Save recent network balances in local storage (#5843)

* Use selector for state.metamask.accounts in all cases.

* Default to cached balance when selecting metamask accounts

* Adds the cached-balances controller

* Documentation and small codes fixes for #5843

Co-Authored-By: danjm <danjm.com@gmail.com>

1 files changed, 137 insertions, 0 deletions

diff --git a/test/unit/app/controllers/cached-balances-test.js b/test/unit/app/controllers/cached-balances-test.js
new file mode 100644
index 000000000..27aeabba2
--- /dev/null
+++ b/test/unit/app/controllers/cached-balances-test.js
@@ -0,0 +1,137 @@
+const assert = require('assert')
+const sinon = require('sinon')
+const CachedBalancesController = require('../../../../app/scripts/controllers/cached-balances')
+
+describe('CachedBalancesController', () => {
+  describe('updateCachedBalances', () => {
+    it('should update the cached balances', async () => {
+      const controller = new CachedBalancesController({
+        getNetwork: () => Promise.resolve(17),
+        accountTracker: {
+          store: {
+            subscribe: () => {},
+          },
+        },
+        initState: {
+          cachedBalances: 'mockCachedBalances',
+        },
+      })
+
+      controller._generateBalancesToCache = sinon.stub().callsFake(() => Promise.resolve('mockNewCachedBalances'))
+
+      await controller.updateCachedBalances({ accounts: 'mockAccounts' })
+
+      assert.equal(controller._generateBalancesToCache.callCount, 1)
+      assert.deepEqual(controller._generateBalancesToCache.args[0], ['mockAccounts', 17])
+      assert.equal(controller.store.getState().cachedBalances, 'mockNewCachedBalances')
+    })
+  })
+
+  describe('_generateBalancesToCache', () => {
+    it('should generate updated account balances where the current network was updated', () => {
+      const controller = new CachedBalancesController({
+        accountTracker: {
+          store: {
+            subscribe: () => {},
+          },
+        },
+        initState: {
+          cachedBalances: {
+            17: {
+              a: '0x1',
+              b: '0x2',
+              c: '0x3',
+            },
+            16: {
+              a: '0xa',
+              b: '0xb',
+              c: '0xc',
+            },
+          },
+        },
+      })
+
+      const result = controller._generateBalancesToCache({
+        a: { balance: '0x4' },
+        b: { balance: null },
+        c: { balance: '0x5' },
+      }, 17)
+
+      assert.deepEqual(result, {
+        17: {
+          a: '0x4',
+          b: '0x2',
+          c: '0x5',
+        },
+        16: {
+          a: '0xa',
+          b: '0xb',
+          c: '0xc',
+        },
+      })
+    })
+
+    it('should generate updated account balances where the a new network was selected', () => {
+      const controller = new CachedBalancesController({
+        accountTracker: {
+          store: {
+            subscribe: () => {},
+          },
+        },
+        initState: {
+          cachedBalances: {
+            17: {
+              a: '0x1',
+              b: '0x2',
+              c: '0x3',
+            },
+          },
+        },
+      })
+
+      const result = controller._generateBalancesToCache({
+        a: { balance: '0x4' },
+        b: { balance: null },
+        c: { balance: '0x5' },
+      }, 16)
+
+      assert.deepEqual(result, {
+        17: {
+          a: '0x1',
+          b: '0x2',
+          c: '0x3',
+        },
+        16: {
+          a: '0x4',
+          c: '0x5',
+        },
+      })
+    })
+  })
+
+  describe('_registerUpdates', () => {
+    it('should subscribe to the account tracker with the updateCachedBalances method', async () => {
+      const subscribeSpy = sinon.spy()
+      const controller = new CachedBalancesController({
+        getNetwork: () => Promise.resolve(17),
+        accountTracker: {
+          store: {
+            subscribe: subscribeSpy,
+          },
+        },
+      })
+      subscribeSpy.resetHistory()
+
+      const updateCachedBalancesSpy = sinon.spy()
+      controller.updateCachedBalances = updateCachedBalancesSpy
+      controller._registerUpdates({ accounts: 'mockAccounts' })
+
+      assert.equal(subscribeSpy.callCount, 1)
+
+      subscribeSpy.args[0][0]()
+
+      assert.equal(updateCachedBalancesSpy.callCount, 1)
+    })
+  })
+
+})