import React, { useState, useEffect, useCallback, useRef } from 'react';
import { Link } from 'react-router-dom';
import { toast } from 'sonner';
import {
  ChevronDown, Plus, Pencil, Trash2, ReceiptText,
} from 'lucide-react';
import { api } from '@/api.js';
import { Button, buttonVariants } from '@/components/ui/button';
import { Input } from '@/components/ui/input';
import { InputDialog } from '@/components/ui/input-dialog';
import {
  AlertDialog, AlertDialogContent, AlertDialogHeader, AlertDialogTitle,
  AlertDialogDescription, AlertDialogFooter, AlertDialogCancel, AlertDialogAction,
} from '@/components/ui/alert-dialog';
import {
  Tooltip, TooltipContent, TooltipProvider, TooltipTrigger,
} from '@/components/ui/tooltip';
import { cn, fmt, fmtDate } from '@/lib/utils';

function plural(count, label) {
  return `${count} ${label}${count === 1 ? '' : 's'}`;
}

function billPreview(names = []) {
  if (!names.length) return 'No bills in this category yet.';
  const visible = names.slice(0, 4).join(', ');
  const more = names.length > 4 ? `, +${names.length - 4} more` : '';
  return `${visible}${more}`;
}

function Chip({ value, label, tone = 'muted', details }) {
  const toneClass = {
    active: 'border-primary/25 bg-primary/10 text-primary',
    muted: 'border-border bg-muted/55 text-muted-foreground',
    info: 'border-sky-500/25 bg-sky-500/10 text-sky-600 dark:text-sky-400',
  }[tone];

  return (
    <Tooltip>
      <TooltipTrigger asChild>
        <span
          tabIndex={0}
          title={details || label}
          aria-label={details || label}
          className={cn(
            'inline-flex h-6 min-w-7 items-center justify-center rounded-full border px-2 text-[11px] font-semibold tabular-nums',
            'focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring',
            toneClass,
          )}
        >
          {value}
        </span>
      </TooltipTrigger>
      <TooltipContent className="max-w-64 leading-relaxed">
        <p>{label}</p>
        {details && details !== label && <p className="opacity-85">{details}</p>}
      </TooltipContent>
    </Tooltip>
  );
}

function StatChips({ category }) {
  const names = billPreview(category.bill_names);
  return (
    <div className="flex flex-wrap items-center gap-1.5">
      <Chip
        value={category.active_bill_count || 0}
        label={plural(category.active_bill_count || 0, 'active bill')}
        details={names}
        tone="active"
      />
      <Chip
        value={category.inactive_bill_count || 0}
        label={plural(category.inactive_bill_count || 0, 'inactive bill')}
        details={names}
      />
      <Chip
        value={category.payment_count || 0}
        label={plural(category.payment_count || 0, 'payment')}
        details={names}
        tone="info"
      />
    </div>
  );
}

function ChipLegend() {
  const items = [
    ['Active', 'active'],
    ['Inactive', 'muted'],
    ['Payments', 'info'],
  ];

  return (
    <div className="flex flex-wrap items-center gap-2 text-xs text-muted-foreground">
      {items.map(([label, tone]) => (
        <span key={label} className="inline-flex items-center gap-1.5">
          <span className={cn(
            'h-2.5 w-2.5 rounded-full border',
            tone === 'active' && 'border-primary/30 bg-primary/45',
            tone === 'muted' && 'border-border bg-muted',
            tone === 'info' && 'border-sky-500/30 bg-sky-500/45',
          )} />
          {label}
        </span>
      ))}
    </div>
  );
}

function StatusPill({ active }) {
  return (
    <span className={cn(
      'inline-flex rounded-full border px-2 py-0.5 text-[10px] font-semibold uppercase tracking-wide',
      active
        ? 'border-emerald-500/25 bg-emerald-500/10 text-emerald-600 dark:text-emerald-400'
        : 'border-border bg-muted text-muted-foreground',
    )}>
      {active ? 'Active' : 'Inactive'}
    </span>
  );
}

function BillName({ bill }) {
  const label = `${bill.name}: due day ${bill.due_day}, ${fmt(bill.expected_amount)} expected`;
  return (
    <Tooltip>
      <TooltipTrigger asChild>
        <span title={label} className="font-medium text-foreground underline-offset-4 hover:underline">
          {bill.name}
        </span>
      </TooltipTrigger>
      <TooltipContent className="max-w-72 leading-relaxed">
        <p>{label}</p>
        <p className="opacity-85">
          {plural(bill.payment_count || 0, 'payment')} / {fmt(bill.total_paid)} paid
        </p>
      </TooltipContent>
    </Tooltip>
  );
}

