"use client";

import { useCallback, useEffect, useMemo, useState } from "react";
import Link from "next/link";
import { Loader2 } from "lucide-react";
import Modal from "@/components/Modal";
import Avatar from "@/components/Avatar";
import { userPath } from "@/lib/urlStyle";
import { useUrlStyle } from "@/components/SiteBrandProvider";

const PAGE_SIZE = 10;

export interface EditHistoryItem {
  id: number;
  editor: {
    id: number;
    username: string;
    nickname: string;
    avatar: string;
  };
  old_title?: string; // 帖子场景有；评论场景无
  old_content: string;
  created_at: string;
}

export type FetchHistoryPage = (
  page: number,
  size: number
) => Promise<{
  items: EditHistoryItem[];
  total: number;
  page: number;
  size: number;
}>;

/* ---------------- 行级 diff（LCS），git diff 风格渲染 ---------------- */

type DiffOp = "del" | "add" | "ctx";

interface DiffLine {
  op: DiffOp;
  text: string;
}

interface Seg {
  chg: boolean;
  text: string;
}

type Row =
  | { kind: "line"; op: DiffOp; text: string; pair: string | null }
  | { kind: "fold"; count: number };

// 超大文本退化为整段替换，避免 O(n·m) 内存膨胀
const MAX_DIFF_CELLS = 400_000;
// 单行超过该长度不做行内变更高亮
const MAX_INLINE_DIFF_LEN = 2000;
// 相同内容行超过该数量时折叠中段
const CONTEXT_FOLD_LIMIT = 8;

function splitLines(text: string): string[] {
  if (!text) return [];
  return text.replace(/\r\n/g, "\n").split("\n");
}

function diffLines(oldText: string, newText: string): DiffLine[] {
  const a = splitLines(oldText);
  const b = splitLines(newText);
  const n = a.length;
  const m = b.length;
  if (n * m > MAX_DIFF_CELLS) {
    return [
      ...a.map((text) => ({ op: "del" as const, text })),
      ...b.map((text) => ({ op: "add" as const, text })),
    ];
  }
  const width = m + 1;
  const dp = new Uint32Array((n + 1) * width);
  for (let i = n - 1; i >= 0; i--) {
    for (let j = m - 1; j >= 0; j--) {
      dp[i * width + j] =
        a[i] === b[j]
          ? dp[(i + 1) * width + (j + 1)] + 1
          : Math.max(dp[(i + 1) * width + j], dp[i * width + (j + 1)]);
    }
  }
  const out: DiffLine[] = [];
  let i = 0;
  let j = 0;
  while (i < n && j < m) {
    if (a[i] === b[j]) {
      out.push({ op: "ctx", text: a[i] });
      i += 1;
      j += 1;
    } else if (dp[(i + 1) * width + j] >= dp[i * width + (j + 1)]) {
      out.push({ op: "del", text: a[i] });
      i += 1;
    } else {
      out.push({ op: "add", text: b[j] });
      j += 1;
    }
  }
  while (i < n) {
    out.push({ op: "del", text: a[i] });
    i += 1;
  }
  while (j < m) {
    out.push({ op: "add", text: b[j] });
    j += 1;
  }
  return normalizeBlocks(out);
}

// 每个连续变更块内统一「先删后增」，与 git diff 呈现一致
function normalizeBlocks(lines: DiffLine[]): DiffLine[] {
  const out: DiffLine[] = [];
  let k = 0;
  while (k < lines.length) {
    if (lines[k].op === "ctx") {
      out.push(lines[k]);
      k += 1;
      continue;
    }
    let end = k;
    while (end < lines.length && lines[end].op !== "ctx") end += 1;
    for (let t = k; t < end; t++) if (lines[t].op === "del") out.push(lines[t]);
    for (let t = k; t < end; t++) if (lines[t].op === "add") out.push(lines[t]);
    k = end;
  }
  return out;
}

// 行内变更高亮：取公共前/后缀，中间差异段标记 chg
function segmentLine(line: string, other: string | null): Seg[] {
  if (
    !other ||
    line === other ||
    line.length + other.length > MAX_INLINE_DIFF_LEN * 2
  ) {
    return [{ chg: false, text: line }];
  }
  const min = Math.min(line.length, other.length);
  let p = 0;
  while (p < min && line[p] === other[p]) p += 1;
  let s = 0;
  while (
    s < min - p &&
    line[line.length - 1 - s] === other[other.length - 1 - s]
  ) {
    s += 1;
  }
  const segs: Seg[] = [];
  if (p > 0) segs.push({ chg: false, text: line.slice(0, p) });
  const mid = line.slice(p, line.length - s);
  if (mid) segs.push({ chg: true, text: mid });
  if (s > 0) segs.push({ chg: false, text: line.slice(line.length - s) });
  return segs.length > 0 ? segs : [{ chg: false, text: line }];
}

