apply.rs

static USAGE: &str = r#"
Apply a series of transformation functions to given CSV column/s. This can be used to
perform typical data-wrangling tasks and/or to harmonize some values, etc.

It has five subcommands:
 1. operations*   - 36 string, format, currency, regex & NLP operators.
 2. emptyreplace* - replace empty cells with <--replacement> string.
 3. datefmt*      - Formats recognized date/s (19 formats recognized) to
                    a specified date format using <--formatstr>.
 4. dynfmt        - Dynamically constructs a new column from other columns using
                    the <--formatstr> template.
 5. calcconv      - parse and evaluate math expressions, with support for units
                    and conversions.
    * subcommand is multi-column capable.

OPERATIONS (multi-column capable)
Multiple operations can be applied, with the comma-delimited operation series
applied in order:

  trim => Trim the cell
  trim,upper => Trim the cell, then transform to uppercase
  lower,simdln => Lowercase the cell, then compute the normalized 
      Damerau-Levenshtein similarity to --comparand

Operations support multi-column transformations. Just make sure the
number of transformed columns with the --rename option is the same. e.g.:

# trim and fold to uppercase the col1,col2 and col3 columns and rename them
# to newcol1,newcol2 and newcol3
$ qsv apply operations trim,upper col1,col2,col3 -r newcol1,newcol2,newcol3 file.csv

It has 36 supported operations:

  * len: Return string length
  * lower: Transform to lowercase
  * upper: Transform to uppercase
  * squeeze: Compress consecutive whitespaces
  * squeeze0: Remove whitespace
  * trim: Trim (drop whitespace left & right of the string)
  * ltrim: Left trim whitespace
  * rtrim: Right trim whitespace
  * mtrim: Trims --comparand matches left & right of the string (Rust trim_matches)
  * mltrim: Left trim --comparand matches (Rust trim_start_matches)
  * mrtrim: Right trim --comparand matches (Rust trim_end_matches)
  * strip_prefix: Removes specified prefix in --comparand
  * strip_suffix: Remove specified suffix in --comparand
  * escape - escape (Rust escape_default)
  * encode64: base64 encode
  * decode64: base64 decode
  * replace: Replace all matches of a pattern (using --comparand)
      with a string (using --replacement) (Rust replace)
  * regex_replace: Replace all regex matches in --comparand w/ --replacement.
  * titlecase - capitalizes English text using Daring Fireball titlecase style
      https://daringfireball.net/2008/05/title_case
  * censor: profanity filter. Add additional comma-delimited profanities with --comparand.
  * censor_check: check if profanity is detected (boolean).
      Add additional comma-delimited profanities with -comparand.
  * censor_count: count of profanities detected.
      Add additional comma-delimited profanities with -comparand.
  * round: Round numeric values to the specified number of decimal places using
      Midpoint Nearest Even Rounding Strategy AKA "Bankers Rounding."
      Specify the number of decimal places with --formatstr (default: 3).
  * thousands: Add thousands separators to numeric values.
      Specify the separator policy with --formatstr (default: comma). The valid policies are:
      comma, dot, space, underscore, hexfour (place a space every four hex digits) and
      indiancomma (place a comma every two digits, except the last three digits).
      The decimal separator can be specified with --replacement (default: '.')
  * currencytonum: Gets the numeric value of a currency. Supports currency symbols
      (e.g. $,¥,£,€,֏,₱,₽,₪,₩,ƒ,฿,₫) and strings (e.g. USD, EUR, RMB, JPY, etc.). 
      Recognizes point, comma and space separators.
  * numtocurrency: Convert a numeric value to a currency. Specify the currency symbol
      with --comparand. Automatically rounds values to two decimal places. Specify
      "euro" formatting (e.g. 1.000,00 instead of 1,000.00 ) by setting --formatstr to "euro".
      Specify conversion rate by setting --replacement to a number.
  * copy: Mark a column for copying
  * simdl: Damerau-Levenshtein similarity to --comparand
  * simdln: Normalized Damerau-Levenshtein similarity to --comparand (between 0.0 & 1.0)
  * simjw: Jaro-Winkler similarity to --comparand (between 0.0 & 1.0)
  * simsd: Sørensen-Dice similarity to --comparand (between 0.0 & 1.0)
  * simhm: Hamming distance to --comparand. Num of positions characters differ.
  * simod: Optimal String Alignment (OSA) Distance to --comparand.
  * eudex: Multi-lingual sounds like --comparand (boolean)
       Tested on English, Catalan, German, Spanish, Swedish and Italian dictionaries.
       It supports all C1 letters (e.g. ü, ö, æ, ß, é, etc.) and takes their sound into account.
       It should work on other European languages that use the Latin alphabet.
  * sentiment: Normalized VADER sentiment score (English only - between -1.0 to 1.0).
  * whatlang: Language Detection for 87 supported languages, with default confidence threshold
       of 0.9, which can be overridden by assigning 0.0 to 1.0 to --comparand.
       If language detection confidence is below the threshold, it will still show the best language
       guess, followed by the confidence score, ending with a question mark.
       If you want to always displays the confidence score, end the --comparand value with a
       question mark (e.g. 0.9?)
       https://github.com/greyblake/whatlang-rs/blob/master/SUPPORTED_LANGUAGES.md

Examples:
Trim, then transform to uppercase the surname field.

  $ qsv apply operations trim,upper surname file.csv

Trim, then transform to uppercase the surname field and rename the column uppercase_clean_surname.

  $ qsv apply operations trim,upper surname -r uppercase_clean_surname file.csv

Trim, then transform to uppercase the surname field and
save it to a new column named uppercase_clean_surname.

  $ qsv apply operations trim,upper surname -c uppercase_clean_surname file.csv

Trim, then transform to uppercase the firstname and surname fields and
rename the columns ufirstname and usurname.

