interface ColumnDef {
  key: string;
  header: string;
  minWidth?: number;
  maxWidth?: number;
  width?: number;
}

function visualWidth(str: string): number {
  let width = 0;
  for (const ch of str) {
    const code = ch.codePointAt(0) ?? 0;
    // CJK Unified, Compatibility, Extension ranges, plus fullwidth forms
    if (
      (code >= 0x4e00 && code <= 0x9fff) ||
      (code >= 0x3400 && code <= 0x4dbf) ||
      (code >= 0x20000 && code <= 0x2a6df) ||
      (code >= 0xf900 && code <= 0xfaff) ||
      (code >= 0xff01 && code <= 0xff60) ||
      (code >= 0xffe0 && code <= 0xffe6)
    ) {
      width += 2;
    } else {
      width += 1;
    }
  }
  return width;
}

function padToWidth(str: string, targetWidth: number): string {
  let padded = str;
  let current = visualWidth(str);
  while (current < targetWidth) {
    padded += " ";
    current += 1;
  }
  return padded;
}

function truncateToWidth(str: string, maxWidth: number): string {
  let result = "";
  let vw = 0;
  for (const ch of str) {
    const charW = visualWidth(ch);
    if (vw + charW > maxWidth - 3) {
      result += "...";
      break;
    }
    result += ch;
    vw += charW;
  }
  if (visualWidth(result) <= maxWidth && result.length < str.length) {
    result += "...";
  }
  return result;
}

export function formatTable(columns: ColumnDef[], rows: Record<string, string>[]): string {
  const minW = 8;
  const maxW = 60;

  const resolved = columns.map((col) => {
    const headerW = visualWidth(col.header);
    let dataW = 0;
    for (const row of rows) {
      const val = row[col.key] ?? "-";
      dataW = Math.max(dataW, visualWidth(val));
    }
    const natural = Math.max(headerW, dataW);
    const lo = col.minWidth ?? minW;
    const hi = col.maxWidth ?? maxW;
    const width = Math.max(lo, Math.min(hi, natural));
    return { ...col, width };
  });

  const padCell = (col: ColumnDef, text: string): string => {
    if (visualWidth(text) > col.width!) {
      return truncateToWidth(text, col.width!);
    }
    return padToWidth(text, col.width!);
  };

  const lines: string[] = [];

  const headerLine = resolved
    .map((col) => padCell(col, col.header))
    .join("  ");
  lines.push(headerLine);

  const sepLine = resolved
    .map((col) => "-".repeat(col.width!))
    .join("  ");
  lines.push(sepLine);

  for (const row of rows) {
    const line = resolved
      .map((col) => padCell(col, row[col.key] ?? "-"))
      .join("  ");
    lines.push(line);
  }

  return lines.join("\n");
}