package host

import (
	"bufio"
	"context"
	"os"
	"path/filepath"
	"strings"
	"time"

	"tower/internal/collectors"
	"tower/internal/model"
)

// NetCollector checks for missing default route while at least one non-loopback
// interface is up.
//
// Rule (PLAN.md):
//   - P1 if no default route AND any non-loopback interface is UP.
//
// Discovery:
//   - Default route from /proc/net/route
//   - Interface UP from /sys/class/net/*/operstate
//
// NOTE: Linux-specific.
type NetCollector struct {
	interval time.Duration

	readFile func(string) ([]byte, error)
	glob     func(string) ([]string, error)
}

func NewNetCollector() *NetCollector {
	return &NetCollector{
		interval: 5 * time.Second,
		readFile: os.ReadFile,
		glob:     filepath.Glob,
	}
}

func (c *NetCollector) Name() string { return "host:net" }

func (c *NetCollector) Interval() time.Duration {
	if c.interval <= 0 {
		return 5 * time.Second
	}
	return c.interval
}

func (c *NetCollector) Collect(ctx context.Context) ([]model.Issue, collectors.Status, error) {
	if err := ctx.Err(); err != nil {
		return nil, collectors.Status{Health: collectors.HealthError, Message: "canceled"}, err
	}

	routeBytes, err := c.readFile("/proc/net/route")
	if err != nil {
		return nil, collectors.Status{Health: collectors.HealthError, Message: "failed reading /proc/net/route"}, err
	}

	hasDefault := hasDefaultRoute(string(routeBytes))

	paths, err := c.glob("/sys/class/net/*/operstate")
	if err != nil {
		return nil, collectors.Status{Health: collectors.HealthError, Message: "failed listing /sys/class/net"}, err
	}
	upIfaces := make([]string, 0, 2)
	for _, p := range paths {
		if err := ctx.Err(); err != nil {
			return nil, collectors.Status{Health: collectors.HealthError, Message: "canceled"}, err
		}
		b, err := c.readFile(p)
		if err != nil {
			continue
		}
		iface := filepath.Base(filepath.Dir(p))
		if iface == "lo" {
			continue
		}
		state := strings.TrimSpace(string(b))
		if isIfaceUp(state) {
			upIfaces = append(upIfaces, iface)
		}
	}

	if hasDefault || len(upIfaces) == 0 {
		return nil, collectors.OKStatus(), nil
	}

	iss := model.Issue{
		ID:       "host:net:default-route-missing",
		Category: model.CategoryNetwork,
		Priority: model.PriorityP1,
		Title:    "No default route",
		Details:  "At least one network interface is up, but no default route is present.",
		Evidence: map[string]string{
			"up_ifaces": strings.Join(upIfaces, ","),
		},
		SuggestedFix: "Check routing and link state:\n  ip route\n  ip link\n  nmcli dev status\nIf on Wi-Fi, reconnect; if on VPN, verify tunnel routes.",
	}
	return []model.Issue{iss}, collectors.OKStatus(), nil
}

func hasDefaultRoute(procNetRoute string) bool {
	// /proc/net/route header:
	// Iface Destination Gateway Flags RefCnt Use Metric Mask MTU Window IRTT
	// Default route has Destination == 00000000.
	s := bufio.NewScanner(strings.NewReader(procNetRoute))
	first := true
	for s.Scan() {
		line := strings.TrimSpace(s.Text())
		if line == "" {
			continue
		}
		if first {
			first = false
			// skip header if present
			if strings.HasPrefix(line, "Iface") {
				continue
			}
		}
		fields := strings.Fields(line)
		if len(fields) < 2 {
			continue
		}
		if fields[1] == "00000000" {
			return true
		}
	}
	return false
}

func isIfaceUp(operstate string) bool {
	// Linux operstate values include: up, down, unknown, dormant, lowerlayerdown.
	s := strings.ToLower(strings.TrimSpace(operstate))
	return s == "up" || s == "unknown"
}

var _ collectors.Collector = (*NetCollector)(nil)