#!/bin/bash

set -euo pipefail


GITIGNORE=".gitignore"


function print_help() {
cat <<EOF
Usage: $(basename "$0") <command> [pattern]

Commands:
  add <pattern>             Add a pattern to $GITIGNORE, if not present
  remove <pattern>          Remove a pattern from $GITIGNORE, if present
  has <pattern>             Check if a pattern is present in $GITIGNORE
  show                      Print $GITIGNORE
  list                      Print sorted $GITIGNORE, skipping blanks and comments
  -h, --help                Show this help message
EOF
}


function add_pattern() {
    local pat="$1"
    if pattern_exists "$pat"; then
        echo "Already present: $pat"
        return 1
    fi
    echo "$pat" >> "$GITIGNORE"
    echo "Added: $pat"
}

function remove_pattern() {
    local pat="$1"
    if ! pattern_exists "$pat"; then
        echo "Not present: $pat"
        return 1
    fi
    grep -Fxv "$pat" "$GITIGNORE" > "$GITIGNORE.tmp"
    mv "$GITIGNORE.tmp" "$GITIGNORE"
    echo "Removed: $pat"
}

function has_pattern() {
    local pat="$1"
    if pattern_exists "$pat"; then
        echo "yes"
        return 0
    else
        echo "no"
        return 1
    fi
}

function show_patterns() {
    cat "$GITIGNORE"
}

function list_patterns() {
    grep -v -e '^\s*#' -e '^\s*$' "$GITIGNORE" | sort -u
}

function pattern_exists() {
    local pat="$1"
    grep -Fxq "$pat" "$GITIGNORE"
}


# Check if -h or --help is anywhere in the arguments
if [[ " $* " == *" -h "* ]] || [[ " $* " == *" --help "* ]]; then
    print_help
    exit
fi


cmd="${1:-}"
pat="${2:-}"


# validate number of arguments
case "$cmd" in
    add|remove|has)
        if [[ $# -ne 2 ]]; then
            echo "Usage: gitignore $cmd <pattern>"
            exit 1
        fi
        ;;
    show|list)
        if [[ $# -ne 1 ]]; then
            echo "Usage: gitignore $cmd"
            exit 1
        fi
        ;;
    *)
        print_help
        exit 1
        ;;
esac


# ensure .gitignore exists
touch "$GITIGNORE"

# dispatch command
case "$cmd" in
    add)        add_pattern "$pat" ;;
    remove)     remove_pattern "$pat" ;;
    has)        has_pattern "$pat" ;;
    show)       show_patterns ;;
    list)       list_patterns ;;
esac