package website

import (
	"fmt"
	"hash/fnv"
	"io"
	"io/fs"
	"mime"
	"os"
	"path/filepath"
	"strings"

	"go.alanpearce.eu/website/internal/log"

	"gitlab.com/tozd/go/errors"
)

type File struct {
	contentType  string
	etag         string
	alternatives map[string]string
}

func (f *File) AvailableEncodings() []string {
	encs := []string{}
	for enc := range f.alternatives {
		encs = append(encs, enc)
	}

	return encs
}

var files = map[string]*File{}

func hashFile(filename string) (string, error) {
	f, err := os.Open(filename)
	if err != nil {
		return "", errors.Wrapf(err, "could not open file %s for hashing", filename)
	}
	defer f.Close()
	hash := fnv.New64a()
	if _, err := io.Copy(hash, f); err != nil {
		return "", errors.Wrapf(err, "could not hash file %s", filename)
	}

	return fmt.Sprintf(`W/"%x"`, hash.Sum(nil)), nil
}

var encodings = map[string]string{
	"br":   ".br",
	"gzip": ".gz",
}

func registerFile(urlpath string, fp string) error {
	hash, err := hashFile(fp)
	if err != nil {
		return err
	}
	f := File{
		contentType: mime.TypeByExtension(filepath.Ext(fp)),
		etag:        hash,
		alternatives: map[string]string{
			"identity": fp,
		},
	}
	for enc, suffix := range encodings {
		_, err := os.Stat(fp + suffix)
		if err != nil {
			if errors.Is(err, os.ErrNotExist) {
				continue
			}

			return err
		}
		f.alternatives[enc] = fp + suffix
	}
	files[urlpath] = &f

	return nil
}

func registerContentFiles(root string, log *log.Logger) error {
	err := filepath.WalkDir(root, func(filePath string, f fs.DirEntry, err error) error {
		if err != nil {
			return errors.WithMessagef(err, "failed to access path %s", filePath)
		}
		relPath, err := filepath.Rel(root, filePath)
		if err != nil {
			return errors.WithMessagef(err, "failed to make path relative, path: %s", filePath)
		}
		urlPath, _ := strings.CutSuffix("/"+relPath, "index.html")
		if !f.IsDir() {
			switch filepath.Ext(relPath) {
			case ".br", ".gz":
				return nil
			}
			log.Debug("registering file", "urlpath", urlPath)

			return registerFile(urlPath, filePath)
		}

		return nil
	})
	if err != nil {
		return errors.Wrap(err, "could not walk directory")
	}

	return nil
}

func GetFile(urlPath string) *File {
	return files[urlPath]
}