// 折叠长段相同内容；同块内删除/新增按序号配对做行内高亮
function buildRows(lines: DiffLine[]): Row[] {
  const rows: Row[] = [];
  let k = 0;
  while (k < lines.length) {
    if (lines[k].op === "ctx") {
      let end = k;
      while (end < lines.length && lines[end].op === "ctx") end += 1;
      const run = end - k;
      if (run > CONTEXT_FOLD_LIMIT) {
        for (let t = k; t < k + 3; t++) {
          rows.push({ kind: "line", op: lines[t].op, text: lines[t].text, pair: null });
        }
        rows.push({ kind: "fold", count: run - 6 });
        for (let t = end - 3; t < end; t++) {
          rows.push({ kind: "line", op: lines[t].op, text: lines[t].text, pair: null });
        }
      } else {
        for (let t = k; t < end; t++) {
          rows.push({ kind: "line", op: lines[t].op, text: lines[t].text, pair: null });
        }
      }
      k = end;
    } else {
      let end = k;
      while (end < lines.length && lines[end].op !== "ctx") end += 1;
      const dels = lines.slice(k, end).filter((l) => l.op === "del");
      const adds = lines.slice(k, end).filter((l) => l.op === "add");
      const pairFor = new Map<DiffLine, string | null>();
      const cnt = Math.min(dels.length, adds.length);
      for (let t = 0; t < cnt; t++) {
        pairFor.set(dels[t], adds[t].text);
        pairFor.set(adds[t], dels[t].text);
      }
      for (let t = k; t < end; t++) {
        rows.push({
          kind: "line",
          op: lines[t].op,
          text: lines[t].text,
          pair: pairFor.get(lines[t]) ?? null,
        });
      }
      k = end;
    }
  }
  return rows;
}

function DiffBody({ before, after }: { before: string; after: string }) {
  const rows = useMemo(() => buildRows(diffLines(before, after)), [before, after]);
  const delCount = rows.filter((r) => r.kind === "line" && r.op === "del").length;
  const addCount = rows.filter((r) => r.kind === "line" && r.op === "add").length;
  return (
    <div className="cmt-diff">
      <div className="cmt-diff-stat">
        <span className="cmt-diff-stat-add">+{addCount}</span>
        <span className="cmt-diff-stat-del">−{delCount}</span>
      </div>
      <div className="cmt-diff-body">
        {rows.map((r, idx) =>
          r.kind === "fold" ? (
            <div key={idx} className="cmt-diff-fold">
              ⋯ 已省略 {r.count} 行相同内容 ⋯
            </div>
          ) : (
            <div key={idx} className={`cmt-diff-line is-${r.op}`}>
              <span className="cmt-diff-sign" aria-hidden>
                {r.op === "del" ? "-" : r.op === "add" ? "+" : " "}
              </span>
              <span className="cmt-diff-text">
                {segmentLine(r.text, r.pair).map((s, si) =>
                  s.chg ? (
                    <mark key={si} className="cmt-diff-chg">
                      {s.text}
                    </mark>
                  ) : (
                    <span key={si}>{s.text}</span>
                  )
                )}
              </span>
            </div>
          )
        )}
      </div>
    </div>
  );
}

/* ---------------- 弹窗 ---------------- */

/**
 * 登录可见：历次编辑的 git diff 风格修订视图（倒序分页）。
 * 后端只存每次编辑前的旧快照：第 i 条的「改后内容」= 第 i-1 条（更新的一条）的快照，
 * 最新一条的「改后内容」= 当前正文（由调用方传入）。帖子场景另传 currentTitle 渲染标题 diff。
 */
export default function EditHistoryModal({
  open,
  title,
  currentTitle,
  currentContent,
  fetchPage,
  onClose,
}: {
  open: boolean;
  title: string;
  currentTitle?: string;
  currentContent: string;
  fetchPage: FetchHistoryPage;
  onClose: () => void;
}) {
  const urlStyle = useUrlStyle();
  const [loading, setLoading] = useState(false);
  const [loadingMore, setLoadingMore] = useState(false);
  const [error, setError] = useState("");
  const [items, setItems] = useState<EditHistoryItem[]>([]);
  const [page, setPage] = useState(1);
  const [total, setTotal] = useState(0);

  const hasMore = items.length < total;

