"use client";

import { useEffect, useMemo, useState, type ReactNode } from "react";
import {
  ChevronDown,
  ChevronUp,
  CornerDownRight,
  ListTree,
  Loader2,
  Plus,
  Save,
  Trash2,
  Upload,
} from "lucide-react";
import {
  apiAdminCreateLibrarySection,
  apiAdminDeleteLibrarySection,
  apiAdminImportLibraryMarkdownBatch,
  apiAdminMoveLibrarySection,
  apiAdminUpdateLibrarySection,
  type LibraryDoc,
  type LibraryImportMdInput,
  type LibrarySectionItem,
} from "@/lib/api";
import { toast } from "@/lib/toast";
import ConfirmDialog from "@/components/ConfirmDialog";
import MarkdownEditor from "@/components/MarkdownEditor";
import { AdminEmpty } from "@/components/admin";
import ImportMdDialog from "./ImportMdDialog";

const MAX_TITLE = 200;
const MAX_CONTENT = 100_000; // 与后端 MaxSectionContent 保持一致

const EMPTY_SNAPSHOT = JSON.stringify({ title: "", content: "" });

/**
 * 「章节与正文」面板：左章节树（章 → 节 两级），右章节编辑器。
 * 数据从 doc.sections 派生（后端 detail 已带全量含 content）；
 * 所有变更后调 onChanged() 让父组件刷新列表，doc.sections 随之更新。
 */
export default function LibrarySectionsPanel({
  doc,
  onChanged,
  onDirtyChange,
}: {
  doc: LibraryDoc;
  /** 数据变更后由父组件刷新（doc.sections 随之更新） */
  onChanged: () => Promise<void>;
  /** dirty 状态上报，供父组件在关闭编辑器 / 切换条目前确认 */
  onDirtyChange: (dirty: boolean) => void;
}) {
  const sections = doc.sections ?? [];

  // 平铺 → 章分组（顺序沿用后端 sort_order）
  const groups = useMemo(() => {
    const gs: { chapter: LibrarySectionItem; subs: LibrarySectionItem[] }[] = [];
    for (const s of sections) {
      if (s.parent_id == null) gs.push({ chapter: s, subs: [] });
      else gs[gs.length - 1]?.subs.push(s);
    }
    return gs;
  }, [sections]);

  const [selectedId, setSelectedId] = useState<number | null>(null);
  const [title, setTitle] = useState("");
  const [content, setContent] = useState("");
  const [snapshot, setSnapshot] = useState(EMPTY_SNAPSHOT);
  const [busy, setBusy] = useState(false);
  const [error, setError] = useState("");
  const [pendingNav, setPendingNav] = useState<(() => void) | null>(null);
  const [deleteTarget, setDeleteTarget] = useState<LibrarySectionItem | null>(null);
  const [deleteBusy, setDeleteBusy] = useState(false);
  const [importOpen, setImportOpen] = useState(false);
  // 新建 / 导入后要选中的章节 id：等 doc.sections 里出现再应用，避免被旧数据清掉
  const [pendingSelectId, setPendingSelectId] = useState<number | null>(null);

  const selected = useMemo(
    () => sections.find((s) => s.id === selectedId) ?? null,
    [sections, selectedId]
  );
  const dirty = JSON.stringify({ title, content }) !== snapshot;

  // dirty 上报给父组件；卸载时归零，避免残留的 dirty 影响父组件的关闭确认
  useEffect(() => {
    onDirtyChange(dirty);
    return () => onDirtyChange(false);
  }, [dirty, onDirtyChange]);

  // 选中项被删除后清空选中
  useEffect(() => {
    if (selectedId != null && !sections.some((s) => s.id === selectedId)) {
      setSelectedId(null);
    }
  }, [sections, selectedId]);

  // 应用待选章节（新建 / 导入完成后）
  useEffect(() => {
    if (pendingSelectId == null) return;
    const s = sections.find((x) => x.id === pendingSelectId);
    if (!s) return;
    setPendingSelectId(null);
    setSelectedId(s.id);
    setTitle(s.title);
    setContent(s.content);
    setSnapshot(JSON.stringify({ title: s.title, content: s.content }));
    setError("");
  }, [sections, pendingSelectId]);

  function loadSection(s: LibrarySectionItem) {
    setSelectedId(s.id);
    setTitle(s.title);
    setContent(s.content);
    setSnapshot(JSON.stringify({ title: s.title, content: s.content }));
    setError("");
  }

