// Package grpcclient provides a Go client for the broad-announce ingestd
// gRPC service (SPEC §19).  It wraps the generated pb.IngestClient and
// adds Bearer-token auth, stream-level retry semantics, and ergonomic
// Send/Recv primitives for use by any peer service that publishes alerts.
package grpcclient

import (
	"context"
	"fmt"
	"io"
	"time"

	pbv1 "git3.techno-world.net/lrosales/broad-announce/gen/go/broadannounce/v1"
	"google.golang.org/grpc"
	"google.golang.org/grpc/credentials"
	"google.golang.org/grpc/credentials/insecure"
	"google.golang.org/grpc/keepalive"
	"google.golang.org/grpc/metadata"
	"google.golang.org/grpc/status"
)

// Client is a gRPC client for the Ingest service.  It is safe for
// concurrent use by multiple goroutines.
type Client struct {
	conn       *grpc.ClientConn
	client     pbv1.IngestClient
	apiKey     string
	maxRetries int
	keepalive  keepalive.ClientParameters
	insecure   bool
}

// Stream represents an open StreamAlerts bidirectional stream.  A single
// Stream is not safe for concurrent use — use one stream per producer
// goroutine, or add external synchronization.
type Stream struct {
	stream pbv1.Ingest_StreamAlertsClient
}

// New connects to the Ingest service at addr and returns a Client.
// It does not perform any I/O; the connection is established lazily on
// the first call to Stream.
//
//   - addr: host:port of the ingestd gRPC server (default :9090)
//   - opts: functional options (WithAPIKey, WithMaxRetries,
//     WithKeepalive, WithInsecure)
//
// Production deployments should use TLS or mTLS.  The default TLS
// credentials use the host's root CA set.  For mTLS, pass a custom
// grpc.DialOption built with credentials.NewTLS(tlsConfig) via a
// private Option (or replace WithInsecure in development only).
func New(addr string, opts ...Option) (*Client, error) {
	c := &Client{maxRetries: 3}
	for _, opt := range opts {
		opt(c)
	}

	var dialOpts []grpc.DialOption

	if c.insecure {
		dialOpts = append(dialOpts, grpc.WithTransportCredentials(insecure.NewCredentials()))
	} else {
		// Secure TLS.  Replace by passing a custom tls.Config with
		// ClientCAs (for mTLS) or ServerName override (for TLS).
		dialOpts = append(dialOpts,
			grpc.WithTransportCredentials(credentials.NewTLS(nil)))
	}

	if c.keepalive.Time > 0 || c.keepalive.Timeout > 0 {
		dialOpts = append(dialOpts, grpc.WithKeepaliveParams(c.keepalive))
	}

	// Unary interceptor: attach API key to every RPC.
	dialOpts = append(dialOpts, grpc.WithUnaryInterceptor(
		func(ctx context.Context, method string, req, reply interface{},
			cc *grpc.ClientConn, invoker grpc.UnaryInvoker, _ ...grpc.CallOption) error {
			if c.apiKey != "" {
				ctx = metadata.AppendToOutgoingContext(ctx,
					"authorization", "Bearer "+c.apiKey)
			}
			return invoker(ctx, method, req, reply, cc)
		}))

	conn, err := grpc.NewClient(addr, dialOpts...)
	if err != nil {
		return nil, fmt.Errorf("grpc.Dial(%q): %w", addr, err)
	}
	c.conn = conn
	c.client = pbv1.NewIngestClient(conn)
	return c, nil
}

// Stream starts a StreamAlerts bidirectional stream.  The caller must call
// CloseSend when done sending.  The context is used for stream deadlines.
func (c *Client) Stream(ctx context.Context) (*Stream, error) {
	if c.apiKey != "" {
		md := metadata.Pairs("authorization", "Bearer "+c.apiKey)
		ctx = metadata.NewOutgoingContext(ctx, md)
	}
	stream, err := c.client.StreamAlerts(ctx)
	if err != nil {
		return nil, fmt.Errorf("StreamAlerts: %w", err)
	}
	return &Stream{stream: stream}, nil
}

// Send delivers one alert to the server.  It blocks until the server
// acknowledges receipt (not processing — that is async).  Send retries on
// RATE_LIMITED / UNAVAILABLE up to c.maxRetries, honouring the
// x-retry-after-ms response header when set.
func (s *Stream) Send(ctx context.Context, alert *pbv1.Alert) error {
	var lastErr error
	for attempt := 0; attempt <= 3; attempt++ {
		select {
		case <-ctx.Done():
			return ctx.Err()
		default:
		}

		lastErr = s.stream.Send(alert)
		if lastErr == nil {
			return nil
		}

		st, ok := status.FromError(lastErr)
		if !ok || !retryable(st.Code()) {
			return lastErr
		}

		if attempt < 3 {
			delay := retryDelay(s.stream.Context(), attempt)
			select {
			case <-ctx.Done():
				return ctx.Err()
			case <-time.After(delay):
			}
		}
	}
	return fmt.Errorf("Stream.Send (retries exhausted): %w", lastErr)
}

// Recv returns the next Ack from the server.  It blocks until an Ack is
// available or the stream is closed.  It retries on UNAVAILABLE up to
// c.maxRetries.  Returns io.EOF when the server closes the stream.
func (s *Stream) Recv(ctx context.Context) (*pbv1.Ack, error) {
	var lastErr error
	for attempt := 0; attempt <= 3; attempt++ {
		select {
		case <-ctx.Done():
			return nil, ctx.Err()
		default:
		}

		ack, err := s.stream.Recv()
		if err == nil {
			return ack, nil
		}
		lastErr = err

		if err == io.EOF {
			return nil, io.EOF
		}
		st, ok := status.FromError(err)
		if !ok || !retryable(st.Code()) {
			return nil, err
		}

		if attempt < 3 {
			delay := retryDelay(s.stream.Context(), attempt)
			select {
			case <-ctx.Done():
				return nil, ctx.Err()
			case <-time.After(delay):
			}
		}
	}
	return nil, fmt.Errorf("Stream.Recv (retries exhausted): %w", lastErr)
}

// CloseSend signals that the caller is done sending alerts.  The server
// will half-close its side of the stream; Recv continues to work until
// the server closes the stream or the context is cancelled.
func (s *Stream) CloseSend() error { return s.stream.CloseSend() }

// Close tears down the underlying gRPC connection.  Call it when the
// Client is no longer needed.
func (c *Client) Close() error { return c.conn.Close() }

// retryDelay returns the sleep interval for a given retry attempt,
// checking the x-retry-after-ms header for a server-specified value.
func retryDelay(streamCtx context.Context, attempt int) time.Duration {
	if md, ok := metadata.FromIncomingContext(streamCtx); ok {
		if vals := md.Get("x-retry-after-ms"); len(vals) > 0 {
			var ms int
			fmt.Sscanf(vals[0], "%d", &ms)
			if ms > 0 {
				return time.Duration(ms) * time.Millisecond
			}
		}
	}
	return time.Duration(100*attempt) * time.Millisecond
}