#!/bin/bash
list_versions() {
    echo "installed versions:"
    for i in "$HOME"/.go/go1*; do basename "$i"; done
    echo ""
}

install_version() {
    check_valid $1
    if [[ $valid != 'true' ]]; then
        echo "invalid version $1"
        echo "using $(go version)"
        exit 1
    fi

    fname="$HOME/.go/downloads/$1.$goos-$goarch.tar.gz"

    if [[ ! -f $fname ]]; then
        curl -Lo $fname https://dl.google.com/go/$1.$goos-$goarch.tar.gz
    fi
    cd $HOME/.go/downloads
    tar -zxf $1.$goos-$goarch.tar.gz
    mv go/ ../$1
    check_exists $1
    link_version $1
}

link_version() {
    if [[ $exists == 'true' ]]; then
        ln -sfn $HOME/.go/$1 $HOME/.go/go
    fi
}

check_valid() {
    if [[ $1 =~ go1\.[0-9]{1,2}\.[0-9]{1,2} ]]; then
        valid='true'
    fi
}

check_exists() {
    if [[ -d $HOME/.go/$1 ]]; then
        exists='true'
    fi
}

remove_version() {
    check_exists $1
    if [[ $exists == 'true' ]]; then
        if [[ $current_link == $1 ]]; then
            echo "cannot remove version $1 because it is currently in use"
        else
            rm -rf $HOME/.go/$1
            echo "removed version $1"
        fi
    else
        echo "version $1 not installed"
    fi
}

prompt_install() {
    echo "$1 not found in $HOME/.go"
    list_versions
    check_valid $1

    if [[ $valid == 'true' ]]; then
        echo "attempt to download and install? [y/n]"
        read input
        if [[ $input == 'y' ]]; then
            install_version $1
        fi
    else
        echo "invalid version $1"
        echo "using $(go version)"
        exit 1
    fi
}

mkdir -p "$HOME/.go/downloads"
current_link=$(basename $(readlink $HOME/.go/go))
uname_m=$(uname -m)
goarch='amd64'
if [[ $uname_m == 'arm64' || $uname_m == 'aarch64' ]]; then
    goarch='arm64'
fi
goos='linux'
if [[ $(uname) == 'Darwin' ]]; then
    goos='darwin'
fi
valid='false'
exists='false'

check_exists $1
if [[ $1 == '' ]]; then
    list_versions
elif [[ $1 == 'list' ]]; then
    list_versions
elif [[ $1 == 'remove' ]]; then
    remove_version $2
elif [[ $1 == 'uninstall' ]]; then
    remove_version $2
elif [[ $1 == 'install' ]]; then
    install_version $2
elif [[ $1 == 'use' ]]; then
    check_exists $2
    if [[ $exists == true ]]; then
        link_version $2
    else
        prompt_install $2
    fi
elif [[ $exists == 'true' ]]; then
    link_version $1
else
    prompt_install $1
fi

echo "using $(go version)"