refactor: clarify the tally report types

This changes the types for the candidate and yesno tallies from arrays into objects. For candidate contests, it splits the former single array that contained both write-ins and ballot candidates into separate properties on an object. For yesno contests, instead of a 2-element tuple we now have an object with "yes" and "no" properties.

I think this is simpler and requires less casting. It also adds a few assertions for situations which shouldn't happen but otherwise might silently fail.

src/AppRoot.tsx

@@ -34,11 +34,10 @@ import {
   VxPrintOnly,
   Tally,
   YesNoVote,
-  TallyCount,
   CandidateVote,
   CandidateVoteTally,
-  WriteInCandidateTally,
   getAppMode,
+  YesNoVoteTally,
 } from './config/types'
 import BallotContext from './contexts/ballotContext'
 import electionSample from './data/electionSample.json'
@@ -766,44 +765,44 @@ class AppRoot extends React.Component<RouteComponentProps, State> {
           const contestIndex = election.contests.findIndex(
             c => c.id === contestId
           )
+          const contestTally = tally[contestIndex]
           // throw error if `contestIndex < 0` ?
           const contest = election.contests[contestIndex]
           /* istanbul ignore else */
           if (contest.type === 'yesno') {
+            const yesnoContestTally = contestTally as YesNoVoteTally
             const vote = votes[contestId] as YesNoVote
-            const yesNoVoteIndex = {
-              yes: 0,
-              no: 1,
-            }
-            ;(tally[contestIndex][yesNoVoteIndex[vote]] as TallyCount)++
+            yesnoContestTally[vote]++
           } else if (contest.type === 'candidate') {
+            const candidateContestTally = contestTally as CandidateVoteTally
             const vote = votes[contestId] as CandidateVote
             vote.forEach(candidate => {
               if (candidate.isWriteIn) {
-                const tallyContestWriteIns = (tally[
-                  contestIndex
-                ] as CandidateVoteTally).filter(
-                  c => typeof c !== 'number'
-                ) as WriteInCandidateTally[]
-                const writeInIndex = tallyContestWriteIns.findIndex(
+                const tallyContestWriteIns = candidateContestTally.writeIns
+                const writeIn = tallyContestWriteIns.find(
                   c => c.name === candidate.name
                 )
-                if (writeInIndex === -1) {
-                  const newWriteIn: WriteInCandidateTally = {
+                if (typeof writeIn === 'undefined') {
+                  tallyContestWriteIns.push({
                     name: candidate.name,
                     tally: 1,
-                  }
-                  ;(tally[contestIndex] as CandidateVoteTally).push(newWriteIn)
+                  })
                 } else {
-                  ;(tally[contestIndex][
-                    contest.candidates.length + writeInIndex
-                  ] as WriteInCandidateTally).tally++
+                  writeIn.tally++
                 }
               } else {
                 const candidateIndex = contest.candidates.findIndex(
                   c => c.id === candidate.id
                 )
-                ;(tally[contestIndex][candidateIndex] as TallyCount)++
+                if (
+                  candidateIndex < 0 ||
+                  candidateIndex >= candidateContestTally.candidates.length
+                ) {
+                  throw new Error(
+                    `unable to find a candidate with id: ${candidate.id}`
+                  )
+                }
+                candidateContestTally.candidates[candidateIndex]++
               }
             })
           }

src/components/PrecinctTallyReport.tsx

@@ -1,6 +1,12 @@
 import React from 'react'
 import styled from 'styled-components'
-import { Election, Tally, Precinct } from '../config/types'
+import {
+  Election,
+  Tally,
+  Precinct,
+  CandidateVoteTally,
+  YesNoVoteTally,
+} from '../config/types'
 
 import Table, { TD } from './Table'
 import Prose from './Prose'
@@ -54,14 +60,14 @@ const PrecinctTallyReport = ({
   return (
     <Report>
       <h1>
-        <NoWrap>{precinct.name}</NoWrap> <NoWrap>{election.title}</NoWrap>{' '}
+        <NoWrap>{precinct.name}</NoWrap> <NoWrap>{election.title}</NoWrap>
         <NoWrap>Tally Report</NoWrap>
       </h1>
       <p>
         This report should be <strong>{reportPurpose}</strong>.
       </p>
       <p>
-        {isPollsOpen ? 'Polls Closed' : 'Polls Opened'} and report printed at:{' '}
+        {isPollsOpen ? 'Polls Closed' : 'Polls Opened'} and report printed at:
         <strong>{currentDateTime}</strong>
       </p>
       <p>
@@ -86,7 +92,8 @@ const PrecinctTallyReport = ({
                           <td>{candidate.name}</td>
                           <TD narrow textAlign="right">
                             {isContestInPrecinct
-                              ? tally[contestIndex][candidateIndex]
+                              ? (tally[contestIndex] as CandidateVoteTally)
+                                  .candidates[candidateIndex]
                               : 'X'}
                           </TD>
                         </tr>
@@ -97,13 +104,17 @@ const PrecinctTallyReport = ({
                       <tr>
                         <td>Yes</td>
                         <TD narrow textAlign="right">
-                          {isContestInPrecinct ? tally[contestIndex][0] : 'X'}
+                          {isContestInPrecinct
+                            ? (tally[contestIndex] as YesNoVoteTally).yes
+                            : 'X'}
                         </TD>
                       </tr>
                       <tr>
                         <td>No</td>
                         <TD narrow textAlign="right">
-                          {isContestInPrecinct ? tally[contestIndex][1] : 'X'}
+                          {isContestInPrecinct
+                            ? (tally[contestIndex] as YesNoVoteTally).no
+                            : 'X'}
                         </TD>
                       </tr>
                     </React.Fragment>

src/config/types.ts

@@ -129,8 +129,14 @@ export interface WriteInCandidateTally {
   tally: number
 }
 export type TallyCount = number
-export type CandidateVoteTally = (TallyCount | WriteInCandidateTally)[]
-export type YesNoVoteTally = TallyCount[]
+export interface CandidateVoteTally {
+  candidates: TallyCount[]
+  writeIns: WriteInCandidateTally[]
+}
+export interface YesNoVoteTally {
+  yes: TallyCount
+  no: TallyCount
+}
 export type Tally = (CandidateVoteTally | YesNoVoteTally)[]
 
 // Ballot

src/utils/election.ts

@@ -1,3 +1,4 @@
+import { Contest } from '@votingworks/ballot-encoder'
 import { BallotStyle, Election, Tally } from '../config/types'
 
 export const getContests = ({
@@ -47,11 +48,17 @@ export const getZeroTally = (election: Election): Tally =>
   election.contests.map(contest => {
     /* istanbul ignore else */
     if (contest.type === 'yesno') {
-      return [0, 0]
+      return { yes: 0, no: 0 }
     } else if (contest.type === 'candidate') {
-      return contest.candidates.map(() => 0)
+      return {
+        candidates: contest.candidates.map(() => 0),
+        writeIns: [],
+      }
     } else {
-      return []
+      // `as Contest` is needed because TS knows 'yesno' and 'candidate' are the
+      // only valid values and so infers `contest` is type `never`, and we want
+      // to fail loudly in this situation.
+      throw new Error(`unexpected contest type: ${(contest as Contest).type}`)
     }
   })