"""Language registry + prompt helpers for localized AI output.

Two surfaces consume this module:
- Per-user LLM call sites (portfolio analysis only at this stage) call
  ``respond_in_clause(user.lang)`` and append the result to their
  system prompt.
- The settings dropdown + its PATCH endpoint consult ``ACTIVE_LANGUAGES``
  to decide which options are selectable. The strategic-log and digest
  translation fan-outs also consult it to decide which languages to
  spend tokens on.

Adding Spanish/French/German support later is a one-line constant
change: extend ``ACTIVE_LANGUAGES`` to include the new code. No other
code change is required — the rest of the system already treats them
as first-class via ``LANGUAGES``.
"""
from __future__ import annotations


# Display labels for every language the system knows about. ES/FR/DE
# are kept here so labels still render in the dropdown (as disabled
# options) without requiring code changes to enable them later.
LANGUAGES: dict[str, str] = {
    "en": "English",
    "it": "Italian",
    "es": "Spanish",
    "fr": "French",
    "de": "German",
}


# Languages users can actually select. Settings POST validates against
# this; the strategic-log + digest translation fan-outs only consider
# these.
ACTIVE_LANGUAGES: set[str] = {"en", "it"}


def respond_in_clause(lang: str | None) -> str:
    """Suffix appended to per-user LLM system prompts.

    Returns an empty string for ``en`` (no nudge needed), an unknown
    code, or ``None``/empty input — those callers want the default
    English path. Otherwise returns ``"\\n\\nRespond in <Language>."``
    keyed off ``LANGUAGES``.
    """
    if not lang or lang == "en" or lang not in LANGUAGES:
        return ""
    return f"\n\nRespond in {LANGUAGES[lang]}."