"""Shared context-budget / truncation helpers (baseline-identical numbers).

🔴 RL rollout AND eval must use the SAME budget (plan §4.3 / §4.4 / eval):
  - model_max = 32000, gen_length(answer) = 800
  - max_retrieval_tokens = 32000 - 800 - 1000 = 30200
  - retrieved-session text exceeding 30200 → char-ratio crop (baseline build_prompt_rag)
  - final full_ids exceeding 32000 → LEFT-truncate (truncation_side="left"): drop the
    earliest retrieved text first, keep recent decision/answer markers.
  - answer max_new_tokens = 800 (RL and eval IDENTICAL — never 200 here / 800 there)
  - decision segment max_new_tokens = 64 (only [MS:*][ACT:*]<query>[EOQ])

estimate_tokens uses len//4 (baseline). The char-ratio crop mirrors baseline exactly.
"""

from typing import List, Tuple

MODEL_MAX = 32000
GEN_LENGTH = 800
RESERVE = 1000
MAX_RETRIEVAL_TOKENS = MODEL_MAX - GEN_LENGTH - RESERVE  # 30200
DECISION_MAX_NEW_TOKENS = 64
ANSWER_MAX_NEW_TOKENS = GEN_LENGTH  # 800


def estimate_tokens(text: str) -> int:
    return len(text) // 4


def crop_retrieval_text(history_string: str, max_tokens: int = MAX_RETRIEVAL_TOKENS) -> str:
    """Char-ratio crop of the assembled retrieved-session string (baseline口径)."""
    est = estimate_tokens(history_string)
    if est > max_tokens:
        ratio = max_tokens / est
        char_limit = int(len(history_string) * ratio)
        return history_string[:char_limit]
    return history_string


def left_truncate_ids(full_ids: List[int], mask: List[bool],
                      max_length: int = MODEL_MAX,
                      *extra_masks: List[bool]):
    """LEFT-truncate full_ids (+ aligned mask and any extra aligned masks) to max_length.

    Drops the earliest tokens (retrieved text sits at the front of the post-decision
    region; the decision prompt itself also sits at the very front). This matches
    baseline tokenizer(truncation=True, truncation_side='left', max_length=32000):
    the most recent answer marker / decision survive, the oldest text is dropped.

    Returns (ids, mask) when no extra masks, else (ids, mask, *extra_masks).
    """
    if len(full_ids) <= max_length:
        return (full_ids, mask) if not extra_masks else (full_ids, mask, *extra_masks)
    cut = len(full_ids) - max_length
    if not extra_masks:
        return full_ids[cut:], mask[cut:]
    return (full_ids[cut:], mask[cut:], *(em[cut:] for em in extra_masks))