filter3

#!/bin/bash

# Usage: cat file.csv | ./filter_lastNdays.sh <date_column_number> <days>
# Example: cat file.csv | ./filter_lastNdays.sh 4 45

if [ -z "$1" ] || [ -z "$2" ]; then
    echo "Usage: $0 <date_column_number> <days>"
    exit 1
fi

DATE_COL="$1"
DAYS="$2"

# Calculate cutoff timestamp (N days ago) in epoch seconds
CUTOFF=$(date -d "-$DAYS days" +%s)

awk -F'~' -v col="$DATE_COL" -v cutoff="$CUTOFF" '
{
    ts = $col

    # Add space before AM/PM if missing
    if (ts ~ /AM$/ || ts ~ /PM$/) {
        ts = gensub(/(AM|PM)$/, " \\1", "g", ts)
    }

    # Replace last colon before milliseconds with dot
    ts = gensub(/:([0-9]{3})(AM|PM)?$/, ".\\1\\2", 1, ts)

    # Remove any remaining milliseconds colons just in case
    gsub(/:([0-9]{3})/, ".\\1", ts)

    # Convert to epoch seconds
    cmd = "date -d \"" ts "\" +%s"
    cmd | getline t
    close(cmd)

    # Print row if timestamp >= cutoff
    if(t >= cutoff) print
}'