## Summary

At present, Substrate has a large number of client SDKs of different languages to interact with the blockchains. However, these client SDKs are oriented to the Substrate-based chain, so the functions provided by them are often limited to the APIs and primitive under the Substrate framework. All of these client SDKs do not support smart contracts.

In the Polkadot ecosystem, not all parachains need to include smart contracts support. In most cases, Runtime can already solve most certain application scenarios. Therefore, the client SDKs for Substrate does not have to support smart contracts. On the other hand, based on the principle of minimization, this type of smart contract SDKs should be developed in the form of an independent library. This is the development goal of Himalia.

A smart contract-based DApp not only needs to develop the contract on the chain, but also needs to develop user-oriented front-end interfaces and micro-services, which means that developers need to interact with contracts from different terminals and based on multiple development languages. 

**Himalia will provide FRAME Contracts SDK supports in a multi-language environment to support WASM DApp development**. Himalia will be [Patract Hub](https://patract.io)'s 7th project for whole WASM contract development support. DApp needs to choose different technology stacks based on its form. For example, a service that provides users with contract status queries is often developed based on Golang, and a contract-based blockchain game can be developed in C# based on game engines such as Unity3D. This means that to expand the application scenarios of DApp, we need SDKs in as many environments as possible. Currently Himalia plans to implement SDK support for the following languages:

![image](https://user-images.githubusercontent.com/2844215/100198842-5e7eb100-2f37-11eb-8c06-292bf4b52d3b.png)

* v0.1(3 weeks): [PatractGo](https://github.com/patractlabs/go-patract), Golang contract SDK, to support micro-service development based on contract status. PatractGo will be based on [Centrifuge's GSRPC](https://github.com/centrifuge/go-substrate-rpc-client), which has already support Substract 2.0.
* v0.2(2 weeks): [PatractPy](https://github.com/patractlabs/py-patract), Python contract SDK, to support the development of scripts interacting with contracts, including automated scripts to support testing. PatractPy will be based on [Polkascan's Python Substrate Interface](https://github.com/polkascan/py-substrate-interface), which has already support Substract 2.0.
* v0.3(4 weeks): [PatractJ](https://github.com/patractlabs/patractj), Java/Scala/Kotlin contract SDK, to support back-end development based on JVM, and also rely on [Emeraldpay's PolkaJ](https://github.com/emeraldpay/polkaj) to complete the support development for Substrate 2.0.
* v0.4(3 weeks): [PatractN](https://github.com/patractlabs/csharp-patract), C# contract SDK, to support applications based on DotNet/Mono development and contract interaction, especially game development based on Unity3D, also rely on [Darkfriend77's SubstrateNetApi](https://github.com/darkfriend77/SubstrateNetApi) or [Usetech's polkadot_api_dotnet](https://github.com/usetech-llc/polkadot_api_dotnet) to complete the support development for Substrate 2.0. 

## v0.1 for PatractGo 

**`PatractGo` is a Golang contract SDK. In addition to supporting the basic interactive API with the contract, it mainly supports the development of micro-services based on the contract status.** For example, for common ERC20 contracts, a service can be developed based on PatractGo to synchronize all transfer information to the database, and based on the database to implement the statistics and processing of transfer data. In addition, developers can also develop some command-line tools based on Golang to assist in testing and debugging. We will be independent of GSRPC and encapsulate the API provided by GSRPC , to adapt to different substrate-based chains.

### Introduction

Most contract behaviors are highly related to context. In addition to interacting with the chain, user-oriented contract applications also need to provide users with current relevant context status information:

```
+--DAPP-Front-End--------------+        +---Chain-------------------------+
|                              |        |                                 |
| +----+  +------------------+ |        | +-------+     +-------+         |
| |    |  |                  | | Commit | |       |     |       |         |
| |    |  |   Polkadot-JS    +------------> Node  +---->+ Node  |         |
| |    +->+                  | |   Tx   | |       |     |       |         |
| |    |  |                  | |        | +-------+     +----+-++         |
| |    |  +------------------+ |        |                    ^ |          |
| | UI |                       |        +---------------------------------+
| |    |  +------------------+ |                             | |
| |    |  |                  | |        +--DAPP-Server--------------------+
| |    |  |                  | |  Push  | +--------+     +-----v-------+  |
| |    +<-+   Model          +<-----------+        +-----+             |  |
| |    |  |                  | |        | | Server |     |  PatractGo  |  |
| |    |  |                  +------------>        +-----+             |  |
| +----+  +------------------+ | Query  | +----+---+     +-----+-------+  |
+------------------------------+        |      |               |          |
                                        |      |         +-----v-------+  |
                                        |      |         |             |  |
                                        |      +-------->+   DataBase  |  |
                                        |                |             |  |
                                        |                +-------------+  |
                                        |                                 |
                                        +---------------------------------+
```

PatractGo is mainly responsible for implementing micro-services in a DApp. Unlike querying the state of the chain API, PatractGo can monitor the calls and events generated by the specified contract. Developers can obtain the state storage based on this information to maintain consistent state with the chain. Through data services based on a typical API-DB architecture, the front-end DApp can efficiently and concisely obtain the state on the chain as context information.