  $ qsv apply operations trim,upper firstname,surname -r ufirstname,usurname file.csv

Trim parentheses & brackets from the description field.

  $ qsv apply operations mtrim description --comparand '()<>' file.csv

Replace ' and ' with ' & ' in the description field.

  $ qsv apply replace description --comparand ' and ' --replacement ' & ' file.csv

Extract the numeric value of the Salary column in a new column named Salary_num.

  $ qsv apply operations currencytonum Salary -c Salary_num file.csv

Convert the USD_Price to PHP_Price using the currency symbol "PHP" with a conversion rate of 60.

  $ qsv apply operations numtocurrency USD_Price -C PHP -R 60 -c PHP_Price file.csv

Base64 encode the plaintext_col column and save the encoded value into new column named encoded_col
and then decode it.

  $ qsv apply operations encode plaintext_col -c encoded_col file.csv | qsv apply operations decode encode_col

Compute the Normalized Damerau-Levenshtein similarity of the neighborhood column to the string 'Roxbury'
and save it to a new column named dln_roxbury_score.

  $ qsv apply operations lower,simdln neighborhood --comparand roxbury -c dln_roxbury_score boston311.csv

You can also use this subcommand command to make a copy of a column:

  $ qsv apply operations copy col_to_copy -c col_copy file.csv

EMPTYREPLACE (multi-column capable)
Replace empty cells with <--replacement> string.
Non-empty cells are not modified. See the `fill` command for more complex empty field operations.

Examples:
Replace empty cells in file.csv Measurement column with 'None'.

$ qsv apply emptyreplace Measurement --replacement None file.csv

Replace empty cells in file.csv Measurement column with 'Unknown Measurement'.

$ qsv apply emptyreplace Measurement --replacement 'Unknown Measurement' file.csv

Replace empty cells in file.csv M1,M2 and M3 columns with 'None'.

$ qsv apply emptyreplace M1,M2,M3 --replacement None file.csv

Replace all empty cells in file.csv for columns that start with 'Measurement' with 'None'.

$ qsv apply emptyreplace '/^Measurement/' --replacement None file.csv

Replace all empty cells in file.csv for columns that start with 'observation'
case insensitive with 'None'.

$ qsv apply emptyreplace --replacement None '/(?i)^observation/' file.csv

DATEFMT (multi-column capable)
Formats recognized date/s to a specified format using <--formatstr>.
See https://github.com/jqnatividad/belt/tree/main/dateparser#accepted-date-formats for
recognized date formats.
See https://docs.rs/chrono/latest/chrono/format/strftime/ for 
accepted date formats for --formatstr.
Defaults to ISO 8601/RFC 3339 format when --formatstr is not specified.
( "%Y-%m-%dT%H:%M:%S%z" - e.g. 2001-07-08T00:34:60.026490+09:30 )

Examples:
Format dates in Open Date column to ISO 8601/RFC 3339 format:

  $ qsv apply datefmt 'Open Date' file.csv

Format multiple date columns in file.csv to ISO 8601/RFC 3339 format:

  $ qsv apply datefmt 'Open Date,Modified Date,Closed Date' file.csv

Format all columns that end with "_date" case-insensitive in file.csv to ISO 8601/RFC 3339 format:

  $ qsv apply datefmt '\(?i)_date$\' file.csv

Format dates in OpenDate column using '%Y-%m-%d' format:

  $ qsv apply datefmt OpenDate --formatstr '%Y-%m-%d' file.csv

Format multiple date columns using '%Y-%m-%d' format:

  $ qsv apply datefmt OpenDate,CloseDate,ReopenDate --formatstr '%Y-%m-%d' file.csv

Get the week number for OpenDate and store it in the week_number column:

  $ qsv apply dateformat OpenDate --formatstr '%V' --new-column week_number file.csv

Get the day of the week for several date columns and store it in the corresponding weekday columns:

  $ qsv apply dateformat OpenDate,CloseDate --formatstr '%u' --rename Open_weekday,Close_weekday file.csv

DYNFMT
Dynamically constructs a new column from other columns using the <--formatstr> template.
The template can contain arbitrary characters. To insert a column value, enclose the
column name in curly braces, replacing all non-alphanumeric characters with underscores.

If you need to dynamically construct a column with more complex formatting requirements and
computed values, check out the py command to take advantage of Python's f-string formatting.

Examples:
Create a new column 'mailing address' from 'house number', 'street', 'city' and 'zip-code' columns:

  $ qsv apply dynfmt --formatstr '{house_number} {street}, {city} {zip_code} USA' -c 'mailing address' file.csv

Create a new column 'FullName' from 'FirstName', 'MI', and 'LastName' columns:

  $ qsv apply dynfmt --formatstr 'Sir/Madam {FirstName} {MI}. {LastName}' -c FullName file.csv

CALCCONV
Parse and evaluate math expressions into a new column, with support for units and conversions.
The math expression is built dynamically using the <--formatstr> template, similar to the DYNFMT
subcommand, with the addition that if the literal '<UNIT>' is found at the end of the template, the
inferred unit will be appended to the result.