function ExpandedBills({ category }) {
  const bills = category.bills || [];

  if (!bills.length) {
    return (
      <div className="border-t border-border/60 bg-muted/15 px-4 py-5 sm:px-6">
        <div className="flex flex-col gap-3 rounded-lg border border-dashed border-border/70 bg-background/65 p-4 text-sm text-muted-foreground sm:flex-row sm:items-center sm:justify-between">
          <span>No bills in this category yet.</span>
          <Button asChild variant="outline" size="sm" className="w-fit">
            <Link to="/bills">Open Bills</Link>
          </Button>
        </div>
      </div>
    );
  }

  return (
    <div className="border-t border-border/60 bg-muted/15 px-4 py-4 sm:px-5">
      <div className="hidden overflow-hidden rounded-lg border border-border/60 bg-background/75 lg:block">
        <table className="w-full text-sm">
          <thead className="bg-muted/45 text-xs uppercase tracking-wide text-muted-foreground">
            <tr>
              <th className="px-4 py-3 text-left font-semibold">Bill</th>
              <th className="px-4 py-3 text-left font-semibold">State</th>
              <th className="px-4 py-3 text-right font-semibold">Expected</th>
              <th className="px-4 py-3 text-right font-semibold">Paid</th>
              <th className="px-4 py-3 text-right font-semibold">History</th>
            </tr>
          </thead>
          <tbody className="divide-y divide-border/50">
            {bills.map(bill => (
              <tr key={bill.id} className="hover:bg-muted/25">
                <td className="px-4 py-3">
                  <BillName bill={bill} />
                  <p className="mt-1 text-xs text-muted-foreground">Due day {bill.due_day}</p>
                </td>
                <td className="px-4 py-3"><StatusPill active={bill.active} /></td>
                <td className="px-4 py-3 text-right font-mono">{fmt(bill.expected_amount)}</td>
                <td className="px-4 py-3 text-right font-mono">{fmt(bill.total_paid)}</td>
                <td className="px-4 py-3 text-right">
                  <p className="tabular-nums">{plural(bill.payment_count || 0, 'payment')}</p>
                  <p className="mt-1 text-xs tabular-nums text-muted-foreground">{fmtDate(bill.last_paid_date)}</p>
                </td>
              </tr>
            ))}
          </tbody>
        </table>
      </div>

      <div className="grid gap-3 lg:hidden">
        {bills.map(bill => (
          <div key={bill.id} className="rounded-lg border border-border/60 bg-background/75 p-4">
            <div className="flex items-start justify-between gap-3">
              <div className="min-w-0">
                <p className="truncate text-sm"><BillName bill={bill} /></p>
                <p className="mt-1 text-xs text-muted-foreground">Due day {bill.due_day}</p>
              </div>
              <StatusPill active={bill.active} />
            </div>
            <div className="mt-4 grid grid-cols-2 gap-3 text-xs sm:grid-cols-4">
              <div>
                <p className="text-muted-foreground">Expected</p>
                <p className="mt-0.5 font-mono font-semibold">{fmt(bill.expected_amount)}</p>
              </div>
              <div>
                <p className="text-muted-foreground">Paid</p>
                <p className="mt-0.5 font-mono font-semibold">{fmt(bill.total_paid)}</p>
              </div>
              <div>
                <p className="text-muted-foreground">Payments</p>
                <p className="mt-0.5 font-semibold tabular-nums">{bill.payment_count || 0}</p>
              </div>
              <div>
                <p className="text-muted-foreground">Last Paid</p>
                <p className="mt-0.5 font-semibold tabular-nums">{fmtDate(bill.last_paid_date)}</p>
              </div>
            </div>
          </div>
        ))}
      </div>
    </div>
  );
}

export default function CategoriesPage() {
  const [categories, setCategories] = useState([]);
  const [loading, setLoading]       = useState(true);
  const [newName, setNewName]       = useState('');
  const [adding, setAdding]         = useState(false);
  const [expanded, setExpanded]     = useState(() => new Set());
  const addInputRef                 = useRef(null);

  const [renameTarget, setRenameTarget] = useState(null);
  const [renaming, setRenaming]         = useState(false);
  const [deleteTarget, setDeleteTarget] = useState(null);
  const [deleting, setDeleting]         = useState(false);

  const load = useCallback(async () => {
    try {
      const cats = await api.categories();
      setCategories(cats);
    } catch (err) {
      toast.error(err.message);
    } finally {
      setLoading(false);
    }
  }, []);

