// Package alarmsocket exposes the narrow group-restricted tera-alarmd protocol.
package alarmsocket

import (
	"bufio"
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"io"
	"net"
	"time"

	"tera-clone/services/tera-api/internal/alarmdelivery"
)

const DefaultSocketPath = "/run/tera-alarmd/alarm-delivery.sock"

type command struct {
	Action     string                `json:"action"`
	DeliveryID string                `json:"delivery_id,omitempty"`
	Request    alarmdelivery.Request `json:"request,omitempty"`
}

type response struct {
	Result *alarmdelivery.Result `json:"result,omitempty"`
	Code   string                `json:"code,omitempty"`
	Error  string                `json:"error,omitempty"`
}

type Server struct{ Controller alarmdelivery.Controller }

func (s Server) Serve(listener net.Listener) error {
	if s.Controller == nil {
		return errors.New("alarm delivery controller is required")
	}
	for {
		connection, err := listener.Accept()
		if err != nil {
			if errors.Is(err, net.ErrClosed) {
				return nil
			}
			if temporary, ok := err.(interface{ Temporary() bool }); ok && temporary.Temporary() {
				continue
			}
			return err
		}
		go s.handle(connection)
	}
}

func (s Server) handle(connection net.Conn) {
	defer connection.Close()
	_ = connection.SetDeadline(time.Now().Add(12 * time.Second))
	payload, err := bufio.NewReader(io.LimitReader(connection, 32769)).ReadBytes('\n')
	if err != nil && !errors.Is(err, io.EOF) {
		s.write(connection, response{Code: "validation_failed", Error: "invalid alarm delivery request"})
		return
	}
	if len(payload) == 0 || len(payload) > 32768 || payload[len(payload)-1] != '\n' {
		s.write(connection, response{Code: "validation_failed", Error: "invalid alarm delivery request"})
		return
	}
	decoder := json.NewDecoder(bytes.NewReader(payload))
	decoder.DisallowUnknownFields()
	var value command
	if err := decoder.Decode(&value); err != nil {
		s.write(connection, response{Code: "validation_failed", Error: "invalid alarm delivery request"})
		return
	}
	var extra any
	if err := decoder.Decode(&extra); !errors.Is(err, io.EOF) {
		s.write(connection, response{Code: "validation_failed", Error: "alarm delivery request must contain one JSON value"})
		return
	}
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	var result alarmdelivery.Result
	switch value.Action {
	case "deliver":
		result, err = s.Controller.Deliver(ctx, value.Request)
	case "status":
		result, err = s.Controller.Status(ctx, value.DeliveryID)
	default:
		s.write(connection, response{Code: "validation_failed", Error: "alarm delivery action is not supported"})
		return
	}
	if err != nil {
		code := "delivery_failed"
		if alarmdelivery.IsUnavailable(err) {
			code = "delivery_unavailable"
		}
		s.write(connection, response{Code: code, Error: err.Error()})
		return
	}
	s.write(connection, response{Result: &result})
}

func (Server) write(connection net.Conn, value response) {
	_ = json.NewEncoder(connection).Encode(value)
}

type Client struct {
	path    string
	timeout time.Duration
}

func NewClient(path string) *Client {
	if path == "" {
		path = DefaultSocketPath
	}
	return &Client{path: path, timeout: 12 * time.Second}
}

func (c *Client) Deliver(ctx context.Context, request alarmdelivery.Request) (alarmdelivery.Result, error) {
	return c.call(ctx, command{Action: "deliver", Request: request})
}

func (c *Client) Status(ctx context.Context, deliveryID string) (alarmdelivery.Result, error) {
	return c.call(ctx, command{Action: "status", DeliveryID: deliveryID})
}

func (c *Client) call(ctx context.Context, command command) (alarmdelivery.Result, error) {
	dialer := net.Dialer{Timeout: c.timeout}
	connection, err := dialer.DialContext(ctx, "unix", c.path)
	if err != nil {
		return alarmdelivery.Result{}, &alarmdelivery.UnavailableError{Reason: "tera-alarmd is not reachable"}
	}
	defer connection.Close()
	deadline := time.Now().Add(c.timeout)
	if contextDeadline, ok := ctx.Deadline(); ok && contextDeadline.Before(deadline) {
		deadline = contextDeadline
	}
	_ = connection.SetDeadline(deadline)
	if err := json.NewEncoder(connection).Encode(command); err != nil {
		return alarmdelivery.Result{}, &alarmdelivery.UnavailableError{Reason: "alarm delivery request failed"}
	}
	var value response
	if err := json.NewDecoder(io.LimitReader(connection, 65536)).Decode(&value); err != nil {
		return alarmdelivery.Result{}, &alarmdelivery.UnavailableError{Reason: "tera-alarmd returned no response"}
	}
	if value.Error != "" {
		if value.Code == "delivery_unavailable" {
			return alarmdelivery.Result{}, &alarmdelivery.UnavailableError{Reason: value.Error}
		}
		return alarmdelivery.Result{}, errors.New(value.Error)
	}
	if value.Result == nil {
		return alarmdelivery.Result{}, errors.New("tera-alarmd returned no delivery result")
	}
	return *value.Result, nil
}