sniff.rs

static USAGE: &str = r#"
Quickly sniff the first n rows and infer CSV metadata (delimiter, header row, number of
preamble rows, quote character, flexible, is_utf8, average record length, number of records,
content length and estimated number of records if sniffing a URL, file size, number of fields,
field names & data types) using a Viterbi algorithm.
(https://en.wikipedia.org/wiki/Viterbi_algorithm)

`sniff` is also a general mime type detector, returning the detected mime type, file size and
last modified date. If --no-infer is enabled, it doesn't even bother to infer the CSV's schema.
This makes it especially useful for accelerated CKAN harvesting and for checking stale/broken
resource URLs.

NOTE: This command "sniffs" a CSV's schema by sampling the first n rows (default: 1000)
of a file. Its inferences are sometimes wrong if the the file is too small to infer a pattern
or if the CSV has unusual formatting - with atypical delimiters, quotes, etc.

In such cases, selectively use the --sample, --delimiter and --quote options to improve
the accuracy of the sniffed schema.

If you want more robust, guaranteed schemata, use the "schema" or "stats" commands
instead as they scan the entire file. However, they only work on local files and well-formed
CSVs, unlike `sniff` which can work with remote files, various CSV dialects and is very fast
regardless of file size.

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

Usage:
    qsv sniff [options] [<input>]
    qsv sniff --help

sniff arguments:
    <input>                  The file to sniff. This can be a local file, stdin or a
                             URL (http and https schemes supported).

                             Note that when input is a URL and is a CSV candidate,
                             sniff will automatically download a sample to a temporary
                             file and sniff it.

                             If the file sample is not a CSV, sniff will return as an error
                             - the detected mime type, file size & last modified date.

                             When --no-infer is enabled, sniff will not bother to infer the
                             CSV schema and just work as a general mime type detector -
                             returning the detected mime type, file size and last modified date.

                             When sniffing a local file, it will scan the file to detect the mime type.
                             When sniffing a URL, it will only download the first chunk of the file if 
                             the --quick option is enabled, otherwise it will download the entire file.
                             
sniff options:
    --sample <size>          First n rows to sample to sniff out the metadata.
                             When sample size is between 0 and 1 exclusive, 
                             it is treated as a percentage of the CSV to sample
                             (e.g. 0.20 is 20 percent).
                             When it is zero, the entire file will be sampled.
                             When the input is a URL, the sample size dictates
                             how many lines to sample without having to
                             download the entire file. Ignored when --no-infer is enabled.
                             [default: 1000]
    --prefer-dmy             Prefer to parse dates in dmy format. Otherwise, use mdy format.
                             Ignored when --no-infer is enabled.
    -d, --delimiter <arg>    The delimiter for reading CSV data.
                             Specify this when the delimiter is known beforehand,
                             as the delimiter inferencing algorithm can sometimes fail.
                             Must be a single ascii character.
    -q, --quote <arg>        The quote character for reading CSV data.
                             Specify this when the quote character is known beforehand,
                             as the quote char inferencing algorithm can sometimes fail.
                             Must be a single ascii character - typically, double quote ("),
                             single quote ('), or backtick (`).
    --json                   Return results in JSON format.
    --pretty-json            Return results in pretty JSON format.
    --save-urlsample <file>  Save the URL sample to a file.
                             Valid only when input is a URL.
    --timeout <secs>         Timeout when sniffing URLs in seconds.
                             [default: 30]
    --user-agent <agent>     Specify custom user agent to use when sniffing a CSV on a URL.
                             It supports the following variables - $QSV_VERSION, $QSV_TARGET,
                             $QSV_BIN_NAME and $QSV_KIND. Try to follow the syntax here -
                             https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/User-Agent
    --stats-types            Use the same data type names as `stats`.
                             (Unsigned, Signed => Integer, Text => String, everything else the same)
    --no-infer               Do not infer the schema. Only return the file's mime type, size and
                             last modified date. Use this to use sniff as a general mime type detector.
    --quick                  When sniffing a non-CSV remote file, only download the first chunk of the file
                             before attempting to detect the mime type. This is faster but less accurate as
                             some mime types cannot be detected with just the first downloaded chunk.
    --harvest-mode           This is a convenience flag when using sniff in CKAN harvesters. 
                             It is equivalent to --quick --timeout 10 --stats-types --json
                             and --user-agent "CKAN-harvest/$QSV_VERSION ($QSV_TARGET; $QSV_BIN_NAME)"

