package storage

import (
	"context"
	"errors"
	"mime"
	"net/http"
	"strings"
	"time"
	"unicode"
	"unicode/utf8"
)

const (
	DispositionAttachment = "attachment"
	DispositionInline     = "inline"
)

// ReadOptions controls the response to one signed GET. Empty Disposition means
// attachment; empty ContentType preserves object metadata. FileName is a display
// name, not an object key or filesystem path. All options are signed.
type ReadOptions struct {
	Disposition string
	FileName    string
	ContentType string
}

// ReadLink grants GET access without additional request headers. ExpiresAt is
// the expiry encoded in the signature, at second precision. Provider credentials
// may expire earlier. Do not log the URL. Issuing another link does not revoke it.
type ReadLink struct {
	URL       string    `json:"url"`
	ExpiresAt time.Time `json:"expiresAt"`
}

// ReadPresigner is optional; existing Store and Presigner implementations do not
// need to change. Cloud GET signatures do not also authorize HEAD requests.
type ReadPresigner interface {
	PresignGetWithOptions(context.Context, string, time.Duration, ReadOptions) (ReadLink, error)
}

// ResponseHeaders validates options and returns a fresh set of response headers
// for provider adapters to include BEFORE signing, requesting private, no-store.
func (o ReadOptions) ResponseHeaders() (http.Header, error) {
	disposition := o.Disposition
	if disposition == "" {
		disposition = DispositionAttachment
	}
	if disposition != DispositionAttachment && disposition != DispositionInline {
		return nil, errors.New("storage: disposition must be inline or attachment")
	}
	if len(o.FileName) > 1024 || !utf8.ValidString(o.FileName) || strings.IndexFunc(o.FileName, unicode.IsControl) >= 0 || strings.ContainsAny(o.FileName, `/\`) || o.FileName == "." || o.FileName == ".." {
		return nil, errors.New("storage: invalid display filename")
	}
	params := map[string]string{}
	if o.FileName != "" {
		params["filename"] = o.FileName
	}
	h := http.Header{"Content-Disposition": {mime.FormatMediaType(disposition, params)}, "Cache-Control": {"private, no-store"}}
	if o.ContentType != "" {
		if !utf8.ValidString(o.ContentType) || strings.IndexFunc(o.ContentType, unicode.IsControl) >= 0 {
			return nil, ErrContentType
		}
		kind, err := MediaType(o.ContentType)
		if err != nil {
			return nil, err
		}
		_, params, _ := mime.ParseMediaType(o.ContentType)
		h.Set("Content-Type", mime.FormatMediaType(kind, params))
	}
	return h, nil
}