HabitTrackerContent() {
   const { theme, isDark, toggleDarkMode, defaultView, habitSort } = useThemeContext();
   const [newHabit, setNewHabit] = useState('');
   const [activeView, setActiveView] = useState<'habits' | 'calendar' | 'settings'>(defaultView);
   const [currentMonth, setCurrentMonth] = useState(new Date());
+  const { user, loading, signOut } = useAuth();
+  const [authView, setAuthView] = useState<'login' | 'signup'>('login');
 
   const { 
     habits, 
@@ -19,8 +27,7 @@ function HabitTrackerContent() {
     addHabit: addHabitApi, 
     toggleHabit, 
     updateHabit, 
-    deleteHabit, 
-    updateStreak 
+    deleteHabit 
   } = useHabits();
   
   const { 
@@ -30,8 +37,6 @@ function HabitTrackerContent() {
     changeWeek 
   } = useWeek();
 
-  const daysOfWeek = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'];
-
   useEffect(() => {
     fetchHabits();
     setCurrentWeek(getCurrentWeekDates());
@@ -122,11 +127,10 @@ function HabitTrackerContent() {
         <HabitList
           habits={getSortedHabits()}
           currentWeek={currentWeek}
-          daysOfWeek={daysOfWeek}
+          daysOfWeek={DAYS_OF_WEEK}
           onToggleHabit={toggleHabit}
           onUpdateHabit={updateHabit}
           onDeleteHabit={deleteHabit}
-          onUpdateStreak={updateStreak}
         />
         <p className="text-sm text-gray-500 dark:text-gray-300 mt-4">Keep up the good work! Consistency is key.</p>
       </div>
@@ -147,163 +151,17 @@ function HabitTrackerContent() {
     />
   );
 
-  const renderSettingsView = () => {
-    const { 
-      theme, 
-      isDark, 
-      showStreaks, 
-      dailyReminder, 
-      defaultView,
-      habitSort,
-      toggleDarkMode, 
-      toggleStreaks, 
-      toggleDailyReminder,
-      setDefaultView,
-      setHabitSort
-    } = useThemeContext();
-    
-    const handleReminderToggle = () => {
-      if (!dailyReminder && Notification.permission === 'default') {
-        Notification.requestPermission().then(permission => {
-          if (permission === 'granted') {
-            toggleDailyReminder();
-          }
-        });
-      } else {
-        toggleDailyReminder();
-      }
-    };
+  if (loading) {
+    return <div>Loading...</div>;
+  }
 
