export type ProviderKind = "vulnerability" | "provenance";

const MEMORY_MAX = 1_073_741_824;
const TASKS_MAX = 64;
const STOP_TIMEOUT_MS = 5_000;
const RUNTIME_GRACE_MS = 10_000;
const UNIT_NAME = /^ca-provider-(?:vulnerability|provenance)-[1-9][0-9]*-[0-9a-f]{24}\.scope$/u;
const UNIT_NONCE = /^[0-9a-f]{24}$/u;
const ENVIRONMENT_NAME = /^[A-Za-z_][A-Za-z0-9_]*$/u;
const ENFORCEMENT_GATE = [
  'cgroup_path=""',
  "while IFS=: read -r hierarchy controllers candidate; do",
  '  if [ "$hierarchy" = 0 ] && [ -z "$controllers" ]; then cgroup_path=$candidate; fi',
  "done < /proc/self/cgroup",
  'if [ -z "$cgroup_path" ]; then',
  "  printf '%s\\n' 'provider cgroup enforcement failed: unified cgroup v2 membership is required' >&2",
  "  exit 125",
  "fi",
  'case "$cgroup_path" in',
  '  */"$0") ;;',
  "  *)",
  "    printf '%s\\n' 'provider cgroup enforcement failed: unit membership is invalid' >&2",
  "    exit 125",
  "    ;;",
  "esac",
  "cgroup_root=/sys/fs/cgroup$cgroup_path",
  "require_cgroup_value() {",
  '  actual=$(/bin/cat "$cgroup_root/$1") || {',
  "    printf 'provider cgroup enforcement failed: cannot read %s\\n' \"$1\" >&2",
  "    exit 125",
  "  }",
  '  if [ "$actual" != "$2" ]; then',
  "    printf 'provider cgroup enforcement failed: %s is %s, expected %s\\n' \"$1\" \"$actual\" \"$2\" >&2",
  "    exit 125",
  "  fi",
  "}",
  `require_cgroup_value memory.max ${MEMORY_MAX}`,
  "require_cgroup_value memory.swap.max 0",
  `require_cgroup_value pids.max ${TASKS_MAX}`,
  "require_cgroup_value cpu.max '100000 100000'",
  'exec "$@"',
].join("\n");

export function formatProviderCgroupUnitName(
  kind: ProviderKind,
  supervisorPid: number,
  nonce: string,
): string {
  if (!Number.isSafeInteger(supervisorPid) || supervisorPid <= 0 || !UNIT_NONCE.test(nonce)) {
    throw new TypeError("provider cgroup unit identity is invalid");
  }
  const unit = `ca-provider-${kind}-${supervisorPid}-${nonce}.scope`;
  assertUnit(unit);
  return unit;
}

export function systemdRunProviderArguments(
  unit: string,
  timeoutMs: number,
  cpuSeconds: number,
  nodeExecutable: string,
  wrapperScript: string,
  reportPath: string,
  reportDev: number,
  reportIno: number,
): string[] {
  assertUnit(unit);
  if (!Number.isSafeInteger(timeoutMs) || timeoutMs <= 0 || timeoutMs > Number.MAX_SAFE_INTEGER - RUNTIME_GRACE_MS) {
    throw new TypeError("provider cgroup runtime is invalid");
  }
  if (!Number.isSafeInteger(cpuSeconds) || cpuSeconds <= 0) {
    throw new TypeError("provider cgroup CPU limit is invalid");
  }
  if (
    !nodeExecutable.startsWith("/") || !wrapperScript.startsWith("/") ||
    !reportPath.startsWith("/") || reportPath.includes("\0") ||
    !Number.isSafeInteger(reportDev) || reportDev <= 0 ||
    !Number.isSafeInteger(reportIno) || reportIno <= 0
  ) {
    throw new TypeError("provider scope wrapper path is invalid");
  }
  return [
    "--user",
    "--scope",
    "--collect",
    "--quiet",
    "--expand-environment=no",
    `--unit=${unit}`,
    `--property=MemoryMax=${MEMORY_MAX}`,
    "--property=MemorySwapMax=0",
    `--property=TasksMax=${TASKS_MAX}`,
    "--property=CPUQuota=100%",
    "--property=CPUQuotaPeriodSec=100ms",
    "--property=KillMode=control-group",
    "--property=SendSIGKILL=yes",
    `--property=TimeoutStopSec=${STOP_TIMEOUT_MS}ms`,
    `--property=RuntimeMaxSec=${timeoutMs + RUNTIME_GRACE_MS}ms`,
    "--",
    "/bin/sh",
    "-eu",
    "-c",
    ENFORCEMENT_GATE,
    unit,
    nodeExecutable,
    wrapperScript,
    String(cpuSeconds),
    reportPath,
    String(reportDev),
    String(reportIno),
  ];
}

export type ProviderScopeFrame = Readonly<{
  bwrapInput: Buffer;
  reportPath: string;
  reportDev: number;
  reportIno: number;
}>;

export function encodeProviderScopeFrame(input: ProviderScopeFrame): Buffer {
  if (
    !Buffer.isBuffer(input.bwrapInput) || input.bwrapInput.byteLength === 0 ||
    !input.reportPath.startsWith("/") || input.reportPath.includes("\0") ||
    !Number.isSafeInteger(input.reportDev) || input.reportDev <= 0 ||
    !Number.isSafeInteger(input.reportIno) || input.reportIno <= 0
  ) {
    throw new TypeError("provider scope frame is invalid");
  }
  const payload = Buffer.from(JSON.stringify({
    bwrapInputBase64: input.bwrapInput.toString("base64"),
    reportPath: input.reportPath,
    reportDev: input.reportDev,
    reportIno: input.reportIno,
  }));
  const frame = Buffer.allocUnsafe(4 + payload.byteLength);
  frame.writeUInt32BE(payload.byteLength, 0);
  payload.copy(frame, 4);
  return frame;
}

export function encodeProviderBwrapInput(
  arguments_: readonly string[],
  environment: Readonly<Record<string, string | undefined>>,
): Buffer {
  if (arguments_.some((argument) => argument.includes("\0"))) {
    throw new TypeError("provider bwrap argument is invalid");
  }
  const entries = Object.entries(environment).sort(([left], [right]) =>
    left < right ? -1 : left > right ? 1 : 0,
  );
  if (entries.some(([name, value]) =>
    !ENVIRONMENT_NAME.test(name) || value === undefined || value.includes("\0")
  )) {
    throw new TypeError("provider bwrap environment is invalid");
  }
  const input = ["--clearenv"];
  for (const [name, value] of entries) input.push("--setenv", name, value ?? "");
  input.push(...arguments_);
  return Buffer.from(`${input.join("\0")}\0`);
}

export function systemctlKillProviderArguments(unit: string): string[] {
  assertUnit(unit);
  return ["--user", "kill", "--kill-whom=all", "--signal=SIGKILL", unit];
}

function assertUnit(unit: string): void {
  if (!UNIT_NAME.test(unit)) throw new TypeError("provider cgroup unit name is invalid");
}