"""Document processing for the MESA task tree.

Two jobs:

1. Tier/domain routing. Each tier lives in its own dataset config, so a leaf
   task loads only its tier and filters by domain here. The filters also drop
   the contamination canary, which is the first record of every data file and
   has no ``domain`` field.

2. Item rendering for continuation loglikelihood. MESA has two stem shapes and
   they must not be rendered the same way:

   * **Cloze** stems carry a ``___`` blank mid-sentence (567 of the 727 English
     items). The option belongs IN the blank, not after the stem. Appending
     instead of substituting leaves the blank unfilled and makes every option
     -- the key included -- ungrammatical, which is not a measurement of
     anything. The context is the text before the blank and the continuation is
     ``option + text after the blank``.

   * **Question** stems are complete questions. These get an ``Answer:`` cue
     and the option is appended.

   The four options of a single item always render through the same branch, so
   the ranking within an item is never comparing two different formats.
"""

import datasets

BLANK = "___"


# ---------------------------------------------------------------- rendering

def _split_stem(stem):
    """Return (before_blank, after_blank), or (None, None) for a question."""
    if BLANK not in stem:
        return None, None
    head, _, tail = stem.partition(BLANK)
    return head.rstrip(), tail


def doc_to_text(doc):
    head, _ = _split_stem(doc["stem"])
    if head is not None:
        return head
    return doc["stem"].rstrip() + "\nAnswer:"


def doc_to_choice(doc):
    _, tail = _split_stem(doc["stem"])
    if tail is not None:
        return [" " + c + tail for c in doc["choices"]]
    return [" " + c for c in doc["choices"]]


# ---------------------------------------------------------------- routing

def _by_domain(domain):
    def fn(dataset: datasets.Dataset) -> datasets.Dataset:
        return dataset.filter(lambda d: d.get("domain") == domain)
    return fn


filter_math = _by_domain("Math")
filter_english = _by_domain("English")
filter_science = _by_domain("Science")
filter_art = _by_domain("Art")