function createCSVScanner(onRow, nonJsonCols) {
  let buffer = '';

  return function scanChunk(chunk) {
    buffer += chunk;
    const lines = buffer.split('\n');
    buffer = lines.pop(); // Save incomplete line

    if(nonJsonCols !== 0)
    {
      for (const line of lines)
      {
        const fields = [];
        let start = 0;
        let commaCount = 0;

        for (let i = 0; i < line.length; i++) {
          if (line[i] === ',' && commaCount < nonJsonCols) {
            fields.push(line.slice(start, i));
            start = i + 1;
            commaCount++;
          }
        }
        
        const jsonStr = line.slice(start);
        let jsonData = null;
        try {
          jsonData = JSON.parse(jsonStr);
        } catch (_e) {
          console.error('Invalid JSON:', jsonStr);
        }
        onRow(...fields, jsonData);
      }
    }
    else
    {
      for (const line of lines)
      {
        const fields = [];
        let start = 0;
        for (let i = 0; i < line.length; i++) {
          if (line[i] === ',') {
            fields.push(line.slice(start, i));
            start = i + 1;
          }
        }
        fields.push(line.slice(start, line.length-1))
        onRow(...fields);
      }      
    }
  };
}

export default async function(url, nonJsonCols, onRow) {
    const response = await fetch(url);

    if (!response.ok) {
        throw new Error(`HTTP error! status: ${response.status}`);
    }

    const reader = response.body.getReader();
    const decoder = new TextDecoder("utf-8");

    const scanner = createCSVScanner(onRow, nonJsonCols);

    while (true)
    {
        const { done, value } = await reader.read();
        if (done) break;
        const chunk = decoder.decode(value, { stream: true });
        scanner(chunk);
    }
}