fix algorithm wantRange plus test it

lib/algorithm.js

@@ -72,10 +72,14 @@ class Algorithm {
   #wantNewestRange(localHaveRange, remoteHaveRange, count) {
     const [minLocalHave, maxLocalHave] = localHaveRange
     const [minRemoteHave, maxRemoteHave] = remoteHaveRange
-    if (maxRemoteHave <= maxLocalHave) return EMPTY_RANGE
+    if (maxRemoteHave < minLocalHave) return EMPTY_RANGE
     const maxWant = maxRemoteHave
     const size = Math.max(maxWant - maxLocalHave, count)
-    const minWant = Math.max(maxWant - size, minRemoteHave)
+    const minWant = Math.max(
+      maxWant - size + 1,
+      maxLocalHave - size + 1,
+      minRemoteHave
+    )
     return [minWant, maxWant]
   }
 
@@ -88,13 +92,19 @@ class Algorithm {
   wantRange(localHave, remoteHave, goal) {
     if (!goal) return EMPTY_RANGE
     if (isEmptyRange(remoteHave)) return EMPTY_RANGE
-    if (goal.type === 'all' || goal.type === 'set' || goal.type === 'record') {
+
+    switch (goal.type) {
+      case 'all':
         return this.#wantAllRange(localHave, remoteHave)
-    } else if (goal.type === 'newest') {
+
+      case 'newest':
         return this.#wantNewestRange(localHave, remoteHave, goal.count)
-    }
+
+      case 'none':
+      default:
         return EMPTY_RANGE
     }
+  }
 
   /**
    * @param {string} rootID

test/want-range.test.js

@@ -0,0 +1,43 @@
+const test = require('node:test')
+const assert = require('node:assert')
+const p = require('node:util').promisify
+const Algorithm = require('../lib/algorithm')
+
+test('want-range for goal=newest-3', async (t) => {
+  const algo = new Algorithm({ db: null })
+  const goal = { type: 'newest', count: 3 }
+
+  assert.deepStrictEqual(algo.wantRange([2, 4], [1, 3], goal), [2, 3])
+  assert.deepStrictEqual(algo.wantRange([2, 4], [1, 5], goal), [3, 5])
+  assert.deepStrictEqual(algo.wantRange([1, 3], [2, 4], goal), [2, 4])
+  assert.deepStrictEqual(algo.wantRange([1, 5], [2, 4], goal), [3, 4])
+  assert.deepStrictEqual(algo.wantRange([1, 3], [4, 6], goal), [4, 6])
+  assert.deepStrictEqual(algo.wantRange([4, 6], [1, 3], goal), [1, 0])
+  assert.deepStrictEqual(algo.wantRange([1, 3], [6, 7], goal), [6, 7])
+})
+
+test('want-range for goal=all', async (t) => {
+  const algo = new Algorithm({ db: null })
+  const goal = { type: 'all' }
+
+  assert.deepStrictEqual(algo.wantRange([2, 4], [1, 3], goal), [1, 3])
+  assert.deepStrictEqual(algo.wantRange([2, 4], [1, 5], goal), [1, 5])
+  assert.deepStrictEqual(algo.wantRange([1, 3], [2, 4], goal), [2, 4])
+  assert.deepStrictEqual(algo.wantRange([1, 5], [2, 4], goal), [2, 4])
+  assert.deepStrictEqual(algo.wantRange([1, 3], [4, 6], goal), [4, 6])
+  assert.deepStrictEqual(algo.wantRange([4, 6], [1, 3], goal), [1, 3])
+  assert.deepStrictEqual(algo.wantRange([1, 3], [6, 7], goal), [6, 7])
+})
+
+test('want-range for goal=record', async (t) => {
+  const algo = new Algorithm({ db: null })
+  const goal = { type: 'record' }
+
+  assert.deepStrictEqual(algo.wantRange([2, 4], [1, 3], goal), [2, 3])
+  assert.deepStrictEqual(algo.wantRange([2, 4], [1, 5], goal), [2, 5])
+  assert.deepStrictEqual(algo.wantRange([1, 3], [2, 4], goal), [2, 4])
+  assert.deepStrictEqual(algo.wantRange([1, 5], [2, 4], goal), [2, 4])
+  assert.deepStrictEqual(algo.wantRange([1, 3], [4, 6], goal), [4, 6])
+  assert.deepStrictEqual(algo.wantRange([4, 6], [1, 3], goal), [1, 0])
+  assert.deepStrictEqual(algo.wantRange([1, 3], [6, 7], goal), [6, 7])
+})