From 25f8b8c99b2d58e6995841b6f2693cda7403ea9f Mon Sep 17 00:00:00 2001
From: Christian Rocha <christian@rocha.is>
Date: Fri, 15 May 2020 16:08:58 -0400
Subject: [PATCH] Simplify pager component and fix pager example

---
 examples/pager/main.go | 73 ++++++++++++++++++++++++++++++++++++++++--
 pager/pager.go         | 21 +++---------
 2 files changed, 75 insertions(+), 19 deletions(-)

diff --git a/examples/pager/main.go b/examples/pager/main.go
index 8268580..e752a84 100644
--- a/examples/pager/main.go
+++ b/examples/pager/main.go
@@ -10,20 +10,87 @@ import (
 )
 
 func main() {
+
+	// Load some text to render
 	content, err := ioutil.ReadFile("artichoke.md")
 	if err != nil {
 		fmt.Println("could not load file:", err)
 		os.Exit(1)
 	}
 
+	// Use the full size of the terminal in its "Alternate Screen Buffer"
 	boba.AltScreen()
 	defer boba.ExitAltScreen()
+
 	if err := boba.NewProgram(
-		pager.Init(string(content)),
-		pager.Update,
-		pager.View,
+		initialize(string(content)),
+		update,
+		view,
 	).Start(); err != nil {
 		fmt.Println("could not run program:", err)
 		os.Exit(1)
 	}
 }
+
+type terminalSizeMsg struct {
+	width  int
+	height int
+	err    error
+}
+
+func (t terminalSizeMsg) Size() (int, int) { return t.width, t.height }
+func (t terminalSizeMsg) Error() error     { return t.err }
+
+type model struct {
+	err     error
+	content string
+	ready   bool
+	pager   pager.Model
+}
+
+func initialize(content string) func() (boba.Model, boba.Cmd) {
+	return func() (boba.Model, boba.Cmd) {
+		return model{
+			content: content,
+		}, getTerminalSize()
+	}
+}
+
+func update(msg boba.Msg, mdl boba.Model) (boba.Model, boba.Cmd) {
+	m, _ := mdl.(model)
+
+	switch msg := msg.(type) {
+	case boba.KeyMsg:
+		if msg.Type == boba.KeyCtrlC {
+			return m, boba.Quit
+		}
+		m.pager, _ = pager.Update(msg, m.pager)
+	case terminalSizeMsg:
+		if msg.Error() != nil {
+			m.err = msg.Error()
+			break
+		}
+		w, h := msg.Size()
+		m.pager = pager.NewModel(w, h)
+		m.pager.SetContent(m.content)
+		m.ready = true
+	}
+
+	return m, nil
+}
+
+func view(mdl boba.Model) string {
+	m, _ := mdl.(model)
+	if m.err != nil {
+		return "\nError:" + m.err.Error()
+	} else if m.ready {
+		return "\n" + pager.View(m.pager)
+	}
+	return "\nInitalizing..."
+}
+
+func getTerminalSize() boba.Cmd {
+	return boba.GetTerminalSize(func(w, h int, err error) boba.TerminalSizeMsg {
+		return terminalSizeMsg{width: w, height: h, err: err}
+	})
+}
diff --git a/pager/pager.go b/pager/pager.go
index a6f01e9..5860f16 100644
--- a/pager/pager.go
+++ b/pager/pager.go
@@ -1,7 +1,6 @@
 package pager
 
 import (
-	"errors"
 	"strings"
 
 	"github.com/charmbracelet/boba"
@@ -18,6 +17,7 @@ type Model struct {
 	lines []string
 }
 
+// Scrollpercent returns the amount scrolled as a float between 0 and 1
 func (m Model) ScrollPercent() float64 {
 	if m.Height >= len(m.lines) {
 		return 1.0
@@ -34,6 +34,7 @@ func (m *Model) SetContent(s string) {
 	m.lines = strings.Split(s, "\n")
 }
 
+// NewModel creates a new pager model. Pass the dimensions of the pager.
 func NewModel(width, height int) Model {
 	return Model{
 		Width:  width,
@@ -43,14 +44,7 @@ func NewModel(width, height int) Model {
 
 // UPDATE
 
-func Update(msg boba.Msg, model boba.Model) (boba.Model, boba.Cmd) {
-	m, ok := model.(Model)
-	if !ok {
-		return Model{
-			Err: errors.New("could not perform assertion on model in update in pager; are you sure you passed the correct model?"),
-		}, nil
-	}
-
+func Update(msg boba.Msg, m Model) (Model, boba.Cmd) {
 	switch msg := msg.(type) {
 
 	case boba.KeyMsg:
@@ -103,18 +97,13 @@ func Update(msg boba.Msg, model boba.Model) (boba.Model, boba.Cmd) {
 		}
 	}
 
-	return model, nil
+	return m, nil
 }
 
 // VIEW
 
 // View renders the viewport into a string
-func View(model boba.Model) string {
-	m, ok := model.(Model)
-	if !ok {
-		return "could not perform assertion on model in view in pager; are you sure you passed the correct model?"
-	}
-
+func View(m Model) string {
 	if m.Err != nil {
 		return m.Err.Error()
 	}