gilo/editor/draw.go

// Editor methods involved in drawing to the console
package editor

import (
	"fmt"
	"strings"
	"timshome.page/gilo/terminal"
)

// ----------------------------------------------------------------------------
// !Editor Methods
// ----------------------------------------------------------------------------

func (e *editor) RefreshScreen() {
	e.scroll()

	ab := newBuffer()

	ab.append(terminal.HideCursor)
	ab.append(terminal.ResetCursor)

	e.drawRows(ab)
	ab.append(terminal.MoveCursor(e.cursor.x, e.cursor.y))

	ab.append(terminal.ShowCursor)

	terminal.Write(ab.toString())
}

func (e *editor) scroll() {
	if e.cursor.y < e.offset.y {
		e.offset.y = e.cursor.y
	}

	if e.cursor.y >= e.offset.y + e.screen.Rows {
		e.offset.y = e.cursor.y - e.screen.Rows + 1
	}
}

func (e *editor) drawRows(ab *buffer) {
	for y :=0; y < e.screen.Rows; y++ {
		fileRow := y + e.offset.y

		if fileRow >= len(e.rows) {
			e.drawPlaceholderRow(y, ab)
		} else {
			row := truncateString(string(e.rows[fileRow].chars), e.screen.Cols)
			ab.append(row)
		}

		ab.append(terminal.ClearLine)

		if y < (e.screen.Rows - 1) {
			ab.append("\r\n")
		}
	}
}

func (e *editor) drawPlaceholderRow(y int, ab *buffer) {
	if len(e.rows) == 0 && y == e.screen.Rows / 3 {
		welcome := fmt.Sprintf("Gilo editor -- version %s", KiloVersion)
		if len(welcome) > e.screen.Cols {
			welcome = truncateString(welcome, e.screen.Cols)
		}

		padding := (e.screen.Cols - len(welcome)) / 2
		if padding > 0 {
			ab.appendRune('~')
			padding--
		}

		for padding > 0 {
			padding--
			ab.appendRune(' ')
		}

		ab.append(welcome)
	} else {
		ab.appendRune('~')
	}
}

// ----------------------------------------------------------------------------
// !Output Buffer
// ----------------------------------------------------------------------------

type buffer struct {
	buf *strings.Builder
}

func newBuffer() *buffer {
	var buf strings.Builder

	b := new(buffer)
	b.buf = &buf

	return b
}

func (b *buffer) appendRune(r rune) int {
	size, _ := b.buf.WriteRune(r)

	return size
}

func (b *buffer) append(s string) int {
	size, _ := b.buf.WriteString(s)

	return size
}

func (b *buffer) appendLn(s string) int {
	str := fmt.Sprintf("%s\r\n", s)
	size, _ := b.buf.WriteString(str)

	return size
}

func (b *buffer) toString() string {
	return b.buf.String()
}