/*
Volt Platform — Machine Fingerprint Generation
Creates a unique, deterministic identifier for the current node
*/
package license

import (
	"bufio"
	"crypto/sha256"
	"fmt"
	"os"
	"strings"
)

// GenerateFingerprint creates a machine fingerprint by hashing:
// - /etc/machine-id
// - CPU model from /proc/cpuinfo
// - Total memory from /proc/meminfo
// Returns a 32-character hex-encoded string
func GenerateFingerprint() (string, error) {
	machineID, err := readMachineID()
	if err != nil {
		return "", fmt.Errorf("failed to read machine-id: %w", err)
	}

	cpuModel, err := readCPUModel()
	if err != nil {
		// CPU model is best-effort
		cpuModel = "unknown"
	}

	totalMem, err := readTotalMemory()
	if err != nil {
		// Memory is best-effort
		totalMem = "unknown"
	}

	// Combine and hash
	data := fmt.Sprintf("volt-fp:%s:%s:%s", machineID, cpuModel, totalMem)
	hash := sha256.Sum256([]byte(data))

	// Return first 32 hex chars (16 bytes)
	return fmt.Sprintf("%x", hash[:16]), nil
}

// readMachineID reads /etc/machine-id
func readMachineID() (string, error) {
	data, err := os.ReadFile("/etc/machine-id")
	if err != nil {
		return "", err
	}
	return strings.TrimSpace(string(data)), nil
}

// readCPUModel reads the CPU model from /proc/cpuinfo
func readCPUModel() (string, error) {
	f, err := os.Open("/proc/cpuinfo")
	if err != nil {
		return "", err
	}
	defer f.Close()

	scanner := bufio.NewScanner(f)
	for scanner.Scan() {
		line := scanner.Text()
		if strings.HasPrefix(line, "model name") {
			parts := strings.SplitN(line, ":", 2)
			if len(parts) == 2 {
				return strings.TrimSpace(parts[1]), nil
			}
		}
	}
	return "", fmt.Errorf("model name not found in /proc/cpuinfo")
}

// readTotalMemory reads total memory from /proc/meminfo
func readTotalMemory() (string, error) {
	f, err := os.Open("/proc/meminfo")
	if err != nil {
		return "", err
	}
	defer f.Close()

	scanner := bufio.NewScanner(f)
	for scanner.Scan() {
		line := scanner.Text()
		if strings.HasPrefix(line, "MemTotal:") {
			fields := strings.Fields(line)
			if len(fields) >= 2 {
				return fields[1], nil
			}
		}
	}
	return "", fmt.Errorf("MemTotal not found in /proc/meminfo")
}