/**
 * Which commands the assistant may run without a per-command approval click,
 * for users who opted into read-only execution.
 *
 * The check parses the command into arguments and matches the resolved binary
 * against the allowlist. Substring matching would be trivially defeated
 * ("df; rm -rf /" contains "df"), so any shell metacharacter that could chain,
 * redirect or substitute a second command rejects the whole string outright.
 */

export const READ_ONLY_COMMANDS = new Set([
  "df",
  "du",
  "free",
  "uptime",
  "uname",
  "whoami",
  "hostname",
  "id",
  "ps",
  "top",
  "systemctl",
  "journalctl",
  "docker",
  "ip",
  "ss",
  "netstat",
  "lsblk",
  "cat",
  "ls",
  "stat",
  "which",
  "date",
  "lscpu",
  "vmstat",
  "iostat",
]);

/** Characters that let one command become several. */
const SHELL_METACHARACTERS = /[;&|`$><\n\r\\]/;

/** Subcommands that are safe for otherwise-powerful binaries. */
const SUBCOMMAND_ALLOWLIST: Record<string, Set<string>> = {
  systemctl: new Set([
    "status",
    "list-units",
    "list-unit-files",
    "is-active",
    "is-enabled",
    "show",
  ]),
  docker: new Set([
    "ps",
    "stats",
    "images",
    "logs",
    "inspect",
    "version",
    "info",
  ]),
  ip: new Set(["a", "addr", "link", "route", "neigh"]),
};

/** Paths `cat` may read. Anything else could disclose credentials. */
const CAT_ALLOWED_PREFIXES = ["/proc/", "/sys/", "/etc/os-release"];

export interface CommandCheck {
  allowed: boolean;
  reason?: string;
}

export function isReadOnlyCommand(raw: string): CommandCheck {
  const command = raw.trim();
  if (!command) return { allowed: false, reason: "Empty command" };

  if (SHELL_METACHARACTERS.test(command)) {
    return {
      allowed: false,
      reason: "Command chaining, redirection and substitution are not allowed",
    };
  }

  const parts = command.split(/\s+/).filter(Boolean);
  if (!parts.length) return { allowed: false, reason: "Empty command" };

  // Reject env-prefixed and privilege-escalating forms outright.
  const head = parts[0];
  if (head === "sudo" || head === "su" || head === "doas" || head === "env") {
    return { allowed: false, reason: `${head} is not allowed` };
  }

  // A path like /usr/bin/df resolves to its basename.
  const binary = head.includes("/")
    ? head.slice(head.lastIndexOf("/") + 1)
    : head;

  if (!READ_ONLY_COMMANDS.has(binary)) {
    return {
      allowed: false,
      reason: `${binary} is not on the read-only allowlist`,
    };
  }

  const allowedSubcommands = SUBCOMMAND_ALLOWLIST[binary];
  if (allowedSubcommands) {
    const subcommand = parts.slice(1).find((part) => !part.startsWith("-"));
    if (!subcommand || !allowedSubcommands.has(subcommand)) {
      return {
        allowed: false,
        reason:
          `${binary} ${subcommand ?? ""}`.trim() +
          " is not on the read-only allowlist",
      };
    }
  }

  if (binary === "cat") {
    const targets = parts.slice(1).filter((part) => !part.startsWith("-"));
    if (!targets.length) {
      return { allowed: false, reason: "cat needs a file path" };
    }
    for (const target of targets) {
      const permitted = CAT_ALLOWED_PREFIXES.some((prefix) =>
        prefix.endsWith("/") ? target.startsWith(prefix) : target === prefix,
      );
      if (!permitted) {
        return {
          allowed: false,
          reason: `cat is limited to ${CAT_ALLOWED_PREFIXES.join(", ")}`,
        };
      }
    }
  }

  return { allowed: true };
}