static USAGE: &str = r#"
Splits the given CSV data into chunks. It has three modes: by size (rowcount),
by number of chunks and by kb-size.

See `partition` command for splitting by a column value.

When splitting by size, the CSV data is split into chunks of the given number of
rows. The last chunk may have fewer rows if the number of records is not evenly
divisible by the given rowcount.

When splitting by number of chunks, the CSV data is split into the given number of
chunks. The number of rows in each chunk is determined by the number of records in
the CSV data and the number of desired chunks. If the number of records is not evenly
divisible by the number of chunks, the last chunk will have fewer records.

When splitting by kb-size, the CSV data is split into chunks of the given size in kilobytes.
The number of rows in each chunk may vary, but the size of each chunk will not exceed the
desired size.

Uses multithreading to go faster if the CSV has an index when splitting by size or
by number of chunks. Splitting by kb-size is always done sequentially with a single thread.

The default is to split by size with a chunk size of 500.

The files are written to the directory given with the name '{start}.csv',
where {start} is the index of the first record of the chunk (starting at 0).

Examples:
    qsv split outdir --size 100 --filename chunk_{}.csv input.csv
    # This will create files with names like chunk_0.csv, chunk_100.csv, etc.
    # in the directory 'outdir', creating the directory if it does not exist.

    qsv split outdir/subdir -s 100 --filename chunk_{}.csv --pad 5 input.csv
    # This will create files with names like chunk_00000.csv, chunk_00100.csv, etc.
    # in the directory 'outdir/subdir', creating the directories if they do not exist.

    qsv split . -s 100 input.csv
    # This will create files like 0.csv, 100.csv, etc. in the current directory.

    qsv split outdir --kb-size 1000 input.csv
    # This will create files with names like 0.csv, 994.csv, etc. in the directory
    # 'outdir', creating the directory if it does not exist. Each file will be close
    # to 1000KB in size.

    cat in.csv | qsv split mysplitoutput -s 1000

    qsv split outdir --chunks 10 input.csv

    qsv split splitoutdir -c 10 -j 4 input.csv

    qsv split outdir -s 100 --filter "gzip $FILE" input.csv
    # This will create files with names like 0.csv, 100.csv, etc. in the directory
    # 'outdir', and then run the command "gzip" on each chunk.

    qsv split outdir --filter "powershell Compress-Archive -Path $FILE -Destination {}.zip" input.csv
    # WINDOWS: This will create files with names like 0.zip, 100.zip, etc. in the directory
    # 'outdir', and then run the command "Compress-Archive" on each chunk.

For more examples, see https://github.com/dathere/qsv/blob/master/tests/test_split.rs.

Usage:
    qsv split [options] (--size <arg> | --chunks <arg> | --kb-size <arg>) <outdir> [<input>]
    qsv split --help

split arguments:
    <outdir>              The directory where the output files will be written.
                          If it does not exist, it will be created.
    <input>               The CSV file to read. If not given, input is read from
                          STDIN.

split options:
    -s, --size <arg>       The number of records to write into each chunk.
                           [default: 500]
    -c, --chunks <arg>     The number of chunks to split the data into.
                           This option is mutually exclusive with --size.
                           The number of rows in each chunk is determined by
                           the number of records in the CSV data and the number
                           of desired chunks. If the number of records is not evenly
                           divisible by the number of chunks, the last chunk will
                           have fewer records.
    -k, --kb-size <arg>    The size of each chunk in kilobytes. The number of rows
                           in each chunk may vary, but the size of each chunk will
                           not exceed the desired size.
                           This option is mutually exclusive with --size and --chunks.

    -j, --jobs <arg>       The number of splitting jobs to run in parallel.
                           This only works when the given CSV data has
                           an index already created. Note that a file handle
                           is opened for each job.
                           When not set, the number of jobs is set to the
                           number of CPUs detected.
    --filename <filename>  A filename template to use when constructing
                           the names of the output files.  The string '{}'
                           will be replaced by the zero-based row number
                           of the first row in the chunk.
                           [default: {}.csv]
    --pad <arg>            The zero padding width that is used in the
                           generated filename.
                           [default: 0]

                            FILTER OPTIONS:
    --filter <command>      Run the specified command on each chunk after it is written.
                            The command should use the FILE environment variable
                            ($FILE on Linux/macOS, %FILE% on Windows), which is
                            set to the path of the output file for each chunk.
                            The string '{}' in the command will be replaced by the
                            zero-based row number of the first row in the chunk.
    --filter-cleanup        Cleanup the original output filename AFTER the filter command
                            is run successfully for EACH chunk. If the filter command is not
                            successful, the original filename is not removed.
                            Only valid when --filter is used.
    --filter-ignore-errors  Ignore errors when running the filter command.
                            Only valid when --filter is used.