Common options:
    -h, --help               Display this message
    -p, --progressbar        Show progress bars. Only valid for URL input.
"#;

use std::{
    cmp::min,
    fmt, fs,
    io::{copy, Seek, SeekFrom, Write},
    path::PathBuf,
    time::{Duration, SystemTime},
};

use bytes::Bytes;
use file_format::FileFormat;
use futures::executor::block_on;
use futures_util::StreamExt;
#[cfg(any(feature = "feature_capable", feature = "lite"))]
use indicatif::{HumanBytes, HumanCount, ProgressBar, ProgressDrawTarget, ProgressStyle};
use qsv_sniffer::{DatePreference, SampleSize, Sniffer};
use reqwest::Client;
use serde::{Deserialize, Serialize};
use serde_json::{json, Value};
use tabwriter::TabWriter;
use tempfile::NamedTempFile;
use thousands::Separable;
use url::Url;

use crate::{
    config::{Config, Delimiter},
    util, CliResult,
};

#[derive(Deserialize)]
struct Args {
    arg_input:           Option<String>,
    flag_sample:         f64,
    flag_prefer_dmy:     bool,
    flag_json:           bool,
    flag_save_urlsample: Option<String>,
    flag_pretty_json:    bool,
    flag_delimiter:      Option<Delimiter>,
    flag_quote:          Option<char>,
    flag_progressbar:    bool,
    flag_timeout:        u16,
    flag_user_agent:     Option<String>,
    flag_stats_types:    bool,
    flag_no_infer:       bool,
    flag_quick:          bool,
    flag_harvest_mode:   bool,
}

#[derive(Serialize, Deserialize, Default, Debug)]
struct SniffStruct {
    path:            String,
    sniff_timestamp: String,
    last_modified:   String,
    delimiter_char:  char,
    header_row:      bool,
    preamble_rows:   usize,
    quote_char:      String,
    flexible:        bool,
    is_utf8:         bool,
    detected_mime:   String,
    retrieved_size:  usize,
    file_size:       usize,
    sampled_records: usize,
    estimated:       bool,
    num_records:     usize,
    avg_record_len:  usize,
    num_fields:      usize,
    stats_types:     bool,
    fields:          Vec<String>,
    types:           Vec<String>,
}
impl fmt::Display for SniffStruct {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        writeln!(
            f,
            "Path: {}",
            // when sniffing a snappy compressed file, it is first decompressed
            // to a temporary file. The original file name is stored in the
            // temporary file name, so we extract the original file name
            if self.path.ends_with("__qsv_temp_decompressed") {
                // use a regular expression to extract the original file name
                // the original file name is between "qsv__" and "__qsv_temp_decompressed"
                let re =
                    regex::Regex::new(r"qsv__(?P<filename>.*)__qsv_temp_decompressed").unwrap();
                let caps = re.captures(&self.path).unwrap();
                let filename = caps.name("filename").unwrap().as_str();
                filename.to_string()
            } else {
                self.path.clone()
            }
        )?;
        writeln!(f, "Sniff Timestamp: {}", self.sniff_timestamp)?;
        writeln!(f, "Last Modified: {}", self.last_modified)?;
        writeln!(
            f,
            "Delimiter: {}",
            if self.delimiter_char == '\t' {
                "tab".to_string()
            } else {
                self.delimiter_char.to_string()
            }
        )?;
        writeln!(f, "Header Row: {}", self.header_row)?;
        writeln!(
            f,
            "Preamble Rows: {}",
            self.preamble_rows.separate_with_commas()
        )?;
        writeln!(f, "Quote Char: {}", self.quote_char)?;
        writeln!(f, "Flexible: {}", self.flexible)?;
        writeln!(f, "Is UTF8: {}", self.is_utf8)?;
        writeln!(f, "Detected Mime Type: {}", self.detected_mime)?;
        writeln!(
            f,
            "Retrieved Size (bytes): {}",
            self.retrieved_size.separate_with_commas()
        )?;
        writeln!(
            f,
            "File Size (bytes): {}",
            self.file_size.separate_with_commas()
        )?;
        writeln!(
            f,
            "Sampled Records: {}",
            self.sampled_records.separate_with_commas()
        )?;
        writeln!(f, "Estimated: {}", self.estimated)?;
        writeln!(
            f,
            "Num Records: {}",
            self.num_records.separate_with_commas()
        )?;
        writeln!(
            f,
            "Avg Record Len (bytes): {}",
            self.avg_record_len.separate_with_commas()
        )?;
        writeln!(f, "Num Fields: {}", self.num_fields.separate_with_commas())?;
        writeln!(f, "Stats Types: {}", self.stats_types)?;
        writeln!(f, "Fields:")?;

