errors.go

// SPDX-FileCopyrightText: 2024 Christoph Mewes
// SPDX-License-Identifier: MIT

package rudi

import (
	"errors"
	"strings"

	"go.xrstf.de/rudi/pkg/lang/parser"
)

// ParseErrors can occur while parsing a Rudi program.
type ParseError struct {
	script string
	err    error
}

var _ error = ParseError{}

// Error returns the underlying parse error.
func (p ParseError) Error() string {
	return p.err.Error()
}

// Snippet is the line of the program where the error occurred, marked with a
// caret and the error message in a second line below that.
func (p ParseError) Snippet() string {
	var lister parser.ErrorLister
	if errors.As(p.err, &lister) {
		var buffer strings.Builder

		for _, e := range lister.Errors() {
			var parserErr parser.ParserError
			if !errors.As(e, &parserErr) {
				return ""
			}

			_, col, off := parserErr.Pos()
			line := extractLine(p.script, off)
			if col >= len(line) {
				col = len(line) - 1
			} else if col > 0 {
				col--
			}
			if col < 0 {
				col = 0
			}
			pos := col
			for _, chr := range line[:col] {
				if chr == '\t' {
					pos += 7
				}
			}

			buffer.WriteString(line + "\n")
			buffer.WriteString(strings.Repeat(" ", pos) + "^")
		}

		return buffer.String()
	}

	return ""
}

func extractLine(input string, initPos int) string {
	if initPos < 0 {
		initPos = 0
	}
	if initPos >= len(input) && len(input) > 0 {
		initPos = len(input) - 1
	}
	startPos := initPos
	endPos := initPos
	for ; startPos > 0; startPos-- {
		if input[startPos] == '\n' {
			if startPos != initPos {
				startPos++
				break
			}
		}
	}
	for ; endPos < len(input); endPos++ {
		if input[endPos] == '\n' {
			if endPos == initPos {
				endPos++
			}
			break
		}
	}
	return input[startPos:endPos]
}