/**
 * pregate/runtime — the Bun a repo command runs under, and the TypeScript twin
 * of the one Bun resolution contract (`gstack_bun_resolve` in
 * bin/gstack-bun-version.sh; test/bun-resolve.test.ts runs both on one
 * layout). Candidates, first eligible wins: the project's exact pin and
 * gstack's install default in the versioned runtime store
 * (`<state root>/runtimes/bun/<version>/bun`), `$BUN_INSTALL/bin`,
 * `~/.bun/bin`, then every `bun` on PATH. Eligible: it runs, is at or above
 * gstack's supported minimum, and satisfies gstack's own `engines.bun` and
 * every project pin (lib/runtime-pins.ts); a file carrying the bun shim's
 * marker is never a candidate.
 *
 * The install verdict for (checkout, project) is the one record install,
 * the shim and admission share. Under the admission condition (GSTACK_CAPY=1,
 * or a verdict exists for this checkout and project) the lanes run the Bun it
 * recorded, and a recorded Bun that is gone or changed is reported as drift;
 * otherwise the verdict check is skipped with an explain line (contributors, CI).
 */
import { spawnSync } from 'node:child_process';
import * as fs from 'node:fs';
import * as path from 'node:path';
import { findInstallVerdict, readInstallVerdict, sourceRoot } from '../install-verdict';
import { resultCodeSuffix } from '../result-codes';
import { collectPins, evaluatePins, parseVersion, satisfies } from '../runtime-pins';
import { resolveStateRoot } from '../state-root';

type Env = NodeJS.ProcessEnv;

const GSTACK_ROOT = path.resolve(import.meta.dir, '..', '..');
const VERSIONS = fs.readFileSync(path.join(GSTACK_ROOT, 'bin/gstack-bun-version.sh'), 'utf8');
const shellValue = (name: string) => VERSIONS.match(new RegExp(`^${name}="([^"]*)"`, 'm'))?.[1] ?? '';

export const BUN_TESTED = shellValue('GSTACK_BUN_TESTED');
export const BUN_DEFAULT = shellValue('GSTACK_BUN_DEFAULT');
export const BUN_VERIFIED = shellValue('GSTACK_BUN_VERIFIED').split(/\s+/).filter(Boolean);
export const BUN_SHIM_MARKER = shellValue('GSTACK_BUN_SHIM_MARKER');

/** `gstack_bun_status <v> = ok`: parseable and not below the supported minimum (a prerelease of it is below). */
export function bunStatusOk(version: string): boolean {
  const m = version.replace(/^v/, '').replace(/\+.*$/, '').match(/^(\d+)\.(\d+)\.(\d+)(?:-([0-9A-Za-z.-]+))?$/);
  const min = BUN_TESTED.split('.').map(Number);
  if (!m) return false;
  for (let i = 0; i < 3; i++) if (Number(m[i + 1]) !== min[i]) return Number(m[i + 1]) > min[i];
  return !m[4];
}

/** `gstack_bun_install_version`: GSTACK_BUN_INSTALL_VERSION or the default; null when not a verified Bun at or above the minimum. */
export function bunInstallVersion(env: Env): string | null {
  const v = env.GSTACK_BUN_INSTALL_VERSION || BUN_DEFAULT;
  return BUN_VERIFIED.includes(v) && bunStatusOk(v) ? v : null;
}

export const bunStore = (stateRoot: string) => path.join(stateRoot, 'runtimes', 'bun');

export type BunRule = 'pin' | 'default' | 'BUN_INSTALL' | 'home' | 'PATH';
export interface BunResolution { bin: string; version: string; rule: BunRule }

function isShim(file: string): boolean {
  try {
    const fd = fs.openSync(file, 'r');
    const buf = Buffer.alloc(512);
    const n = fs.readSync(fd, buf, 0, 512, 0);
    fs.closeSync(fd);
    return buf.subarray(0, n).toString('latin1').includes(BUN_SHIM_MARKER);
  } catch { return false; }
}

function bunVersionOf(bin: string, env: Env): string {
  const r = spawnSync(bin, ['--version'], { encoding: 'utf8', timeout: 15_000, env });
  return r.status === 0 ? (r.stdout ?? '').split('\n')[0].replace(/[^A-Za-z0-9.+-]/g, '') : '';
}

/**
 * The resolution contract. `accept` is the caller's project-pin check;
 * `judged` lists the candidates that ran and were refused.
 */
export function resolveBun(opts: { store: string; env: Env; pinExact?: string | null; accept?: (version: string, bin: string) => boolean }): { resolution: BunResolution | null; judged: string[] } {
  const { store, env } = opts;
  const installVersion = bunInstallVersion(env);
  const candidates: [BunRule, string][] = [];
  if (opts.pinExact) candidates.push(['pin', path.join(store, opts.pinExact, 'bun')]);
  if (installVersion) candidates.push(['default', path.join(store, installVersion, 'bun')]);
  if (env.BUN_INSTALL) candidates.push(['BUN_INSTALL', path.join(env.BUN_INSTALL, 'bin', 'bun')]);
  if (env.HOME) candidates.push(['home', path.join(env.HOME, '.bun', 'bin', 'bun')]);
  for (const dir of (env.PATH ?? '').split(':')) if (dir) candidates.push(['PATH', path.join(dir, 'bun')]);
  const seen = new Set<string>();
  const judged: string[] = [];
  for (const [rule, file] of candidates) {
    let real: string;
    try {
      if (!fs.statSync(file).isFile()) continue;
      fs.accessSync(file, fs.constants.X_OK);
      if (isShim(file)) continue;
      real = fs.realpathSync(file);
    } catch { continue; }
    if (seen.has(real)) continue;
    seen.add(real);
    const version = bunVersionOf(real, env);
    if (!bunStatusOk(version) || (opts.accept && !opts.accept(version, real))) { judged.push(`bun ${version || 'unknown'} at ${real} (${rule})`); continue; }
    return { resolution: { bin: real, version, rule }, judged };
  }
  return { resolution: null, judged };
}