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

  function toggleCategory(id) {
    setExpanded(prev => {
      const next = new Set(prev);
      if (next.has(id)) next.delete(id);
      else next.add(id);
      return next;
    });
  }

  function onRowKeyDown(event, id) {
    if (event.key === 'Enter' || event.key === ' ') {
      event.preventDefault();
      toggleCategory(id);
    }
  }

  async function handleAdd(e) {
    e.preventDefault();
    const trimmed = newName.trim();
    if (!trimmed) {
      toast.error('Enter a category name');
      addInputRef.current?.focus();
      return;
    }
    setAdding(true);
    try {
      await api.createCategory({ name: trimmed });
      toast.success(`"${trimmed}" added`);
      setNewName('');
      addInputRef.current?.focus();
      load();
    } catch (err) {
      toast.error(err.message);
    } finally {
      setAdding(false);
    }
  }

  function openRename(event, cat) {
    event.stopPropagation();
    setRenameTarget(cat);
  }

  async function handleRename(name) {
    setRenaming(true);
    try {
      await api.updateCategory(renameTarget.id, { name });
      toast.success('Category renamed');
      setRenameTarget(null);
      load();
    } catch (err) {
      toast.error(err.message);
    } finally {
      setRenaming(false);
    }
  }

  function openDelete(event, cat) {
    event.stopPropagation();
    setDeleteTarget(cat);
  }

  async function handleDelete() {
    setDeleting(true);
    try {
      await api.deleteCategory(deleteTarget.id);
      toast.success(`"${deleteTarget.name}" deleted`);
      setExpanded(prev => {
        const next = new Set(prev);
        next.delete(deleteTarget.id);
        return next;
      });
      setDeleteTarget(null);
      load();
    } catch (err) {
      toast.error(err.message || 'Could not delete category.');
    } finally {
      setDeleting(false);
    }
  }

  const activeBills = categories.reduce((sum, cat) => sum + (cat.active_bill_count || 0), 0);
  const inactiveBills = categories.reduce((sum, cat) => sum + (cat.inactive_bill_count || 0), 0);
  const paymentCount = categories.reduce((sum, cat) => sum + (cat.payment_count || 0), 0);

  return (
    <TooltipProvider delayDuration={180}>
      <div className="mx-auto w-full max-w-5xl space-y-5">
        <div className="flex flex-col gap-4 lg:flex-row lg:items-end lg:justify-between">
          <div className="min-w-0">
            <div className="flex items-center gap-2">
              <div className="flex h-9 w-9 items-center justify-center rounded-lg border border-border/70 bg-card shadow-sm">
                <ReceiptText className="h-4 w-4 text-primary" />
              </div>
              <div>
                <h1 className="text-2xl font-bold tracking-tight">Categories</h1>
                <p className="mt-0.5 text-sm text-muted-foreground">Organize bills by purpose, status, and payment activity.</p>
              </div>
            </div>
          </div>
          <ChipLegend />
        </div>

        <div className="grid gap-3 md:grid-cols-[1fr_minmax(20rem,26rem)]">
          <div className="grid grid-cols-2 gap-3 sm:grid-cols-4">
            {[
              ['Categories', categories.length],
              ['Active bills', activeBills],
              ['Inactive', inactiveBills],
              ['Payments', paymentCount],
            ].map(([label, value]) => (
              <div key={label} className="rounded-xl border border-border/70 bg-card/80 px-4 py-3 shadow-sm">
                <p className="text-[11px] font-semibold uppercase tracking-wide text-muted-foreground">{label}</p>
                <p className="mt-1 font-mono text-xl font-bold text-foreground">{value}</p>
              </div>
            ))}
          </div>

          <form onSubmit={handleAdd} className="flex min-w-0 flex-col gap-2 rounded-xl border border-border/70 bg-card/80 p-3 shadow-sm sm:flex-row md:flex-col lg:flex-row">
            <Input
              ref={addInputRef}
              value={newName}
              onChange={(e) => setNewName(e.target.value)}
              placeholder="New category name..."
              disabled={adding}
              className="h-9 min-w-0 text-sm"
            />
            <Button type="submit" size="sm" className="h-9 shrink-0 sm:w-auto" disabled={adding || !newName.trim()}>
              <Plus className="mr-1.5 h-3.5 w-3.5" />
              {adding ? 'Adding...' : 'Add'}
            </Button>
          </form>
        </div>

