# Band Protocol

## Introduction <a href="#introduction" id="introduction"></a>

Developers building on Opera can now leverage [Band Protocol](https://www.bandprotocol.com/)’s decentralized oracle infrastructure. With Band’s oracles, they now have access to various cryptocurrency price data to integrate into their applications.

## Supported Tokens <a href="#supported-tokens" id="supported-tokens"></a>

Currently, the list of supported symbols can be found below. Going forward, this list will continue to expand based on developer needs and community feedback.

| **Crypto** |       |       |      |       |
| ---------- | ----- | ----- | ---- | ----- |
| AAVE       | BAND  | BNB   | BTC  | COVER |
| BAND       | CREAM | CRV   | ETH  | FTM   |
| BNB        | HEGIC | KP3R  | LINK | SFI   |
| BTC        | SNX   | SUSHI | YFI  |       |

| **Stablecoins** |      |      |   |   |   |
| --------------- | ---- | ---- | - | - | - |
| FRAX            | USDC | SUSD |   |   |   |

| **Commodities** |     |     |   |   |   |   |
| --------------- | --- | --- | - | - | - | - |
| OIL             | XAG | XAU |   |   |   |   |

| **Forex** |     |     |     |     |
| --------- | --- | --- | --- | --- |
| CHF       | CNY | EUR | GBP | JPY |

### **Price Pairs** <a href="#price-pairs" id="price-pairs"></a>

The methods in the following sections can work with any combination of base/quote token pairs, as long as the base and quote symbols are supported by the dataset.

## Querying Prices <a href="#querying-prices" id="querying-prices"></a>

Currently, there are two methods for developers to query prices from Band’s oracle: through Band’s `StdReference` smart contract on BSC and through their [`bandchain.js`](https://www.npmjs.com/package/%40bandprotocol%2Fbandchain.js) JavaScript helper library.

### **Solidity Smart Contract** <a href="#solidity-smart-contract" id="solidity-smart-contract"></a>

To query prices from Band’s oracle, a smart contract should reference Band’s StdReference contract, specifically the `getReferenceData` and `getReferenceDatabulk` methods.

`getReferenceData` takes two strings as the inputs, the base and quote symbol, respectively. It then queries the `StdReference` contract for the latest rates for those two tokens and returns a `ReferenceData` struct, shown below.

```
struct ReferenceData {
    uint256 rate; // base/quote exchange rate, multiplied by 1e18.
    uint256 lastUpdatedBase; // UNIX epoch of the last time when base price gets updated.
    uint256 lastUpdatedQuote; // UNIX epoch of the last time when quote price gets updated.
}
```

`getReferenceDataBulk` instead takes two lists, one of the `base` tokens, and one of the `quotes`. It then proceeds to similarly queries the price for each base/quote pair at each index, and returns an array of `ReferenceData` structs.

For example, if we call `getReferenceDataBulk` with `['BTC','BTC','ETH']` and `['USD','ETH','BNB']`, the returned `ReferenceData` array will contain information regarding the pairs:

* `BTC/USD`
* `BTC/ETH`
* `ETH/BNB`

### **Contract Addresses**

| Blockchain      | Contract Address                           | Explorer                                                                       |
| --------------- | ------------------------------------------ | ------------------------------------------------------------------------------ |
| Opera (Mainnet) | 0xDA7a001b254CD22e46d3eAB04d937489c93174C3 | [Link](https://ftmscan.com/address/0xDA7a001b254CD22e46d3eAB04d937489c93174C3) |

#### **Example Usage**

This [contract](https://gist.github.com/tansawit/a66d460d4e896aa94a0790df299251db) demonstrates an example of using Band’s `StdReference` contract and the `getReferenceData` function.

### **BandChain.JS** <a href="#bandchainjs" id="bandchainjs"></a>

Band’s node helper library [`bandchain.js`](https://www.npmjs.com/package/@bandprotocol/bandchain.js) also supports a similar `getReferenceData` function. This function takes one argument, a list of token pairs to query the result. It then returns a list of corresponding rate values.

#### **Example Usage**

The code below shows an example usage of the function:

```solidity
const { Client } = require('@bandprotocol/bandchain.js');

// BandChain's REST Endpoint
const endpoint = 'https://rpc.bandchain.org';
const client = new Client(endpoint);

// This example demonstrates how to query price data from
// Band's standard dataset
async function exampleGetReferenceData() {
  const rate = await client.getReferenceData(['BTC/ETH','BAND/EUR', 'FTM/USD']);
  return rate;
}

(async () => {
  console.log(await exampleGetReferenceData());
})();

```

The corresponding result will then be similar to:

```solidity
$ node index.js
[ 
    { 
        pair: 'BTC/ETH',
        rate: 30.998744363906173,
        updatedAt: { base: 1615866954, quote: 1615866954 },
        requestID: { base: 2206590, quote: 2206590 } 
    },
    { 
        pair: 'BAND/EUR',
        rate: 10.566138918332376,
        updatedAt: { base: 1615866845, quote: 1615866911 },
        requestID: { base: 2206539, quote: 2206572 } 
    }, 
    { 
        pair: 'FTM/USD',
        rate: 0.36662363,
        updatedAt: { base: 1615866851, quote: 1615866960 },
        requestID: { base: 2206543, quote: 0 } 
    }
]
```

For each pair, the following information will be returned:

* `pair`: The base/quote symbol pair string.
* `rate`: The resulting rate of the given pair.
* `updated`: The timestamp at which the base and quote symbols were last updated on BandChain. For `USD`, this will be the current timestamp.
* `rawRate`: This object consists of two parts.
  * `value` is the `BigInt` value of the actual rate, multiplied by `10^decimals`.
  * `decimals` is then the exponent by which `rate` was multiplied by to get `rawRate`.


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