fintext/utils.py

"""Post-processing utilities for transaction extraction.

Ported from the Android Kotlin GLiNER2 ONNX runner. Provides tokenisation,
span decoding, amount parsing, and date normalisation for bank SMS messages.
"""

from __future__ import annotations

import re
from typing import Optional

import numpy as np

# ---------------------------------------------------------------------------
# Constants
# ---------------------------------------------------------------------------

SCHEMA_TOKENS: list[str] = [
    "(", "[P]", "transaction_type",
    "(", "[L]", "DEBIT", "[L]", "CREDIT", ")", ")",
    "[SEP_STRUCT]",
    "(", "[P]", "transaction_info",
    "(", "[C]", "transaction_amount",
    "[C]", "transaction_date",
    "[C]", "transaction_description",
    "[C]", "masked_account_digits", ")", ")",
    "[SEP_TEXT]",
]
"""Fixed schema token sequence matching the exported ONNX model."""

EXTRACTION_FIELDS: list[str] = [
    "transaction_amount",
    "transaction_date",
    "transaction_description",
    "masked_account_digits",
]
"""Ordered field names for the span-extraction head."""

CLASSIFICATION_LABELS: list[str] = ["DEBIT", "CREDIT"]
"""Labels emitted by the classification head."""

# ---------------------------------------------------------------------------
# Tokenisation
# ---------------------------------------------------------------------------

_WORD_PATTERN = re.compile(
    r"(?:https?://\S+|www\.\S+)"          # URLs
    r"|[a-z0-9._%+\-]+@[a-z0-9.\-]+\.[a-z]{2,}"  # emails
    r"|@[a-z0-9_]+"                        # @-mentions
    r"|\w+(?:[-_]\w+)*"                    # words (with hyphens/underscores)
    r"|\S",                                # single non-space fallback
    re.IGNORECASE,
)


def split_into_words(text: str) -> list[tuple[str, int, int]]:
    """Whitespace-aware tokeniser matching GLiNER2's WhitespaceTokenSplitter.

    Returns a list of *(word, char_start, char_end)* tuples.
    """
    return [(m.group(), m.start(), m.end()) for m in _WORD_PATTERN.finditer(text)]


# ---------------------------------------------------------------------------
# Amount parsing
# ---------------------------------------------------------------------------

_CURRENCY_PATTERN = re.compile(r"(?:Rs\.?|INR|₹)\s*", re.IGNORECASE)
_NUMBER_PATTERN = re.compile(r"[\d,]+(?:\.\d+)?")


def parse_amount(raw: str) -> float | None:
    """Strip currency symbols and extract the first numeric value.

    Handles Rs., Rs, INR, and the rupee sign.  Commas are removed before
    conversion.  Returns *None* when no number can be found.
    """
    cleaned = _CURRENCY_PATTERN.sub("", raw).strip()
    match = _NUMBER_PATTERN.search(cleaned)
    if not match:
        return None
    try:
        return float(match.group().replace(",", ""))
    except ValueError:
        return None


# ---------------------------------------------------------------------------
# Date normalisation
# ---------------------------------------------------------------------------

_MONTH_MAP: dict[str, int] = {
    "jan": 1, "january": 1,
    "feb": 2, "february": 2,
    "mar": 3, "march": 3,
    "apr": 4, "april": 4,
    "may": 5,
    "jun": 6, "june": 6,
    "jul": 7, "july": 7,
    "aug": 8, "august": 8,
    "sep": 9, "september": 9,
    "oct": 10, "october": 10,
    "nov": 11, "november": 11,
    "dec": 12, "december": 12,
}

