/**
 * Resolve how to invoke the Fusion CLI from server-side code (automations,
 * generated commands, docs snippets).
 *
 * Order of preference:
 *   1. `fn`      — short canonical name
 *   2. `fusion`  — long alias name
 *   3. `npx -y runfusion.ai` — zero-install fallback that always works
 *
 * The npm bin name on disk varies by install path and platform. Prefer
 * reading the installed package manifest from the resolved binary path so we
 * don't execute older buggy global installs just to discover their version.
 */

import { spawn } from "node:child_process";
import { existsSync, readFileSync, realpathSync, statSync } from "node:fs";
import { platform, tmpdir } from "node:os";
import { posix, win32 } from "node:path";

/*
FNXC:FnBinaryProbe 2026-07-15-10:05:
Native/bundled `fn` installs (e.g. ~/.local/share/fusion/fn) are multi‑MB binaries.
resolveShimTargets must never readFileSync the whole file then regex‑scan it — that hung detectFnBinary for ~77s on a real host and timed out the default vitest suite.
Only open small text shims (shebang / cmd/ps1 wrappers), capped to a few KB.
*/

interface ProbeResult {
  exitCode: number | null;
  stdout: string;
  stderr: string;
}

/**
 * Run a command with an explicit argv (no shell) and capture stdout/stderr.
 * Always resolves; on spawn failure exitCode is null and stderr carries the
 * error message. Used here for safe, dependency-free PATH lookups and
 * version probes — do not use for general command execution.
 */
function runProbe(command: string, args: string[], timeoutMs: number): Promise<ProbeResult> {
  return new Promise((resolve) => {
    let stdout = "";
    let stderr = "";
    let settled = false;
    const finish = (result: ProbeResult) => {
      if (settled) return;
      settled = true;
      clearTimeout(timer);
      resolve(result);
    };
    // Run probes from the OS temp directory so a buggy CLI version (older
    // `runfusion.ai` releases initialise an engine — and a fresh
    // `.fusion/<project>/.fusion/` tree — even on `--version`) cannot leave
    // artefacts under whichever project happens to be the parent's cwd.
    const child = spawn(command, args, {
      stdio: ["ignore", "pipe", "pipe"],
      shell: false,
      cwd: tmpdir(),
    });
    /*
    FNXC:FnBinaryProbe 2026-07-15-10:05:
    Always settle the probe on timeout even if SIGKILL does not promptly emit close —
    otherwise detectFnBinary can hang past vitest's default 15s and leave orphan children.
    */
    const timer = setTimeout(() => {
      try { child.kill("SIGKILL"); } catch { /* ignore */ }
      finish({ exitCode: null, stdout, stderr: stderr || "probe timed out" });
    }, timeoutMs);
    child.stdout?.on("data", (chunk: Buffer) => { stdout += chunk.toString("utf8"); });
    child.stderr?.on("data", (chunk: Buffer) => { stderr += chunk.toString("utf8"); });
    child.on("error", (err) => {
      finish({ exitCode: null, stdout, stderr: stderr || err.message });
    });
    child.on("close", (exitCode) => {
      finish({ exitCode, stdout, stderr });
    });
  });
}

/** npm package that publishes the `fn`/`fusion` bins. Used for npx fallback. */
export const FN_NPM_PACKAGE = "runfusion.ai";

/** Recommended one-line installer URL surfaced in UI/docs. */
export const FN_INSTALL_CURL = "curl -fsSL https://runfusion.ai/install.sh | sh";

/** Recommended npm install command surfaced in UI/docs. */
export const FN_INSTALL_NPM = `npm install -g ${FN_NPM_PACKAGE}`;

/** Zero-install invocation prefix used when no global binary is present. */
export const FN_NPX_INVOCATION = `npx -y ${FN_NPM_PACKAGE}`;

/** Candidate binary names checked, in preference order. */
const CANDIDATES = ["fn", "fusion"] as const;
const FUSION_PACKAGE_NAMES = new Set(["runfusion.ai", "@runfusion/fusion"]);

type PathApi = Pick<typeof posix, "dirname" | "resolve" | "sep">;

export type FnBinaryName = (typeof CANDIDATES)[number];

export interface FnBinaryStatus {
  /** True if a working `fn` or `fusion` binary was found on PATH. */
  installed: boolean;
  /** Which binary name resolved, if any. */
  binary?: FnBinaryName;
  /** Absolute path to the resolved binary, when available. */
  path?: string;
  /** Version reported by `<bin> --version`, when available. */
  version?: string;
  /**
   * Command prefix to use when scripting against the CLI. This is either
   * the binary name itself (when installed) or {@link FN_NPX_INVOCATION}.
   */
  invocation: string;
}

/**
 * Look up an executable on PATH using the platform-appropriate command.
 * Returns the first absolute path or undefined.
 */
async function whichBinary(name: string): Promise<string | undefined> {
  const isWindows = platform() === "win32";
  const lookup = isWindows ? "where" : "which";
  const result = await runProbe(lookup, [name], 5_000);
  if (result.exitCode !== 0) return undefined;
  const firstLine = result.stdout.split(/\r?\n/).map((s) => s.trim()).find(Boolean);
  return firstLine || undefined;
}

function getPathApi(pathValue: string): PathApi {
  return /^[A-Za-z]:[\\/]/.test(pathValue) || pathValue.includes("\\")
    ? win32
    : posix;
}

function readPackageVersionFromPath(startPath: string): string | undefined {
  const pathApi = getPathApi(startPath);
  let dir = pathApi.dirname(startPath);

