/**
 * Active-model resolution for the `--context-window auto` probe (B8b).
 *
 * Reads the configured model the way Claude Code itself resolves it, so the
 * window probe (context-window.mjs `modelToContextWindow`) sees the real model:
 *   1. the shell `ANTHROPIC_MODEL` override (applies to the launched session);
 *   2. otherwise the settings cascade `model` field — user `~/.claude`, then
 *      project `.claude`, then project-local `.claude` (local > project > user).
 *
 * Reads the cascade files directly (like isBundledSkillsDisabled) rather than via
 * config-discovery classification, and takes an injectable `env` so it is
 * deterministic and hermetic under the test HOME. Returns null when no model is
 * pinned anywhere — the honest signal that `auto` must fall back to advisory.
 *
 * Zero external dependencies (repo invariant).
 */

import { join } from 'node:path';
import { readTextFile } from './file-discovery.mjs';
import { parseJson } from './yaml-parser.mjs';

/**
 * @param {string|null|undefined} projectPath - project root, to also read project + local settings
 * @param {{ env?: Record<string,string|undefined> }} [opts]
 * @returns {Promise<string|null>} the resolved model id/alias, or null if unset
 */
export async function resolveActiveModel(projectPath, { env = process.env } = {}) {
  // 1. Shell ANTHROPIC_MODEL overrides settings (CC: applies to the session).
  const envModel = typeof env?.ANTHROPIC_MODEL === 'string' ? env.ANTHROPIC_MODEL.trim() : '';
  if (envModel) return envModel;

  // 2. Settings cascade: user -> project -> project-local, later wins.
  const home = (env && (env.HOME || env.USERPROFILE)) || '';
  const candidates = [];
  if (home) candidates.push(join(home, '.claude', 'settings.json'));
  if (projectPath) {
    candidates.push(join(projectPath, '.claude', 'settings.json'));
    candidates.push(join(projectPath, '.claude', 'settings.local.json'));
  }

  let model = null;
  for (const p of candidates) {
    const content = await readTextFile(p);
    if (!content) continue;
    const parsed = parseJson(content);
    if (parsed && typeof parsed.model === 'string' && parsed.model.trim()) {
      model = parsed.model.trim();
    }
  }
  return model;
}