From d6051158e52db719ae506fc48a45d22975b16a8b Mon Sep 17 00:00:00 2001
From: Marcin Chrzanowski <marcin.j.chrzanowski@gmail.com>
Date: Wed, 23 Aug 2017 20:19:52 -0400
Subject: Implement again

---
 __tests__/dice.test.js | 28 +++++++++++++++++++++++++++-
 src/dice.js            | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+), 1 deletion(-)

diff --git a/__tests__/dice.test.js b/__tests__/dice.test.js
index 15941cb..a18584c 100644
--- a/__tests__/dice.test.js
+++ b/__tests__/dice.test.js
@@ -9,7 +9,8 @@ const {
   negative,
   explode,
   keepHigh,
-  keepLow
+  keepLow,
+  again
 } = require('../src/dice.js')
 
 const defaultNumberRolls = 500
@@ -534,3 +535,28 @@ describe('keep', () => {
     testDie(die, basicDieTestSpecs(1, 20))
   })
 })
+
+describe('again', () => {
+  describe('10A1d10', () => {
+    const die = again(constant(10), d(constant(1), constant(10)))
+
+    testDie(die, {
+      variableDiceCount: {
+        min: 1,
+        max: Infinity
+      },
+      average: {
+        average: 6.11
+      },
+      variance: {
+        variance: 19.03
+      },
+      bounds: {
+        low: 1,
+        high: Infinity,
+        expectLow: true,
+        expectHigh: false
+      }
+    })
+  })
+})
diff --git a/src/dice.js b/src/dice.js
index 6f3b7da..ef67edf 100644
--- a/src/dice.js
+++ b/src/dice.js
@@ -111,6 +111,43 @@ const keepLow = (die1, die2) => {
   }
 }
 
+const again = (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
+  }
+}
+
+
 exports.pool = pool
 exports.roll = roll
 exports.constant = constant
@@ -123,3 +160,4 @@ exports.negative = negative
 exports.explode = explode
 exports.keepHigh = keepHigh
 exports.keepLow = keepLow
+exports.again = again
-- 
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