"""Configuration model for the aissurance compliance plugin.

Populated from the ``compliance`` block of the Router's ``config.yaml`` (see
config.Config). ``${VAR}`` references in the YAML are already expanded by
``Config._expand_env_refs`` before this model is constructed; on top of that,
the aissurance-specific environment variables (``AISSURANCE_KEY`` etc.) are
honoured as defaults so the plugin works with env-only configuration too.

This module imports nothing from the Router, so config.py can import it
without creating a cycle.
"""
import os
import socket
from typing import Optional

from pydantic import BaseModel, Field, field_validator


def _env_or_none(name: str) -> Optional[str]:
    val = os.getenv(name)
    return val if val else None


class ComplianceSettings(BaseModel):
    """The ``compliance:`` config block."""

    enabled: bool = False

    # Full URL of the discovery receive endpoint. Health and config-report URLs
    # are derived from this by replacing the trailing ``/receive`` path.
    server_url: str = "https://www.aissurance.eu/api/v1/discovery/receive"

    # Tenant-provisioned secret (AISSURANCE_KEY). Used both as the Bearer token
    # and as the HMAC signing key unless ``hmac_secret`` overrides the latter.
    api_key: Optional[str] = Field(default_factory=lambda: _env_or_none("AISSURANCE_KEY"))
    # Optional per-tenant HMAC secret override (AISSURANCE_HMAC_SECRET).
    hmac_secret: Optional[str] = Field(default_factory=lambda: _env_or_none("AISSURANCE_HMAC_SECRET"))
    # Tenant UUID, if not embedded in the key (AISSURANCE_TENANT_ID).
    tenant_id: Optional[str] = Field(default_factory=lambda: _env_or_none("AISSURANCE_TENANT_ID"))

    # Unique identifier for this Router instance. Multiple instances per tenant
    # are allowed, so this defaults to the hostname rather than the tenant id.
    router_id: str = Field(default_factory=socket.gethostname)

    polling_interval: int = 300        # seconds between discovery snapshots
    health_interval: int = 3600        # seconds between health/config-sync calls
    batch_size: int = 50               # max models per payload
    max_retry_attempts: int = 10       # in-cycle send retries before buffering
    retry_backoff_base: int = 2        # exponential backoff base (seconds)

    buffer_dir: str = "./compliance-buffer"  # persistent encrypted retry storage
    max_buffer_payloads: int = 100           # oldest dropped first when full

    # TLS verification. AISSURANCE_VERIFY_TLS=0 disables it (dev only).
    verify_tls: bool = Field(
        default_factory=lambda: os.getenv("AISSURANCE_VERIFY_TLS", "1") != "0"
    )

    @field_validator("api_key", "hmac_secret", "tenant_id", mode="before")
    @classmethod
    def _empty_to_none(cls, v):
        # config.yaml ``${VAR}`` expansion yields "" for unset vars; treat as None
        # so the env-var default_factory can take over.
        if v == "":
            return None
        return v

    @property
    def discovery_base_url(self) -> str:
        """Base discovery URL, derived by stripping a trailing ``/receive``."""
        url = self.server_url.rstrip("/")
        if url.endswith("/receive"):
            url = url[: -len("/receive")]
        return url

    @property
    def receive_url(self) -> str:
        return self.server_url

    @property
    def health_url(self) -> str:
        tid = self.tenant_id or "unknown"
        return f"{self.discovery_base_url}/health/{tid}"

    @property
    def config_report_url(self) -> str:
        return f"{self.discovery_base_url}/config/report"

    def validation_errors(self) -> list[str]:
        """Return human-readable reasons the plugin cannot run, or [] if OK."""
        errors: list[str] = []
        if not self.api_key:
            errors.append("AISSURANCE_KEY / compliance.api_key is not set")
        if not self.server_url.lower().startswith("https://"):
            errors.append(f"server_url must be HTTPS (got {self.server_url!r})")
        if self.polling_interval < 60:
            errors.append("polling_interval must be >= 60 seconds")
        return errors