start

#!/usr/bin/env bash
#
# Checks the version of Bazel found in the PATH, and then initializes
# a new Bazel workspace with dummy Haskell build targets.

MIN_BAZEL_MAJOR=0
MIN_BAZEL_MINOR=29

MAX_BAZEL_MAJOR=2
MAX_BAZEL_MINOR=0

set -e

usage () {
    cat >&2 <<"EOF"
start [--use-bindists|--use-nix|--help]

Set up a minimal rules_haskell bazel configuration.

--use-bindists: The project is set up to provision GHC from binary distributions. This does not require nix to build.
--use-nix: The project is set up to provision GHC from nixpkgs. This requires nix to build.

If no argument is given, `--use-bindists` is assumed
and a helpful message is printed that `--use-nix` also exists.

For more information visit https://haskell.build/
EOF
    exit "$1"
}

# either bindists or nix
mode=
print_nix_usage_info="no"

parse_args () {
    if [ $# -lt 1 ]; then
        mode="bindists"
        print_nix_usage_info="yes"
        return
    fi

    [ "$1" = "--help" ] && usage 0
    case "$1" in
        "--help") usage 0 ;;
        "--use-bindists") mode="bindists" ;;
        "--use-nix") mode="nix" ;;
        *) usage 1 ;;
    esac
}

check_files_dont_exist () {
    if [ -e WORKSPACE ] || [ -e BUILD ] || [ -e BazelExample.hs ]
    then
        echo "Current directory already has WORKSPACE and/or BUILD and/or BazelExample.hs files." >&2
        exit 1
    fi
}

check_bazel_version () {
    actual_raw=$(bazel version | grep -E '^Build label:' | grep -E -o '[0-9.]+')

    # shellcheck disable=SC2034
    IFS=. read -r actual_major actual_minor actual_patch <<EOF
$actual_raw
EOF

    expected_min=$MIN_BAZEL_MAJOR.$MIN_BAZEL_MINOR.0
    expected_max=$MAX_BAZEL_MAJOR.$MAX_BAZEL_MINOR.x

    if [ "$actual_major" -gt "$MAX_BAZEL_MAJOR" ] || {
        [ "$actual_major" -eq "$MAX_BAZEL_MAJOR" ] &&
            [ "$actual_minor" -gt "$MAX_BAZEL_MINOR" ]
         }
    then
	      echo "Warning: a too new version of Bazel detected: v${actual_raw}."  >&2
	      echo "         Recommended versions are from v${expected_min} to v${expected_max}."  >&2
    elif [ "$actual_major" -lt "$MIN_BAZEL_MAJOR" ] || {
          [ "$actual_major" -eq "$MIN_BAZEL_MAJOR" ] &&
            [ "$actual_minor" -lt "$MIN_BAZEL_MINOR" ]
         }
    then
        echo "Error: Need at least Bazel v${expected_min} but v${actual_raw} detected." >&2
        exit 1
    fi
}

insert_if_equal () {
    [ "$1" = "$2" ] && printf '%s' "$3"
}

parse_args "$@"

if [ "$print_nix_usage_info" = "yes" ]; then
    # shellcheck disable=SC2016
    echo 'INFO: Creating a WORKSPACE file based on GHC bindists. If you want to use a nix-based setup (e.g. on NixOS), call with `--use-nix`. See `--help` for more info.' >&2
fi

check_files_dont_exist
check_bazel_version

bindist_toolchain=$(cat <<EOF
# Download a GHC binary distribution from haskell.org and register it as a toolchain.
rules_haskell_toolchains()
EOF
)

nix_toolchain=$(cat <<EOF
# Load nixpkgs_git_repository from rules_nixpkgs,
# which was already initialized by rules_haskell_dependencies above.
load(
    "@io_tweag_rules_nixpkgs//nixpkgs:nixpkgs.bzl",
    "nixpkgs_git_repository",
    "nixpkgs_python_configure",
)

nixpkgs_python_configure(
    repository = "@nixpkgs",
)

