string_calc/

lib.rs

//! `string_calc` is a collection of utilities to perform checked arithmetics on
//! &str, to counter against floating point errors. It supports (checked) addition, 
//! subtraction, and multiplication. It does not support division due to the 
//! nature of division's ability to generate infinite amount of decimals. 
//! 
//! If your calculations have too many decimal points such that it can't fit i128 
//! range AFTER calculation, it'll raise an error. 
//! If you pass in weird values that's not integer or floats/decimals, it'll raise an error. 
//! Return result will be Ok(String) which you can call .unwrap() or other methods to get
//! its internal value, if everything goes right. 

use std::cmp;

/// Perform checked_add on floating points. 
/// Inherits the "checked_add" property of rust in integers. 
/// When failed, it'll return Err(message). Success, Ok(value). 
/// 
/// NOTE: Must use basic numbers UTF-8 or it'll fail. 
/// 
/// Example: 
/// ```
/// let lhs = "172.28";
/// let rhs = "192.168";
/// 
/// assert_eq!(string_calc::checked_add(lhs, rhs).unwrap(), 
///   "364.448".to_owned());
/// ``` 
pub fn checked_add(lhs: impl Into<String>, rhs: impl Into<String>) -> Result<String, &'static str> {
  // Check for longest decimals. We find the "dot index"
  let lhs: String = lhs.into();
  let rhs: String = rhs.into();
  let lhs: &str = lhs.as_str();
  let rhs: &str = rhs.as_str(); 
  let res = check_str(lhs);
  let res2 = check_str(rhs);
  if res.is_err() { return Err("LHS is invalid decimal. Please check."); }
  if res2.is_err() { return Err("RHS is invalid decimal. Please check."); }

  let (lhs_i128, rhs_i128, max_decimal) = convert_to_i128(lhs, rhs);

  let value = lhs_i128.checked_add(rhs_i128);
  if value.is_none() { return Err("Sorry, i128 add encounters overflow. Please find other methods to add."); }

  // Add back the decimal points. 
  let mut value_str: String = value.unwrap().to_string();
  let insert_loc = value_str.len().checked_sub(max_decimal);
  if max_decimal != 0 && insert_loc.is_some() { 
    let insert_loc = insert_loc.unwrap();
    value_str.insert(insert_loc, '.');
    if insert_loc == 0 { value_str.insert(insert_loc, '0'); }
    value_str = value_str.trim_end_matches('0').to_owned();
  };
  value_str = value_str.trim_end_matches(".").to_owned();

  return Ok(value_str);
}


/// Performs checked_sub on floating points. 
/// Inherits the checked_sub property of rust in integers. 
/// When failed, it'll return Err(message). Success, Ok(value). 
/// 
/// NOTE: Must use basic numbers UTF-8 or it'll fail. 
/// 
/// Example: 
/// ```
/// let lhs = "192.168";
/// let rhs = "172.28";
/// 
/// assert_eq!(string_calc::checked_sub(lhs, rhs).unwrap(),
///   "19.888".to_owned());
/// ``` 
pub fn checked_sub(lhs: impl Into<String>, rhs: impl Into<String>) -> Result<String, &'static str> {
  let lhs: String = lhs.into();
  let rhs: String = rhs.into();
  let lhs: &str = lhs.as_str();
  let rhs: &str = rhs.as_str(); 

  let res = check_str(lhs);
  let res2 = check_str(rhs);
  if res.is_err() { return Err("LHS is invalid decimal. Please check."); }
  if res2.is_err() { return Err("RHS is invalid decimal. Please check."); }

  let (lhs_i128, rhs_i128, max_decimal) = convert_to_i128(lhs, rhs);

  let value = lhs_i128.checked_sub(rhs_i128);
  if value.is_none() { return Err("Sorry, i128 add encounters overflow. Please find other methods to add."); }

