// Package bootstrap assembles the standalone proxy-checker process. Checker
// execution is intentionally isolated from Gateway request handling and from
// all Redis/PostgreSQL access.
package bootstrap

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"net"
	"net/http"
	"reflect"
	"strings"
	"sync/atomic"

	"github.com/prometheus/client_golang/prometheus"
	"google.golang.org/grpc"
	"google.golang.org/grpc/credentials"

	controlplanev1 "proxy-pool/gen/controlplane/v1"
	"proxy-pool/internal/checker/controlplane"
	"proxy-pool/internal/checker/probe"
	"proxy-pool/internal/config"
	"proxy-pool/internal/controlplane/clienttransport"
	"proxy-pool/internal/controlplane/tlsreload"
	"proxy-pool/internal/domain/workerruntime"
	"proxy-pool/internal/platform/httpserver"
	"proxy-pool/internal/platform/lifecycle"
	platformMetrics "proxy-pool/internal/platform/metrics"
)

var (
	ErrInvalidOptions = errors.New("invalid checker bootstrap options")
	ErrStartup        = errors.New("checker startup failed")
	ErrNotReady       = errors.New("checker control plane is not ready")
)

type Options struct {
	ConfigPath          string
	Resolver            config.Resolver
	ControlPlaneAddress string
	CheckerID           string
	InstanceID          string
	AutoIdentity        bool
	MaxInFlight         int
	SupportedLevels     []controlplanev1.CheckLevel
	GRPCTransport       credentials.TransportCredentials
	MetricsListener     net.Listener
	HTTP                httpserver.Options
}

func Run(ctx context.Context, options Options) error {
	if err := validateOptions(ctx, options); err != nil {
		return err
	}
	configuration, err := loadConfiguration(ctx, options.ConfigPath, options.Resolver)
	if err != nil {
		return fmt.Errorf("%w: load configuration: %w", ErrStartup, err)
	}
	if !configuration.ControlPlane.Enabled {
		return errors.Join(ErrInvalidOptions, errors.New("controlPlane must be enabled"))
	}
	options, err = resolveIdentity(configuration, options)
	if err != nil {
		return fmt.Errorf("%w: %w", ErrStartup, err)
	}
	runtime, err := newRuntime(ctx, configuration, options)
	if err != nil {
		return fmt.Errorf("%w: %w", ErrStartup, err)
	}
	defer runtime.Close()
	return runtime.Run(ctx)
}

func newRuntime(ctx context.Context, configuration *config.Config, options Options) (*runtime, error) {
	if ctx == nil || configuration == nil {
		return nil, ErrInvalidOptions
	}
	transport, err := clienttransport.New(
		configuration.ControlPlane, options.ControlPlaneAddress, configuration.ControlPlane.CheckerTLS, options.GRPCTransport, "checkerTLS",
	)
	if err != nil {
		return nil, fmt.Errorf("%w: %w", ErrInvalidOptions, err)
	}
	connection, err := grpc.NewClient(options.ControlPlaneAddress,
		grpc.WithTransportCredentials(transport),
		grpc.WithDefaultCallOptions(
			grpc.MaxCallRecvMsgSize(configuration.ControlPlane.MaxMessageBytes),
			grpc.MaxCallSendMsgSize(configuration.ControlPlane.MaxMessageBytes),
		),
	)
	if err != nil {
		return nil, fmt.Errorf("dial control plane: %w", err)
	}
	closeConnection := true
	defer func() {
		if closeConnection {
			_ = connection.Close()
		}
	}()
	client := controlplane.NewGeneratedClient(controlplanev1.NewCheckerControlPlaneClient(connection))
	readiness := &controlPlaneReadiness{}
	runner, err := controlplane.NewRunner(client, probe.NewExecutor(), controlplane.Options{
		CheckerID: options.CheckerID, InstanceID: options.InstanceID, MaxInFlight: options.MaxInFlight,
		SupportedLevels: append([]controlplanev1.CheckLevel(nil), options.SupportedLevels...),
		ReportBatchSize: options.MaxInFlight, OnSuccessfulPull: readiness.MarkReady, OnFailedPull: readiness.MarkUnavailable,
	})
	if err != nil {
		return nil, fmt.Errorf("build checker runner: %w", err)
	}
	runners := []lifecycle.Runner{runner}
	if configuration.Metrics.Enabled {
		metrics, metricsErr := newMetricsRuntime(ctx, configuration.Metrics, options, readiness)
		if metricsErr != nil {
			return nil, metricsErr
		}
		runners = append(runners, metrics)
	} else if options.MetricsListener != nil {
		return nil, ErrInvalidOptions
	}
	group, err := lifecycle.NewGroup(runners...)
	if err != nil {
		return nil, err
	}
	closeConnection = false
	return &runtime{connection: connection, group: group}, nil
}

