/**
 * Thin wrapper around the sl0ppij binary.
 *
 * sl0ppi orchestrates, it does not reimplement: every piece of state comes back
 * out of `list-tabs`/`list-panes`, so there is nothing here to desync.
 *
 * Index conventions, both verified against a live session rather than inferred,
 * because getting either wrong closes or focuses the wrong tab:
 *
 *   list-tabs `position`     0-based
 *   close-tab --tab-id       0-based  (same numbering as `position`)
 *   go-to-tab <INDEX>        1-BASED  (matches the `GoToTab 1` keybinds)
 *
 * Closing also RENUMBERS the tabs after it, so a batch of closes must run in
 * descending position order.
 */

import { spawnSync } from "node:child_process";

export const DEFAULT_BIN = "sl0ppij";

export interface TabInfo {
  position: number;
  name: string;
  purpose?: string;
  active?: boolean;
}

export interface PaneInfo {
  id: number;
  tab_id: number;
  is_plugin: boolean;
  title: string;
  purpose?: string;
  exited?: boolean;
  is_held?: boolean;
  terminal_command?: string | null;
}

export interface RunResult {
  code: number;
  stdout: string;
  stderr: string;
}

export class Sl0ppijError extends Error {
  constructor(
    message: string,
    readonly result: RunResult,
  ) {
    super(message);
    this.name = "Sl0ppijError";
  }
}

/**
 * The variables that tell a sl0ppij process "you are inside a session".
 *
 * Both spellings, because the fork exports `SL0PPIJ*` and keeps `ZELLIJ*` for
 * ecosystem compatibility.
 */
export const SESSION_ENV_KEYS = [
  "SL0PPIJ",
  "SL0PPIJ_SESSION_NAME",
  "SL0PPIJ_PANE_ID",
  "ZELLIJ",
  "ZELLIJ_SESSION_NAME",
  "ZELLIJ_PANE_ID",
] as const;

/** A copy of `env` with the "inside a session" markers removed. */
export function withoutSessionEnv(env: NodeJS.ProcessEnv = process.env): NodeJS.ProcessEnv {
  const copy = { ...env };
  for (const key of SESSION_ENV_KEYS) delete copy[key];
  return copy;
}

export interface ClientOptions {
  bin?: string;
  session?: string;
}

export class Sl0ppij {
  readonly bin: string;
  readonly session?: string;

  constructor(options: ClientOptions = {}) {
    this.bin = options.bin ?? process.env.SL0PPI_BIN ?? DEFAULT_BIN;
    this.session = options.session;
  }

  /** Same client, pinned to a session. */
  forSession(session: string): Sl0ppij {
    return new Sl0ppij({ bin: this.bin, session });
  }

  run(
    args: string[],
    { session = true, detached = false }: { session?: boolean; detached?: boolean } = {},
  ): RunResult {
    const argv = session && this.session ? ["-s", this.session, ...args] : args;
    if (process.env.SL0PPI_DEBUG) {
      process.stderr.write(`sl0ppi: exec ${this.bin} ${argv.map((a) => JSON.stringify(a)).join(" ")}\n`);
    }
    const proc = spawnSync(this.bin, argv, {
      encoding: "utf8",
      env: detached ? withoutSessionEnv() : process.env,
    });
    if (proc.error) {
      throw new Sl0ppijError(`could not run ${this.bin}: ${proc.error.message}`, {
        code: -1,
        stdout: "",
        stderr: String(proc.error.message),
      });
    }
    return {
      code: proc.status ?? -1,
      stdout: proc.stdout ?? "",
      stderr: proc.stderr ?? "",
    };
  }

  private runOk(
    args: string[],
    what: string,
    opts?: { session?: boolean; detached?: boolean },
  ): RunResult {
    const result = this.run(args, opts);
    if (result.code !== 0) {
      throw new Sl0ppijError(`${what} failed: ${result.stderr.trim() || result.stdout.trim()}`, result);
    }
    return result;
  }

  listTabs(): TabInfo[] {
    return this.readList<TabInfo>(["action", "list-tabs", "--json"], "list-tabs");
  }

  listPanes(): PaneInfo[] {
    return this.readList<PaneInfo>(["action", "list-panes", "--json"], "list-panes");
  }

  /**
   * Read a `--json` listing, tolerating a flaky underlying CLI.
   *
   * Measured on a 2-vCPU Debian box against a live session: `list-tabs` and
   * `list-panes` each fail about 60% of the time when the session is detached,
   * and about 25% when a client is attached. The failure is either an empty
   * stdout with exit 0, or "There is no active session!" from the action client
   * -- which checks `get_active_session()` before it even looks at `-s`.
   *
   * That is a defect in the terminal, not something a workspace tool should
   * inherit: these are idempotent reads, so retry them. If the session really
   * is gone, say so instead of retrying into a wall.
   */
  private readList<T>(args: string[], what: string, attempts = 5): T[] {
    let lastProblem = "";
    for (let attempt = 0; attempt < attempts; attempt++) {
      const result = this.run(args);
      if (result.code === 0) {
        const text = result.stdout.trim();
        if (text.length > 0) return parseJsonList<T>(text, what);
        lastProblem = "empty output";
      } else {
        lastProblem = (result.stderr.trim() || result.stdout.trim()).split("\n")[0] ?? "";
      }
      if (process.env.SL0PPI_DEBUG) {
        process.stderr.write(`sl0ppi: ${what} attempt ${attempt + 1}: ${lastProblem}\n`);
      }
      pause(120 * (attempt + 1));
    }

