/**
 * A thin wrapper over the incus CLI. Thin on purpose: the lab's value is in the scenario
 * model, not in re-describing a hypervisor.
 *
 * Everything here goes through incus's own channel and never over IP. A scenario is a
 * closed address space — two scenarios raised from one declaration hold the same
 * addresses and must never meet — so the workstation has no route into either, and
 * reaching a machine by address would make concurrency impossible in the worst way:
 * not with an error, but with one scenario's traffic arriving in another.
 *
 * See novox/hq 02-DECISIONS/0032-a-scenario-is-an-isolated-address-space.md
 */

import { spawn } from "node:child_process";

/**
 * How to invoke incus. Overridable because the socket is group-owned and a session that
 * predates the group grant cannot reach it — which is a real thing that happens on the
 * machine that just installed it.
 */
const INCUS = (process.env["MESH_LAB_INCUS"] ?? "incus").split(" ").filter(Boolean);

export interface IncusResult {
  stdout: string;
  stderr: string;
}

export class IncusError extends Error {
  readonly args: string[];
  readonly stderr: string;
  readonly exitCode: number | null;

  constructor(args: string[], stderr: string, exitCode: number | null) {
    const detail = stderr.trim() || (exitCode === null ? "timed out" : `exit ${exitCode}`);
    super(`incus ${args.join(" ")} failed: ${detail}`);
    this.name = "IncusError";
    this.args = args;
    this.stderr = stderr;
    this.exitCode = exitCode;
  }
}

/**
 * Runs incus with **stdin closed**, which is not incidental.
 *
 * Several incus subcommands accept a YAML definition on stdin and, given a descriptor
 * that is not a terminal, wait for one. Under a shell that never happens because stdin is
 * a TTY; under a spawned process it hangs until the timeout kills it — and the timeout
 * kill produces an empty stderr, so the failure arrives with no explanation at all.
 *
 * Found exactly that way: the first raise reported "failed: (no output)" on a command
 * that worked perfectly when typed.
 */
export async function incus(args: string[], timeoutMs = 60_000): Promise<IncusResult> {
  const [command, ...prefix] = INCUS;
  if (!command) throw new Error("MESH_LAB_INCUS is empty");

  return new Promise((resolve, reject) => {
    const child = spawn(command, [...prefix, ...args], {
      stdio: ["ignore", "pipe", "pipe"],
    });

    let stdout = "";
    let stderr = "";
    let timedOut = false;

    const timer = setTimeout(() => {
      timedOut = true;
      child.kill("SIGKILL");
    }, timeoutMs);

    child.stdout.on("data", (chunk) => (stdout += chunk));
    child.stderr.on("data", (chunk) => (stderr += chunk));

    child.on("error", (err) => {
      clearTimeout(timer);
      reject(new IncusError(args, err.message, null));
    });

    child.on("close", (code) => {
      clearTimeout(timer);
      if (timedOut) {
        reject(new IncusError(args, `timed out after ${timeoutMs}ms`, null));
      } else if (code === 0) {
        resolve({ stdout, stderr });
      } else {
        reject(new IncusError(args, stderr, code));
      }
    });
  });
}

/**
 * Like `incus`, but a failure is an answer rather than an exception. Returns the command's
 * output, or `null` if it failed.
 *
 * **Never truthiness-test this.** Plenty of incus commands succeed with no output at all —
 * `exec … true`, `network delete`, `start` — so an empty string means *worked and said
 * nothing*, and `if (await incusOk(...))` reads that as failure. Use `succeeds()` when the
 * question is whether it worked, and `!== null` when the output matters.
 *
 * This is the mesh's own recurring fault in miniature: absence and success made
 * indistinguishable. It cost a raise that reported a machine unreachable while `incus exec`
 * on that machine worked perfectly.
 */
export async function incusOk(args: string[], timeoutMs = 60_000): Promise<string | null> {
  try {
    return (await incus(args, timeoutMs)).stdout;
  } catch {
    return null;
  }
}

