"""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 _find_yaml(scenario_id: str, base: Path) -> Path | None:
    """Resolve a scenario id to its YAML path.

    Searches the scenarios root and any one-level subdirectory (e.g.
    customer_service/). Supports two alias forms for backward compatibility:
      - cs_<id> -> customer_service_<id>.yaml  (v0.1 call sites used the long form)
      - customer_service_<id> -> cs_<id>.yaml  (reverse, for the renamed v01 file)
    """
    primary = base / f"{scenario_id}.yaml"
    if primary.exists():
        return primary
    cs_alias = base / f"{scenario_id.replace('cs_', 'customer_service_')}.yaml"
    if cs_alias.exists():
        return cs_alias
    long_alias = base / f"{scenario_id.replace('customer_service_', 'cs_')}.yaml"
    if long_alias.exists():
        return long_alias
    # One-level subdirectory walk (subdir named by skill, e.g. customer_service/).
    for d in sorted(base.glob("*/")):
        if not d.is_dir():
            continue
        for cand in (
            d / f"{scenario_id}.yaml",
            d / f"{scenario_id.replace('cs_', 'customer_service_')}.yaml",
            d / f"{scenario_id.replace('customer_service_', 'cs_')}.yaml",
        ):
            if cand.exists():
                return cand
    return None


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

    Args:
        scenario_id: e.g. 'cs_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 = _find_yaml(scenario_id, base)
    if path is None:
        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 tree (root + one-level subdirs)."""
    base = scenarios_dir or _DEFAULT_SCENARIOS_DIR
    out: list[Scenario] = []
    paths = sorted(base.glob("*.yaml")) + sorted(base.glob("*/**/*.yaml"))
    seen: set[Path] = set()
    for p in paths:
        if p in seen or p.name == "index.yaml" or p.name == "cost_rates.yaml":
            continue
        seen.add(p)
        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"]