package handlers

import (
	"strings"

	"github.com/labstack/echo/v5"
)

// deriveBaseURL returns the base URL to use for constructing self-referential
// links (OPDS feeds, sidecar config, etc.). It prefers the database-configured
// base_url when available, and falls back to deriving the URL from the incoming
// HTTP request (Host header + scheme), which is always reachable by the client.
//
// Proxy header support: X-Forwarded-Proto and X-Forwarded-Host are respected so
// that deployments behind TLS-terminating reverse proxies advertise the correct
// external URL.
func deriveBaseURL(c *echo.Context, dbBaseURL string) string {
	if dbBaseURL != "" {
		return strings.TrimRight(dbBaseURL, "/")
	}

	scheme := "http"
	if c.Request().TLS != nil {
		scheme = "https"
	}
	if proto := c.Request().Header.Get("X-Forwarded-Proto"); proto != "" {
		scheme = proto
	}

	host := c.Request().Host
	if forwarded := c.Request().Header.Get("X-Forwarded-Host"); forwarded != "" {
		host = forwarded
	}

	return scheme + "://" + host
}