import { h } from '@ui-arch/frame';
import type { DiffViewProps } from './types.js';

// 一条差异：same 原样、add 只在右边、del 只在左边
type DiffOp = { type: 'same' | 'add' | 'del'; text: string };
// 比较用的一行：text 是显示原文，key 是比对键（忽略空白模式下把行内空白压成一个空格再 trim）
type Row = { text: string; key: string };
// LCS 计算上限：中间段行数乘积超过这个值就退化为「整段替换」，避免大文件把主线程卡住
const DP_LIMIT = 400_000;

/*** 比对键归一：行内连续空白压成一个空格并去掉首尾空白；显示仍用原文，缩进不丢 ***/
function normalize(line: string): string {
  return line.replace(/\s+/g, ' ').trim();
}

/*** 切行：末尾换行不产生一行空内容（否则每个文件都会多出一条假的空行差异） ***/
function toRows(text: string, ignore: boolean): Row[] {
  const lines = text.split(/\r?\n/);
  if (lines.length > 1 && lines[lines.length - 1] === '') lines.pop(); // 尾部换行忽略
  return lines.map((line) => ({ text: line, key: ignore ? normalize(line) : line }));
}

/*** 中间段做 LCS 对齐：先剪掉公共前后缀，剩下的才真算，日常改动只占几行 ***/
function alignMiddle(a: Row[], b: Row[]): DiffOp[] {
  if (!a.length || !b.length) return [...a.map((r) => ({ type: 'del' as const, text: r.text })), ...b.map((r) => ({ type: 'add' as const, text: r.text }))];
  if (a.length * b.length > DP_LIMIT) return [...a.map((r) => ({ type: 'del' as const, text: r.text })), ...b.map((r) => ({ type: 'add' as const, text: r.text }))]; // 超限：整段替换，语义仍正确
  const dp: number[][] = Array.from({ length: a.length + 1 }, () => new Array<number>(b.length + 1).fill(0)); // dp[i][j]：a 前 i 行与 b 前 j 行的 LCS 长度
  for (let i = a.length - 1; i >= 0; i -= 1) {
    for (let j = b.length - 1; j >= 0; j -= 1) {
      dp[i][j] = a[i].key === b[j].key ? dp[i + 1][j + 1] + 1 : Math.max(dp[i + 1][j], dp[i][j + 1]);
    }
  }
  const ops: DiffOp[] = [];
  let i = 0;
  let j = 0;
  while (i < a.length && j < b.length) {
    if (a[i].key === b[j].key) { ops.push({ type: 'same', text: a[i].text }); i += 1; j += 1; continue; }
    if (dp[i + 1][j] >= dp[i][j + 1]) { ops.push({ type: 'del', text: a[i].text }); i += 1; continue; }
    ops.push({ type: 'add', text: b[j].text }); j += 1;
  }
  for (; i < a.length; i += 1) ops.push({ type: 'del', text: a[i].text });
  for (; j < b.length; j += 1) ops.push({ type: 'add', text: b[j].text });
  return ops;
}

/*** 逐行差异：剪公共前后缀后对齐中间段，输出完整 same / add / del 序列 ***/
function diffLines(before: string, after: string, ignore: boolean): DiffOp[] {
  const a = toRows(before, ignore);
  const b = toRows(after, ignore);
  let head = 0;
  while (head < a.length && head < b.length && a[head].key === b[head].key) head += 1; // 公共前缀
  let tail = 0;
  while (tail < a.length - head && tail < b.length - head && a[a.length - 1 - tail].key === b[b.length - 1 - tail].key) tail += 1; // 公共后缀
  const midA = a.slice(head, a.length - tail);
  const midB = b.slice(head, b.length - tail);
  return [
    ...a.slice(0, head).map((r) => ({ type: 'same' as const, text: r.text })),
    ...alignMiddle(midA, midB),
    ...a.slice(a.length - tail).map((r) => ({ type: 'same' as const, text: r.text })),
  ];
}

/*** 文本差异对比：行级对齐 + 增删着色 + 双行号列，超限时退化为整段替换（只影响精度不影响语义） ***/
export function diffView(props: DiffViewProps): HTMLElement {
  const ignore = props.ignoreWhitespace === true; // 只在显式开启时归一行内空白
  const ops = diffLines(props.before, props.after, ignore);
  const added = ops.filter((o) => o.type === 'add').length; // 新增行数：统计条与读屏共用
  const removed = ops.filter((o) => o.type === 'del').length; // 删除行数
  let oldNo = 0;
  let newNo = 0;
  const rows = ops.map((op) => {
    if (op.type !== 'add') oldNo += 1; // same 与 del 占旧行号
    if (op.type !== 'del') newNo += 1; // same 与 add 占新行号
    const sign = op.type === 'add' ? '+' : op.type === 'del' ? '−' : ' ';
    return h(
      'div',
      { class: `ua-diff-row is-${op.type}` },
      h('span', { class: 'ua-diff-no' }, op.type === 'add' ? '' : String(oldNo)),
      h('span', { class: 'ua-diff-no' }, op.type === 'del' ? '' : String(newNo)),
      h('span', { class: 'ua-diff-sign', 'aria-hidden': 'true' }, sign),
      h('span', { class: 'ua-diff-text' }, op.text || ' '),
    );
  });
  const stats = props.showStats === false
    ? null
    : h(
      'div',
      { class: 'ua-diff-stats' },
      h('span', { class: 'ua-diff-add' }, `+${added}`),
      h('span', { class: 'ua-diff-del' }, `−${removed}`),
      ignore ? h('span', { class: 'ua-diff-note' }, '已忽略行内空白差异') : null, // 归一口径必须写在脸上，否则「为什么不报这几行」说不清
    );
  return h(
    'div',
    { class: 'ua-diff', role: 'group', 'aria-label': props.ariaLabel ?? `文本差异：新增 ${added} 行，删除 ${removed} 行` },
    stats,
    h('div', { class: 'ua-diff-body' }, ...rows),
  );
}