use CoinGecko instead of CoinMarketcap for exchange rates

[ayrat555]

CoinMarketcap deprecated and took offline its v1 API. They have
v2 API which has a free plan and requires API keys. But as part of
#234 we already
implemented fetching from CoinGecko.

Now, coin id should be set for CoinGecko for the required coin.

config :explorer, Explorer.ExchangeRates.Source.CoinGecko,
  coin_id: System.get_env("COIN_GECKO_ID", "poa-network")

Or the COIN_GECKO_ID env var should be set. For example, COIN_GECKO_ID=poa-network

fixes #2579

Changelog

• use CoinGecko instead of CoinMarketcap for exchange rates

[coveralls]

Pull Request Test Coverage Report for Build f5294a8b-3d7c-43e2-bba0-b1a459720715

• 12 of 16 (75.0%) changed or added relevant lines in 5 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.05%) to 78.818%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
apps/block_scout_web/lib/block_scout_web/views/chain_view.ex	1	2	50.0%
apps/explorer/lib/explorer/exchange_rates/source/token_bridge.ex	2	3	66.67%
apps/explorer/lib/explorer/exchange_rates/source/coin_gecko.ex	5	7	71.43%

Files with Coverage Reduction	New Missed Lines	%
apps/block_scout_web/lib/block_scout_web/views/chain_view.ex	1	25.0%

Totals
Change from base Build 980ef580-9796-4557-8088-71e40cd46204:	0.05%
Covered Lines:	5120
Relevant Lines:	6496

---

💛 - Coveralls

[vbaranov]

@ayrat555

did you try with export COIN_GECKO_ID=ethereum ?

[ayrat555]

@vbaranov it was json decoding issue. fixed

[vbaranov]

@ayrat555 it works in case of Ethereum now. However,

1. If I export COIN_GECKO_ID=poa-network charts are ampty, price and marcet cap are 0
2. The solution is not compatible with COINMARKETCAP_PAGES ENV var. RSK market cap chart is broken

[ayrat555]

@vbaranov

1. It works for me. Along with COIN_GECKO_ID, COIN env var should be set
2. correct id can be found here https://api.coingecko.com/api/v3/coins/list

[vbaranov]

@ayrat555

I see the different values on chart hover and at the bottom:

And also it doesn't correlate with the data from API:

https://api.coingecko.com/api/v3/coins/markets?vs_currency=usd&ids=poa-network&order=market_cap_desc&per_page=100&page=1&sparkline=false

[
  {
    "id": "poa-network",
    "symbol": "poa",
    "name": "POA Network",
    "image": "https://assets.coingecko.com/coins/images/3157/large/poa-network.png?1548331565",
    "current_price": 0.01555225,
    "market_cap": 3424101,
    "market_cap_rank": 470,
    "total_volume": 134238,
    "high_24h": 0.01670786,
    "low_24h": 0.01545265,
    "price_change_24h": -0.00056939,
    "price_change_percentage_24h": -3.53183,
    "market_cap_change_24h": -123209.85896952,
    "market_cap_change_percentage_24h": -3.47333,
    "circulating_supply": 220167621,
    "total_supply": 252193195,
    "ath": 0.935923,
    "ath_change_percentage": -98.33653,
    "ath_date": "2018-05-10T09:45:31.809Z",
    "roi": null,
    "last_updated": "2019-08-27T09:46:28.885Z"
  }
]

correct id can be found here https://api.coingecko.com/api/v3/coins/list

Sure thing, but why do we need that ENV var if we use another api provider now?

[ayrat555]

@vbaranov https://api.coingecko.com/api/v3/coins/poa-network is used for exchange data and market cap. Locally, I don't see this issue. How can I reproduce it?

[vbaranov]

@ayrat555 let's remove?

[ayrat555]

I added deprecated in version - master.

[vbaranov]

@ayrat555

Locally, I don't see this issue. How can I reproduce it?

I still see this issue:

Why is the difference? Just start this branch for POA chain instance

[ayrat555]

@vbaranov I fixed a market cap calculation