package fetch

import (
	"mime"
	"net/http"
	"path"
	"path/filepath"
	"strings"
	"unicode/utf8"
)

const (
	maxFileNameBytes  = 200
	maxExtensionBytes = 16
	fallbackFileName  = "download"
)

func FileNameFromResponse(response *http.Response) string {
	if disposition := response.Header.Get("Content-Disposition"); disposition != "" {
		if _, parameters, err := mime.ParseMediaType(disposition); err == nil {
			if name := SanitizeFileName(parameters["filename"]); name != "" {
				return name
			}
		}
	}
	if response.Request != nil && response.Request.URL != nil {
		if name := SanitizeFileName(path.Base(response.Request.URL.Path)); name != "" {
			return name
		}
	}
	return fallbackFileName
}

func SanitizeFileName(raw string) string {
	name := path.Base(strings.ReplaceAll(raw, "\\", "/"))
	name = strings.Map(dropUnsafeRune, name)
	name = strings.TrimSpace(strings.TrimLeft(name, ". "))
	if name == "" {
		return ""
	}
	return truncate(name)
}

func dropUnsafeRune(character rune) rune {
	if character < 0x20 || character == 0x7f || character == '/' || character == utf8.RuneError {
		return -1
	}
	return character
}

func truncate(name string) string {
	if len(name) <= maxFileNameBytes {
		return name
	}
	extension := filepath.Ext(name)
	if len(extension) > maxExtensionBytes {
		extension = ""
	}
	base := strings.TrimSuffix(name, extension)
	for len(base)+len(extension) > maxFileNameBytes {
		_, size := utf8.DecodeLastRuneInString(base)
		base = base[:len(base)-size]
	}
	return base + extension
}