From 5b77a409c912f7251da8c170bd4a3aa8826d989b Mon Sep 17 00:00:00 2001
From: Marcin Chrzanowski <marcin.j.chrzanowski@gmail.com>
Date: Wed, 30 Aug 2017 16:30:23 -0400
Subject: Implement again under

---
 __tests__/dice.test.js   | 24 ++++++++++++++++++++++++
 __tests__/lexer.test.js  | 10 ++++++++++
 __tests__/parser.test.js | 10 ++++++++++
 index.js                 |  2 ++
 src/dice.js              | 37 +++++++++++++++++++++++++++++++++++++
 src/lexer.js             |  1 +
 src/parser.js            |  1 +
 7 files changed, 85 insertions(+)

diff --git a/__tests__/dice.test.js b/__tests__/dice.test.js
index d4e2802..272f436 100644
--- a/__tests__/dice.test.js
+++ b/__tests__/dice.test.js
@@ -12,6 +12,7 @@ const {
   keepHigh,
   keepLow,
   again,
+  againUnder,
   threshold
 } = require('../src/dice.js')
 
@@ -579,6 +580,29 @@ describe('again', () => {
       }
     })
   })
+
+  describe('1a1d6', () => {
+    const die = againUnder(constant(1), d(constant(1), constant(6)))
+
+    testDie(die, {
+      variableDiceCount: {
+        min: 1,
+        max: Infinity
+      },
+      average: {
+        average: 4.2
+      },
+      variance: {
+        variance: 2.24
+      },
+      bounds: {
+        low: 2,
+        high: Infinity,
+        expectLow: true,
+        expectHigh: false
+      }
+    })
+  })
 })
 
 describe('threshold', () => {
diff --git a/__tests__/lexer.test.js b/__tests__/lexer.test.js
index 0336f44..25ef816 100644
--- a/__tests__/lexer.test.js
+++ b/__tests__/lexer.test.js
@@ -203,6 +203,16 @@ describe('lex', () => {
         { type: 'constant', value: 6 }
       ])
     })
+
+    test('6a3d6', () => {
+      expect(lex('6a3d6')).toEqual([
+        { type: 'constant', value: 6 },
+        { type: 'a' },
+        { type: 'constant', value: 3 },
+        { type: 'd' },
+        { type: 'constant', value: 6 }
+      ])
+    })
   })
 
   describe('threshold', () => {
diff --git a/__tests__/parser.test.js b/__tests__/parser.test.js
index 765388d..ad67fc4 100644
--- a/__tests__/parser.test.js
+++ b/__tests__/parser.test.js
@@ -219,6 +219,16 @@ describe('parse', () => {
         right: { type: 'constant', value: 10 }
       }
     })
+
+    expect(parse('10a3d10')).toEqual({
+      type: 'a',
+      left: { type: 'constant', value: 10 },
+      right: {
+        type: 'd',
+        left: { type: 'constant', value: 3 },
+        right: { type: 'constant', value: 10 }
+      }
+    })
   })
 
   it('parases dice with threshold', () => {
diff --git a/index.js b/index.js
index 8c52ad1..740b96e 100644
--- a/index.js
+++ b/index.js
@@ -17,6 +17,8 @@ const interpret = tree => {
     return D.keepLow(interpret(tree.left), interpret(tree.right))
   case 'A':
     return D.again(interpret(tree.left), interpret(tree.right))
+  case 'a':
+    return D.againUnder(interpret(tree.left), interpret(tree.right))
   case 'T':
     return D.threshold(interpret(tree.left), interpret(tree.right))
   case 'add':
diff --git a/src/dice.js b/src/dice.js
index e96aca9..e580c9d 100644
--- a/src/dice.js
+++ b/src/dice.js
@@ -162,6 +162,42 @@ const again = (die1, die2) => {
   }
 }
 
+const againUnder = (die1, die2) => {
+  return () => {
+    const againOn = roll(die1)
+    let rolls = []
+    let rollAgain = []
+
+    const rollDie = (die) => {
+      const roll = die()
+
+      if (roll <= againOn) {
+        rollAgain.push(die)
+      }
+
+      let returnedOriginal = false
+      rolls.push(() => {
+        if (!returnedOriginal) {
+          returnedOriginal = true
+          return roll
+        } else {
+          return die()
+        }
+      })
+    }
+
+    die2().forEach(rollDie)
+
+    while (rollAgain.length > 0) {
+      const oldRollAgain = rollAgain
+      rollAgain = []
+      oldRollAgain.forEach(rollDie)
+    }
+
+    return rolls
+  }
+}
+
 const threshold = (die1, die2) => {
   return () => {
     const cutoff = roll(die1)
@@ -193,4 +229,5 @@ exports.explodeUnder = explodeUnder
 exports.keepHigh = keepHigh
 exports.keepLow = keepLow
 exports.again = again
+exports.againUnder = againUnder
 exports.threshold = threshold
diff --git a/src/lexer.js b/src/lexer.js
index 7eb95b0..f33dc87 100644
--- a/src/lexer.js
+++ b/src/lexer.js
@@ -27,6 +27,7 @@ newLexemeType('e', 'e')
 newLexemeType('K', 'K')
 newLexemeType('k', 'k')
 newLexemeType('A', 'A')
+newLexemeType('a', 'a')
 newLexemeType('T', 'T')
 
 const lex = (expressionString) => {
diff --git a/src/parser.js b/src/parser.js
index 124d686..f8e2a5b 100644
--- a/src/parser.js
+++ b/src/parser.js
@@ -65,6 +65,7 @@ newDieOperation('e')
 newDieOperation('K')
 newDieOperation('k')
 newDieOperation('A')
+newDieOperation('a')
 newDieOperation('T')
 
 newInfix('bigPlus', 20, { type: 'add' })
-- 
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