package httpserver

import (
	"bytes"
	"encoding/json"
	"io"
	"mime"
	"net/http"
	"reflect"
	"strconv"
	"strings"
	"time"

	"git.yuntuo.hk/k2safe/orbit/internal/fault"
	"git.yuntuo.hk/k2safe/orbit/internal/jsonvalue"
	core "git.yuntuo.hk/k2safe/orbit/model"
)

const EventSubprotocol = "orbit.events.v1"
const eventMaxFrame = 512 << 10

type eventFrame struct {
	Version   string          `json:"protocol_version"`
	Type      string          `json:"type"`
	MessageID core.ID         `json:"message_id"`
	ReplyTo   core.ID         `json:"reply_to,omitempty"`
	SessionID core.ID         `json:"session_id,omitempty"`
	Body      json.RawMessage `json:"body,omitempty"`
	Error     *fault.Error    `json:"error,omitempty"`
}
type eventHello struct {
	SubscriptionID core.ID `json:"subscription_id"`
	Capacity       uint32  `json:"capacity"`
}
type eventWelcome struct {
	SessionID           core.ID   `json:"session_id"`
	SubscriptionID      core.ID   `json:"subscription_id"`
	Capacity            uint32    `json:"capacity"`
	LeaseDurationMS     int64     `json:"lease_duration_ms"`
	HeartbeatIntervalMS int64     `json:"heartbeat_interval_ms"`
	ServerTime          time.Time `json:"server_time"`
	Enabled             bool      `json:"enabled"`
}
type eventPong struct {
	ServerTime time.Time `json:"server_time"`
	Enabled    bool      `json:"enabled"`
}

func decodeEventBody(r *http.Request, out any) error {
	content, _, err := mime.ParseMediaType(r.Header.Get("Content-Type"))
	if err != nil || content != "application/json" {
		return fault.New("UNSUPPORTED_MEDIA_TYPE", "Content-Type must be application/json")
	}
	raw, err := io.ReadAll(io.LimitReader(r.Body, eventMaxFrame+1))
	if err != nil {
		return fault.Invalid("cannot read request body")
	}
	if len(raw) > eventMaxFrame {
		return fault.New("BODY_TOO_LARGE", "request body exceeds 512 KiB")
	}
	return decodeEventJSON(raw, out)
}
func decodeEventJSON(raw []byte, out any) error {
	if len(raw) == 0 || len(raw) > eventMaxFrame {
		return fault.Invalid("invalid event message size")
	}
	if _, err := jsonvalue.Canonical(raw); err != nil {
		return fault.Invalid("invalid event JSON")
	}
	typ := reflect.TypeOf(out).Elem()
	if exactFields(raw, typ) != nil || requiredEventFields(raw, typ) != nil {
		return fault.Invalid("missing, unknown or invalid event field")
	}
	d := json.NewDecoder(bytes.NewReader(raw))
	d.DisallowUnknownFields()
	if d.Decode(out) != nil {
		return fault.Invalid("invalid event field value")
	}
	return nil
}

// requiredEventFields 同时验证显式控制意图及规范十进制字符串；可选历史游标允许0和null。
func requiredEventFields(raw []byte, typ reflect.Type) error {
	if typ == reflect.TypeOf(json.RawMessage{}) || typ == reflect.TypeOf(time.Time{}) {
		return nil
	}
	if typ.Kind() == reflect.Pointer {
		if bytes.Equal(bytes.TrimSpace(raw), []byte("null")) {
			return nil
		}
		return requiredEventFields(raw, typ.Elem())
	}
	if typ.Kind() == reflect.Array || typ.Kind() == reflect.Slice {
		var values []json.RawMessage
		if json.Unmarshal(raw, &values) != nil {
			return fault.Invalid("invalid event array")
		}
		for _, v := range values {
			if err := requiredEventFields(v, typ.Elem()); err != nil {
				return err
			}
		}
		return nil
	}
	if typ.Kind() != reflect.Struct {
		return nil
	}
	var fields map[string]json.RawMessage
	if json.Unmarshal(raw, &fields) != nil {
		return fault.Invalid("invalid event object")
	}
	for i := 0; i < typ.NumField(); i++ {
		field := typ.Field(i)
		tags := strings.Split(field.Tag.Get("json"), ",")
		if tags[0] == "" || tags[0] == "-" {
			continue
		}
		optional, numberString := false, false
		for _, v := range tags[1:] {
			optional = optional || v == "omitempty"
			numberString = numberString || v == "string"
		}
		value, found := fields[tags[0]]
		if !found {
			if optional {
				continue
			}
			return fault.Invalid("missing event field")
		}
		ft := field.Type
		nullable := ft.Kind() == reflect.Pointer
		if nullable {
			if bytes.Equal(bytes.TrimSpace(value), []byte("null")) {
				continue
			}
			ft = ft.Elem()
		}
		if ft.Kind() == reflect.Uint64 && numberString {
			var text string
			if json.Unmarshal(value, &text) != nil {
				return fault.Invalid("event counter must be a decimal string")
			}
			n, err := strconv.ParseUint(text, 10, 64)
			if err != nil || strconv.FormatUint(n, 10) != text || (!nullable && n == 0) {
				return fault.Invalid("invalid event counter")
			}
		}
		if err := requiredEventFields(value, field.Type); err != nil {
			return err
		}
	}
	return nil
}
func decodeEventRequest(raw []byte, hello bool) (eventFrame, error) {
	var frame eventFrame
	if err := decodeEventJSON(raw, &frame); err != nil {
		return frame, err
	}
	if frame.Version != "1" || frame.MessageID.Validate() != nil || len(frame.Body) == 0 {
		return frame, fault.Invalid("invalid event envelope")
	}
	var fields map[string]json.RawMessage
	_ = json.Unmarshal(raw, &fields)
	if fields["error"] != nil || fields["reply_to"] != nil {
		return frame, fault.Invalid("response fields are not allowed in event requests")
	}
	if hello {
		if frame.Type != "events.hello" || fields["session_id"] != nil {
			return frame, fault.Invalid("invalid event hello")
		}
	} else if frame.SessionID.Validate() != nil || (frame.Type != "event.ack" && frame.Type != "events.ping") {
		return frame, fault.Invalid("invalid event session or type")
	}
	return frame, nil
}