// SPDX-License-Identifier: Unlicense

package main

import (
	"bufio"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"regexp"
	"strings"
)

var goSpdxHeader = `// SPDX-License-Identifier: Unlicense`
var tmplSpdxHeader = `{{/* SPDX-License-Identifier: Unlicense */`

type MissingSPDXError struct {
	Name string
}

func (m MissingSPDXError) Error() string {
	return fmt.Sprintf("missing or incorrect SPDX header: %s", m.Name)
}

func checkFileSPDX(header string, name string) error {
	f, err := os.Open(name)
	if err != nil {
		return err
	}
	defer f.Close()

	r := bufio.NewReader(f)
	pattern := `(?m:^` + regexp.QuoteMeta(header) + `)`
	matched, err := regexp.MatchReader(pattern, r)
	if err != nil {
		return err
	}
	if !matched {
		return MissingSPDXError{Name: name}
	}
	return nil
}

func walkSPDX(header string, extension string) error {
	var errs []error
	filepath.WalkDir(".", func(path string, d fs.DirEntry, err error) error {
		if path != "." && strings.HasPrefix(path, ".") {
			if d.IsDir() {
				return filepath.SkipDir
			}
			return nil
		}
		if err != nil {
			errs = append(errs, err)
			return nil
		}

		if filepath.Ext(path) != extension {
			return nil
		}
		errs = append(errs, checkFileSPDX(header, path))
		return nil
	})
	return errors.Join(errs...)
}

func checkSPDX() error {
	err := errors.Join(
		walkSPDX(goSpdxHeader, ".go"),
		walkSPDX(tmplSpdxHeader, ".tmpl"),
	)
	if err != nil {
		return fmt.Errorf("Check SPDX Headers:\n%w", err)
	}
	return nil
}

func run() error {
	return checkSPDX()
}

func main() {
	err := run()
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
}