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. (default: ,)
    -q, --quiet            Do not display an output summary to stderr.
"#;

use std::{fs, io, path::Path, process::Command};

use dunce;
use log::{debug, error};
use rayon::iter::{IntoParallelIterator, ParallelIterator};
use serde::Deserialize;

use crate::{
    CliResult,
    config::{Config, Delimiter},
    index::Indexed,
    util::{self, FilenameTemplate},
};

#[derive(Clone, Deserialize)]
struct Args {
    arg_input:                 Option<String>,
    arg_outdir:                String,
    flag_size:                 usize,
    flag_chunks:               Option<usize>,
    flag_kb_size:              Option<usize>,
    flag_jobs:                 Option<usize>,
    flag_filename:             FilenameTemplate,
    flag_pad:                  usize,
    flag_no_headers:           bool,
    flag_delimiter:            Option<Delimiter>,
    flag_quiet:                bool,
    flag_filter:               Option<String>,
    flag_filter_cleanup:       bool,
    flag_filter_ignore_errors: bool,
}

pub fn run(argv: &[&str]) -> CliResult<()> {
    let mut args: Args = util::get_args(USAGE, argv)?;
    if args.flag_size == 0 {
        return fail_incorrectusage_clierror!("--size must be greater than 0.");
    }

    // check if outdir is set correctly
    if Path::new(&args.arg_outdir).is_file() && args.arg_input.is_none() {
        return fail_incorrectusage_clierror!("<outdir> is not specified or is a file.");
    }

    fs::create_dir_all(&args.arg_outdir)?;

    // if no input file is provided, use stdin and save to a temp file
    if args.arg_input.is_none() {
        // Get or initialize temp directory that persists until program exit
        let temp_dir =
            crate::config::TEMP_FILE_DIR.get_or_init(|| tempfile::TempDir::new().unwrap().keep());

        // Create a temporary file with .csv extension to store stdin input
        let mut temp_file = tempfile::Builder::new()
            .suffix(".csv")
            .tempfile_in(temp_dir)?;
        io::copy(&mut io::stdin(), &mut temp_file)?;

        // Get path as string, unwrap is safe as temp files are always valid UTF-8
        let temp_path = temp_file.path().to_str().unwrap().to_string();

        // Keep temp file from being deleted when it goes out of scope
        // it will be deleted when the program exits when TEMP_FILE_DIR is deleted
        temp_file
            .keep()
            .map_err(|e| format!("Failed to keep temporary stdin file: {e}"))?;

        args.arg_input = Some(temp_path);
    }

    if let Some(kb_size) = args.flag_kb_size {
        args.split_by_kb_size(kb_size)
    } else {
        // we're splitting by rowcount or by number of chunks
        match args.rconfig().indexed()? {
            Some(idx) => args.parallel_split(&idx),
            None => args.sequential_split(),
        }
    }
}

impl Args {
    fn split_by_kb_size(&self, chunk_size: usize) -> CliResult<()> {
        let rconfig = self.rconfig();
        let mut rdr = rconfig.reader()?;
        let headers = rdr.byte_headers()?.clone();

        let header_byte_size = if self.flag_no_headers {
            0
        } else {
            let mut headerbuf_wtr = csv::WriterBuilder::new().from_writer(vec![]);
            headerbuf_wtr.write_byte_record(&headers)?;

            // safety: we know the inner vec is valid
            headerbuf_wtr.into_inner().unwrap().len()
        };

        let mut wtr = self.new_writer(&headers, 0, self.flag_pad)?;
        let mut i = 0;
        let mut num_chunks = 0;
        let mut chunk_start = 0; // Track the start index of current chunk
        let mut row = csv::ByteRecord::new();
        let chunk_size_bytes = chunk_size * 1024;
        let mut chunk_size_bytes_left = chunk_size_bytes - header_byte_size;

        let mut not_empty = rdr.read_byte_record(&mut row)?;
        let mut curr_size_bytes;
        let mut next_size_bytes;
        wtr.write_byte_record(&row)?;

        while not_empty {
            let mut buf_curr_wtr = csv::WriterBuilder::new().from_writer(vec![]);
            buf_curr_wtr.write_byte_record(&row)?;

            curr_size_bytes = buf_curr_wtr.into_inner().unwrap().len();

            not_empty = rdr.read_byte_record(&mut row)?;
            next_size_bytes = if not_empty {
                let mut buf_next_wtr = csv::WriterBuilder::new().from_writer(vec![]);
                buf_next_wtr.write_byte_record(&row)?;

