"""Environment helper (D-108, REQ-159, REQ-164, REQ-330).

During the Nova rebrand transition window (P2–P4), `get_env` read
`NOVA_*` preferred with the legacy `ACDL_*` name as the fallback. **P5
(REQ-164) removed the fallback** — `get_env` now reads `NOVA_*` only.

`get_env(name, default=None)` resolves `NOVA_<name>`, then returns
`default` if unset. Direct-read paths that bypass this helper (the
`.env.secrets` shell export in `scripts/run_platform.sh` and the Python
parser in `core/regression_verify.py`) were updated to NOVA-only in P5
(the G-106 dual-read contract was retired with the fallback).

P2 (REQ-330): `synthesize_local_env(contract_path, environment)` produces
a purely synthetic local env dict (account_id placeholder, region
"local", no real AWS resources) from a contract YAML. Mirrors the shape
of core/environments/*.json (validates against
schemas/environment.schema.json) so `nova apply --local` can run the
contract resolver + Terraform adapter without provisioning cloud
resources. This is the local-tier counterpart of
core/onboarding.py:generate_env_file() (the request-path binding
generator).
"""

from __future__ import annotations

import os
from pathlib import Path
from typing import Any, Dict, Optional

import yaml

__all__ = ["get_env", "synthesize_local_env"]


def get_env(name: str, default: Optional[str] = None) -> Optional[str]:
    """Resolve a config value from the `NOVA_*` environment.

    `name` is the bare key WITHOUT the prefix (e.g. ``"AWS_ACCOUNT_ID"``).
    Returns ``NOVA_<name>`` if set and non-empty, else ``default``.
    """
    val = os.environ.get(f"NOVA_{name}")
    if val:
        return val
    return default


# Default confidence thresholds per environment name (mirrors the schema
# description: dev 0.50, qa 0.75, prod 0.90, dr 0.95). Used by
# synthesize_local_env so the synthetic env matches the real env semantics.
_DEFAULT_THRESHOLDS: Dict[str, float] = {
    "dev": 0.50,
    "qa": 0.75,
    "prod": 0.90,
    "dr": 0.95,
}


def synthesize_local_env(
    contract_path: str,
    environment: Optional[str] = None,
) -> Dict[str, Any]:
    """Synthesize a local env dict from a contract YAML (REQ-330).

    Reads the contract YAML (``yaml.safe_load``), derives a placeholder
    environment binding that ``nova apply --local`` can use WITHOUT
    provisioning real AWS resources. The produced dict:

      - ``name`` — the environment name (from the arg or the contract's
        ``environment`` field, defaulting to ``"dev"``).
      - ``account_id`` — ``"000000000000"`` (the schema-allowed placeholder
        for an unbound environment; real account id filled by the platform).
      - ``region`` — ``"local"`` (the local-tier sentinel; never a real
        AWS region).
      - ``state_backend`` — ``{bucket: "local-tfstate", lock_table:
        "local-locks"}`` (local state; LocalS3StateBackend rewrites the
        terraform backend to ``backend "local"`` using the stack name as
        the state path, so no S3 bucket is used).
      - ``network`` — a local RFC1918 CIDR + a single fake AZ.
      - ``runner_role_arn`` — a placeholder ARN for the local tier.
      - ``autonomy`` — ``"full"`` (the local tier is autonomous).
      - ``confidence_threshold`` — the per-env default (0.50 for dev).

    The dict mirrors the shape of ``core/environments/*.json`` and
    validates against ``schemas/environment.schema.json``. No cloud
    provisioning occurs — purely synthetic.

    Args:
        contract_path: Path to the contract YAML file.
        environment: Optional environment name override (defaults to the
            contract's ``environment`` field, or ``"dev"``).

    Returns:
        The synthetic local env dict.
    """
    contract_path_obj = Path(contract_path)
    contract: Dict[str, Any] = {}
    if contract_path_obj.is_file():
        with open(contract_path_obj) as fh:
            contract = yaml.safe_load(fh) or {}

    env_name = environment or contract.get("environment", "dev")
    stack_name = contract.get("id", env_name)
    threshold = _DEFAULT_THRESHOLDS.get(env_name, 0.50)

    return {
        "name": env_name,
        "description": (
            f"Synthetic local-tier environment for contract '{stack_name}' "
            f"(environment={env_name}). No real AWS resources — generated "
            f"by core.env.synthesize_local_env (REQ-330) for nova apply --local."
        ),
        "account_id": "000000000000",
        "region": "local",
        "state_backend": {
            "bucket": "local-tfstate",
            "lock_table": "local-locks",
        },
        "network": {
            "vpc_cidr": "10.250.0.0/16",
            "azs": ["local-a"],
        },
        "runner_role_arn": "arn:aws:iam::000000000000:role/local-runner",
        "autonomy": "full",
        "confidence_threshold": threshold,
    }