From 5ec1f66a88855fa07e29bd160bb5a401b4061853 Mon Sep 17 00:00:00 2001
From: Oliver Steele <steele@osteele.com>
Date: Wed, 28 Jun 2017 16:43:18 -0400
Subject: [PATCH] Implement remaining numeric filters

---
 README.md              | 12 ++++++++----
 filters/filter_test.go | 29 ++++++++++++++++++++++++-----
 filters/filters.go     | 28 ++++++++++++++++++++++++++++
 3 files changed, 60 insertions(+), 9 deletions(-)

diff --git a/README.md b/README.md
index 4bdea1c..7265314 100644
--- a/README.md
+++ b/README.md
@@ -19,7 +19,9 @@
   - [ ] Control Flow
     - [x] `if`/`else`/`elsif`
     - [x] `unless`
-    - [ ] `case`/`when`
+    - [ ] `case`
+      - [x] `when`
+      - [ ] `else`
   - [ ] Iteration
       - [x] modifiers (`limit`, `reversed`, `offset`)
       - [ ] `range`
@@ -28,10 +30,12 @@
       - [ ] `tablerow`
       - [ ] `cycle`
   - [x] Raw
-  - [ ] Variables
+  - [x] Variables
     - [x] Assign
     - [x] Capture
-- [ ] Filters (partial)
+- [ ] Filters
+  - [ ] `sort_natural`, `uniq`, `escape`, `truncatewords`, `url_decode`, `url_encode`
+  - [x] everything else
 
 ## Install
 
@@ -76,7 +80,7 @@ Kyoung-chan Lee's <https://github.com/leekchan/timeutil> for formatting dates.
 
 Michael Hamrah's [Lexing with Ragel and Parsing with Yacc using Go](https://medium.com/@mhamrah/lexing-with-ragel-and-parsing-with-yacc-using-go-81e50475f88f) was essential to understanding `go yacc`.
 
-The [original Liquid engine](https://shopify.github.io/liquid), of course, for the design and documentation of the Liquid template language.
+The [original Liquid engine](https://shopify.github.io/liquid), of course, for the design and documentation of the Liquid template language. Many of the tag and filter test cases are taken directly from the Liquid documentation.
 
 (That said, this is a clean-room implementation to make sure it just implements the documented design.)
 
diff --git a/filters/filter_test.go b/filters/filter_test.go
index 1588017..ffd7228 100644
--- a/filters/filter_test.go
+++ b/filters/filter_test.go
@@ -86,14 +86,33 @@ var filterTests = []struct {
 	{`183.357 | ceil`, 184},
 	{`"3.5" | ceil`, 4},
 
-	// {`16 | divided_by: 4`, 4},
-	// {`5 | divided_by: 3`, 1},
-	// {`20 | divided_by: 7.0`, 123},
-
 	{`1.2 | floor`, 1},
 	{`2.0 | floor`, 2},
 	{`183.357 | floor`, 183},
-	// TODO divided_by, minus, modulo, plus, round,times
+
+	{`4 | plus: 2`, 6},
+	{`183.357 | plus: 12`, 195.357},
+
+	{`4 | minus: 2`, 2},
+	{`16 | minus: 4`, 12},
+	{`183.357 | minus: 12`, 171.357},
+
+	{`3 | times: 2`, 6},
+	{`24 | times: 7`, 168},
+	{`183.357 | times: 12`, 2200.284},
+
+	{`3 | modulo: 2`, 1},
+	{`24 | modulo: 7`, 3},
+	// {`183.357 | modulo: 12`, 3.357}, // TODO test suit use inexact
+
+	{`16 | divided_by: 4`, 4},
+	{`5 | divided_by: 3`, 1},
+	{`20 | divided_by: 7`, 2},
+	{`20 | divided_by: 7.0`, 2.857142857142857},
+
+	{`1.2 | round`, 1},
+	{`2.7 | round`, 3},
+	{`183.357 | round: 2`, 183.36},
 
 	// Jekyll extensions; added here for convenient testing
 	// TODO add this just to the test environment
diff --git a/filters/filters.go b/filters/filters.go
index cd3cb98..6562a69 100644
--- a/filters/filters.go
+++ b/filters/filters.go
@@ -74,6 +74,34 @@ func DefineStandardFilters() {
 	expressions.DefineFilter("abs", math.Abs)
 	expressions.DefineFilter("ceil", math.Ceil)
 	expressions.DefineFilter("floor", math.Floor)
+	expressions.DefineFilter("modulo", math.Mod)
+	expressions.DefineFilter("minus", func(a, b float64) float64 {
+		return a - b
+	})
+	expressions.DefineFilter("plus", func(a, b float64) float64 {
+		return a + b
+	})
+	expressions.DefineFilter("times", func(a, b float64) float64 {
+		return a * b
+	})
+	expressions.DefineFilter("divided_by", func(a float64, b interface{}) interface{} {
+		switch bt := b.(type) {
+		case int, int16, int32, int64:
+			return int(a) / bt.(int)
+		case float32, float64:
+			return a / float64(b.(float64))
+		default:
+			return nil
+		}
+	})
+	expressions.DefineFilter("round", func(n float64, places interface{}) float64 {
+		pl, ok := places.(int)
+		if !ok {
+			pl = 0
+		}
+		exp := math.Pow10(pl)
+		return math.Floor(n*exp+0.5) / exp
+	})
 
 	// sequences
 	expressions.DefineFilter("size", generics.Length)