<script setup lang="ts">
import { computed, ref } from 'vue'
import {
  useClipboard,
  useColorMode,
  useInfiniteScroll,
  useLocalStorage,
  useTitle,
} from '@vueuse/core'

type Todo = {
  id: number
  text: string
  done: boolean
}

const seedTexts = [
  'Review project goals',
  'Plan the next sprint',
  'Reply to client email',
]

const defaultTodos = Array.from({ length: 36 }, (_, index) => ({
  id: index + 1,
  text:
    seedTexts[index % seedTexts.length] +
    (index >= seedTexts.length ? ` #${index + 1}` : ''),
  done: index % 7 === 0,
}))

const todos = useLocalStorage<Todo[]>('focus-flow-todos', defaultTodos)
const nextId = ref(
  todos.value.reduce((max, todo) => Math.max(max, todo.id), 0) + 1,
)
const newTodo = ref('')

const totalCount = computed(() => todos.value.length)
const remainingCount = computed(() =>
  todos.value.filter((todo) => !todo.done).length,
)
const completedCount = computed(
  () => totalCount.value - remainingCount.value,
)

useTitle(computed(() => `Todos (${remainingCount.value})`))

const mode = useColorMode({
  attribute: 'data-theme',
  disableTransition: false,
})
const isDark = computed(() => mode.value === 'dark')

const toggleMode = () => {
  mode.value = isDark.value ? 'light' : 'dark'
}

const { copy, copied, isSupported } = useClipboard()
const lastCopiedId = ref<number | null>(null)

const handleCopy = async (todo: Todo) => {
  await copy(todo.text)
  lastCopiedId.value = todo.id
}

const pageSize = 8
const visibleCount = ref(Math.min(pageSize, todos.value.length))
const visibleTodos = computed(() => todos.value.slice(0, visibleCount.value))

const listRef = ref<HTMLElement | null>(null)
const { isLoading } = useInfiniteScroll(
  listRef,
  () => {
    if (visibleCount.value < todos.value.length) {
      visibleCount.value = Math.min(
        visibleCount.value + pageSize,
        todos.value.length,
      )
    }
  },
  {
    distance: 120,
    canLoadMore: () => visibleCount.value < todos.value.length,
  },
)

const syncVisibleCount = () => {
  if (todos.value.length <= pageSize) {
    visibleCount.value = todos.value.length
    return
  }

  if (visibleCount.value === 0) {
    visibleCount.value = pageSize
    return
  }

  if (visibleCount.value > todos.value.length) {
    visibleCount.value = todos.value.length
  }
}

const addTodo = () => {
  const value = newTodo.value.trim()
  if (!value)
    return

  todos.value.unshift({
    id: nextId.value++,
    text: value,
    done: false,
  })
  newTodo.value = ''
  syncVisibleCount()
}

const removeTodo = (id: number) => {
  todos.value = todos.value.filter((todo) => todo.id !== id)
  syncVisibleCount()
}
</script>

<template>
  <div class="page">
    <div class="shell">
      <header class="header">
        <div>
          <p class="eyebrow">Minimal todo tracker</p>
          <h1>Focus Flow</h1>
          <p class="subtitle">
            Keep a lightweight list, copy tasks with a click, and scroll as the
            list grows.
          </p>
        </div>
        <button class="btn ghost mode-toggle" type="button" @click="toggleMode">
          <span class="mode-dot" :class="{ dark: isDark }" />
          <span>{{ isDark ? 'Dark' : 'Light' }} mode</span>
        </button>
      </header>

      <form class="composer" @submit.prevent="addTodo">
        <div class="input-wrap">
          <input
            v-model="newTodo"
            type="text"
            maxlength="120"
            placeholder="Add a new task"
            aria-label="Add a new task"
          />
          <button class="btn primary" type="submit" :disabled="!newTodo.trim()">
            Add task
          </button>
        </div>
        <div class="stats">
          <div class="stat">
            <span>Total</span>
            <strong>{{ totalCount }}</strong>
          </div>
          <div class="stat">
            <span>Remaining</span>
            <strong>{{ remainingCount }}</strong>
          </div>
          <div v-if="completedCount" class="stat">
            <span>Done</span>
            <strong>{{ completedCount }}</strong>
          </div>
        </div>
      </form>

