bubbletea/examples/pager/main.go

package main

// An example program demonstrating the pager component from the Bubbles
// component library.

import (
	"fmt"
	"io/ioutil"
	"os"
	"strings"

	"github.com/charmbracelet/bubbles/viewport"
	tea "github.com/charmbracelet/bubbletea"
	"github.com/mattn/go-runewidth"
)

const (
	// You generally won't need this unless you're processing stuff with some
	// pretty complicated ANSI escape sequences. Turn it on if you notice
	// flickering.
	//
	// Also note that high performance rendering only works for programs that
	// use the full size of the terminal. We're enabling that below with
	// tea.EnterAltScreen().
	useHighPerformanceRenderer = false

	headerHeight = 3
	footerHeight = 3
)

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)
	}

	// Set PAGER_LOG to a path to log to a file. For example:
	//
	//     export PAGER_LOG=debug.log
	//
	// This becomes handy when debugging stuff since you can't debug to stdout
	// because the UI is occupying it!
	path := os.Getenv("PAGER_LOG")
	if path != "" {
		f, err := tea.LogToFile(path, "pager")
		if err != nil {
			fmt.Printf("Could not open file %s: %v", path, err)
			os.Exit(1)
		}
		defer f.Close()
	}

	p := tea.NewProgram(model{content: string(content)})

	// Use the full size of the terminal in its "alternate screen buffer"
	p.EnterAltScreen()
	defer p.ExitAltScreen()

	// We also turn on mouse support so we can track the mouse wheel
	p.EnableMouseCellMotion()
	defer p.DisableMouseCellMotion()

	if err := p.Start(); err != nil {
		fmt.Println("could not run program:", err)
		os.Exit(1)
	}
}

type model struct {
	content  string
	ready    bool
	viewport viewport.Model
}

func (m model) Init() tea.Cmd {
	return nil
}

func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
	var (
		cmd  tea.Cmd
		cmds []tea.Cmd
	)

	switch msg := msg.(type) {
	case tea.KeyMsg:
		// Ctrl+c exits
		if k := msg.String(); k == "ctrl+c" || k == "q" {
			return m, tea.Quit
		}

	case tea.WindowSizeMsg:
		verticalMargins := headerHeight + footerHeight

		if !m.ready {
			// Since this program is using the full size of the viewport we need
			// to wait until we've received the window dimensions before we
			// can initialize the viewport. The initial dimensions come in
			// quickly, though asynchronously, which is why we wait for them
			// here.
			m.viewport = viewport.Model{Width: msg.Width, Height: msg.Height - verticalMargins}
			m.viewport.YPosition = headerHeight
			m.viewport.HighPerformanceRendering = useHighPerformanceRenderer
			m.viewport.SetContent(m.content)
			m.ready = true
		} else {
			m.viewport.Width = msg.Width
			m.viewport.Height = msg.Height - verticalMargins
		}

		if useHighPerformanceRenderer {
			// Render (or re-render) the whole viewport. Necessary both to
			// initialize the viewport and when the window is resized.
			//
			// This is needed for high-performance rendering only.
			cmds = append(cmds, viewport.Sync(m.viewport))
		}
	}

	// Because we're using the viewport's default update function (with pager-
	// style navigation) it's important that the viewport's update function:
	//
	// * Receives messages from the Bubble Tea runtime
	// * Returns commands to the Bubble Tea runtime
	//
	m.viewport, cmd = m.viewport.Update(msg)
	if useHighPerformanceRenderer {
		cmds = append(cmds, cmd)
	}

	return m, tea.Batch(cmds...)
}

func (m model) View() string {
	if !m.ready {
		return "\n  Initializing..."
	}

	headerTop := "╭───────────╮"
	headerMid := "│ Mr. Pager ├"
	headerBot := "╰───────────╯"
	headerMid += strings.Repeat("─", m.viewport.Width-runewidth.StringWidth(headerMid))
	header := fmt.Sprintf("%s\n%s\n%s", headerTop, headerMid, headerBot)

	footerTop := "╭──────╮"
	footerMid := fmt.Sprintf("┤ %3.f%% │", m.viewport.ScrollPercent()*100)
	footerBot := "╰──────╯"
	gapSize := m.viewport.Width - runewidth.StringWidth(footerMid)
	footerTop = strings.Repeat(" ", gapSize) + footerTop
	footerMid = strings.Repeat("─", gapSize) + footerMid
	footerBot = strings.Repeat(" ", gapSize) + footerBot
	footer := fmt.Sprintf("%s\n%s\n%s", footerTop, footerMid, footerBot)

	return fmt.Sprintf("%s\n%s\n%s", header, m.viewport.View(), footer)
}