"use client";

import Link from "next/link";
import { usePathname } from "next/navigation";
import { curriculum } from "@/lib/curriculum";
import { cn } from "@/lib/utils";
import { useState } from "react";

const unitColorMap = {
  "unit-1": {
    active: "bg-unit-1-light text-unit-1-dark border-unit-1/20",
    dot: "bg-unit-1",
    heading: "text-unit-1-dark",
    hoverBg: "hover:bg-unit-1-light/50",
  },
  "unit-2": {
    active: "bg-unit-2-light text-unit-2-dark border-unit-2/20",
    dot: "bg-unit-2",
    heading: "text-unit-2-dark",
    hoverBg: "hover:bg-unit-2-light/50",
  },
  "unit-3": {
    active: "bg-unit-3-light text-unit-3-dark border-unit-3/20",
    dot: "bg-unit-3",
    heading: "text-unit-3-dark",
    hoverBg: "hover:bg-unit-3-light/50",
  },
  "unit-4": {
    active: "bg-unit-4-light text-unit-4-dark border-unit-4/20",
    dot: "bg-unit-4",
    heading: "text-unit-4-dark",
    hoverBg: "hover:bg-unit-4-light/50",
  },
};

export function Sidebar() {
  const pathname = usePathname();
  const [openUnits, setOpenUnits] = useState<Set<number>>(() => {
    const open = new Set<number>();
    for (const unit of curriculum) {
      if (pathname.includes(unit.slug)) {
        open.add(unit.number);
      }
    }
    if (open.size === 0) open.add(1);
    return open;
  });

  function toggleUnit(num: number) {
    setOpenUnits((prev) => {
      const next = new Set(prev);
      if (next.has(num)) next.delete(num);
      else next.add(num);
      return next;
    });
  }

  return (
    <aside className="hidden w-64 shrink-0 border-r border-border/60 bg-surface lg:block">
      <nav className="sticky top-[4.125rem] h-[calc(100vh-4.125rem)] overflow-y-auto p-4">
        <Link
          href="/lessons"
          className={cn(
            "mb-4 flex items-center gap-2 rounded-xl px-3 py-2 text-sm font-medium transition-all duration-200",
            pathname === "/lessons"
              ? "bg-foreground text-background shadow-[var(--shadow-sm)]"
              : "text-muted hover:bg-background hover:text-foreground",
          )}
        >
          <svg className="h-4 w-4" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={2}>
            <path strokeLinecap="round" strokeLinejoin="round" d="M4 6h16M4 10h16M4 14h16M4 18h16" />
          </svg>
          All Topics
        </Link>

        <div className="mb-3 h-px bg-border/60" />

        {curriculum.map((unit) => {
          const colors = unitColorMap[unit.color];
          const isOpen = openUnits.has(unit.number);

          return (
            <div key={unit.slug} className="mb-1">
              <button
                onClick={() => toggleUnit(unit.number)}
                className={cn(
                  "flex w-full items-center justify-between rounded-xl px-3 py-2 text-left text-sm font-semibold transition-all duration-200",
                  colors.heading,
                  colors.hoverBg,
                )}
              >
                <span className="truncate">Unit {unit.number}: {unit.title}</span>
                <svg
                  className={cn(
                    "h-4 w-4 shrink-0 transition-transform duration-200",
                    isOpen && "rotate-90",
                  )}
                  fill="none"
                  viewBox="0 0 24 24"
                  stroke="currentColor"
                  strokeWidth={2}
                >
                  <path strokeLinecap="round" strokeLinejoin="round" d="M9 5l7 7-7 7" />
                </svg>
              </button>

              {isOpen && (
                <div className="ml-2 mt-0.5 space-y-0.5 border-l-2 border-border/40 pl-2">
                  {unit.topics.map((topic) => {
                    const href = `/lessons/${unit.slug}/${topic.slug}`;
                    const isActive = pathname === href;

                    return (
                      <Link
                        key={topic.slug}
                        href={href}
                        className={cn(
                          "flex items-center gap-2 rounded-lg px-2.5 py-1.5 text-sm transition-all duration-200",
                          isActive
                            ? cn(colors.active, "font-medium shadow-[var(--shadow-sm)]")
                            : "text-muted hover:text-foreground",
                        )}
                      >
                        <span
                          className={cn(
                            "h-1.5 w-1.5 shrink-0 rounded-full transition-colors",
                            isActive ? colors.dot : "bg-border",
                          )}
                        />
                        <span className="truncate">{topic.shortTitle}</span>
                      </Link>
                    );
                  })}
                </div>
              )}
            </div>
          );
        })}
      </nav>
    </aside>
  );
}