/** Did the command work? For commands whose output is not the point. */
export async function succeeds(args: string[], timeoutMs = 60_000): Promise<boolean> {
  return (await incusOk(args, timeoutMs)) !== null;
}

export async function isReachable(): Promise<boolean> {
  return succeeds(["info"], 15_000);
}

/** Storage drivers the daemon offers. It only advertises those whose tooling it found. */
export async function supportedDrivers(): Promise<string[]> {
  const info = (await incusOk(["info"], 15_000)) ?? "";
  const block = info.split("storage_supported_drivers:")[1] ?? "";
  return [...block.matchAll(/-\s+name:\s*(\w+)/g)].map((m) => m[1] ?? "");
}

export interface Pool {
  name: string;
  driver: string;
}

export async function pools(): Promise<Pool[]> {
  const csv = (await incusOk(["storage", "list", "--format", "csv"])) ?? "";
  return csv
    .split("\n")
    .filter(Boolean)
    .map((line) => {
      const [name = "", driver = ""] = line.split(",");
      return { name, driver };
    });
}

export async function networkExists(name: string): Promise<boolean> {
  return succeeds(["network", "show", name], 15_000);
}

export async function instanceExists(name: string): Promise<boolean> {
  return succeeds(["config", "show", name], 15_000);
}

export interface TaggedInstance {
  name: string;
  status: string;
  instanceId: string;
  machine: string;
}

/**
 * Instances this lab owns, identified by the config keys set when they were created —
 * never by parsing their names.
 *
 * Names were parsed at first, splitting on the last dash to separate machine from
 * instance. That works until a machine is called something like `home-server`, at which
 * point the instance id absorbs half the machine name and `destroy` silently finds
 * nothing. Metadata is what the instance actually knows about itself.
 */
export async function taggedInstances(): Promise<TaggedInstance[]> {
  const json = (await incusOk(["list", "--format", "json"], 30_000)) ?? "[]";
  let parsed: unknown;
  try {
    parsed = JSON.parse(json);
  } catch {
    return [];
  }
  if (!Array.isArray(parsed)) return [];

  const tagged: TaggedInstance[] = [];
  for (const entry of parsed) {
    const item = entry as { name?: string; status?: string; config?: Record<string, string> };
    const instanceId = item.config?.["user.mesh-lab.instance"];
    const machine = item.config?.["user.mesh-lab.machine"];
    if (!instanceId || !machine || !item.name) continue;
    tagged.push({ name: item.name, status: item.status ?? "", instanceId, machine });
  }
  return tagged;
}

export interface TaggedNetwork {
  name: string;
  instanceId: string;
  segment: string;
  /** Absent on a link raised before segment shape was recorded. */
  kind?: "public" | "private";
  cidr: string[];
  mtu?: number;
}

export async function taggedNetworks(): Promise<TaggedNetwork[]> {
  const json = (await incusOk(["network", "list", "--format", "json"], 30_000)) ?? "[]";
  let parsed: unknown;
  try {
    parsed = JSON.parse(json);
  } catch {
    return [];
  }
  if (!Array.isArray(parsed)) return [];

  const tagged: TaggedNetwork[] = [];
  for (const entry of parsed) {
    const item = entry as { name?: string; config?: Record<string, string> };
    const instanceId = item.config?.["user.mesh-lab.instance"];
    const segment = item.config?.["user.mesh-lab.segment"];
    if (!instanceId || !segment || !item.name) continue;
    const kind = item.config?.["user.mesh-lab.kind"];
    const cidr = item.config?.["user.mesh-lab.cidr"];
    tagged.push({
      name: item.name,
      instanceId,
      segment,
      ...(kind === "public" || kind === "private" ? { kind } : {}),
      cidr: cidr ? cidr.split(",").filter(Boolean) : [],
      ...(Number.isFinite(Number(item.config?.["user.mesh-lab.mtu"]))
        ? { mtu: Number(item.config?.["user.mesh-lab.mtu"]) }
        : {}),
    });
  }
  return tagged;
}