import { useEffect, useMemo, useState, type CSSProperties, type ReactNode } from "react";
import { Link, useLocation } from "react-router-dom";
import { CourseCover, ProgressBar } from "@stc/ui";
import type { CoursePayload, OutlineLesson, OutlineModule } from "../../shared/types";
import { courseHref, ensureStyles, fmtMinutes, fmtTime, lessonHref, useSearch, type Look } from "../api";
import { Check, Chev, Lock } from "../icons";
import { HeaderExtras } from "./HeaderExtras";
import { TitleText } from "../lesson/TitleText";

const fold = (s: string) => s.normalize("NFKD").replace(/[̀-ͯ]/g, "").toLowerCase();

export function lessonKind(l: OutlineLesson): string {
  if (l.type === "video") return l.minutes ? (l.minutes < 60 ? fmtTime(l.minutes * 60) : fmtMinutes(l.minutes)) : "Video";
  if (l.type === "exercise") return "Exercise";
  return l.hasDeck ? "Slides" : "Text";
}

export function courseDone(c: CoursePayload): { done: number; total: number } {
  const all = c.modules.flatMap((m) => m.lessons);
  return { done: all.filter((l) => c.progress[l.id]?.state === "done").length, total: all.length };
}

/** Display number of a module: courses whose first module id ends in 0 ("m00") count from 0. */
export function moduleNumber(course: { modules: { id: string }[] }, index: number): number {
  return /(^|\D)0+$/.test(course.modules[0]?.id ?? "") ? index : index + 1;
}

export function accentStyle(accent: string | null | undefined): CSSProperties | undefined {
  return accent ? ({ "--accent": accent } as CSSProperties) : undefined;
}

/** The course page frame: outline sidebar (an overlay on narrow screens) and the main column. */
export function CourseFrame({ course, currentLessonId, look, lookMode, children }: {
  course: CoursePayload;
  currentLessonId: string | null;
  look: Look;
  lookMode: "toggle" | "work" | null;
  children: ReactNode;
}) {
  ensureStyles();
  const [open, setOpen] = useState(false);
  const loc = useLocation();
  useEffect(() => { setOpen(false); }, [loc.pathname]);
  useEffect(() => {
    if (!open) return;
    const onKey = (e: KeyboardEvent) => { if (e.key === "Escape") setOpen(false); };
    document.addEventListener("keydown", onKey);
    return () => document.removeEventListener("keydown", onKey);
  }, [open]);
  return (
    <div className={open ? "lr lr-shell side-open" : "lr lr-shell"} data-look={look} style={accentStyle(course.accent)}>
      <HeaderExtras
        course={{ id: course.id, title: course.title, coverUrl: course.coverUrl, accent: course.accent }}
        lookMode={lookMode}
        outline={{ open, toggle: () => setOpen(!open) }}
      />
      <aside className="lr-side" id="lr-side" aria-label="Course outline">
        <Outline course={course} currentLessonId={currentLessonId} />
      </aside>
      <div className="lr-scrim" onClick={() => setOpen(false)} />
      <main className="lr-main">{children}</main>
    </div>
  );
}

export function Outline({ course, currentLessonId }: { course: CoursePayload; currentLessonId: string | null }) {
  const [q] = useSearch();
  const query = fold(q.trim());
  const current = course.modules.find((m) => m.lessons.some((l) => l.id === currentLessonId));
  const [openMods, setOpenMods] = useState<Set<string>>(() => new Set(current ? [current.id] : course.modules[0] ? [course.modules[0].id] : []));
  useEffect(() => { if (current) setOpenMods((s) => (s.has(current.id) ? s : new Set([...s, current.id]))); }, [current?.id]);
  const loc = useLocation();
  useEffect(() => {
    document.querySelector(".lr-les[aria-current='page']")?.scrollIntoView({ block: "nearest" });
  }, [currentLessonId]);
  const { done, total } = courseDone(course);
  const pct = total ? done / total : 0;
  const notesPath = `${courseHref(course.id)}/notes`;

  const filtered = useMemo(() => course.modules
    .map((m) => ({ m, lessons: query ? m.lessons.filter((l) => fold(l.title).includes(query)) : m.lessons }))
    .filter(({ m, lessons }) => !query || lessons.length || fold(m.title).includes(query)), [course, query]);

