package responsemodifers

import (
	"bytes"
	"io"
	"ladder/proxychain"
	"net/url"
	"strings"

	"golang.org/x/net/html"
)

type HTMLResourceURLRewriter struct {
	src      io.Reader
	buffer   *bytes.Buffer // buffer to temporarily hold rewritten output for the reader
	proxyURL *url.URL      // proxyURL is the URL of the proxy, not the upstream URL
}

func NewHTMLResourceURLRewriter(src io.Reader, proxyURL *url.URL) *HTMLResourceURLRewriter {
	return &HTMLResourceURLRewriter{
		src:      src,
		buffer:   new(bytes.Buffer),
		proxyURL: proxyURL,
	}
}

func rewriteToken(token *html.Token, baseURL *url.URL) {
	attrsToRewrite := map[string]bool{"href": true, "src": true, "action": true, "srcset": true}
	for i := range token.Attr {
		attr := &token.Attr[i]
		if attrsToRewrite[attr.Key] && strings.HasPrefix(attr.Val, "/") {
			// Make URL absolute
			attr.Val = "/https://" + baseURL.Host + attr.Val
		}
	}
}

func (r *HTMLResourceURLRewriter) Read(p []byte) (int, error) {
	if r.buffer.Len() != 0 {
		return r.buffer.Read(p)
	}

	tokenizer := html.NewTokenizer(r.src)
	for {
		tokenType := tokenizer.Next()
		if tokenType == html.ErrorToken {
			err := tokenizer.Err()
			if err == io.EOF {
				return 0, io.EOF // End of document
			}
			return 0, err // Actual error
		}

		token := tokenizer.Token()
		if tokenType == html.StartTagToken || tokenType == html.SelfClosingTagToken {
			rewriteToken(&token, r.proxyURL)
		}
		r.buffer.WriteString(token.String())
		if r.buffer.Len() > 0 {
			break
		}
	}
	return r.buffer.Read(p)
}

// RewriteHTMLResourceURLs updates src/href attributes in HTML content to route through the proxy.
func RewriteHTMLResourceURLs() proxychain.ResponseModification {
	return func(chain *proxychain.ProxyChain) error {
		ct := chain.Response.Header.Get("content-type")
		if ct != "text/html" {
			return nil
		}
		// TODO: implement chaining rewriter chaining method
		// so we can compose multiple body rewriters together
		return nil
	}
}