# Fetch a version of nixpkgs from GitHub.
# For more information see the documentation of rules_nixpkgs at
# https://github.com/tweag/rules_nixpkgs/blob/master/README.md
nixpkgs_git_repository(
    name = "nixpkgs",
    revision = "19.03",
    # sha256 = …
)

load(
    "@rules_haskell//haskell:nixpkgs.bzl",
    "haskell_register_ghc_nixpkgs",
)

# Fetch a GHC binary distribution from nixpkgs and register it as a toolchain.
# For more information:
# https://api.haskell.build/haskell/nixpkgs.html#haskell_register_ghc_nixpkgs
haskell_register_ghc_nixpkgs(
    repository = "@nixpkgs",
    attribute_path = "ghc",
    version = "8.6.4",
)
EOF
)

get_toolchain () {
    case $mode in
        bindists) printf '%s' "$bindist_toolchain" ;;
        nix) printf '%s' "$nix_toolchain" ;;
    esac
}

echo "Creating WORKSPACE" >&2
cat > WORKSPACE <<EOF
# Give your project a name. :)
workspace(name = "YOUR_PROJECT_NAME_HERE")

# Load the repository rule to download an http archive.
load(
    "@bazel_tools//tools/build_defs/repo:http.bzl",
    "http_archive"
)

# Download rules_haskell and make it accessible as "@rules_haskell".
http_archive(
    name = "rules_haskell",
    strip_prefix = "rules_haskell-0.11",
    urls = ["https://github.com/tweag/rules_haskell/archive/v0.11.tar.gz"],
    sha256 = "40fd6de12324b515042634ba13b02fa19f5c6e274eae6350be2e4d1e023fcd90",
)

load(
    "@rules_haskell//haskell:repositories.bzl",
    "rules_haskell_dependencies",
)

# Setup all Bazel dependencies required by rules_haskell.
rules_haskell_dependencies()

load(
    "@rules_haskell//haskell:toolchain.bzl",
    "rules_haskell_toolchains",
)

$(get_toolchain)
EOF

echo "Creating .bazelrc" >&2
cat > .bazelrc <<EOF
build:ci --loading_phase_threads=1
build:ci --jobs=2
build:ci --verbose_failures
common:ci --color=no
test:ci --test_output=errors

$(insert_if_equal $mode "nix" '
# This project uses a GHC provisioned via nix.
# We need to use the rules_haskell nix toolchain accordingly:
build --host_platform=@rules_haskell//haskell/platforms:linux_x86_64_nixpkgs
run --host_platform=@rules_haskell//haskell/platforms:linux_x86_64_nixpkgs'
)

# test environment does not propagate locales by default
# some tests reads files written in UTF8, we need to propagate the correct
# environment variables, such as LOCALE_ARCHIVE
# We also need to setup an utf8 locale
test --test_env=LANG=en_US.utf8 --test_env=LOCALE_ARCHIVE

try-import .bazelrc.local
EOF

echo "Creating BUILD.bazel" >&2
cat > BUILD.bazel <<"EOF"
# Set all target’s visibility in this package to "public".
package(default_visibility = ["//visibility:public"])

# Load rules_haskell rules.
load(
    "@rules_haskell//haskell:defs.bzl",
    "haskell_toolchain_library",
    "haskell_library",
    "haskell_binary",
)

# haskell_toolchain_library can access builtin GHC packages
# and assign them a bazel target name, so that they
# can be referenced as dependencies.
haskell_toolchain_library(name = "base")

# You can add your own libraries with haskell_library.
# haskell_library(
#     name = "MY_LIBRARY_NAME",
#     src_strip_prefix = "src",
#     srcs = glob(['src/**/*.hs']),
#     deps = [
#         "base_pkg"
#     ],
# )

# An example binary using the Prelude module from the
# GHC base package, to print the hello world.
haskell_binary(
    name = "example",
    srcs = [":Example.hs"],
    deps = [":base"],
)
EOF

echo "Creating Example.hs" >&2
cat > Example.hs <<"EOF"
module Main where

import Prelude (putStrLn)

main = putStrLn "Hello from rules_haskell!"
EOF

cat >&2 <<"EOF"
WORKSPACE and initial BUILD files created. To run Bazel and build the example:

    $ bazel run //:example
EOF