        let mut tabwtr = TabWriter::new(vec![]);

        for (i, ty) in self.types.iter().enumerate() {
            let data_type = if self.stats_types {
                match ty.as_str() {
                    "Unsigned" | "Signed" => "Integer",
                    "Text" => "String",
                    _ => ty,
                }
            } else {
                ty
            };

            writeln!(
                &mut tabwtr,
                "\t{i}:\t{data_type}\t{}",
                self.fields.get(i).unwrap_or(&String::new())
            )
            .unwrap_or_default();
        }
        tabwtr.flush().unwrap();

        let tabbed_field_list = String::from_utf8(tabwtr.into_inner().unwrap()).unwrap();
        writeln!(f, "{tabbed_field_list}")?;

        Ok(())
    }
}

#[derive(Debug, Clone)]
struct SniffFileStruct {
    display_path:       String,
    file_to_sniff:      String,
    detected_mime:      String,
    tempfile_flag:      bool,
    retrieved_size:     usize,
    file_size:          usize,
    last_modified:      String,
    downloaded_records: usize,
}

const fn rowcount(
    metadata: &qsv_sniffer::metadata::Metadata,
    sniff_file_info: &SniffFileStruct,
    count: usize,
) -> (usize, bool) {
    let mut estimated = false;
    let rowcount = if count == usize::MAX {
        // if the count == usize::MAX, it's a sentinel value for "Unknown" as the server
        // didn't provide a Content-Length header, so we estimate the rowcount by
        // dividing the file_size by avg_rec_len
        estimated = true;
        sniff_file_info.file_size / metadata.avg_record_len
    } else {
        count
    };

    let has_header_row = metadata.dialect.header.has_header_row;
    let num_preamble_rows = metadata.dialect.header.num_preamble_rows;
    let mut final_rowcount = rowcount;

    if !has_header_row {
        final_rowcount += 1;
    }

    final_rowcount -= num_preamble_rows;
    (final_rowcount, estimated)
}

async fn get_file_to_sniff(args: &Args, tmpdir: &tempfile::TempDir) -> CliResult<SniffFileStruct> {
    if let Some(uri) = args.arg_input.clone() {
        match uri {
            // its a URL, download sample to temp file
            url if Url::parse(&url).is_ok() && url.starts_with("http") => {
                let snappy_flag = url.to_lowercase().ends_with(".sz");

                // setup the reqwest client
                let client = match Client::builder()
                    .user_agent(util::set_user_agent(args.flag_user_agent.clone())?)
                    .brotli(true)
                    .gzip(true)
                    .deflate(true)
                    .use_rustls_tls()
                    .http2_adaptive_window(true)
                    .build()
                {
                    Ok(c) => c,
                    Err(e) => {
                        return fail_clierror!("Cannot build reqwest client: {e}.");
                    }
                };

                let res = client
                    .get(url.clone())
                    .timeout(Duration::from_secs(
                        util::timeout_secs(args.flag_timeout).unwrap_or(30),
                    ))
                    .send()
                    .await
                    .map_err(|e| format!("Download failed: {e}"))?;

                let last_modified = match res.headers().get("Last-Modified") {
                    Some(lm) => match lm.to_str() {
                        Ok(s) => {
                            // convert Last-Modified RFC2822 to RFC3339 format
                            let dt = chrono::DateTime::parse_from_rfc2822(s).unwrap();
                            dt.to_rfc3339_opts(chrono::SecondsFormat::Secs, false)
                        }
                        // server did not return Last-Modified header
                        Err(_) => String::from("Unknown"),
                    },
                    None => String::from("Unknown"),
                };

                let total_size = match res.content_length() {
                    Some(l) => l as usize,
                    None => {
                        // if we can't get the content length, just set it to a large value
                        // so we just end up downloading the entire file
                        usize::MAX
                    }
                };

