import React, { useState, useEffect, useCallback } from 'react';
import { useNavigate } from 'react-router-dom';
import { toast } from 'sonner';
import { AlertCircle, CalendarDays, Copy, Eye, KeyRound, Moon, RefreshCw, ShieldOff, Sun, Users } from 'lucide-react';
import { api } from '@/api';
import { cn } from '@/lib/utils';
import { Button } from '@/components/ui/button';
import { Input } from '@/components/ui/input';
import {
  Select, SelectTrigger, SelectValue, SelectContent, SelectItem,
} from '@/components/ui/select';
import { Switch } from '@/components/ui/switch';
import { useTheme } from '@/contexts/ThemeContext';
import { useAuth } from '@/hooks/useAuth';

export const LINK_IMPORT_PREF_KEY = 'link_import_ask';
export function getLinkImportPref() {
  return localStorage.getItem(LINK_IMPORT_PREF_KEY) !== 'false';
}

// ─── Card wrapper ─────────────────────────────────────────────────────────────

function SectionCard({ title, children }) {
  return (
    <div className="table-surface mb-4">
      <div className="px-6 py-4 border-b border-border/50">
        <h2 className="text-xs font-bold uppercase tracking-widest text-muted-foreground">{title}</h2>
      </div>
      <div className="divide-y divide-border/50">
        {children}
      </div>
    </div>
  );
}

// ─── Setting Row ──────────────────────────────────────────────────────────────

function SettingRow({ label, description, children }) {
  return (
    <div className="px-4 py-4 flex flex-col gap-3 sm:px-6 sm:flex-row sm:items-center sm:justify-between">
      <div className="flex-1 min-w-0 sm:mr-8">
        <p className="text-sm font-medium">{label}</p>
        {description && (
          <p className="text-xs text-muted-foreground mt-0.5">{description}</p>
        )}
      </div>
      <div className="shrink-0">
        {children}
      </div>
    </div>
  );
}

// ─── Theme Card ───────────────────────────────────────────────────────────────

function ThemeCard({ value, label, icon: Icon, currentTheme, onSelect }) {
  const selected = currentTheme === value;
  return (
    <button
      type="button"
      onClick={() => onSelect(value)}
      className={cn(
        'flex flex-col items-center gap-1.5 rounded-lg border px-3 py-2.5 text-xs font-medium transition-all',
        'hover:border-muted-foreground/50',
        selected
          ? 'border-primary bg-primary/5 text-primary'
          : 'border-border bg-card text-muted-foreground',
      )}
    >
      <Icon className="h-4 w-4" />
      <span>{label}</span>
    </button>
  );
}

// ─── Appearance Section ───────────────────────────────────────────────────────

function AppearanceSection() {
  const { theme, setTheme } = useTheme();

  return (
    <SectionCard title="Appearance">
      <SettingRow label="Theme" description="Choose your preferred color scheme.">
        <div className="flex gap-2">
          <ThemeCard value="light" label="Light" icon={Sun} currentTheme={theme} onSelect={setTheme} />
          <ThemeCard value="dark"  label="Dark"  icon={Moon} currentTheme={theme} onSelect={setTheme} />
        </div>
      </SettingRow>
    </SectionCard>
  );
}

function LoginModeRecoverySection() {
  const navigate = useNavigate();
  const { singleUserMode, refresh } = useAuth();
  const [restoring, setRestoring] = useState(false);

  if (!singleUserMode) return null;

  const handleRestore = async () => {
    setRestoring(true);
    try {
      await api.restoreMultiUserMode();
      toast.success('Multi-user login restored.');
      refresh();
      navigate('/login', { replace: true });
    } catch (err) {
      toast.error(err.message || 'Failed to restore multi-user mode.');
    } finally {
      setRestoring(false);
    }
  };

  return (
    <SectionCard title="Login Mode">
      <SettingRow
        label="Single-user mode is active"
        description="Restore the normal login screen so each user signs in with their own account."
      >
        <Button size="sm" variant="outline" onClick={handleRestore} disabled={restoring}>
          <Users className="h-3.5 w-3.5 mr-1.5" />
          {restoring ? 'Restoring…' : 'Restore Multi-User Mode'}
        </Button>
      </SettingRow>
    </SectionCard>
  );
}

