position.go

package main

import (
	"errors"

	"github.com/xyproto/vt100"
)

// Position represents a position on the screen, including how far down the view has scrolled
type Position struct {
	sx          int // the position of the cursor in the current scrollview
	sy          int // the position of the cursor in the current scrollview
	offset      int // how far one has scrolled
	scrollSpeed int // how many lines to scroll, when scrolling
	savedX      int // for smart down cursor movement
}

// NewPosition returns a new Position struct
func NewPosition(scrollSpeed int) *Position {
	return &Position{0, 0, 0, scrollSpeed, 0}
}

// Copy will create a new Position struct that is a copy of this one
func (p *Position) Copy() Position {
	var p2 Position
	p2.sx = p.sx
	p2.sy = p.sy
	p2.offset = p.offset
	p2.scrollSpeed = p.scrollSpeed
	p2.savedX = p.savedX
	return p2
}

// ScreenX returns the screen X position in the current view
func (p *Position) ScreenX() int {
	return p.sx
}

// ScreenY returns the screen Y position in the current view
func (p *Position) ScreenY() int {
	return p.sy
}

// Offset returns the scroll offset for the current view
func (p *Position) Offset() int {
	return p.offset
}

// SetX will set the screen X position
func (p *Position) SetX(x int) {
	p.sx = x
}

// SetY will set the screen Y position
func (p *Position) SetY(y int) {
	p.sy = y
}

// SetOffset will set the screen scolling offset
func (p *Position) SetOffset(offset int) {
	p.offset = offset
}

// Up will move the cursor up
func (p *Position) Up() error {
	if p.sy <= 0 {
		return errors.New("already at the top of the canvas")
	}
	p.sy--
	return nil
}

// Down will move the cursor down
func (p *Position) Down(c *vt100.Canvas) error {
	h := 25
	if c != nil {
		h = int(c.H())
	}
	if p.sy >= h-1 {
		return errors.New("already at the bottom of the canvas")
	}
	p.sy++
	return nil
}

// AtStartOfLine returns true if the position is at the very start of the line, regardless of whitespace
func (p *Position) AtStartOfLine() bool {
	return p.sx == 0
}