package systemcontrol

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

const DefaultSocketPath = "/run/tera-hwd/system-control.sock"

type request struct {
	Action string `json:"action"`
}

type response struct {
	State   string `json:"state,omitempty"`
	Pressed *bool  `json:"pressed,omitempty"`
	Code    string `json:"code,omitempty"`
	Error   string `json:"error,omitempty"`
}

type Server struct {
	Controller  Controller
	ResetButton ResetButtonReader
	RebootDelay time.Duration
	rebootOnce  sync.Once
}

func (s *Server) Serve(listener net.Listener) error {
	if s == nil || s.Controller == nil {
		return errors.New("system controller is required")
	}
	for {
		connection, err := listener.Accept()
		if err != nil {
			if errors.Is(err, net.ErrClosed) {
				return nil
			}
			continue
		}
		go s.handle(connection)
	}
}

func (s *Server) handle(connection net.Conn) {
	defer connection.Close()
	_ = connection.SetDeadline(time.Now().Add(5 * time.Second))
	payload, err := bufio.NewReader(io.LimitReader(connection, 4097)).ReadBytes('\n')
	if err != nil && !errors.Is(err, io.EOF) || len(payload) == 0 || len(payload) > 4096 || payload[len(payload)-1] != '\n' {
		s.write(connection, response{Code: "validation_failed", Error: "invalid system control request"})
		return
	}
	decoder := json.NewDecoder(bytes.NewReader(payload))
	decoder.DisallowUnknownFields()
	var command request
	if err := decoder.Decode(&command); err != nil {
		s.write(connection, response{Code: "validation_failed", Error: "invalid system control request"})
		return
	}
	var extra any
	if err := decoder.Decode(&extra); !errors.Is(err, io.EOF) {
		s.write(connection, response{Code: "validation_failed", Error: "system control request must contain one JSON value"})
		return
	}
	if command.Action == "reset_button_state" {
		if s.ResetButton == nil {
			s.write(connection, response{Code: "unavailable", Error: "reset button is not configured"})
			return
		}
		pressed, err := s.ResetButton.ResetButtonPressed(context.Background())
		if err != nil {
			s.write(connection, response{Code: "unavailable", Error: err.Error()})
			return
		}
		s.write(connection, response{State: "ready", Pressed: &pressed})
		return
	}
	if command.Action != "reboot" {
		s.write(connection, response{Code: "validation_failed", Error: "system control action is not supported"})
		return
	}
	delay := s.RebootDelay
	if delay <= 0 {
		delay = 2 * time.Second
	}
	s.write(connection, response{State: "scheduled"})
	s.rebootOnce.Do(func() {
		time.AfterFunc(delay, func() {
			if err := s.Controller.Reboot(context.Background()); err != nil {
				log.Printf("tera-hwd scheduled reboot failed: %v", err)
			}
		})
	})
}

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

type Client struct {
	path string
}

func NewClient(path string) *Client {
	if path == "" {
		path = DefaultSocketPath
	}
	return &Client{path: path}
}

func (c *Client) Reboot(ctx context.Context) error {
	result, err := c.request(ctx, "reboot")
	if err != nil {
		return err
	}
	if result.State != "scheduled" {
		return errors.New("system reboot was not scheduled")
	}
	return nil
}

func (c *Client) ResetButtonPressed(ctx context.Context) (bool, error) {
	result, err := c.request(ctx, "reset_button_state")
	if err != nil {
		return false, err
	}
	if result.State != "ready" || result.Pressed == nil {
		return false, errors.New("reset button state is unavailable")
	}
	return *result.Pressed, nil
}

func (c *Client) request(ctx context.Context, action string) (response, error) {
	dialer := net.Dialer{Timeout: 3 * time.Second}
	connection, err := dialer.DialContext(ctx, "unix", c.path)
	if err != nil {
		return response{}, errors.New("privileged system control is not reachable")
	}
	defer connection.Close()
	deadline := time.Now().Add(5 * time.Second)
	if value, ok := ctx.Deadline(); ok && value.Before(deadline) {
		deadline = value
	}
	_ = connection.SetDeadline(deadline)
	if err := json.NewEncoder(connection).Encode(request{Action: action}); err != nil {
		return response{}, errors.New("system control request could not be sent")
	}
	var result response
	if err := json.NewDecoder(io.LimitReader(connection, 4096)).Decode(&result); err != nil {
		return response{}, errors.New("privileged system control returned no response")
	}
	if result.Code != "" {
		if result.Error != "" {
			return response{}, errors.New(result.Error)
		}
		return response{}, errors.New("system control request failed")
	}
	return result, nil
}