                #[allow(clippy::cast_precision_loss)]
                let lines_sample_size = if snappy_flag {
                    // if it's a snappy compressed file, we need to download the entire file
                    // to sniff it
                    usize::MAX
                } else if args.flag_sample > 1.0 {
                    args.flag_sample.round() as usize
                } else if args.flag_sample.abs() < f64::EPSILON {
                    // sample size is zero, so we want to download the entire file
                    usize::MAX
                } else {
                    // sample size is a percentage, download percentage number of lines
                    // from the file. Since we don't know how wide the lines are, we
                    // just download a percentage of the bytes, assuming the lines are
                    // 100 characters wide as a rough estimate.
                    ((total_size / 100_usize) as f64 * args.flag_sample) as usize
                };

                // prep progress bar
                #[cfg(any(feature = "feature_capable", feature = "lite"))]
                let show_progress =
                    args.flag_progressbar || util::get_envvar_flag("QSV_PROGRESSBAR");

                #[cfg(any(feature = "feature_capable", feature = "lite"))]
                let progress = ProgressBar::with_draw_target(
                    Some(total_size.try_into().unwrap_or(u64::MAX)),
                    ProgressDrawTarget::stderr_with_hz(5),
                );
                #[cfg(any(feature = "feature_capable", feature = "lite"))]
                if show_progress {
                    progress.set_style(
                        ProgressStyle::default_bar()
                            .template(
                                "{msg}\n{spinner:.green} [{elapsed_precise}] \
                                 [{wide_bar:.white/blue}] {bytes}/{total_bytes} ({bytes_per_sec}, \
                                 {eta})",
                            )
                            .unwrap(),
                    );
                    if lines_sample_size == usize::MAX {
                        progress.set_message(format!(
                            "Downloading {}...",
                            HumanBytes(total_size as u64)
                        ));
                    } else {
                        progress.set_message(format!(
                            "Downloading {} samples...",
                            HumanCount(lines_sample_size as u64)
                        ));
                    }
                } else {
                    progress.set_draw_target(ProgressDrawTarget::hidden());
                }

                let mut file = NamedTempFile::new()?;
                let mut downloaded = 0_usize;
                let mut stream = res.bytes_stream();
                let mut downloaded_lines = 0_usize;
                #[allow(unused_assignments)]
                let mut chunk = Bytes::new(); // amortize the allocation
                let mut firstchunk = Bytes::new();

                // download chunks until we have the desired sample size
                while let Some(item) = stream.next().await {
                    chunk = item.map_err(|_| "Error while downloading file")?;

                    file.write_all(&chunk)
                        .map_err(|_| "Error while writing to file")?;
                    let chunk_len = chunk.len();

                    if downloaded == 0 && !snappy_flag && args.flag_quick {
                        let mime = FileFormat::from_bytes(&chunk).media_type().to_string();
                        log::debug!("scanned first {chunk_len} bytes - detected mime: {mime}");
                        if !mime.starts_with("text/") && mime != "application/csv" {
                            downloaded = chunk_len;
                            firstchunk = chunk.clone();
                            break;
                        }
                    }

                    downloaded = min(downloaded + chunk_len, total_size);

                    #[cfg(any(feature = "feature_capable", feature = "lite"))]
                    if show_progress {
                        progress.inc(chunk_len as u64);
                    }

                    // check if we're downloading the entire file
                    if lines_sample_size != usize::MAX {
                        // we're not downloading the entire file, so we need to
                        // scan chunk for newlines
                        let num_lines = chunk.into_iter().filter(|&x| x == b'\n').count();
                        // and keep track of the number of lines downloaded which is ~= sample_size
                        downloaded_lines += num_lines;
                        // we downloaded enough samples, stop downloading
                        if downloaded_lines > lines_sample_size {
                            downloaded_lines -= 1; // subtract 1 because we don't want to count the header row
                            break;
                        }
                    }
                }
                drop(client);
                file.flush()?;

                #[cfg(any(feature = "feature_capable", feature = "lite"))]
                if show_progress {
                    if snappy_flag {
                        progress.finish_with_message(format!(
                            "Downloaded {}.",
                            HumanBytes(downloaded as u64)
                        ));
                    } else {
                        progress.finish_with_message(format!(
                            "Downloaded {} samples.",
                            HumanCount(downloaded_lines as u64)
                        ));
                    }
                }

                let wtr_file_path;
                let mut csv_candidate = true;
                let mut detected_mime = String::new();

                if !args.flag_quick {
                    detected_mime = FileFormat::from_file(file.path())?.media_type().to_string();
                    csv_candidate =
                        detected_mime.starts_with("text/") || detected_mime == "application/csv";
                }

