import { useMemo, useState } from "react";
import { useTranslation } from "react-i18next";
import { Link } from "react-router-dom";
import { ArrowLeft, Search, Printer, ChevronsDownUp, ChevronsUpDown } from "lucide-react";
import { useCategoryTaxonomy } from "../hooks/useCategoryTaxonomy";
import CategoryTaxonomyTree, {
  TAXONOMY_COLLAPSE_ACCESSORS,
} from "../components/categories/CategoryTaxonomyTree";
import type { TaxonomyNode } from "../services/categoryTaxonomyService";
import { useCollapsibleGroups } from "../hooks/useCollapsibleGroups";

function countNodes(nodes: TaxonomyNode[]): {
  roots: number;
  subcategories: number;
  leaves: number;
} {
  let roots = 0;
  let subcategories = 0;
  let leaves = 0;
  for (const root of nodes) {
    roots += 1;
    for (const child of root.children) {
      if (child.children.length === 0) {
        // direct leaf under a root (rare but possible)
        leaves += 1;
      } else {
        subcategories += 1;
        for (const leaf of child.children) {
          if (leaf.children.length === 0) leaves += 1;
          else subcategories += 1;
        }
      }
    }
  }
  return { roots, subcategories, leaves };
}

// Flattens the taxonomy to a single array so the hook's bulk ops
// (expandAll/collapseAll/allExpanded/groupCount) can walk every parent at any depth.
function flattenNodes(nodes: TaxonomyNode[]): TaxonomyNode[] {
  const flat: TaxonomyNode[] = [];
  const walk = (n: TaxonomyNode) => {
    flat.push(n);
    n.children.forEach(walk);
  };
  nodes.forEach(walk);
  return flat;
}

export default function CategoriesStandardGuidePage() {
  const { t } = useTranslation();
  const { taxonomy } = useCategoryTaxonomy();
  const [search, setSearch] = useState("");

  // State machine only (issue #290): in-memory (storageKey null), collapsed by
  // default so the guide opens on roots — the previous local Set behaviour.
  const groups = useCollapsibleGroups<TaxonomyNode>(null, TAXONOMY_COLLAPSE_ACCESSORS, {
    defaultExpanded: false,
  });

  const counts = useMemo(() => countNodes(taxonomy.roots), [taxonomy.roots]);
  const total = counts.roots + counts.subcategories + counts.leaves;

  // Flattened nodes for the bulk ops (expand/collapse all, allExpanded).
  const flatNodes = useMemo(() => flattenNodes(taxonomy.roots), [taxonomy.roots]);

  const handleExpandAll = () => groups.expandAll(flatNodes);
  const handleCollapseAll = () => groups.collapseAll(flatNodes);

  const handlePrint = () => {
    // window.print() opens the browser print dialog; @media print rules strip chrome.
    window.print();
  };

  // Correct "all expanded" test (issue #290): every collapsible group must be open,
  // not merely "at least one node open" (the old expanded.size > 0 bug, which
  // flipped the button to "Collapse all" after a single node was expanded).
  const allExpanded = groups.allExpanded(flatNodes);

  return (
    <div className="p-6 max-w-4xl mx-auto space-y-6">
      {/* Back link (hidden in print) */}
      <div className="print:hidden">
        <Link
          to="/settings/data"
          className="inline-flex items-center gap-2 text-sm text-[var(--muted-foreground)] hover:text-[var(--foreground)] transition-colors"
        >
          <ArrowLeft size={16} />
          {t("categoriesSeed.guidePage.backToSettings")}
        </Link>
      </div>

      {/* Header */}
      <header className="space-y-1">
        <h1 className="text-2xl font-bold">
          {t("categoriesSeed.guidePage.title")}
        </h1>
        <p className="text-sm text-[var(--muted-foreground)]">
          {t("categoriesSeed.guidePage.subtitle")}
        </p>
      </header>

      {/* Intro card */}
      <section className="bg-[var(--card)] border border-[var(--border)] rounded-xl p-5 space-y-2">
        <h2 className="text-lg font-semibold">
          {t("categoriesSeed.guidePage.intro.title")}
        </h2>
        <p className="text-sm text-[var(--muted-foreground)]">
          {t("categoriesSeed.guidePage.intro.body")}
        </p>
      </section>

      {/* Counter + toolbar */}
      <section className="bg-[var(--card)] border border-[var(--border)] rounded-xl p-5 space-y-4">
        <p
          className="text-sm text-[var(--muted-foreground)]"
          aria-live="polite"
        >
          {t("categoriesSeed.guidePage.counter", {
            roots: counts.roots,
            subcategories: counts.subcategories,
            leaves: counts.leaves,
            total,
          })}
        </p>

        {/* Toolbar: search + actions (hidden in print) */}
        <div className="print:hidden flex flex-col sm:flex-row gap-3">
          <div className="relative flex-1">
            <Search
              size={16}
              className="absolute left-3 top-1/2 -translate-y-1/2 text-[var(--muted-foreground)] pointer-events-none"
              aria-hidden="true"
            />
            <input
              type="search"
              value={search}
              onChange={(e) => setSearch(e.target.value)}
              placeholder={t("categoriesSeed.guidePage.searchPlaceholder")}
              aria-label={t("categoriesSeed.guidePage.searchPlaceholder")}
              className="w-full pl-9 pr-3 py-2 rounded-lg border border-[var(--border)] bg-[var(--background)] text-sm focus:outline-none focus:ring-2 focus:ring-[var(--primary)]/30"
            />
          </div>
          <div className="flex items-center gap-2">
            <button
              type="button"
              onClick={allExpanded ? handleCollapseAll : handleExpandAll}
              className="inline-flex items-center gap-2 px-3 py-2 text-sm rounded-lg border border-[var(--border)] hover:bg-[var(--muted)] transition-colors"
            >
              {allExpanded ? (
                <>
                  <ChevronsDownUp size={16} />
                  {t("categoriesSeed.guidePage.collapseAll")}
                </>
              ) : (
                <>
                  <ChevronsUpDown size={16} />
                  {t("categoriesSeed.guidePage.expandAll")}
                </>
              )}
            </button>
            <button
              type="button"
              onClick={handlePrint}
              className="inline-flex items-center gap-2 px-3 py-2 text-sm rounded-lg bg-[var(--primary)] text-white hover:opacity-90 transition-opacity"
              title={t("categoriesSeed.guidePage.printHint")}
            >
              <Printer size={16} />
              {t("categoriesSeed.guidePage.print")}
            </button>
          </div>
        </div>
      </section>

      {/* Tree */}
      <section className="bg-[var(--card)] border border-[var(--border)] rounded-xl p-3 taxonomy-tree-print">
        <CategoryTaxonomyTree
          nodes={taxonomy.roots}
          isCollapsed={groups.isCollapsed}
          onToggle={groups.toggle}
          searchQuery={search}
        />
      </section>
    </div>
  );
}