// Package greenledsocket exposes the narrow local tera-hwd LED control
// protocol. It carries only gpio-leds state, force, and bounded pulse actions.
package greenledsocket

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

	"tera-clone/services/tera-api/internal/hardware/greenled"
)

const DefaultSocketPath = "/run/tera-hwd/green-leds.sock"

const maxRequestBytes = 4096

type request struct {
	Action  string `json:"action"`
	Channel string `json:"channel,omitempty"`
	Force   *bool  `json:"force,omitempty"`
	DwellMS int    `json:"dwell_ms,omitempty"`
}

type response struct {
	States []greenled.State `json:"states,omitempty"`
	State  *greenled.State  `json:"state,omitempty"`
	Code   string           `json:"code,omitempty"`
	Error  string           `json:"error,omitempty"`
}

// Server delegates all hardware operations to a Controller. The caller owns
// listener lifecycle; this keeps signal and systemd supervision outside the
// protocol library.
type Server struct {
	Controller greenled.Controller
}

func (s Server) Serve(listener net.Listener) error {
	if s.Controller == nil {
		return errors.New("green LED 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.handleConnection(connection)
	}
}

func (s Server) handleConnection(connection net.Conn) {
	defer connection.Close()
	_ = connection.SetDeadline(time.Now().Add(10 * time.Second))
	payload, err := bufio.NewReader(io.LimitReader(connection, maxRequestBytes+1)).ReadBytes('\n')
	if err != nil && !errors.Is(err, io.EOF) {
		s.writeResponse(connection, response{Code: "validation_failed", Error: "invalid hardware control request"})
		return
	}
	if len(payload) == 0 || len(payload) > maxRequestBytes || payload[len(payload)-1] != '\n' {
		s.writeResponse(connection, response{Code: "validation_failed", Error: "invalid hardware control request"})
		return
	}
	decoder := json.NewDecoder(bytes.NewReader(payload))
	decoder.DisallowUnknownFields()
	var command request
	if err := decoder.Decode(&command); err != nil {
		s.writeResponse(connection, response{Code: "validation_failed", Error: "invalid hardware control request"})
		return
	}
	var extra any
	if err := decoder.Decode(&extra); !errors.Is(err, io.EOF) {
		s.writeResponse(connection, response{Code: "validation_failed", Error: "hardware control request must contain a single JSON value"})
		return
	}

	ctx, cancel := context.WithTimeout(context.Background(), 8*time.Second)
	defer cancel()
	switch command.Action {
	case "states":
		states, err := s.Controller.States(ctx)
		if err != nil {
			s.writeError(connection, err)
			return
		}
		s.writeResponse(connection, response{States: states})
	case "set_force":
		if command.Force == nil {
			s.writeResponse(connection, response{Code: "validation_failed", Error: "force must be provided"})
			return
		}
		state, err := s.Controller.SetForce(ctx, command.Channel, *command.Force)
		if err != nil {
			s.writeError(connection, err)
			return
		}
		s.writeResponse(connection, response{State: &state})
	case "pulse":
		state, err := s.Controller.Pulse(ctx, command.Channel, time.Duration(command.DwellMS)*time.Millisecond)
		if err != nil {
			s.writeError(connection, err)
			return
		}
		s.writeResponse(connection, response{State: &state})
	default:
		s.writeResponse(connection, response{Code: "validation_failed", Error: "hardware control action is not supported"})
	}
}

func (s Server) writeError(connection net.Conn, err error) {
	code := "hardware_failed"
	if greenled.IsUnavailable(err) {
		code = "hardware_unavailable"
	}
	s.writeResponse(connection, response{Code: code, Error: err.Error()})
}

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

// Client implements greenled.Controller for the unprivileged tera-api
// process. Unix-socket file permissions are the local process boundary.
type Client struct {
	path    string
	timeout time.Duration
}

func NewClient(path string) *Client {
	if path == "" {
		path = DefaultSocketPath
	}
	return &Client{path: path, timeout: 10 * time.Second}
}

func (c *Client) States(ctx context.Context) ([]greenled.State, error) {
	result, err := c.exchange(ctx, request{Action: "states"})
	if err != nil {
		return nil, err
	}
	return result.States, nil
}

func (c *Client) SetForce(ctx context.Context, channel string, force bool) (greenled.State, error) {
	result, err := c.exchange(ctx, request{Action: "set_force", Channel: channel, Force: &force})
	if err != nil {
		return greenled.State{}, err
	}
	if result.State == nil {
		return greenled.State{}, errors.New("green LED hardware helper returned no state")
	}
	return *result.State, nil
}

func (c *Client) Pulse(ctx context.Context, channel string, dwell time.Duration) (greenled.State, error) {
	result, err := c.exchange(ctx, request{Action: "pulse", Channel: channel, DwellMS: int(dwell / time.Millisecond)})
	if err != nil {
		return greenled.State{}, err
	}
	if result.State == nil {
		return greenled.State{}, errors.New("green LED hardware helper returned no state")
	}
	return *result.State, nil
}

func (c *Client) exchange(ctx context.Context, command request) (response, error) {
	dialer := net.Dialer{Timeout: c.timeout}
	connection, err := dialer.DialContext(ctx, "unix", c.path)
	if err != nil {
		return response{}, &greenled.UnavailableError{Reason: "tera-hwd 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 response{}, fmt.Errorf("green LED hardware request failed")
	}
	var result response
	if err := json.NewDecoder(io.LimitReader(connection, 65536)).Decode(&result); err != nil {
		return response{}, &greenled.UnavailableError{Reason: "tera-hwd returned no response"}
	}
	if result.Error != "" {
		if result.Code == "hardware_unavailable" {
			return response{}, &greenled.UnavailableError{Reason: result.Error}
		}
		return response{}, errors.New(result.Error)
	}
	return result, nil
}