  // Add back the decimal points. 
  let mut value_str: String = value.unwrap().to_string();
  let insert_loc = value_str.len().checked_sub(max_decimal);
  if max_decimal != 0 && insert_loc.is_some() { 
    let insert_loc = insert_loc.unwrap();
    value_str.insert(insert_loc, '.');
    if insert_loc == 0 { value_str.insert(insert_loc, '0'); }
    value_str = value_str.trim_end_matches('0').to_owned();
  };
  value_str = value_str.trim_end_matches(".").to_owned();

  return Ok(value_str);
}

/// Performs checked_mul on floating points. 
/// Inherits the checked_mul property of rust in integers. 
/// When failed, it'll return Err(message). Success, Ok(value). 
/// 
/// NOTE: Must use basic numbers UTF-8 or it'll fail. 
/// 
/// Example: 
/// ```
/// let lhs = "12.35";
/// let rhs = "15.6";
/// 
/// assert_eq!(string_calc::checked_mul(lhs, rhs).unwrap(),
///   "192.66".to_owned());
/// ```
pub fn checked_mul(lhs: impl Into<String>, rhs: impl Into<String>) -> Result<String, &'static str> {
  let lhs: String = lhs.into();
  let rhs: String = rhs.into();
  let lhs: &str = lhs.as_str();
  let rhs: &str = rhs.as_str(); 

  let res = check_str(lhs);
  let res2 = check_str(rhs);
  if res.is_err() { return Err("LHS is invalid decimal. Please check."); }
  if res2.is_err() { return Err("RHS is invalid decimal. Please check."); }

  let (lhs_i128, rhs_i128, max_decimal) = convert_to_i128(lhs, rhs);
  let total_decimal = max_decimal.checked_mul(2);
  if total_decimal.is_none() { return Err("Please report Bug: Failed to multiply total_decimal. "); }
  let total_decimal = total_decimal.unwrap();
  
  let value = lhs_i128.checked_mul(rhs_i128);
  if value.is_none() { return Err("Sorry, i128 add encounters overflow. Please find other methods to add."); }

  // Add back decimal points. 
  let mut value_str: String = value.unwrap().to_string();
  let insert_loc = value_str.len().checked_sub(total_decimal);
  if total_decimal != 0 && insert_loc.is_some() { 
    let insert_loc = insert_loc.unwrap();
    value_str.insert(insert_loc, '.');
    if insert_loc == 0 { value_str.insert(insert_loc, '0'); }
    value_str = value_str.trim_end_matches("0").to_owned();
  };
  value_str = value_str.trim_end_matches(".").to_owned();  // if last value is '.', trim. 

  return Ok(value_str)
}

/// Performs comparison between 2 values. 
/// When failed, it'll return Err(message). Success, Ok(bool). 
/// 
/// Available comparator are: "le", "ge", "lt", "gt", "eq" which 
/// corresponds to "less than equal", "greater than equal", 
/// "less than", "greater than", and "equal". 
/// 
/// The signs are compared to LHS. For example, less than equal would
/// check if lhs <= rhs. 
/// 
/// Example: 
/// ```
/// let lhs = "12.35";
/// let rhs = "17.5";
/// 
/// assert!(string_calc::compare(lhs, rhs, "lt").unwrap());
/// assert!(!string_calc::compare(lhs, rhs, "ge").unwrap());
/// ```
pub fn compare(lhs: impl Into<String>, rhs: impl Into<String>, 
  comparator: &str
) -> Result<bool, &'static str> {
  let lhs: String = lhs.into();
  let rhs: String = rhs.into();
  let lhs: &str = lhs.as_str();
  let rhs: &str = rhs.as_str(); 

  let res = check_str(lhs);
  let res2 = check_str(rhs);
  if res.is_err() { return Err("LHS is invalid decimal. Please check."); }
  if res2.is_err() { return Err("RHS is invalid decimal. Please check."); }

  let (lhs_i128, rhs_i128, _) = convert_to_i128(lhs, rhs);
  match comparator {
    "le" => return Ok(lhs_i128 <= rhs_i128),
    "ge" => return Ok(lhs_i128 >= rhs_i128),
    "lt" => return Ok(lhs_i128 < rhs_i128),
    "gt" => return Ok(lhs_i128 > rhs_i128),
    "eq" => return Ok(lhs_i128 == rhs_i128),
    _ => return Err("Invalid comparator. Choose between le, ge, lt, gt, and eq.")
  };
}


