package util

import (
	"net/http"
	"strings"
)

// ApplyCustomHeadersFromAttrs applies user-defined headers stored in the provided attributes map.
// Custom headers override built-in defaults when conflicts occur.
func ApplyCustomHeadersFromAttrs(r *http.Request, attrs map[string]string) {
	if r == nil {
		return
	}
	applyCustomHeaders(r, extractCustomHeaders(attrs))
}

func extractCustomHeaders(attrs map[string]string) map[string]string {
	if len(attrs) == 0 {
		return nil
	}
	headers := make(map[string]string)
	for k, v := range attrs {
		if !strings.HasPrefix(k, "header:") {
			continue
		}
		name := strings.TrimSpace(strings.TrimPrefix(k, "header:"))
		if name == "" {
			continue
		}
		val := strings.TrimSpace(v)
		if val == "" {
			continue
		}
		headers[name] = val
	}
	if len(headers) == 0 {
		return nil
	}
	return headers
}

func applyCustomHeaders(r *http.Request, headers map[string]string) {
	if r == nil || len(headers) == 0 {
		return
	}
	for k, v := range headers {
		if k == "" || v == "" {
			continue
		}
		// Host is read from req.Host (not req.Header) by net/http when
		// writing the request; setting it via Header.Set is silently
		// dropped on the wire. Handle it explicitly so user-configured
		// virtual-host overrides actually take effect upstream.
		if http.CanonicalHeaderKey(k) == "Host" {
			r.Host = v
			continue
		}
		r.Header.Set(k, v)
	}
}