package fs

import (
	"context"
	"io/fs"
	"strings"
	"text/template"

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

// GeminiFileHandler builds a handler which serves up files from a file system.
//
// It only serves responses for paths which do not correspond to directories on disk.
func GeminiFileHandler(fileSystem fs.FS) gus.Handler {
	return func(ctx context.Context, request *gus.Request) *gus.Response {
		filepath, file, err := ResolveFile(request, fileSystem)
		if err != nil {
			return gemini.Failure(err)
		}

		if file == nil {
			return nil
		}

		return gemini.Success(mediaType(filepath), file)
	}
}

// GeminiDirectoryDefault serves up default files for directory path requests.
//
// If any of the supported filenames are found, the contents of the file is returned
// as the gemini response.
//
// It returns nil for any paths which don't correspond to a directory.
//
// When it encounters a directory path which doesn't end in a trailing slash (/) it
// redirects to a URL with the trailing slash appended. This is necessary for relative
// links inot the directory's contents to function properly.
//
// It requires that files from the provided fs.FS implement fs.ReadDirFile. If they
// don't, it will produce nil responses for any directory paths.
func GeminiDirectoryDefault(fileSystem fs.FS, filenames ...string) gus.Handler {
	return func(ctx context.Context, request *gus.Request) *gus.Response {
		dirpath, dir, response := handleDirGemini(request, fileSystem)
		if response != nil {
			return response
		}
		if dir == nil {
			return nil
		}
		defer func() { _ = dir.Close() }()

		filepath, file, err := ResolveDirectoryDefault(fileSystem, dirpath, dir, filenames)
		if err != nil {
			return gemini.Failure(err)
		}
		if file == nil {
			return nil
		}

		return gemini.Success(mediaType(filepath), file)
	}
}

// GeminiDirectoryListing produces a listing of the contents of any requested directories.
//
// It returns "51 Not Found" for any paths which don't correspond to a filesystem directory.
//
// When it encounters a directory path which doesn't end in a trailing slash (/) it
// redirects to a URL with the trailing slash appended. This is necessary for relative
// links inot the directory's contents to function properly.
//
// It requires that files from the provided fs.FS implement fs.ReadDirFile. If they
// don't, it will produce "51 Not Found" responses for any directory paths.
//
// The template may be nil, in which case DefaultGeminiDirectoryList is used instead. The
// template is then processed with RenderDirectoryListing.
func GeminiDirectoryListing(fileSystem fs.FS, template *template.Template) gus.Handler {
	return func(ctx context.Context, request *gus.Request) *gus.Response {
		dirpath, dir, response := handleDirGemini(request, fileSystem)
		if response != nil {
			return response
		}
		if dir == nil {
			return nil
		}
		defer func() { _ = dir.Close() }()

		if template == nil {
			template = DefaultGeminiDirectoryList
		}
		body, err := RenderDirectoryListing(dirpath, dir, template, request.Server)
		if err != nil {
			return gemini.Failure(err)
		}

		return gemini.Success("text/gemini", body)
	}
}

// DefaultGeminiDirectoryList is a template which renders a reasonable gemtext dir list.
var DefaultGeminiDirectoryList = template.Must(template.New("gemini_dirlist").Parse(`
# {{ .DirName }}
{{ range .Entries }}
=> {{ .Name }}{{ if .IsDir }}/{{ end -}}
{{ end }}
=> ../
`[1:]))

func handleDirGemini(request *gus.Request, fileSystem fs.FS) (string, fs.ReadDirFile, *gus.Response) {
	path, dir, err := ResolveDirectory(request, fileSystem)
	if err != nil {
		return "", nil, gemini.Failure(err)
	}

	if dir == nil {
		return "", nil, nil
	}

	if !strings.HasSuffix(request.Path, "/") {
		_ = dir.Close()
		url := *request.URL
		url.Path += "/"
		return "", nil, gemini.Redirect(url.String())
	}

	return path, dir, nil
}