package fs

import (
	"context"
	"io/fs"
	"mime"
	"strings"

	"tildegit.org/tjp/gus"
	"tildegit.org/tjp/gus/gemini"
)

// FileHandler builds a handler function which serves up a file system.
func FileHandler(fileSystem fs.FS) gus.Handler {
	return func(ctx context.Context, req *gus.Request) *gus.Response {
		file, err := fileSystem.Open(strings.TrimPrefix(req.Path, "/"))
		if isNotFound(err) {
			return nil
		}
		if err != nil {
			return gemini.Failure(err)
		}

		isDir, err := fileIsDir(file)
		if err != nil {
			return gemini.Failure(err)
		}

		if isDir {
			return nil
		}

		return gemini.Success(mediaType(req.Path), file)
	}
}

func mediaType(filePath string) string {
	if strings.HasSuffix(filePath, ".gmi") {
		// This may not be present in the listings searched by mime.TypeByExtension,
		// so provide a dedicated fast path for it here.
		return "text/gemini"
	}

	slashIdx := strings.LastIndex(filePath, "/")
	dotIdx := strings.LastIndex(filePath[slashIdx+1:], ".")
	if dotIdx == -1 {
		return "application/octet-stream"
	}
	ext := filePath[slashIdx+1+dotIdx:]

	mtype := mime.TypeByExtension(ext)
	if mtype == "" {
		return "application/octet-stream"
	}
	return mtype
}