"use client";

import Link from "next/link";
import { usePathname } from "next/navigation";
import { useEffect, useState } from "react";
import { listProjects } from "../utils/api";
import type { ProjectDto } from "../types";
import { ThemeToggle } from "./ThemeToggle";

// Anchors on the project overview page (/projects/[id]).
const PROJECT_SECTIONS = [
  { id: "verlauf", label: "Verlauf", icon: "↺" },
  { id: "verteilungen", label: "Verteilungen", icon: "⌁" },
  { id: "projektgeraete", label: "Projektgeräte", icon: "⚙" },
] as const;

// Separate project sub-routes (/projects/[id]/<segment>).
const PROJECT_ROUTES = [
  { segment: "struktur", label: "Gebäudestruktur", icon: "▥" },
  { segment: "grobbilanz", label: "Grobe Leistungsbilanz", icon: "Σ" },
] as const;

// Matches the project overview and all of its sub-routes (group 2 = rest).
const PROJECT_PATH_PATTERN = /^\/projects\/([^/]+)(\/.*)?$/;

interface SidebarProps {
  isCollapsed: boolean;
  onToggleCollapsed: () => void;
}

export function Sidebar({ isCollapsed, onToggleCollapsed }: SidebarProps) {
  const pathname = usePathname();
  const projectMatch = pathname?.match(PROJECT_PATH_PATTERN);
  const activeProjectId = projectMatch ? projectMatch[1] : null;
  const projectSubPath = projectMatch?.[2] ?? "";
  // Section anchors only exist (and are observed) on the overview itself.
  const overviewProjectId =
    activeProjectId && (projectSubPath === "" || projectSubPath === "/")
      ? activeProjectId
      : null;

  const [projects, setProjects] = useState<ProjectDto[]>([]);
  const [activeSection, setActiveSection] = useState<string | null>(null);

  useEffect(() => {
    function refreshProjects() {
      listProjects()
        .then(setProjects)
        .catch(() => setProjects([]));
    }

    refreshProjects();
    window.addEventListener("leistungsbilanz:projects-changed", refreshProjects);
    return () =>
      window.removeEventListener("leistungsbilanz:projects-changed", refreshProjects);
  }, []);

  useEffect(() => {
    if (!overviewProjectId) {
      setActiveSection(null);
      return;
    }

    const elements = PROJECT_SECTIONS.map((section) =>
      document.getElementById(section.id)
    ).filter((element): element is HTMLElement => element !== null);

    if (!elements.length) {
      return;
    }

    const observer = new IntersectionObserver(
      (entries) => {
        const visible = entries
          .filter((entry) => entry.isIntersecting)
          .sort((a, b) => a.boundingClientRect.top - b.boundingClientRect.top);
        if (visible[0]) {
          setActiveSection(visible[0].target.id);
        }
      },
      { rootMargin: "-20% 0px -70% 0px", threshold: 0 }
    );

    elements.forEach((element) => observer.observe(element));
    return () => observer.disconnect();
  }, [overviewProjectId]);

  return (
    <aside className={isCollapsed ? "sidebar sidebar-collapsed" : "sidebar"}>
      <div className="sidebar-brand">
        <div className="sidebar-brand-text">
          <div className="sidebar-wordmark">Leistungsbilanz</div>
          <div className="sidebar-bar" />
          <div className="sidebar-tag">Stromkreis- &amp; Lastberechnung</div>
        </div>
        <button
          aria-label={isCollapsed ? "Seitenleiste ausklappen" : "Seitenleiste einklappen"}
          className="sidebar-toggle"
          onClick={onToggleCollapsed}
          title={isCollapsed ? "Seitenleiste ausklappen" : "Seitenleiste einklappen"}
          type="button"
        >
          {isCollapsed ? "»" : "«"}
        </button>
      </div>
      <nav className="sidebar-nav">
        <Link
          href="/projects"
          className={pathname === "/projects" ? "sidebar-link active" : "sidebar-link"}
          title="Alle Projekte"
        >
          <span className="sidebar-icon">▦</span>
          <span className="sidebar-label">Alle Projekte</span>
        </Link>

        <div className="sidebar-section-label">Projekte</div>
        {projects.map((project) => (
          <Link
            key={project.id}
            href={`/projects/${project.id}`}
            className={
              project.id === activeProjectId ? "sidebar-link active" : "sidebar-link"
            }
            title={project.name}
          >
            <span className="sidebar-icon">▣</span>
            <span className="sidebar-label">{project.name}</span>
          </Link>
        ))}
        {!projects.length ? (
          <div className="sidebar-section-label" style={{ opacity: 0.6 }}>
            Noch keine Projekte
          </div>
        ) : null}

        {activeProjectId && (
          <>
            <div className="sidebar-section-label">In diesem Projekt</div>
            {PROJECT_SECTIONS.map(({ id, label, icon }) =>
              overviewProjectId ? (
                <a
                  key={id}
                  href={`#${id}`}
                  className={activeSection === id ? "sidebar-link active" : "sidebar-link"}
                  title={label}
                >
                  <span className="sidebar-icon">{icon}</span>
                  <span className="sidebar-label">{label}</span>
                </a>
              ) : (
                <Link
                  key={id}
                  href={`/projects/${activeProjectId}#${id}`}
                  className="sidebar-link"
                  title={label}
                >
                  <span className="sidebar-icon">{icon}</span>
                  <span className="sidebar-label">{label}</span>
                </Link>
              )
            )}
            {PROJECT_ROUTES.map(({ segment, label, icon }) => {
              const href = `/projects/${activeProjectId}/${segment}`;
              const isActive =
                pathname === href || Boolean(pathname?.startsWith(`${href}/`));
              return (
                <Link
                  key={segment}
                  href={href}
                  aria-current={isActive ? "page" : undefined}
                  className={isActive ? "sidebar-link active" : "sidebar-link"}
                  title={label}
                >
                  <span className="sidebar-icon">{icon}</span>
                  <span className="sidebar-label">{label}</span>
                </Link>
              );
            })}
          </>
        )}
      </nav>
      <div className="sidebar-footer">
        <ThemeToggle />
      </div>
    </aside>
  );
}