assemble.go

package main

import (
	"bufio"
	"fmt"
	"io"
	"regexp"
	"strings"

	"github.com/willbicks/dsdii-assembler/instruction"
	"github.com/willbicks/dsdii-assembler/output"
)

// commentRegex matches comments so they can be stripped from the input.
var commentRegex *regexp.Regexp

type config struct {
	in      io.Reader     // input reader
	out     output.Writer // output writer
	nopBuff uint          // number of nop instructions to include after each instruction
}

// stripComment removes any comments from the provided string, and returns a string containing only the instruction.
func stripComment(s string) string {
	if commentRegex == nil {
		commentRegex = regexp.MustCompile(`#.*?$`)
	}
	return strings.TrimSpace(commentRegex.ReplaceAllString(s, ""))
}

// assemble a series of instructions using the provided configuration, and return the number of lines assembled, and an error if one occurred.
func assemble(c config) (lines uint64, err error) {
	if err := c.out.WriteStart("generated by dsdii-assembler"); err != nil {
		return 0, fmt.Errorf("writing start: %v", err)
	}

	var line uint64
	var mc uint32
	inScan := bufio.NewScanner(c.in)
	for inScan.Scan() {
		line++

		// strip comments and whitespace and skip parsing if result is empty
		instWComment := strings.TrimSpace(inScan.Text())
		instString := stripComment(instWComment)
		if instString == "" {
			continue
		}

		// assemble and write instruction
		mc, err = instruction.Assemble(instString)
		if err != nil {
			return 0, fmt.Errorf("on line %d: %s", line, err)
		}
		if err := c.out.WriteInstruction(mc, instWComment); err != nil {
			return 0, fmt.Errorf("writing instruction: %v", err)
		}

		// add nop buffer as configured
		for i := uint(0); i < c.nopBuff; i++ {
			if err := c.out.WriteInstruction(0, "nop buffer"); err != nil {
				return 0, fmt.Errorf("writing nop: %v", err)
			}
		}
	}

	if err := inScan.Err(); err != nil {
		return 0, fmt.Errorf("scan: %v", err)
	}

	if err := c.out.WriteEnd(); err != nil {
		return 0, fmt.Errorf("writing end: %v", err)
	}

	return line, nil
}