-    return (
-      <div className={`rounded-lg shadow p-6 ${theme.cardBackground}`}>
-        <h2 className="text-2xl font-bold mb-6 dark:text-white">Settings</h2>
-        <div className="space-y-6">
-          <div className="flex items-center justify-between">
-            <span className="dark:text-white">Dark Mode</span>
-            <button
-              onClick={toggleDarkMode}
-              className="p-2 rounded-full hover:bg-gray-100 dark:hover:bg-gray-800"
-            >
-              {isDark ? (
-                <Sun className="h-5 w-5 dark:text-white" />
-              ) : (
-                <Moon className="h-5 w-5" />
-              )}
-            </button>
-          </div>
-          
-          <div className="flex items-center justify-between">
-            <span className="dark:text-white">Show Streaks</span>
-            <button
-              onClick={toggleStreaks}
-              className={`
-                relative inline-flex h-6 w-11 items-center rounded-full
-                transition-colors duration-200 ease-in-out
-                ${showStreaks ? 'bg-[#2ecc71]' : 'bg-gray-200 dark:bg-gray-700'}
-              `}
-            >
-              <span
-                className={`
-                  inline-block h-4 w-4 transform rounded-full bg-white
-                  transition-transform duration-200 ease-in-out
-                  ${showStreaks ? 'translate-x-6' : 'translate-x-1'}
-                `}
-              />
-            </button>
-          </div>
-
-          <div className="flex items-center justify-between">
-            <div>
-              <span className="dark:text-white">Daily Reminder</span>
-              <p className="text-sm text-gray-500 dark:text-gray-400">Get notified at 10:00 AM daily</p>
-            </div>
-            <button
-              onClick={handleReminderToggle}
-              className={`
-                relative inline-flex h-6 w-11 items-center rounded-full
-                transition-colors duration-200 ease-in-out
-                ${dailyReminder ? 'bg-[#2ecc71]' : 'bg-gray-200 dark:bg-gray-700'}
-              `}
-            >
-              <span
-                className={`
-                  inline-block h-4 w-4 transform rounded-full bg-white
-                  transition-transform duration-200 ease-in-out
-                  ${dailyReminder ? 'translate-x-6' : 'translate-x-1'}
-                `}
-              />
-            </button>
-          </div>
-
-          <div className="flex items-center justify-between">
-            <div>
-              <span className="dark:text-white">Default View</span>
-              <p className="text-sm text-gray-500 dark:text-gray-400">Choose your starting page</p>
-            </div>
-            <div className="flex gap-2">
-              <button
-                onClick={() => setDefaultView('habits')}
-                className={`
-                  px-3 py-1.5 rounded-lg text-sm transition-colors duration-200
-                  ${defaultView === 'habits' 
-                    ? 'bg-[#2ecc71] text-white' 
-                    : 'bg-gray-200 dark:bg-gray-700 text-gray-700 dark:text-gray-300'
-                  }
-                `}
-              >
-                Habits
-              </button>
-              <button
-                onClick={() => setDefaultView('calendar')}
-                className={`
-                  px-3 py-1.5 rounded-lg text-sm transition-colors duration-200
-                  ${defaultView === 'calendar' 
-                    ? 'bg-[#2ecc71] text-white' 
-                    : 'bg-gray-200 dark:bg-gray-700 text-gray-700 dark:text-gray-300'
-                  }
-                `}
-              >
-                Calendar
-              </button>
-            </div>
-          </div>
-
-          <div className="flex items-center justify-between">
-            <div>
-              <span className="dark:text-white">Sort Habits</span>
-              <p className="text-sm text-gray-500 dark:text-gray-400">Choose how to order your habits</p>
-            </div>
-            <div className="flex gap-2">
-              <button
-                onClick={() => setHabitSort('dateCreated')}
-                className={`
-                  px-3 py-1.5 rounded-lg text-sm transition-colors duration-200
-                  ${habitSort === 'dateCreated' 
-                    ? 'bg-[#2ecc71] text-white' 
-                    : 'bg-gray-200 dark:bg-gray-700 text-gray-700 dark:text-gray-300'
-                  }
-                `}
-              >
-                Date Created
-              </button>
-              <button
-                onClick={() => setHabitSort('alphabetical')}
-                className={`
-                  px-3 py-1.5 rounded-lg text-sm transition-colors duration-200
-                  ${habitSort === 'alphabetical' 
-                    ? 'bg-[#2ecc71] text-white' 
-                    : 'bg-gray-200 dark:bg-gray-700 text-gray-700 dark:text-gray-300'
-                  }
-                `}
-              >
-                Alphabetical
-              </button>
-            </div>
-          </div>
-        </div>
-      </div>
+  if (!user) {
+    return authView === 'login' ? (
+      <Login onSwitchToSignUp={() => setAuthView('signup')} />
+    ) : (
+      <SignUp onSwitchToLogin={() => setAuthView('login')} />
     );
-  };
+  }
 
   return (
     <div className={`min-h-screen ${theme.background}`}>
@@ -312,7 +170,7 @@ function HabitTrackerContent() {
         <main className="flex-1 p-8">
           {activeView === 'habits' && renderHabitsView()}
           {activeView === 'calendar' && renderCalendarView()}
-          {activeView === 'settings' && renderSettingsView()}
+          {activeView === 'settings' && <SettingsView />}
         </main>
       </div>
     </div>
@@ -321,8 +179,10 @@ function HabitTrackerContent() {
 
 export default function HabitTracker() {
   return (
-    <ThemeProvider>
-      <HabitTrackerContent />
-    </ThemeProvider>
+    <AuthProvider>
+      <ThemeProvider>
+        <HabitTrackerContent />
+      </ThemeProvider>
+    </AuthProvider>
   );
 }
\ No newline at end of file
diff --git a/src/components/HabitList.tsx b/src/components/HabitList.tsx
index 91749dc..e2c3857 100644
--- a/src/components/HabitList.tsx
+++ b/src/components/HabitList.tsx
@@ -1,7 +1,8 @@
-import React, { useEffect } from 'react';
+import React from 'react';
 import { Trash2 } from 'lucide-react';
 import { Habit } from '../types';
 import { useThemeContext } from '../contexts/ThemeContext';
+import { calculateStreak } from '../utils/streakCalculator';
 
 interface HabitListProps {
   habits: Habit[];
@@ -10,83 +11,9 @@ interface HabitListProps {
   onToggleHabit: (id: number, date: string) => void;
   onUpdateHabit: (id: number, name: string) => void;
   onDeleteHabit: (id: number) => void;
-  onUpdateStreak: (id: number, newStreak: number) => Promise<void>;
+  onUpdateStreak?: (id: number, newStreak: number) => Promise<void>;
 }
 