For a complete list of supported units, constants, operators and functions, see https://docs.rs/cpc

Examples:
Do simple arithmetic:
$ qsv apply calcconv --formatstr '{col1} + {col2} * {col3}' --new-column result file.csv

With support for operators like % and ^:
$ qsv apply calcconv --formatstr '{col1} % 3' --new-column remainder file.csv

Convert from one unit to another:
$ qsv apply calcconv --formatstr '{col1}mb in gigabytes' -c gb file.csv
$ qsv apply calcconv --formatstr '{col1} Fahrenheit in Celsius" -c metric_temperature file.csv

Mix units and conversions are automatically done for you:
$ qsv apply calcconv --formatstr '{col1}km + {col2}mi in meters' -c meters file.csv

You can append the inferred unit at the end of the result by ending the expression with '<UNIT>':
$ qsv apply calcconv --formatstr '({col1} + {col2})km to light years <UNIT>' -c light_years file.csv

You can even do complex temporal unit conversions:
$ qsv apply calcconv --formatstr '{col1}m/s + {col2}mi/h in kilometers per h' -c kms_per_h file.csv

Use math functions - see https://docs.rs/cpc/latest/cpc/enum.FunctionIdentifier.html for list of functions:
$ qsv apply calcconv --formatstr 'round(sqrt{col1}^4)! liters' -c liters file.csv

Use percentages:
$ qsv apply calcconv --formatstr '10% of abs(sin(pi)) horsepower to watts' -c watts file.csv

And use very large numbers:
$ qsv apply calcconv --formatstr '{col1} Billion Trillion * {col2} quadrillion vigintillion' -c num_atoms file.csv 

For more extensive examples, see https://github.com/jqnatividad/qsv/blob/master/tests/test_apply.rs.

Usage:
qsv apply operations <operations> [options] <column> [<input>]
qsv apply emptyreplace --replacement=<string> [options] <column> [<input>]
qsv apply datefmt [--formatstr=<string>] [options] <column> [<input>]
qsv apply dynfmt --formatstr=<string> [options] --new-column=<name> [<input>]
qsv apply calcconv --formatstr=<string> [options] --new-column=<name> [<input>]
qsv apply --help

apply arguments:
    <column>                        The column/s to apply the transformation to.
                                    Note that the <column> argument supports multiple columns
                                    for the operations, emptyreplace & datefmt subcommands.
                                    See 'qsv select --help' for the format details.

    OPERATIONS subcommand:
        <operations>                The operation/s to apply.
        <column>                    The column/s to apply the operations to.

    EMPTYREPLACE subcommand:
        --replacement=<string>      The string to use to replace empty values.
        <column>                    The column/s to check for emptiness.

    DATEFMT subcommand:
        --formatstr=<string>        The date format to use for the datefmt operation.
                                    See DATEFMT section in the --formatstr option below
                                    for more details.
        <column>                    The date column/s to apply the datefmt operation to.

    DYNFMT subcommand:
        --formatstr=<string>        The template to use for the dynfmt operation.
                                    See DYNFMT example above for more details.
        --new-column=<name>         Put the generated values in a new column.

    CALCONV subcommand:
        --formatstr=<string>        The calculation/conversion expression to use.
        --new-column=<name>         Put the calculated/converted values in a new column.
        
    <input>                     The input file to read from. If not specified, reads from stdin.

apply options:
    -c, --new-column <name>     Put the transformed values in a new column instead.
    -r, --rename <name>         New name for the transformed column.
    -C, --comparand=<string>    The string to compare against for replace & similarity operations.
                                Also used with numtocurrency operation to specify currency symbol.
    -R, --replacement=<string>  The string to use for the replace & emptyreplace operations.
                                Also used with numtocurrency operation to conversion rate.
    --prefer-dmy                Prefer to parse dates in dmy format. Otherwise, use mdy format.
                                Only used with the DATEFMT subcommand.
    --keep-zero-time            If a formatted date ends with "T00:00:00+00:00", keep the time
                                instead of removing it. Only used with the DATEFMT subcommand.
    -f, --formatstr=<string>    This option is used by several subcommands:

                                OPERATIONS: 
                                  numtocurrency
                                    If set to "euro", will format the currency to use "." instead of ","
                                    as separators (e.g. 1.000,00 instead of 1,000.00 )

                                  thousands
                                    The thousands separator policy to use. The available policies are:
                                    comma, dot, space, underscore, hexfour (place a space every four 
                                    hex digits) and indiancomma (place a comma every two digits,
                                    except the last three digits). (default: comma)

                                  round
                                    The number of decimal places to round to (default: 3)

                                DATEFMT: The date format to use. For formats, see
                                  https://docs.rs/chrono/latest/chrono/format/strftime/
                                  Default to ISO 8601 / RFC 3339 date & time format -
                                  "%Y-%m-%dT%H:%M:%S%z" - e.g. 2001-07-08T00:34:60.026490+09:30
                                  [default: %+]

                                DYNFMT: the template to use to construct a new column.

    -j, --jobs <arg>            The number of jobs to run in parallel.
                                When not set, the number of jobs is set to the number of CPUs detected.
    -b, --batch <size>          The number of rows per batch to load into memory, before running in parallel.
                                [default: 50000]

Common options:
    -h, --help                  Display this message
    -o, --output <file>         Write output to <file> instead of stdout.
    -n, --no-headers            When set, the first row will not be interpreted
                                as headers.
    -d, --delimiter <arg>       The field delimiter for reading CSV data.
                                Must be a single character. (default: ,)
    -p, --progressbar           Show progress bars. Not valid for stdin.
"#;

use std::{str::FromStr, sync::OnceLock};

use censor::{Censor, Sex, Zealous};
use cpc::{eval, units::Unit};
use data_encoding::BASE64;
use dynfmt::Format;
use eudex::Hash;
use indicatif::{ProgressBar, ProgressDrawTarget};
use log::debug;
use qsv_currency::Currency;
use qsv_dateparser::parse_with_preference;
use rayon::{
    iter::{IndexedParallelIterator, ParallelIterator},
    prelude::IntoParallelRefIterator,
};
use regex::Regex;
use serde::Deserialize;
use strsim::{
    damerau_levenshtein, hamming, jaro_winkler, normalized_damerau_levenshtein, osa_distance,
    sorensen_dice,
};
use strum_macros::EnumString;
use thousands::{policies, Separable, SeparatorPolicy};
use titlecase::titlecase;
use vader_sentiment::SentimentIntensityAnalyzer;
use whatlang::detect;

use crate::{
    clitypes::CliError,
    config::{Config, Delimiter},
    regex_oncelock,
    select::SelectColumns,
    util, CliResult,
};

