from __future__ import annotations
from pathlib import Path
import yaml
from .paths import presets_root
import re

def load_yaml(path: Path) -> dict:
    if not path.exists():
        return {}
    return yaml.safe_load(path.read_text(encoding="utf-8")) or {}

def deep_merge(a: dict, b: dict) -> dict:
    out = dict(a)
    for k, v in (b or {}).items():
        if isinstance(v, dict) and isinstance(out.get(k), dict):
            out[k] = deep_merge(out[k], v)
        else:
            out[k] = v
    return out

def load_customer_preset(repo_root: Path, customer_key: str) -> dict:
    key = customer_key.strip().lower()
    if not re.fullmatch(r"[a-z0-9_-]+", key):
        raise ValueError("Customer key must contain only letters, digits, _ or -")
    local = presets_root(repo_root)
    if (local / "customers" / f"{key}.yaml").is_file():
        return load_yaml(local / "customers" / f"{key}.yaml")
    # Prefer per-customer file
    file_preset = repo_root / "presets" / "customers" / f"{key}.yaml"
    if file_preset.exists():
        return load_yaml(file_preset)
    # Fallback to shared customers.yaml
    shared = load_yaml(repo_root / "presets" / "customers.yaml").get("customers", {})
    return shared.get(key, {})