// bash-normalize.mjs — Normalize bash parameter expansion evasion techniques.
//
// Attackers can evade command-name matching by inserting shell metacharacters
// that are transparent to bash but break regex patterns.
//
// This module strips these constructs from command names so that downstream
// pattern matching sees the canonical form.
//
// Exported as a shared module — used by pre-bash-destructive.mjs and
// pre-install-supply-chain.mjs.
//
// Pipeline (defense-in-depth layer above Claude Code 2.1.98+ harness fixes):
//   T1 — empty single quotes:       w''get           -> wget
//   T2 — empty double quotes:       r""m             -> rm
//   T3 — parameter expansion:       ${x} / ${FOO}    -> x / ''
//   T4 — backslash-between-words:   c\u\r\l          -> curl
//   T5 — IFS word-splitting:        rm${IFS}-rf${IFS}/ -> rm -rf /
//   T6 — ANSI-C hex quoting:        $'\x72\x6d' -rf / -> rm -rf /
//
// T5 and T6 run before T1-T4 so their outputs feed the rest of the pipeline
// in canonical form. Both preserve single-quoted literals (false-positive
// probe: `echo '${IFS}'` stays untouched).

/**
 * T5 — strip IFS-based word splitting outside single-quoted regions.
 *
 * Patterns matched: ${IFS}, ${IFS:0:1}, $IFS. Each replaced with a single
 * space. Content inside '...' is preserved via placeholder masking so the
 * literal string `'${IFS}'` never expands.
 */
function normalizeIFS(cmd) {
  const placeholders = [];
  const MARK = '\x00';
  const masked = cmd.replace(/'[^']*'/g, (match) => {
    placeholders.push(match);
    return `${MARK}${placeholders.length - 1}${MARK}`;
  });
  const normalized = masked
    .replace(/\$\{IFS:0:1\}/g, ' ')
    .replace(/\$\{IFS\}/g, ' ')
    .replace(/\$IFS\b/g, ' ');
  return normalized.replace(
    new RegExp(`${MARK}(\\d+)${MARK}`, 'g'),
    (_, idx) => placeholders[parseInt(idx, 10)],
  );
}

/**
 * T6 — decode ANSI-C hex quoting inside `$'...'` contexts only.
 *
 * Shell treats $'\x72\x6d' as the bytes r and m. Attackers use this to
 * hide command names from regex gates. We decode only the \xHH escape
 * sequences inside the $'...' wrapper. Regular single-quoted strings
 * '...' are not touched.
 */
function normalizeAnsiCHex(cmd) {
  return cmd.replace(/\$'([^']*)'/g, (match, content) => {
    return content.replace(/\\x([0-9a-fA-F]{2})/g, (_, hex) =>
      String.fromCharCode(parseInt(hex, 16)),
    );
  });
}

/**
 * Normalize bash parameter expansion and quoting evasion in a command string.
 *
 * Strips (T1-T6):
 *   - T1 Empty single quotes: '' (e.g., w''get -> wget)
 *   - T2 Empty double quotes: "" (e.g., r""m -> rm)
 *   - T3 Single-char parameter expansion: ${x} -> x (evasion: attacker sets x=x)
 *   - T3 Multi-char parameter expansion: ${ANYTHING} -> '' (unknown value)
 *   - T4 Backslash escapes between word chars, iteratively (c\u\r\l -> curl)
 *   - T5 IFS word-splitting: ${IFS}, ${IFS:0:1}, $IFS -> ' '
 *   - T6 ANSI-C hex quoting inside $'...' -> decoded bytes
 *   - Backtick subshell with empty/whitespace content
 *
 * Does NOT strip:
 *   - Quotes around arguments (only targets empty quotes that split command names)
 *   - $VAR without braces outside IFS (not an evasion pattern)
 *   - Backslashes before non-word chars (\n, \t, etc.)
 *   - Content inside single-quoted regions (T5 preserves them; `echo '${IFS}'` untouched)
 *
 * @param {string} cmd - Raw command string
 * @returns {string} Normalized command string
 */
export function normalizeBashExpansion(cmd) {
  if (!cmd || typeof cmd !== 'string') return cmd || '';

  // T5 + T6 run first so their outputs feed the rest of the pipeline in
  // canonical form. Order inside T5/T6 is internal; externally we label
  // the full pipeline T1-T6.
  let result = normalizeIFS(cmd);
  result = normalizeAnsiCHex(result);

  result = result
    // T1 Strip empty single quotes: w''get -> wget
    .replace(/''/g, '')
    // T2 Strip empty double quotes: r""m -> rm
    .replace(/""/g, '')
    // T3 Single-char ${x} -> x (evasion: c${u}rl -> curl, assumes x=x)
    .replace(/\$\{(\w)\}/g, '$1')
    // T3 Multi-char ${ANYTHING} -> '' (unknown value, strip entirely)
    .replace(/\$\{[^}]*\}/g, '')
    // Strip backtick subshell with empty/whitespace content
    .replace(/`\s*`/g, '');

  // T4 Iteratively strip backslash between word chars (c\u\r\l needs 2 passes)
  let prev;
  do {
    prev = result;
    result = result.replace(/(\w)\\(\w)/g, '$1$2');
  } while (result !== prev);

  return result;
}