# Patterns ordered from most specific to least specific.
_DATE_PATTERNS: list[re.Pattern[str]] = [
    # DD-MM-YYYY or DD/MM/YYYY
    re.compile(r"(\d{1,2})[/\-](\d{1,2})[/\-](\d{4})"),
    # DD-Mon-YYYY or DD/Mon/YYYY
    re.compile(
        r"(\d{1,2})[/\-]([A-Za-z]+)[/\-](\d{4})"
    ),
    # DD-MM-YY or DD/MM/YY
    re.compile(r"(\d{1,2})[/\-](\d{1,2})[/\-](\d{2})(?!\d)"),
    # DD-Mon-YY or DD/Mon/YY
    re.compile(
        r"(\d{1,2})[/\-]([A-Za-z]+)[/\-](\d{2})(?!\d)"
    ),
    # DDMonYYYY  (e.g. 23Dec2025)
    re.compile(r"(\d{1,2})([A-Za-z]+)(\d{4})"),
]


def _century_window(yy: int) -> int:
    """Apply century windowing: YY > 50 -> 19YY, else 20YY."""
    return 1900 + yy if yy > 50 else 2000 + yy


def _parse_month(token: str) -> int | None:
    """Return 1-12 for a numeric or named month, or *None*."""
    if token.isdigit():
        val = int(token)
        return val if 1 <= val <= 12 else None
    return _MONTH_MAP.get(token.lower())


def normalize_date(raw: str, received_date: str | None = None) -> str | None:
    """Parse a date string in various Indian SMS formats and return DD-MM-YYYY.

    Supported input formats:
        DD-MM-YYYY, DD/MM/YYYY, DD-MM-YY, DD/MM/YY,
        DD-Mon-YYYY, DD-Mon-YY, DDMonYYYY.

    Falls back to *received_date* (which must already be DD-MM-YYYY) when
    *raw* cannot be parsed.  Returns *None* if nothing works.
    """
    for pattern in _DATE_PATTERNS:
        m = pattern.search(raw)
        if not m:
            continue

        day_s, month_s, year_s = m.group(1), m.group(2), m.group(3)

        day = int(day_s)
        month = _parse_month(month_s)
        if month is None:
            continue

        year = int(year_s)
        if year < 100:
            year = _century_window(year)

        # Basic validation
        if not (2000 <= year <= 2100):
            continue
        if not (1 <= month <= 12):
            continue
        if not (1 <= day <= 31):
            continue

        return f"{day:02d}-{month:02d}-{year}"

    # Fallback
    if received_date is not None:
        return received_date

    return None


# ---------------------------------------------------------------------------
# Span decoding
# ---------------------------------------------------------------------------

def decode_spans(
    span_scores: np.ndarray,
    text: str,
    words: list[str],
    word_spans: list[tuple[int, int]],
    threshold: float = 0.3,
) -> dict[str, Optional[tuple[str, float]]]:
    """Decode the span-extraction head output into field values.

    Parameters
    ----------
    span_scores:
        Array of shape ``[4, num_words, max_width]`` — one slice per
        extraction field.
    text:
        The original SMS text.
    words:
        Tokenised words (from :func:`split_into_words`).
    word_spans:
        ``(char_start, char_end)`` pairs for each word.
    threshold:
        Minimum confidence to accept a span.

    Returns
    -------
    dict
        Mapping of field name to ``(extracted_text, confidence)`` or
        *None* when no span exceeds *threshold*.
    """
    num_words = len(words)
    result: dict[str, Optional[tuple[str, float]]] = {}

    for field_idx, field_name in enumerate(EXTRACTION_FIELDS):
        field_scores = span_scores[field_idx]  # [num_words, max_width]
        best_score = 0.0
        best_span: tuple[int, int, float] | None = None

        for start in range(min(num_words, field_scores.shape[0])):
            for width in range(field_scores.shape[1]):
                end = start + width
                if end >= num_words:
                    break
                score = float(field_scores[start, width])
                if score > best_score and score > threshold:
                    best_score = score
                    best_span = (start, end, score)

        if best_span is not None:
            s, e, conf = best_span
            char_start = word_spans[s][0]
            char_end = word_spans[e][1]
            result[field_name] = (text[char_start:char_end], conf)
        else:
            result[field_name] = None

    return result