function parseCellRef()

in packages/core/micro/src/formula.ts [34:126]
72 lines of code
35 McCabe index (conditional complexity)

function parseCellRef(id: string): Reference | string {
    let col1 = 0;

    let pos = 0;
    const end = id.length;
    
    if (pos < end && id.charCodeAt(pos) === CharacterCodes.$) {
        pos++;
    }

    // Parse column letters
    while (pos < end) {
        const ch = id.charCodeAt(pos);
        if (ch >= CharacterCodes.A && ch <= CharacterCodes.Z) {
            col1 = col1 * 26 + (ch - 64);
            pos++;
            continue;
        }
        else if (ch >= CharacterCodes.a && ch <= CharacterCodes.z) {
            col1 = col1 * 26 + (ch - 96);
            pos++;
            continue;
        }
        break;
    }

    if (col1 > maxCol) { return id; }

    if (pos < end && id.charCodeAt(pos) === CharacterCodes.$) {
        pos++;
    }

    const start = pos;
    while (pos < end && isDigit(id.charCodeAt(pos))) {
        pos++;
    }

    if (start === pos) { return id };

    const row1 = Number(id.substring(start, pos));
    if (isNaN(row1) || row1 > maxRow) {
        return id;
    }

    if (pos === end) { return { row1: row1 - 1, col1: col1 - 1 } }

    if (pos < end && id.charCodeAt(pos) !== CharacterCodes.colon) {
        return id;
    }

    // Skips the ':'
    pos++;

    if (pos < end && id.charCodeAt(pos) === CharacterCodes.$) {
        pos++;
    }

    let col2 = 0;
    while (pos < end) {
        const ch = id.charCodeAt(pos);
        if (ch >= CharacterCodes.A && ch <= CharacterCodes.Z) {
            col2 = col2 * 26 + (ch - 64);
            pos++;
            continue;
        }
        else if (ch >= CharacterCodes.a && ch <= CharacterCodes.z) {
            col2 = col2 * 26 + (ch - 96);
            pos++;
            continue;
        }
        break;
    }

    if (col2 > maxCol) { return id; }

    if (pos < end && id.charCodeAt(pos) === CharacterCodes.$) {
        pos++;
    }

    const start2 = pos;
    while (pos < end && isDigit(id.charCodeAt(pos))) {
        pos++;
    }

    if (start2 === pos) { return id };

    const row2 = Number(id.substring(start2, pos));
    if (isNaN(row2) || row2 > maxRow) {
        return id;
    }

    return pos === end ? { row1: row1 - 1, col1: col1 - 1, row2: row2 - 1, col2: col2 - 1 } : id;
}