      <section class="list-card">
        <div class="list-head">
          <h2>Todo list</h2>
          <span class="list-hint">
            {{ visibleTodos.length }} / {{ totalCount }} shown
          </span>
        </div>
        <div ref="listRef" class="todo-list" aria-live="polite">
          <article
            v-for="(todo, index) in visibleTodos"
            :key="todo.id"
            class="todo-item"
            :class="{ done: todo.done }"
            :style="{ animationDelay: `${index * 0.03}s` }"
          >
            <label class="todo-check">
              <input v-model="todo.done" type="checkbox" />
              <span class="checkmark" />
            </label>
            <p class="todo-text">{{ todo.text }}</p>
            <div class="todo-actions">
              <button
                class="btn ghost"
                type="button"
                :disabled="!isSupported"
                :title="isSupported ? 'Copy task text' : 'Clipboard not supported'"
                @click="handleCopy(todo)"
              >
                {{ copied && lastCopiedId === todo.id ? 'Copied' : 'Copy' }}
              </button>
              <button class="btn danger" type="button" @click="removeTodo(todo.id)">
                Remove
              </button>
            </div>
          </article>

          <p v-if="!visibleTodos.length" class="empty">
            No tasks yet. Add your first todo above.
          </p>

          <div v-if="visibleTodos.length" class="list-footer">
            <span class="footer-status">
              <span v-if="isLoading">Loading more...</span>
              <span v-else-if="visibleTodos.length < totalCount">
                Scroll to load more
              </span>
              <span v-else>All caught up</span>
            </span>
          </div>
        </div>
      </section>
    </div>
  </div>
</template>

<style>
@import url('https://fonts.googleapis.com/css2?family=Sora:wght@400;500;600;700&family=Space+Mono:wght@400;700&display=swap');

:root {
  color-scheme: light;
  --bg: #f6f7fb;
  --bg-spot: rgba(59, 130, 246, 0.18);
  --bg-spot-2: rgba(34, 197, 94, 0.18);
  --card: rgba(255, 255, 255, 0.92);
  --surface: rgba(255, 255, 255, 0.84);
  --border: rgba(148, 163, 184, 0.35);
  --text: #0f172a;
  --muted: #64748b;
  --accent: #2563eb;
  --accent-strong: #1d4ed8;
  --accent-soft: rgba(37, 99, 235, 0.18);
  --danger: #ef4444;
  --danger-soft: rgba(239, 68, 68, 0.15);
  --shadow: 0 24px 60px rgba(15, 23, 42, 0.12);
  --radius: 22px;
}

:root[data-theme='dark'] {
  color-scheme: dark;
  --bg: #0b1222;
  --bg-spot: rgba(56, 189, 248, 0.18);
  --bg-spot-2: rgba(16, 185, 129, 0.16);
  --card: rgba(15, 23, 42, 0.86);
  --surface: rgba(15, 23, 42, 0.7);
  --border: rgba(148, 163, 184, 0.25);
  --text: #f8fafc;
  --muted: #94a3b8;
  --accent: #38bdf8;
  --accent-strong: #0ea5e9;
  --accent-soft: rgba(56, 189, 248, 0.2);
  --danger: #f87171;
  --danger-soft: rgba(248, 113, 113, 0.2);
  --shadow: 0 26px 70px rgba(2, 6, 23, 0.55);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: 'Sora', system-ui, -apple-system, sans-serif;
  color: var(--text);
  background:
    radial-gradient(900px circle at top left, var(--bg-spot), transparent 55%),
    radial-gradient(700px circle at bottom right, var(--bg-spot-2), transparent 50%),
    var(--bg);
  transition: background 0.4s ease, color 0.4s ease;
}

#app {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: clamp(20px, 4vw, 48px);
}

.page {
  width: min(980px, 100%);
}

.shell {
  display: grid;
  gap: clamp(20px, 3vw, 28px);
  padding: clamp(20px, 4vw, 36px);
  border-radius: var(--radius);
  background: var(--card);
  border: 1px solid var(--border);
  box-shadow: var(--shadow);
  backdrop-filter: blur(18px);
}