  const toggle = (id: string) => setOpenMods((s) => { const n = new Set(s); if (n.has(id)) n.delete(id); else n.add(id); return n; });
  const sourceLine = course.authors.length ? course.authors.join(", ") : course.tracks.length > 1 ? `Tracks: ${course.tracks.map((t) => t.label).join(", ")}` : course.pitch ?? "";
  const errors = course.diagnostics.filter((d) => d.level === "error");

  return (
    <>
      <div className="lr-side-head">
        <span style={{ "--cw": "36px" } as CSSProperties}><CourseCover title={course.title} image={course.coverUrl ?? undefined} accent={course.accent ?? undefined} /></span>
        <div style={{ flex: 1, minWidth: 0 }}>
          <h2><Link to={courseHref(course.id)}>{course.title}</Link></h2>
          {sourceLine ? <div className="src">{sourceLine}</div> : null}
          {course.signedIn ? (
            <div className="lr-prog"><ProgressBar value={pct} label="Course progress" /><span className="tnum">{Math.round(pct * 100)}%</span></div>
          ) : null}
          <div className="lr-side-links">
            <Link to={courseHref(course.id)} aria-current={loc.pathname === courseHref(course.id) ? "page" : undefined}>Overview</Link>
            {course.signedIn ? <Link to={notesPath} aria-current={loc.pathname === notesPath ? "page" : undefined}>Your notes</Link> : null}
          </div>
        </div>
      </div>
      {errors.length ? (
        <div className="lr-diag" role="note">
          <b>{errors.length === 1 ? "1 problem" : `${errors.length} problems`} in this course</b> (only authors see this)
          <ul>{errors.slice(0, 6).map((d, i) => <li key={i}>{d.lessonId ? `${d.lessonId}: ` : ""}{d.message}{d.path ? ` (${d.path})` : ""}</li>)}</ul>
        </div>
      ) : null}
      {filtered.map(({ m, lessons }) => (
        <ModuleBlock key={m.id} course={course} m={m} lessons={lessons} open={!!query || openMods.has(m.id)} current={m.id === current?.id} currentLessonId={currentLessonId} onToggle={() => toggle(m.id)} />
      ))}
      {query && filtered.length === 0 ? <p className="lr-nohit">No lessons match “{q.trim()}”.</p> : null}
    </>
  );
}

function ModuleBlock({ course, m, lessons, open, current, currentLessonId, onToggle }: {
  course: CoursePayload; m: OutlineModule; lessons: OutlineLesson[]; open: boolean; current: boolean; currentLessonId: string | null; onToggle: () => void;
}) {
  const d = m.lessons.filter((l) => course.progress[l.id]?.state === "done").length;
  const pct = m.lessons.length ? d / m.lessons.length : 0;
  const number = String(moduleNumber(course, m.index));
  return (
    <div className={current ? "lr-mod is-current" : "lr-mod"}>
      <button type="button" className="lr-mod-head" aria-expanded={open} onClick={onToggle}>
        <span className="n tnum">{m.locked ? <Lock /> : number}</span>
        <span>{m.title}{m.locked ? <span className="sr"> (locked)</span> : null}</span>
        <span className="c tnum">{course.signedIn ? `${d}/${m.lessons.length}` : m.lessons.length}</span>
        <Chev />
      </button>
      {course.signedIn ? <ProgressBar value={pct} dim={pct === 1 || !current} label={`${m.title} progress`} /> : <span style={{ display: "block", height: 4 }} />}
      {open ? (
        <ol className="lr-lessons">
          {lessons.map((l) => {
            const isDone = course.progress[l.id]?.state === "done";
            const cls = ["lr-les", isDone && "done", m.locked && "locked"].filter(Boolean).join(" ");
            return (
              <li key={l.id}>
                <Link className={cls} to={lessonHref(course.id, l.id)} aria-current={l.id === currentLessonId ? "page" : undefined}>
                  <span className="m">{isDone ? <Check /> : m.locked ? <Lock /> : null}</span>
                  <span><TitleText text={l.title} /><span className="sr">{isDone ? ", done" : l.id === currentLessonId ? ", current" : ""}</span></span>
                  <span className="d tnum">{lessonKind(l)}</span>
                </Link>
              </li>
            );
          })}
        </ol>
      ) : null}
    </div>
  );
}