/* ==============================================
   TaskFlow - Modern Task Management Application
   ============================================== */

/* CSS Custom Properties for Theming */
:root {
  /* Primary Colors */
  --primary-50: #eff6ff;
  --primary-100: #dbeafe;
  --primary-500: #3b82f6;
  --primary-600: #2563eb;
  --primary-700: #1d4ed8;
  --primary-900: #1e3a8a;

  /* Semantic Colors */
  --success-50: #ecfdf5;
  --success-100: #d1fae5;
  --success-500: #10b981;
  --success-600: #059669;
  --success-700: #047857;

  --warning-50: #fffbeb;
  --warning-100: #fef3c7;
  --warning-500: #f59e0b;
  --warning-600: #d97706;
  --warning-700: #b45309;

  --error-50: #fef2f2;
  --error-100: #fee2e2;
  --error-500: #ef4444;
  --error-600: #dc2626;
  --error-700: #b91c1c;

  /* Neutral Colors */
  --gray-50: #f9fafb;
  --gray-100: #f3f4f6;
  --gray-200: #e5e7eb;
  --gray-300: #d1d5db;
  --gray-400: #9ca3af;
  --gray-500: #6b7280;
  --gray-600: #4b5563;
  --gray-700: #374151;
  --gray-800: #1f2937;
  --gray-900: #111827;

  /* Typography */
  --font-family-sans: 'Inter', system-ui, -apple-system, sans-serif;
  --font-family-mono: 'Fira Code', 'Consolas', monospace;

  --text-xs: 0.75rem;    /* 12px */
  --text-sm: 0.875rem;   /* 14px */
  --text-base: 1rem;     /* 16px */
  --text-lg: 1.125rem;   /* 18px */
  --text-xl: 1.25rem;    /* 20px */
  --text-2xl: 1.5rem;    /* 24px */
  --text-3xl: 1.875rem;  /* 30px */

  --leading-tight: 1.25;
  --leading-normal: 1.5;
  --leading-relaxed: 1.625;

  /* Spacing */
  --space-1: 0.25rem;   /* 4px */
  --space-2: 0.5rem;    /* 8px */
  --space-3: 0.75rem;   /* 12px */
  --space-4: 1rem;      /* 16px */
  --space-5: 1.25rem;   /* 20px */
  --space-6: 1.5rem;    /* 24px */
  --space-8: 2rem;      /* 32px */
  --space-10: 2.5rem;   /* 40px */
  --space-12: 3rem;     /* 48px */

  /* Layout */
  --header-height: 4rem;
  --sidebar-width: 16rem;
  --border-radius: 0.5rem;
  --border-radius-sm: 0.25rem;
  --border-radius-lg: 0.75rem;

  /* Shadows */
  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
  --shadow-xl: 0 20px 25px -5px rgb(0 0 0 / 0.1), 0 8px 10px -6px rgb(0 0 0 / 0.1);

  /* Transitions */
  --transition-fast: 150ms ease-in-out;
  --transition-normal: 250ms ease-in-out;
  --transition-slow: 350ms ease-in-out;

  /* Z-index Scale */
  --z-dropdown: 1000;
  --z-sticky: 1020;
  --z-fixed: 1030;
  --z-modal-backdrop: 1040;
  --z-modal: 1050;
  --z-popover: 1060;
  --z-tooltip: 1070;
  --z-toast: 1080;
}

/* Dark Theme Variables */
[data-theme="dark"] {
  --gray-50: #111827;
  --gray-100: #1f2937;
  --gray-200: #374151;
  --gray-300: #4b5563;
  --gray-400: #6b7280;
  --gray-500: #9ca3af;
  --gray-600: #d1d5db;
  --gray-700: #e5e7eb;
  --gray-800: #f3f4f6;
  --gray-900: #f9fafb;
}

/* Base Styles */
* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  height: 100%;
  font-size: 16px;
}

body {
  font-family: var(--font-family-sans);
  font-size: var(--text-base);
  line-height: var(--leading-normal);
  color: var(--gray-900);
  background-color: var(--gray-50);
  min-height: 100vh;
  overflow-x: hidden;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
  font-weight: 600;
  line-height: var(--leading-tight);
  color: var(--gray-900);
}

h1 { font-size: var(--text-3xl); }
h2 { font-size: var(--text-2xl); }
h3 { font-size: var(--text-xl); }
h4 { font-size: var(--text-lg); }
h5 { font-size: var(--text-base); }
h6 { font-size: var(--text-sm); }

p {
  margin-bottom: var(--space-4);
  color: var(--gray-700);
}

a {
  color: var(--primary-500);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--primary-600);
  text-decoration: underline;
}

code {
  font-family: var(--font-family-mono);
  font-size: var(--text-sm);
  background-color: var(--gray-100);
  padding: var(--space-1) var(--space-2);
  border-radius: var(--border-radius-sm);
  color: var(--gray-800);
}

