if test (count $argv) -ne 1
    echo "usage: deploy-to <host>" >&2
    return 2
end

set host $argv[1]

git rev-parse --show-toplevel >/dev/null 2>&1
or begin
    echo "deploy-to: run this from a git checkout" >&2
    return 2
end

set repository_root (git rev-parse --show-toplevel)
or return $status

set untracked_nix_files (git -C $repository_root ls-files --others --exclude-standard -- '*.nix' flake.nix flake.lock)
if test (count $untracked_nix_files) -gt 0
    echo "deploy-to: warning: untracked Nix files are not part of Git flake evaluation" >&2
    printf '  %s\n' $untracked_nix_files >&2
end

set installable "$repository_root#nixosConfigurations.$host.config.system.build.toplevel"

echo "deploy-to: building $installable" >&2
set system_path (nix build --no-link --print-out-paths $installable)
or begin
    echo "deploy-to: build failed for $host" >&2
    return $status
end

if test (count $system_path) -ne 1
    echo "deploy-to: expected one build output, got "(count $system_path) >&2
    return 1
end

echo "deploy-to: copying $system_path to $host" >&2
nix copy --to ssh://$host $system_path
or begin
    echo "deploy-to: copy failed for $host" >&2
    return $status
end

echo "deploy-to: activating $system_path on $host" >&2
ssh -t $host sudo "$system_path/bin/switch-to-configuration" switch
or begin
    echo "deploy-to: activation failed for $host" >&2
    return $status
end