//go:build linux

package main

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

// spec:26174-planctl-context-tokens/R1.2+R6.3+D§3.3
// ppidOf returns the parent PID of pid by reading /proc/<pid>/status.
// Returns 0 on error.
func ppidOf(pid int) int {
	data, err := os.ReadFile(fmt.Sprintf("/proc/%d/status", pid))
	if err != nil {
		return 0
	}
	for _, line := range strings.Split(string(data), "\n") {
		if strings.HasPrefix(line, "PPid:") {
			s := strings.TrimSpace(strings.TrimPrefix(line, "PPid:"))
			n, err := strconv.Atoi(s)
			if err != nil {
				return 0
			}
			return n
		}
	}
	return 0
}

// spec:26174-planctl-context-tokens/R6.3+D§3.3
// processAlive reports whether a process with pid exists.
func processAlive(pid int) bool {
	if pid <= 0 {
		return false
	}
	return syscall.Kill(pid, 0) == nil
}

// spec:26174-planctl-context-tokens/R6.3+D§3.3+D§4.1
// processStartTimeSec returns the process start time as raw clock ticks since boot,
// read from /proc/<pid>/stat field 22 (starttime). The hook writes the same units
// (clock ticks) on Linux per §5.5/§4.1, so comparison units match.
//
// The name retains "Sec" for API symmetry with the macOS implementation (which
// returns epoch seconds). Within a platform both sides match; cross-platform
// comparison never happens.
//
// /proc/<pid>/stat is a single line: "pid (comm) state ppid ... starttime ...".
// `comm` can contain spaces and parens. We find the LAST ')' and tokenize the
// remainder so comm noise can't shift field indices.
func processStartTimeSec(pid int) (int64, error) {
	data, err := os.ReadFile(fmt.Sprintf("/proc/%d/stat", pid))
	if err != nil {
		return 0, err
	}
	return parseStatStartTime(string(data))
}