func validateOptions(ctx context.Context, options Options) error {
	if ctx == nil || strings.TrimSpace(options.ConfigPath) != options.ConfigPath || options.ConfigPath == "" ||
		nilInterface(options.Resolver) || !clienttransport.ValidDialAddress(options.ControlPlaneAddress) ||
		(options.CheckerID != "" && !workerruntime.ValidIdentifier(options.CheckerID)) ||
		(options.InstanceID != "" && !workerruntime.ValidIdentifier(options.InstanceID)) ||
		(!options.AutoIdentity && (!workerruntime.ValidIdentifier(options.CheckerID) || !workerruntime.ValidIdentifier(options.InstanceID))) ||
		options.MaxInFlight <= 0 || len(options.SupportedLevels) == 0 {
		return ErrInvalidOptions
	}
	return nil
}

func resolveIdentity(configuration *config.Config, options Options) (Options, error) {
	if configuration == nil {
		return Options{}, ErrInvalidOptions
	}
	if !options.AutoIdentity {
		return options, nil
	}
	if configuration.ControlPlane.TLS.Mode != "mtls" {
		return Options{}, errors.Join(ErrInvalidOptions, errors.New("auto identity requires controlPlane mTLS"))
	}
	identity, err := tlsreload.ResolveSPIFFEIdentity(
		configuration.ControlPlane.CheckerTLS.CertFile, configuration.ControlPlane.CheckerTLS.KeyFile,
		configuration.ControlPlane.TLS.TrustDomain, configuration.ControlPlane.TLS.Environment, "checker",
	)
	if err != nil {
		return Options{}, fmt.Errorf("resolve checker SPIFFE identity: %w", err)
	}
	if options.CheckerID == "" {
		options.CheckerID = identity
	}
	if options.InstanceID == "" {
		options.InstanceID = identity
	}
	if !workerruntime.ValidIdentifier(options.CheckerID) || !workerruntime.ValidIdentifier(options.InstanceID) || options.CheckerID != identity {
		return Options{}, errors.Join(ErrInvalidOptions, errors.New("checker identity does not match SPIFFE certificate"))
	}
	return options, nil
}

type runtime struct {
	connection *grpc.ClientConn
	group      *lifecycle.Group
}

func (runtime *runtime) Run(ctx context.Context) error {
	if runtime == nil || runtime.connection == nil || runtime.group == nil || ctx == nil {
		return ErrInvalidOptions
	}
	return runtime.group.Run(ctx)
}

func (runtime *runtime) Close() {
	if runtime != nil && runtime.connection != nil {
		_ = runtime.connection.Close()
	}
}

type controlPlaneReadiness struct {
	ready atomic.Bool
}

func (readiness *controlPlaneReadiness) MarkReady() {
	if readiness != nil {
		readiness.ready.Store(true)
	}
}

func (readiness *controlPlaneReadiness) MarkUnavailable() {
	if readiness != nil {
		readiness.ready.Store(false)
	}
}

func (readiness *controlPlaneReadiness) Ready(ctx context.Context) error {
	if ctx == nil || readiness == nil || !readiness.ready.Load() {
		return ErrNotReady
	}
	return ctx.Err()
}

type metricsRuntime struct {
	listener net.Listener
	handler  http.Handler
	options  httpserver.Options
}

func newMetricsRuntime(
	ctx context.Context,
	configuration config.Metrics,
	options Options,
	readiness *controlPlaneReadiness,
) (*metricsRuntime, error) {
	if ctx == nil || !configuration.Enabled || readiness == nil {
		return nil, ErrInvalidOptions
	}
	handler, err := platformMetrics.NewHandler(platformMetrics.Dependencies{
		Gatherer: prometheus.DefaultGatherer, Readiness: readiness,
	})
	if err != nil {
		return nil, fmt.Errorf("build checker metrics handler: %w", err)
	}
	listener := options.MetricsListener
	if listener == nil {
		listener, err = (&net.ListenConfig{}).Listen(ctx, "tcp", configuration.Listen)
		if err != nil {
			return nil, fmt.Errorf("listen checker metrics: %w", err)
		}
	}
	return &metricsRuntime{listener: listener, handler: handler, options: options.HTTP}, nil
}

func (runtime *metricsRuntime) Run(ctx context.Context) error {
	if runtime == nil || runtime.listener == nil || runtime.handler == nil || ctx == nil {
		return ErrInvalidOptions
	}
	return httpserver.Serve(ctx, runtime.options, httpserver.Endpoint{
		Name: "metrics", Listener: runtime.listener, Handler: runtime.handler,
	})
}

func loadConfiguration(ctx context.Context, path string, resolver config.Resolver) (*config.Config, error) {
	if ctx == nil || strings.TrimSpace(path) != path || path == "" || nilInterface(resolver) {
		return nil, ErrInvalidOptions
	}
	if err := ctx.Err(); err != nil {
		return nil, err
	}
	content, err := resolver.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("read configuration %q: %w", path, err)
	}
	configuration, err := config.LoadResolved(bytes.NewReader(content), resolver)
	if err != nil {
		return nil, fmt.Errorf("decode configuration %q: %w", path, err)
	}
	return configuration, nil
}

func nilInterface(value any) bool {
	if value == nil {
		return true
	}
	reflected := reflect.ValueOf(value)
	switch reflected.Kind() {
	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Pointer, reflect.Slice:
		return reflected.IsNil()
	default:
		return false
	}
}