feat: log seed used when --seed not passed

Author: mbhall88

README.md

@@ -404,12 +404,11 @@ of the reads.
 
 ##### `-s`, `--seed`
 
-This option allows you to specify the [random seed][seed] used by the random subsampler.
-By explicitly setting this parameter, you make the subsample for the input reproducible.
-The seed is an integer, and by default it is not set, meaning the operating system will
-seed the random subsampler. You should only pass this parameter if you are likely to
-want to subsample the same input file again in the future and want the same subset of
-reads.
+This option allows you to specify the [random seed][seed] used by the random subsampler. By explicitly setting this 
+parameter, you make the subsample for the input reproducible. You only need to pass this parameter if you are likely 
+to want to subsample the same input file again in the future and want the same subset of reads. However, if you forget 
+to use this option, the seed generated by the system will be printed to the log output, allowing you to use it in the
+future.
 
 #### Verbosity
 

src/alignment.rs

@@ -55,7 +55,11 @@ impl Runner for Alignment {
 
         let mut rng = match self.seed {
             Some(s) => rand_pcg::Pcg64::seed_from_u64(s),
-            None => rand_pcg::Pcg64::seed_from_u64(random()),
+            None => {
+                let seed = random();
+                info!("Using seed: {}", seed);
+                rand_pcg::Pcg64::seed_from_u64(seed)
+            }
         };
 
         let mut reader =

src/subsampler.rs

@@ -1,3 +1,4 @@
+use log::info;
 use rand::prelude::*;
 
 /// A `Struct` for dealing with the randomised part of sub-sampling.
@@ -39,9 +40,14 @@ impl SubSampler {
     /// ```
     fn shuffled_indices<T>(&self, v: &[T]) -> Vec<u32> {
         let mut indices: Vec<u32> = (0..v.len() as u32).collect();
+
         let mut rng = match self.seed {
             Some(s) => rand_pcg::Pcg64::seed_from_u64(s),
-            None => rand_pcg::Pcg64::seed_from_u64(random()),
+            None => {
+                let seed = random();
+                info!("Using seed: {}", seed);
+                rand_pcg::Pcg64::seed_from_u64(seed)
+            }
         };
 
         indices.shuffle(&mut rng);