package windsurf

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

// Platform identifies a (OS, architecture) pair that Windsurf may support.
// OS values match runtime.GOOS ("linux", "darwin", "windows"), and Arch
// values match runtime.GOARCH ("amd64", "arm64").
type Platform struct {
	OS   string
	Arch string
}

// String renders the platform as "os/arch" (e.g. "darwin/arm64").
func (p Platform) String() string { return p.OS + "/" + p.Arch }

// procTranslatedProbe reports whether the current process is running under
// Rosetta 2 translation (an amd64 Go binary on Apple Silicon). It is mocked
// by tests.
var procTranslatedProbe = defaultProcTranslatedProbe

// defaultProcTranslatedProbe runs `sysctl sysctl.proc_translated` on darwin
// and returns true when the value is "1". On non-darwin platforms it always
// returns false. The sysctl key is only defined on darwin, so we skip the
// exec on every other OS to avoid spurious errors.
func defaultProcTranslatedProbe() bool {
	if runtime.GOOS != "darwin" {
		return false
	}
	out, err := exec.Command("sysctl", "-n", "sysctl.proc_translated").Output()
	if err != nil {
		return false
	}
	return strings.TrimSpace(string(out)) == "1"
}

// DetectPlatform returns the platform for which we should load the LS binary.
// It accounts for Rosetta translation: an amd64 Go binary running on Apple
// Silicon should load the arm64 LS, not the x64 one, because the native
// Mac arm64 binary performs better and the x64 build may not exist.
func DetectPlatform() Platform {
	return detectPlatformFor(runtime.GOOS, runtime.GOARCH, procTranslatedProbe())
}

func detectPlatformFor(goos, goarch string, rosetta bool) Platform {
	p := Platform{OS: goos, Arch: goarch}
	if p.OS == "darwin" && p.Arch == "amd64" && rosetta {
		p.Arch = "arm64"
	}
	return p
}

// ErrUnsupportedPlatform is returned when no Windsurf LS binary exists for
// the current platform. Callers should fall back to ls_mode=docker.
var ErrUnsupportedPlatform = fmt.Errorf("windsurf: no language server binary for this platform")

// BinaryFilename returns the official Windsurf LS binary filename for the
// given platform, matching the mapping used by the Windsurf VS Code
// extension (extracted from extension.js PlatformArch enum).
func BinaryFilename(p Platform) (string, error) {
	switch {
	case p.OS == "linux" && p.Arch == "amd64":
		return "language_server_linux_x64", nil
	case p.OS == "linux" && p.Arch == "arm64":
		return "language_server_linux_arm", nil
	case p.OS == "darwin" && p.Arch == "arm64":
		return "language_server_macos_arm", nil
	case p.OS == "darwin" && p.Arch == "amd64":
		return "language_server_macos_x64", nil
	case p.OS == "windows" && p.Arch == "amd64":
		return "language_server_windows_x64.exe", nil
	case p.OS == "windows" && p.Arch == "arm64":
		return "language_server_windows_arm.exe", nil
	default:
		return "", fmt.Errorf("%w: %s — use ls_mode=docker to run the Linux LS in a container", ErrUnsupportedPlatform, p)
	}
}