#!/bin/bash

: "${CACHE_DIR:=$PWD/AppData/Local/K3s-Cache}"

DOWNLOAD_URL="https://github.com/k3s-io/k3s/releases/download"

# This function determines the latest k3s build for a given k8s version.
# Starting with the latest cached version, it checks if any newer versions
# are available from Github.
#
# NOTE: This function does *NOT* verify that build 1 exists, i.e. that
# the provided k8s version is valid. This will be detected by the actual
# download attempt.
function latest_build {
    local k8s_version="$1"

    # check if the k8s version already includes the k3s build suffix
    local regex='\+k3s[0-9]+$'
    if [[ ${k8s_version} =~ ${regex} ]]; then
        echo "${k8s_version}"
        return
    fi

    # locate latest k3s build of k8s_version in the cache
    local k3s_build
    k3s_build=$(ls -1d "${CACHE_DIR}/${k8s_version}"+k3s* 2>/dev/null \
                    | sed 's/.*+k3s//' | sort -h -r | head -1)

    # if no cached version exists, assume at least build 1 exist on Github.
    if [ -z "${k3s_build}" ]; then
        k3s_build=1
    fi

    # find latest published build (there may be tags that don't have builds)
    while true; do
        local version="${k8s_version}+k3s$((k3s_build+1))"
        local url="${DOWNLOAD_URL}/${version}/k3s"
        # TODO: what is a reasonable timeout to assume no internet connectivity?
        if ! wget --quiet --spider --tries 1 --timeout 5 -O /dev/null "${url}"; then
            echo "${k8s_version}+k3s${k3s_build}"
            return
        fi
        k3s_build=$((k3s_build+1))
    done

}

# Verify that the current directory has a complete set of downloaded binaries.
function verify_binaries {
    # Verify sha256sum only once after download to check for
    # truncated files; it takes several seconds to run.
    if [ -f .verified ]; then
        # Just make sure the files still exist
        for asset in k3s k3s-airgap-images-amd64.tar; do
            if [ ! -f ${asset} ]; then
                return 1
            fi
        done
        return 0
    fi

    if [ ! -f sha256sum-amd64.txt ]; then
        return 1
    fi

    # Don't look for k3s-images.txt; we don't download it.
    # `sha256sum --ignore-missing --check` doesn't seem to work.
    if ! cat sha256sum-amd64.txt | grep -v txt$ | sha256sum --quiet --check; then
        return 1
    fi

    touch .verified
}

# Download binaries for specified k8s version and return the fully qualified
# path to the cache directory. Non-zero exit means the binaries don't exist
# or couldn't be downloaded.
function get_binaries {
    local version
    version="$(latest_build "$1")"

    local dir="${CACHE_DIR}/${version}"
    mkdir -p "${dir}"
    pushd "${dir}" >/dev/null

    if ! verify_binaries; then
        for asset in k3s k3s-airgap-images-amd64.tar sha256sum-amd64.txt; do
            if ! wget --quiet --output-document "${asset}" \
                 "${DOWNLOAD_URL}/${version}/${asset}"; then
                rm "${asset}"
            fi
        done
        if ! verify_binaries; then
            >&2 echo "Version ${version} is not in cache and couldn't be downloaded"
            popd >/dev/null
            rmdir "${dir}"
            return 1
        fi
    fi

    popd >/dev/null
    echo "${dir}/${version}"
}

for version in "$@"; do
    get_binaries "${version}"
done