From 79bb597a332836cbeeeb884ba2d07de329d1c357 Mon Sep 17 00:00:00 2001
From: Caleb Bassi <calebjbassi@gmail.com>
Date: Sat, 26 Jan 2019 22:32:08 -0800
Subject: [PATCH] Add scrolling to List widget

---
 _examples/list.go | 10 +++++++--
 go.mod            |  1 +
 go.sum            |  2 ++
 symbols.go        |  3 +++
 widgets/list.go   | 57 +++++++++++++++++++++++++++++++++++++++--------
 5 files changed, 62 insertions(+), 11 deletions(-)

diff --git a/_examples/list.go b/_examples/list.go
index 6d5b1b2..dbbdf75 100644
--- a/_examples/list.go
+++ b/_examples/list.go
@@ -32,8 +32,8 @@ func main() {
 		"[7] nsf/termbox-go",
 	}
 	l.TextStyle = ui.NewStyle(ui.ColorYellow)
-	l.Wrap = false
-	l.SetRect(0, 0, 25, 50)
+	l.WrapText = false
+	l.SetRect(0, 0, 25, 5)
 
 	ui.Render(l)
 
@@ -43,6 +43,12 @@ func main() {
 		switch e.ID {
 		case "q", "<C-c>":
 			return
+		case "j", "<Down>":
+			l.ScrollDown()
+			ui.Render(l)
+		case "k", "<Up>":
+			l.ScrollUp()
+			ui.Render(l)
 		}
 	}
 }
diff --git a/go.mod b/go.mod
index 7d0b1c6..ca49f9d 100644
--- a/go.mod
+++ b/go.mod
@@ -5,4 +5,5 @@ require (
 	github.com/mattn/go-runewidth v0.0.2
 	github.com/mitchellh/go-wordwrap v0.0.0-20150314170334-ad45545899c7
 	github.com/nsf/termbox-go v0.0.0-20190121233118-02980233997d
+	golang.org/x/arch v0.0.0-20181203225421-5a4828bb7045 // indirect
 )
diff --git a/go.sum b/go.sum
index 495684f..121df84 100644
--- a/go.sum
+++ b/go.sum
@@ -6,3 +6,5 @@ github.com/mitchellh/go-wordwrap v0.0.0-20150314170334-ad45545899c7 h1:DpOJ2HYzC
 github.com/mitchellh/go-wordwrap v0.0.0-20150314170334-ad45545899c7/go.mod h1:ZXFpozHsX6DPmq2I0TCekCxypsnAUbP2oI0UX1GXzOo=
 github.com/nsf/termbox-go v0.0.0-20190121233118-02980233997d h1:x3S6kxmy49zXVVyhcnrFqxvNVCBPb2KZ9hV2RBdS840=
 github.com/nsf/termbox-go v0.0.0-20190121233118-02980233997d/go.mod h1:IuKpRQcYE1Tfu+oAQqaLisqDeXgjyyltCfsaoYN18NQ=
+golang.org/x/arch v0.0.0-20181203225421-5a4828bb7045 h1:Pn8fQdvx+z1avAi7fdM2kRYWQNxGlavNDSyzrQg2SsU=
+golang.org/x/arch v0.0.0-20181203225421-5a4828bb7045/go.mod h1:cYlCBUl1MsqxdiKgmc4uh7TxZfWSFLOGSRR090WDxt8=
diff --git a/symbols.go b/symbols.go
index b7bda5f..6db7d1c 100644
--- a/symbols.go
+++ b/symbols.go
@@ -3,6 +3,9 @@ package termui
 const (
 	DOT      = '•'
 	ELLIPSES = '…'
+
+	UP_ARROW   = '▲'
+	DOWN_ARROW = '▼'
 )
 
 var (
diff --git a/widgets/list.go b/widgets/list.go
index b6497bd..61c74e3 100644
--- a/widgets/list.go
+++ b/widgets/list.go
@@ -12,15 +12,19 @@ import (
 
 type List struct {
 	Block
-	Rows      []string
-	Wrap      bool
-	TextStyle Style
+	Rows             []string
+	WrapText         bool
+	TextStyle        Style
+	SelectedRow      uint
+	topRow           uint
+	SelectedRowStyle Style
 }
 
 func NewList() *List {
 	return &List{
-		Block:     *NewBlock(),
-		TextStyle: Theme.List.Text,
+		Block:            *NewBlock(),
+		TextStyle:        Theme.List.Text,
+		SelectedRowStyle: Theme.List.Text,
 	}
 }
 
@@ -29,24 +33,59 @@ func (self *List) Draw(buf *Buffer) {
 
 	point := self.Inner.Min
 
-	for row := 0; row < len(self.Rows) && point.Y < self.Inner.Max.Y; row++ {
+	for row := self.topRow; row < uint(len(self.Rows)) && point.Y < self.Inner.Max.Y; row++ {
 		cells := ParseText(self.Rows[row], self.TextStyle)
-		if self.Wrap {
+		if self.WrapText {
 			cells = WrapCells(cells, uint(self.Inner.Dx()))
 		}
 		for j := 0; j < len(cells) && point.Y < self.Inner.Max.Y; j++ {
+			style := cells[j].Style
+			if row == self.SelectedRow {
+				style = self.SelectedRowStyle
+			}
 			if cells[j].Rune == '\n' {
 				point = image.Pt(self.Inner.Min.X, point.Y+1)
 			} else {
 				if point.X+1 == self.Inner.Max.X+1 && len(cells) > self.Inner.Dx() {
-					buf.SetCell(NewCell(ELLIPSES, cells[j].Style), point.Add(image.Pt(-1, 0)))
+					buf.SetCell(NewCell(ELLIPSES, style), point.Add(image.Pt(-1, 0)))
 					break
 				} else {
-					buf.SetCell(cells[j], point)
+					buf.SetCell(NewCell(cells[j].Rune, style), point)
 					point = point.Add(image.Pt(1, 0))
 				}
 			}
 		}
 		point = image.Pt(self.Inner.Min.X, point.Y+1)
 	}
+
+	if self.topRow > 0 {
+		buf.SetCell(
+			NewCell(UP_ARROW, NewStyle(ColorWhite)),
+			image.Pt(self.Inner.Max.X-1, self.Inner.Min.Y),
+		)
+	}
+	if len(self.Rows) > int(self.topRow)+self.Inner.Dy() {
+		buf.SetCell(
+			NewCell(DOWN_ARROW, NewStyle(ColorWhite)),
+			image.Pt(self.Inner.Max.X-1, self.Inner.Max.Y-1),
+		)
+	}
+}
+
+func (self *List) ScrollUp() {
+	if self.SelectedRow > 0 {
+		self.SelectedRow--
+		if self.SelectedRow < self.topRow {
+			self.topRow--
+		}
+	}
+}
+
+func (self *List) ScrollDown() {
+	if self.SelectedRow < uint(len(self.Rows))-1 {
+		self.SelectedRow++
+		if self.SelectedRow-self.topRow > uint(self.Inner.Dy()-1) {
+			self.topRow++
+		}
+	}
 }