package main

import (
	"bytes"
	"fmt"
	"os"
	"strconv"
	"strings"
)

// readProcEnviron reads /proc/{pid}/environ (NUL-delimited KEY=VALUE pairs)
// and returns the environment as a map.
func readProcEnviron(procRoot string, pid int32) (map[string]string, error) {
	path := fmt.Sprintf("%s/%d/environ", procRoot, pid)
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, err
	}

	env := make(map[string]string)
	for _, entry := range bytes.Split(data, []byte{0}) {
		if len(entry) == 0 {
			continue
		}
		parts := bytes.SplitN(entry, []byte("="), 2)
		if len(parts) == 2 {
			env[string(parts[0])] = string(parts[1])
		}
	}
	return env, nil
}

// getParentPid reads /proc/{pid}/status and extracts the PPid field.
// Returns 0 if pid 1 (init) is reached or the field cannot be parsed.
func getParentPid(procRoot string, pid int32) (int32, error) {
	path := fmt.Sprintf("%s/%d/status", procRoot, pid)
	data, err := os.ReadFile(path)
	if err != nil {
		return 0, err
	}

	for _, line := range strings.Split(string(data), "\n") {
		if strings.HasPrefix(line, "PPid:") {
			fields := strings.Fields(line)
			if len(fields) >= 2 {
				ppid, err := strconv.ParseInt(fields[1], 10, 32)
				if err != nil {
					return 0, fmt.Errorf("parse PPid in %s: %w", path, err)
				}
				return int32(ppid), nil
			}
		}
	}
	return 0, fmt.Errorf("PPid not found in %s", path)
}