  const loadPage = useCallback(
    async (nextPage: number, append: boolean) => {
      if (!open) return;
      if (append) setLoadingMore(true);
      else {
        setLoading(true);
        setError("");
      }
      try {
        const res = await fetchPage(nextPage, PAGE_SIZE);
        const batch = res.items || [];
        setError("");
        setTotal(res.total ?? 0);
        setPage(res.page ?? nextPage);
        setItems((prev) => (append ? [...prev, ...batch] : batch));
      } catch (e) {
        const msg = e instanceof Error ? e.message : "加载失败";
        if (append) {
          // 追加失败不清空已有列表
          setError(msg);
        } else {
          setError(msg);
          setItems([]);
          setTotal(0);
        }
      } finally {
        setLoading(false);
        setLoadingMore(false);
      }
    },
    [open, fetchPage]
  );

  useEffect(() => {
    if (!open) return;
    setItems([]);
    setPage(1);
    setTotal(0);
    setError("");
    void loadPage(1, false);
  }, [open, loadPage]);

  const hasTitle = typeof currentTitle === "string";

  return (
    <Modal
      open={open}
      title={title}
      description={total > 0 ? `共 ${total} 条修订记录 · - 移除内容 / + 新增内容` : undefined}
      onClose={onClose}
      // 对齐详情页中间评论栏可用宽度（1440 三栏布局下约 800px）
      maxWidthClass="max-w-[min(840px,calc(100vw-2rem))]"
      panelClassName="p-5 sm:p-6 max-h-[85vh] flex flex-col min-h-0 overflow-hidden"
      bodyClassName="overflow-y-auto min-h-0 flex-1 -mx-1 px-1"
      footer={
        <button type="button" className="btn btn-line btn-sm" onClick={onClose}>
          关闭
        </button>
      }
    >
      {loading ? (
        <div className="flex items-center justify-center gap-2 py-10 meta text-[13px]">
          <Loader2 size={16} className="animate-spin" />
          加载中…
        </div>
      ) : error && items.length === 0 ? (
        <p className="text-[13.5px] py-6 text-center" style={{ color: "var(--danger)" }}>
          {error}
        </p>
      ) : items.length === 0 ? (
        <p className="meta text-[13.5px] py-8 text-center">暂无编辑记录</p>
      ) : (
        <div className="flex flex-col gap-4">
          <ul className="flex flex-col gap-4">
            {items.map((it, idx) => {
              const name = it.editor.nickname || it.editor.username || "用户";
              // 本次编辑的改后内容：上一条（更新的）快照；最新一条为当前正文
              const afterContent = idx === 0 ? currentContent : items[idx - 1].old_content;
              const afterTitle = hasTitle
                ? idx === 0
                  ? (currentTitle ?? "")
                  : (items[idx - 1].old_title ?? "")
                : undefined;
              const titleChanged = hasTitle && it.old_title !== afterTitle;
              const contentChanged = it.old_content !== afterContent;
              return (
                <li
                  key={it.id}
                  className="rounded-md p-3 sm:p-4"
                  style={{ background: "var(--panel-2)", border: "1px solid var(--line)" }}
                >
                  <div className="flex items-center gap-2 mb-2.5">
                    <Link href={userPath(urlStyle, it.editor.id)} className="shrink-0">
                      <Avatar name={name} src={it.editor.avatar || undefined} size={28} />
                    </Link>
                    <div className="min-w-0 flex-1">
                      <Link
                        href={userPath(urlStyle, it.editor.id)}
                        className="text-[13px] hover:text-[var(--accent)]"
                        style={{ color: "var(--ink)" }}
                      >
                        {name}
                      </Link>
                      <p className="meta text-[11.5px] tabular-nums">
                        {new Date(it.created_at).toLocaleString("zh-CN")} · 第{" "}
                        {total - idx} 次编辑
                      </p>
                    </div>
                  </div>
                  {titleChanged && (
                    <div className="mb-3">
                      <p className="meta text-[11.5px] mb-1">标题</p>
                      <DiffBody before={it.old_title ?? ""} after={afterTitle ?? ""} />
                    </div>
                  )}
                  {contentChanged ? (
                    <DiffBody before={it.old_content} after={afterContent} />
                  ) : (
                    !titleChanged && (
                      <p className="meta text-[12.5px]">本次仅变更了标签或其他元数据，未修改标题/正文。</p>
                    )
                  )}
                </li>
              );
            })}
          </ul>

          {error && items.length > 0 && (
            <p className="text-[12.5px] text-center" style={{ color: "var(--danger)" }}>
              {error}
            </p>
          )}

          {hasMore && (
            <div className="flex justify-center pt-1 pb-1">
              <button
                type="button"
                className="btn btn-line btn-sm"
                disabled={loadingMore}
                onClick={() => void loadPage(page + 1, true)}
              >
                {loadingMore ? (
                  <span className="inline-flex items-center gap-1.5">
                    <Loader2 size={14} className="animate-spin" />
                    加载中…
                  </span>
                ) : (
                  `加载更多（已显示 ${items.length}/${total}）`
                )}
              </button>
            </div>
          )}
        </div>
      )}
    </Modal>
  );
}