package proc

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

// ClockTicks returns the system clock ticks per second (SC_CLK_TCK)
// On most Linux systems this is 100, but we read it from the system
const DefaultClockTicks = 100

// SystemInfo holds system-wide information from /proc
type SystemInfo struct {
	MemTotal     uint64 // Total physical memory in bytes
	MemFree      uint64 // Free memory in bytes
	MemAvailable uint64 // Available memory in bytes
	Buffers      uint64 // Buffer memory in bytes
	Cached       uint64 // Cached memory in bytes
	CPUCount     int    // Number of CPUs
}

// DiscoverPIDs scans /proc and returns a list of all process PIDs
func DiscoverPIDs(procPath string) ([]int, error) {
	entries, err := os.ReadDir(procPath)
	if err != nil {
		return nil, fmt.Errorf("reading proc directory: %w", err)
	}

	var pids []int
	for _, entry := range entries {
		if !entry.IsDir() {
			continue
		}

		pid, err := strconv.Atoi(entry.Name())
		if err != nil {
			// Not a PID directory
			continue
		}

		pids = append(pids, pid)
	}

	return pids, nil
}

// ReadSystemInfo reads system-wide memory information from /proc/meminfo
func ReadSystemInfo(procPath string) (*SystemInfo, error) {
	info := &SystemInfo{}

	// Read /proc/meminfo
	data, err := os.ReadFile(fmt.Sprintf("%s/meminfo", procPath))
	if err != nil {
		return nil, fmt.Errorf("reading meminfo: %w", err)
	}

	lines := strings.Split(string(data), "\n")
	for _, line := range lines {
		parts := strings.SplitN(line, ":", 2)
		if len(parts) != 2 {
			continue
		}

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

		switch key {
		case "MemTotal":
			info.MemTotal = value
		case "MemFree":
			info.MemFree = value
		case "MemAvailable":
			info.MemAvailable = value
		case "Buffers":
			info.Buffers = value
		case "Cached":
			info.Cached = value
		}
	}

	// Count CPUs from /proc/cpuinfo
	cpuData, err := os.ReadFile(fmt.Sprintf("%s/cpuinfo", procPath))
	if err == nil {
		for _, line := range strings.Split(string(cpuData), "\n") {
			if strings.HasPrefix(line, "processor") {
				info.CPUCount++
			}
		}
	}

	if info.CPUCount == 0 {
		info.CPUCount = 1 // Default to 1 CPU
	}

	return info, nil
}

// ReadSystemCPU reads the total CPU time from /proc/stat
// Returns: user, nice, system, idle, iowait, irq, softirq times (in clock ticks)
func ReadSystemCPU(procPath string) (user, nice, system, idle, iowait, irq, softirq uint64, err error) {
	data, err := os.ReadFile(fmt.Sprintf("%s/stat", procPath))
	if err != nil {
		return 0, 0, 0, 0, 0, 0, 0, fmt.Errorf("reading /proc/stat: %w", err)
	}

	lines := strings.Split(string(data), "\n")
	for _, line := range lines {
		if strings.HasPrefix(line, "cpu ") {
			fields := strings.Fields(line)
			if len(fields) < 8 {
				return 0, 0, 0, 0, 0, 0, 0, fmt.Errorf("invalid cpu line format")
			}

			user, _ = strconv.ParseUint(fields[1], 10, 64)
			nice, _ = strconv.ParseUint(fields[2], 10, 64)
			system, _ = strconv.ParseUint(fields[3], 10, 64)
			idle, _ = strconv.ParseUint(fields[4], 10, 64)
			iowait, _ = strconv.ParseUint(fields[5], 10, 64)
			irq, _ = strconv.ParseUint(fields[6], 10, 64)
			softirq, _ = strconv.ParseUint(fields[7], 10, 64)

			return user, nice, system, idle, iowait, irq, softirq, nil
		}
	}

	return 0, 0, 0, 0, 0, 0, 0, fmt.Errorf("cpu line not found in /proc/stat")
}

// ProcessInfo combines stat and status information for a process
type ProcessInfo struct {
	Stat   *ProcStat
	Status *ProcStatus
}

// ReadProcess reads both stat and status for a single process
func ReadProcess(procPath string, pid int) (*ProcessInfo, error) {
	stat, err := ReadStat(procPath, pid)
	if err != nil {
		return nil, err
	}

	status, err := ReadStatus(procPath, pid)
	if err != nil {
		return nil, err
	}

	return &ProcessInfo{
		Stat:   stat,
		Status: status,
	}, nil
}

// ReadAllProcesses reads information for all processes
// It skips processes that disappear during collection (race-safe)
func ReadAllProcesses(procPath string) ([]*ProcessInfo, error) {
	pids, err := DiscoverPIDs(procPath)
	if err != nil {
		return nil, err
	}

	var processes []*ProcessInfo
	for _, pid := range pids {
		info, err := ReadProcess(procPath, pid)
		if err != nil {
			// Process may have exited, skip it
			continue
		}
		processes = append(processes, info)
	}

	return processes, nil
}