package api

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"regexp"
	"strconv"
	"time"

	"git.amiirkhl.ir/starcoach-hackathon/zarinpal-analytics-backend/internal/growthreport"
)

var growthReportIDPattern = regexp.MustCompile(`^growth_[a-f0-9]{24}$`)

type growthReportService interface {
	Create(context.Context, int64, int64, growthreport.CreateRequest, string) (growthreport.Record, bool, error)
	Get(context.Context, int64, string) (growthreport.Record, error)
	Latest(context.Context, int64, string) (growthreport.Record, error)
}

func (s *Server) createGrowthReport(w http.ResponseWriter, r *http.Request) {
	if s.growth == nil {
		s.problem(w, r, 404, "RESOURCE_NOT_FOUND", "Resource not found")
		return
	}
	key := r.Header.Get("Idempotency-Key")
	if !validIdempotencyKey(key) {
		s.problem(w, r, 422, "VALIDATION_FAILED", "A valid Idempotency-Key is required")
		return
	}
	var input growthreport.CreateRequest
	if err := decodeStrictJSON(w, r, &input); err != nil || len(input.TerminalID) > 128 {
		s.problem(w, r, 422, "VALIDATION_FAILED", "Invalid growth report request")
		return
	}
	session := sessionFrom(r.Context())
	record, cached, err := s.growth.Create(r.Context(), session.UserID, session.MerchantID, input, key)
	if err != nil {
		s.handleGrowthCreateError(w, r, err)
		return
	}
	status := http.StatusAccepted
	if cached {
		status = http.StatusOK
	}
	w.Header().Set("Location", "/api/v1/analytics/growth-reports/"+record.ReportID)
	s.writeJSON(w, status, record.Report)
}

func (s *Server) handleGrowthCreateError(w http.ResponseWriter, r *http.Request, err error) {
	var limit *growthreport.RefreshLimitError
	switch {
	case errors.Is(err, growthreport.ErrDisabled):
		s.problem(w, r, 404, "RESOURCE_NOT_FOUND", "Resource not found")
	case errors.Is(err, growthreport.ErrUnknownTerminal):
		s.problem(w, r, 422, "VALIDATION_FAILED", "Unknown terminal")
	case errors.Is(err, growthreport.ErrIdempotencyConflict):
		s.problem(w, r, 409, "IDEMPOTENCY_CONFLICT", "Idempotency key was already used for another request")
	case errors.As(err, &limit):
		seconds := max(int64(1), int64(time.Until(limit.NextRefreshAt).Seconds()))
		w.Header().Set("Retry-After", strconv.FormatInt(seconds, 10))
		w.Header().Set("Content-Type", "application/problem+json")
		w.WriteHeader(429)
		_ = json.NewEncoder(w).Encode(map[string]any{"type": "https://zarinpal.amiirkhl.ir/docs/errors/refresh-limited", "title": "Too Many Requests", "status": 429, "code": "REFRESH_LIMITED", "detail": "Daily refresh is not available yet", "instance": r.URL.Path, "requestId": w.Header().Get("X-Request-ID"), "nextRefreshAt": limit.NextRefreshAt})
	case errors.Is(err, growthreport.ErrRateLimited):
		s.problem(w, r, 429, "RATE_LIMITED", "Too many growth report requests")
	default:
		s.logger.Error("growth report creation failed", "error", err)
		s.problem(w, r, 503, "ANALYTICS_UNAVAILABLE", "Growth analytics unavailable")
	}
}

func (s *Server) latestGrowthReport(w http.ResponseWriter, r *http.Request) {
	if s.growth == nil {
		s.problem(w, r, 404, "RESOURCE_NOT_FOUND", "Resource not found")
		return
	}
	for key := range r.URL.Query() {
		if key != "terminalId" {
			s.problem(w, r, 422, "VALIDATION_FAILED", "Unknown query parameter")
			return
		}
	}
	terminalID := r.URL.Query().Get("terminalId")
	if len(terminalID) > 128 {
		s.problem(w, r, 422, "VALIDATION_FAILED", "Invalid terminal")
		return
	}
	record, err := s.growth.Latest(r.Context(), sessionFrom(r.Context()).MerchantID, terminalID)
	s.writeGrowthResult(w, r, record, err)
}

