// Package daemonserver accepts local CLI requests over the frozen Unix Socket.
package daemonserver

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"net"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"yms-daemon/internal/backendupdate"
	"yms-daemon/internal/daemonapi"
	"yms-daemon/internal/transaction"
)

const maximumRequestBytes = 1 << 20

type backendUpdater interface {
	UpdateRepack(context.Context, string, backendupdate.ProgressReporter) (transaction.Transaction, error)
	UpdateNativeJAR(context.Context, string, backendupdate.ProgressReporter) (transaction.Transaction, error)
	UpdateContainerImage(context.Context, string, backendupdate.ProgressReporter) (transaction.Transaction, error)
	Restart(context.Context, backendupdate.ProgressReporter) (transaction.Transaction, error)
}

// Server owns the local Unix Socket and dispatches requests to the transaction orchestrator.
type Server struct {
	socketPath string
	updater    backendUpdater
	logger     *slog.Logger
}

func New(socketPath string, updater backendUpdater, logger *slog.Logger) (*Server, error) {
	if !filepath.IsAbs(socketPath) || filepath.Clean(socketPath) != socketPath {
		return nil, errors.New("daemon Unix Socket path must be a clean absolute path")
	}
	if updater == nil {
		return nil, errors.New("backend updater is required")
	}
	if logger == nil {
		logger = slog.Default()
	}
	return &Server{socketPath: socketPath, updater: updater, logger: logger}, nil
}

// Serve listens until ctx is canceled. Each accepted request owns its response connection.
func (s *Server) Serve(ctx context.Context) error {
	if err := prepareSocketPath(s.socketPath); err != nil {
		return err
	}
	listener, err := net.Listen("unix", s.socketPath)
	if err != nil {
		return fmt.Errorf("listen on daemon Unix Socket %s: %w", s.socketPath, err)
	}
	if err := os.Chmod(s.socketPath, 0o600); err != nil {
		_ = listener.Close()
		return fmt.Errorf("set daemon Unix Socket permissions: %w", err)
	}
	defer func() {
		_ = listener.Close()
		_ = os.Remove(s.socketPath)
	}()

	s.logger.InfoContext(ctx, "daemon server listening", "socket", s.socketPath)
	var connections sync.WaitGroup
	defer connections.Wait()
	go func() {
		<-ctx.Done()
		_ = listener.Close()
	}()
	for {
		connection, err := listener.Accept()
		if err != nil {
			if ctx.Err() != nil {
				return nil
			}
			return fmt.Errorf("accept daemon Unix Socket connection: %w", err)
		}
		connections.Add(1)
		go func() {
			defer connections.Done()
			s.handle(ctx, connection)
		}()
	}
}