-const calculateStreak = (completedDates: string[]): { currentStreak: number; bestStreak: number } => {
-  if (!completedDates || completedDates.length === 0) {
-    return { currentStreak: 0, bestStreak: 0 };
-  }
-
-  // Get today at midnight in UTC
-  const today = new Date();
-  const utcToday = new Date(Date.UTC(today.getUTCFullYear(), today.getUTCMonth(), today.getUTCDate()));
-  
-  const todayStr = utcToday.toISOString().split('T')[0];
-
-  // Sort dates in descending order (most recent first)
-  const sortedDates = [...completedDates]
-    .filter(date => !isNaN(new Date(date).getTime()))
-    .sort((a, b) => new Date(b).getTime() - new Date(a).getTime());
-
-  let currentStreak = 0;
-  let bestStreak = 0;
-  let tempStreak = 0;
-
-  // Check if today is completed to maintain streak
-  const hasTodayCompleted = sortedDates.includes(todayStr);
-  
-  // Initialize current streak based on today's completion
-  if (hasTodayCompleted) {
-    currentStreak = 1;
-    let checkDate = new Date(utcToday);
-    
-    // Check previous days
-    while (true) {
-      checkDate.setUTCDate(checkDate.getUTCDate() - 1);
-      const dateStr = checkDate.toISOString().split('T')[0];
-      
-      if (sortedDates.includes(dateStr)) {
-        currentStreak++;
-      } else {
-        break;
-      }
-    }
-  }
-
-  // Calculate best streak
-  for (let i = 0; i < sortedDates.length; i++) {
-    const currentDate = new Date(sortedDates[i]);
-    currentDate.setHours(0, 0, 0, 0); // Normalize time part for comparison
-    
-    if (i === 0) {
-      tempStreak = 1;
-    } else {
-      const prevDate = new Date(sortedDates[i - 1]);
-      const diffDays = Math.floor(
-        (prevDate.getTime() - currentDate.getTime()) / (1000 * 60 * 60 * 24)
-      );
-      
-      if (diffDays === 1) {
-        tempStreak++;
-      } else if (diffDays === 0) {
-        // Same day, skip
-        continue;
-      } else {
-        // Reset streak on gap
-        bestStreak = Math.max(bestStreak, tempStreak);
-        tempStreak = 1;
-      }
-    }
-  }
-
-  // Final check for best streak
-  bestStreak = Math.max(bestStreak, tempStreak);
-  bestStreak = Math.max(bestStreak, currentStreak);
-
-  return { currentStreak, bestStreak };
-};
-
 export function HabitList({
   habits,
   currentWeek,
@@ -94,17 +21,15 @@ export function HabitList({
   onToggleHabit,
   onUpdateHabit,
   onDeleteHabit,
-  onUpdateStreak,
 }: HabitListProps) {
   const { showStreaks } = useThemeContext();
-  
-  useEffect(() => {
-    console.log('Current week dates:', 
-      currentWeek.map(date => 
-        `${new Date(date).toLocaleDateString()} (${daysOfWeek[new Date(date).getDay() === 0 ? 6 : new Date(date).getDay() - 1]})`
-      )
-    );
-  }, []);
+
+  // Helper function to get day name
+  const getDayName = (dateStr: string) => {
+    const date = new Date(dateStr);
+    const dayIndex = date.getDay() === 0 ? 6 : date.getDay() - 1;
+    return daysOfWeek[dayIndex];
+  };
 
