"""UX-13 P5: the page's words, app/ui_text/<lang>.json, in English or Dutch.

One file per language with the same keys. A key missing from a language falls
back to English, key by key, the way the Supervisor's translations do.
test_ui_text.py holds both files to STYLE.md and to each other.
"""

import copy
import io
import json
import os

DIR = os.path.join(os.path.dirname(os.path.abspath(__file__)), "ui_text")
LANGS = ("en", "nl")
_CACHE: dict = {}


def lang_of(value) -> str:
    """"nl", "nl-BE" or "nl_NL" -> "nl"; anything else -> "en"."""
    head = str(value or "").strip().lower().replace("_", "-").split("-")[0]
    return head if head in LANGS else "en"


def raw(lang: str) -> dict:
    """One language file as written, without the English fallback."""
    if lang not in _CACHE:
        with io.open(os.path.join(DIR, f"{lang}.json"), encoding="utf-8") as f:
            _CACHE[lang] = json.load(f)
    return _CACHE[lang]


def _merge(base, over):
    if not (isinstance(base, dict) and isinstance(over, dict)):
        return copy.deepcopy(over)
    out = copy.deepcopy(base)
    for k, v in over.items():
        out[k] = _merge(base.get(k), v) if k in base else copy.deepcopy(v)
    return out


def words(lang="en") -> dict:
    """Every word in `lang`, English where a key is missing."""
    lang = lang_of(lang)
    return raw("en") if lang == "en" else _merge(raw("en"), raw(lang))


def say(template: str, **values) -> str:
    """Fill `{name}` placeholders, as settings.js `say()` does."""
    for k, v in values.items():
        template = template.replace("{" + k + "}", str(v))
    return template