how to replace content in viewport

[seth-shi]

Hi, this is my minimality code, i am doing a article app, when user press n key, load next page reply,

package main

import (
	"fmt"
	"regexp"
	"strings"

	"github.com/charmbracelet/bubbles/viewport"
	tea "github.com/charmbracelet/bubbletea"
	"github.com/charmbracelet/lipgloss"
	"github.com/dromara/carbon/v2"
	"github.com/seth-shi/go-v2ex/internal/model/messages"
	"github.com/seth-shi/go-v2ex/internal/model/response"
)

type Model struct {
	viewport  viewport.Model
	replies   []response.V2ReplyResult
	replyPage int
}

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 msgType := msg.(type) {
	case messages.GetReplyResponse:
		m.replies = append(m.replies, msgType.Data.Result...)
		m.replyPage++
		cmds = append(cmds, m.initViewport())
	case tea.WindowSizeMsg:
		cmds = append(cmds, m.initViewport())
	case tea.KeyMsg:
		switch {
		case msgType.String() == "n":
			// load more reply
			return m, tea.Sequence(
				messages.LoadingRequestReply.PostStart(),
				// api request next page reply : m.replyPage
				messages.LoadingRequestReply.PostEnd(),
			)
		case msgType.String() == "i":
			// load more reply
			return m, m.replaceLinks()
		}
	}

	m.viewport, cmd = m.viewport.Update(msg)
	cmds = append(cmds, cmd)
	return m, tea.Batch(cmds...)
}

func (m Model) View() string {
	return m.viewport.View()
}

func (m *Model) replaceLinks() tea.Cmd {
	imgurPattern := regexp.MustCompile(`https://i\.imgur\.com/[a-zA-Z0-9]+(?:\.\w+)?`)
	list := imgurPattern.FindAllString(m.viewport.View(), -1)
	// imgMap = api.request(list)
	// replaceItems = [x1.png, ansiitext, x2.png, ansiitext]
	replaceItems := list
	// i try this way, but it's wrong, because press n key, image will replace
	r := strings.NewReplacer(replaceItems...)
	m.viewport.SetContent(r.Replace(m.viewport.View()))
	return nil
}

func (m *Model) initViewport() tea.Cmd {

	var (
		content strings.Builder
	)

	content.WriteString("\n\n")
	if len(m.replies) > 0 {
		var replies strings.Builder
		for i, r := range m.replies {
			floor := fmt.Sprintf(
				"#%d · %s @%s",
				i+1,
				carbon.CreateFromTimestamp(r.Created),
				r.Member.Username,
			)
			replies.WriteString(lipgloss.NewStyle().Bold(true).Render(floor))
			replies.WriteString("\n")
			replies.WriteString(r.GetContent())
			replies.WriteString("\n\n")
		}
		content.WriteString(replies.String())
	}

	m.viewport.SetContent(content.String())

	return nil
}

But I have a new feature, reply content includes image link, likely https://xxx.com/a.png, I need to replace with ASCII text (I'm already ok), But I don't know when to make the replacement. (at View() or initViewport() )