// Package gofmt refuses a Go file of the catalogue that gofmt would change (the second of a kind in one milestone:
// buildstep's generated.go and claude-code's config_test.go reached a join unformatted). A check here holds every
// module to it, where a module's own tests hold only themselves.
package gofmt

import (
	"bytes"
	"go/format"
	"io/fs"
	"os"
	"path/filepath"
	"sort"
	"strings"
)

// Files are the Go files under root, relative to it: every .go file but those in .git, node_modules and a testdata
// directory (a test's fixture may be anything).
func Files(root string) ([]string, error) {
	var out []string
	err := filepath.WalkDir(root, func(p string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if d.IsDir() {
			switch d.Name() {
			case ".git", "node_modules", "testdata":
				return filepath.SkipDir
			}
			return nil
		}
		if strings.HasSuffix(d.Name(), ".go") && d.Type().IsRegular() {
			rel, _ := filepath.Rel(root, p)
			out = append(out, filepath.ToSlash(rel))
		}
		return nil
	})
	sort.Strings(out)
	return out, err
}

// Unformatted are the files gofmt would change, and why for one that does not parse.
func Unformatted(root string, files []string) (map[string]string, error) {
	out := map[string]string{}
	for _, f := range files {
		src, err := os.ReadFile(filepath.Join(root, f))
		if err != nil {
			return nil, err
		}
		got, err := format.Source(src)
		switch {
		case err != nil:
			out[f] = "it does not parse: " + err.Error()
		case !bytes.Equal(got, src):
			out[f] = "gofmt changes it: run gofmt -w " + f
		}
	}
	return out, nil
}