// Package widgetapi exposes the bounded widget catalog and preview contract.
package widgetapi

import (
	"encoding/json"
	"errors"
	"io"
	"net/http"
	"strings"

	"github.com/itworx/pulse/internal/problem"
	"github.com/itworx/pulse/internal/widget"
	"github.com/itworx/pulse/internal/widgetpreview"
)

type Handler struct{ Registry widget.Registry }

func (h Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if err := r.Context().Err(); err != nil {
		return
	}
	switch {
	case r.URL.Path == "/api/v1/widgets/catalog" && r.Method == http.MethodGet:
		write(w, http.StatusOK, map[string]any{"items": h.Registry.Catalog()})
	case r.URL.Path == "/api/v1/widgets/preview" && r.Method == http.MethodPost:
		contentType := strings.ToLower(strings.TrimSpace(strings.Split(r.Header.Get("Content-Type"), ";")[0]))
		if contentType != "" && contentType != "application/json" {
			problem.Write(w, r, http.StatusUnsupportedMediaType, "UNSUPPORTED_MEDIA_TYPE", "Unsupported media type", "Widget previews require application/json.", nil)
			return
		}
		var body struct {
			Widget map[string]any `json:"widget"`
			State  string         `json:"state"`
		}
		decoder := json.NewDecoder(http.MaxBytesReader(w, r.Body, 1<<20))
		decoder.DisallowUnknownFields()
		if err := decoder.Decode(&body); err != nil || body.Widget == nil {
			problem.Write(w, r, http.StatusBadRequest, "INVALID_PREVIEW", "Invalid preview", "A bounded widget configuration is required.", nil)
			return
		}
		var trailing any
		if err := decoder.Decode(&trailing); !errors.Is(err, io.EOF) {
			problem.Write(w, r, http.StatusBadRequest, "INVALID_PREVIEW", "Invalid preview", "The request must contain one JSON document.", nil)
			return
		}
		preview, err := widgetpreview.Preview(body.Widget, body.State)
		if err != nil {
			var invalid widgetpreview.InvalidConfig
			if errors.As(err, &invalid) {
				problem.Write(w, r, http.StatusBadRequest, "INVALID_WIDGET_CONFIG", "Invalid widget", "The widget configuration is invalid.", invalid.Fields)
				return
			}
			problem.Write(w, r, http.StatusBadRequest, "INVALID_WIDGET_CONFIG", "Invalid widget", "The widget configuration is invalid.", nil)
			return
		}
		write(w, http.StatusOK, map[string]any{"preview": preview})
	case r.URL.Path == "/api/v1/widgets/catalog" || r.URL.Path == "/api/v1/widgets/preview":
		problem.Write(w, r, http.StatusMethodNotAllowed, "METHOD_NOT_ALLOWED", "Method not allowed", "The requested method is not supported for this widget route.", nil)
	default:
		problem.Write(w, r, http.StatusNotFound, "NOT_FOUND", "Not found", "The requested widget route does not exist.", nil)
	}
}

func write(w http.ResponseWriter, status int, value any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(value)
}