#!/usr/bin/env bash
# Build Fenrir with a suitable Go toolchain without changing the system Go.
set -euo pipefail

projectDir=$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)

fail() {
    echo "Error: $*" >&2
    exit 1
}

usage() {
    cat <<'EOF'
Usage: build-fenrir.sh [-o PATH | --output PATH] [-- GO_BUILD_FLAGS...]

Build Fenrir, downloading a suitable Go toolchain when needed.

  -o, --output PATH  Write the binary to PATH (default: checkout/fenrir).
                    Relative paths are resolved from the caller's directory.
                    Missing parent directories are created.
  -h, --help         Show this help without checking build dependencies.
  --                 Pass remaining flags to go build, e.g. -- -trimpath.

Go environment variables such as GOFLAGS, GOCACHE, GOMODCACHE, GOTMPDIR,
and CGO_CFLAGS/CGO_LDFLAGS are inherited. This script only builds the binary;
package installation and resource staging belong in the packaging recipe.
EOF
}

outputPath="$projectDir/fenrir"
buildFlags=()
while (( $# )); do
    case $1 in
        -o|--output)
            (( $# >= 2 )) || fail "$1 requires a path."
            [[ -n $2 && $2 != -* ]] || fail "$1 requires a path (use ./ for a path starting with '-')."
            outputPath=$2
            shift 2
            ;;
        -h|--help)
            usage
            exit 0
            ;;
        --)
            shift
            buildFlags=("$@")
            break
            ;;
        *) fail "Unknown argument: $1. See --help." ;;
    esac
done
if [[ $outputPath != /* ]]; then
    outputPath="$PWD/$outputPath"
fi
[[ ! -d $outputPath ]] || fail "Output path is a directory; specify the binary filename."
cd -- "$projectDir"

[[ $(uname -s) == Linux ]] || fail "Fenrir requires Linux."
command -v pkg-config >/dev/null || fail "Install pkg-config and the native development libraries listed in README.md."
missingLibraries=()
for library in libevdev x11 vterm alsa; do
    if ! pkg-config --exists "$library"; then
        missingLibraries+=("$library")
    fi
done
if (( ${#missingLibraries[@]} )); then
    fail "Missing development libraries (pkg-config names): ${missingLibraries[*]}. See README.md."
fi

requiredVersion=$(awk '$1 == "go" { print $2; exit }' go.mod)
[[ $requiredVersion =~ ^1\.[0-9]+\.[0-9]+$ ]] || fail "Cannot read the required Go version from go.mod."

# Go 1.21+ downloads and verifies the toolchain selected by go.mod itself.
# Probe the bundled version so a user's GOTOOLCHAIN setting cannot affect this check.
unset GOROOT
goCommand=""
if command -v go >/dev/null; then
    installedVersion=$(GOTOOLCHAIN=local go version 2>/dev/null || true)
    if [[ $installedVersion =~ go1\.([0-9]+) ]] && (( 10#${BASH_REMATCH[1]} >= 21 )); then
        goCommand=$(command -v go)
    fi
fi

if [[ -z $goCommand ]]; then
    case $(uname -m) in
        x86_64) archiveArch=amd64 ;;
        aarch64|arm64) archiveArch=arm64 ;;
        armv6l|armv7l) archiveArch=armv6l ;;
        i386|i486|i586|i686) archiveArch=386 ;;
        ppc64le|riscv64|s390x|loong64) archiveArch=$(uname -m) ;;
        loongarch64) archiveArch=loong64 ;;
        *) fail "No Go bootstrap archive configured for $(uname -m). Install Go 1.21 or newer and rerun this script." ;;
    esac
    toolchainDir="${XDG_CACHE_HOME:-$HOME/.cache}/fenrir/toolchains/go${requiredVersion}.linux-${archiveArch}"
    goCommand="$toolchainDir/go/bin/go"
    if [[ ! -x $goCommand ]]; then
        command -v curl >/dev/null || fail "Install curl to download Go, or install Go 1.21 or newer."
        command -v tar >/dev/null || fail "Install tar to unpack Go."
        mkdir -p -- "$(dirname -- "$toolchainDir")"
        downloadDir=$(mktemp -d "${toolchainDir}.download.XXXXXX")
        trap 'rm -rf -- "$downloadDir"' EXIT
        echo "Downloading Go $requiredVersion for Linux/$archiveArch from go.dev..."
        curl --fail --location --show-error --proto '=https' --proto-redir '=https' \
            --output "$downloadDir/go.tar.gz" \
            "https://go.dev/dl/go${requiredVersion}.linux-${archiveArch}.tar.gz"
        tar -xzf "$downloadDir/go.tar.gz" -C "$downloadDir"
        [[ -x $downloadDir/go/bin/go ]] || fail "The downloaded archive does not contain Go."
        # Another build may have finished the same download while ours ran.
        if [[ ! -x $goCommand ]]; then
            mkdir -p -- "$toolchainDir"
            mv -T -- "$downloadDir/go" "$toolchainDir/go" || [[ -x $goCommand ]]
        fi
    fi
fi

# Apply automatic selection only to this build, including when the caller has
# disabled it globally.
export GOTOOLCHAIN=auto
echo "Using $("$goCommand" version)"
mkdir -p -- "$(dirname -- "$outputPath")"
"$goCommand" build "${buildFlags[@]}" -o "$outputPath" ./cmd/fenrir
echo "Fenrir has been built: $outputPath"