/// Sum of all values given a Vec<String> or Vec<str> of valid items; 
/// 
/// Example: 
/// ```
/// let data: Vec<String> = [100.325, 40.272, 51.23]
///   .map(|c| c.to_string())
///   .to_vec();
/// 
/// assert_eq!(string_calc::sum(data).unwrap(), "191.827".to_owned());
/// 
/// let data2 = vec!["20.0", "17", "28"];
/// assert_eq!(string_calc::sum(data2).unwrap(), "65".to_owned());
/// ``` 
pub fn sum(values: Vec<impl Into<String> + Clone>) -> Result<String, &'static str> {
  let mut _temp_vals: Vec<String> = Vec::new();
  // let m = values[3];
  for i in 0..values.len() {
    let g: String = values[i].clone().into();
    _temp_vals.push(g);
  }
  // Because g didn't live long enough to convert to .as_str() inside. 
  let new_values: Vec<&str> = _temp_vals.iter().map(|c| c.as_str()).collect();

  if new_values.iter().any(|c| check_str(*c).is_err()) {
    // Unfortunately, we didn't check for exact indices where it fails, for now. 
    return Err("There are values which didn't pass check_str. Please inspect and fix.");
  }

  let (new_vec, max_decimal) = convert_all_to_i128(new_values);

  let sum_val: i128 = new_vec.iter().sum();

  // Add back the decimal point. 
  let mut value_str: String = sum_val.to_string();
  let insert_loc = value_str.len().checked_sub(max_decimal);
  if max_decimal != 0 && insert_loc.is_some() { 
    let insert_loc = insert_loc.unwrap();
    value_str.insert(insert_loc, '.');
    if insert_loc == 0 { value_str.insert(insert_loc, '0'); }
    value_str = value_str.trim_end_matches('0').to_owned();
  };
  value_str = value_str.trim_end_matches(".").to_owned();

  return Ok(value_str);
}




// ==========================================================================
fn check_str(str: &str) -> Result<(), &'static str> {
  let mut dot_count = 0;
  for c in str.chars() {
    if !['0', '1', '2', '3', '4', '5', '6', 
      '7', '8', '9', '.', '-'].contains(&c) 
    {
      return Err("Invalid String. Must be numbers and decimal point only.");
    }

    if c == '.' { dot_count += 1; }
    if dot_count > 1 { return Err("Invalid String. Cannot have more than one decimal."); }
  }
  return Ok(());
}

/// Get the decimal point given a string. 
/// di stands for dot index. 
/// So 12 will return 0, while 12.1 will return 1. 
fn get_decimal_points(num: &str) -> usize {
  let num_len = num.len();
  let num_di = num.find(".").unwrap_or(num_len - 1);
  return num_len - (num_di + 1);
}

/// Preprocess the value by: 
/// 1. Remove the dot. 
/// 2. Add appropriate number of zeros at the back. 
/// 
/// curr_d = current decimals. NEED TO PASS IN CORRECT VALUE OR FAILED.
/// Use cache value because it won't refigure it out, which waste computing power.
fn preprocess_value(num: &str, curr_d: usize, max_d: usize) -> String {
  let mut num_str = num.to_owned();
  let num_di = num.find(".");
  if num_di.is_some() { num_str.remove(num_di.unwrap()); }

  // Add zeros where appropriate
  let repeat_no = max_d - curr_d;
  if repeat_no >= 1 {
    for _ in 0..repeat_no {
      num_str.push('0');
    }
  }

  return num_str;
}

// Changed to i128 to support negative numbers. 
fn convert_to_i128(lhs: &str, rhs: &str) -> (i128, i128, usize) {
  let lhs_decimals = get_decimal_points(lhs);
  let rhs_decimals = get_decimal_points(rhs);
  let max_decimal = cmp::max(lhs_decimals, rhs_decimals);

