Modify gas price statistics (#2947)

* gas price distribution + median + tests

* put histogram in util

* use the util histogram

* remove the default gas price implementation

* histogram rpc

* fix empty corpus

* Add JS ethcore_gasPriceHistogram

* Fix typo (s/types/type/) & subsequent failing test

* Fix return type & formatting

* bucketBounds

* Add jsapi e2e test verification

js/src/api/format/output.js

@@ -70,6 +70,20 @@ export function outDate (date) {
   return new Date(outNumber(date).toNumber() * 1000);
 }
 
+export function outHistogram (histogram) {
+  if (histogram) {
+    Object.keys(histogram).forEach((key) => {
+      switch (key) {
+        case 'bucketBounds':
+        case 'counts':
+          histogram[key] = histogram[key].map(outNumber);
+      }
+    });
+  }
+
+  return histogram;
+}
+
 export function outLog (log) {
   Object.keys(log).forEach((key) => {
     switch (key) {

js/src/api/format/output.spec.js

@@ -16,7 +16,7 @@
 
 import BigNumber from 'bignumber.js';
 
-import { outBlock, outAccountInfo, outAddress, outDate, outNumber, outPeers, outReceipt, outTransaction, outTrace } from './output';
+import { outBlock, outAccountInfo, outAddress, outDate, outHistogram, outNumber, outPeers, outReceipt, outTransaction, outTrace } from './output';
 import { isAddress, isBigNumber, isInstanceOf } from '../../../test/types';
 
 describe('api/format/output', () => {
@@ -120,6 +120,18 @@ describe('api/format/output', () => {
     });
   });
 
+  describe('outHistogram', () => {
+    ['bucketBounds', 'counts'].forEach((type) => {
+      it(`formats ${type} as number arrays`, () => {
+        expect(
+          outHistogram({ [type]: [0x123, 0x456, 0x789] })
+        ).to.deep.equal({
+          [type]: [new BigNumber(0x123), new BigNumber(0x456), new BigNumber(0x789)]
+        });
+      });
+    });
+  });
+
   describe('outNumber', () => {
     it('returns a BigNumber equalling the value', () => {
       const bn = outNumber('0x123456');

js/src/api/rpc/ethcore/ethcore.e2e.js

@@ -27,6 +27,16 @@ describe('ethapi.ethcore', () => {
     });
   });
 
+  describe('gasPriceHistogram', () => {
+    it('returns and translates the target', () => {
+      return ethapi.ethcore.gasPriceHistogram().then((result) => {
+        expect(Object.keys(result)).to.deep.equal(['bucketBounds', 'counts']);
+        expect(result.bucketBounds.length > 0).to.be.true;
+        expect(result.counts.length > 0).to.be.true;
+      });
+    });
+  });
+
   describe('netChain', () => {
     it('returns and the chain', () => {
       return ethapi.ethcore.netChain().then((value) => {

js/src/api/rpc/ethcore/ethcore.js

@@ -15,7 +15,7 @@
 // along with Parity.  If not, see <http://www.gnu.org/licenses/>.
 
 import { inAddress, inData, inNumber16 } from '../../format/input';
-import { outAddress, outNumber, outPeers } from '../../format/output';
+import { outAddress, outHistogram, outNumber, outPeers } from '../../format/output';
 
 export default class Ethcore {
   constructor (transport) {
@@ -69,6 +69,12 @@ export default class Ethcore {
       .then(outNumber);
   }
 
+  gasPriceHistogram () {
+    return this._transport
+      .execute('ethcore_gasPriceHistogram')
+      .then(outHistogram);
+  }
+
   generateSecretPhrase () {
     return this._transport
       .execute('ethcore_generateSecretPhrase');

js/src/jsonrpc/interfaces/ethcore.js

@@ -104,6 +104,25 @@ export default {
     }
   },
 
+  gasPriceHistogram: {
+    desc: 'Returns a snapshot of the historic gas prices',
+    params: [],
+    returns: {
+      type: Object,
+      desc: 'Historic values',
+      details: {
+        bucketBounds: {
+          type: Array,
+          desc: 'Array of U256 bound values'
+        },
+        count: {
+          type: Array,
+          desc: 'Array of U64 counts'
+        }
+      }
+    }
+  },
+
   generateSecretPhrase: {
     desc: 'Creates a secret phrase that can be associated with an account',
     params: [],