package managementaccess

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

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

const maxMessageBytes = 16 * 1024

type socketRequest struct {
	Action   string                          `json:"action"`
	Settings domain.ManagementAccessSettings `json:"settings"`
}

type socketResponse struct {
	OK    bool   `json:"ok"`
	Code  string `json:"code,omitempty"`
	Error string `json:"error,omitempty"`
}

type SocketServer struct{ Controller Controller }

func (s SocketServer) Serve(listener net.Listener) error {
	if s.Controller == nil {
		return errors.New("management access 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 SocketServer) handle(connection net.Conn) {
	defer connection.Close()
	_ = connection.SetDeadline(time.Now().Add(12 * time.Second))
	payload, err := bufio.NewReader(io.LimitReader(connection, maxMessageBytes+1)).ReadBytes('\n')
	if err != nil && !errors.Is(err, io.EOF) {
		s.respond(connection, socketResponse{Code: "validation_failed", Error: "invalid management access request"})
		return
	}
	if len(payload) == 0 || len(payload) > maxMessageBytes || payload[len(payload)-1] != '\n' {
		s.respond(connection, socketResponse{Code: "validation_failed", Error: "invalid management access request"})
		return
	}
	decoder := json.NewDecoder(bytes.NewReader(payload))
	decoder.DisallowUnknownFields()
	var request socketRequest
	if err := decoder.Decode(&request); err != nil {
		s.respond(connection, socketResponse{Code: "validation_failed", Error: "invalid management access request"})
		return
	}
	var extra any
	if err := decoder.Decode(&extra); !errors.Is(err, io.EOF) {
		s.respond(connection, socketResponse{Code: "validation_failed", Error: "management access request must contain one JSON value"})
		return
	}
	if request.Action != "apply" {
		s.respond(connection, socketResponse{Code: "validation_failed", Error: "management access action is not supported"})
		return
	}
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	if err := s.Controller.Apply(ctx, request.Settings); err != nil {
		code := "management_access_failed"
		if IsUnavailable(err) {
			code = "management_access_unavailable"
		}
		s.respond(connection, socketResponse{Code: code, Error: err.Error()})
		return
	}
	s.respond(connection, socketResponse{OK: true})
}

func (SocketServer) respond(connection net.Conn, response socketResponse) {
	_ = json.NewEncoder(connection).Encode(response)
}

type SocketClient struct {
	path    string
	timeout time.Duration
}

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

func (c *SocketClient) Apply(ctx context.Context, settings domain.ManagementAccessSettings) error {
	if err := Validate(settings); err != nil {
		return err
	}
	dialer := net.Dialer{Timeout: c.timeout}
	connection, err := dialer.DialContext(ctx, "unix", c.path)
	if err != nil {
		return &UnavailableError{Reason: "tera-accessd 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(socketRequest{Action: "apply", Settings: settings}); err != nil {
		return errors.New("management access request failed")
	}
	var response socketResponse
	if err := json.NewDecoder(io.LimitReader(connection, maxMessageBytes)).Decode(&response); err != nil {
		return &UnavailableError{Reason: "tera-accessd returned no response"}
	}
	if response.Error != "" {
		if response.Code == "management_access_unavailable" {
			return &UnavailableError{Reason: response.Error}
		}
		return fmt.Errorf("tera-accessd: %s", response.Error)
	}
	if !response.OK {
		return errors.New("tera-accessd rejected the request")
	}
	return nil
}