  for (let i = 0; i < 8; i += 1) {
    const packageJsonPath = pathApi.resolve(dir, "package.json");
    if (existsSync(packageJsonPath)) {
      try {
        const parsed = JSON.parse(readFileSync(packageJsonPath, "utf-8")) as {
          name?: string;
          version?: string;
        };
        if (
          typeof parsed.name === "string"
          && typeof parsed.version === "string"
          && FUSION_PACKAGE_NAMES.has(parsed.name)
        ) {
          return parsed.version;
        }
      } catch {
        // Ignore malformed manifests and keep walking upward.
      }
    }

    const parent = pathApi.dirname(dir);
    if (parent === dir) break;
    dir = parent;
  }

  return undefined;
}

/** Max bytes to read when sniffing npm/cmd/ps1 shims for package paths. */
const SHIM_READ_MAX_BYTES = 16_384;

function isLikelyTextShim(resolvedPath: string, size: number): boolean {
  /*
  FNXC:FnBinaryProbe 2026-07-15-10:05:
  Windows npm shims are .cmd/.ps1 text; POSIX shims are small scripts with a shebang.
  Skip Mach-O/ELF/PE binaries and any file larger than SHIM_READ_MAX_BYTES before reading.
  */
  if (size <= 0 || size > SHIM_READ_MAX_BYTES) return false;
  const lower = resolvedPath.toLowerCase();
  if (lower.endsWith(".cmd") || lower.endsWith(".bat") || lower.endsWith(".ps1")) {
    return true;
  }
  try {
    // Read only a tiny head — never the whole path before classification.
    const fdContents = readFileSync(resolvedPath, { encoding: "utf-8", flag: "r" });
    const head = fdContents.slice(0, 64);
    // Shebang scripts only; refuse binary garbage that would thrash the regex.
    return head.startsWith("#!") || /^@?ECHO\s/i.test(head) || head.includes("node_modules");
  } catch {
    return false;
  }
}

function resolveShimTargets(resolvedPath: string): string[] {
  let size = 0;
  try {
    const st = statSync(resolvedPath);
    if (!st.isFile()) return [];
    size = st.size;
  } catch {
    return [];
  }
  if (!isLikelyTextShim(resolvedPath, size)) return [];

  const pathApi = getPathApi(resolvedPath);
  const basedir = pathApi.dirname(resolvedPath);
  let contents: string;

  try {
    // Size already gated by SHIM_READ_MAX_BYTES; still slice as a hard ceiling.
    contents = readFileSync(resolvedPath, { encoding: "utf-8", flag: "r" }).slice(0, SHIM_READ_MAX_BYTES);
  } catch {
    return [];
  }

  const targets = new Set<string>();
  const pattern = /([^\r\n"'`]*node_modules[\\/](?:runfusion\.ai|@runfusion[\\/](?:fusion))[^\r\n"'`]*(?:\.js|package\.json))/gi;

  for (const match of contents.matchAll(pattern)) {
    const raw = match[1];
    if (!raw) continue;

    const trimmed = raw.trim().replace(/^['"]|['"]$/g, "");
    const normalized = trimmed
      .replace(/^%~?dp0%?/i, "")
      .replace(/^\$basedir/i, "")
      .replace(/^\$PSScriptRoot/i, "")
      .replace(/^[\\/]+/, "")
      .replace(/[\\/]/g, pathApi.sep);

    targets.add(pathApi.resolve(basedir, normalized));
  }

  return Array.from(targets);
}

function readVersionFromResolvedBinaryPath(resolvedPath: string): string | undefined {
  const candidatePaths = new Set<string>([resolvedPath]);

  try {
    candidatePaths.add(realpathSync(resolvedPath));
  } catch {
    // Fall back to the original resolved path.
  }

  // FNXC:CliBinaryProbe 2026-07-15-14:45: Check the resolved
  // executable and its realpath before scanning shim contents. Dashboard
  // status polling calls this path; parsing a normal JavaScript entrypoint as
  // an npm shim can trap the server event loop in the shim-target regex.
  for (const candidatePath of candidatePaths) {
    const version = readPackageVersionFromPath(candidatePath);
    if (version) return version;
  }

  // A package manifest was not adjacent to either direct path, so this may be
  // an npm-generated Windows shim whose target is the only useful clue.
  for (const shimTarget of resolveShimTargets(resolvedPath)) {
    const version = readPackageVersionFromPath(shimTarget);
    if (version) return version;
  }

  return undefined;
}

/**
 * Best-effort version probe. Returns undefined if the binary refuses the
 * flag or produces no parseable output — the caller should treat undefined
 * as "installed but version unknown" rather than "not installed".
 */
async function probeVersion(binary: string): Promise<string | undefined> {
  const result = await runProbe(binary, ["--version"], 10_000);
  if (result.exitCode !== 0) return undefined;
  const text = (result.stdout || result.stderr).trim();
  if (!text) return undefined;
  // Match the first semver-ish token so we strip prefixes like "fn v0.13.0".
  const match = text.match(/\d+\.\d+\.\d+(?:-[\w.]+)?/);
  return match ? match[0] : text.split(/\s+/)[0];
}

/**
 * Detect whether the `fn` (or `fusion`) CLI is installed on PATH and
 * return the recommended invocation prefix.
 *
 * Never throws — on any error it falls through to the npx fallback so
 * callers can rely on `invocation` always being usable.
 */
export async function detectFnBinary(): Promise<FnBinaryStatus> {
  for (const candidate of CANDIDATES) {
    try {
      const resolvedPath = await whichBinary(candidate);
      if (!resolvedPath) continue;
      const version = readVersionFromResolvedBinaryPath(resolvedPath) ?? await probeVersion(candidate);
      return {
        installed: true,
        binary: candidate,
        path: resolvedPath,
        version,
        invocation: candidate,
      };
    } catch {
      // Try the next candidate.
    }
  }
  return {
    installed: false,
    invocation: FN_NPX_INVOCATION,
  };
}