// Package httpapi exposes the addrkit domain over a small, versioned JSON API.
//
// It contains no business logic: handlers decode requests, call the resolver
// and encode responses. Cross-cutting concerns (timeouts, recovery, request
// ids, logging) live in middleware.
package httpapi

import (
	"context"
	"encoding/json"
	"net/http"
	"time"
	"unicode/utf8"

	"log/slog"

	"git.totmin.ru/en2zmax/addrkit/internal/domain/match"
)

// Resolver is the read side of the domain (implemented by *match.Resolver).
type Resolver interface {
	Resolve(ctx context.Context, raw string) match.Result
	ResolveInCity(ctx context.Context, raw, city string) match.Result
	MatchCity(query string) (string, bool)
	Version() string
	Ready() bool
	Cities() []string
}

// maxAddressRunes bounds user input. A real address is far shorter; the limit
// keeps a pathological string from turning into a CPU-bound fuzzy scan.
const maxAddressRunes = 512

// maxCityQueryRunes bounds the separate city-only endpoint.
const maxCityQueryRunes = 128

// Server wires the domain to HTTP.
type Server struct {
	resolver Resolver
	log      *slog.Logger
	timeout  time.Duration
}

// New builds a server.
func New(resolver Resolver, log *slog.Logger) *Server {
	if log == nil {
		log = slog.Default()
	}
	return &Server{
		resolver: resolver,
		log:      log,
		timeout:  10 * time.Second,
	}
}

// Handler returns the fully wrapped HTTP handler.
func (s *Server) Handler() http.Handler {
	mux := http.NewServeMux()
	mux.HandleFunc("POST /v1/resolve", s.handleResolve)
	mux.HandleFunc("POST /v1/city", s.handleCity)
	mux.HandleFunc("GET /v1/cities", s.handleCities)
	mux.HandleFunc("GET /v1/healthz", s.handleHealthz)
	mux.HandleFunc("GET /v1/readyz", s.handleReadyz)
	mux.HandleFunc("GET /v1/version", s.handleVersion)

	// Logging sits outside recovery so a panic is still recorded as a 500.
	return requestIDMW(loggingMW(s.log)(recoverMW(s.log)(timeoutMW(s.timeout)(mux))))
}

type resolveRequest struct {
	Address string `json:"address"`
	// City is an optional hint for clients that keep the city separate from
	// the street line. It overrides a city found in the address text.
	City string `json:"city"`
}

func (s *Server) handleResolve(w http.ResponseWriter, r *http.Request) {
	req, ok := s.decode(w, r)
	if !ok {
		return
	}
	writeJSON(w, http.StatusOK, s.resolver.ResolveInCity(r.Context(), req.Address, req.City))
}

type cityRequest struct {
	Query string `json:"query"`
}

type cityResponse struct {
	Status string `json:"status"`
	City   string `json:"city,omitempty"`
}

// handleCity normalizes a city-only query ("нск", "г. Новосибирск",
// "Новосибирская область"). It is the small, separate use case for projects
// that need city names but not streets.
func (s *Server) handleCity(w http.ResponseWriter, r *http.Request) {
	var req cityRequest
	r.Body = http.MaxBytesReader(w, r.Body, 16*1024)
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid json body")
		return
	}
	if req.Query == "" {
		writeError(w, http.StatusBadRequest, "query is required")
		return
	}
	if utf8.RuneCountInString(req.Query) > maxCityQueryRunes {
		writeError(w, http.StatusBadRequest, "query is too long")
		return
	}
	if city, ok := s.resolver.MatchCity(req.Query); ok {
		writeJSON(w, http.StatusOK, cityResponse{Status: "found", City: city})
		return
	}
	writeJSON(w, http.StatusOK, cityResponse{Status: "not_found"})
}

func (s *Server) handleCities(w http.ResponseWriter, _ *http.Request) {
	cities := s.resolver.Cities()
	if cities == nil {
		cities = []string{}
	}
	writeJSON(w, http.StatusOK, map[string][]string{"cities": cities})
}

func (s *Server) handleHealthz(w http.ResponseWriter, _ *http.Request) {
	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
}

func (s *Server) handleReadyz(w http.ResponseWriter, _ *http.Request) {
	if !s.resolver.Ready() {
		writeJSON(w, http.StatusServiceUnavailable, map[string]string{"status": "not_ready"})
		return
	}
	writeJSON(w, http.StatusOK, map[string]string{"status": "ready"})
}

func (s *Server) handleVersion(w http.ResponseWriter, _ *http.Request) {
	writeJSON(w, http.StatusOK, map[string]string{"data_version": s.resolver.Version()})
}

// decode reads the JSON body into a resolveRequest, writing a 400 on failure.
func (s *Server) decode(w http.ResponseWriter, r *http.Request) (resolveRequest, bool) {
	var req resolveRequest
	r.Body = http.MaxBytesReader(w, r.Body, 64*1024)
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid json body")
		return resolveRequest{}, false
	}
	if req.Address == "" {
		writeError(w, http.StatusBadRequest, "address is required")
		return resolveRequest{}, false
	}
	if utf8.RuneCountInString(req.Address) > maxAddressRunes {
		writeError(w, http.StatusBadRequest, "address is too long")
		return resolveRequest{}, false
	}
	if utf8.RuneCountInString(req.City) > 128 {
		writeError(w, http.StatusBadRequest, "city is too long")
		return resolveRequest{}, false
	}
	return req, true
}

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

func writeError(w http.ResponseWriter, status int, msg string) {
	writeJSON(w, status, map[string]any{"error": 1, "message": msg})
}