#[derive(Clone, EnumString)]
#[strum(use_phf)]
#[strum(ascii_case_insensitive)]
#[allow(non_camel_case_types)]
enum Operations {
    Censor,
    Censor_Check,
    Censor_Count,
    Copy,
    Currencytonum,
    Decode,
    Encode,
    Escape,
    Eudex,
    Len,
    Lower,
    Ltrim,
    Mltrim,
    Mrtrim,
    Mtrim,
    Numtocurrency,
    Regex_Replace,
    Replace,
    Round,
    Rtrim,
    Sentiment,
    Simdl,
    Simdln,
    Simhm,
    Simjw,
    Simod,
    Simsd,
    Squeeze,
    Squeeze0,
    Strip_Prefix,
    Strip_Suffix,
    Thousands,
    Titlecase,
    Trim,
    Upper,
    Whatlang,
}

#[derive(Deserialize)]
struct Args {
    arg_column:          SelectColumns,
    cmd_operations:      bool,
    arg_operations:      String,
    cmd_datefmt:         bool,
    cmd_dynfmt:          bool,
    cmd_emptyreplace:    bool,
    cmd_calcconv:        bool,
    arg_input:           Option<String>,
    flag_rename:         Option<String>,
    flag_comparand:      String,
    flag_replacement:    String,
    flag_prefer_dmy:     bool,
    flag_keep_zero_time: bool,
    flag_formatstr:      String,
    flag_batch:          u32,
    flag_jobs:           Option<usize>,
    flag_new_column:     Option<String>,
    flag_output:         Option<String>,
    flag_no_headers:     bool,
    flag_delimiter:      Option<Delimiter>,
    flag_progressbar:    bool,
}

static CENSOR: OnceLock<Censor> = OnceLock::new();
static EUDEX_COMPARAND_HASH: OnceLock<eudex::Hash> = OnceLock::new();
static REGEX_REPLACE: OnceLock<Regex> = OnceLock::new();
static SENTIMENT_ANALYZER: OnceLock<SentimentIntensityAnalyzer> = OnceLock::new();
static THOUSANDS_POLICY: OnceLock<SeparatorPolicy> = OnceLock::new();
static ROUND_PLACES: OnceLock<u32> = OnceLock::new();
static WHATLANG_CONFIDENCE_THRESHOLD: OnceLock<f64> = OnceLock::new();

// default confidence threshold for whatlang language detection - 90% confidence
const DEFAULT_THRESHOLD: f64 = 0.9;

// default number of decimal places to round to
const DEFAULT_ROUND_PLACES: u32 = 3;

// for thousands operator
static INDIANCOMMA_POLICY: SeparatorPolicy = SeparatorPolicy {
    separator: ",",
    groups:    &[3, 2],
    digits:    thousands::digits::ASCII_DECIMAL,
};

// valid subcommands
enum ApplySubCmd {
    Operations,
    DateFmt,
    DynFmt,
    EmptyReplace,
    CalcConv,
}

#[inline]
fn replace_column_value(
    record: &csv::StringRecord,
    column_index: usize,
    new_value: &str,
) -> csv::StringRecord {
    record
        .into_iter()
        .enumerate()
        .map(|(i, v)| if i == column_index { new_value } else { v })
        .collect()
}

pub fn run(argv: &[&str]) -> CliResult<()> {
    let args: Args = util::get_args(USAGE, argv)?;
    let rconfig = Config::new(&args.arg_input)
        .delimiter(args.flag_delimiter)
        .no_headers(args.flag_no_headers)
        .select(args.arg_column);

    let mut rdr = rconfig.reader()?;
    let mut wtr = Config::new(&args.flag_output).writer()?;

    let headers = rdr.byte_headers()?.clone();
    let sel = rconfig.selection(&headers)?;
    let column_index = *sel.iter().next().unwrap();

    let mut headers = rdr.headers()?.clone();

    if let Some(new_name) = args.flag_rename {
        let new_col_names = util::ColumnNameParser::new(&new_name).parse()?;
        if new_col_names.len() != sel.len() {
            return fail_incorrectusage_clierror!(
                "Number of new columns does not match input column selection."
            );
        }
        for (i, col_index) in sel.iter().enumerate() {
            headers = replace_column_value(&headers, *col_index, &new_col_names[i]);
        }
    }

    if !rconfig.no_headers {
        if let Some(new_column) = &args.flag_new_column {
            headers.push_field(new_column);
        }
        wtr.write_record(&headers)?;
    }

    // for dynfmt, safe_headers are the "safe" version of colnames - alphanumeric only,
    // all other chars replaced with underscore
    // dynfmt_fields are the columns used in the dynfmt --formatstr option
    // we prep it so we only populate the lookup vec with the index of these columns
    // so SimpleCurlyFormat is performant
    let mut dynfmt_fields = Vec::with_capacity(10); // 10 is a reasonable default to save allocs
    let mut dynfmt_template = args.flag_formatstr.clone();
    if args.cmd_dynfmt || args.cmd_calcconv {
        if args.flag_no_headers {
            return fail_incorrectusage_clierror!("dynfmt/calcconv subcommand requires headers.");
        }
        // first, get the fields used in the dynfmt template
        let (safe_headers, _) = util::safe_header_names(&headers, false, false, None, "", true);
        let formatstr_re: &'static Regex = crate::regex_oncelock!(r"\{(?P<key>\w+)?\}");
        for format_fields in formatstr_re.captures_iter(&args.flag_formatstr) {
            dynfmt_fields.push(format_fields.name("key").unwrap().as_str());
        }
        // we sort the fields so we can do binary_search
        dynfmt_fields.sort_unstable();
        // now, get the indices of the columns for the lookup vec
        for (i, field) in safe_headers.iter().enumerate() {
            if dynfmt_fields.binary_search(&field.as_str()).is_ok() {
                let field_with_curly = format!("{{{field}}}");
                let field_index = format!("{{{i}}}");
                dynfmt_template = dynfmt_template.replace(&field_with_curly, &field_index);
            }
        }
        debug!("dynfmt_fields: {dynfmt_fields:?}  dynfmt_template: {dynfmt_template}");
    }

