From ddbd11bc34e0836193e4cbd76192bcce97d618bb Mon Sep 17 00:00:00 2001
From: Angus MacDonald <amacdonald@google.com>
Date: Fri, 27 Nov 2020 14:18:16 -0600
Subject: [PATCH] Add iterableIteratorf and functions

---
 src/iterable-iterator/iterable-iteratorf.ts | 97 +++++++++++++++++++++
 1 file changed, 97 insertions(+)
 create mode 100644 src/iterable-iterator/iterable-iteratorf.ts

diff --git a/src/iterable-iterator/iterable-iteratorf.ts b/src/iterable-iterator/iterable-iteratorf.ts
new file mode 100644
index 0000000000..a0784e300e
--- /dev/null
+++ b/src/iterable-iterator/iterable-iteratorf.ts
@@ -0,0 +1,97 @@
+export class iterableIteratorf {
+  /**
+   * Return values from the given iterator matching the provided filter fn.
+   * Equivalent to calling filter on an array.
+   */
+  static filter<T>(
+      iterableIterator: IterableIterator<T>,
+      filterFn: (v: T) => boolean
+  ): T[] {
+    const result = [];
+    let nextEntry = iterableIterator.next();
+    while (!nextEntry.done) {
+      if (filterFn(nextEntry.value)) {
+        result.push(nextEntry.value);
+      }
+      nextEntry = iterableIterator.next();
+    }
+    return result;
+  }
+
+  /**
+   * Run the given function on values in the iterator.
+   * Equivalent to calling forEach on an array.
+   */
+  static forEach<T>(
+      iterableIterator: IterableIterator<T>,
+      callback: (value: T) => void
+  ): void {
+    let nextEntry = iterableIterator.next();
+    while (!nextEntry.done) {
+      callback(nextEntry.value);
+      nextEntry = iterableIterator.next();
+    }
+  }
+
+  /**
+   * Return an array with the results from calling the given function on
+   * values in the iterator.
+   * Equivalent to calling map on an array.
+   */
+  static map<T, V>(
+      iterableIterator: IterableIterator<T>,
+      callback: (value: T) => V
+  ): V[] {
+    const result: V[] = [];
+    let nextEntry = iterableIterator.next();
+    while (!nextEntry.done) {
+      result.push(callback(nextEntry.value));
+      nextEntry = iterableIterator.next();
+    }
+
+    return result;
+  }
+
+  /**
+   * Return the value in the iterator that generated the highest score when
+   * passed to the given scoreFn.
+   * Similar to arrayf.max
+   */
+  static max<T>(
+      iterableIterator: IterableIterator<T>,
+      scoreFn: (value: T) => number
+  ): T {
+    let maxValue;
+    let maxScore = Number.NEGATIVE_INFINITY;
+
+    let nextEntry = iterableIterator.next();
+    while (!nextEntry.done) {
+      const score = scoreFn(nextEntry.value);
+      if (maxScore < score) {
+        maxValue = nextEntry.value;
+        maxScore = score;
+      }
+      nextEntry = iterableIterator.next();
+    }
+
+    return maxValue;
+  }
+
+  /**
+   * Return true if some value in the iterator returns true for the given
+   * function.
+   */
+  static some<T>(
+      iterableIterator: IterableIterator<T>,
+      filterFn: (v: T) => boolean
+  ): boolean {
+    let nextEntry = iterableIterator.next();
+    while (!nextEntry.done) {
+      if (filterFn(nextEntry.value)) {
+        return true;
+      }
+      nextEntry = iterableIterator.next();
+    }
+    return false;
+  }
+}