#!/bin/bash

# Script to convert absolute symlinks to relative symlinks in a directory
# Usage: ./relativize_symlinks.sh [directory]

set -e

# Function to calculate relative path from source to target
calculate_relative_path() {
    local source="$1"
    local target="$2"
    
    # Convert to absolute paths to ensure consistency
    source=$(realpath -m "$source")
    target=$(realpath -m "$target")
    
    # Split paths into arrays
    IFS='/' read -ra source_parts <<< "${source#/}"
    IFS='/' read -ra target_parts <<< "${target#/}"
    
    # Find common prefix length
    local common_length=0
    local min_length=$((${#source_parts[@]} < ${#target_parts[@]} ? ${#source_parts[@]} : ${#target_parts[@]}))
    
    for ((i=0; i<min_length; i++)); do
        if [[ "${source_parts[i]}" == "${target_parts[i]}" ]]; then
            ((common_length++))
        else
            break
        fi
    done
    
    # Calculate number of directories to go up from source
    local up_dirs=$((${#source_parts[@]} - common_length - 1))
    
    # Build relative path
    local relative_path=""
    
    # Add ../ for each directory we need to go up
    for ((i=0; i<up_dirs; i++)); do
        if [[ -n "$relative_path" ]]; then
            relative_path="${relative_path}/.."
        else
            relative_path=".."
        fi
    done
    
    # Add the remaining target path components
    for ((i=common_length; i<${#target_parts[@]}; i++)); do
        if [[ -n "$relative_path" ]]; then
            relative_path="${relative_path}/${target_parts[i]}"
        else
            relative_path="${target_parts[i]}"
        fi
    done
    
    # Handle case where source and target are the same
    if [[ -z "$relative_path" ]]; then
        relative_path="."
    fi
    
    echo "$relative_path"
}

# Function to process symlinks in a directory
process_directory() {
    local dir="$1"
    local base_dir="$2"
    
    echo "Processing directory: $dir"
    
    # Find all symbolic links in the directory
    while IFS= read -r -d '' symlink; do
        # Get the target of the symlink
        local target
        target=$(readlink "$symlink")
        
        # Check if it's an absolute path
        if [[ "$target" == /* ]]; then
            echo "Found absolute symlink: $symlink -> $target"
            
            # Calculate the directory containing the symlink
            local symlink_dir
            symlink_dir=$(dirname "$symlink")
            
            # Convert absolute target to be relative to base directory
            local adjusted_target="${base_dir}${target}"
            
            # Calculate relative path from symlink location to target
            local relative_target
            relative_target=$(calculate_relative_path "$symlink_dir/dummy" "$adjusted_target")
            
            echo "  Converting to: $symlink -> $relative_target"
            
            # Remove the old symlink and create the new relative one
            rm "$symlink"
            ln -s "$relative_target" "$symlink"
            
            echo "  ✓ Converted successfully"
        fi
    done < <(find "$dir" -type l -print0)
}

# Main script
main() {
    local target_dir="${1:-.}"
    
    # Validate directory exists
    if [[ ! -d "$target_dir" ]]; then
        echo "Error: Directory '$target_dir' does not exist" >&2
        exit 1
    fi
    
    # Get absolute path of target directory to use as base
    local abs_target_dir
    abs_target_dir=$(realpath "$target_dir")
    
    echo "Relativizing symlinks in: $abs_target_dir"
    echo "Using current directory as filesystem root"
    echo
    
    # Process the directory
    process_directory "$target_dir" "$abs_target_dir"
    
    echo
    echo "Symlink relativization complete!"
}

# Show usage if --help is passed
if [[ "$1" == "--help" || "$1" == "-h" ]]; then
    echo "Usage: $0 [directory]"
    echo
    echo "Convert absolute symlinks to relative symlinks in the specified directory."
    echo "If no directory is specified, the current directory is used."
    echo
    echo "Example:"
    echo "  $0 ./extracted_filesystem"
    echo
    echo "This will convert symlinks like:"
    echo "  usr/lib/libz.so -> /lib/libz.so.1.2.11"
    echo "To:"
    echo "  usr/lib/libz.so -> ../../lib/libz.so.1.2.11"
    exit 0
fi

# Run main function
main "$@"