  /** dirty 时先弹确认，再执行动作（切换章节 / 打开导入 / 新增章节） */
  function guardNav(action: () => void) {
    if (dirty && !busy) setPendingNav(() => action);
    else action();
  }

  function selectSection(s: LibrarySectionItem) {
    if (s.id === selectedId) return;
    guardNav(() => loadSection(s));
  }

  async function addSection(parent: LibrarySectionItem | null) {
    setBusy(true);
    setError("");
    try {
      const { section } = await apiAdminCreateLibrarySection(doc.id, {
        parent_id: parent?.id,
        title: parent ? "新节" : "新章",
      });
      await onChanged();
      setPendingSelectId(section.id);
      toast(parent ? "小节已添加" : "章已添加", "ok");
    } catch (e) {
      setError(e instanceof Error ? e.message : "添加章节失败");
    } finally {
      setBusy(false);
    }
  }

  async function save() {
    if (selectedId == null) return;
    const t = title.trim();
    if (!t) {
      setError("章节标题不能为空");
      return;
    }
    setBusy(true);
    setError("");
    try {
      const { section } = await apiAdminUpdateLibrarySection(selectedId, {
        title: t,
        content,
      });
      await onChanged();
      // 以服务端返回为准（后端会 trim 标题），保证 dirty 归零
      setTitle(section.title);
      setContent(section.content);
      setSnapshot(JSON.stringify({ title: section.title, content: section.content }));
      toast("章节已保存", "ok");
    } catch (e) {
      setError(e instanceof Error ? e.message : "保存章节失败");
    } finally {
      setBusy(false);
    }
  }

  async function move(s: LibrarySectionItem, direction: "up" | "down") {
    setBusy(true);
    setError("");
    try {
      await apiAdminMoveLibrarySection(s.id, direction);
      await onChanged(); // 选中 id 不变，原地刷新顺序
    } catch (e) {
      setError(e instanceof Error ? e.message : "移动章节失败");
    } finally {
      setBusy(false);
    }
  }

  async function removeSection() {
    if (!deleteTarget) return;
    const target = deleteTarget;
    setDeleteBusy(true);
    try {
      await apiAdminDeleteLibrarySection(target.id);
      toast(target.parent_id == null ? "章已删除" : "小节已删除", "ok");
      setDeleteTarget(null);
      await onChanged();
      if (target.id === selectedId) {
        setSelectedId(null);
        setTitle("");
        setContent("");
        setSnapshot(EMPTY_SNAPSHOT);
        setError("");
      }
    } catch (e) {
      toast(e instanceof Error ? e.message : "删除章节失败");
    } finally {
      setDeleteBusy(false);
    }
  }

  async function handleImport(input: LibraryImportMdInput) {
    const res = await apiAdminImportLibraryMarkdownBatch(doc.id, input);
    await onChanged();
    return res.sections;
  }

  function closeImport(created?: LibrarySectionItem[]) {
    setImportOpen(false);
    if (created && created.length > 0) setPendingSelectId(created[0].id);
  }

  /** 该章节在同级兄弟中的位置（供上移/下移禁用判断） */
  function siblingPos(s: LibrarySectionItem): { first: boolean; last: boolean } {
    if (s.parent_id == null) {
      const i = groups.findIndex((g) => g.chapter.id === s.id);
      return { first: i <= 0, last: i < 0 || i >= groups.length - 1 };
    }
    const g = groups.find((x) => x.subs.some((y) => y.id === s.id));
    const subs = g?.subs ?? [];
    const i = subs.findIndex((y) => y.id === s.id);
    return { first: i <= 0, last: i < 0 || i >= subs.length - 1 };
  }

  function RowAction({
    label,
    onClick,
    disabled,
    children,
  }: {
    label: string;
    onClick: () => void;
    disabled?: boolean;
    children: ReactNode;
  }) {
    return (
      <button
        type="button"
        className="w-6 h-6 shrink-0 rounded-md flex items-center justify-center hover:bg-[var(--panel)] transition-colors disabled:opacity-40 disabled:cursor-not-allowed"
        style={{ color: "var(--ink-3)" }}
        title={label}
        aria-label={label}
        disabled={disabled}
        onClick={onClick}
      >
        {children}
      </button>
    );
  }

