// Copyright 2023 Woodpecker Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Package grpc provides gRPC server implementation with JWT-based authentication.
//
// # Authentication Flow
//
// Uses a two-token approach:
//
//  1. Agent Token (long-lived): Configured via WOODPECKER_AGENT_SECRET, used only for initial Auth() call
//  2. JWT Access Token (short-lived, 1 hour): Obtained from Auth(), included in metadata["token"] for all service calls
//
// # Interceptor Architecture
//
// Authorizer interceptors validate JWT tokens on every request:
//  1. Extract JWT from metadata["token"]
//  2. Verify signature and expiration
//  3. Extract and add agent_id to metadata for downstream handlers
//
// Auth endpoint (/proto.WoodpeckerAuth/Auth) bypasses validation to allow initial authentication.
//
// # Usage
//
//	// Server setup
//	jwtManager := NewJWTManager(c.String("grpc-secret"))
//	authorizer := NewAuthorizer(jwtManager)
//	grpcServer := grpc.NewServer(
//	    grpc.StreamInterceptor(authorizer.StreamInterceptor),
//	    grpc.UnaryInterceptor(authorizer.UnaryInterceptor),
//	)
//
//	// Client usage
//	resp, _ := authClient.Auth(ctx, &proto.AuthRequest{AgentToken: "secret", AgentId: -1})
//	ctx = metadata.AppendToOutgoingContext(ctx, "token", resp.AccessToken)
//	workflow, _ := woodpeckerClient.Next(ctx, &proto.NextRequest{...})
package grpc

import (
	"context"
	"fmt"

	"google.golang.org/grpc"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/metadata"
	"google.golang.org/grpc/status"
)

// StreamContextWrapper wraps gRPC ServerStream to allow context modification.
type StreamContextWrapper interface {
	grpc.ServerStream
	SetContext(context.Context)
}

type wrapper struct {
	grpc.ServerStream
	ctx context.Context
}

func (w *wrapper) Context() context.Context {
	return w.ctx
}

func (w *wrapper) SetContext(ctx context.Context) {
	w.ctx = ctx
}

func newStreamContextWrapper(inner grpc.ServerStream) StreamContextWrapper {
	ctx := inner.Context()
	return &wrapper{
		inner,
		ctx,
	}
}

// Authorizer validates JWT tokens and enriches context with agent information.
type Authorizer struct {
	jwtManager *JWTManager
}

// NewAuthorizer creates a new JWT authorizer.
func NewAuthorizer(jwtManager *JWTManager) *Authorizer {
	return &Authorizer{jwtManager: jwtManager}
}

// StreamInterceptor validates JWT tokens for streaming gRPC calls.
func (a *Authorizer) StreamInterceptor(srv any, stream grpc.ServerStream, info *grpc.StreamServerInfo, handler grpc.StreamHandler) error {
	_stream := newStreamContextWrapper(stream)

	newCtx, err := a.authorize(stream.Context(), info.FullMethod)
	if err != nil {
		return err
	}

	_stream.SetContext(newCtx)

	return handler(srv, _stream)
}

// UnaryInterceptor validates JWT tokens for unary gRPC calls.
func (a *Authorizer) UnaryInterceptor(ctx context.Context, req any, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (any, error) {
	newCtx, err := a.authorize(ctx, info.FullMethod)
	if err != nil {
		return nil, err
	}
	return handler(newCtx, req)
}

// authorize validates JWT and enriches context with agent_id metadata.
// Bypasses validation for /proto.WoodpeckerAuth/Auth endpoint.
func (a *Authorizer) authorize(ctx context.Context, fullMethod string) (context.Context, error) {
	// bypass auth for token endpoint
	if fullMethod == "/proto.WoodpeckerAuth/Auth" {
		return ctx, nil
	}

	md, ok := metadata.FromIncomingContext(ctx)
	if !ok {
		return ctx, status.Errorf(codes.Unauthenticated, "metadata is not provided")
	}

	values := md["token"]
	if len(values) == 0 {
		return ctx, status.Errorf(codes.Unauthenticated, "token is not provided")
	}

	accessToken := values[0]
	claims, err := a.jwtManager.Verify(accessToken)
	if err != nil {
		return ctx, status.Errorf(codes.Unauthenticated, "access token is invalid: %v", err)
	}

	md.Append("agent_id", fmt.Sprintf("%d", claims.AgentID))

	return metadata.NewIncomingContext(ctx, md), nil
}