    // Out of retries. Distinguish "the session is gone" (an answer) from "the
    // terminal would not talk to us" (a problem worth reporting).
    if (this.session !== undefined && !this.sessionExists(this.session)) return [];
    throw new Sl0ppijError(`${what} failed ${attempts}x (last: ${lastProblem})`, {
      code: -1,
      stdout: "",
      stderr: lastProblem,
    });
  }

  /** Adds a tab from a KDL layout string. Returns its new position. */
  newTab(layoutKdl: string): number {
    const { stdout } = this.runOk(
      ["action", "new-tab", "--layout-string", layoutKdl],
      "new-tab",
    );
    return Number.parseInt(stdout.trim(), 10);
  }

  /** `position` is the 0-based `position` from list-tabs. */
  closeTab(position: number): void {
    this.runOk(["action", "close-tab", "--tab-id", String(position)], "close-tab");
  }

  /** Takes a 0-based position and converts to go-to-tab's 1-based index. */
  focusTab(position: number): void {
    this.runOk(["action", "go-to-tab", String(position + 1)], "go-to-tab");
  }

  /**
   * Every session sl0ppij knows about, live or dead-but-resurrectable.
   *
   * `--short` lists EXITED sessions too with no way to tell them apart, so we
   * parse the long form. (The same trap is documented in the pane-finder
   * installer.) The dead ones matter enormously: see `deadSessions`.
   */
  sessions(): { name: string; dead: boolean }[] {
    const result = this.run(["list-sessions", "--no-formatting"], { session: false });
    if (result.code !== 0) return []; // "no sessions" exits non-zero, not a failure
    return result.stdout
      .split("\n")
      .filter((line) => line.trim().length > 0)
      .map((line) => ({
        name: line.trim().split(/\s+/)[0] as string,
        dead: line.includes("EXITED"),
      }))
      .filter((session) => session.name.length > 0);
  }

  liveSessions(): string[] {
    return this.sessions().filter((s) => !s.dead).map((s) => s.name);
  }

  /**
   * Sessions that are gone but still resurrectable.
   *
   * These are not cosmetic. `attach --create-background NAME` on one of these
   * RESURRECTS it from the serialised copy and silently ignores `--layout`, so
   * "create a session from this layout" quietly becomes "restore whatever was
   * there before" -- which is how a root full of projects came back as plain
   * shells with no agents.
   */
  deadSessions(): string[] {
    return this.sessions().filter((s) => s.dead).map((s) => s.name);
  }

  sessionExists(name: string): boolean {
    return this.liveSessions().includes(name);
  }

  /** Discards a session AND its serialised copy, so the name is reusable. */
  deleteSession(name: string): void {
    this.run(["delete-session", name], { session: false, detached: true });
  }

  /**
   * Block until a session is actually answering, or give up.
   *
   * Creating (or resurrecting) a session returns before the server is
   * registered, so querying it straight away fails with "There is no active
   * session!". Poll for readiness rather than sleeping a guessed interval:
   * usually it is ready on the first check, and a slow box still works.
   */
  waitForSession(name: string, timeoutMs = 10_000): boolean {
    const deadline = Date.now() + timeoutMs;
    for (;;) {
      if (this.sessionExists(name)) return true;
      if (Date.now() >= deadline) return false;
      pause(150);
    }
  }

  /**
   * Creates a detached session from a layout file, without attaching.
   *
   * Runs with the session markers stripped: `attach --create-background` fails
   * with "There is no active session!" when the caller is itself inside a
   * session, and sl0ppi is nearly always invoked from inside one. We are
   * creating a new detached session, not nesting, so dropping the markers is
   * exactly right.
   */
  createBackground(name: string, layoutPath: string): void {
    this.runOk(["--layout", layoutPath, "attach", "--create-background", name], "create session", {
      session: false,
      detached: true,
    });
  }
}

/**
 * Parse a `--json` listing.
 *
 * Empty stdout with a zero exit is a real state, not corruption: it is what
 * `action list-panes` returns once the session has died underneath us. Treat it
 * as "nothing", and keep the raw text in the error for anything genuinely
 * malformed -- a bare "JSON Parse error: Unexpected EOF" tells a user nothing.
 */
export function parseJsonList<T>(stdout: string, what: string): T[] {
  const text = stdout.trim();
  if (text.length === 0) return [];
  try {
    const parsed = JSON.parse(text);
    return Array.isArray(parsed) ? (parsed as T[]) : [];
  } catch (error) {
    throw new Sl0ppijError(
      `${what} returned something that is not JSON: ${text.slice(0, 200)}`,
      { code: 0, stdout, stderr: "" },
    );
  }
}

/** Synchronous pause. These commands are one-shot and strictly sequential. */
function pause(ms: number): void {
  Atomics.wait(new Int32Array(new SharedArrayBuffer(4)), 0, 0, ms);
}

/** True when we are running inside a sl0ppij/zellij pane already. */
export function insideSession(env: NodeJS.ProcessEnv = process.env): string | null {
  return env.SL0PPIJ_SESSION_NAME ?? env.ZELLIJ_SESSION_NAME ?? null;
}