// Copyright © 2023 Ory Corp
// SPDX-License-Identifier: Apache-2.0

package proxy

import (
	"bytes"
	"compress/gzip"
	"io"
	"net/http"
	"net/url"
	"path"
	"strings"

	"github.com/pkg/errors"
)

type compressableBody struct {
	buf bytes.Buffer
	w   io.WriteCloser
}

// we require a read and write for websocket connections
var _ io.ReadWriteCloser = new(compressableBody)

func (b *compressableBody) Close() error {
	if b != nil {
		b.buf.Reset()
		if b.w != nil {
			return b.w.Close()
		}
	}
	return nil
}

func (b *compressableBody) Write(d []byte) (int, error) {
	if b == nil {
		// this happens when the body is empty
		return 0, nil
	}

	var w io.Writer = &b.buf
	if b.w != nil {
		w = b.w
		defer b.w.Close()
	}
	return w.Write(d)
}

func (b *compressableBody) Read(p []byte) (n int, err error) {
	if b == nil {
		// this happens when the body is empty
		return 0, io.EOF
	}
	return b.buf.Read(p)
}

func headerRequestRewrite(req *http.Request, c *HostConfig) {
	req.URL.Scheme = c.UpstreamScheme
	req.URL.Host = c.UpstreamHost
	req.URL.Path = strings.TrimPrefix(req.URL.Path, c.PathPrefix)

	if _, ok := req.Header["User-Agent"]; !ok {
		// explicitly disable User-Agent so it's not set to default value
		req.Header.Set("User-Agent", "")
	}
}

func headerResponseRewrite(resp *http.Response, c *HostConfig) error {
	redir, err := resp.Location()
	if err != nil {
		if !errors.Is(err, http.ErrNoLocation) {
			return errors.WithStack(err)
		}
	} else if redir.Host == c.TargetHost {
		redir.Scheme = c.originalScheme
		redir.Host = c.originalHost
		redir.Path = path.Join(c.PathPrefix, redir.Path)
		resp.Header.Set("Location", redir.String())
	}

	ReplaceCookieDomainAndSecure(resp, c.TargetHost, c.CookieDomain, c.originalScheme == "https")

	return nil
}

// ReplaceCookieDomainAndSecure replaces the domain of all matching Set-Cookie headers in the response.
func ReplaceCookieDomainAndSecure(resp *http.Response, original, replacement string, secure bool) {
	original, replacement = stripPort(original), stripPort(replacement) // cookies don't distinguish ports

	cookies := resp.Cookies()
	resp.Header.Del("Set-Cookie")
	for _, co := range cookies {
		co.Domain = replacement
		co.Secure = secure
		if !secure {
			co.SameSite = http.SameSiteLaxMode
		}
		resp.Header.Add("Set-Cookie", co.String())
	}
}

func bodyResponseRewrite(resp *http.Response, c *HostConfig) ([]byte, *compressableBody, error) {
	if resp.ContentLength == 0 {
		return nil, nil, nil
	}

	body, cb, err := readBody(resp.Header, resp.Body)
	if err != nil {
		return nil, nil, err
	}

	if c.TargetScheme == "" {
		c.TargetScheme = "https"
	}

	return bytes.ReplaceAll(body, []byte(c.TargetScheme+"://"+c.TargetHost), []byte(c.originalScheme+"://"+c.originalHost+c.PathPrefix)), cb, nil
}

func readBody(h http.Header, body io.ReadCloser) ([]byte, *compressableBody, error) {
	defer body.Close()

	cb := &compressableBody{}

	switch h.Get("Content-Encoding") {
	case "gzip":
		var err error
		body, err = gzip.NewReader(body)
		if err != nil {
			return nil, nil, errors.WithStack(err)
		}

		cb.w = gzip.NewWriter(&cb.buf)
	default:
		// do nothing, we can read directly
	}

	b, err := io.ReadAll(body)
	if err != nil {
		return nil, nil, errors.WithStack(err)
	}
	return b, cb, nil
}

func handleWebsocketResponse(n int, cb *compressableBody, body io.ReadCloser) (int, io.ReadWriteCloser, error) {
	var err error
	readWriteCloser, ok := body.(io.ReadWriteCloser)
	if ok {
		if cb != nil {
			n, err = readWriteCloser.Write(cb.buf.Bytes())
			if err != nil {
				return 0, nil, errors.WithStack(err)
			}
		}
		return n, readWriteCloser, nil
	}
	return n, cb, nil
}

// stripPort removes the optional port from the host.
func stripPort(host string) string {
	return (&url.URL{Host: host}).Hostname()
}