  function row(s: LibrarySectionItem, depth: 0 | 1, isFirst: boolean, isLast: boolean) {
    const active = s.id === selectedId;
    const pos = siblingPos(s);
    return (
      <div
        key={s.id}
        className="flex items-center gap-0.5 pr-1.5"
        style={{
          paddingLeft: depth === 0 ? 4 : 22,
          background: active ? "var(--accent-soft)" : undefined,
          boxShadow: active ? "inset 2px 0 0 var(--accent)" : undefined,
        }}
      >
        <button
          type="button"
          onClick={() => selectSection(s)}
          aria-current={active ? "true" : undefined}
          className="min-w-0 flex-1 text-left px-2 py-2 flex items-center gap-1 rounded-md transition-colors hover:bg-[var(--panel-2)]"
          title={s.title}
        >
          {depth === 1 ? (
            <CornerDownRight
              size={12}
              className="shrink-0"
              style={{ color: "var(--ink-3)" }}
              aria-hidden
            />
          ) : null}
          <span
            className="truncate text-[13px]"
            style={{
              color: active ? "var(--accent)" : "var(--ink)",
              fontWeight: depth === 0 ? 600 : 400,
            }}
          >
            {s.title || "未命名章节"}
          </span>
        </button>
        {active ? (
          <>
            <RowAction label="上移" disabled={pos.first || busy} onClick={() => void move(s, "up")}>
              <ChevronUp size={13} aria-hidden />
            </RowAction>
            <RowAction label="下移" disabled={pos.last || busy} onClick={() => void move(s, "down")}>
              <ChevronDown size={13} aria-hidden />
            </RowAction>
            {depth === 0 ? (
              <RowAction
                label="添加小节"
                disabled={busy}
                onClick={() => void addSection(s)}
              >
                <CornerDownRight size={13} aria-hidden />
              </RowAction>
            ) : null}
            <RowAction label="删除" onClick={() => setDeleteTarget(s)}>
              <Trash2 size={13} aria-hidden />
            </RowAction>
          </>
        ) : null}
      </div>
    );
  }

  return (
    <div className="flex h-full min-h-0">
      {/* 左：章节树 */}
      <aside
        className="w-52 sm:w-60 shrink-0 flex flex-col min-h-0"
        style={{ borderRight: "1px solid var(--line)" }}
        aria-label="章节树"
      >
        <div
          className="shrink-0 flex items-center gap-1.5 px-2.5 py-2.5 flex-wrap"
          style={{ borderBottom: "1px solid var(--line)", background: "var(--panel-2)" }}
        >
          <button
            type="button"
            className="btn btn-line btn-sm"
            disabled={busy}
            onClick={() => guardNav(() => void addSection(null))}
          >
            <Plus size={13} aria-hidden /> 添加章
          </button>
          <button
            type="button"
            className="btn btn-line btn-sm"
            disabled={busy}
            onClick={() => guardNav(() => setImportOpen(true))}
          >
            <Upload size={13} aria-hidden /> 导入
          </button>
        </div>
        <div className="flex-1 min-h-0 overflow-y-auto j13-rail-scroll py-1.5">
          {groups.length === 0 ? (
            <p className="meta text-[12.5px] px-3 py-3 leading-relaxed">
              还没有章节。点上方「添加章」手动编写，或「导入」批量导入 .md / .epub（epub 按目录顺序拆章）。
            </p>
          ) : (
            groups.map((g, gi) => (
              <div key={g.chapter.id}>
                {row(g.chapter, 0, gi === 0, gi === groups.length - 1)}
                {g.subs.map((sub, si) => row(sub, 1, si === 0, si === g.subs.length - 1))}
              </div>
            ))
          )}
        </div>
        <div
          className="shrink-0 px-3 py-2 meta text-[11.5px] tabular-nums"
          style={{ borderTop: "1px solid var(--line)" }}
        >
          {sections.length} 章节
        </div>
      </aside>