   return (
     <div className="overflow-x-auto">
@@ -112,13 +37,11 @@ export function HabitList({
         <thead>
           <tr>
             <th className="text-left px-4 py-2 dark:text-white">Habit</th>
-            {currentWeek.map((dateStr, index) => {
+            {currentWeek.map((dateStr) => {
               const date = new Date(dateStr);
-              const dayIndex = date.getDay() === 0 ? 6 : date.getDay() - 1;
-              
               return (
                 <th key={dateStr} className="px-4 py-2 text-center dark:text-white">
-                  <div>{daysOfWeek[dayIndex]}</div>
+                  <div>{getDayName(dateStr)}</div>
                   <div className="text-xs text-gray-500 dark:text-gray-400">
                     {date.getDate()}
                   </div>
@@ -155,12 +78,6 @@ export function HabitList({
                       checked={habit.completedDates.includes(date)}
                       onChange={() => {
                         onToggleHabit(habit.id, date);
-                        const newCompletedDates = habit.completedDates.includes(date)
-                          ? habit.completedDates.filter(d => d !== date)
-                          : [...habit.completedDates, date];
-                        
-                        const { bestStreak } = calculateStreak(newCompletedDates);
-                        onUpdateStreak(habit.id, bestStreak);
                       }}
                       aria-label={`Mark ${habit.name} as completed for ${date}`}
                       className="sr-only"
diff --git a/src/components/Login.tsx b/src/components/Login.tsx
new file mode 100644
index 0000000..62eeda2
--- /dev/null
+++ b/src/components/Login.tsx
@@ -0,0 +1,67 @@
+import { useState } from 'react';
+import { useAuth } from '../contexts/AuthContext';
+import { useThemeContext } from '../contexts/ThemeContext';
+
+export function Login({ onSwitchToSignUp }: { onSwitchToSignUp: () => void }) {
+  const [email, setEmail] = useState('');
+  const [password, setPassword] = useState('');
+  const [error, setError] = useState('');
+  const { signIn } = useAuth();
+  const { theme } = useThemeContext();
+
+  const handleSubmit = async (e: React.FormEvent) => {
+    e.preventDefault();
+    try {
+      setError('');
+      await signIn(email, password);
+    } catch (error) {
+      setError('Failed to sign in');
+    }
+  };
+
+  return (
+    <div className="min-h-screen flex items-center justify-center">
+      <div className={`max-w-md w-full p-6 rounded-lg shadow-lg ${theme.cardBackground}`}>
+        <h2 className={`text-2xl font-bold mb-6 ${theme.text}`}>Log In</h2>
+        {error && <div className="text-red-500 mb-4">{error}</div>}
+        <form onSubmit={handleSubmit} className="space-y-4">
+          <div>
+            <input
+              type="email"
+              value={email}
+              onChange={(e) => setEmail(e.target.value)}
+              placeholder="Email"
+              className={`w-full px-4 py-2 rounded-lg ${theme.input}`}
+              required
+            />
+          </div>
+          <div>
+            <input
+              type="password"
+              value={password}
+              onChange={(e) => setPassword(e.target.value)}
+              placeholder="Password"
+              className={`w-full px-4 py-2 rounded-lg ${theme.input}`}
+              required
+            />
+          </div>
+          <button
+            type="submit"
+            className={`w-full py-2 rounded-lg ${theme.button.primary}`}
+          >
+            Log In
+          </button>
+        </form>
+        <p className={`mt-4 text-center ${theme.text}`}>
+          Don't have an account?{' '}
+          <button
+            onClick={onSwitchToSignUp}
+            className="text-blue-500 hover:underline"
+          >
+            Sign Up
+          </button>
+        </p>
+      </div>
+    </div>
+  );
+} 
\ No newline at end of file
diff --git a/src/components/SettingsView.tsx b/src/components/SettingsView.tsx
new file mode 100644
index 0000000..328e3b2
--- /dev/null
+++ b/src/components/SettingsView.tsx
@@ -0,0 +1,120 @@
+import React from 'react';
+import { Sun, Moon } from 'lucide-react';
+import { useThemeContext } from '../contexts/ThemeContext';
+
+export function SettingsView() {
+  const { 
+    theme, 
+    isDark, 
+    showStreaks, 
+    dailyReminder, 
+    defaultView,
+    habitSort,
+    toggleDarkMode, 
+    toggleStreaks, 
+    toggleDailyReminder,
+    setDefaultView,
+    setHabitSort
+  } = useThemeContext();
+
+  const handleReminderToggle = () => {
+    if (!dailyReminder && Notification.permission === 'default') {
