package proc

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

// ProcStatus holds memory-related information from /proc/[pid]/status
type ProcStatus struct {
	PID      int
	Name     string // Process name
	VmSize   uint64 // Virtual memory size in bytes
	VmRSS    uint64 // Resident Set Size in bytes (actual RAM used)
	VmPeak   uint64 // Peak virtual memory size in bytes
	VmData   uint64 // Data segment size in bytes
	VmStk    uint64 // Stack size in bytes
	VmExe    uint64 // Text (code) size in bytes
	VmLib    uint64 // Shared library code size in bytes
	RssAnon  uint64 // Anonymous RSS in bytes
	RssFile  uint64 // File-backed RSS in bytes
	RssShmem uint64 // Shared memory RSS in bytes
	Threads  int    // Number of threads
	UID      int    // Real user ID
	GID      int    // Real group ID
}

// ReadStatus reads and parses /proc/[pid]/status for the given PID
func ReadStatus(procPath string, pid int) (*ProcStatus, error) {
	path := fmt.Sprintf("%s/%d/status", procPath, pid)
	file, err := os.Open(path)
	if err != nil {
		return nil, fmt.Errorf("opening status file: %w", err)
	}
	defer func() { _ = file.Close() }()

	return parseStatus(pid, file)
}

// parseStatus parses the content of /proc/[pid]/status
func parseStatus(pid int, file *os.File) (*ProcStatus, error) {
	status := &ProcStatus{PID: pid}
	scanner := bufio.NewScanner(file)

	for scanner.Scan() {
		line := scanner.Text()
		parts := strings.SplitN(line, ":", 2)
		if len(parts) != 2 {
			continue
		}

		key := strings.TrimSpace(parts[0])
		value := strings.TrimSpace(parts[1])

		switch key {
		case "Name":
			status.Name = value
		case "VmSize":
			status.VmSize = parseMemoryValue(value)
		case "VmRSS":
			status.VmRSS = parseMemoryValue(value)
		case "VmPeak":
			status.VmPeak = parseMemoryValue(value)
		case "VmData":
			status.VmData = parseMemoryValue(value)
		case "VmStk":
			status.VmStk = parseMemoryValue(value)
		case "VmExe":
			status.VmExe = parseMemoryValue(value)
		case "VmLib":
			status.VmLib = parseMemoryValue(value)
		case "RssAnon":
			status.RssAnon = parseMemoryValue(value)
		case "RssFile":
			status.RssFile = parseMemoryValue(value)
		case "RssShmem":
			status.RssShmem = parseMemoryValue(value)
		case "Threads":
			if n, err := strconv.Atoi(value); err == nil {
				status.Threads = n
			}
		case "Uid":
			// Format: "Uid: real effective saved filesystem"
			fields := strings.Fields(value)
			if len(fields) > 0 {
				if uid, err := strconv.Atoi(fields[0]); err == nil {
					status.UID = uid
				}
			}
		case "Gid":
			// Format: "Gid: real effective saved filesystem"
			fields := strings.Fields(value)
			if len(fields) > 0 {
				if gid, err := strconv.Atoi(fields[0]); err == nil {
					status.GID = gid
				}
			}
		}
	}

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

	return status, nil
}

// parseMemoryValue parses memory values from /proc/[pid]/status
// Format is typically "1234 kB"
func parseMemoryValue(value string) uint64 {
	fields := strings.Fields(value)
	if len(fields) == 0 {
		return 0
	}

	num, err := strconv.ParseUint(fields[0], 10, 64)
	if err != nil {
		return 0
	}

	// Convert to bytes if unit is specified
	if len(fields) > 1 {
		unit := strings.ToLower(fields[1])
		switch unit {
		case "kb":
			num *= 1024
		case "mb":
			num *= 1024 * 1024
		case "gb":
			num *= 1024 * 1024 * 1024
		}
	}

	return num
}

// TotalRSS returns the total RSS (RssAnon + RssFile + RssShmem)
// Falls back to VmRSS if the detailed fields are not available
func (s *ProcStatus) TotalRSS() uint64 {
	total := s.RssAnon + s.RssFile + s.RssShmem
	if total == 0 {
		return s.VmRSS
	}
	return total
}