#!/bin/bash

# Handle --dry-run flag
DRY_RUN=0
if [ "$1" = "--dry-run" ]; then
    DRY_RUN=1
    shift
fi

# Directory to process (default: current directory)
DIR="."
if [ -n "$1" ]; then
    DIR="$1"
fi

# Function to process and rename a file
process_file() {
    local original="$1"
    local base ext modified sanitized_base

    # Skip directories and non-regular files
    [ -f "$original" ] || return 0

    # Split base and extension
    if [[ "$original" == *.* ]]; then
        ext=".${original##*.}"
        base="${original%.*}"
    else
        base="$original"
        ext=""
    fi

    # Sanitize base only, not the extension
    sanitized_base=$(echo "$base" | tr ' ' '_' | tr '[:upper:]' '[:lower:]')
    sanitized_base=$(echo "$sanitized_base" | sed 's/[^a-zA-Z0-9._-]//g')

    # Truncate base to 250 chars to avoid hitting filesystem limits
    base_truncated="${sanitized_base:0:250}"

    # Rebuild filename with sanitized base and original extension
    modified="$base_truncated$ext"

    # Collapse multiple underscores
    modified=$(echo "$modified" | tr -s '_')

    # Trim leading/trailing underscores
    modified=$(echo "$modified" | sed 's/^_//' | sed 's/_$//')

    # Skip if empty
    if [ -z "$modified" ]; then
        echo "Error: Empty filename after sanitizing '$original'" >&2
        return 1
    fi

    # Skip if no change
    if [ "$original" = "$modified" ]; then
        echo "No changes needed: '$original'"
        return 0
    fi

    # Collision handling
    counter=1
    original_modified="$modified"
    while [ -e "$modified" ]; do
        modified="${base_truncated}_${counter}${ext}"
        # Truncate again to avoid going over 255 chars
        modified="${modified:0:255}"
        ((counter++))
    done

    # Dry run
    if [ "$DRY_RUN" -eq 1 ]; then
        echo "Dry-run: Would rename '$original' → '$modified'"
        return 0
    fi

    # Rename file
    if mv -- "$original" "$modified"; then
        echo "Renamed: '$original' → '$modified'"
    else
        echo "Error: Failed to rename '$original'" >&2
        return 1
    fi
}

# Enter target directory
cd "$DIR" || { echo "Error: Failed to change directory to '$DIR'" >&2; exit 1; }

# Process all non-hidden files
for file in *; do
    process_file "$file"
done

# Optional: process hidden files (uncomment below)
# for file in .??*; do
#     process_file "$file"
# done