+      Notification.requestPermission().then(permission => {
+        if (permission === 'granted') {
+          toggleDailyReminder();
+        }
+      });
+    } else {
+      toggleDailyReminder();
+    }
+  };
+
+  return (
+    <div className={`rounded-lg shadow p-6 ${theme.cardBackground}`}>
+      <h2 className="text-xl font-semibold mb-6 dark:text-white">Settings</h2>
+      
+      {/* Theme Toggle */}
+      <div className="mb-6">
+        <h3 className="text-lg font-medium mb-2 dark:text-white">Theme</h3>
+        <button
+          onClick={toggleDarkMode}
+          className={`flex items-center space-x-2 px-4 py-2 rounded-lg transition-colors duration-200
+            ${isDark 
+              ? 'bg-gray-700 text-white hover:bg-gray-600' 
+              : 'bg-gray-100 text-gray-900 hover:bg-gray-200'}`}
+        >
+          {isDark ? <Moon className="h-5 w-5" /> : <Sun className="h-5 w-5" />}
+          <span>{isDark ? 'Dark Mode' : 'Light Mode'}</span>
+        </button>
+      </div>
+
+      {/* Streaks Toggle */}
+      <div className="mb-6">
+        <h3 className="text-lg font-medium mb-2 dark:text-white">Streaks</h3>
+        <label className="flex items-center cursor-pointer">
+          <div className="relative">
+            <input
+              type="checkbox"
+              className="sr-only"
+              checked={showStreaks}
+              onChange={toggleStreaks}
+            />
+            <div className={`w-10 h-6 rounded-full transition-colors duration-200 
+              ${showStreaks ? 'bg-green-500' : 'bg-gray-300'}`}>
+              <div className={`absolute w-4 h-4 rounded-full bg-white transition-transform duration-200 transform 
+                ${showStreaks ? 'translate-x-5' : 'translate-x-1'} top-1`} />
+            </div>
+          </div>
+          <span className="ml-3 dark:text-white">Show Streaks</span>
+        </label>
+      </div>
+
+      {/* Daily Reminder Toggle */}
+      <div className="mb-6">
+        <h3 className="text-lg font-medium mb-2 dark:text-white">Notifications</h3>
+        <label className="flex items-center cursor-pointer">
+          <div className="relative">
+            <input
+              type="checkbox"
+              className="sr-only"
+              checked={dailyReminder}
+              onChange={handleReminderToggle}
+            />
+            <div className={`w-10 h-6 rounded-full transition-colors duration-200 
+              ${dailyReminder ? 'bg-green-500' : 'bg-gray-300'}`}>
+              <div className={`absolute w-4 h-4 rounded-full bg-white transition-transform duration-200 transform 
+                ${dailyReminder ? 'translate-x-5' : 'translate-x-1'} top-1`} />
+            </div>
+          </div>
+          <span className="ml-3 dark:text-white">Daily Reminder</span>
+        </label>
+      </div>
+
+      {/* Default View */}
+      <div className="mb-6">
+        <h3 className="text-lg font-medium mb-2 dark:text-white">Default View</h3>
+        <select
+          value={defaultView}
+          onChange={(e) => setDefaultView(e.target.value as 'habits' | 'calendar')}
+          className="mt-1 block w-full pl-3 pr-10 py-2 text-base border-gray-300 focus:outline-none focus:ring-2 focus:ring-green-500 focus:border-green-500 sm:text-sm rounded-md dark:bg-gray-700 dark:border-gray-600 dark:text-white"
+        >
+          <option value="habits">Habits</option>
+          <option value="calendar">Calendar</option>
+        </select>
+      </div>
+
+      {/* Habit Sort */}
+      <div className="mb-6">
+        <h3 className="text-lg font-medium mb-2 dark:text-white">Sort Habits By</h3>
+        <select
+          value={habitSort}
+          onChange={(e) => setHabitSort(e.target.value as 'dateCreated' | 'alphabetical')}
+          className="mt-1 block w-full pl-3 pr-10 py-2 text-base border-gray-300 focus:outline-none focus:ring-2 focus:ring-green-500 focus:border-green-500 sm:text-sm rounded-md dark:bg-gray-700 dark:border-gray-600 dark:text-white"
+        >
+          <option value="dateCreated">Date Created</option>
+          <option value="alphabetical">Alphabetical</option>
+        </select>
+      </div>
+    </div>
+  );
+} 
\ No newline at end of file
diff --git a/src/components/Sidebar.tsx b/src/components/Sidebar.tsx
index f653652..c7921e5 100644
--- a/src/components/Sidebar.tsx
+++ b/src/components/Sidebar.tsx
@@ -1,6 +1,7 @@
 import React from 'react';
-import { Plus, CalendarIcon, SettingsIcon } from 'lucide-react';
+import { Plus, CalendarIcon, SettingsIcon, LogOut } from 'lucide-react';
 import { useThemeContext } from '../contexts/ThemeContext';
+import { useAuth } from '../contexts/AuthContext';
 
