xan 0.40.0

use std::collections::hash_map::Entry;
use std::collections::{HashMap, HashSet};
use std::fs;
use std::io;
use std::path::Path;

use csv;
use regex::Regex;

use crate::config::{Config, Delimiter};
use crate::select::SelectColumns;
use crate::util::{self, FilenameTemplate, ImmutableRecordHelpers};
use crate::CliResult;

static USAGE: &str = "
Partitions the given CSV data into chunks based on the value of a column

The files are written to the output directory with filenames based on the
values in the partition column and the `--filename` flag.

Note that most operating systems avoid opening more than 1024 files at once,
so if you know the cardinality of the paritioned column is very high, please
sort the file on this column beforehand and use the -S/--sorted flag.

Usage:
    xan partition [options] <column> <outdir> [<input>]
    xan partition --help

partition options:
    --filename <filename>    A filename template to use when constructing
                             the names of the output files.  The string '{}'
                             will be replaced by a value based on the value
                             of the field, but sanitized for shell safety.
                             [default: {}.csv]
    -p, --prefix-length <n>  Truncate the partition column after the
                             specified number of bytes when creating the
                             output file.
    -S, --sorted             Use this flag if you know the file is sorted
                             on the partition column in advance, so the command
                             can run faster and with less memory and resources
                             opened.
    --drop                   Drop the partition column from results.

Common options:
    -h, --help             Display this message
    -n, --no-headers       When set, the first row will NOT be interpreted
                           as column names. Otherwise, the first row will
                           appear in all chunks as the header row.
    -d, --delimiter <arg>  The field delimiter for reading CSV data.
                           Must be a single character.
";

#[derive(Clone, Deserialize)]
struct Args {
    arg_column: SelectColumns,
    arg_input: Option<String>,
    arg_outdir: String,
    flag_filename: FilenameTemplate,
    flag_prefix_length: Option<usize>,
    flag_drop: bool,
    flag_no_headers: bool,
    flag_delimiter: Option<Delimiter>,
    flag_sorted: bool,
}

pub fn run(argv: &[&str]) -> CliResult<()> {
    let args: Args = util::get_args(USAGE, argv)?;
    fs::create_dir_all(&args.arg_outdir)?;

    // It would be nice to support efficient parallel partitions, but doing
    // do would involve more complicated inter-thread communication, with
    // multiple readers and writers, and some way of passing buffers
    // between them.
    args.sequential_partition()
}

impl Args {
    /// Configuration for our reader.
    fn rconfig(&self) -> Config {
        Config::new(&self.arg_input)
            .delimiter(self.flag_delimiter)
            .no_headers(self.flag_no_headers)
            .select(self.arg_column.clone())
    }

    /// Get the column to use as a key.
    fn key_column(&self, rconfig: &Config, headers: &csv::ByteRecord) -> CliResult<usize> {
        let select_cols = rconfig.selection(headers)?;
        if select_cols.len() == 1 {
            Ok(select_cols[0])
        } else {
            Err("can only partition on one column")?
        }
    }

    /// A basic sequential partition.
    fn sequential_partition(&self) -> CliResult<()> {
        let rconfig = self.rconfig();
        let mut rdr = rconfig.reader()?;
        let mut headers = rdr.byte_headers()?.clone();
        let key_col = self.key_column(&rconfig, &headers)?;
        let mut gen = WriterGenerator::new(self.flag_filename.clone());

        if self.flag_drop {
            headers = headers.remove(key_col);
        }

        let mut row = csv::ByteRecord::new();

        if self.flag_sorted {
            let mut current: Option<(Vec<u8>, BoxedWriter)> = None;

            while rdr.read_byte_record(&mut row)? {
                // Decide what file to put this in.
                let column = &row[key_col];
                let key = match self.flag_prefix_length {
                    // We exceed --prefix-length, so ignore the extra bytes.
                    Some(len) if len < column.len() => &column[0..len],
                    _ => column,
                };

                match current {
                    Some((ref k, _)) if k == key => {}
                    _ => {
                        let mut wtr = gen.writer(&self.arg_outdir, key)?;

                        if !rconfig.no_headers {
                            wtr.write_record(&headers)?;
                        }

                        current = Some((key.to_vec(), wtr));
                    }
                };

                let wtr = &mut current.as_mut().unwrap().1;

                if self.flag_drop {
                    wtr.write_record(&row.remove(key_col))?;
                } else {
                    wtr.write_byte_record(&row)?;
                }
            }
        } else {
            let mut writers: HashMap<Vec<u8>, BoxedWriter> = HashMap::new();

            while rdr.read_byte_record(&mut row)? {
                // Decide what file to put this in.
                let column = &row[key_col];
                let key = match self.flag_prefix_length {
                    // We exceed --prefix-length, so ignore the extra bytes.
                    Some(len) if len < column.len() => &column[0..len],
                    _ => column,
                };

                let mut entry = writers.entry(key.to_vec());
                let wtr = match entry {
                    Entry::Occupied(ref mut occupied) => occupied.get_mut(),
                    Entry::Vacant(vacant) => {
                        // We have a new key, so make a new writer.
                        let mut wtr = gen.writer(&self.arg_outdir, key)?;
                        if !rconfig.no_headers {
                            wtr.write_record(&headers)?;
                        }
                        vacant.insert(wtr)
                    }
                };

                if self.flag_drop {
                    wtr.write_record(&row.remove(key_col))?;
                } else {
                    wtr.write_byte_record(&row)?;
                }
            }
        }

        Ok(())
    }
}

type BoxedWriter = csv::Writer<Box<dyn io::Write + 'static>>;

/// Generates unique filenames based on CSV values.
struct WriterGenerator {
    template: FilenameTemplate,
    counter: usize,
    used: HashSet<String>,
    non_word_char: Regex,
}

impl WriterGenerator {
    fn new(template: FilenameTemplate) -> WriterGenerator {
        WriterGenerator {
            template,
            counter: 1,
            used: HashSet::new(),
            non_word_char: Regex::new(r"\W").unwrap(),
        }
    }

    /// Create a CSV writer for `key`.  Does not add headers.
    fn writer<P>(&mut self, path: P, key: &[u8]) -> io::Result<BoxedWriter>
    where
        P: AsRef<Path>,
    {
        let unique_value = self.unique_value(key);
        self.template.writer(path.as_ref(), &unique_value)
    }

    /// Generate a unique value for `key`, suitable for use in a
    /// "shell-safe" filename.  If you pass `key` twice, you'll get two
    /// different values.
    fn unique_value(&mut self, key: &[u8]) -> String {
        // Sanitize our key.
        let utf8 = String::from_utf8_lossy(key);
        let safe = self.non_word_char.replace_all(&utf8, "").into_owned();
        let base = if safe.is_empty() {
            "empty".to_owned()
        } else {
            safe
        };

        // Now check for collisions.
        if !self.used.contains(&base) {
            self.used.insert(base.clone());
            base
        } else {
            loop {
                let candidate = format!("{}_{}", &base, self.counter);
                self.counter = self.counter.checked_add(1).unwrap_or_else(|| {
                    // We'll run out of other things long before we ever
                    // reach this, but we'll check just for correctness and
                    // completeness.
                    panic!("Cannot generate unique value")
                });
                if !self.used.contains(&candidate) {
                    self.used.insert(candidate.clone());
                    return candidate;
                }
            }
        }
    }
}