                // create a temporary file to write the download file to
                let wtr_file = NamedTempFile::new()?;

                // keep the temporary file around so we can sniff it later
                // we'll delete it when we're done
                let (mut tmp_file, path) =
                    wtr_file.keep().map_err(|_| "Cannot keep temporary file")?;

                let mut downloaded_records = 0_usize;

                if snappy_flag {
                    // we downloaded a snappy compressed file, we need to decompress it
                    // before we can sniff it
                    wtr_file_path =
                        util::decompress_snappy_file(&file.path().to_path_buf(), tmpdir)?;
                } else if args.flag_quick && !csv_candidate {
                    // when --quick is enabled, we short-circuit downloading by checking
                    // the file type from the first chunk. If the file is not a CSV,
                    // we just write the first chunk to a file and return
                    wtr_file_path = path.display().to_string();
                    tmp_file.write_all(&firstchunk)?;
                    tmp_file.flush()?;
                } else if csv_candidate {
                    // we downloaded a non-snappy file and it might be a CSV file.
                    // Rewrite it so we only have the exact sample size and truncate potentially
                    // incomplete lines. We do this coz we streamed the download and the downloaded
                    // file may be more than the sample size, and the final line may be incomplete.
                    wtr_file_path = path.display().to_string();
                    let mut wtr = Config::new(&Some(wtr_file_path.clone()))
                        .no_headers(false)
                        .flexible(true)
                        .quote_style(csv::QuoteStyle::NonNumeric)
                        .writer()?;

                    let retrieved_name = file.path().to_str().unwrap().to_string();
                    let config = Config::new(&Some(retrieved_name))
                        .delimiter(args.flag_delimiter)
                        // we say no_headers so we can just copy the downloaded file over
                        // including headers, to the exact sanple size file
                        .no_headers(true)
                        .flexible(true);

                    let mut rdr = config.reader()?;

                    // amortize allocation
                    #[allow(unused_assignments)]
                    let mut record = csv::ByteRecord::with_capacity(100, 20);

                    let header_row = rdr.byte_headers()?;
                    wtr.write_byte_record(header_row)?;
                    rdr.byte_records().next();

                    for rec in rdr.byte_records() {
                        record = rec?;
                        if downloaded_records >= lines_sample_size {
                            break;
                        }
                        downloaded_records += 1;
                        wtr.write_byte_record(&record)?;
                    }
                    wtr.flush()?;
                } else {
                    // we downloaded a non-snappy file and its not a CSV file just copy it over
                    wtr_file_path = path.display().to_string();
                    file.seek(SeekFrom::Start(0))?;
                    copy(&mut file, &mut tmp_file)?;
                    log::debug!("Not a CSV file, just copy it over");
                }

                Ok(SniffFileStruct {
                    display_path: url,
                    file_to_sniff: wtr_file_path,
                    detected_mime,
                    tempfile_flag: true,
                    retrieved_size: downloaded,
                    file_size: if total_size == usize::MAX {
                        // the server didn't give us content length
                        // so send usize::MAX to indicate that we don't know the file size
                        usize::MAX
                    } else {
                        total_size
                    },
                    last_modified,
                    downloaded_records,
                })
            }
            // its a file. If its a snappy file, decompress it first
            // aftwerwards, check if its one of the supported file types
            // finally, check if its a utf8 file
            path => {
                let mut path = path;

                let mut pathbuf = PathBuf::from(path.clone());
                let file_ext = pathbuf.extension();
                match file_ext {
                    Some(ext) => {
                        let mut lower_ext =
                            ext.to_str().unwrap().to_lowercase().as_str().to_owned();
                        if lower_ext == "sz" {
                            path = util::decompress_snappy_file(&pathbuf, tmpdir)?;
                            pathbuf = PathBuf::from(path.clone());
                            lower_ext = pathbuf
                                .extension()
                                .unwrap()
                                .to_os_string()
                                .into_string()
                                .unwrap();
                            log::info!("Decompressed {lower_ext} file to {path}");
                        }
                    }
                    None => {
                        log::warn!("File extension not found");
                    }
                }

                let metadata = fs::metadata(&path)
                    .map_err(|_| format!("Cannot get metadata for file '{path}'"))?;

                let file_size = metadata.len() as usize;
                let last_modified = match metadata.modified() {
                    Ok(time) => {
                        let timestamp = time
                            .duration_since(SystemTime::UNIX_EPOCH)
                            .unwrap()
                            .as_secs();
                        let naive = chrono::NaiveDateTime::from_timestamp_opt(timestamp as i64, 0)
                            .unwrap_or_default();
                        let datetime =
                            chrono::DateTime::<chrono::Utc>::from_utc(naive, chrono::Utc);
                        // format the datetime to RFC3339
                        format!("{datetime}", datetime = datetime.format("%+"))
                    }
                    Err(_) => "N/A".to_string(),
                };

                let canonical_path = fs::canonicalize(&path)?.to_str().unwrap().to_string();

