feat: add -r parameter for subcli tail

src/cli/tail.rs

@@ -7,6 +7,7 @@ use std::time::Instant;
 pub fn tail_n_records(
     input: Option<&String>,
     number: usize,
+    rdc: bool,
     output: Option<&String>,
     compression_level: u32,
 ) -> Result<()> {
@@ -21,17 +22,26 @@ pub fn tail_n_records(
     info!("get tail {} records", number);
 
     let mut fo = fastq::Writer::new(file_writer(output, compression_level)?);
-    let mut total = 0usize;
+    if rdc {
+        let mut total = 0usize;
+        for _ in fp.records() {
+            total += 1;
+        }
+        info!("fastq file total reads number: {}", total);
 
-    for _ in fp.records() {
-        total += 1;
-    }
-    info!("fastq file total reads number: {}", total);
-    let skip_n = total - number;
-
-    let fp2 = fastq::Reader::new(file_reader(input)?);
-    for rec in fp2.records().skip(skip_n).flatten() {
-        fo.write_record(&rec)?;
+        let skip_n = total - number;
+        let fp2 = fastq::Reader::new(file_reader(input)?);
+        for rec in fp2.records().skip(skip_n).flatten() {
+            fo.write_record(&rec)?;
+        }
+    } else {
+        let mut tail = vec![];
+        for rec in fp.records().map_while(Result::ok) {
+            tail.push(rec);
+        }
+        for rec in tail.iter().rev().take(number).rev(){
+            fo.write_record(rec)?;
+        }
     }
     fo.flush()?;
 

src/command.rs

@@ -66,12 +66,16 @@ pub enum Subcli {
         out: Option<String>,
     },
     /// get last N records from fastq file
+    #[command(before_help = "note: if the -r parameter is not specified, all data will be read into memory")]
     tail {
         /// input fastq file, or read from stdin
         input: Option<String>,
         /// print last N fastq records
         #[arg(short = 'n', long = "num", default_value_t = 10, value_name = "INT")]
         num: usize,
+        /// read files twice to reduce much memory but cost more time, can't use in Stream
+        #[arg(short = 'r', long = "rdc", help_heading = Some("FLAGS"))]
+        rdc: bool,
         /// output fastq file name or write to stdout, files ending in .gz/.bz2/.xz will be compressed automatically
         #[arg(short = 'o', long = "out", value_name = "FILE")]
         out: Option<String>,
@@ -478,7 +482,7 @@ pub enum Subcli {
     },
     /// check the validity of a fastq record
     #[command(
-        before_help = "note: this function will return an Err if one of the following conditions is met:\n
+        before_help = "note: this function will return an Err if one of the following conditions is met\n
       1. the record identifier is empty.
       2. there is a non-ASCII character found in either the sequence or quality strings.
       3. the sequence and quality strings do not have the same length.\n"

src/main.rs

@@ -22,8 +22,8 @@ fn main() -> Result<(), Error> {
         Subcli::topn { input, num, out } => {
             top_n_records(input.as_ref(), num, out.as_ref(), arg.compression_level)?;
         }
-        Subcli::tail { input, num, out } => {
-            tail_n_records(input.as_ref(), num, out.as_ref(), arg.compression_level)?;
+        Subcli::tail { input, num, rdc, out } => {
+            tail_n_records(input.as_ref(), num, rdc, out.as_ref(), arg.compression_level)?;
         }
         Subcli::subfq {
             input,