// Where s3d keeps its config and data on each OS, mirroring the lookup in
// s3d's cmd/s3d/main.go (configSearchPaths / applicationDirectoryOS) so the
// GUI and a hand-run `s3d` always agree on which instance they are touching.

import fs from 'node:fs';
import os from 'node:os';
import path from 'node:path';

// s3d's Linux defaults (/etc/s3d, /var/lib/s3d) suit a system service. A
// desktop user who cannot write there, and has no system config, gets the
// XDG per-user places instead; new configs then name that directory
// explicitly, so a hand-run s3d with S3D_CONFIG_FILE agrees.
const xdg = (envName, fallback) => process.env[envName] || path.join(os.homedir(), ...fallback);
const userConfigFile = () => path.join(xdg('XDG_CONFIG_HOME', ['.config']), 's3d', 's3d.yml');
const userDataDir = () => path.join(xdg('XDG_DATA_HOME', ['.local', 'share']), 's3d');

function writable(p) {
  // the nearest existing folder decides whether p could be created
  for (let d = p; ; d = path.dirname(d)) {
    if (fs.existsSync(d)) { try { fs.accessSync(d, fs.constants.W_OK); return true; } catch { return false; } }
    if (path.dirname(d) === d) return false;
  }
}

export function linuxUserMode() {
  if (process.platform === 'win32' || process.platform === 'darwin') return false;
  if (['/etc/s3d/s3d.yml', '/var/lib/s3d/s3d.yml'].some((p) => fs.existsSync(p))) return false;
  return !(writable('/etc/s3d') && writable('/var/lib/s3d'));
}

export function defaultDataDir() {
  switch (process.platform) {
    case 'win32': return path.join(process.env.APPDATA || path.join(os.homedir(), 'AppData', 'Roaming'), 's3d');
    case 'darwin': return path.join(os.homedir(), 'Library', 'Application Support', 's3d');
    default: return linuxUserMode() ? userDataDir() : '/var/lib/s3d';
  }
}

export function configSearchPaths() {
  const paths = [];
  if (process.env.S3D_DATA_DIR) paths.push(path.join(process.env.S3D_DATA_DIR, 's3d.yml'));
  switch (process.platform) {
    case 'win32': paths.push(path.join(defaultDataDir(), 's3d.yml')); break;
    case 'darwin': paths.push(path.join(defaultDataDir(), 's3d.yml')); break;
    default:
      if (linuxUserMode()) paths.push(userConfigFile());
      paths.push('/etc/s3d/s3d.yml', '/var/lib/s3d/s3d.yml');
  }
  return paths;
}

// The config file this GUI manages: an explicit S3D_CONFIG_FILE wins, then the
// first existing search path, then the first search path (created on save).
export function resolveConfigPath(explicit) {
  if (explicit) return path.resolve(explicit);
  if (process.env.S3D_CONFIG_FILE) return path.resolve(process.env.S3D_CONFIG_FILE);
  const candidates = configSearchPaths();
  return candidates.find((p) => fs.existsSync(p)) || candidates[0];
}

const EXE = process.platform === 'win32' ? 's3d.exe' : 's3d';

// Binary lookup: explicit path, S3D_BIN, the vendored copy next to Pithos, then PATH.
export function resolveBinary(explicit, vendorDir) {
  const tries = [explicit, process.env.S3D_BIN, vendorDir && path.join(vendorDir, EXE)].filter(Boolean);
  for (const p of tries) if (fs.existsSync(p)) return path.resolve(p);
  for (const dir of (process.env.PATH || '').split(path.delimiter)) {
    if (!dir) continue;
    const p = path.join(dir, EXE);
    if (fs.existsSync(p)) return p;
  }
  return null;
}