  // Remove the dot. 
  let lhs_int = preprocess_value(lhs, lhs_decimals, max_decimal);
  let rhs_int = preprocess_value(rhs, rhs_decimals, max_decimal);

  let lhs_i128: i128 = lhs_int.parse().unwrap();
  let rhs_i128: i128 = rhs_int.parse().unwrap();

  return (lhs_i128, rhs_i128, max_decimal);
}

// Convert all to i128
// Unfortunately, can't reduce the iteration cause we need max_decimal first, before
// we can continue. 
fn convert_all_to_i128(our_vec: Vec<&str>) -> (Vec<i128>, usize) {
  let decimals: Vec<usize> = our_vec.iter()
    .map(|c| get_decimal_points(*c))
    .collect();
  let max_decimal: usize = *decimals.iter().max().unwrap();

  let ret_val: Vec<i128> = our_vec.iter().enumerate().map(|(i, c)| {
    let value = preprocess_value(c, decimals[i], max_decimal);
    let value_i128 = value.parse().unwrap();
    value_i128
  }).collect();

  return (ret_val, max_decimal);
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_alphabets_wont_work() {
      let result = check_str("123str");
      assert!(result.is_err());
    }

    #[test]
    fn test_char_wont_work() {
      let result = check_str("我爱你");
      assert!(result.is_err());
    }

    #[test]
    fn test_floats_work() {
      let result = check_str("12.376");
      assert!(result.is_ok());
    }

    #[test]
    fn test_ip_addr_not_work() {
      let result = check_str("192.168.10.1");
      assert!(result.is_err());
    }

    #[test]
    fn correct_decimal() {
      let decimal = get_decimal_points("12.376");
      assert_eq!(decimal, 3);
    }

    #[test]
    fn correct_integer() {
      let decimal = get_decimal_points("123");
      assert_eq!(decimal, 0);
    }

    #[test]
    fn preprocess_value_case_1() {
      let value = preprocess_value("12.237", 3, 3);
      assert_eq!(value, "12237");
    }

    #[test]
    fn preprocess_value_case_2() {
      let value = preprocess_value("12.237", 3, 5);
      assert_eq!(value, "1223700");
    }

    #[test]
    fn preprocess_value_case_3() {
      let value = preprocess_value("12", 0, 3);
      assert_eq!(value, "12000");
    }

    #[test]
    fn preprocess_value_case_4() {
      let value = preprocess_value("12", 0, 0);
      assert_eq!(value, "12");
    }

    #[test]
    fn checked_add_case_1() {
      let value = checked_add("12.32", "15.6");
      assert_eq!(value.unwrap(), "27.92".to_owned());
    }

    #[test]
    fn checked_add_case_2() {
      let value = checked_add("12.3", "17");
      assert_eq!(value.unwrap(), "29.3".to_owned());
    }

    #[test]
    fn checked_add_case_3() {
      let value = checked_add("12", "15");
      assert_eq!(value.unwrap(), "27".to_owned());
    }

    #[test]
    fn checked_add_case_4() {
      let value = checked_add("meh", "12");
      assert!(value.is_err());
    }

    #[test]
    fn checked_add_case_5() {
      let value = checked_add("12", "meh");
      assert!(value.is_err());
    }

    // not sure if we can test overflow or not for addition; 
    // but certainly can do for multiplication. 

    #[test]
    fn checked_sub_case_1() {
      let value = checked_sub("12.367", "9.3");
      assert_eq!(value.unwrap(), "3.067".to_owned());
    }

    #[test]
    fn checked_sub_case_2() {
      let value = checked_sub("12", "6.3");
      assert_eq!(value.unwrap(), "5.7".to_owned());
    }

    #[test]
    fn checked_sub_case_3() {
      let value = checked_sub("12", "6");
      assert_eq!(value.unwrap(), "6".to_owned());
    }

    #[test]
    fn checked_sub_case_4() {
      let value = checked_sub("meh", "6");
      assert!(value.is_err());
    }

    #[test]
    fn checked_sub_case_5() {
      let value = checked_sub("6", "meh");
      assert!(value.is_err());
    }

    #[test]
    fn checked_mul_case_1() {
      let value = checked_mul("19.87", "13.625");
      assert_eq!(value.unwrap(), "270.72875".to_owned());
    }

    #[test]
    fn checked_mul_case_2() {
      let value = checked_mul("12.3", "6");
      let value2 = checked_mul("6", "12.3");
      assert_eq!(value.clone().unwrap(), "73.8".to_owned());
      assert_eq!(value.unwrap(), value2.unwrap());
    }