function enginesBun(file: string): string | null {
  try { const v = JSON.parse(fs.readFileSync(file, 'utf8'))?.engines?.bun; return typeof v === 'string' && v.trim() ? v.trim() : null; } catch { return null; }
}

const PLATFORM_LANE: Record<string, string> = { linux: 'linux', darwin: 'macos', win32: 'windows' };

/** The project's pins as the resolver's eligibility hook, and its one applicable exact Bun pin. */
export function projectBunPins(repoRoot: string | null): { pinExact: string | null; accept: (version: string) => boolean } {
  const gstackPin = enginesBun(path.join(GSTACK_ROOT, 'package.json'));
  const pins = repoRoot ? collectPins(repoRoot).filter(p => p.tool === 'bun') : [];
  const here = PLATFORM_LANE[process.platform] ?? 'any';
  const exact = [...new Set(pins.filter(p => p.kind === 'exact' && (p.lane === 'any' || p.lane === here)).map(p => p.constraint.replace(/^v/, '')))];
  return {
    pinExact: exact.length === 1 && parseVersion(exact[0]) ? exact[0] : null,
    accept: (version: string) => (!gstackPin || satisfies(version, gstackPin) === true) && evaluatePins(pins, { bun: version }).failures.length === 0,
  };
}

export interface LaunchRuntime {
  dir: string | null;
  version: string | null;
  env: NodeJS.ProcessEnv;
  label: string;
  /** The install-verdict check: ok, drift (recorded Bun gone or changed), missing (GSTACK_CAPY=1 without one) or skipped. */
  verdict: 'ok' | 'drift' | 'missing' | 'skipped';
  verdictLine: string;
}

/** The Bun the lanes and guards run under, its dir first on PATH; the env is unchanged when nothing qualifies. */
export function launchRuntime(repoRoot: string, env: NodeJS.ProcessEnv): LaunchRuntime {
  let project: string | null = null;
  try { project = fs.realpathSync(repoRoot); } catch { /* unresolvable: no project */ }
  const checkout = sourceRoot(GSTACK_ROOT);
  const file = findInstallVerdict(checkout, project, env);
  const recorded = readInstallVerdict(file);
  const bound = recorded && (recorded.schema_version === 1 || (recorded.project ?? '') === (project ?? '')) ? recorded : null;
  const launch = (bin: string, version: string, why: string, verdict: LaunchRuntime['verdict'], verdictLine: string): LaunchRuntime => {
    const dir = path.dirname(bin);
    return { dir, version, env: { ...env, PATH: [dir, env.PATH ?? ''].filter(Boolean).join(path.delimiter) }, label: `bun ${version} at ${bin} (${why})${verdictLine ? `; ${verdictLine}` : ''}`, verdict, verdictLine };
  };
  let verdict: LaunchRuntime['verdict'] = 'skipped';
  let verdictLine = '';
  if (env.GSTACK_CAPY !== '1' && !bound) {
    verdictLine = 'install verdict: not checked (no GSTACK_CAPY=1 and no verdict for this checkout and project)';
  } else if (!bound) {
    verdict = 'missing';
    verdictLine = `install verdict: none for ${project ?? 'this directory'} at ${file}; fix: run the Capy skill installer (scripts/install.sh --check --for review) here ${resultCodeSuffix('INSTALL_UNVERIFIED')}`;
  } else if (bound.bun_path) {
    const now = fs.existsSync(bound.bun_path) ? bunVersionOf(bound.bun_path, env) : '';
    if (now && now === bound.bun_version) return launch(bound.bun_path, now, 'recorded by the install verdict', 'ok', '');
    verdict = 'drift';
    verdictLine = `install verdict: recorded bun ${bound.bun_version} at ${bound.bun_path} ${now ? `now reports ${now}` : 'is gone'}; fix: re-run the Capy skill installer with --check (scripts/install.sh --check --for review) ${resultCodeSuffix('BUN_RESOLUTION_DRIFT')}`;
  } else {
    verdict = 'ok';
  }
  const { pinExact, accept } = projectBunPins(project);
  const { resolution } = resolveBun({ store: bunStore(resolveStateRoot(env)), env, pinExact, accept });
  if (resolution) return launch(resolution.bin, resolution.version, `resolved: ${resolution.rule}`, verdict, verdictLine);
  return { dir: null, version: null, env, label: `PATH (no eligible Bun in the runtime store, $BUN_INSTALL/bin, ~/.bun/bin or PATH)${verdictLine ? `; ${verdictLine}` : ''}`, verdict, verdictLine };
}