.header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
}

.eyebrow {
  text-transform: uppercase;
  letter-spacing: 0.2em;
  font-size: 0.72rem;
  color: var(--muted);
  margin: 0 0 10px;
}

h1 {
  margin: 0;
  font-size: clamp(2rem, 3vw, 2.6rem);
}

.subtitle {
  margin: 10px 0 0;
  color: var(--muted);
  max-width: 520px;
}

.composer {
  display: grid;
  gap: 16px;
}

.input-wrap {
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 12px;
}

input[type='text'] {
  padding: 12px 14px;
  border-radius: 14px;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  font-size: 1rem;
  transition: border 0.2s ease, box-shadow 0.2s ease;
}

input[type='text']:focus {
  outline: none;
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-soft);
}

.stats {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
}

.stat {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 8px 12px;
  border-radius: 999px;
  background: var(--surface);
  border: 1px solid var(--border);
  font-size: 0.9rem;
  color: var(--muted);
}

.stat strong {
  font-family: 'Space Mono', ui-monospace, SFMono-Regular, monospace;
  color: var(--text);
  font-size: 0.95rem;
}

.list-card {
  display: grid;
  gap: 16px;
}

.list-head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 12px;
}

.list-head h2 {
  margin: 0;
  font-size: 1.2rem;
}

.list-hint {
  font-size: 0.85rem;
  color: var(--muted);
  font-family: 'Space Mono', ui-monospace, SFMono-Regular, monospace;
}

.todo-list {
  max-height: clamp(320px, 55vh, 520px);
  overflow-y: auto;
  display: grid;
  gap: 12px;
  padding: 6px;
  margin: -6px;
}

.todo-item {
  display: grid;
  grid-template-columns: auto 1fr auto;
  gap: 12px;
  align-items: center;
  padding: 14px 16px;
  border-radius: 16px;
  background: var(--surface);
  border: 1px solid var(--border);
  animation: fadeUp 0.4s ease both;
}

.todo-item.done {
  opacity: 0.7;
}

.todo-text {
  margin: 0;
  font-size: 0.98rem;
}

.todo-item.done .todo-text {
  text-decoration: line-through;
  color: var(--muted);
}

.todo-check {
  display: inline-flex;
  align-items: center;
}

.todo-check input {
  width: 18px;
  height: 18px;
  accent-color: var(--accent);
}

.checkmark {
  display: none;
}

.todo-actions {
  display: inline-flex;
  gap: 8px;
  flex-wrap: wrap;
}

.btn {
  border: 1px solid var(--border);
  background: transparent;
  color: var(--text);
  padding: 8px 14px;
  border-radius: 999px;
  font-size: 0.88rem;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  gap: 8px;
  transition: all 0.2s ease;
}

.btn:disabled {
  cursor: not-allowed;
  opacity: 0.6;
}

.btn.primary {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
  font-weight: 600;
}

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

.btn.ghost:hover:not(:disabled) {
  border-color: var(--accent);
  color: var(--accent);
}

.btn.danger {
  border-color: transparent;
  color: var(--danger);
  background: var(--danger-soft);
}

.mode-toggle {
  white-space: nowrap;
}

.mode-dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: #facc15;
  box-shadow: 0 0 0 3px rgba(250, 204, 21, 0.2);
}

.mode-dot.dark {
  background: #38bdf8;
  box-shadow: 0 0 0 3px rgba(56, 189, 248, 0.2);
}

.empty {
  text-align: center;
  padding: 32px 12px;
  color: var(--muted);
  border-radius: 16px;
  border: 1px dashed var(--border);
}

.list-footer {
  text-align: center;
  font-size: 0.85rem;
  color: var(--muted);
  padding: 8px 0 12px;
}

@keyframes fadeUp {
  from {
    opacity: 0;
    transform: translateY(8px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@media (max-width: 820px) {
  .header {
    flex-direction: column;
    align-items: flex-start;
  }

  .input-wrap {
    grid-template-columns: 1fr;
  }

  .todo-item {
    grid-template-columns: auto 1fr;
  }

  .todo-actions {
    grid-column: 1 / -1;
    justify-content: flex-end;
  }
}
</style>