      {/* 右：章节编辑器 */}
      <div className="flex-1 min-w-0 flex flex-col min-h-0">
        {selected ? (
          <>
            <div className="flex-1 min-h-0 overflow-y-auto j13-rail-scroll px-4 sm:px-5 py-4 flex flex-col gap-4">
              <div className="admin-doc-field">
                <label className="admin-doc-label" htmlFor="lib-section-title">
                  章节标题
                </label>
                <input
                  id="lib-section-title"
                  className="admin-field-input"
                  maxLength={MAX_TITLE}
                  value={title}
                  onChange={(e) => {
                    setError("");
                    setTitle(e.target.value);
                  }}
                  placeholder="例如：第一章 …"
                  disabled={busy}
                />
              </div>
              {/* flex-1 撑满滚动区剩余高度：编辑框最大化、提示行紧贴底部操作条上方 */}
              <div className="admin-doc-md flex flex-col flex-1 min-h-0">
                <label className="admin-doc-label" htmlFor="lib-section-content">
                  正文（Markdown）
                </label>
                <MarkdownEditor
                  id="lib-section-content"
                  value={content}
                  onChange={(v) => {
                    setError("");
                    setContent(v.slice(0, MAX_CONTENT));
                  }}
                  maxChars={MAX_CONTENT}
                  allowHide={false}
                  entriesAuto={doc.entries_auto ?? false}
                  placeholder="本章正文，支持 Markdown…"
                  rows={16}
                  ariaLabel="章节正文"
                />
              </div>
            </div>

            {/* 底部操作条：不随正文滚动 */}
            <footer
              className="shrink-0 flex items-center gap-2 px-3.5 sm:px-4 py-3"
              style={{ borderTop: "1px solid var(--line)", background: "var(--panel-2)" }}
            >
              <div className="mr-auto flex items-center gap-3 min-w-0">
                {error ? (
                  <p className="admin-settings-row-error" role="alert">
                    {error}
                  </p>
                ) : dirty ? (
                  <span className="meta text-[12px]">有未保存的修改</span>
                ) : null}
              </div>
              <button
                type="button"
                className="btn btn-line btn-sm"
                disabled={busy || deleteBusy}
                onClick={() => setDeleteTarget(selected)}
              >
                <Trash2 size={13} aria-hidden /> 删除章节
              </button>
              <button
                type="button"
                className="btn btn-primary btn-sm"
                disabled={busy || !dirty}
                title={dirty ? undefined : "没有需要保存的修改"}
                onClick={() => void save()}
                aria-busy={busy || undefined}
              >
                {busy ? (
                  <Loader2 size={13} className="animate-spin" aria-hidden />
                ) : (
                  <Save size={13} aria-hidden />
                )}
                {busy ? "保存中…" : "保存章节"}
              </button>
            </footer>
          </>
        ) : (
          <div className="flex-1 min-h-0 flex items-center justify-center p-6">
            <AdminEmpty
              icon={<ListTree size={22} />}
              title="未选择章节"
              description="从左侧选择章节编辑，或添加章 / 导入 Markdown"
            />
          </div>
        )}
      </div>

      {/* 未保存切换章节确认 */}
      <ConfirmDialog
        open={!!pendingNav}
        title="放弃未保存的修改？"
        message="当前章节有未保存的修改，继续将丢失这些改动。"
        danger
        confirmLabel="放弃修改"
        cancelLabel="继续编辑"
        onCancel={() => setPendingNav(null)}
        onConfirm={() => {
          const action = pendingNav;
          setPendingNav(null);
          action?.();
        }}
      />

      {/* 删除章节确认 */}
      <ConfirmDialog
        open={!!deleteTarget}
        title={deleteTarget?.parent_id == null ? "删除章" : "删除小节"}
        message={
          deleteTarget
            ? `确定删除「${deleteTarget.title}」吗？${
                deleteTarget.parent_id == null ? "其下所有小节将一并删除，" : ""
              }且不可恢复。`
            : ""
        }
        danger
        busy={deleteBusy}
        confirmLabel="删除"
        onCancel={() => !deleteBusy && setDeleteTarget(null)}
        onConfirm={() => void removeSection()}
      />

      {/* 导入 Markdown 拆章 */}
      {importOpen ? <ImportMdDialog onImport={handleImport} onClose={closeImport} /> : null}
    </div>
  );
}