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package main

import (
	"fmt"
	"os"
	"os/exec"
	"strings"
)

const flakeRef = "/home/philip/kot/Profpatsch"

func main() {
	opts := parseArgs(os.Args[1:])

	if opts.remoteBuild {
		deployRemoteBuild(opts)
	} else {
		deployLocalBuild(opts)
	}
}

type options struct {
	remoteBuild bool
	machine     string
	// profilePath is non-empty when --profile=<path> is given.
	// The nix evaluation will be profiled and the flamegraph written there.
	profilePath string
}

func parseArgs(args []string) options {
	var opts options
	for _, a := range args {
		switch {
		case a == "--remote-build":
			opts.remoteBuild = true
		case strings.HasPrefix(a, "--profile="):
			opts.profilePath = strings.TrimPrefix(a, "--profile=")
		case a == "--profile":
			// bare --profile without a path: use a default filename
			opts.profilePath = "nix-eval.profile"
		default:
			opts.machine = a
		}
		
	}
	if opts.machine == "" {
		fmt.Fprintln(os.Stderr, "usage: deploy [--remote-build] [--profile[=<path>]] <machine>")
		os.Exit(1)
	}
	return opts
}

// evalProfileArgs returns the extra nix options to enable flamegraph profiling,
// or nil when profiling is not requested.
func evalProfileArgs(opts options) []string {
	if opts.profilePath == "" {
		return nil
	}
	return []string{
		"--option", "eval-profiler", "flamegraph",
		"--option", "eval-profile-file", opts.profilePath,
	}
}

// cmd runs a command with inherited stdin/stdout/stderr, printing it first.
// Exits with a non-zero status on failure.
func cmd(args ...string) {
	fmt.Fprintln(os.Stderr, "$", strings.Join(args, " "))
	c := exec.Command(args[0], args[1:]...)
	c.Stdin = os.Stdin
	c.Stdout = os.Stdout
	c.Stderr = os.Stderr
	if err := c.Run(); err != nil {
		fmt.Fprintf(os.Stderr, "deploy: %v\n", err)
		os.Exit(1)
	}
}

// cmdOutput runs a command, prints it, and returns trimmed stdout.
// Exits with a non-zero status on failure.
func cmdOutput(args ...string) string {
	fmt.Fprintln(os.Stderr, "$", strings.Join(args, " "))
	c := exec.Command(args[0], args[1:]...)
	c.Stderr = os.Stderr
	out, err := c.Output()
	if err != nil {
		fmt.Fprintf(os.Stderr, "deploy: %v\n", err)
		os.Exit(1)
	}
	return strings.TrimSpace(string(out))
}

func toplevelAttr(machine string) string {
	return flakeRef + "#nixosConfigurations." + machine + ".config.system.build.toplevel"
}

// deployLocalBuild builds the system closure locally, copies it to the
// remote, then activates via nixos-rebuild switch.
func deployLocalBuild(opts options) {
	nixBuildArgs := append(
		[]string{"nix", "build", "--no-link", "--print-out-paths"},
		evalProfileArgs(opts)...,
	)
	nixBuildArgs = append(nixBuildArgs, toplevelAttr(opts.machine))
	outPath := cmdOutput(nixBuildArgs...)

	cmd(
		"nix", "copy",
		"--to", "ssh://root@"+opts.machine,
		"--substitute-on-destination",
		outPath,
	)

	cmd(
		"ssh", "root@"+opts.machine,
		"nix-env", "--profile", "/nix/var/nix/profiles/system", "--set", outPath,
	)

	cmd(
		"ssh", "root@"+opts.machine,
		outPath+"/bin/switch-to-configuration", "switch",
	)

	if opts.profilePath != "" {
		fmt.Fprintf(os.Stderr, "eval profile written to: %s\n", opts.profilePath)
	}
}

// deployRemoteBuild evaluates the derivation locally, copies the .drv to the
// remote, builds there, then activates directly via switch-to-configuration.
func deployRemoteBuild(opts options) {
	nixPathInfoArgs := append(
		[]string{"nix", "path-info", "--derivation"},
		evalProfileArgs(opts)...,
	)
	nixPathInfoArgs = append(nixPathInfoArgs, toplevelAttr(opts.machine))
	drvPath := cmdOutput(nixPathInfoArgs...)

	cmd(
		"nix", "copy",
		"--derivation",
		"--to", "ssh://root@"+opts.machine,
		drvPath,
	)

	outPath := cmdOutput(
		"ssh", "root@"+opts.machine,
		"nix", "build", "--no-link", "--print-out-paths", drvPath+"^*",
	)

	cmd(
		"ssh", "root@"+opts.machine,
		"nix-env", "--profile", "/nix/var/nix/profiles/system", "--set", outPath,
	)

	cmd(
		"ssh", "root@"+opts.machine,
		outPath+"/bin/switch-to-configuration", "switch",
	)

	if opts.profilePath != "" {
		fmt.Fprintf(os.Stderr, "eval profile written to: %s\n", opts.profilePath)
	}
}