// ─── Settings Skeleton ────────────────────────────────────────────────────────

function SettingsSkeleton() {
  return (
    <div>
      {/* Page header */}
      <div className="mb-8">
        <h1 className="h-8 w-48 rounded-md bg-muted/50"></h1>
        <p className="h-4 w-64 mt-2 rounded-md bg-muted/50"></p>
      </div>

      {/* Appearance */}
      <div className="table-surface mb-4">
        <div className="px-6 py-4 border-b border-border/50">
          <h2 className="h-3 w-24 rounded bg-muted/50"></h2>
        </div>
        <div className="divide-y divide-border/50">
          <div className="px-6 py-4 flex flex-col gap-3 sm:flex-row sm:items-center sm:justify-between">
            <div className="flex-1 min-w-0 sm:mr-8">
              <p className="h-4 w-32 rounded-md bg-muted/50"></p>
              <p className="h-3 w-48 mt-2 rounded-md bg-muted/50"></p>
            </div>
            <div className="shrink-0 flex gap-2">
              <div className="h-12 w-20 rounded-lg bg-muted/50"></div>
              <div className="h-12 w-20 rounded-lg bg-muted/50"></div>
            </div>
          </div>
        </div>
      </div>

      {/* Login mode */}
      <div className="table-surface mb-4">
        <div className="px-6 py-4 border-b border-border/50">
          <h2 className="h-3 w-24 rounded bg-muted/50"></h2>
        </div>
        <div className="divide-y divide-border/50">
          <div className="px-6 py-4 flex flex-col gap-3 sm:flex-row sm:items-center sm:justify-between">
            <div className="flex-1 min-w-0 sm:mr-8">
              <p className="h-4 w-48 rounded-md bg-muted/50"></p>
              <p className="h-3 w-64 mt-2 rounded-md bg-muted/50"></p>
            </div>
            <div className="shrink-0 h-9 w-48 rounded-md bg-muted/50"></div>
          </div>
        </div>
      </div>

      {/* General */}
      <div className="table-surface mb-4">
        <div className="px-6 py-4 border-b border-border/50">
          <h2 className="h-3 w-24 rounded bg-muted/50"></h2>
        </div>
        <div className="divide-y divide-border/50">
          <div className="px-6 py-4 flex flex-col gap-3 sm:flex-row sm:items-center sm:justify-between">
            <div className="flex-1 min-w-0 sm:mr-8">
              <p className="h-4 w-32 rounded-md bg-muted/50"></p>
              <p className="h-3 w-48 mt-2 rounded-md bg-muted/50"></p>
            </div>
            <div className="shrink-0 h-9 w-32 rounded-md bg-muted/50"></div>
          </div>
          <div className="px-6 py-4 flex flex-col gap-3 sm:flex-row sm:items-center sm:justify-between">
            <div className="flex-1 min-w-0 sm:mr-8">
              <p className="h-4 w-32 rounded-md bg-muted/50"></p>
              <p className="h-3 w-48 mt-2 rounded-md bg-muted/50"></p>
            </div>
            <div className="shrink-0 h-9 w-32 rounded-md bg-muted/50"></div>
          </div>
        </div>
      </div>

      {/* Billing */}
      <div className="table-surface mb-4">
        <div className="px-6 py-4 border-b border-border/50">
          <h2 className="h-3 w-24 rounded bg-muted/50"></h2>
        </div>
        <div className="divide-y divide-border/50">
          <div className="px-6 py-4 flex flex-col gap-3 sm:flex-row sm:items-center sm:justify-between">
            <div className="flex-1 min-w-0 sm:mr-8">
              <p className="h-4 w-32 rounded-md bg-muted/50"></p>
              <p className="h-3 w-48 mt-2 rounded-md bg-muted/50"></p>
            </div>
            <div className="shrink-0 h-9 w-32 rounded-md bg-muted/50"></div>
          </div>
        </div>
      </div>
    </div>
  );
}