                buf_next_wtr.into_inner().unwrap().len()
            } else {
                0
            };

            if curr_size_bytes + next_size_bytes >= chunk_size_bytes_left {
                wtr.flush()?;
                // Run filter command if specified
                if self.flag_filter.is_some() {
                    self.run_filter_command(chunk_start, self.flag_pad)?;
                }
                chunk_start = i; // Set start index for next chunk
                wtr = self.new_writer(&headers, i, self.flag_pad)?;
                chunk_size_bytes_left = chunk_size_bytes - header_byte_size;
                num_chunks += 1;
            }
            if next_size_bytes > 0 {
                wtr.write_byte_record(&row)?;
                chunk_size_bytes_left -= curr_size_bytes;
                i += 1;
            }
        }
        wtr.flush()?;
        // Run filter command for the last chunk if specified
        if self.flag_filter.is_some() {
            self.run_filter_command(chunk_start, self.flag_pad)?;
        }

        if !self.flag_quiet {
            eprintln!(
                "Wrote chunk/s to '{}'. Size/chunk: <= {}KB; Num chunks: {}",
                dunce::canonicalize(Path::new(&self.arg_outdir))?.display(),
                chunk_size,
                num_chunks + 1
            );
        }

        Ok(())
    }

    fn sequential_split(&self) -> CliResult<()> {
        let rconfig = self.rconfig();
        let mut rdr = rconfig.reader()?;
        let headers = rdr.byte_headers()?.clone();

        #[allow(clippy::cast_precision_loss)]
        let chunk_size = if let Some(flag_chunks) = self.flag_chunks {
            let count = util::count_rows(&rconfig)?;
            let chunk = flag_chunks;
            if chunk == 0 {
                return fail_incorrectusage_clierror!("--chunk must be greater than 0.");
            }
            (count as f64 / chunk as f64).ceil() as usize
        } else {
            self.flag_size
        };

        let mut wtr = self.new_writer(&headers, 0, self.flag_pad)?;
        let mut i = 0;
        let mut nchunks: usize = 0;
        let mut row = csv::ByteRecord::new();
        while rdr.read_byte_record(&mut row)? {
            if i > 0 && i % chunk_size == 0 {
                wtr.flush()?;
                // Run filter command if specified
                if self.flag_filter.is_some() {
                    self.run_filter_command(i - chunk_size, self.flag_pad)?;
                }
                nchunks += 1;
                wtr = self.new_writer(&headers, i, self.flag_pad)?;
            }
            wtr.write_byte_record(&row)?;
            i += 1;
        }
        wtr.flush()?;
        // Run filter command for the last chunk if specified
        if self.flag_filter.is_some() {
            // Calculate the start index for the last chunk
            let last_chunk_start = ((i - 1) / chunk_size) * chunk_size;
            self.run_filter_command(last_chunk_start, self.flag_pad)?;
        }

        if !self.flag_quiet {
            eprintln!(
                "Wrote {} chunk/s to '{}'. Rows/chunk: {} Num records: {}",
                nchunks + 1,
                dunce::canonicalize(Path::new(&self.arg_outdir))?.display(),
                chunk_size,
                i
            );
        }

        Ok(())
    }

    fn parallel_split(&self, idx: &Indexed<fs::File, fs::File>) -> CliResult<()> {
        let chunk_size;
        let idx_count = idx.count();

        #[allow(clippy::cast_precision_loss)]
        let nchunks = if let Some(flag_chunks) = self.flag_chunks {
            chunk_size = (idx_count as f64 / flag_chunks as f64).ceil() as usize;
            flag_chunks
        } else {
            chunk_size = self.flag_size;
            util::num_of_chunks(idx_count as usize, self.flag_size)
        };
        if nchunks == 1 {
            // there's only one chunk, we can just do a sequential split
            // which has less overhead and better error handling
            return self.sequential_split();
        }

        util::njobs(self.flag_jobs);

        // safety: we cannot use ? here because we're in a closure
        (0..nchunks).into_par_iter().for_each(|i| {
            let conf = self.rconfig();
            // safety: safe to unwrap because we know the file is indexed
            let mut idx = conf.indexed().unwrap().unwrap();
            // safety: the only way this can fail is if the file first row of the chunk
            // is not a valid CSV record, which is impossible because we're reading
            // from a file with a valid index
            let headers = idx.byte_headers().unwrap();

            let mut wtr = self
                // safety: the only way this can fail is if we cannot create a file
                .new_writer(headers, i * chunk_size, self.flag_pad)
                .unwrap();

