"""Versioned system prompts for `legex-classify`.

Each version lives in `legex/prompts/{version}.py` and exposes one of:

  # single-call mode (one LLM call per case)
  PROMPT: str                       — template with {rules_block}/{isic_block}
  build(rules, isic) -> str          — returns the filled prompt

  # per-column mode (one LLM call per Classification field per case)
  MODE = "per_column"
  build_columns(rules, isic) -> dict[column_name, system_prompt]

`load_plan(...)` normalises both shapes into a `PromptPlan`.
"""

from dataclasses import dataclass
from importlib import import_module


@dataclass
class PromptPlan:
    mode: str  # "single" or "per_column"
    system: str | None = None
    column_systems: dict[str, str] | None = None


def load_plan(
    version: str,
    rules: list[tuple[str, str]],
    isic: list[tuple[str, str, str]],
) -> PromptPlan:
    try:
        mod = import_module(f"legex.prompts.{version}")
    except ImportError as e:
        raise ValueError(f"Unknown prompt version: {version!r}") from e
    mode = getattr(mod, "MODE", "single")
    if mode == "per_column":
        return PromptPlan(mode="per_column", column_systems=mod.build_columns(rules, isic))
    return PromptPlan(mode="single", system=mod.build(rules, isic))


def build_prompt(
    version: str,
    rules: list[tuple[str, str]],
    isic: list[tuple[str, str, str]],
) -> str:
    """Single-mode shortcut. Raises if the version is per-column."""
    plan = load_plan(version, rules, isic)
    if plan.mode != "single" or plan.system is None:
        raise ValueError(
            f"build_prompt() is single-mode only; prompt version {version!r} is {plan.mode}"
        )
    return plan.system