/* Layout Components */
.app-header {
  background-color: white;
  border-bottom: 1px solid var(--gray-200);
  height: var(--header-height);
  position: sticky;
  top: 0;
  z-index: var(--z-sticky);
  box-shadow: var(--shadow-sm);
}

.header-content {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 var(--space-6);
}

.logo-section {
  display: flex;
  align-items: center;
  gap: var(--space-3);
}

.logo {
  width: 2rem;
  height: 2rem;
}

.app-title {
  font-size: var(--text-xl);
  font-weight: 700;
  color: var(--gray-900);
  margin: 0;
}

.main-nav {
  display: flex;
  gap: var(--space-2);
}

.nav-btn {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-2) var(--space-4);
  border: none;
  background: transparent;
  color: var(--gray-600);
  font-size: var(--text-sm);
  font-weight: 500;
  border-radius: var(--border-radius-sm);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.nav-btn:hover {
  background-color: var(--gray-100);
  color: var(--gray-900);
}

.nav-btn.active {
  background-color: var(--primary-100);
  color: var(--primary-700);
}

.header-actions {
  display: flex;
  align-items: center;
  gap: var(--space-3);
}

.action-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 2.5rem;
  height: 2.5rem;
  border: 1px solid var(--gray-300);
  background-color: white;
  color: var(--gray-600);
  border-radius: var(--border-radius-sm);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.action-btn:hover {
  background-color: var(--gray-50);
  border-color: var(--gray-400);
}

.action-btn.primary {
  background-color: var(--primary-500);
  border-color: var(--primary-500);
  color: white;
  padding: 0 var(--space-4);
  width: auto;
  gap: var(--space-2);
  font-weight: 500;
}

.action-btn.primary:hover {
  background-color: var(--primary-600);
  border-color: var(--primary-600);
}

/* Main Content */
.app-main {
  max-width: 1200px;
  margin: 0 auto;
  padding: var(--space-6);
  display: flex;
  flex-direction: column;
  gap: var(--space-8);
}

/* Statistics Section */
.stats-section {
  margin-bottom: var(--space-8);
}

.stats-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: var(--space-6);
}

.stat-card {
  background-color: white;
  border: 1px solid var(--gray-200);
  border-radius: var(--border-radius-lg);
  padding: var(--space-6);
  display: flex;
  align-items: center;
  gap: var(--space-4);
  box-shadow: var(--shadow-sm);
  transition: all var(--transition-normal);
}

.stat-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.stat-icon {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 3rem;
  height: 3rem;
  border-radius: var(--border-radius-lg);
  flex-shrink: 0;
}

.stat-content {
  flex: 1;
}

.stat-number {
  font-size: var(--text-2xl);
  font-weight: 700;
  color: var(--gray-900);
  margin: 0 0 var(--space-1) 0;
}

.stat-label {
  font-size: var(--text-sm);
  color: var(--gray-600);
  margin: 0;
}

/* Task Management */
.filters-section {
  background-color: white;
  border: 1px solid var(--gray-200);
  border-radius: var(--border-radius-lg);
  padding: var(--space-6);
  margin-bottom: var(--space-6);
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-4);
  align-items: end;
}

.filter-group {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
  min-width: 150px;
}

.filter-label {
  font-size: var(--text-sm);
  font-weight: 500;
  color: var(--gray-700);
}

.filter-select,
.filter-input {
  padding: var(--space-2) var(--space-3);
  border: 1px solid var(--gray-300);
  border-radius: var(--border-radius-sm);
  font-size: var(--text-sm);
  background-color: white;
  color: var(--gray-900);
  transition: border-color var(--transition-fast);
}

.filter-select:focus,
.filter-input:focus {
  outline: none;
  border-color: var(--primary-500);
  box-shadow: 0 0 0 3px rgb(59 130 246 / 0.1);
}

/* Task Board */
.task-board {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: var(--space-6);
  align-items: start;
}

.task-column {
  background-color: white;
  border: 1px solid var(--gray-200);
  border-radius: var(--border-radius-lg);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
}

.column-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-4) var(--space-6);
  background-color: var(--gray-50);
  border-bottom: 1px solid var(--gray-200);
}

.column-title {
  font-size: var(--text-lg);
  font-weight: 600;
  color: var(--gray-900);
  margin: 0;
}