func (s *Server) getGrowthReport(w http.ResponseWriter, r *http.Request) {
	if s.growth == nil {
		s.problem(w, r, 404, "RESOURCE_NOT_FOUND", "Resource not found")
		return
	}
	id := r.PathValue("reportId")
	if !growthReportIDPattern.MatchString(id) {
		s.problem(w, r, 404, "RESOURCE_NOT_FOUND", "Resource not found")
		return
	}
	record, err := s.growth.Get(r.Context(), sessionFrom(r.Context()).MerchantID, id)
	s.writeGrowthResult(w, r, record, err)
}

func (s *Server) writeGrowthResult(w http.ResponseWriter, r *http.Request, record growthreport.Record, err error) {
	if errors.Is(err, growthreport.ErrNotFound) {
		s.problem(w, r, 404, "RESOURCE_NOT_FOUND", "Resource not found")
		return
	}
	if err != nil {
		s.problem(w, r, 503, "ANALYTICS_UNAVAILABLE", "Growth analytics unavailable")
		return
	}
	s.writeJSON(w, 200, record.Report)
}

func (s *Server) growthReportEvents(w http.ResponseWriter, r *http.Request) {
	if s.growth == nil {
		s.problem(w, r, 404, "RESOURCE_NOT_FOUND", "Resource not found")
		return
	}
	id := r.PathValue("reportId")
	if !growthReportIDPattern.MatchString(id) {
		s.problem(w, r, 404, "RESOURCE_NOT_FOUND", "Resource not found")
		return
	}
	merchantID := sessionFrom(r.Context()).MerchantID
	record, err := s.growth.Get(r.Context(), merchantID, id)
	if errors.Is(err, growthreport.ErrNotFound) {
		s.problem(w, r, 404, "RESOURCE_NOT_FOUND", "Resource not found")
		return
	}
	if err != nil {
		s.problem(w, r, 503, "ANALYTICS_UNAVAILABLE", "Growth analytics unavailable")
		return
	}
	flusher, ok := w.(http.Flusher)
	if !ok {
		s.problem(w, r, 500, "INTERNAL_ERROR", "Streaming unavailable")
		return
	}
	w.Header().Set("Content-Type", "text/event-stream; charset=utf-8")
	w.Header().Set("Cache-Control", "no-cache, no-transform")
	w.Header().Set("X-Accel-Buffering", "no")
	ticker := time.NewTicker(2 * time.Second)
	defer ticker.Stop()
	heartbeat := time.NewTicker(15 * time.Second)
	defer heartbeat.Stop()
	last := ""
	for {
		eventID := record.ReportID + ":" + strconv.FormatInt(record.UpdatedAt.UnixNano(), 10)
		if eventID != last {
			payload, _ := json.Marshal(map[string]any{"eventId": eventID, "report": record.Report})
			_, _ = fmt.Fprintf(w, "id: %s\nevent: report.snapshot\ndata: %s\n\n", eventID, payload)
			flusher.Flush()
			last = eventID
		}
		if record.Status.Terminal() {
			return
		}
		select {
		case <-r.Context().Done():
			return
		case <-ticker.C:
			record, err = s.growth.Get(r.Context(), merchantID, id)
			if err != nil {
				return
			}
		case <-heartbeat.C:
			_, _ = fmt.Fprint(w, ": heartbeat\n\n")
			flusher.Flush()
		}
	}
}

func validIdempotencyKey(key string) bool {
	if len(key) < 8 || len(key) > 128 {
		return false
	}
	for _, value := range []byte(key) {
		if value < 0x21 || value > 0x7e {
			return false
		}
	}
	return true
}
func decodeStrictJSON(w http.ResponseWriter, r *http.Request, value any) error {
	decoder := json.NewDecoder(http.MaxBytesReader(w, r.Body, 16<<10))
	decoder.DisallowUnknownFields()
	if err := decoder.Decode(value); err != nil {
		return err
	}
	var extra any
	if err := decoder.Decode(&extra); !errors.Is(err, io.EOF) {
		return errors.New("trailing JSON")
	}
	return nil
}