#!/bin/bash
set -e

# 获取文件的增长速度
# 参数：
#   $1: 文件路径
#   $2: 时间间隔 (秒)
# 输出：
#   文件的增长速度 (B/s, MB/s, GB/s)

function usage() {
    if [ $# -ne 1 ]; then
        echo "Usage: $0 <file_name>" 
        echo "       $0 <file_name> <duration_in_seconds, default is 5>"
        exit 1
    fi

    file="$1"
    n="${2:-5}"

    # 检测平台并设置获取文件大小的命令
    if stat --version >/dev/null 2>&1; then
        # GNU stat (Linux)
        get_size() {
            stat -c%s "$1"
        }
    else
        # BSD stat (macOS)
        get_size() {
            stat -f%z "$1"
        }
    fi
    

    size1=$(get_size "$file")
    echo "before $1 size: $size1"
    echo "wait $n seconds..."
    sleep "$n"
    size2=$(get_size "$file")
    echo "after $1 size: $size2"
    growth=$(echo "scale=2; ($size2 - $size1) / $n" | bc)

    if (( $(echo "$growth >= 1073741824" | bc) )); then
        echo "$(echo "scale=2; $growth / 1073741824" | bc) GB/s"
    elif (( $(echo "$growth >= 1048576" | bc) )); then
        echo "$(echo "scale=2; $growth / 1048576" | bc) MB/s"
    else
        echo "$growth B/s"
    fi
}

usage "$@"