            // safety: we know that there is more than one chunk, so we can safely
            // seek to the start of the chunk
            idx.seek((i * chunk_size) as u64).unwrap();
            let mut write_row;
            for row in idx.byte_records().take(chunk_size) {
                write_row = row.unwrap();
                wtr.write_byte_record(&write_row).unwrap();
            }
            // safety: safe to unwrap because we know the writer is a file
            // the only way this can fail is if we cannot write to the file
            wtr.flush().unwrap();

            // Run filter command if specified
            if self.flag_filter.is_some() {
                // We can't use ? here because we're in a closure
                if let Err(e) = self.run_filter_command(i * chunk_size, self.flag_pad) {
                    eprintln!("Error running filter command: {e}");
                }
            }
        });

        if !self.flag_quiet {
            eprintln!(
                "Wrote {} chunk/s to '{}'. Rows/chunk: {} Num records: {}",
                nchunks,
                dunce::canonicalize(Path::new(&self.arg_outdir))?.display(),
                chunk_size,
                idx_count
            );
        }

        Ok(())
    }

    fn new_writer(
        &self,
        headers: &csv::ByteRecord,
        start: usize,
        width: usize,
    ) -> CliResult<csv::Writer<Box<dyn io::Write + 'static>>> {
        let dir = Path::new(&self.arg_outdir);
        let path = dir.join(self.flag_filename.filename(&format!("{start:0>width$}")));
        let spath = Some(path.display().to_string());
        let mut wtr = Config::new(spath.as_ref()).writer()?;
        if !self.rconfig().no_headers {
            wtr.write_record(headers)?;
        }
        Ok(wtr)
    }

    fn run_filter_command(&self, start: usize, width: usize) -> CliResult<()> {
        if let Some(ref filter_cmd) = self.flag_filter {
            let outdir = Path::new(&self.arg_outdir).canonicalize()?;
            let filename = self.flag_filename.filename(&format!("{start:0>width$}"));
            let file_path = outdir.join(&filename);

            debug!(
                "Processing filter command for file: {}",
                file_path.display()
            );

            // Check if the file exists before running the filter command
            if !file_path.exists() {
                wwarn!(
                    "File {} does not exist, skipping filter command",
                    file_path.display()
                );
                return Ok(());
            }

            // Replace {} in the command with the start index
            let cmd = filter_cmd.replace("{}", &format!("{start:0>width$}"));
            debug!("Filter command template: {cmd}");

            // Use dunce to get a canonicalized path that works well on Windows
            // on non-Windows systems, its equivalent to std::fs::canonicalize
            let canonical_path = match dunce::canonicalize(&file_path) {
                Ok(path) => path,
                Err(e) => {
                    return fail_clierror!(
                        "Failed to canonicalize path {}: {e}",
                        file_path.display()
                    );
                },
            };

            let path_str = canonical_path.to_string_lossy().to_string();
            debug!("Canonicalized path: {path_str}");

            let canonical_outdir = match dunce::canonicalize(&outdir) {
                Ok(path) => path,
                Err(e) => {
                    return fail_clierror!(
                        "Failed to canonicalize outdir path {}: {e}",
                        outdir.display()
                    );
                },
            };

            // Execute the command using the appropriate shell based on platform
            let status = if cfg!(windows) {
                debug!("Running Windows command: cmd /C {cmd}");
                let cmd_vec = cmd.split(' ').collect::<Vec<&str>>();
                Command::new("cmd")
                    .arg("/C")
                    .args(&cmd_vec)
                    .current_dir(&canonical_outdir)
                    .env("FILE", path_str)
                    .status()
            } else {
                debug!("Running Unix command: sh -c {cmd}");
                Command::new("sh")
                    .arg("-c")
                    .arg(&cmd)
                    .current_dir(&canonical_outdir)
                    .env("FILE", path_str)
                    .status()
            };

            let status = match status {
                Ok(status) => status,
                Err(e) => {
                    return fail_clierror!("Failed to execute filter command: {e}");
                },
            };

            if !status.success() && !self.flag_filter_ignore_errors {
                return fail_clierror!(
                    "Filter command failed with exit code: {}",
                    status.code().unwrap_or(-1)
                );
            }

            // Cleanup the original output filename if the filter command was successful
            if self.flag_filter_cleanup {
                debug!("Cleaning up original file: {}", file_path.display());
                if let Err(e) = fs::remove_file(&file_path) {
                    wwarn!("Failed to remove file {}: {e}", file_path.display());
                }
            }
        }
        Ok(())
    }

    fn rconfig(&self) -> Config {
        Config::new(self.arg_input.as_ref())
            .delimiter(self.flag_delimiter)
            .no_headers(self.flag_no_headers)
    }
}
