package i18n

import (
    "context"
    "google.golang.org/grpc"
    "google.golang.org/grpc/metadata"
)

// UnaryServerInterceptor grpc i18n 服务端拦截器
// 客户端将通过metadata传递其lang
// 将语言Key (lang) 从 grpc-metadata 中取出并注入到context中
// see github.com\zeromicro\go-zero\zrpc\server.go#AddUnaryInterceptors
// see google.golang.org\grpc\interceptor.go
func UnaryServerInterceptor() grpc.UnaryServerInterceptor {
    return func(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (resp interface{}, err error) {
        var md metadata.MD
        requestMetadata, ok := metadata.FromIncomingContext(ctx)
        if ok {
            md = requestMetadata.Copy()
        } else {
            md = metadata.MD{}
        }
        lngs := md.Get(KeyLang)
        if len(lngs) > 0 {
            lang := lngs[0]
            if len(lang) > 0 {
                ctx = context.WithValue(ctx, KeyLang, lang)
            }
        }

        resp, err = handler(ctx, req)
        return
    }
}

// UnaryClientInterceptor i18n grpc 客户端拦截器
// 将context中的lang注入到metadata中，传递给服务端
// see google.golang.org\grpc\interceptor.go
func UnaryClientInterceptor() grpc.UnaryClientInterceptor {
    return func(ctx context.Context, method string, req, reply interface{}, cc *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {
        var md metadata.MD
        requestMetadata, ok := metadata.FromOutgoingContext(ctx)
        if ok {
            md = requestMetadata.Copy()
        } else {
            md = metadata.MD{}
        }
        if lang, ok := ctx.Value(KeyLang).(string); ok && len(lang) > 0 {
            md.Set(KeyLang, lang)
        }
        ctx = metadata.NewOutgoingContext(ctx, md)
        return invoker(ctx, method, req, reply, cc, opts...)
    }
}