                Ok(SniffFileStruct {
                    display_path: canonical_path,
                    file_to_sniff: path,
                    detected_mime: String::new(),
                    tempfile_flag: false,
                    retrieved_size: file_size,
                    file_size,
                    last_modified,
                    downloaded_records: 0,
                })
            }
        }
    } else {
        // read from stdin and write to a temp file
        let mut stdin_file = NamedTempFile::new()?;
        let stdin = std::io::stdin();
        let mut stdin_handle = stdin.lock();
        std::io::copy(&mut stdin_handle, &mut stdin_file)?;
        drop(stdin_handle);
        let (file, path) = stdin_file
            .keep()
            .map_err(|_| "Cannot keep temporary file")?;

        if !util::isutf8_file(&path)? {
            return fail_clierror!("stdin input is not UTF8-encoded");
        }

        let metadata = file
            .metadata()
            .map_err(|_| "Cannot get metadata for stdin file")?;

        let file_size = metadata.len() as usize;
        // set last_modified to now in RFC3339 format
        let last_modified = chrono::Utc::now().format("%+").to_string();
        let path_string = path
            .into_os_string()
            .into_string()
            .unwrap_or_else(|_| "???".to_string());

        Ok(SniffFileStruct {
            display_path: "stdin".to_string(),
            file_to_sniff: path_string,
            detected_mime: String::new(),
            tempfile_flag: true,
            retrieved_size: file_size,
            file_size,
            last_modified,
            downloaded_records: 0,
        })
    }
}

fn cleanup_tempfile(
    tempfile_flag: bool,
    tempfile: String,
) -> Result<(), crate::clitypes::CliError> {
    if tempfile_flag {
        fs::remove_file(tempfile)?;
    }
    Ok(())
}

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

    let rt = tokio::runtime::Runtime::new().unwrap();
    rt.block_on(sniff_main(args))?;

    Ok(())
}

#[allow(clippy::unused_async)] // false positive lint
async fn sniff_main(mut args: Args) -> CliResult<()> {
    if args.flag_harvest_mode {
        args.flag_quick = true;
        args.flag_timeout = 10;
        args.flag_stats_types = true;
        args.flag_json = true;
        args.flag_user_agent =
            Some("CKAN-harvest/$QSV_VERSION ($QSV_TARGET; $QSV_BIN_NAME)".to_string());
    }

    let mut sample_size = args.flag_sample;
    if sample_size < 0.0 {
        if args.flag_json || args.flag_pretty_json {
            let json_result = json!({
                "errors": [{
                    "title": "sniff error",
                    "detail": "Sample size must be greater than or equal to zero."
                }]
            });
            return fail_clierror!("{json_result}");
        }
        return fail_clierror!("Sample size must be greater than or equal to zero.");
    }

    let sniffed_ts = chrono::Utc::now().to_rfc3339();
    let tmpdir = tempfile::tempdir()?;

    let future = get_file_to_sniff(&args, &tmpdir);
    let sfile_info = block_on(future)?;
    let tempfile_to_delete = sfile_info.file_to_sniff.clone();
    #[allow(unused_assignments)]
    let mut file_type = String::new();

    // if we have a detected mime type earlier, we can skip the sniffing
    // unless it was a snappy file and --no-infer is disabled,
    // as we need to sniff the uncompressed file
    if sfile_info.detected_mime.is_empty()
        || sfile_info.detected_mime == "application/x-snappy-framed" && !args.flag_no_infer
    {
        file_type = FileFormat::from_file(&sfile_info.file_to_sniff)?
            .media_type()
            .to_string();
    } else {
        file_type = sfile_info.detected_mime.clone();
    }

