package handler

import (
	"bytes"
	"encoding/json"
	"errors"
	"io"
	"net/http"
	"strconv"

	"github.com/go-playground/validator/v10"
	"go.uber.org/zap"

	"github.com/dbiz/cdp/ingestion/ingest/internal/apperr"
	"github.com/dbiz/cdp/ingestion/ingest/internal/middleware"
	"github.com/dbiz/cdp/ingestion/ingest/internal/model"
	"github.com/dbiz/cdp/ingestion/ingest/internal/service"
)

type EventHandler struct {
	svc *service.IngestService
	val *validator.Validate
	log *zap.Logger
}

func NewEventHandler(svc *service.IngestService, log *zap.Logger) *EventHandler {
	return &EventHandler{
		svc: svc,
		val: validator.New(),
		log: log,
	}
}

// ---------------------------------------------------------------------------
// Routes
// ---------------------------------------------------------------------------

// Single-event endpoints. They differ only in the `type` they force on the
// body, so they all funnel into one handler.

func (h *EventHandler) Track(w http.ResponseWriter, r *http.Request) {
	h.handleSingle(w, r, model.EventTypeTrack)
}

func (h *EventHandler) Identify(w http.ResponseWriter, r *http.Request) {
	h.handleSingle(w, r, model.EventTypeIdentify)
}

func (h *EventHandler) Page(w http.ResponseWriter, r *http.Request) {
	h.handleSingle(w, r, model.EventTypePage)
}

func (h *EventHandler) Group(w http.ResponseWriter, r *http.Request) {
	h.handleSingle(w, r, model.EventTypeGroup)
}

func (h *EventHandler) Alias(w http.ResponseWriter, r *http.Request) {
	h.handleSingle(w, r, model.EventTypeAlias)
}

func (h *EventHandler) Screen(w http.ResponseWriter, r *http.Request) {
	h.handleSingle(w, r, model.EventTypeScreen)
}

func (h *EventHandler) Batch(w http.ResponseWriter, r *http.Request) {
	body, err := io.ReadAll(r.Body)
	if err != nil {
		h.writeErr(w, apperr.PayloadTooLarge("payload too large"))
		return
	}

	var env model.BatchEnvelope
	if err := json.Unmarshal(body, &env); err != nil {
		h.writeErr(w, apperr.BadRequest("invalid json body", "", err))
		return
	}
	if err := h.val.Struct(&env); err != nil {
		h.writeErr(w, apperr.BadRequest("validation failed", firstField(err), err))
		return
	}

	ictx := h.ingestCtx(r, body)
	results := h.svc.IngestBatch(r.Context(), ictx, env.Batch)

	// Per-event status -- 200 OK, with an array of {message_id, ok, error}.
	type item struct {
		MessageID string `json:"messageId"`
		OK        bool   `json:"ok"`
		Error     string `json:"error,omitempty"`
		Field     string `json:"field,omitempty"`
	}
	out := make([]item, len(env.Batch))
	for i, e := range env.Batch {
		it := item{MessageID: e.MessageID, OK: true}
		if results[i] != nil {
			it.OK = false
			if ae, ok := apperr.As(results[i]); ok {
				it.Error = ae.Message
				it.Field = ae.Field
			} else {
				it.Error = "internal error"
			}
		}
		out[i] = it
	}
	writeJSON(w, http.StatusOK, map[string]any{"results": out})
}

// ---------------------------------------------------------------------------
// Health / Ready
// ---------------------------------------------------------------------------

func (h *EventHandler) Health(w http.ResponseWriter, r *http.Request) {
	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
}

func (h *EventHandler) Ready(w http.ResponseWriter, r *http.Request) {
	// Liveness is enough for k8s readiness in this scaffold. Wire in real
	// dependency checks (PG ping, Kafka ping) when needed.
	writeJSON(w, http.StatusOK, map[string]string{"status": "ready"})
}

// ---------------------------------------------------------------------------
// shared helpers
// ---------------------------------------------------------------------------

func (h *EventHandler) handleSingle(w http.ResponseWriter, r *http.Request, t model.EventType) {
	body, err := io.ReadAll(r.Body)
	if err != nil {
		h.writeErr(w, apperr.PayloadTooLarge("payload too large"))
		return
	}

	var raw model.RawEvent
	if err := json.NewDecoder(bytes.NewReader(body)).Decode(&raw); err != nil {
		h.writeErr(w, apperr.BadRequest("invalid json body", "", err))
		return
	}
	if raw.Type == "" {
		raw.Type = t
	}
	if err := h.val.Struct(&raw); err != nil {
		h.writeErr(w, apperr.BadRequest("validation failed", firstField(err), err))
		return
	}

	ictx := h.ingestCtx(r, body)
	if err := h.svc.Ingest(r.Context(), ictx, &raw); err != nil {
		h.writeErr(w, err)
		return
	}
	writeJSON(w, http.StatusOK, map[string]bool{"ok": true})
}

func (h *EventHandler) ingestCtx(r *http.Request, body []byte) service.IngestContext {
	wk := middleware.WriteKeyFromCtx(r.Context())
	return service.IngestContext{
		WorkspaceID: wk.WorkspaceID,
		SourceID:    wk.SourceID,
		IP:          clientIP(r),
		UserAgent:   r.UserAgent(),
		RawBody:     body,
	}
}

func (h *EventHandler) writeErr(w http.ResponseWriter, err error) {
	if ae, ok := apperr.As(err); ok {
		if ae.RetryAfter > 0 {
			w.Header().Set("Retry-After", strconv.Itoa(ae.RetryAfter))
		}
		writeJSON(w, ae.Code, errorResponse{Error: ae.Message, Field: ae.Field})
		if ae.Err != nil {
			h.log.Warn("request error",
				zap.Int("code", ae.Code),
				zap.String("msg", ae.Message),
				zap.Error(ae.Err))
		}
		return
	}
	h.log.Error("unhandled error", zap.Error(err))
	writeJSON(w, http.StatusInternalServerError, errorResponse{Error: "internal server error"})
}

type errorResponse struct {
	Error string `json:"error"`
	Field string `json:"field,omitempty"`
}

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

func firstField(err error) string {
	var verrs validator.ValidationErrors
	if errors.As(err, &verrs) && len(verrs) > 0 {
		return verrs[0].Field()
	}
	return ""
}

// clientIP duplicates middleware.clientIP -- intentionally small, no shared types.
func clientIP(r *http.Request) string {
	if h := r.Header.Get("X-Forwarded-For"); h != "" {
		return h
	}
	return r.RemoteAddr
}