Based on the API of chain nodes, PatractGo obtains block information and summarizes and filters it, and sends contract-related messages and events based on metadata analysis to the handler protocol specified by the developer. For example, for a typical ERC20 contract, the developer can use the channel to subscribe to all transfer events that occur, and then synchronize them into the database, so that other microservices can provide services corresponding to the token data of the account, such as querying the current token holding distribution and other logics.

Therefor, PatractGo will achieve the following support:

* Complete the secondary packaging of the contract module interface, complete operations such as `put_code`, `call`, `instantiate`, etc.
* Parse the metadata.json information of the contract, and support the automatic generation of http service interface for the metadata corresponding contract
* Scanning and monitoring support of the contract status on the chain for statistics and analysis
* Basic command line tool support for native interaction with the contract, mainly used to test the security of the contract
* SDK development examples for ERC20 contract support

### Design

PatractGo consists of the following packages:

* `patractgo/metadata` contract metadata processing, and metadata-based contract processing
* `patractgo/rpc/native` re-encapsulation of the contract module interface to provide the contract-related interaction based on chain RPC
* `patractgo/rpc` implement the interaction with the contract based on metadata
* `patractgo/rest` implements an http service based on metadata to interact with the contract
* `patractgo/scanner` Scanning support for contract status on chain
* `patractgo/observer` Monitoring support for contract status on the chain
* `patractgo/contracts/erc20` supports ERC20 contracts
* `patractgo/cmd/patractgo` a command line tool for interacting with contracts
* `patractgo/cmd/pdumper` monitors contract status and events and synchronizes them to the database
* `patractgo/examples` SDK instance

## v0.2 for PatractPy

**`PatractPy` is a contract SDK to support the development of Python scripts that interact with contracts, including automated scripts to support testing.** Unlike PatractGo, PatractPy is mainly for script development, so PatractPy mainly completes contract-related RPC interfaces, and completes contract deployment and instantiation-related operations. At the same time, PatractPy will implement PatractGo-based interaction and contract status monitoring support.

As a result, PatractPy will achieve the following support:

* Complete the secondary packaging of the contract module interface, complete operations such as `put_code`, `call`, `instantiate`, etc.
* Contract-based metadata information and contract interaction
* Based on `PatractGo`, provide HTTP service for contract-based metadata information and contract interaction
* Based on `PatractGo`, provide Scanning and monitoring support for contract to do statistics and analysis
* Provide a SDK development example for ERC20 contract

## Detailed timeline for v0.1 ~ v0.2  (5 weeks, 1 Dec ~ 5 Jan)

### M1: v0.1 PatractGo（2 developers * 3 weeks)

* Initialize the project and complete the native contract interaction API
* Complete the contract interaction API and HTTP contract interaction service based on metadata.json
* Complete contract status scan support
* Monitor service support and complete the example to write into the database
* Complete ERC20 contract support and complete the corresponding command line tools
* Improve sample code and unboxing documentation

### M2: v0.2 PatractPy (2 developers * 2 weeks)

* Initialize the project and complete the native contract interaction API
* Complete the contract interaction API based on metadata.json
* Through `PatractGo`, complete the contract interaction API based on metadata.json
* Through `PatractGo`, complete the monitoring service support, and complete the example to write into the database
* Complete ERC20 contract support
* Improve sample code and unboxing documentation

### M3&M4: v0.3&v0.4, PatractJ & PatractN.

We have finished the design for the Java and .NET SDK, but because the chain SDK teams hasn't completed the Substrate 2.0 support , so we may need to wait for them to finish it and apply later, so the timeline maybe uncertain.

## Cost of v0.1 & 0.2 (10 developers * weeks)

* Operating activities: $2000 ( Rent and Devices: $200 per developer * week )
* Employee payments: $19000 ($1900 per developer * week)
* —————————— +
* Total Cost: $21000
* Exchange Rate: $45 / KSM
* Treasury Proposal: 466 KSM

## Verification of v0.1: Report & Github Source & Jupiter and Canvas testnet:

* Through unit test cases, based on Docker and verify all interactive APIs
* Through unit test cases, all contract events and calls can be synchronized and written to the log and database through the monitoring service
* Provide sample code for RPC package and Observer package, based on the README document, you can complete the test environment and debug the sample code

## Verification of v0.2: Report & Github Source & Jupiter and Canvas testnet:

* Through unit test cases, based on Docker and http service to verify all interactive APIs
* Provide sample code, based on the README document, you can complete the test environment and debug the sample code

- Substrate has different client SDKs for interacting with blockchains, but they don't support smart contracts.
- Himalia is a project that aims to develop smart contract SDKs in different languages.
- The first version of Himalia, called PatractGo, will be a Golang contract SDK for developing micro-services based on contract status.
- The second version, called PatractPy, will be a Python contract SDK for developing scripts that interact with contracts.
- The goal is to support DApp development in multiple languages and environments.

#370 Patract Hub's treasury proposal for Himalia v0.1 & v0.2 (WASM contract sdks in Go and Python)