    // we also accept text/* files, as sniff may still be able to suss out
    // if the file is a CSV, even if its not using a CSV extension
    // we can also be here if the user has specified --no-infer
    if (file_type != "application/csv" && !file_type.starts_with("text/")) || args.flag_no_infer {
        cleanup_tempfile(sfile_info.tempfile_flag, tempfile_to_delete)?;

        let size = if sfile_info.file_size == usize::MAX {
            "Unknown".to_string()
        } else {
            sfile_info.file_size.to_string()
        };
        let last_modified = sfile_info.last_modified;

        if args.flag_json || args.flag_pretty_json {
            if args.flag_no_infer {
                let json_result = json!({
                    "title": "sniff mime type",
                    "meta": {
                        "detected_mime_type": file_type,
                        "size": size,
                        "last_modified": last_modified,
                    }
                });
                if args.flag_pretty_json {
                    woutinfo!("{}", serde_json::to_string_pretty(&json_result).unwrap());
                    return Ok(());
                }
                woutinfo!("{json_result}");
                return Ok(());
            }
            let json_result = json!({
                "errors": [{
                    "title": "sniff error",
                    "detail": format!("File is not a CSV file. Detected mime type: {file_type}"),
                    "meta": {
                        "detected_mime_type": file_type,
                        "size": size,
                        "last_modified": last_modified,
                    }
                }]
            });
            if args.flag_pretty_json {
                return fail_clierror!("{}", serde_json::to_string_pretty(&json_result).unwrap());
            }
            return fail_clierror!("{json_result}");
        }
        if args.flag_no_infer {
            woutinfo!(
                "Detected mime type: {file_type}, size: {size}, last modified: {last_modified}"
            );
            return Ok(());
        }
        return fail_clierror!(
            "File is not a CSV file. Detected mime type: {file_type}, size: {size}, last \
             modified: {last_modified}"
        );
    }

    let conf = Config::new(&Some(sfile_info.file_to_sniff.clone()))
        .flexible(true)
        .delimiter(args.flag_delimiter);
    let n_rows = if sfile_info.downloaded_records == 0 {
        //if we have the whole file and not just a sample, we can count the number of rows
        match util::count_rows(&conf) {
            Ok(n) => n as usize,
            Err(e) => {
                cleanup_tempfile(sfile_info.tempfile_flag, tempfile_to_delete)?;

                if args.flag_json || args.flag_pretty_json {
                    let json_result = json!({
                        "errors": [{
                            "title": "count rows error",
                            "detail": e.to_string()
                        }]
                    });
                    return fail_clierror!("{json_result}");
                }
                return fail_clierror!("{}", e);
            }
        }
    } else {
        // usize::MAX is a sentinel value to let us
        // know that we need to estimate the number of records
        // since we only downloaded a sample, not the entire file
        usize::MAX
    };

    // its an empty file, exit with an error
    if n_rows == 0 {
        cleanup_tempfile(sfile_info.tempfile_flag, tempfile_to_delete)?;

        if args.flag_json || args.flag_pretty_json {
            let json_result = json!({
                "errors": [{
                    "title": "sniff error",
                    "detail": "Empty file"
                }]
            });
            return fail_clierror!("{json_result}");
        }
        return fail_clierror!("Empty file");
    }

    let mut sample_all = false;
    // its a percentage, get the actual sample size
    #[allow(clippy::cast_precision_loss)]
    if sample_size < 1.0 {
        sample_size *= n_rows as f64;
    } else if (sample_size).abs() < f64::EPSILON {
        // its zero, the epsilon bit is because comparing a float
        // is really not precise - see https://floating-point-gui.de/errors/comparison/
        sample_all = true;
    }

    // for a local file and stdin, set sampled_records to the sample size
    // for a remote file, set sampled_records to the number of rows downloaded
    let sampled_records = if sfile_info.downloaded_records == 0 {
        sample_size as usize
    } else {
        sample_all = true;
        sfile_info.downloaded_records
    };

    let rdr = conf.reader_file()?;

    let dt_preference = if args.flag_prefer_dmy || conf.get_dmy_preference() {
        DatePreference::DmyFormat
    } else {
        DatePreference::MdyFormat
    };

    if let Some(save_urlsample) = args.flag_save_urlsample {
        fs::copy(sfile_info.file_to_sniff.clone(), save_urlsample)?;
    }

    let quote_char = match args.flag_quote {
        Some(quote_char) => {
            qsv_sniffer::metadata::Quote::Some(*quote_char.to_string().as_bytes().first().unwrap())
        }
        _ => qsv_sniffer::metadata::Quote::None,
    };