 type View = 'habits' | 'calendar' | 'settings';
 
@@ -11,13 +12,14 @@ interface SidebarProps {
 
 export const Sidebar: React.FC<SidebarProps> = ({ activeView, setActiveView }) => {
   const { theme } = useThemeContext();
+  const { signOut } = useAuth();
   
   return (
-    <nav className={`w-64 border-r ${theme.border} ${theme.sidebarBackground}`}>
+    <nav className={`w-64 border-r ${theme.border} ${theme.sidebarBackground} flex flex-col`}>
       <div className="p-4">
         <h1 className={`text-2xl font-bold ${theme.text}`}>Habit Tracker</h1>
       </div>
-      <ul className="space-y-2 p-4">
+      <ul className="space-y-2 p-4 flex-grow">
         <li>
           <button
             onClick={() => setActiveView('habits')}
@@ -58,6 +60,15 @@ export const Sidebar: React.FC<SidebarProps> = ({ activeView, setActiveView }) =
           </button>
         </li>
       </ul>
+      <div className="p-4 border-t border-gray-200">
+        <button
+          onClick={signOut}
+          className={`w-full px-4 py-2 text-left rounded-lg ${theme.text} ${theme.habitItem}`}
+        >
+          <LogOut className="inline-block mr-2 h-4 w-4" />
+          Sign Out
+        </button>
+      </div>
     </nav>
   );
 }; 
\ No newline at end of file
diff --git a/src/components/SignUp.tsx b/src/components/SignUp.tsx
new file mode 100644
index 0000000..8dbb7ef
--- /dev/null
+++ b/src/components/SignUp.tsx
@@ -0,0 +1,67 @@
+import { useState } from 'react';
+import { useAuth } from '../contexts/AuthContext';
+import { useThemeContext } from '../contexts/ThemeContext';
+
+export function SignUp({ onSwitchToLogin }: { onSwitchToLogin: () => void }) {
+  const [email, setEmail] = useState('');
+  const [password, setPassword] = useState('');
+  const [error, setError] = useState('');
+  const { signUp } = useAuth();
+  const { theme } = useThemeContext();
+
+  const handleSubmit = async (e: React.FormEvent) => {
+    e.preventDefault();
+    try {
+      setError('');
+      await signUp(email, password);
+    } catch (error) {
+      setError('Failed to create an account');
+    }
+  };
+
+  return (
+    <div className="min-h-screen flex items-center justify-center">
+      <div className={`max-w-md w-full p-6 rounded-lg shadow-lg ${theme.cardBackground}`}>
+        <h2 className={`text-2xl font-bold mb-6 ${theme.text}`}>Sign Up</h2>
+        {error && <div className="text-red-500 mb-4">{error}</div>}
+        <form onSubmit={handleSubmit} className="space-y-4">
+          <div>
+            <input
+              type="email"
+              value={email}
+              onChange={(e) => setEmail(e.target.value)}
+              placeholder="Email"
+              className={`w-full px-4 py-2 rounded-lg ${theme.input}`}
+              required
+            />
+          </div>
+          <div>
+            <input
+              type="password"
+              value={password}
+              onChange={(e) => setPassword(e.target.value)}
+              placeholder="Password"
+              className={`w-full px-4 py-2 rounded-lg ${theme.input}`}
+              required
+            />
+          </div>
+          <button
+            type="submit"
+            className={`w-full py-2 rounded-lg ${theme.button.primary}`}
+          >
+            Sign Up
+          </button>
+        </form>
+        <p className={`mt-4 text-center ${theme.text}`}>
+          Already have an account?{' '}
+          <button
+            onClick={onSwitchToLogin}
+            className="text-blue-500 hover:underline"
+          >
+            Log In
+          </button>
+        </p>
+      </div>
+    </div>
+  );
+} 
\ No newline at end of file
diff --git a/src/contexts/AuthContext.tsx b/src/contexts/AuthContext.tsx
new file mode 100644
index 0000000..fe0b233
--- /dev/null
+++ b/src/contexts/AuthContext.tsx
@@ -0,0 +1,68 @@
+import { createContext, useContext, useEffect, useState } from 'react';
+import { User } from '@supabase/supabase-js';
+import { supabase } from '../lib/supabase';
+
+interface AuthContextType {
+  user: User | null;
+  loading: boolean;
+  signUp: (email: string, password: string) => Promise<void>;
+  signIn: (email: string, password: string) => Promise<void>;
+  signOut: () => Promise<void>;
+}
+
+const AuthContext = createContext<AuthContextType | undefined>(undefined);
+
+export function AuthProvider({ children }: { children: React.ReactNode }) {
+  const [user, setUser] = useState<User | null>(null);
+  const [loading, setLoading] = useState(true);
+
+  useEffect(() => {
+    // Check active sessions and sets the user
+    supabase.auth.getSession().then(({ data: { session } }) => {
+      setUser(session?.user ?? null);
+      setLoading(false);
+    });
+
+    // Listen for auth changes
+    const { data: { subscription } } = supabase.auth.onAuthStateChange((_event, session) => {
+      setUser(session?.user ?? null);
+    });
+
+    return () => subscription.unsubscribe();
+  }, []);
+
+  const signUp = async (email: string, password: string) => {
+    const { error } = await supabase.auth.signUp({
+      email,
+      password,
+    });
+    if (error) throw error;
+  };
+
+  const signIn = async (email: string, password: string) => {
+    const { error } = await supabase.auth.signInWithPassword({
+      email,
+      password,
+    });
+    if (error) throw error;
+  };
+
+  const signOut = async () => {
+    const { error } = await supabase.auth.signOut();
+    if (error) throw error;
+  };
+
+  return (
+    <AuthContext.Provider value={{ user, loading, signUp, signIn, signOut }}>
+      {children}
+    </AuthContext.Provider>
+  );
+}
+
+export const useAuth = () => {
+  const context = useContext(AuthContext);
+  if (context === undefined) {
+    throw new Error('useAuth must be used within an AuthProvider');
+  }
+  return context;
+}; 
\ No newline at end of file
diff --git a/src/hooks/useHabits.ts b/src/hooks/useHabits.ts
index a83614e..b98f6f6 100644
--- a/src/hooks/useHabits.ts
+++ b/src/hooks/useHabits.ts
@@ -1,12 +1,28 @@
-import { useState } from 'react';
+import { useState, useEffect } from 'react';
 import { supabase } from '../lib/supabase';
 import { Habit } from '../types';
 import { calculateStreak } from '../utils/streakCalculator';
+import { useAuth } from '../contexts/AuthContext';
 
