package llms

import (
	"io/fs"
	"net/http"
	"path"
	"strings"

	"github.com/go-chi/chi/v5"
)

const (
	versionPlaceholder = "{{VERSION}}"
	baseURLPlaceholder = "{{BASE_URL}}"
	pageSuffix         = ".md"
	cacheControl       = "public, max-age=300"
	notBuiltNotice     = "The LLM documentation was not generated for this build. Run `task build:llms`."
)

type Handler struct {
	docs    fs.FS
	version string
	baseURL string
}

func NewHandler(docs fs.FS, version string, publicURL string) *Handler {
	return &Handler{
		docs:    docs,
		version: version,
		baseURL: strings.TrimRight(publicURL, "/"),
	}
}

func (h *Handler) Register(r chi.Router) {
	r.Get("/llms.txt", h.serve("llms.txt", "text/plain; charset=utf-8"))
	r.Get("/llms-full.txt", h.serve("llms-full.txt", "text/plain; charset=utf-8"))
	r.Get("/openapi.json", h.serve("openapi.json", "application/json"))
	r.Get("/llms/{page}", h.page)
}

func (h *Handler) page(w http.ResponseWriter, r *http.Request) {
	name := chi.URLParam(r, "page")
	if !strings.HasSuffix(name, pageSuffix) || strings.ContainsAny(name, "/\\") {
		h.notFound(w)
		return
	}
	h.write(w, path.Join("llms", name), "text/markdown; charset=utf-8")
}

func (h *Handler) serve(name string, contentType string) http.HandlerFunc {
	return func(w http.ResponseWriter, _ *http.Request) {
		h.write(w, name, contentType)
	}
}

func (h *Handler) write(w http.ResponseWriter, name string, contentType string) {
	if h.docs == nil {
		h.notFound(w)
		return
	}
	raw, err := fs.ReadFile(h.docs, name)
	if err != nil {
		h.notFound(w)
		return
	}
	text := strings.NewReplacer(versionPlaceholder, h.version, baseURLPlaceholder, h.baseURL).Replace(string(raw))
	w.Header().Set("Content-Type", contentType)
	w.Header().Set("Cache-Control", cacheControl)
	_, _ = w.Write([]byte(text))
}

func (h *Handler) notFound(w http.ResponseWriter) {
	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
	w.WriteHeader(http.StatusNotFound)
	_, _ = w.Write([]byte(notBuiltNotice))
}