♻️ refactor(network_bandwidth): more flexibility and less spaghetti

- Use the internationally recommended unit symbol
- Commentary for next contributor
- Remove spaghetti code
- More flexible for future evolution

Signed-off-by: Adrien Kara <adrien@iglou.eu>

scripts/network_bandwidth.sh

@@ -1,51 +1,69 @@
 #!/usr/bin/env bash
 
-INTERVAL="1"  # update interval in seconds
+# INTERVAL is equal to 1s because we want to express the bandwidth in sec
+readonly INTERVAL=1
+
+# UPLOAD and DOWNLOAD index
+readonly UPLOAD=0
+readonly DOWNLOAD=1
+
+# SIZE index are the multiple of the unit byte and value the internationally recommended unit symbol in sec
+readonly SIZE=(
+  [1]='B/s'
+  [1024]='kB/s'
+  [1048576]='MB/s'
+  [1073741824]='GB/s'
+)
 
 network_name=$(tmux show-option -gqv "@dracula-network-bandwidth")
 
+# interface_bytes give interface name and signal tx/rx return Bytes
+interface_bytes() {
+  cat "/sys/class/net/$1/statistics/$2_bytes"
+}
+
+# get_bandwidth return the number of bytes exchanged for tx and rx
+get_bandwidth() {
+  upload="$(interface_bytes "$network_name" "tx")"
+  download="$(interface_bytes "$network_name" "rx")"
+
+  #wait the interval for Wait for interval to calculate the difference
+  sleep "$INTERVAL"
+
+  upload="$(bc <<<"$(interface_bytes "$network_name" "tx") - $upload")"
+  download="$(bc <<<"$(interface_bytes "$network_name" "rx") - $download")"
+
+  #set to 0 by default useful for non-existent interface
+  echo "${upload:-0} ${download:-0}"
+}
+
+# bandwidth_to_unit convert bytes into its highest unit and add unit symbol in sec
+bandwidth_to_unit() {
+  local size=1
+  for i in "${!SIZE[@]}"; do
+    if (($1 < i)); then
+      break
+    fi
+
+    size="$i"
+  done
+
+  local result="0.00"
+  if (($1 != 0)); then
+    result="$(bc <<<"scale=2; $1 / $size")"
+  fi
+
+  echo "$result ${SIZE[$size]}"
+}
+
 main() {
-  while true
-  do
-    output_download=""
-    output_upload=""
-    output_download_unit=""
-    output_upload_unit=""
+  bandwidth=()
 
-    initial_download=$(cat /sys/class/net/$network_name/statistics/rx_bytes)
-    initial_upload=$(cat /sys/class/net/$network_name/statistics/tx_bytes)
-
-    sleep $INTERVAL
-
-    final_download=$(cat /sys/class/net/$network_name/statistics/rx_bytes)
-    final_upload=$(cat /sys/class/net/$network_name/statistics/tx_bytes)
-
-    total_download_bps=$(expr $final_download - $initial_download)
-    total_upload_bps=$(expr $final_upload - $initial_upload)
-
-    if [ $total_download_bps -gt 1073741824 ]; then
-      output_download=$(echo "$total_download_bps 1024" | awk '{printf "%.2f \n", $1/($2 * $2 * $2)}')
-      output_download_unit="gB/s"
-    elif [ $total_download_bps -gt 1048576 ]; then
-      output_download=$(echo "$total_download_bps 1024" | awk '{printf "%.2f \n", $1/($2 * $2)}')
-      output_download_unit="mB/s"
-    else
-      output_download=$(echo "$total_download_bps 1024" | awk '{printf "%.2f \n", $1/$2}')
-      output_download_unit="kB/s"
-    fi
-
-    if [ $total_upload_bps -gt 1073741824 ]; then
-      output_upload=$(echo "$total_download_bps 1024" | awk '{printf "%.2f \n", $1/($2 * $2 * $2)}')
-      output_upload_unit="gB/s"
-    elif [ $total_upload_bps -gt 1048576 ]; then
-      output_upload=$(echo "$total_upload_bps 1024" | awk '{printf "%.2f \n", $1/($2 * $2)}')
-      output_upload_unit="mB/s"
-    else
-      output_upload=$(echo "$total_upload_bps 1024" | awk '{printf "%.2f \n", $1/$2}')
-      output_upload_unit="kB/s"
-    fi
-
-    echo "↓ $output_download $output_download_unit • ↑ $output_upload $output_upload_unit"
+  while true; do
+    IFS=" " read -ra bandwidth <<<"$(get_bandwidth)"
+    echo "↓ $(bandwidth_to_unit "${bandwidth[$DOWNLOAD]}") • ↑ $(bandwidth_to_unit "${bandwidth[$UPLOAD]}")"
   done
 }
+
+#run main driver
 main