#!/bin/bash

# A script to replace text_a with text_b in a file and report the changes.
#
# Usage: ./replace_and_report.sh <filename> "text_a" "text_b"

# Check if the correct number of arguments are provided
if [ "$#" -ne 3 ]; then
  echo "Error: Incorrect number of arguments."
  echo "Usage: $0 <filename> \"text_a\" \"text_b\""
  exit 1
fi

FILE="$1"
TEXT_A="$2"
TEXT_B="$3"

# Check if the file exists
if [ ! -f "$FILE" ]; then
  echo "Error: File '$FILE' not found."
  exit 1
fi

echo "Searching for '$TEXT_A' in '$FILE' and replacing it with '$TEXT_B'..."
echo "---"

# Use `grep` to find the line numbers where TEXT_A exists
# The output is a list of line numbers
LINE_NUMBERS=$(grep -n "$TEXT_A" "$FILE" | cut -d: -f1)

# Check if any matches were found
if [ -z "$LINE_NUMBERS" ]; then
  echo "No occurrences of '$TEXT_A' found. No replacements made."
  exit 0
fi

# Loop through each line number where a replacement will be made
for line_number in $LINE_NUMBERS; do
  # Get the original line content before the replacement
  original_line=$(sed -n "${line_number}p" "$FILE")
  
  # Perform the replacement using `sed` on the specific line
  sed -i "${line_number}s/${TEXT_A}/${TEXT_B}/g" "$FILE"
  
  # Get the new line content after the replacement
  new_line=$(sed -n "${line_number}p" "$FILE")
  
  echo "Line $line_number:"
  echo "  - Original: $original_line"
  echo "  - New:      $new_line"
  echo "---"
done

echo "Replacements complete. Changes saved to '$FILE'."