.task-count {
  background-color: var(--gray-200);
  color: var(--gray-700);
  padding: var(--space-1) var(--space-2);
  border-radius: 9999px;
  font-size: var(--text-xs);
  font-weight: 600;
}

.task-list {
  padding: var(--space-4);
  min-height: 200px;
}

.task-list[data-dropzone="true"] {
  transition: all var(--transition-normal);
}

.task-list[data-dropzone="true"]:hover {
  background-color: var(--gray-50);
}

/* Task Card */
.task-card {
  background-color: white;
  border: 1px solid var(--gray-200);
  border-radius: var(--border-radius);
  padding: var(--space-4);
  margin-bottom: var(--space-3);
  cursor: pointer;
  transition: all var(--transition-fast);
  box-shadow: var(--shadow-sm);
}

.task-card:hover {
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
  border-color: var(--gray-300);
}

.task-card.dragging {
  opacity: 0.5;
  transform: rotate(5deg);
}

.task-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  margin-bottom: var(--space-3);
}

.task-title {
  font-size: var(--text-base);
  font-weight: 600;
  color: var(--gray-900);
  margin: 0;
  flex: 1;
}

.task-priority {
  padding: var(--space-1) var(--space-2);
  border-radius: var(--border-radius-sm);
  font-size: var(--text-xs);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.task-priority.high {
  background-color: var(--error-100);
  color: var(--error-700);
}

.task-priority.medium {
  background-color: var(--warning-100);
  color: var(--warning-700);
}

.task-priority.low {
  background-color: var(--success-100);
  color: var(--success-700);
}

.task-description {
  font-size: var(--text-sm);
  color: var(--gray-600);
  margin: 0 0 var(--space-3) 0;
  line-height: var(--leading-relaxed);
}

.task-meta {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  align-items: center;
}

.task-tags {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-1);
}

.task-tag {
  background-color: var(--gray-100);
  color: var(--gray-700);
  padding: var(--space-1) var(--space-2);
  border-radius: var(--border-radius-sm);
  font-size: var(--text-xs);
}

.task-date {
  font-size: var(--text-xs);
  color: var(--gray-500);
}

/* Modal Styles */
.modal-overlay {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background-color: rgba(0, 0, 0, 0.5);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: var(--z-modal-backdrop);
  opacity: 0;
  visibility: hidden;
  transition: all var(--transition-normal);
}

.modal-overlay.active {
  opacity: 1;
  visibility: visible;
}

.modal {
  background-color: white;
  border-radius: var(--border-radius-lg);
  box-shadow: var(--shadow-xl);
  max-width: 500px;
  width: 90%;
  max-height: 90vh;
  overflow-y: auto;
  transform: scale(0.9) translateY(20px);
  transition: transform var(--transition-normal);
}

.modal-overlay.active .modal {
  transform: scale(1) translateY(0);
}

.modal-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-6);
  border-bottom: 1px solid var(--gray-200);
}

.modal-title {
  font-size: var(--text-xl);
  font-weight: 600;
  color: var(--gray-900);
  margin: 0;
}

.modal-close {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 2rem;
  height: 2rem;
  border: none;
  background: transparent;
  color: var(--gray-500);
  cursor: pointer;
  border-radius: var(--border-radius-sm);
  transition: all var(--transition-fast);
}

.modal-close:hover {
  background-color: var(--gray-100);
  color: var(--gray-700);
}

.modal-content {
  padding: var(--space-6);
}

.form-group {
  margin-bottom: var(--space-4);
}

.form-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-4);
}

.form-label {
  display: block;
  font-size: var(--text-sm);
  font-weight: 500;
  color: var(--gray-700);
  margin-bottom: var(--space-2);
}

.form-input,
.form-select,
.form-textarea {
  width: 100%;
  padding: var(--space-3);
  border: 1px solid var(--gray-300);
  border-radius: var(--border-radius-sm);
  font-size: var(--text-base);
  background-color: white;
  color: var(--gray-900);
  transition: border-color var(--transition-fast);
}

.form-input:focus,
.form-select:focus,
.form-textarea:focus {
  outline: none;
  border-color: var(--primary-500);
  box-shadow: 0 0 0 3px rgb(59 130 246 / 0.1);
}

.form-textarea {
  resize: vertical;
  min-height: 80px;
}

.form-error {
  font-size: var(--text-sm);
  color: var(--error-500);
  margin-top: var(--space-1);
}

.modal-actions {
  display: flex;
  gap: var(--space-3);
  justify-content: flex-end;
  margin-top: var(--space-6);
  padding-top: var(--space-4);
  border-top: 1px solid var(--gray-200);
}

