#!/usr/bin/env bash
set -e

function detect_platform_type () {
    local -r canon_name="canon-name/src/canon-name"

    if ! gmake --question --file="mk/canon-name.mk" >/dev/null 2>&1; then
        gmake --file="mk/canon-name.mk" >&2
    fi

    "$canon_name"
}

function detect_number_of_cpus () {
    if sysctl -n "hw.ncpu" 2>/dev/null; then
        # This works for most BSDs.
        :
    elif grep -qF processor /proc/cpuinfo 2>/dev/null; then
        # Linux sucks...
        grep -cF processor /proc/cpuinfo
    else
        echo "WARNING: I don't know how to detect the number of processors on this platform." >&2
        echo "WARNING: GHC will be built using only 1 processor. Expect some slowdown." >&2
        echo 1
    fi
}

function detect_gnu_tar () {
    if which gnutar >/dev/null 2>&1; then
        echo "gnutar"
    elif which gtar >/dev/null 2>&1; then
        echo "gtar"
    else
        echo "We need GNU tar to be installed." >&2
        exit 1
    fi
}

function detect_gnu_sed () {
    if which gsed >/dev/null 2>&1; then
        echo "gsed"
    elif sed --version | grep -qF GNU; then
        echo "sed"
    else
        echo "We need GNU sed to be installed." >&2
        exit 1
    fi
}

function say_hello () {
    local -r self=$(basename "$0")
    local -r platform=$(detect_platform_type)
    local -r n_cpus=$(detect_number_of_cpus)

    echo -n "This is $self, running on $platform with $n_cpus "
    if (( $n_cpus == 1 )); then
        echo "processor."
    else
        echo "processors."
    fi
}

function srcpath () {
    local -r archive="work/archive"
    local srcpath=""

    if [[ -e "$archive" ]]; then
        srcpath=$(cat "$archive")
    fi

    if [[ -z "$srcpath" || ! -e "$srcpath" ]]; then
        mkdir -p work
        read -e -p "Enter the file path to ghc-x.y.z-src.tar.bz2: " srcpath
        if [[ -e "$srcpath" ]]; then
            mkdir -p work
            echo "$srcpath" > "$archive"
        else
            echo "$srcpath not found." >&2
            exit 1
        fi
    fi

    echo "$srcpath"
}

function build_hc_pkg () {
    local -r srcpath="$(srcpath)"

    gmake \
        -j $(($(detect_number_of_cpus) + 1)) \
        -f mk/main.mk \
        SRCPATH="$srcpath" \
        PLATFORM="$(detect_platform_type)" \
        GNUTAR="$(detect_gnu_tar)" \
        GNUSED="$(detect_gnu_sed)" \
        SHELL="$SHELL"

    echo "If you are done, run \"$0 clean\" to cleanup the working directory."
}

function main () {
    case "$1" in
        "")
            say_hello
            build_hc_pkg
            exit
            ;;
        "clean")
            echo "Cleaning..."
            rm -rf work
            exit
            ;;
        *)
            echo "Usage: $0 [clean]" >&2
            exit 1
            ;;
    esac
}

main $@