// ─── Link-import preference toggle (localStorage-backed) ─────────────────────

function LinkImportToggle() {
  const [enabled, setEnabled] = useState(getLinkImportPref);

  function toggle(next) {
    localStorage.setItem(LINK_IMPORT_PREF_KEY, String(next));
    setEnabled(next);
    toast.success(next
      ? 'Past payments will be offered for import when linking a bill.'
      : 'Past payment import prompt is disabled.');
  }

  return (
    <SettingRow
      label="Ask to import past payments when linking"
      description="When you connect a bill to bank transactions (via merchant rule or recommendation), offer to import matching past payments as well."
    >
      <Switch checked={enabled} onCheckedChange={toggle} aria-label="Ask to import past payments when linking" />
    </SettingRow>
  );
}

function CalendarFeedSection() {
  const [feed, setFeed] = useState(null);
  const [preview, setPreview] = useState([]);
  const [loading, setLoading] = useState(true);
  const [busy, setBusy] = useState(null);

  const loadFeed = useCallback(async () => {
    setLoading(true);
    try {
      const data = await api.calendarFeed();
      setFeed(data);
      if (data?.active) {
        const nextPreview = await api.calendarFeedPreview(10);
        setPreview(nextPreview.events || []);
      } else {
        setPreview([]);
      }
    } catch (err) {
      toast.error(err.message || 'Failed to load calendar feed.');
    } finally {
      setLoading(false);
    }
  }, []);

  useEffect(() => { loadFeed(); }, [loadFeed]);

  const active = !!feed?.active && !!feed?.feed_url;

  async function createFeed() {
    setBusy('create');
    try {
      const data = await api.createCalendarFeed();
      setFeed(data);
      const nextPreview = await api.calendarFeedPreview(10);
      setPreview(nextPreview.events || []);
      toast.success('Calendar feed created.');
    } catch (err) {
      toast.error(err.message || 'Failed to create calendar feed.');
    } finally {
      setBusy(null);
    }
  }

  async function copyFeedUrl() {
    if (!feed?.feed_url) return;
    try {
      await navigator.clipboard.writeText(feed.feed_url);
      toast.success('Calendar feed URL copied.');
    } catch {
      toast.error('Copy failed. Select the URL and copy it manually.');
    }
  }

  async function regenerateFeed() {
    setBusy('regenerate');
    try {
      const data = await api.regenerateCalendarFeed();
      setFeed(data);
      const nextPreview = await api.calendarFeedPreview(10);
      setPreview(nextPreview.events || []);
      toast.success('Calendar feed regenerated. Update any subscribed calendars with the new URL.');
    } catch (err) {
      toast.error(err.message || 'Failed to regenerate calendar feed.');
    } finally {
      setBusy(null);
    }
  }

  async function revokeFeed() {
    setBusy('revoke');
    try {
      const data = await api.revokeCalendarFeed();
      setFeed(data);
      setPreview([]);
      toast.success('Calendar feed revoked.');
    } catch (err) {
      toast.error(err.message || 'Failed to revoke calendar feed.');
    } finally {
      setBusy(null);
    }
  }

  return (
    <SectionCard title="Calendar Feed">
      <div className="px-4 py-4 sm:px-6">
        <div className="flex flex-col gap-4 lg:flex-row lg:items-start lg:justify-between">
          <div className="min-w-0 flex-1">
            <div className="flex items-center gap-2">
              <CalendarDays className="h-4 w-4 text-primary" />
              <p className="text-sm font-medium">Subscribe from Apple Calendar, Google Calendar, Android, or Outlook</p>
            </div>
            <p className="mt-1 max-w-2xl text-xs leading-5 text-muted-foreground">
              This creates a private ICS feed URL. Calendar apps refresh subscribed feeds on their own schedule, so Google and Apple may take time to show updates.
            </p>
          </div>

          {!loading && !active && (
            <Button size="sm" onClick={createFeed} disabled={!!busy} className="w-full gap-2 sm:w-auto">
              <KeyRound className="h-3.5 w-3.5" />
              {busy === 'create' ? 'Creating...' : 'Create Feed'}
            </Button>
          )}
        </div>

        {loading && (
          <div className="mt-4 h-24 animate-pulse rounded-lg bg-muted/50" />
        )}

        {!loading && active && (
          <div className="mt-4 space-y-4">
            <div className="rounded-lg border border-amber-500/25 bg-amber-500/[0.08] px-3 py-2 text-xs leading-5 text-amber-800 dark:text-amber-200">
              Anyone with this URL can see the bill events in this feed. Regenerate or revoke it if it was shared somewhere it should not be.
            </div>

            <div className="flex flex-col gap-2 sm:flex-row">
              <Input value={feed.feed_url} readOnly className="min-w-0 flex-1 font-mono text-xs" aria-label="Calendar feed URL" />
              <Button size="sm" variant="outline" onClick={copyFeedUrl} className="gap-2">
                <Copy className="h-3.5 w-3.5" />
                Copy
              </Button>
              <Button asChild size="sm" variant="outline" className="gap-2">
                <a href={feed.feed_url} target="_blank" rel="noreferrer">
                  <Eye className="h-3.5 w-3.5" />
                  Preview ICS
                </a>
              </Button>
            </div>

