buffer.go

package main

import (
	"bufio"
	"errors"
	"log"
	"os"
)

// A Buffer is a view into a file on the servers computer
type Buffer struct {
	prev *Stack
	curr *string
	next *Stack

	file *string
}

// EmptyBuffer returns a new, empty, buffer
func EmptyBuffer() *Buffer {
	return &Buffer{
		prev: new(Stack),
		curr: nil,
		next: new(Stack),
	}
}

// BufferFromFile returns a new buffer of the given filepath
func BufferFromFile(filepath string) *Buffer {
	buff := EmptyBuffer()
	buff.file = &filepath

	file, err := os.Open(filepath)
	if err != nil {
		log.Printf("Opening a new file [%s]", filepath)
		return buff
	}
	defer file.Close()

	scanner := bufio.NewScanner(file)
	scanner.Split(bufio.ScanLines)

	for scanner.Scan() {
		buff.Append(scanner.Text())
	}

	buff.Goto(1)
	return buff
}

// Write writes the buffer to the file associated with it
func (buff *Buffer) Write() error {
	if buff.file == nil {
		return errors.New("Buffer has no file associated with it")
	}

	file, err := os.Create(*buff.file)
	if err != nil {
		return err
	}
	defer file.Close()

	orgLine := buff.GetLineNum()

	lastLine := 0
	buff.Goto(1)
	for buff.GetLineNum() != lastLine {
		file.WriteString(buff.GetLine() + "\n")

		lastLine = buff.GetLineNum()
		buff.NextLine()
	}

	buff.Goto(orgLine)
	return nil
}

// GetLine returns the current line from the buffer
func (buff *Buffer) GetLine() string {
	if buff.curr != nil {
		return *buff.curr
	}

	return ""
}

// GetLineNum returns the current line number
func (buff Buffer) GetLineNum() int {
	return buff.prev.Len() + 1
}

// GetTotalLines returns the total line count
func (buff Buffer) GetTotalLines() int {
	var current int
	if buff.curr != nil {
		current = 1
	}
	return buff.prev.Len() + buff.next.Len() + current
}

// NextLine shifts the lines forwards
func (buff *Buffer) NextLine() {
	el := buff.next.Pop()
	if el == nil {
		return
	}
	buff.prev.Push(*buff.curr)
	buff.curr = el
}

// PrevLine shifts the lines backwards
func (buff *Buffer) PrevLine() {
	el := buff.prev.Pop()
	if el == nil {
		return
	}

	buff.next.Push(*buff.curr)
	buff.curr = el
}

// Goto shifts the lines to the specified line
func (buff *Buffer) Goto(num int) {
	if buff.GetTotalLines() == 0 {
		return
	}

	if num < 1 {
		num = 1
	} else if num > buff.GetTotalLines() {
		num = buff.GetTotalLines()
	}

	for buff.GetLineNum() != num {
		if buff.GetLineNum() > num {
			buff.PrevLine()
		} else {
			buff.NextLine()
		}
	}
}

// Insert puts text before the current line
// And sets the current line to the inserted text
func (buff *Buffer) Insert(text string) {
	if buff.curr != nil {
		buff.next.Push(*buff.curr)
	}

	buff.curr = &text
}

// Append puts text after the current line
// And sets the current line to the appended text
func (buff *Buffer) Append(text string) {
	if buff.curr != nil {
		buff.prev.Push(*buff.curr)
	}

	buff.curr = &text
}