    let sniff_results = if sample_all {
        log::info!("Sniffing ALL rows...");
        if let Some(delimiter) = args.flag_delimiter {
            Sniffer::new()
                .sample_size(SampleSize::All)
                .date_preference(dt_preference)
                .delimiter(delimiter.as_byte())
                .quote(quote_char)
                .sniff_reader(rdr.into_inner())
        } else {
            Sniffer::new()
                .sample_size(SampleSize::All)
                .date_preference(dt_preference)
                .sniff_reader(rdr.into_inner())
        }
    } else {
        let mut sniff_size = sample_size as usize;
        // sample_size is at least 20
        if sniff_size < 20 {
            sniff_size = 20;
        }
        log::info!("Sniffing {sniff_size} rows...");
        if let Some(delimiter) = args.flag_delimiter {
            Sniffer::new()
                .sample_size(SampleSize::Records(sniff_size))
                .date_preference(dt_preference)
                .delimiter(delimiter.as_byte())
                .quote(quote_char)
                .sniff_reader(rdr.into_inner())
        } else {
            Sniffer::new()
                .sample_size(SampleSize::Records(sniff_size))
                .date_preference(dt_preference)
                .sniff_reader(rdr.into_inner())
        }
    };

    let mut processed_results = SniffStruct::default();
    let mut sniff_error: Option<String> = None;

    match sniff_results {
        Ok(metadata) => {
            let (num_records, estimated) = rowcount(&metadata, &sfile_info, n_rows);

            let sniffedfields = metadata
                .fields
                .iter()
                .map(std::string::ToString::to_string)
                .collect();
            let sniffedtypes = metadata
                .types
                .iter()
                .map(std::string::ToString::to_string)
                .collect();

            processed_results = SniffStruct {
                path: sfile_info.display_path,
                sniff_timestamp: sniffed_ts,
                last_modified: sfile_info.last_modified.clone(),
                delimiter_char: metadata.dialect.delimiter as char,
                header_row: metadata.dialect.header.has_header_row,
                preamble_rows: metadata.dialect.header.num_preamble_rows,
                quote_char: match metadata.dialect.quote {
                    qsv_sniffer::metadata::Quote::Some(chr) => format!("{}", char::from(chr)),
                    qsv_sniffer::metadata::Quote::None => "none".into(),
                },
                flexible: metadata.dialect.flexible,
                is_utf8: metadata.dialect.is_utf8,
                detected_mime: file_type.clone(),
                retrieved_size: sfile_info.retrieved_size,
                file_size: sfile_info.file_size,
                sampled_records: if sampled_records > num_records {
                    num_records
                } else {
                    sampled_records
                },
                estimated,
                num_records,
                avg_record_len: metadata.avg_record_len,
                num_fields: metadata.num_fields,
                fields: sniffedfields,
                types: sniffedtypes,
                stats_types: args.flag_stats_types,
            };
        }
        Err(e) => {
            sniff_error = Some(format!("{e}"));
        }
    }

    cleanup_tempfile(sfile_info.tempfile_flag, tempfile_to_delete)?;

    // safety: we just created all these json values above, so they are safe to unwrap
    if args.flag_json || args.flag_pretty_json {
        if sniff_error.is_none() {
            if args.flag_pretty_json {
                println!(
                    "{}",
                    serde_json::to_string_pretty(&processed_results).unwrap()
                );
            } else {
                println!("{}", serde_json::to_string(&processed_results).unwrap());
            };
            Ok(())
        } else {
            #[allow(unused_assignments)]
            let mut sniff_error_json: serde_json::Value = Value::default();
            {
                sniff_error_json = json!({
                    "title": "sniff error",
                    "detail": format!("{}", sniff_error.unwrap()),
                    "meta": {
                        "detected_mime_type": file_type,
                        "size": sfile_info.file_size,
                        "last_modified": sfile_info.last_modified,
                    }
                });
            }
            let error_msg = if args.flag_pretty_json {
                serde_json::to_string_pretty(&sniff_error_json).unwrap()
            } else {
                serde_json::to_string(&sniff_error_json).unwrap()
            };
            fail_clierror!("{error_msg}")
        }
    } else if sniff_error.is_none() {
        println!("{processed_results}");
        Ok(())
    } else {
        fail_clierror!(
            "{error}; size: {size}, last_modified: {last_modified}",
            error = sniff_error.unwrap(),
            size = sfile_info.file_size,
            last_modified = sfile_info.last_modified
        )
    }
}