            <div className="grid gap-3 text-xs text-muted-foreground lg:grid-cols-4">
              <div className="rounded-md bg-muted/35 p-3">
                <p className="font-medium text-foreground">Apple Calendar</p>
                <p className="mt-1">Add a calendar subscription using the copied URL. The feed uses all-day DATE events to avoid timezone shifts.</p>
              </div>
              <div className="rounded-md bg-muted/35 p-3">
                <p className="font-medium text-foreground">Google Calendar</p>
                <p className="mt-1">Use Google Calendar on the web: Other calendars, From URL. Android sync follows your Google Calendar settings.</p>
              </div>
              <div className="rounded-md bg-muted/35 p-3">
                <p className="font-medium text-foreground">Outlook</p>
                <p className="mt-1">Subscribe from Outlook on the web with this URL. Imported copies will not update; subscribed calendars will.</p>
              </div>
              <div className="rounded-md bg-muted/35 p-3">
                <p className="font-medium text-foreground">Duplicate Safety</p>
                <p className="mt-1">Bill Tracker emits stable event IDs per bill cycle, so subscribed calendars can update without double-adding events.</p>
              </div>
            </div>

            <div className="rounded-lg border border-border/70">
              <div className="flex items-center justify-between border-b border-border/60 px-3 py-2">
                <p className="text-xs font-semibold uppercase tracking-wide text-muted-foreground">Next events</p>
                <span className="text-xs text-muted-foreground">
                  Last fetched: {feed.last_used_at ? new Date(feed.last_used_at).toLocaleString() : 'Not yet'}
                </span>
              </div>
              <div className="divide-y divide-border/50">
                {preview.length === 0 && (
                  <p className="px-3 py-4 text-sm text-muted-foreground">No upcoming bill events in the preview window.</p>
                )}
                {preview.map(event => (
                  <div key={event.uid} className="flex items-center justify-between gap-3 px-3 py-2 text-sm">
                    <div className="min-w-0">
                      <p className="truncate font-medium">{event.name}</p>
                      <p className="text-xs text-muted-foreground">{event.due_date} · {event.cycle_type}</p>
                    </div>
                    <span className="tracker-number shrink-0 text-xs font-semibold">${Number(event.amount || 0).toFixed(2)}</span>
                  </div>
                ))}
              </div>
            </div>

            <div className="flex flex-col gap-2 sm:flex-row sm:justify-end">
              <Button size="sm" variant="outline" onClick={regenerateFeed} disabled={!!busy} className="gap-2">
                <RefreshCw className="h-3.5 w-3.5" />
                {busy === 'regenerate' ? 'Regenerating...' : 'Regenerate URL'}
              </Button>
              <Button size="sm" variant="outline" onClick={revokeFeed} disabled={!!busy} className="gap-2 border-destructive/30 text-destructive hover:bg-destructive/10">
                <ShieldOff className="h-3.5 w-3.5" />
                {busy === 'revoke' ? 'Revoking...' : 'Revoke Feed'}
              </Button>
            </div>
          </div>
        )}
      </div>
    </SectionCard>
  );
}

// ─── SettingsPage ─────────────────────────────────────────────────────────────

export default function SettingsPage() {
  const DEFAULTS = {
    currency:              'USD',
    date_format:           'MM/DD/YYYY',
    grace_period_days:     3,
    drift_threshold_pct:   '5',
  };

  const [settings, setSettings] = useState(DEFAULTS);
  const [loading,   setLoading]   = useState(true);
  const [loadError, setLoadError] = useState(null);
  const [saving,    setSaving]    = useState(false);

  const loadSettings = useCallback(() => {
    setLoading(true);
    setLoadError(null);
    api.settings()
      .then((d) => setSettings({ ...DEFAULTS, ...d }))
      .catch((err) => setLoadError(err.message || 'Failed to load settings'))
      .finally(() => setLoading(false));
  }, []); // eslint-disable-line react-hooks/exhaustive-deps

  useEffect(() => { loadSettings(); }, [loadSettings]);

  const set = (k, v) => setSettings((p) => ({ ...p, [k]: v }));

