"""Scenario loader — YAML → Pydantic Scenario (D-018).

Loads a scenario by id from the scenarios/ directory, validates it against the
Pydantic schema, and returns a typed Scenario object. Used by the pipeline
(TASK-03-07) and the e2e smoke test.
"""

from __future__ import annotations

from pathlib import Path

import yaml

from server.scenarios.schema import Scenario, ValidationError

_DEFAULT_SCENARIOS_DIR = Path(__file__).resolve().parent.parent.parent / "scenarios"


def load(scenario_id: str, scenarios_dir: Path | None = None) -> Scenario:
    """Load and validate a scenario by id.

    Args:
        scenario_id: e.g. 'customer_service_refund_ca_v01' (the YAML filename stem).
        scenarios_dir: override the scenarios directory (default: repo /scenarios).

    Returns:
        A validated Scenario object.

    Raises:
        FileNotFoundError: if the YAML file doesn't exist.
        ValidationError: if the YAML fails schema validation (typed Pydantic error).
    """
    base = scenarios_dir or _DEFAULT_SCENARIOS_DIR
    path = base / f"{scenario_id}.yaml"
    if not path.exists():
        # Try the id-with-cs-prefix alias (RESEARCH example used 'cs_refund_ca_v01').
        path = base / f"{scenario_id.replace('cs_', 'customer_service_')}.yaml"
        if not path.exists():
            raise FileNotFoundError(f"Scenario YAML not found: {scenario_id} in {base}")

    with path.open("r", encoding="utf-8") as f:
        raw = yaml.safe_load(f)

    return Scenario.model_validate(raw)


def load_all(scenarios_dir: Path | None = None) -> list[Scenario]:
    """Load all scenarios in the directory (for the future scenario library)."""
    base = scenarios_dir or _DEFAULT_SCENARIOS_DIR
    out: list[Scenario] = []
    for p in sorted(base.glob("*.yaml")):
        with p.open("r", encoding="utf-8") as f:
            raw = yaml.safe_load(f)
        out.append(Scenario.model_validate(raw))
    return out


__all__ = ["load", "load_all", "ValidationError"]