 export const useHabits = () => {
   const [habits, setHabits] = useState<Habit[]>([]);
+  const { user } = useAuth();
+
+  // Automatically fetch habits when user changes
+  useEffect(() => {
+    if (user) {
+      fetchHabits();
+    } else {
+      setHabits([]); // Clear habits when user logs out
+    }
+  }, [user?.id]); // Depend on user.id to prevent unnecessary rerenders
 
   const fetchHabits = async () => {
+    if (!user) {
+      setHabits([]);
+      return;
+    }
+    
     try {
       const { data, error } = await supabase
         .from('habits')
@@ -15,19 +31,23 @@ export const useHabits = () => {
           name,
           created_at,
           best_streak,
-          habit_completions (completion_date)
-        `);
+          habit_completions (
+            completion_date
+          )
+        `)
+        .eq('user_id', user.id)
+        .order('created_at', { ascending: false });
 
       if (error) throw error;
 
-      const formattedHabits = data.map(habit => ({
+      const formattedHabits = (data || []).map(habit => ({
         id: habit.id,
         name: habit.name,
         created_at: habit.created_at,
         best_streak: habit.best_streak,
-        completedDates: habit.habit_completions.map(
+        completedDates: habit.habit_completions?.map(
           (completion: { completion_date: string }) => completion.completion_date
-        )
+        ) || []
       }));
 
       setHabits(formattedHabits);
@@ -38,18 +58,22 @@ export const useHabits = () => {
   };
 
   const addHabit = async (name: string) => {
+    if (!user) return false;
+    
     try {
-      const { error } = await supabase
+      const { data, error } = await supabase
         .from('habits')
         .insert([{ 
           name, 
           best_streak: 0,
-          created_at: new Date().toISOString() 
+          created_at: new Date().toISOString(),
+          user_id: user.id
         }])
-        .select()
+        .select('id')
         .single();
 
       if (error) throw error;
+      
       await fetchHabits();
       return true;
     } catch (error) {
@@ -59,56 +83,89 @@ export const useHabits = () => {
   };
 
   const toggleHabit = async (id: number, date: string) => {
+    if (!user) return;
+    
     try {
-      const { data: existing } = await supabase
-        .from('habit_completions')
-        .select()
-        .eq('habit_id', id)
-        .eq('completion_date', date)
+      // First verify this habit belongs to the user
+      const { data: habitData, error: habitError } = await supabase
+        .from('habits')
+        .select('id')
+        .eq('id', id)
+        .eq('user_id', user.id)
         .single();
 
+      if (habitError || !habitData) {
+        throw new Error('Unauthorized access to habit');
+      }
+
+      // Keep the original date string without any timezone conversion
+      const formattedDate = date;
+
+      console.log('Toggling habit:', { id, date, formattedDate });
+
+      // Check for existing completion
+      const { data: existing, error: existingError } = await supabase
+        .from('habit_completions')
+        .select('*')
+        .eq('habit_id', id)
+        .eq('completion_date', formattedDate)
+        .eq('user_id', user.id)
+        .single();
+
+      if (existingError && existingError.code !== 'PGRST116') {
+        throw existingError;
+      }
+
       if (existing) {
-        await supabase
+        const { error: deleteError } = await supabase
           .from('habit_completions')
           .delete()
           .eq('habit_id', id)
-          .eq('completion_date', date);
-      } else {
-        await supabase
-          .from('habit_completions')
-          .insert([{ habit_id: id, completion_date: date }]);
-      }
+          .eq('completion_date', formattedDate)
+          .eq('user_id', user.id);
 
