// ABOUTME: Reads cgroup information from /proc/[pid]/cgroup.
// ABOUTME: Supports both cgroup v1 and v2 formats.
package proc

import (
	"bufio"
	"fmt"
	"os"
	"strings"
)

// CgroupInfo holds cgroup information for a process
type CgroupInfo struct {
	Path string // The cgroup path (unified for v2, or from memory controller for v1)
}

// ReadCgroup reads /proc/[pid]/cgroup and extracts the cgroup path
func ReadCgroup(procPath string, pid int) (*CgroupInfo, error) {
	path := fmt.Sprintf("%s/%d/cgroup", procPath, pid)

	file, err := os.Open(path)
	if err != nil {
		return nil, fmt.Errorf("opening cgroup file: %w", err)
	}
	defer func() { _ = file.Close() }()

	var cgroupPath string
	scanner := bufio.NewScanner(file)

	for scanner.Scan() {
		line := scanner.Text()

		// Try cgroup v2 first (unified hierarchy)
		// Format: 0::/path
		if path, found := strings.CutPrefix(line, "0::"); found {
			cgroupPath = path
			break
		}

		// Fall back to cgroup v1 - look for memory controller
		// Format: X:memory:/path or X:memory,other:/path
		parts := strings.SplitN(line, ":", 3)
		if len(parts) == 3 {
			controllers := parts[1]
			if strings.Contains(controllers, "memory") {
				cgroupPath = parts[2]
				// Don't break - prefer v2 if found later
			}
		}
	}

	if err := scanner.Err(); err != nil {
		return nil, fmt.Errorf("scanning cgroup file: %w", err)
	}

	return &CgroupInfo{
		Path: cgroupPath,
	}, nil
}