#!/usr/bin/env bash
set -euo pipefail

# cd to the directory where this script lives
cd "$(dirname "$0")"

echo "Running make..."
make

# detect MPI launcher
if command -v mpirun >/dev/null 2>&1; then
    MPI_LAUNCHER=mpirun
    MPI_FLAG="-np"
elif command -v mpiexec >/dev/null 2>&1; then
    MPI_LAUNCHER=mpiexec
    MPI_FLAG="-n"
else
    echo "Error: neither mpirun nor mpiexec found in PATH." >&2
    exit 2
fi

# detect number of processes (fallback to 4)
if command -v nproc >/dev/null 2>&1; then
    NP=$(nproc)
elif [ -n "${NUMBER_OF_PROCESSORS-}" ]; then
    NP=$NUMBER_OF_PROCESSORS
else
    NP=4
fi

echo "Using $MPI_LAUNCHER $MPI_FLAG $NP"

# helper to measure elapsed "real" time (seconds) while also showing program output
measure_time() {
    local label="$1"; shift
    local -a cmd=("$@")
    echo "---- Running: $label ----"
    echo "Command: ${cmd[*]}"

    local outfile timefile
    outfile=$(mktemp)
    timefile=$(mktemp)

    if command -v /usr/bin/time >/dev/null 2>&1; then
        # /usr/bin/time prints real time with %e (seconds) into timefile
        /usr/bin/time -f "%e" -o "$timefile" "${cmd[@]}" 2>&1 | tee "$outfile"
        elapsed=$(<"$timefile")
    else
        # bash builtin time: capture stderr (which receives the timing) and stdout separately
        TIMEFORMAT='%R'
        { time "${cmd[@]}" 1> "$outfile"; } 2> "$timefile"
        elapsed=$(<"$timefile")
        # also print program output
        cat "$outfile"
    fi

    rm -f "$outfile" "$timefile"
    # normalize elapsed to a number (strip spaces)
    echo "${elapsed//[[:space:]]/}"
}

# ensure executables exist
for exe in mpi_hello_world mpi_pi serial_pi; do
    if [ ! -x "./$exe" ]; then
        echo "Error: executable ./$exe not found or not executable. Did make build it?" >&2
        exit 3
    fi
done

# run mpi_hello_world (show output, don't measure for comparison)
echo "==> Executing mpi_hello_world"
"$MPI_LAUNCHER" "$MPI_FLAG" "$NP" ./mpi_hello_world

# measure mpi_pi
mpi_elapsed=$(measure_time "mpi_pi" "$MPI_LAUNCHER" "$MPI_FLAG" "$NP" ./mpi_pi)

# measure serial_pi
serial_elapsed=$(measure_time "serial_pi" ./serial_pi)

# compute comparison
# protect against zero
if awk "BEGIN{exit($mpi_elapsed <= 0)}"; then
    echo "Error: measured mpi_pi time is zero or negative." >&2
    exit 4
fi

speedup=$(awk -v s="$serial_elapsed" -v m="$mpi_elapsed" 'BEGIN{ if(m==0){print "inf"; exit} printf "%.3f", s/m }')
diff=$(awk -v s="$serial_elapsed" -v m="$mpi_elapsed" 'BEGIN{printf "%.3f", s-m }')

echo
echo "Summary:"
echo "  mpi_pi   time (s): $mpi_elapsed"
echo "  serial_pi time (s): $serial_elapsed"
echo "  Difference (serial - mpi) (s): $diff"
echo "  Speedup (serial / mpi): $speedup x"

exit 0