src/alignment.py

from dataclasses import asdict
from typing import Optional

import Levenshtein
import pandas as pd

from .types import CharacterIndices, Triplet, WordSpans


def find_closest_text(
    *,
    original: pd.Series,
    replacement: pd.Series,
) -> pd.Series:
    # Returns a series of the replacement values aligned to the original values
    no_space_replacements = {text.replace(" ", ""): text for text in replacement}
    original_text = original.str.replace(" ", "")
    result = original_text.map(no_space_replacements)
    non_perfect_matches = result.isna().sum()

    assert non_perfect_matches / len(original) <= 0.20, (
        "Poor alignment with replacement text. "
        f"{non_perfect_matches:,} of {len(original),} rows did not match well"
    )

    def closest(text: str) -> str:
        distances = replacement.apply(
            lambda comparison: Levenshtein.distance(text, comparison)
        )
        return replacement.iloc[distances.argmin()]

    result.loc[result.isna()] = original_text[result.isna()].apply(closest)
    result = result.str.strip()
    return result


def to_character_indices_series(row: pd.Series) -> pd.Series:
    result = to_character_indices(triplet=row.triples, text=row.text)
    return pd.Series(asdict(result))


def to_character_indices(
    *,
    triplet: Triplet,
    text: str,
) -> CharacterIndices:
    aspect_span, opinion_span, _ = triplet
    assert _is_sequential(aspect_span), f"aspect span not sequential: {aspect_span}"
    assert _is_sequential(opinion_span), f"opinion span not sequential: {opinion_span}"

    spans = WordSpans.make(text)

    aspect_start_index, aspect_end_index = spans.to_indices(aspect_span)
    aspect_term = text[aspect_start_index : aspect_end_index + 1]
    opinion_start_index, opinion_end_index = spans.to_indices(opinion_span)
    opinion_term = text[opinion_start_index : opinion_end_index + 1]

    return CharacterIndices(
        aspect_start_index=aspect_start_index,
        aspect_end_index=aspect_end_index,
        aspect_term=aspect_term,
        opinion_start_index=opinion_start_index,
        opinion_end_index=opinion_end_index,
        opinion_term=opinion_term,
    )


def to_aligned_character_indices_series(row: pd.Series) -> pd.Series:
    indices = to_character_indices(triplet=row.triples, text=row.original)
    result = to_aligned_character_indices(
        original=row.original,
        replacement=row.text,
        original_indices=indices,
    )
    return pd.Series(asdict(result))


def to_aligned_character_indices(
    *,
    original: str,
    replacement: str,
    original_indices: CharacterIndices,
) -> CharacterIndices:
    indices = _aligned_character_indices(original=original, replacement=replacement)

    aspect_start_index = _aligned_start_index(
        text=replacement,
        original_index=original_indices.aspect_start_index,
        indices=indices,
    )
    aspect_end_index = _aligned_end_index(
        text=replacement,
        original_index=original_indices.aspect_end_index,
        indices=indices,
    )
    aspect_term = replacement[aspect_start_index : aspect_end_index + 1]

    opinion_start_index = _aligned_start_index(
        text=replacement,
        original_index=original_indices.opinion_start_index,
        indices=indices,
    )
    opinion_end_index = _aligned_end_index(
        text=replacement,
        original_index=original_indices.opinion_end_index,
        indices=indices,
    )
    opinion_term = replacement[opinion_start_index : opinion_end_index + 1]

    return CharacterIndices(
        aspect_start_index=aspect_start_index,
        aspect_end_index=aspect_end_index,
        aspect_term=aspect_term,
        opinion_start_index=opinion_start_index,
        opinion_end_index=opinion_end_index,
        opinion_term=opinion_term,
    )


def _is_sequential(span: tuple[int, ...]) -> bool:
    return all(span[index + 1] - span[index] == 1 for index in range(len(span) - 1))


def _aligned_character_indices(original: str, replacement: str) -> list[Optional[int]]:
    indices: list[Optional[int]] = list(range(len(original)))
    for operation, _source_position, destination_position in Levenshtein.editops(
        original, replacement
    ):
        if operation == "replace":
            indices[destination_position] = None
        elif operation == "insert":
            indices.insert(destination_position, None)
        elif operation == "delete":
            del indices[destination_position]
    return indices


def _aligned_start_index(
    text: str, original_index: int, indices: list[Optional[int]]
) -> int:
    closest_after = min(
        index for index in indices if index is not None and index >= original_index
    )
    index = indices.index(closest_after)

    # Not every character in the original text is aligned to a character in the
    # replacement text. The replacement text may have deleted it, or replaced
    # it. Can step back through each letter until the word boundary is found or
    # an aligned character is found.
    while index > 0:
        if indices[index - 1] is not None:
            break
        if text[index - 1] == " ":
            break
        index -= 1
    return index


def _aligned_end_index(
    text: str, original_index: int, indices: list[Optional[int]]
) -> int:
    closest_before = max(
        index for index in indices if index is not None and index <= original_index
    )
    index = indices.index(closest_before)

    # Not every character in the original text is aligned to a character in the
    # replacement text. The replacement text may have deleted it, or replaced
    # it. Can step back through each letter until the word boundary is found or
    # an aligned character is found.
    while index < len(indices) - 1:
        if indices[index + 1] is not None:
            break
        if text[index + 1] == " ":
            break
        index += 1
    return index