package client

import (
	"io"
	"net/http"
	"sync"
)

// Transport is an http.RoundTripper that makes registry HTTP requests,
// wrapping a base RoundTripper and adding an Authorization header
// from an Auth source
type Transport struct {
	AuthSource  Authorizer
	ExtraHeader http.Header

	Base http.RoundTripper

	mu     sync.Mutex                      // guards modReq
	modReq map[*http.Request]*http.Request // original -> modified
}

// RoundTrip authorizes and authenticates the request with an
// access token. If no token exists or token is expired,
// tries to refresh/fetch a new token.
func (t *Transport) RoundTrip(req *http.Request) (*http.Response, error) {
	req2 := t.cloneRequest(req)
	if t.AuthSource != nil {
		if err := t.AuthSource.Authorize(req2); err != nil {
			return nil, err
		}
	}
	t.setModReq(req, req2)
	res, err := t.base().RoundTrip(req2)
	if err != nil {
		t.setModReq(req, nil)
		return nil, err
	}
	res.Body = &onEOFReader{
		rc: res.Body,
		fn: func() { t.setModReq(req, nil) },
	}
	return res, nil
}

// CancelRequest cancels an in-flight request by closing its connection.
func (t *Transport) CancelRequest(req *http.Request) {
	type canceler interface {
		CancelRequest(*http.Request)
	}
	if cr, ok := t.base().(canceler); ok {
		t.mu.Lock()
		modReq := t.modReq[req]
		delete(t.modReq, req)
		t.mu.Unlock()
		cr.CancelRequest(modReq)
	}
}

func (t *Transport) base() http.RoundTripper {
	if t.Base != nil {
		return t.Base
	}
	return http.DefaultTransport
}

func (t *Transport) setModReq(orig, mod *http.Request) {
	t.mu.Lock()
	defer t.mu.Unlock()
	if t.modReq == nil {
		t.modReq = make(map[*http.Request]*http.Request)
	}
	if mod == nil {
		delete(t.modReq, orig)
	} else {
		t.modReq[orig] = mod
	}
}

// cloneRequest returns a clone of the provided *http.Request.
// The clone is a shallow copy of the struct and its Header map.
func (t *Transport) cloneRequest(r *http.Request) *http.Request {
	// shallow copy of the struct
	r2 := new(http.Request)
	*r2 = *r
	// deep copy of the Header
	r2.Header = make(http.Header, len(r.Header))
	for k, s := range r.Header {
		r2.Header[k] = append([]string(nil), s...)
	}
	for k, s := range t.ExtraHeader {
		r2.Header[k] = append(r2.Header[k], s...)
	}
	return r2
}

type onEOFReader struct {
	rc io.ReadCloser
	fn func()
}

func (r *onEOFReader) Read(p []byte) (n int, err error) {
	n, err = r.rc.Read(p)
	if err == io.EOF {
		r.runFunc()
	}
	return
}

func (r *onEOFReader) Close() error {
	err := r.rc.Close()
	r.runFunc()
	return err
}

func (r *onEOFReader) runFunc() {
	if fn := r.fn; fn != nil {
		fn()
		r.fn = nil
	}
}