"""Versioned BFB input contract. Immutable originals; only CRLF/CR -> LF.

Offsets are Python Unicode character boundaries, not UTF-16 or byte indices.
The interior boundary of CRLF is deliberately unrepresentable after normalization.
"""
from dataclasses import dataclass
import re

VERSION = 'bfb111-lf-v1'
SENT = re.compile(r'''[.!?。！？…]+["'”’」』》〉】〕)>]*(?=\s|$)|[”’」』](?=\s|$)''')
ABBREV = re.compile(r'\b(?:Mr|Mrs|Ms|Dr|St|Prof|vs|Sr|Jr)\.$', re.I)


@dataclass
class InputText:
    original: str
    text: str
    to_original: list
    to_canonical: list

    def original_span(self, start, end):
        return self.to_original[start], self.to_original[end]

    def position(self, original_position):
        p = self.to_canonical[original_position]
        if self.to_original[p] != original_position:
            raise ValueError('Boundary lies inside CRLF')
        return p


def normalize(original):
    out, back, forward = [], [0], [0] * (len(original) + 1)
    i = 0
    while i < len(original):
        start = i
        if original[i] == '\r':
            i += 2 if original[i:i+2] == '\r\n' else 1
            ch = '\n'
        else:
            ch = original[i]
            i += 1
        out.append(ch)
        for j in range(start+1, i+1):
            forward[j] = len(out)
        back.append(i)
    return InputText(original, ''.join(out), back, forward)


def candidates(text, language):
    """Candidate locations only. Punctuation never supplies semantic labels."""
    last_content = len(text.rstrip())
    result = []
    for match in SENT.finditer(text):
        p = match.end()
        if p >= last_content:
            continue
        if language == 'en' and ABBREV.search(text[max(0, p-25):p].strip()):
            continue
        result.append(p)
    return sorted(set(result))


def original_candidates(inp, language):
    return [inp.to_original[p] for p in candidates(inp.text, language)]