package starlink

import (
	"context"
	"errors"
	"fmt"
	"net"
	"time"

	"google.golang.org/grpc"
	"google.golang.org/grpc/credentials/insecure"

	pb "git.eeqj.de/sneak/rtnetmon/internal/starlink/pb"
)

// errNoDishStatus is returned when the dish answers but the response
// carries no dish status.
var errNoDishStatus = errors.New("no dish status in response")

// Per-call deadlines so a silent dish never wedges the monitor loop.
const (
	probeTimeout  = 2 * time.Second
	statusTimeout = 3 * time.Second
)

// DialFunc opens a TCP connection to addr bound to a chosen interface. The
// monitor supplies one that binds the same way its TCP latency probes do,
// so the dish is reached over the physical (non-VPN) interface rather than
// a VPN tunnel that may hold the default route.
type DialFunc func(ctx context.Context, addr string) (net.Conn, error)

// GRPCClient is the real Client: it reaches a dish at Address over whatever
// interface dial binds to.
type GRPCClient struct {
	dial DialFunc
}

// NewClient returns a client that talks to a dish at Address, dialing with
// dial so the connection leaves the intended interface.
func NewClient(dial DialFunc) *GRPCClient {
	return &GRPCClient{dial: dial}
}

// Probe connects to the dish's endpoint and closes it. A successful TCP
// connect over the bound interface is the detection signal.
func (c *GRPCClient) Probe(ctx context.Context) bool {
	ctx, cancel := context.WithTimeout(ctx, probeTimeout)
	defer cancel()

	conn, err := c.dial(ctx, Address)
	if err != nil {
		return false
	}

	_ = conn.Close()

	return true
}

// Status calls the dish's get_status RPC and reduces the response to the
// fields rtnetmon shows.
func (c *GRPCClient) Status(ctx context.Context) (Status, error) {
	ctx, cancel := context.WithTimeout(ctx, statusTimeout)
	defer cancel()

	// passthrough:/// hands Address straight to our dialer, with no name
	// resolution, so the connection is made over the bound interface.
	conn, err := grpc.NewClient("passthrough:///"+Address,
		grpc.WithTransportCredentials(insecure.NewCredentials()),
		grpc.WithContextDialer(func(ctx context.Context, addr string) (net.Conn, error) {
			return c.dial(ctx, addr)
		}),
	)
	if err != nil {
		return Status{}, fmt.Errorf("starlink dial: %w", err)
	}
	defer func() { _ = conn.Close() }()

	resp, err := pb.NewDeviceClient(conn).Handle(ctx, &pb.Request{
		Request: &pb.Request_GetStatus{GetStatus: &pb.GetStatusRequest{}},
	})
	if err != nil {
		return Status{}, fmt.Errorf("starlink get_status: %w", err)
	}

	dish := resp.GetDishGetStatus()
	if dish == nil {
		return Status{}, errNoDishStatus
	}

	return statusFromDish(dish), nil
}

// statusFromDish reduces the dish's status message to a Status. The
// generated getters are nil-safe, so absent sub-messages read as zero.
func statusFromDish(d *pb.DishGetStatusResponse) Status {
	obstruction := float64(d.GetObstructionStats().GetFractionObstructed())
	//nolint:gosec // G115: dish uptime in seconds never approaches int64 max
	uptime := time.Duration(d.GetDeviceState().GetUptimeS()) * time.Second

	return Status{
		State:          d.GetState().String(),
		Uptime:         uptime,
		ObstructionPct: obstruction * percentScale,
		Alerts:         countAlerts(d.GetAlerts()),
		PopPingMs:      float64(d.GetPopPingLatencyMs()),
		PopPingDropPct: float64(d.GetPopPingDropRate()) * percentScale,
		DownlinkMbps:   float64(d.GetDownlinkThroughputBps()) / bitsPerMegabit,
		UplinkMbps:     float64(d.GetUplinkThroughputBps()) / bitsPerMegabit,
	}
}

// countAlerts counts the active dish alert flags.
func countAlerts(a *pb.DishAlerts) int {
	n := 0

	for _, on := range []bool{
		a.GetMotorsStuck(),
		a.GetThermalShutdown(),
		a.GetThermalThrottle(),
		a.GetUnexpectedLocation(),
	} {
		if on {
			n++
		}
	}

	return n
}