/* Button Styles */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  padding: var(--space-2) var(--space-4);
  border: 1px solid transparent;
  border-radius: var(--border-radius-sm);
  font-size: var(--text-sm);
  font-weight: 500;
  text-decoration: none;
  cursor: pointer;
  transition: all var(--transition-fast);
  white-space: nowrap;
}

.btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

.btn-primary {
  background-color: var(--primary-500);
  border-color: var(--primary-500);
  color: white;
}

.btn-primary:hover:not(:disabled) {
  background-color: var(--primary-600);
  border-color: var(--primary-600);
}

.btn-secondary {
  background-color: white;
  border-color: var(--gray-300);
  color: var(--gray-700);
}

.btn-secondary:hover:not(:disabled) {
  background-color: var(--gray-50);
  border-color: var(--gray-400);
}

/* Loading States */
.loading-overlay {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background-color: rgba(255, 255, 255, 0.8);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: var(--z-modal-backdrop);
  opacity: 0;
  visibility: hidden;
  transition: all var(--transition-normal);
}

.loading-overlay.active {
  opacity: 1;
  visibility: visible;
}

.loading-spinner {
  text-align: center;
}

.spinner {
  width: 2rem;
  height: 2rem;
  border: 2px solid var(--gray-200);
  border-top: 2px solid var(--primary-500);
  border-radius: 50%;
  animation: spin 1s linear infinite;
  margin: 0 auto var(--space-3);
}

@keyframes spin {
  to {
    transform: rotate(360deg);
  }
}

.loading-text {
  font-size: var(--text-sm);
  color: var(--gray-600);
  margin: 0;
}

/* Toast Notifications */
.toast-container {
  position: fixed;
  top: var(--space-4);
  right: var(--space-4);
  z-index: var(--z-toast);
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}

.toast {
  background-color: white;
  border: 1px solid var(--gray-200);
  border-radius: var(--border-radius);
  padding: var(--space-4);
  box-shadow: var(--shadow-lg);
  max-width: 300px;
  transform: translateX(100%);
  transition: transform var(--transition-normal);
}

.toast.show {
  transform: translateX(0);
}

.toast-success {
  border-left: 4px solid var(--success-500);
}

.toast-error {
  border-left: 4px solid var(--error-500);
}

.toast-warning {
  border-left: 4px solid var(--warning-500);
}

/* Drag and Drop States */
.task-list.drag-over {
  background-color: var(--primary-50);
  border: 2px dashed var(--primary-300);
}

.task-card.dragging {
  opacity: 0.5;
  transform: rotate(2deg);
}

/* Responsive Design */
@media (max-width: 768px) {
  .header-content {
    padding: 0 var(--space-4);
  }
  
  .main-nav {
    display: none;
  }
  
  .app-main {
    padding: var(--space-4);
  }
  
  .stats-grid {
    grid-template-columns: 1fr;
  }
  
  .filters-section {
    flex-direction: column;
    gap: var(--space-3);
  }
  
  .filter-group {
    min-width: auto;
  }
  
  .task-board {
    grid-template-columns: 1fr;
  }
  
  .form-row {
    grid-template-columns: 1fr;
  }
  
  .modal {
    width: 95%;
    margin: var(--space-4);
  }
}

@media (max-width: 480px) {
  .header-content {
    padding: 0 var(--space-3);
  }
  
  .app-title {
    display: none;
  }
  
  .action-btn.primary {
    padding: var(--space-2);
    width: 2.5rem;
  }
  
  .action-btn.primary span {
    display: none;
  }
}

/* Print Styles */
@media print {
  .app-header,
  .filters-section,
  .modal-overlay,
  .loading-overlay,
  .toast-container {
    display: none !important;
  }
  
  .task-board {
    display: block;
  }
  
  .task-column {
    break-inside: avoid;
    margin-bottom: var(--space-4);
  }
}

/* Accessibility Improvements */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

/* Focus visible for better keyboard navigation */
.btn:focus-visible,
.nav-btn:focus-visible,
.action-btn:focus-visible,
.form-input:focus-visible,
.form-select:focus-visible,
.form-textarea:focus-visible {
  outline: 2px solid var(--primary-500);
  outline-offset: 2px;
}

/* High contrast mode support */
@media (prefers-contrast: high) {
  :root {
    --gray-200: #000000;
    --gray-300: #000000;
    --gray-600: #000000;
  }
  
  .task-card,
  .stat-card,
  .modal {
    border-width: 2px;
  }
}