func (s *Server) handle(ctx context.Context, connection net.Conn) {
	defer connection.Close()
	_ = connection.SetReadDeadline(time.Now().Add(10 * time.Second))
	request, err := decodeRequest(connection)
	_ = connection.SetReadDeadline(time.Time{})
	if err != nil {
		_ = s.writeResponse(connection, daemonapi.Response{Kind: daemonapi.ResponseResult, Error: err.Error()})
		return
	}
	if request.Service != "backend" {
		_ = s.writeResponse(connection, daemonapi.Response{Kind: daemonapi.ResponseResult, Error: "service must be backend"})
		return
	}
	progressWritable := true
	report := func(progress backendupdate.Progress) {
		if !progressWritable {
			return
		}
		err := s.writeResponse(connection, daemonapi.Response{
			Kind:          daemonapi.ResponseProgress,
			TransactionID: progress.TransactionID,
			State:         string(progress.State),
			Message:       progress.Message,
		})
		if err != nil {
			progressWritable = false
			s.logger.WarnContext(ctx, "write daemon update progress", "error", err)
		}
	}
	var record transaction.Transaction
	var updateErr error
	switch request.Operation {
	case daemonapi.OperationUpdate:
		switch request.InputType {
		case daemonapi.InputTypeRepackZIP:
			if request.File == "" || request.ImageReference != "" {
				_ = s.writeResponse(connection, daemonapi.Response{Kind: daemonapi.ResponseResult, Error: "repack-zip requires file and does not accept imageReference"})
				return
			}
			record, updateErr = s.updater.UpdateRepack(ctx, request.File, report)
		case daemonapi.InputTypeNativeJAR:
			if request.File == "" || request.ImageReference != "" {
				_ = s.writeResponse(connection, daemonapi.Response{Kind: daemonapi.ResponseResult, Error: "native-jar requires file and does not accept imageReference"})
				return
			}
			record, updateErr = s.updater.UpdateNativeJAR(ctx, request.File, report)
		case daemonapi.InputTypeContainerImage:
			if request.File != "" || request.ImageReference == "" {
				_ = s.writeResponse(connection, daemonapi.Response{Kind: daemonapi.ResponseResult, Error: "container-image requires imageReference and does not accept file"})
				return
			}
			record, updateErr = s.updater.UpdateContainerImage(ctx, request.ImageReference, report)
		default:
			_ = s.writeResponse(connection, daemonapi.Response{Kind: daemonapi.ResponseResult, Error: "inputType must be repack-zip, native-jar, or container-image"})
			return
		}
	case daemonapi.OperationRestart:
		if request.InputType != "" || request.File != "" || request.ImageReference != "" {
			_ = s.writeResponse(connection, daemonapi.Response{Kind: daemonapi.ResponseResult, Error: "restart does not accept inputType or file"})
			return
		}
		record, updateErr = s.updater.Restart(ctx, report)
	default:
		_ = s.writeResponse(connection, daemonapi.Response{Kind: daemonapi.ResponseResult, Error: "operation must be update or restart"})
		return
	}
	response := daemonapi.Response{Kind: daemonapi.ResponseResult, TransactionID: record.ID, State: string(record.State)}
	if updateErr != nil {
		response.Error = updateErr.Error()
		s.logger.ErrorContext(ctx, "backend operation failed", "operation", request.Operation, "transaction_id", record.ID, "state", record.State, "error", updateErr)
	} else {
		s.logger.InfoContext(ctx, "backend operation completed", "operation", request.Operation, "transaction_id", record.ID, "state", record.State)
	}
	if err := s.writeResponse(connection, response); err != nil {
		s.logger.ErrorContext(ctx, "write daemon operation result", "operation", request.Operation, "transaction_id", record.ID, "error", err)
	}
}

func (s *Server) writeResponse(connection net.Conn, response daemonapi.Response) error {
	return json.NewEncoder(connection).Encode(response)
}

func decodeRequest(reader io.Reader) (daemonapi.Request, error) {
	limited := io.LimitReader(reader, maximumRequestBytes+1)
	decoder := json.NewDecoder(limited)
	decoder.DisallowUnknownFields()
	var request daemonapi.Request
	if err := decoder.Decode(&request); err != nil {
		return daemonapi.Request{}, fmt.Errorf("decode daemon request: %w", err)
	}
	var trailing any
	if err := decoder.Decode(&trailing); !errors.Is(err, io.EOF) {
		if err == nil {
			return daemonapi.Request{}, errors.New("daemon request contains multiple JSON values")
		}
		return daemonapi.Request{}, fmt.Errorf("decode daemon request trailing content: %w", err)
	}
	if strings.TrimSpace(request.Operation) != request.Operation || strings.TrimSpace(request.Service) != request.Service || strings.TrimSpace(request.InputType) != request.InputType || strings.TrimSpace(request.File) != request.File || strings.TrimSpace(request.ImageReference) != request.ImageReference {
		return daemonapi.Request{}, errors.New("daemon request fields must not contain surrounding whitespace")
	}
	return request, nil
}

func prepareSocketPath(socketPath string) error {
	if err := os.MkdirAll(filepath.Dir(socketPath), 0o755); err != nil {
		return fmt.Errorf("create daemon Unix Socket directory: %w", err)
	}
	info, err := os.Lstat(socketPath)
	if errors.Is(err, os.ErrNotExist) {
		return nil
	}
	if err != nil {
		return fmt.Errorf("inspect daemon Unix Socket path: %w", err)
	}
	if info.Mode()&os.ModeSocket == 0 {
		return fmt.Errorf("daemon Unix Socket path is occupied by a non-socket file: %s", socketPath)
	}
	if err := os.Remove(socketPath); err != nil {
		return fmt.Errorf("remove stale daemon Unix Socket: %w", err)
	}
	return nil
}