    let mut ops_vec: Vec<Operations> = Vec::new();

    let apply_cmd = if args.cmd_operations {
        match validate_operations(
            &args.arg_operations.split(',').collect(),
            &args.flag_comparand,
            &args.flag_replacement,
            &args.flag_new_column,
            &args.flag_formatstr,
        ) {
            Ok(operations_vec) => ops_vec = operations_vec,
            Err(e) => return Err(e),
        }
        ApplySubCmd::Operations
    } else if args.cmd_datefmt {
        ApplySubCmd::DateFmt
    } else if args.cmd_dynfmt {
        ApplySubCmd::DynFmt
    } else if args.cmd_emptyreplace {
        ApplySubCmd::EmptyReplace
    } else if args.cmd_calcconv {
        ApplySubCmd::CalcConv
    } else {
        return fail_incorrectusage_clierror!("Unknown apply subcommand.");
    };

    // prep progress bar
    let show_progress =
        (args.flag_progressbar || util::get_envvar_flag("QSV_PROGRESSBAR")) && !rconfig.is_stdin();

    let progress = ProgressBar::with_draw_target(None, ProgressDrawTarget::stderr_with_hz(5));
    if show_progress {
        util::prep_progress(&progress, util::count_rows(&rconfig)?);
    } else {
        progress.set_draw_target(ProgressDrawTarget::hidden());
    }

    let prefer_dmy = args.flag_prefer_dmy || rconfig.get_dmy_preference();

    // amortize memory allocation by reusing record
    #[allow(unused_assignments)]
    let mut batch_record = csv::StringRecord::new();

    // reuse batch buffers
    let batchsize: usize = args.flag_batch as usize;
    let mut batch = Vec::with_capacity(batchsize);
    let mut batch_results = Vec::with_capacity(batchsize);

    // set RAYON_NUM_THREADS
    util::njobs(args.flag_jobs);

    // main loop to read CSV and construct batches for parallel processing.
    // each batch is processed via Rayon parallel iterator.
    // loop exits when batch is empty.
    'batch_loop: loop {
        for _ in 0..batchsize {
            match rdr.read_record(&mut batch_record) {
                Ok(has_data) => {
                    if has_data {
                        batch.push(batch_record.clone());
                    } else {
                        // nothing else to add to batch
                        break;
                    }
                },
                Err(e) => {
                    return fail_clierror!("Error reading file: {e}");
                },
            }
        }

        if batch.is_empty() {
            // break out of infinite loop when at EOF
            break 'batch_loop;
        }

        // do actual apply command via Rayon parallel iterator
        batch
            .par_iter()
            .map(|record_item| {
                let mut record = record_item.clone();
                match apply_cmd {
                    ApplySubCmd::Operations => {
                        let mut cell = String::new();
                        for col_index in &*sel {
                            record[*col_index].clone_into(&mut cell);
                            apply_operations(
                                &ops_vec,
                                &mut cell,
                                &args.flag_comparand,
                                &args.flag_replacement,
                                &args.flag_formatstr,
                            );
                            if args.flag_new_column.is_some() {
                                record.push_field(&cell);
                            } else {
                                record = replace_column_value(&record, *col_index, &cell);
                            }
                        }
                    },
                    ApplySubCmd::EmptyReplace => {
                        let mut cell = String::new();
                        for col_index in &*sel {
                            record[*col_index].clone_into(&mut cell);
                            if cell.trim().is_empty() {
                                cell = args.flag_replacement.clone();
                            }
                            if args.flag_new_column.is_some() {
                                record.push_field(&cell);
                            } else {
                                record = replace_column_value(&record, *col_index, &cell);
                            }
                        }
                    },
                    ApplySubCmd::DateFmt => {
                        let mut cell = String::new();
                        for col_index in &*sel {
                            record[*col_index].clone_into(&mut cell);
                            if !cell.is_empty() {
                                let parsed_date = parse_with_preference(&cell, prefer_dmy);
                                if let Ok(format_date) = parsed_date {
                                    let formatted_date =
                                        format_date.format(&args.flag_formatstr).to_string();
                                    if !args.flag_keep_zero_time
                                        && formatted_date.ends_with("T00:00:00+00:00")
                                    {
                                        cell = formatted_date[..10].to_string();
                                    } else {
                                        cell = formatted_date;
                                    }
                                }
                            }
                            if args.flag_new_column.is_some() {
                                record.push_field(&cell);
                            } else {
                                record = replace_column_value(&record, *col_index, &cell);
                            }
                        }
                    },
                    ApplySubCmd::DynFmt => {
                        let mut cell = record[column_index].to_owned();
                        if !cell.is_empty() {
                            let mut record_vec: Vec<String> = Vec::with_capacity(record.len());
                            for field in &record {
                                record_vec.push(field.to_string());
                            }
                            if let Ok(formatted) =
                                dynfmt::SimpleCurlyFormat.format(&dynfmt_template, record_vec)
                            {
                                cell = formatted.to_string();
                            }
                        }
                        if args.flag_new_column.is_some() {
                            record.push_field(&cell);
                        } else {
                            record = replace_column_value(&record, column_index, &cell);
                        }
                    },
                    ApplySubCmd::CalcConv => {
                        let result = if record[column_index].is_empty() {
                            String::new()
                        } else {
                            let mut cell = record[column_index].to_owned();
                            let mut record_vec: Vec<String> = Vec::with_capacity(record.len());
                            for field in &record {
                                record_vec.push(field.to_string());
                            }
                            if let Ok(formatted) =
                                dynfmt::SimpleCurlyFormat.format(&dynfmt_template, record_vec)
                            {
                                cell = formatted.to_string();
                            }

