export type Cpp14PolicySeverity = "error" | "warning" | "hint";

export type Cpp14PolicyIssue = {
  id: string;
  severity: Cpp14PolicySeverity;
  message: string;
  detail: string;
  line: number;
  column: number;
  endLine: number;
  endColumn: number;
};

type RegexRule = {
  id: string;
  severity: Cpp14PolicySeverity;
  pattern: RegExp;
  message: string;
  detail: string;
};

const REGEX_RULES: RegexRule[] = [
  {
    id: "cpp17-header",
    severity: "error",
    pattern: /#\s*include\s*<\s*(optional|variant|any|string_view|filesystem|charconv|execution)\s*>/g,
    message: "检测到 C++17+ 头文件",
    detail: "福建 CSP-J/S 环境通常以 C++14 为准，建议改为 C++14 可用写法。",
  },
  {
    id: "if-constexpr",
    severity: "error",
    pattern: /\bif\s+constexpr\b/g,
    message: "检测到 if constexpr（C++17）",
    detail: "请改用普通条件分支或模板特化方案。",
  },
  {
    id: "structured-binding",
    severity: "error",
    pattern: /\b(?:const\s+)?auto(?:\s*&|\s*&&)?\s*\[[^\]\n]+\]\s*=/g,
    message: "检测到结构化绑定（C++17）",
    detail: "可改为 pair.first/second 或自定义结构体字段。",
  },
  {
    id: "cpp17-stdlib",
    severity: "error",
    pattern: /\bstd::(optional|variant|any|string_view|filesystem|byte|clamp|gcd|lcm)\b/g,
    message: "检测到 C++17+ 标准库符号",
    detail: "请替换为 C++14 可用实现，避免提交到老版本 GCC 报 CE。",
  },
  {
    id: "void-main",
    severity: "error",
    pattern: /\bvoid\s+main\s*\(/g,
    message: "main 函数返回类型不规范",
    detail: "请使用 int main()，并在末尾 return 0;",
  },
  {
    id: "windows-i64d",
    severity: "warning",
    pattern: /%I64d/g,
    message: "检测到 %I64d（Windows 特有）",
    detail: "Linux 评测机请使用 %lld 读写 long long。",
  },
  {
    id: "windows-int64",
    severity: "warning",
    pattern: /\b__int64\b/g,
    message: "检测到 __int64（非标准）",
    detail: "建议改为标准类型 long long。",
  },
  {
    id: "bits-header",
    severity: "warning",
    pattern: /#\s*include\s*<\s*bits\/stdc\+\+\.h\s*>/g,
    message: "检测到 <bits/stdc++.h>",
    detail: "福建实战建议优先使用标准头文件，提升环境兼容性。",
  },
];

export const CSP_CPP14_TIPS: string[] = [
  "编译标准固定为 C++14（建议按 -std=gnu++14 习惯编码），不要使用 C++17+ 特性。",
  "main 必须是 int main()，结尾写 return 0;。",
  "long long 的 scanf/printf 请使用 %lld，不要使用 %I64d。",
  "命名/提交包按考场须知执行：题目目录与源码名使用英文小写。",
  "福建二轮常见要求是文件读写（freopen），赛前请按官方样例再核对一次。",
];

function buildLineStarts(text: string): number[] {
  const starts = [0];
  for (let i = 0; i < text.length; i += 1) {
    if (text[i] === "\n") starts.push(i + 1);
  }
  return starts;
}

function offsetToPosition(lineStarts: number[], offset: number): { line: number; column: number } {
  let lo = 0;
  let hi = lineStarts.length - 1;
  while (lo <= hi) {
    const mid = (lo + hi) >> 1;
    if (lineStarts[mid] <= offset) lo = mid + 1;
    else hi = mid - 1;
  }
  const lineIdx = Math.max(0, hi);
  return {
    line: lineIdx + 1,
    column: offset - lineStarts[lineIdx] + 1,
  };
}

function pushIssue(
  issues: Cpp14PolicyIssue[],
  id: string,
  severity: Cpp14PolicySeverity,
  message: string,
  detail: string,
  line: number,
  column: number,
  endLine: number,
  endColumn: number
) {
  issues.push({ id, severity, message, detail, line, column, endLine, endColumn });
}

export function analyzeCpp14Policy(code: string): Cpp14PolicyIssue[] {
  const text = (code ?? "").replace(/\r\n?/g, "\n");
  if (!text.trim()) return [];

  const issues: Cpp14PolicyIssue[] = [];
  const lineStarts = buildLineStarts(text);

  for (const rule of REGEX_RULES) {
    const matcher = new RegExp(rule.pattern.source, rule.pattern.flags);
    let match = matcher.exec(text);
    while (match) {
      const start = match.index;
      const end = start + Math.max(1, match[0].length);
      const p1 = offsetToPosition(lineStarts, start);
      const p2 = offsetToPosition(lineStarts, end);
      pushIssue(
        issues,
        rule.id,
        rule.severity,
        rule.message,
        rule.detail,
        p1.line,
        p1.column,
        p2.line,
        p2.column
      );
      if (matcher.lastIndex === match.index) matcher.lastIndex += 1;
      match = matcher.exec(text);
    }
  }

  if (/\bint\s+main\s*\(/.test(text) && !/\breturn\s+0\s*;/.test(text)) {
    const idx = text.search(/\bint\s+main\s*\(/);
    const pos = offsetToPosition(lineStarts, Math.max(0, idx));
    pushIssue(
      issues,
      "main-return-zero",
      "warning",
      "建议在 main 末尾显式 return 0;",
      "部分考场与评测环境会严格检查主函数返回行为。",
      pos.line,
      pos.column,
      pos.line,
      pos.column + 3
    );
  }

  if (/\blong\s+long\b/.test(text) && /\b(?:scanf|printf)\s*\(/.test(text) && !/%lld/.test(text)) {
    const idx = text.search(/\b(?:scanf|printf)\s*\(/);
    const pos = offsetToPosition(lineStarts, Math.max(0, idx));
    pushIssue(
      issues,
      "ll-format",
      "warning",
      "检测到 long long + scanf/printf，建议确认格式符为 %lld",
      "Linux 评测环境不支持 %I64d。",
      pos.line,
      pos.column,
      pos.line,
      pos.column + 6
    );
  }

  return issues;
}