/**
 * `.env` loader for verifier extensions.
 *
 * Both `verifiable.ts` (builder) and `verifier.ts` (verifier) call this on
 * session_start with their `ctx.cwd`. Each agent loads `.env` from its own
 * working directory — defensive: even if tmux drops env vars between spawn
 * and child, the verifier independently loads the same `.env` because it
 * shares cwd (the launcher passes `-c <cwd>` to tmux).
 *
 * Precedence (matches dotenv conventions):
 *   1. Existing `process.env` values are preserved (env-vars-already-set wins).
 *   2. Values in `.env` fill in only the gaps.
 *
 * Uses `process.loadEnvFile()` (Node >= 21.7) when available; falls back to a
 * manual parser for Node 20.6.x to 21.6.x so the declared engine range
 * (`>=20.6.0`) is actually respected. If `.env` doesn't exist, this is a no-op
 * (silent). The Pi CLI's own authenticated model configuration is the default
 * path; `.env` is only for users who want to provide provider API keys explicitly.
 */

import { promises as fs } from "node:fs";
import * as path from "node:path";

export interface LoadResult {
  loaded: boolean;
  path: string;
  reason?: string;
}

/**
 * Load `.env` from `cwd` into `process.env` if the file exists.
 *
 * - Non-existent `.env` → returns `{ loaded: false }` silently. Most users rely
 *   on Pi CLI auth / SSO instead; that's fine.
 * - Malformed `.env` → returns `{ loaded: false, reason }`. Caller decides
 *   whether to surface the warning to the user.
 * - Successful load → `{ loaded: true, path }`. Caller may choose to notify.
 *
 * Existing `process.env` keys are preserved: the manual parser skips keys
 * already in `process.env`, and `process.loadEnvFile` has the same semantics.
 */
export async function loadDotEnv(cwd: string): Promise<LoadResult> {
  const envPath = path.join(cwd, ".env");
  try {
    await fs.access(envPath);
  } catch {
    return { loaded: false, path: envPath };
  }
  try {
    if (typeof process.loadEnvFile === "function") {
      // Node >= 21.7 — fast path, no extra parsing.
      process.loadEnvFile(envPath);
    } else {
      // Node 20.6.x to 21.6.x — manual dotenv parser.
      // Matches the same syntax process.loadEnvFile supports:
      //   KEY=value
      //   KEY="quoted value"
      //   KEY='quoted value'
      //   export KEY=value
      //   mixed_CASE_Keys=value
      // Leading `export ` is stripped; surrounding quotes are removed.
      const raw = await fs.readFile(envPath, "utf8");
      for (const line of raw.split("\n")) {
        const trimmed = line.trim();
        if (!trimmed || trimmed.startsWith("#")) continue;
        const noExport = trimmed.replace(/^export\s+/i, "");
        const m = noExport.match(/^\s*([A-Za-z_][A-Za-z0-9_]*)\s*=\s*(.*)$/);
        if (!m) continue;
        const key = m[1];
        if (!key || key in process.env) continue;
        let value = m[2].trim();
        // Strip surrounding single or double quotes
        if (
          (value.startsWith('"') && value.endsWith('"')) ||
          (value.startsWith("'") && value.endsWith("'"))
        ) {
          value = value.slice(1, -1);
        }
        process.env[key] = value;
      }
    }
    return { loaded: true, path: envPath };
  } catch (err) {
    return {
      loaded: false,
      path: envPath,
      reason: `failed to parse: ${(err as Error).message}`,
    };
  }
}