finances: pcmc.ts converted to new format

[denversc]

No description provided.

[gemini-code-assist]

Code Review

This pull request refactors the PDF parsing utility options by replacing resultPrefix with a more flexible resultTransform function, and integrates the PC Mastercard statement parser into the main finances documents framework while removing the old standalone script. Feedback on the changes highlights that the new transformMonthNameToNumber implementation is fragile compared to the previous version because it relies on exact substring matches of hardcoded month names. A more robust regex-based prefix-matching approach is suggested to handle variations in month abbreviations.

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[gemini-code-assist]

The current implementation of transformMonthNameToNumber is fragile and represents a regression in robustness compared to the previous implementation in finances/pcmc.ts.

Specifically:

1. It relies on exact substring matching of hardcoded month names (some with dots like 'Jan.', others without like 'May').
2. If a PDF statement uses a different abbreviation (e.g., 'Sep.' instead of 'Sept.', or 'Jul.' instead of 'July'), or omits/adds a period, the parsing will fail with a DocumentParseError.
3. The previous implementation was much more robust: it extracted the month name, took the first 3 characters, lowercased them, and mapped them.

We can restore and improve upon that robustness by matching the leading month word with a regular expression, extracting its 3-letter prefix, and replacing it safely using string slicing.

const monthNumberByPrefix: Record<string, string> = {
  jan: '01',
  feb: '02',
  mar: '03',
  apr: '04',
  may: '05',
  jun: '06',
  jul: '07',
  aug: '08',
  sep: '09',
  oct: '10',
  nov: '11',
  dec: '12',
};

function transformMonthNameToNumber(s: string): string | DocumentParseError {
  const match = s.match(/^([A-Za-z]+)(\\.?)/);
  if (!match) {
    return {
      type: 'DocumentParseError',
      message: 'unrecognized date format: ' + s,
    };
  }

  const [fullMatch, monthStr] = match;
  const prefix = monthStr.toLowerCase().substring(0, 3);
  const monthNumber = monthNumberByPrefix[prefix];
  if (!monthNumber) {
    return {
      type: 'DocumentParseError',
      message:
        'unrecognized month name in date: ' + s + ' ' +
        '(recognized month prefixes are: ' +
        Object.keys(monthNumberByPrefix).join(', ') +
        ')',
    };
  }

  return monthNumber + s.slice(fullMatch.length);
}