#!/usr/bin/env node

// Rejects unresolved merge conflict markers in tracked files.
import { spawnSync } from "node:child_process";
import fs from "node:fs";
import path from "node:path";
import { fileURLToPath } from "node:url";

const CONFLICT_MARKER_GREP_PATTERN = "^(<<<<<<< |\\|\\|\\|\\|\\|\\|\\| |=======$|>>>>>>> )";

function isBinaryBuffer(buffer) {
  return buffer.includes(0);
}

/**
 * Returns one-based line numbers containing merge conflict markers.
 */
export function findConflictMarkerLines(content) {
  const lines = content.split(/\r?\n/u);
  const matches = [];
  for (const [index, line] of lines.entries()) {
    if (
      line.startsWith("<<<<<<< ") ||
      line.startsWith("||||||| ") ||
      line === "=======" ||
      line.startsWith(">>>>>>> ")
    ) {
      matches.push(index + 1);
    }
  }
  return matches;
}

/**
 * Scans a list of files for merge conflict markers, skipping binary content.
 * This is kept for direct, small-scale use (tests); the tracked-files path
 * uses git grep directly to avoid reading large files into memory.
 */
export function findConflictMarkersInFiles(filePaths, readFile = fs.readFileSync) {
  const violations = [];
  for (const filePath of filePaths) {
    let content;
    try {
      content = readFile(filePath);
    } catch {
      continue;
    }
    if (!Buffer.isBuffer(content)) {
      content = Buffer.from(String(content));
    }
    if (isBinaryBuffer(content)) {
      continue;
    }
    const lines = findConflictMarkerLines(content.toString("utf8"));
    if (lines.length > 0) {
      violations.push({
        filePath,
        lines,
      });
    }
  }
  return violations;
}

/**
 * Parses output from `git grep -n -z -o -I -E` into violation records.
 * The record format is:
 *   path\0line-number\0match-text\n
 * The path must be read from its NUL delimiter before any newline-based
 * record splitting: -z reports paths verbatim, and git allows newlines in
 * tracked filenames, so splitting the output on newlines first would cut a
 * newline-containing path across two records and silently mangle it.
 * Keeping parsing to exact grep match records avoids reading candidate files
 * whole and keeps memory bounded regardless of file size.
 */
function parseGitGrepConflictMarkerOutput(stdout) {
  const byPath = new Map();
  const output = stdout.toString("utf8");
  let cursor = 0;

  while (cursor < output.length) {
    const pathEnd = output.indexOf("\0", cursor);
    if (pathEnd === -1) {
      break;
    }
    const lineNumberEnd = output.indexOf("\0", pathEnd + 1);
    if (lineNumberEnd === -1) {
      break;
    }
    // With -o the match text is a single-line match, so the record ends at
    // the next newline after the line-number field.
    const matchEnd = output.indexOf("\n", lineNumberEnd + 1);
    const relativePath = output.slice(cursor, pathEnd);
    const lineNumber = Number(output.slice(pathEnd + 1, lineNumberEnd));
    cursor = matchEnd === -1 ? output.length : matchEnd + 1;
    if (!relativePath || !Number.isFinite(lineNumber) || lineNumber <= 0) {
      continue;
    }
    const existing = byPath.get(relativePath);
    if (existing) {
      existing.push(lineNumber);
    } else {
      byPath.set(relativePath, [lineNumber]);
    }
  }

  const violations = [];
  for (const [relativePath, lineNumbers] of byPath) {
    lineNumbers.sort((a, b) => a - b);
    violations.push({
      filePath: relativePath,
      lines: lineNumbers,
    });
  }
  violations.sort((a, b) => a.filePath.localeCompare(b.filePath));
  return violations;
}

/**
 * Uses git grep to find exact conflict-marker matches in tracked files.
 */
export function findConflictMarkersInTrackedFiles(cwd = process.cwd(), run = spawnSync) {
  const result = run(
    "git",
    ["grep", "--no-color", "-n", "-z", "-o", "-I", "-E", CONFLICT_MARKER_GREP_PATTERN, "--", "."],
    {
      cwd,
      encoding: "buffer",
    },
  );
  if (result.status === 1) {
    return [];
  }
  if (result.status !== 0) {
    const stderr = result.stderr?.toString("utf8").trim();
    throw new Error(stderr || `git grep failed with status ${result.status ?? "unknown"}`);
  }
  return parseGitGrepConflictMarkerOutput(result.stdout);
}

/**
 * Runs the merge conflict marker check.
 */
export async function main() {
  const cwd = process.cwd();
  const violations = findConflictMarkersInTrackedFiles(cwd);
  if (violations.length === 0) {
    return;
  }

  console.error("Found unresolved merge conflict markers:");
  for (const violation of violations) {
    // findConflictMarkersInTrackedFiles already returns paths relative to cwd.
    console.error(`- ${violation.filePath}:${violation.lines.join(",")}`);
  }
  process.exitCode = 1;
}

if (process.argv[1] && path.resolve(process.argv[1]) === fileURLToPath(import.meta.url)) {
  main().catch(
    /** @param {unknown} error */ (error) => {
      console.error(error);
      process.exit(1);
    },
  );
}