// Package handler wires up the public, read-only OpenGoods HTTP API.
// The OpenGoods service is a public-good product information API: it only
// collects and serves product facts. It exposes no purchase, checkout, or
// commerce endpoints by design.
package handler

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

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

	"github.com/baicai2026-baicai/goods/api/internal/store"
)

// APIVersion is the current public API version prefix.
const APIVersion = "v1"

const (
	defaultPageSize = 20
	maxPageSize     = 100
)

// Handler holds dependencies shared by the HTTP routes.
type Handler struct {
	store *store.Store
	spa   fs.FS
}

// New constructs a Handler backed by the given store. spa may be nil (JSON-only).
func New(s *store.Store, spa fs.FS) *Handler {
	return &Handler{store: s, spa: spa}
}

// Router builds the top-level HTTP handler with middleware and routes mounted.
func (h *Handler) Router() http.Handler {
	r := chi.NewRouter()
	r.Use(middleware.RequestID)
	r.Use(middleware.RealIP)
	r.Use(middleware.Recoverer)

	r.Get("/healthz", h.Healthz)

	r.Route("/api/"+APIVersion, func(r chi.Router) {
		r.Route("/products", func(r chi.Router) {
			r.Get("/barcode/{gtin}", h.ProductByBarcode)
			r.Get("/search", h.SearchProducts)
			r.Get("/{id}", h.ProductByID)
			r.Get("/{id}/nutriments", h.ProductNutriments)
			r.Get("/{id}/msrp", h.ProductMSRP)
		})
		r.Get("/brands", h.ListBrands)
		r.Get("/categories", h.ListCategories)
		r.Get("/sources/{id}", h.SourceByID)
	})

	// Public SPA (homepage + search + contribute). API routes above take
	// precedence; everything else falls back to the embedded single-page app.
	if h.spa != nil {
		r.Handle("/*", http.HandlerFunc(h.serveSPA))
	}

	return r
}

func (h *Handler) serveSPA(w http.ResponseWriter, r *http.Request) {
	rel := strings.TrimPrefix(r.URL.Path, "/")
	if rel == "" {
		rel = "index.html"
	}
	if f, err := h.spa.Open(rel); err == nil {
		f.Close()
		http.FileServer(http.FS(h.spa)).ServeHTTP(w, r)
		return
	}
	// SPA fallback: serve index.html for client-side routes.
	data, err := fs.ReadFile(h.spa, "index.html")
	if err != nil {
		http.NotFound(w, r)
		return
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	_, _ = w.Write(data)
}

// Healthz reports liveness of the service.
func (h *Handler) Healthz(w http.ResponseWriter, r *http.Request) {
	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
}

// ProductByBarcode returns a product by its GTIN.
func (h *Handler) ProductByBarcode(w http.ResponseWriter, r *http.Request) {
	p, err := h.store.ProductByGTIN(r.Context(), chi.URLParam(r, "gtin"))
	if h.handleErr(w, r, err) {
		return
	}
	writeJSON(w, http.StatusOK, p)
}

// ProductByID returns a product by its UUID.
func (h *Handler) ProductByID(w http.ResponseWriter, r *http.Request) {
	p, err := h.store.ProductByID(r.Context(), chi.URLParam(r, "id"))
	if h.handleErr(w, r, err) {
		return
	}
	writeJSON(w, http.StatusOK, p)
}

// SearchProducts runs a fuzzy name search with optional category filter + paging.
func (h *Handler) SearchProducts(w http.ResponseWriter, r *http.Request) {
	q := r.URL.Query().Get("q")
	category := r.URL.Query().Get("category")
	page, size := pageParams(r)

	items, total, err := h.store.SearchProducts(r.Context(), q, category, size, (page-1)*size)
	if h.handleErr(w, r, err) {
		return
	}
	writeJSON(w, http.StatusOK, map[string]any{
		"items": items,
		"page":  page,
		"size":  size,
		"total": total,
	})
}

// ProductNutriments returns just the nutrition facts of a product.
func (h *Handler) ProductNutriments(w http.ResponseWriter, r *http.Request) {
	n, err := h.store.Nutriments(r.Context(), chi.URLParam(r, "id"))
	if h.handleErr(w, r, err) {
		return
	}
	writeJSON(w, http.StatusOK, n)
}

// ProductMSRP returns official suggested retail price snapshots (no purchase link).
func (h *Handler) ProductMSRP(w http.ResponseWriter, r *http.Request) {
	items, err := h.store.ListMSRP(r.Context(), chi.URLParam(r, "id"))
	if h.handleErr(w, r, err) {
		return
	}
	writeJSON(w, http.StatusOK, map[string]any{
		"items":      items,
		"disclaimer": "厂商建议零售价历史快照，仅供参考，不构成购买建议，本服务不提供任何购买入口。",
	})
}

// ListBrands returns a paginated list of brands.
func (h *Handler) ListBrands(w http.ResponseWriter, r *http.Request) {
	page, size := pageParams(r)
	items, total, err := h.store.ListBrands(r.Context(), size, (page-1)*size)
	if h.handleErr(w, r, err) {
		return
	}
	writeJSON(w, http.StatusOK, map[string]any{
		"items": items, "page": page, "size": size, "total": total,
	})
}

// ListCategories returns the full category tree.
func (h *Handler) ListCategories(w http.ResponseWriter, r *http.Request) {
	items, err := h.store.ListCategories(r.Context())
	if h.handleErr(w, r, err) {
		return
	}
	writeJSON(w, http.StatusOK, map[string]any{"items": items})
}

// SourceByID returns a single data source.
func (h *Handler) SourceByID(w http.ResponseWriter, r *http.Request) {
	src, err := h.store.SourceByID(r.Context(), chi.URLParam(r, "id"))
	if h.handleErr(w, r, err) {
		return
	}
	writeJSON(w, http.StatusOK, src)
}

// handleErr writes an appropriate error response; returns true if it handled one.
func (h *Handler) handleErr(w http.ResponseWriter, r *http.Request, err error) bool {
	if err == nil {
		return false
	}
	if errors.Is(err, store.ErrNotFound) {
		writeError(w, r, http.StatusNotFound, "not_found", "resource not found")
		return true
	}
	writeError(w, r, http.StatusInternalServerError, "internal_error", "internal server error")
	return true
}

func pageParams(r *http.Request) (page, size int) {
	page = atoiDefault(r.URL.Query().Get("page"), 1)
	if page < 1 {
		page = 1
	}
	size = atoiDefault(r.URL.Query().Get("size"), defaultPageSize)
	if size < 1 {
		size = defaultPageSize
	}
	if size > maxPageSize {
		size = maxPageSize
	}
	return page, size
}

func atoiDefault(s string, fallback int) int {
	if s == "" {
		return fallback
	}
	v, err := strconv.Atoi(s)
	if err != nil {
		return fallback
	}
	return v
}

func writeJSON(w http.ResponseWriter, status int, body any) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(body)
}

func writeError(w http.ResponseWriter, r *http.Request, status int, code, message string) {
	writeJSON(w, status, map[string]any{
		"error": map[string]string{
			"code":       code,
			"message":    message,
			"request_id": middleware.GetReqID(r.Context()),
		},
	})
}