// 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 (
	_ "embed"
	"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/ratelimit"
	"github.com/baicai2026-baicai/goods/api/internal/store"
)

//go:embed openapi.json
var openAPISpec []byte

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

// QualifiedMinScore is the quality_score threshold at or above which a product
// record is considered "qualified" (合格) for public stats.
const QualifiedMinScore = 0.6

const (
	defaultPageSize = 20
	maxPageSize     = 100

	// defaultAnonLimit is the per-minute request budget for unauthenticated
	// callers (identified by client IP) when none is configured.
	defaultAnonLimit = 60

	// defaultAnonTotalQuota is the lifetime number of calls an anonymous caller
	// (by IP) may make before being asked to register for a higher quota.
	defaultAnonTotalQuota = 1000

	// defaultRegRatePerMin / defaultRegQuotaTotal are the per-minute budget and
	// cumulative quota granted to a self-registered API key.
	defaultRegRatePerMin = 300
	defaultRegQuotaTotal = 100000

	// registerRatePerMin caps account registration/login attempts per IP to
	// curb abuse; these endpoints sit outside the metered quota group.
	registerRatePerMin = 10
)

// Handler holds dependencies shared by the HTTP routes.
type Handler struct {
	store          *store.Store
	spa            fs.FS
	limiter        *ratelimit.Limiter
	anonLimit      int
	anonTotalQuota int64
	regRatePerMin  int
	regQuotaTotal  int64
}

// New constructs a Handler backed by the given store. spa may be nil (JSON-only).
// Rate limiting is disabled until WithRateLimit is called.
func New(s *store.Store, spa fs.FS) *Handler {
	return &Handler{
		store:          s,
		spa:            spa,
		anonLimit:      defaultAnonLimit,
		anonTotalQuota: defaultAnonTotalQuota,
		regRatePerMin:  defaultRegRatePerMin,
		regQuotaTotal:  defaultRegQuotaTotal,
	}
}

// WithRateLimit attaches a Redis-backed limiter and the anonymous per-minute
// budget, enabling rate limiting + usage tracking on the public API routes.
// A non-positive anonPerMin keeps the default.
func (h *Handler) WithRateLimit(l *ratelimit.Limiter, anonPerMin int) *Handler {
	h.limiter = l
	if anonPerMin > 0 {
		h.anonLimit = anonPerMin
	}
	return h
}

// WithQuotas configures the cumulative free quota for anonymous callers and the
// per-minute rate + cumulative quota self-registered keys receive. Non-positive
// values keep the defaults.
func (h *Handler) WithQuotas(anonTotal, regPerMin, regTotal int) *Handler {
	if anonTotal > 0 {
		h.anonTotalQuota = int64(anonTotal)
	}
	if regPerMin > 0 {
		h.regRatePerMin = regPerMin
	}
	if regTotal > 0 {
		h.regQuotaTotal = int64(regTotal)
	}
	return h
}

// 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) {
		// Machine-readable spec; not rate limited so tooling can always fetch it.
		r.Get("/openapi.json", h.OpenAPI)

		r.Group(func(r chi.Router) {
			r.Use(h.rateLimit)
			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)
			r.Get("/stats", h.Stats)
		})

		// Self-service account routes. Lightly IP-throttled to curb abuse but
		// outside the metered quota group so a user can always register or
		// check their key even after exhausting the free anonymous quota.
		r.Group(func(r chi.Router) {
			r.Use(h.registerLimit)
			r.Post("/register", h.Register)
			r.Post("/account", h.AccountInfo)
			r.Post("/account/regenerate", h.RegenerateKey)
		})
	})

	// 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"})
}

// Stats returns catalog totals and the count of qualified records.
func (h *Handler) Stats(w http.ResponseWriter, r *http.Request) {
	st, err := h.store.Stats(r.Context(), QualifiedMinScore)
	if h.handleErr(w, r, err) {
		return
	}
	writeJSON(w, http.StatusOK, st)
}

// OpenAPI serves the embedded OpenAPI 3 specification for the public API.
func (h *Handler) OpenAPI(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	_, _ = w.Write(openAPISpec)
}

// 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 trigram-fuzzy name search with optional
// category/brand/country filters, ranked by relevance, plus paging.
func (h *Handler) SearchProducts(w http.ResponseWriter, r *http.Request) {
	qv := r.URL.Query()
	filters := store.SearchFilters{
		Query:    strings.TrimSpace(qv.Get("q")),
		Category: strings.TrimSpace(qv.Get("category")),
		Brand:    strings.TrimSpace(qv.Get("brand")),
		Country:  strings.TrimSpace(qv.Get("country")),
	}
	page, size := pageParams(r)

	items, total, err := h.store.SearchProducts(r.Context(), filters, 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()),
		},
	})
}