  const handleSave = async () => {
    setSaving(true);
    try {
      await api.saveSettings({
        currency: settings.currency,
        date_format: settings.date_format,
        grace_period_days: settings.grace_period_days,
        drift_threshold_pct: settings.drift_threshold_pct,
      });
      toast.success('Settings saved.');
    } catch (err) {
      toast.error(err.message || 'Failed to save settings.');
    } finally {
      setSaving(false);
    }
  };

  if (loading) {
    return (
      <div className="flex items-center justify-center py-12">
        <SettingsSkeleton />
      </div>
    );
  }

  if (loadError) {
    return (
      <div className="flex flex-col items-center justify-center py-24 text-center rounded-xl border border-destructive/20 bg-destructive/5">
        <AlertCircle className="h-10 w-10 text-destructive mb-3" />
        <p className="text-sm font-medium text-foreground">Failed to load settings</p>
        <p className="mt-1 text-xs text-muted-foreground">{loadError}</p>
        <Button size="sm" variant="outline" onClick={loadSettings}
          className="mt-4 gap-1.5 text-xs border-destructive/30 hover:bg-destructive/10 hover:text-destructive hover:border-destructive/50">
          <RefreshCw className="h-3 w-3" />
          Try again
        </Button>
      </div>
    );
  }

  return (
    <div>

      {/* Page header — flat on background */}
      <div className="mb-8">
        <h1 className="text-2xl font-bold tracking-tight">Settings</h1>
        <p className="text-sm text-muted-foreground mt-0.5">Manage your display and billing preferences</p>
      </div>

      {/* Appearance */}
      <AppearanceSection />

      {/* Login mode recovery */}
      <LoginModeRecoverySection />

      {/* General */}
      <SectionCard title="General">
        <SettingRow label="Currency" description="Default currency for bill amounts.">
          <Select value={settings.currency} onValueChange={(v) => set('currency', v)}>
            <SelectTrigger className="w-48">
              <SelectValue />
            </SelectTrigger>
            <SelectContent>
              <SelectItem value="USD">USD — US Dollar</SelectItem>
              <SelectItem value="EUR">EUR — Euro</SelectItem>
              <SelectItem value="GBP">GBP — British Pound</SelectItem>
              <SelectItem value="CAD">CAD — Canadian Dollar</SelectItem>
            </SelectContent>
          </Select>
        </SettingRow>

        <SettingRow label="Date format" description="How dates are displayed throughout the app.">
          <Select value={settings.date_format} onValueChange={(v) => set('date_format', v)}>
            <SelectTrigger className="w-48">
              <SelectValue />
            </SelectTrigger>
            <SelectContent>
              <SelectItem value="MM/DD/YYYY">MM/DD/YYYY</SelectItem>
              <SelectItem value="DD/MM/YYYY">DD/MM/YYYY</SelectItem>
              <SelectItem value="YYYY-MM-DD">YYYY-MM-DD</SelectItem>
            </SelectContent>
          </Select>
        </SettingRow>
      </SectionCard>

      {/* Billing Behavior */}
      <SectionCard title="Billing Behavior">
        <LinkImportToggle />
        <SettingRow
          label="Grace period"
          description="Days after the due date before a bill is marked overdue."
        >
          <div className="flex items-center gap-2">
            <Input
              type="number"
              min={0}
              max={30}
              value={settings.grace_period_days}
              onChange={(e) => set('grace_period_days', parseInt(e.target.value, 10) || 0)}
              className="w-20"
            />
            <span className="text-sm text-muted-foreground">days</span>
          </div>
        </SettingRow>
        <SettingRow
          label="Price change sensitivity"
          description="Flag a bill when recent payments differ from the expected amount by at least this percentage."
        >
          <div className="flex items-center gap-2">
            <Input
              type="number"
              min={1}
              max={25}
              step={1}
              value={settings.drift_threshold_pct ?? '5'}
              onChange={(e) => set('drift_threshold_pct', e.target.value)}
              className="w-20 font-mono"
            />
            <span className="text-sm text-muted-foreground">%</span>
          </div>
        </SettingRow>
      </SectionCard>

      {/* Save button — right-aligned below all cards */}
      <div className="flex justify-end mt-6">
        <Button size="sm" onClick={handleSave} disabled={saving}>
          {saving ? 'Saving…' : 'Save Settings'}
        </Button>
      </div>

      <div id="calendar-feed" className="mt-6 scroll-mt-24">
        <CalendarFeedSection />
      </div>

    </div>
  );
}