                            let mut append_unit = false;
                            let cell_for_eval = if cell.ends_with("<UNIT>") {
                                append_unit = true;
                                cell.trim_end_matches("<UNIT>")
                            } else {
                                &cell
                            };
                            match eval(cell_for_eval, true, Unit::Celsius, false) {
                                Ok(answer) => {
                                    if append_unit {
                                        format!("{} {:?}", answer.value, answer.unit)
                                    } else {
                                        answer.value.to_string()
                                    }
                                },
                                Err(e) => {
                                    format!("ERROR: {e}")
                                },
                            }
                        };

                        if args.flag_new_column.is_some() {
                            record.push_field(&result);
                        } else {
                            record = replace_column_value(&record, column_index, &result);
                        }
                    },
                }

                record
            })
            .collect_into_vec(&mut batch_results);

        // rayon collect() guarantees original order, so we can just append results each batch
        for result_record in &batch_results {
            wtr.write_record(result_record)?;
        }

        if show_progress {
            progress.inc(batch.len() as u64);
        }

        batch.clear();
    } // end batch loop

    if show_progress {
        util::finish_progress(&progress);
    }
    Ok(wtr.flush()?)
}

// validate apply operations for required options
// and prepare operations enum vec
fn validate_operations(
    operations: &Vec<&str>,
    flag_comparand: &str,
    flag_replacement: &str,
    flag_new_column: &Option<String>,
    flag_formatstr: &str,
) -> Result<Vec<Operations>, CliError> {
    let mut censor_invokes = 0_u8;
    let mut copy_invokes = 0_u8;
    let mut eudex_invokes = 0_u8;
    let mut regex_replace_invokes = 0_u8;
    let mut replace_invokes = 0_u8;
    let mut sentiment_invokes = 0_u8;
    let mut sim_invokes = 0_u8;
    let mut strip_invokes = 0_u8;
    let mut whatlang_invokes = 0_u8;

    let mut ops_vec: Vec<Operations> = Vec::with_capacity(operations.len());

    for op in operations {
        let Ok(operation) = Operations::from_str(op) else {
            return fail_incorrectusage_clierror!("Unknown '{op}' operation");
        };
        match operation {
            Operations::Censor | Operations::Censor_Check | Operations::Censor_Count => {
                if flag_new_column.is_none() {
                    return fail_incorrectusage_clierror!(
                        "--new_column (-c) is required for censor operations."
                    );
                }
                if censor_invokes == 0
                    && CENSOR
                        .set({
                            let mut censored_words = Censor::Standard + Zealous + Sex;
                            for word in flag_comparand.split(',') {
                                censored_words += word.trim();
                            }
                            censored_words
                        })
                        .is_err()
                {
                    return fail!("Cannot initialize Censor engine.");
                }
                censor_invokes = censor_invokes.saturating_add(1);
            },
            Operations::Copy => {
                if flag_new_column.is_none() {
                    return fail_incorrectusage_clierror!(
                        "--new_column (-c) is required for copy operation."
                    );
                }
                copy_invokes = copy_invokes.saturating_add(1);
            },
            Operations::Eudex => {
                if flag_comparand.is_empty() || flag_new_column.is_none() {
                    return fail_incorrectusage_clierror!(
                        "--comparand (-C) and --new_column (-c) is required for eudex."
                    );
                }
                if eudex_invokes == 0
                    && EUDEX_COMPARAND_HASH
                        .set(eudex::Hash::new(flag_comparand))
                        .is_err()
                {
                    return fail!("Cannot initialize Eudex.");
                }
                eudex_invokes = eudex_invokes.saturating_add(1);
            },
            Operations::Mtrim | Operations::Mltrim | Operations::Mrtrim => {
                if flag_comparand.is_empty() {
                    return fail_incorrectusage_clierror!(
                        "--comparand (-C) is required for match trim operations."
                    );
                }
            },
            Operations::Regex_Replace => {
                if flag_comparand.is_empty() || flag_replacement.is_empty() {
                    return fail_incorrectusage_clierror!(
                        "--comparand (-C) and --replacement (-R) are required for regex_replace \
                         operation."
                    );
                }
                if regex_replace_invokes == 0 {
                    let re = match regex::Regex::new(flag_comparand) {
                        Ok(re) => re,
                        Err(err) => {
                            return fail_clierror!("regex_replace expression error: {err:?}");
                        },
                    };
                    #[allow(clippy::let_underscore_untyped)]
                    let _ = REGEX_REPLACE.set(re);
                }
                regex_replace_invokes = regex_replace_invokes.saturating_add(1);
            },
            Operations::Replace => {
                if flag_comparand.is_empty() || flag_replacement.is_empty() {
                    return fail_incorrectusage_clierror!(
                        "--comparand (-C) and --replacement (-R) are required for replace \
                         operation."
                    );
                }
                replace_invokes = replace_invokes.saturating_add(1);
            },
            Operations::Sentiment => {
                if flag_new_column.is_none() {
                    return fail_incorrectusage_clierror!(
                        "--new_column (-c) is required for sentiment operation."
                    );
                }
                sentiment_invokes = sentiment_invokes.saturating_add(1);
            },
            Operations::Simdl
            | Operations::Simdln
            | Operations::Simjw
            | Operations::Simsd
            | Operations::Simhm
            | Operations::Simod => {
                if flag_comparand.is_empty() || flag_new_column.is_none() {
                    return fail_incorrectusage_clierror!(
                        "--comparand (-C) and --new_column (-c) is required for similarity \
                         operations."
                    );
                }
                sim_invokes = sim_invokes.saturating_add(1);
            },
            Operations::Strip_Prefix | Operations::Strip_Suffix => {
                if flag_comparand.is_empty() {
                    return fail!("--comparand (-C) is required for strip operations.");
                }
                strip_invokes = strip_invokes.saturating_add(1);
            },
            Operations::Thousands => {
                let separator_policy = match flag_formatstr {
                    "dot" => policies::DOT_SEPARATOR,
                    "space" => policies::SPACE_SEPARATOR,
                    "underscore" => policies::UNDERSCORE_SEPARATOR,
                    "hexfour" => policies::HEX_FOUR,
                    "indiancomma" => INDIANCOMMA_POLICY,
                    _ => policies::COMMA_SEPARATOR,
                };
                if THOUSANDS_POLICY.set(separator_policy).is_err() {
                    return fail!("Cannot initialize Thousands policy.");
                };
            },
            Operations::Round => {
                if ROUND_PLACES
                    .set(
                        flag_formatstr
                            .parse::<u32>()
                            .unwrap_or(DEFAULT_ROUND_PLACES),
                    )
                    .is_err()
                {
                    return fail!("Cannot initialize Round precision.");
                };
            },
            Operations::Whatlang => {
                if flag_new_column.is_none() {
                    return fail_incorrectusage_clierror!(
                        "--new_column (-c) is required for whatlang language detection."
                    );
                }

