#!/usr/bin/env bash
export LC_ALL=C
set -e -o pipefail

# Determine the maximum number of jobs to run simultaneously (overridable by
# environment)
MAX_JOBS="${MAX_JOBS:-$(nproc)}"

# Download the depends sources now as we won't have internet access in the build
# container
make -C "${PWD}/depends" -j"$MAX_JOBS" download ${V:+V=1} ${SOURCES_PATH:+SOURCES_PATH="$SOURCES_PATH"}

# Determine the reference time used for determinism (overridable by environment)
SOURCE_DATE_EPOCH="${SOURCE_DATE_EPOCH:-$(git log --format=%at -1)}"

# Execute "$@" in a pinned, possibly older version of Guix, for reproducibility
# across time.
time-machine() {
    guix time-machine --url=https://github.com/dongcarl/guix.git \
                      --commit=cf347affd642c709f7e423f7111794ffdb09f5a6 \
                      -- "$@"
}

# Deterministically build Bitcoin Core for HOSTs (overriable by environment)
# shellcheck disable=SC2153
for host in ${HOSTS=x86_64-linux-gnu arm-linux-gnueabihf aarch64-linux-gnu riscv64-linux-gnu x86_64-w64-mingw32}; do

    # Display proper warning when the user interrupts the build
    trap 'echo "** INT received while building ${host}, you may want to clean up the relevant output and distsrc-* directories before rebuilding"' INT

    (
        # Required for 'contrib/guix/manifest.scm' to output the right manifest
        # for the particular $HOST we're building for
        export HOST="$host"

        # Run the build script 'contrib/guix/libexec/build.sh' in the build
        # container specified by 'contrib/guix/manifest.scm'.
        #
        # Explanation of `guix environment` flags:
        #
        #   --container        run command within an isolated container
        #
        #     Running in an isolated container minimizes build-time differences
        #     between machines and improves reproducibility
        #
        #   --pure             unset existing environment variables
        #
        #     Same rationale as --container
        #
        #   --no-cwd           do not share current working directory with an
        #                      isolated container
        #
        #     When --container is specified, the default behavior is to share
        #     the current working directory with the isolated container at the
        #     same exact path (e.g. mapping '/home/satoshi/bitcoin/' to
        #     '/home/satoshi/bitcoin/'). This means that the $PWD inside the
        #     container becomes a source of irreproducibility. --no-cwd disables
        #     this behaviour.
        #
        #   --share=SPEC       for containers, share writable host file system
        #                      according to SPEC
        #
        #   --share="$PWD"=/bitcoin
        #
        #                     maps our current working directory to /bitcoin
        #                     inside the isolated container, which we later cd
        #                     into.
        #
        #     While we don't want to map our current working directory to the
        #     same exact path (as this introduces irrepreducibility), we do want
        #     it to be at a _fixed_ path _somewhere_ inside the isolated
        #     container so that we have something to build. '/bitcoin' was
        #     chosen arbitrarily.
        #
        #   ${SOURCES_PATH:+--share="$SOURCES_PATH"}
        #
        #                     make the downloaded depends sources path available
        #                     inside the isolated container
        #
        #     The isolated container has no network access as it's in a
        #     different network namespace from the main machine, so we have to
        #     make the downloaded depends sources available to it. The sources
        #     should have been downloaded prior to this invocation.
        #
        # shellcheck disable=SC2086
        time-machine environment --manifest="${PWD}/contrib/guix/manifest.scm" \
                                 --container \
                                 --pure \
                                 --no-cwd \
                                 --share="$PWD"=/bitcoin \
                                 ${SOURCES_PATH:+--share="$SOURCES_PATH"} \
                                 ${ADDITIONAL_GUIX_ENVIRONMENT_FLAGS} \
                                 -- env HOST="$host" \
                                        MAX_JOBS="$MAX_JOBS" \
                                        SOURCE_DATE_EPOCH="${SOURCE_DATE_EPOCH:?unable to determine value}" \
                                        ${V:+V=1} \
                                        ${SOURCES_PATH:+SOURCES_PATH="$SOURCES_PATH"} \
                                      bash -c "cd /bitcoin && bash contrib/guix/libexec/build.sh"
    )

done