    #[test]
    fn checked_mul_case_3() {
      let value = checked_mul("12.5", "6");
      assert_eq!(value.unwrap(), "75".to_owned());
    }

    #[test]
    fn checked_mul_case_4() {
      let value = checked_mul("meh", "6");
      assert!(value.is_err());
    }

    #[test]
    fn checked_mul_case_5() {
      let value = checked_mul("6", "meh");
      assert!(value.is_err());
    }

    #[test]
    fn check_comparator_le() {
      assert!(compare("12.5", "17.6", "le").unwrap());
      assert!(!compare("17.6", "12.5", "le").unwrap());
      assert!(compare("12.5", "12.5", "le").unwrap());
    }

    #[test]
    fn check_comparator_lt() {
      assert!(compare("12.5", "17.6", "lt").unwrap());
      assert!(!compare("17.6", "12.5", "lt").unwrap());
      assert!(!compare("12.5", "12.5", "lt").unwrap());
    }

    #[test]
    fn check_comparator_ge() {
      assert!(!compare("12.5", "17.6", "ge").unwrap());
      assert!(compare("17.6", "12.5", "ge").unwrap());
      assert!(compare("12.5", "12.5", "ge").unwrap());
    }

    #[test]
    fn check_comparator_gt() {
      assert!(!compare("12.5", "17.6", "gt").unwrap());
      assert!(compare("17.6", "12.5", "gt").unwrap());
      assert!(!compare("12.5", "12.5", "gt").unwrap());
    }

    #[test]
    fn check_comparator_eq() {
      assert!(!compare("12.5", "17.6", "eq").unwrap());
      assert!(!compare("17.6", "12.5", "eq").unwrap());
      assert!(compare("12.5", "12.5", "eq").unwrap());
    }

    #[test]
    fn check_comparator_wrong() {
      assert!(compare("12.5", "17.6", "meh").is_err());
    }

    #[test]
    fn check_after_minus_no_decimal_no_cause_error() {
      assert!(checked_sub("12.70", "12.7").is_ok());
      assert_eq!(checked_sub("25.400", "12.8").unwrap(), "12.6".to_owned());
      assert_eq!(checked_sub("12.8", "11.8".to_owned()).unwrap(), "1".to_owned());
      assert_eq!(checked_sub("12.8", "12.0000").unwrap(), "0.8".to_owned());
      assert!(checked_mul("12.52", "0").is_ok());
    }

    #[test]
    fn check_string_works_not_only_str() {
      assert_eq!(checked_add("12.5".to_owned(), "13.70".to_owned()).unwrap(), "26.2".to_owned());
      assert_eq!(checked_sub("12.5".to_owned(), "9.62".to_owned()).unwrap(), "2.88".to_owned());
      assert_eq!(checked_mul("12.5".to_owned(), "7.2".to_owned()).unwrap(), "90".to_owned());
    }

    #[test]
    fn checked_can_run_negative_numbers() {
      assert_eq!(checked_sub("12.8", "17.5").unwrap(), "-4.7".to_owned());
    }

    #[test]
    fn check_special_case_negative_numbers() {
      assert_eq!(checked_add("-12.800", "12.8").unwrap(), "0".to_owned());
      assert_eq!(checked_sub("-12.8", "-12.80").unwrap(), "0".to_owned());
      assert_eq!(checked_sub("-12.8", "-11.0").unwrap(), "-1.8".to_owned());
      assert_eq!(checked_add("12.8", "-12.0000").unwrap(), "0.8".to_owned());
    }

    #[test]
    fn check_convert_all_to_i128_works() {
      let vec: Vec<&str> = vec!["12.368", "1.14", "28"];
      let (new_vec, max_decimal) = convert_all_to_i128(vec);
      assert_eq!(new_vec, vec![12368, 1140, 28000]);
      assert_eq!(max_decimal, 3);
    }

    #[test]
    fn check_sum_all_with_negative_numbers() {
      let vec = vec!["-12.42", "3.87", "2.323"];
      assert_eq!(sum(vec).unwrap(), "-6.227".to_owned());
    }
}