// Shared CSV reader for the expense-export tests (tests/expenses-export.test.js
// and tests/expense-csv.test.js). Not a test file — it registers no tests and
// is therefore not listed in tests/index.js.

import assert from 'node:assert/strict';

// U+FEFF. buildExpenseCsv returns the complete file including the BOM, so both
// the pure function's output and the HTTP body must carry it.
export const BOM = '';

// A strict RFC 4180 reader. It doubles as an assertion: it rejects a bare LF or
// CR outside a quoted field, so a file with LF endings fails here.
export function parseCsv(text) {
  assert.ok(text.startsWith(BOM), 'CSV must be prefixed with the UTF-8 BOM');
  const body = text.slice(1);
  const rows = [];
  let row = [];
  let field = '';
  let quoted = false;

  for (let i = 0; i < body.length; i += 1) {
    const ch = body[i];
    if (quoted) {
      if (ch !== '"') { field += ch; continue; }
      if (body[i + 1] === '"') { field += '"'; i += 1; continue; }
      quoted = false;
    } else if (ch === '"') {
      quoted = true;
    } else if (ch === ',') {
      row.push(field);
      field = '';
    } else if (ch === '\r' && body[i + 1] === '\n') {
      row.push(field);
      field = '';
      rows.push(row);
      row = [];
      i += 1;
    } else if (ch === '\n' || ch === '\r') {
      assert.fail('bare CR/LF outside a quoted field — line endings must be CRLF');
    } else {
      field += ch;
    }
  }
  if (field !== '' || row.length) {
    row.push(field);
    rows.push(row);
  }
  assert.equal(quoted, false, 'unterminated quoted field');
  return rows;
}

// Turn the parsed grid into header + row objects keyed by column name.
export function readCsv(text) {
  const grid = parseCsv(text);
  const header = grid[0];
  const rows = grid.slice(1).map((cells) => {
    assert.equal(cells.length, header.length, `row has ${cells.length} cells, header has ${header.length}`);
    return Object.fromEntries(cells.map((c, i) => [header[i], c]));
  });
  return { header, rows };
}