package files

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

	"github.com/Southclaws/fault"
	"github.com/Southclaws/fault/fmsg"
	"go.alanpearce.eu/homestead/internal/buffer"
	"go.alanpearce.eu/homestead/internal/storage"
)

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

func (r *Reader) OpenFile(path string, filename string) (*storage.File, error) {
	f, err := os.Open(filename)
	if err != nil {
		return nil, fault.Wrap(err, fmsg.With("could not open file for reading"))
	}
	defer f.Close()
	stat, err := f.Stat()
	if err != nil {
		return nil, fault.Wrap(err, fmsg.With("could not stat file"))
	}

	buf := new(buffer.Buffer)
	if _, err := f.WriteTo(buf); err != nil {
		return nil, fault.Wrap(err, fmsg.With("could not read file"))
	}

	etag, err := etag(buf)
	if err != nil {
		return nil, fault.Wrap(err, fmsg.With("could not calculate etag"))
	}

	file := &storage.File{
		Path:         path,
		ContentType:  mime.TypeByExtension(filepath.Ext(filename)),
		LastModified: stat.ModTime(),
		Etag:         etag,
		Encodings: map[string]*buffer.Buffer{
			"identity": buf,
		},
	}

	err = file.CalculateStyleHash()
	if err != nil {
		return nil, fault.Wrap(err)
	}

	for enc, suffix := range encodings {
		_, err := os.Stat(filename + suffix)
		if err != nil {
			if errors.Is(err, os.ErrNotExist) {
				continue
			}

			return nil, fault.Wrap(
				err,
				fmsg.With(fmt.Sprintf("could not stat file %s", filename+suffix)),
			)
		}
		bytes, err := os.ReadFile(filename + suffix)
		if err != nil {
			return nil, fault.Wrap(
				err,
				fmsg.With(fmt.Sprintf("could not read file %s", filename+suffix)),
			)
		}
		buf := buffer.NewBuffer(bytes)
		file.Encodings[enc] = buf
	}

	return file, nil
}

func etag(f io.Reader) (string, error) {
	hash := fnv.New64a()
	if _, err := io.Copy(hash, f); err != nil {
		return "", fault.Wrap(err, fmsg.With("could not hash file"))
	}

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

func pathNameToFileName(pathname string) string {
	if strings.HasSuffix(pathname, "/") {
		pathname += "index.html"
	}

	return strings.TrimPrefix(pathname, "/")
}

func cutSuffix(s, suffix string) string {
	out, _ := strings.CutSuffix(s, suffix)

	return out
}

func fileNameToPathName(filename string) string {
	return cutSuffix(
		cutSuffix(filename, "index.html"),
		".html",
	)
}