        <div className="table-surface overflow-hidden rounded-xl">
          {loading ? (
            <div className="py-16 text-center text-sm text-muted-foreground">Loading...</div>
          ) : categories.length === 0 ? (
            <div className="py-16 text-center text-sm text-muted-foreground">
              No categories yet. Add one above.
            </div>
          ) : (
            <div className="divide-y divide-border/50">
              {categories.map((cat) => {
                const isExpanded = expanded.has(cat.id);
                const preview = billPreview(cat.bill_names);
                return (
                  <section key={cat.id} className="bg-card/35">
                    <div
                      role="button"
                      tabIndex={0}
                      aria-expanded={isExpanded}
                      title={preview}
                      onClick={() => toggleCategory(cat.id)}
                      onKeyDown={event => onRowKeyDown(event, cat.id)}
                      className={cn(
                        'group grid cursor-pointer gap-4 px-4 py-4 transition-colors sm:px-5 md:grid-cols-[minmax(0,1fr)_auto] md:items-center',
                        'hover:bg-muted/35 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-inset',
                        isExpanded && 'bg-muted/25',
                      )}
                    >
                      <div className="flex min-w-0 flex-1 items-start gap-3">
                        <ChevronDown
                          className={cn(
                            'mt-0.5 h-4 w-4 shrink-0 text-muted-foreground transition-transform',
                            isExpanded && 'rotate-180 text-foreground',
                          )}
                        />
                        <div className="min-w-0 flex-1">
                          <div className="flex flex-col gap-2 sm:flex-row sm:items-center">
                            <Tooltip>
                              <TooltipTrigger asChild>
                                <span className="truncate text-sm font-semibold tracking-tight text-foreground" title={preview}>
                                  {cat.name}
                                </span>
                              </TooltipTrigger>
                              <TooltipContent className="max-w-72 leading-relaxed">
                                <p className="font-medium">{cat.name}</p>
                                <p className="opacity-85">{preview}</p>
                              </TooltipContent>
                            </Tooltip>
                            <StatChips category={cat} />
                          </div>
                          <p className="mt-1 line-clamp-1 text-xs text-muted-foreground">{preview}</p>
                        </div>
                      </div>

                      <div className="flex items-center justify-end gap-1 opacity-80 transition-opacity group-hover:opacity-100">
                        <Button
                          type="button"
                          variant="ghost"
                          size="icon"
                          className="h-8 w-8"
                          onClick={(event) => openRename(event, cat)}
                          aria-label={`Rename ${cat.name}`}
                        >
                          <Pencil className="h-3.5 w-3.5" />
                        </Button>
                        <Button
                          type="button"
                          variant="ghost"
                          size="icon"
                          className="h-8 w-8 text-destructive hover:text-destructive"
                          onClick={(event) => openDelete(event, cat)}
                          aria-label={`Delete ${cat.name}`}
                        >
                          <Trash2 className="h-3.5 w-3.5" />
                        </Button>
                      </div>
                    </div>

                    {isExpanded && <ExpandedBills category={cat} />}
                  </section>
                );
              })}
            </div>
          )}
        </div>

        <div className="text-xs text-muted-foreground">
          Category totals include active and inactive bills in your account only.
        </div>

        <InputDialog
          open={!!renameTarget}
          onOpenChange={(open) => { if (!open) setRenameTarget(null); }}
          title="Rename Category"
          label="Name"
          defaultValue={renameTarget?.name ?? ''}
          placeholder="Category name"
          confirmLabel="Rename"
          loading={renaming}
          onConfirm={handleRename}
        />

        <AlertDialog open={!!deleteTarget} onOpenChange={(open) => { if (!open) setDeleteTarget(null); }}>
          <AlertDialogContent>
            <AlertDialogHeader>
              <AlertDialogTitle>Delete {deleteTarget?.name}?</AlertDialogTitle>
              <AlertDialogDescription>
                Bills in this category will become uncategorized. No bills or payments will be deleted.
              </AlertDialogDescription>
            </AlertDialogHeader>
            <AlertDialogFooter>
              <AlertDialogCancel disabled={deleting}>Cancel</AlertDialogCancel>
              <AlertDialogAction
                className={cn(buttonVariants({ variant: 'destructive' }))}
                onClick={handleDelete}
                disabled={deleting}
              >
                {deleting ? 'Deleting...' : 'Delete Category'}
              </AlertDialogAction>
            </AlertDialogFooter>
          </AlertDialogContent>
        </AlertDialog>
      </div>
    </TooltipProvider>
  );
}