                if whatlang_invokes == 0
                    && WHATLANG_CONFIDENCE_THRESHOLD
                        .set(if flag_comparand.is_empty() {
                            DEFAULT_THRESHOLD
                        } else {
                            let preparsed_threshold;
                            let show_confidence = if flag_comparand.ends_with('?') {
                                preparsed_threshold = flag_comparand.trim_end_matches('?');
                                true
                            } else {
                                preparsed_threshold = flag_comparand;
                                false
                            };
                            let desired_threshold = preparsed_threshold
                                .parse::<f64>()
                                .unwrap_or(DEFAULT_THRESHOLD);
                            // desired threshold can be 0.0 to 1.0
                            let final_threshold = if (0.0..=1.0).contains(&desired_threshold) {
                                desired_threshold
                            } else {
                                // its outside the valid range
                                // just set it to the default threshold
                                DEFAULT_THRESHOLD
                            };
                            if show_confidence {
                                final_threshold * -1.0
                            } else {
                                final_threshold
                            }
                        })
                        .is_err()
                {
                    return fail!("cannot initialize WhatLang language detection.");
                }
                whatlang_invokes = whatlang_invokes.saturating_add(1);
            },
            _ => {},
        }
        ops_vec.push(operation);
    }
    if censor_invokes > 1
        || copy_invokes > 1
        || eudex_invokes > 1
        || regex_replace_invokes > 1
        || replace_invokes > 1
        || sentiment_invokes > 1
        || sim_invokes > 1
        || strip_invokes > 1
        || whatlang_invokes > 1
    {
        return fail_incorrectusage_clierror!(
            "you can only use censor({censor_invokes}), copy({copy_invokes}), \
             eudex({eudex_invokes}), regex_replace({regex_replace_invokes}), \
             replace({replace_invokes}), sentiment({sentiment_invokes}), \
             similarity({sim_invokes}), strip({strip_invokes}), and whatlang({whatlang_invokes}) \
             ONCE per operation series."
        );
    };

    Ok(ops_vec) // no validation errors
}

#[inline]
fn apply_operations(
    ops_vec: &Vec<Operations>,
    cell: &mut String,
    comparand: &str,
    replacement: &str,
    formatstr: &str,
) {
    for op in ops_vec {
        match op {
            Operations::Len => {
                *cell = cell.len().to_string();
            },
            Operations::Lower => {
                *cell = cell.to_lowercase();
            },
            Operations::Upper => {
                *cell = cell.to_uppercase();
            },
            Operations::Squeeze => {
                let squeezer: &'static Regex = regex_oncelock!(r"\s+");
                *cell = squeezer.replace_all(cell, " ").to_string();
            },
            Operations::Squeeze0 => {
                let squeezer: &'static Regex = regex_oncelock!(r"\s+");
                *cell = squeezer.replace_all(cell, "").to_string();
            },
            Operations::Trim => {
                *cell = String::from(cell.trim());
            },
            Operations::Ltrim => {
                *cell = String::from(cell.trim_start());
            },
            Operations::Rtrim => {
                *cell = String::from(cell.trim_end());
            },
            Operations::Mtrim => {
                let chars_to_trim: &[char] = &comparand.chars().collect::<Vec<_>>();
                *cell = String::from(cell.trim_matches(chars_to_trim));
            },
            Operations::Mltrim => {
                *cell = String::from(cell.trim_start_matches(comparand));
            },
            Operations::Mrtrim => {
                *cell = String::from(cell.trim_end_matches(comparand));
            },
            Operations::Encode => {
                *cell = BASE64.encode(cell.as_bytes());
            },
            Operations::Decode => {
                let mut output = vec![0; BASE64.decode_len(cell.len()).unwrap_or_default()];
                *cell = match BASE64.decode_mut(cell.as_bytes(), &mut output) {
                    Ok(len) => simdutf8::basic::from_utf8(&output[0..len])
                        .unwrap_or_default()
                        .to_owned(),
                    Err(e) => format!("decoding error: {e:?}"),
                };
            },
            Operations::Escape => {
                *cell = cell.escape_default().to_string();
            },
            Operations::Strip_Prefix => {
                if let Some(stripped) = cell.strip_prefix(comparand) {
                    *cell = String::from(stripped);
                }
            },
            Operations::Strip_Suffix => {
                if let Some(stripped) = cell.strip_suffix(comparand) {
                    *cell = String::from(stripped);
                }
            },
            Operations::Titlecase => {
                *cell = titlecase(cell);
            },
            Operations::Replace => {
                *cell = cell.replace(comparand, replacement);
            },
            Operations::Regex_Replace => {
                let regexreplace = REGEX_REPLACE.get().unwrap();
                *cell = regexreplace.replace_all(cell, replacement).to_string();
            },
            Operations::Censor => {
                let censor = CENSOR.get().unwrap();
                *cell = censor.censor(cell);
            },
            Operations::Censor_Check => {
                let censor = CENSOR.get().unwrap();
                *cell = censor.check(cell).to_string();
            },
            Operations::Censor_Count => {
                let censor = CENSOR.get().unwrap();
                *cell = censor.count(cell).to_string();
            },
            Operations::Thousands => {
                if let Ok(num) = cell.parse::<f64>() {
                    let mut temp_string = num.separate_by_policy(*THOUSANDS_POLICY.get().unwrap());

