// Package blender: host GPU backend detection for AMD/NVIDIA/Intel.
package blender

import (
	"bufio"
	"os"
	"os/exec"
	"path/filepath"
	"strconv"
	"strings"
)

// DetectGPUBackends detects whether AMD, NVIDIA, and/or Intel GPUs are available
// using host-level hardware probing only.
func DetectGPUBackends() (hasAMD, hasNVIDIA, hasIntel bool, ok bool) {
	return detectGPUBackendsFromHost()
}

func detectGPUBackendsFromHost() (hasAMD, hasNVIDIA, hasIntel bool, ok bool) {
	if amd, nvidia, intel, found := detectGPUBackendsFromDRM(); found {
		return amd, nvidia, intel, true
	}
	if amd, nvidia, intel, found := detectGPUBackendsFromLSPCI(); found {
		return amd, nvidia, intel, true
	}
	return false, false, false, false
}

func detectGPUBackendsFromDRM() (hasAMD, hasNVIDIA, hasIntel bool, ok bool) {
	entries, err := os.ReadDir("/sys/class/drm")
	if err != nil {
		return false, false, false, false
	}

	for _, entry := range entries {
		name := entry.Name()
		if !isDRMCardNode(name) {
			continue
		}

		vendorPath := filepath.Join("/sys/class/drm", name, "device", "vendor")
		vendorRaw, err := os.ReadFile(vendorPath)
		if err != nil {
			continue
		}
		vendor := strings.TrimSpace(strings.ToLower(string(vendorRaw)))
		switch vendor {
		case "0x1002":
			hasAMD = true
			ok = true
		case "0x10de":
			hasNVIDIA = true
			ok = true
		case "0x8086":
			hasIntel = true
			ok = true
		}
	}

	return hasAMD, hasNVIDIA, hasIntel, ok
}

func isDRMCardNode(name string) bool {
	if !strings.HasPrefix(name, "card") {
		return false
	}
	if strings.Contains(name, "-") {
		// Connector entries like card0-DP-1 are not GPU device nodes.
		return false
	}
	if len(name) <= len("card") {
		return false
	}
	_, err := strconv.Atoi(strings.TrimPrefix(name, "card"))
	return err == nil
}

func detectGPUBackendsFromLSPCI() (hasAMD, hasNVIDIA, hasIntel bool, ok bool) {
	if _, err := exec.LookPath("lspci"); err != nil {
		return false, false, false, false
	}

	out, err := exec.Command("lspci").CombinedOutput()
	if err != nil {
		return false, false, false, false
	}

	scanner := bufio.NewScanner(strings.NewReader(string(out)))
	for scanner.Scan() {
		line := strings.ToLower(strings.TrimSpace(scanner.Text()))
		if !isGPUControllerLine(line) {
			continue
		}

		if strings.Contains(line, "nvidia") {
			hasNVIDIA = true
			ok = true
		}
		if strings.Contains(line, "amd") || strings.Contains(line, "ati") || strings.Contains(line, "radeon") {
			hasAMD = true
			ok = true
		}
		if strings.Contains(line, "intel") {
			hasIntel = true
			ok = true
		}
	}

	return hasAMD, hasNVIDIA, hasIntel, ok
}

func isGPUControllerLine(line string) bool {
	return strings.Contains(line, "vga compatible controller") ||
		strings.Contains(line, "3d controller") ||
		strings.Contains(line, "display controller")
}