github.com/d0sbit/gocode@v0.0.0-20211001144653-a968ce917518/srcedit/diff/diff.go

package diff

import (
	"bytes"
	"errors"
	"fmt"
	"io/fs"
	"io/ioutil"

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

// Run walks the out fs and compares to in, rooted at rootDir ("." means root of fs),
// and report differences in a map of filenames to diff output.
// The outType indicates the output format, "html" will produce HTML output, any other
// value will product "term" output which is console/terminal output with highlighting.
func Run(in, out fs.FS, rootDir string, outType string) (map[string]string, error) {

	ret := make(map[string]string)

	trimPath := func(p string) string {
		// return strings.TrimPrefix(strings.TrimPrefix(p, rootDir), "/")
		return p
	}

	// walk the output directory and compare each file to the input
	err := fs.WalkDir(out, rootDir, fs.WalkDirFunc(func(p string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}

		if d.IsDir() {
			return nil
		}

		outf, err := out.Open(p)
		if err != nil {
			return fmt.Errorf("error opening output file %q: %w", p, err)
		}
		defer outf.Close()
		outb, err := ioutil.ReadAll(outf)
		if err != nil {
			return err
		}

		inf, err := in.Open(p)
		if err != nil {
			if !errors.Is(err, fs.ErrNotExist) {
				return fmt.Errorf("error opening input file %q: %w", p, err)
			}
			// if no input file, then diff against empty string
			df := diffContents("", string(outb), outType)
			ret[trimPath(p)] = df
			return nil
		}
		defer inf.Close()
		inb, err := ioutil.ReadAll(inf)
		if err != nil {
			return err
		}

		// check if they are exactly the same
		if bytes.Equal(inb, outb) {
			return nil // no difference to report
		}

		// diff out against in file
		df := diffContents(string(inb), string(outb), outType)
		ret[trimPath(p)] = df
		return nil
	}))
	if err != nil {
		return nil, err
	}

	return ret, nil
}

// diffContents performs a diff on the from and to contents of a file.
// The format of the returned byte slice depends on outType.
func diffContents(from, to string, outType string) string {

	// 	// fileAdmp, fileBdmp, dmpStrings := dmp.DiffLinesToChars(fileAtext, fileBtext)
	// 	// _ = dmpStrings
	// 	diffs := dmp.DiffMain(fileAtext, fileBtext, false)
	// 	// diffs := dmp.DiffMain(fileAdmp, fileBdmp, false)
	// 	// diffs = dmp.DiffCharsToLines(diffs, dmpStrings)
	// 	// diffs = dmp.DiffCleanupSemantic(diffs)
	// 	diffs = dmp.DiffCleanupSemanticLossless(diffs)
	// 	// diffs = dmp.DiffCharsToLines(diffs, dmpStrings)

	dmp := diffmatchpatch.New()

	diffs := dmp.DiffMain(from, to, true)

	diffs = dmp.DiffCleanupSemanticLossless(diffs)

	if outType == "html" {
		return dmp.DiffPrettyHtml(diffs)
	}

	return dmp.DiffPrettyText(diffs)
}