                    // if there is a decimal separator (fractional part > 0.0), use the requested
                    // decimal separator in --replacement
                    if num.fract() > 0.0 {
                        // if replacement is empty, use the default decimal separator (.)
                        *cell = if replacement.is_empty() {
                            temp_string
                        } else {
                            // else replace the decimal separator (last '.') w/ the requested one
                            match temp_string.rfind('.') {
                                Some(last_dot) => {
                                    temp_string.replace_range(last_dot..=last_dot, replacement);
                                    temp_string
                                },
                                None => temp_string,
                            }
                        };
                    } else {
                        *cell = temp_string;
                    }
                }
            },
            Operations::Round => {
                if let Ok(num) = cell.parse::<f64>() {
                    *cell = util::round_num(num, *ROUND_PLACES.get().unwrap());
                }
            },
            Operations::Currencytonum => {
                // this is a workaround around current limitation of qsv-currency
                // and also of upstream currency-rs, that it cannot
                // handle currency amounts properly with three decimal places
                // to get around this limitation, we append a 0 at the end to make it four
                // decimal places without affecting the value
                let fract_3digits: &'static Regex = regex_oncelock!(r"\.\d\d\d$");
                let cell_val = if fract_3digits.is_match(cell) {
                    format!("{cell}0")
                } else {
                    cell.clone()
                };

                if let Ok(currency_val) = Currency::from_str(&cell_val) {
                    // currency is stored as a BigInt, with
                    // 1 currency unit being 100 coins
                    let currency_coins = currency_val.value();
                    let coins = format!("{:03}", &currency_coins);
                    let coinlen = coins.len();
                    if coinlen > 2 && coins != "000" {
                        let decpoint = coinlen - 2;
                        let coin_num = &coins[..decpoint];
                        let coin_frac = &coins[decpoint..];
                        *cell = format!("{coin_num}.{coin_frac}");
                    }
                }
            },
            Operations::Numtocurrency => {
                // same 3 decimal place workaround as currencytonum
                let fract_3digits2: &'static Regex = regex_oncelock!(r"\.\d\d\d$");
                let cell_val = if fract_3digits2.is_match(cell) {
                    format!("{cell}0")
                } else {
                    cell.clone()
                };

                if let Ok(currency_value) = Currency::from_str(&cell_val) {
                    let currency_wrk = currency_value
                        .convert(replacement.parse::<f64>().unwrap_or(1.0_f64), comparand);
                    *cell = if formatstr.contains("euro") {
                        format!("{currency_wrk:e}")
                    } else {
                        format!("{currency_wrk}")
                    };
                }
            },
            Operations::Simdl => {
                *cell = damerau_levenshtein(cell, comparand).to_string();
            },
            Operations::Simdln => {
                *cell = normalized_damerau_levenshtein(cell, comparand).to_string();
            },
            Operations::Simjw => {
                *cell = jaro_winkler(cell, comparand).to_string();
            },
            Operations::Simsd => {
                *cell = sorensen_dice(cell, comparand).to_string();
            },
            Operations::Simhm => {
                let ham_val = hamming(cell, comparand);
                match ham_val {
                    Ok(val) => *cell = val.to_string(),
                    Err(_) => *cell = String::from("ERROR: Different lengths"),
                }
            },
            Operations::Simod => *cell = osa_distance(cell, comparand).to_string(),
            Operations::Eudex => {
                let eudex_comparand_hash = EUDEX_COMPARAND_HASH.get().unwrap();
                let cell_hash = Hash::new(cell);
                *cell = format!("{}", (cell_hash - *eudex_comparand_hash).similar());
            },
            Operations::Sentiment => {
                let sentiment_analyzer = SENTIMENT_ANALYZER
                    .get_or_init(vader_sentiment::SentimentIntensityAnalyzer::new);
                let sentiment_scores = sentiment_analyzer.polarity_scores(cell);
                *cell = sentiment_scores.get("compound").unwrap_or(&0.0).to_string();
            },
            Operations::Whatlang => {
                let lang_info = detect(cell);
                if let Some(lang_info) = lang_info {
                    let whatlang_confidence_threshold =
                        *WHATLANG_CONFIDENCE_THRESHOLD.get().unwrap();
                    let lang_confidence = lang_info.confidence();
                    let lang = lang_info.lang();
                    if lang_confidence >= whatlang_confidence_threshold.abs() {
                        if whatlang_confidence_threshold >= 0.0 {
                            *cell = format!("{lang:?}");
                        } else {
                            *cell = format!("{lang:?}({lang_confidence:.3})");
                        }
                    } else {
                        // if confidence < confidence_threshold; show best-guessed language,
                        // confidence to 3 decimal places enclosed in parens and
                        // end with a question mark
                        *cell = format!("{lang:?}({lang_confidence:.3})?");
                    }
                }
            },
            Operations::Copy => {}, // copy is a noop
        }
    }
}