-      // After toggling, recalculate streak
-      const habit = habits.find(h => h.id === id);
-      if (habit) {
-        const newCompletedDates = existing
-          ? habit.completedDates.filter(d => d !== date)
-          : [...habit.completedDates, date];
-        
-        const { bestStreak } = calculateStreak(newCompletedDates);
-        
-        // Update best_streak if the new streak is higher
-        if (bestStreak > habit.best_streak) {
-          await supabase
-            .from('habits')
-            .update({ best_streak: bestStreak })
-            .eq('id', id);
-        }
+        if (deleteError) throw deleteError;
+      } else {
+        const { error: insertError } = await supabase
+          .from('habit_completions')
+          .insert([{ 
+            habit_id: id, 
+            completion_date: formattedDate,
+            user_id: user.id
+          }]);
+
+        if (insertError) throw insertError;
       }
 
       await fetchHabits();
     } catch (error) {
       console.error('Error toggling habit:', error);
+      throw error;
     }
   };
 
   const updateHabit = async (id: number, name: string) => {
+    if (!user) return;
+    
     try {
+      // First verify this habit belongs to the user
+      const { data: habitData, error: habitError } = await supabase
+        .from('habits')
+        .select('id')
+        .eq('id', id)
+        .eq('user_id', user.id)
+        .single();
+
+      if (habitError || !habitData) {
+        throw new Error('Unauthorized access to habit');
+      }
+
       await supabase
         .from('habits')
         .update({ name })
-        .eq('id', id);
+        .eq('id', id)
+        .eq('user_id', user.id);
+
       await fetchHabits();
     } catch (error) {
       console.error('Error updating habit:', error);
@@ -116,11 +173,27 @@ export const useHabits = () => {
   };
 
   const deleteHabit = async (id: number) => {
+    if (!user) return;
+    
     try {
+      // First verify this habit belongs to the user
+      const { data: habitData, error: habitError } = await supabase
+        .from('habits')
+        .select('id')
+        .eq('id', id)
+        .eq('user_id', user.id)
+        .single();
+
+      if (habitError || !habitData) {
+        throw new Error('Unauthorized access to habit');
+      }
+
       await supabase
         .from('habits')
         .delete()
-        .eq('id', id);
+        .eq('id', id)
+        .eq('user_id', user.id);
+
       await fetchHabits();
     } catch (error) {
       console.error('Error deleting habit:', error);
diff --git a/src/hooks/useWeek.ts b/src/hooks/useWeek.ts
index 9e82a5e..cdc5855 100644
--- a/src/hooks/useWeek.ts
+++ b/src/hooks/useWeek.ts
@@ -5,23 +5,38 @@ export const useWeek = () => {
 
   const getCurrentWeekDates = () => {
     const now = new Date();
-    const dayOfWeek = now.getDay();
-    const diff = now.getDate() - dayOfWeek + (dayOfWeek === 0 ? -6 : 1);
-    const monday = new Date(now.setDate(diff));
+    const currentDay = now.getDay();
+    const diff = currentDay === 0 ? -6 : 1 - currentDay;
+    
+    const monday = new Date(now);
+    monday.setDate(now.getDate() + diff);
+    monday.setHours(0, 0, 0, 0);
+    
     return Array.from({ length: 7 }, (_, i) => {
       const date = new Date(monday);
       date.setDate(monday.getDate() + i);
-      return date.toISOString().split('T')[0];
+      const year = date.getFullYear();
+      const month = String(date.getMonth() + 1).padStart(2, '0');
+      const day = String(date.getDate()).padStart(2, '0');
+      return `${year}-${month}-${day}`;
     });
   };
 
   const changeWeek = (direction: 'prev' | 'next') => {
+    if (currentWeek.length === 0) return;
+    
     const firstDay = new Date(currentWeek[0]);
-    const newFirstDay = new Date(firstDay.setDate(firstDay.getDate() + (direction === 'prev' ? -7 : 7)));
+    firstDay.setHours(0, 0, 0, 0);
+    const newFirstDay = new Date(firstDay);
+    newFirstDay.setDate(firstDay.getDate() + (direction === 'prev' ? -7 : 7));
+    
     setCurrentWeek(Array.from({ length: 7 }, (_, i) => {
       const date = new Date(newFirstDay);
       date.setDate(newFirstDay.getDate() + i);
-      return date.toISOString().split('T')[0];
+      const year = date.getFullYear();
+      const month = String(date.getMonth() + 1).padStart(2, '0');
+      const day = String(date.getDate()).padStart(2, '0');
+      return `${year}-${month}-${day}`;
     }));
   };