tools/src/substr/substr.go

// Copyright 2021 The Dawn & Tint Authors
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package substr

import (
	diff "github.com/sergi/go-diff/diffmatchpatch"
)

// Fix attempts to reconstruct substr by comparing it to body.
// substr is a fuzzy substring of body.
// Fix returns a new exact substring of body, by calculating a diff of the text.
// If no match could be made, Fix() returns an empty string.
func Fix(body, substr string) string {
	dmp := diff.New()

	diffs := dmp.DiffMain(body, substr, false)
	if len(diffs) == 0 {
		return ""
	}

	front := func() diff.Diff { return diffs[0] }
	back := func() diff.Diff { return diffs[len(diffs)-1] }

	start, end := 0, len(body)

	// Trim edits that remove text from body start
	for len(diffs) > 0 && front().Type == diff.DiffDelete {
		start += len(front().Text)
		diffs = diffs[1:]
	}

	// Trim edits that remove text from body end
	for len(diffs) > 0 && back().Type == diff.DiffDelete {
		end -= len(back().Text)
		diffs = diffs[:len(diffs)-1]
	}

	// New substring is the span for the remainder of the edits
	return body[start:end]
}