Fix typescript problems with length method

src/commonTypes.ts

@@ -1,5 +1,6 @@
 export interface Dictionary<T> {[index: string]: T}
 
+export type Length = number
 export type Ngram = string
 export type Position = number
 export type Term = string
@@ -9,7 +10,7 @@ export type NormaliseFunction = (term: Term) => Ngram
 export type Indexable = string | number | symbol
 
 export type Description = Record<Indexable, Position[]>
-export type Positions = Dictionary<Position>
+export type Lengths = Dictionary<Length>
 export type Locations = Dictionary<Position[]>
 export type StringDescription = Record<string, Position[]>
 export type Terms = Term[] | Record<Indexable, Term>

src/search.ts

@@ -1,5 +1,4 @@
 import {
-    add,
     filter,
     filterObject,
     flatten,
@@ -13,19 +12,18 @@ import {
     mergeAll,
     not,
     pick,
-    pipe,
     reduce,
     splitAt,
     values,
 } from 'rambdax'
 
-import { empty, ids, match, nonEmpty } from './utils/helpers'
+import { empty, ids, lengthFromPositions, match, nonEmpty } from './utils/helpers'
 import { ngram } from './ngram'
 
 import type {
     Description,
     Indexable,
-    Positions,
+    Lengths,
     Locations,
     Ngram,
     NgramIndex,
@@ -202,10 +200,9 @@ export class Index {
     /**
      * Lengths of all the terms in the index
      */
-    lengths (): Positions {
+    lengths (): Lengths {
         const descriptions: Description[] = this._ends()
-        const lengthFromPositions = pipe(last, add(1))  // get length from last position
-        const lengths: Positions = map(
+        const lengths: Lengths = map(
             lengthFromPositions,
             mergeAll(descriptions),
         )

src/utils/helpers.test.ts

@@ -2,6 +2,7 @@ import tap from 'tap'
 
 import {
     ids,
+    lengthFromPositions,
     match,
     nonEmpty,
 } from './helpers'
@@ -12,6 +13,13 @@ tap.test('utils ids', assert => {
     assert.end()
 })
 
+tap.test('utils lengthFromPositions', assert => {
+    assert.same(lengthFromPositions([]), 0)
+    assert.same(lengthFromPositions([0]), 1)
+    assert.same(lengthFromPositions([0, 1]), 2)
+    assert.end()
+})
+
 tap.test('utils nonEmpty', assert => {
     assert.ok(nonEmpty({a: []}))
     assert.notOk(nonEmpty({}))

src/utils/helpers.ts

@@ -12,6 +12,7 @@ import {
 import type {
     Description,
     Indexable,
+    Length,
     Position,
     StringDescription,
 } from '../commonTypes'
@@ -22,6 +23,19 @@ export const nil: Position[] = []
 
 export const ids = (obj: object): Indexable[] => keys(obj)
 
+/**
+ * Get length from last position
+ */
+export function lengthFromPositions (
+    positions: Position[]
+): Length {
+    if (isEmpty(positions)) return 0
+
+    const length: Length = positions[positions.length - 1] + 1
+
+    return length
+}
+
 /**
  * Rambda’s {@link https://selfrefactor.github.io/rambdax/#/?id=isempty|isEmpty} complemented (negated).
  * @returns true for non-empty things.