// Lazy-loads the vendored Leaflet bundle (priv/static/vendor/leaflet/)
// the first time any Leaflet hook mounts. Per AGENTS.md we can't put
// inline <script> tags in templates, so we inject the <link>/<script>
// from JS instead. Returns a cached promise so concurrent hooks share
// one load attempt.

declare global {
  interface Window {
    L?: unknown
  }
}

let leafletLoad: Promise<void> | null = null

export function ensureLeaflet(): Promise<void> {
  if (typeof window.L !== "undefined") return Promise.resolve()
  if (leafletLoad) return leafletLoad

  leafletLoad = new Promise<void>((resolve, reject) => {
    if (!document.getElementById("leaflet-css")) {
      const css = document.createElement("link")
      css.id = "leaflet-css"
      css.rel = "stylesheet"
      css.href = "/vendor/leaflet/leaflet.css"
      document.head.appendChild(css)
    }

    const existing = document.getElementById("leaflet-js") as HTMLScriptElement | null
    if (existing) {
      if (typeof window.L !== "undefined") {
        resolve()
      } else {
        existing.addEventListener("load", () => resolve(), { once: true })
        existing.addEventListener("error", (e) => reject(e), { once: true })
      }
      return
    }

    const script = document.createElement("script")
    script.id = "leaflet-js"
    script.src = "/vendor/leaflet/leaflet.js"
    script.async = true
    script.onload = () => resolve()
    script.onerror = (e) => reject(e)
    document.head.appendChild(script)
  })

  return leafletLoad
}