#!/bin/bash

# chatgpt 2025
# bak: Backup one or more files into ~/bak while preserving their path structures
# with deduplication based on file content hash

# usage:
# bak file1 file2

backup_root="$HOME/bak"
index_file="$backup_root/.bak_index"
timestamp="$(date +%Y%m%d-%H%M%S)"

mkdir -p "$backup_root"
touch "$index_file"

if [ "$#" -eq 0 ]; then
    echo "Usage: bak <file1> [file2 ...]"
    exit 1
fi

while [ "$#" -gt 0 ]; do
    file=$1
    shift

    if [ ! -f "$file" ]; then
        echo "Skipping: '$file' is not a regular file"
        continue
    fi

    sha256=$(sha256sum "$file" | awk '{print $1}')

    # Check if this hash already exists
    if grep -q "$sha256" "$index_file"; then
        echo "✗ Skipping '$file' — identical content already backed up"
        continue
    fi

    abs_path="$(realpath "$file")"
    rel_path="${abs_path#/}"
    dest_path="$backup_root/$rel_path.$timestamp"

    mkdir -p "$(dirname "$dest_path")"
    cp -- "$file" "$dest_path"

    echo "$sha256  $abs_path" >> "$index_file"

    echo "✓ Backed up '$file' → '$dest_path'"
done