package insights

import (
	"time"

	json "github.com/goccy/go-json"
	"github.com/google/uuid"
)

// Values implementing this interface are used by insights clients to notify
// the application when a message send succeeded or failed.
//
// Callback methods are called by a client's internal goroutines. There are no
// guarantees about which goroutine triggers the callbacks, whether calls are
// made sequentially or in parallel, or whether callback order matches enqueue order.
//
// Callback methods must return quickly and avoid long blocking operations so
// they do not interfere with the client's internal workflow.
type Callback interface {

	// Success is called for every message that was successfully sent to the API.
	Success(APIMessage)

	// Failure is called for every message that failed to be sent to the API and
	// will be discarded by the client. The error describes the send or serialization failure.
	Failure(APIMessage, error)
}

// This interface is used to represent insights objects that can be sent via
// a client.
//
// Types like insights.Capture, insights.Alias, etc... implement this interface
// and therefore can be passed to the insights.Client.Enqueue method.
type Message interface {

	// Validate checks the internal structure of the message. It returns nil when
	// the message is valid or an error describing the invalid field.
	Validate() error
	// APIfy converts the message into its PostHog batch API representation.
	APIfy() APIMessage

	// internal prevents external packages from satisfying Message. Calling it panics.
	internal()
}

// Returns the time value passed as first argument, unless it's the zero-value,
// in that case the default value passed as second argument is returned.
func makeTimestamp(t time.Time, def time.Time) time.Time {
	if t == (time.Time{}) {
		return def
	}
	return t
}

// makeUUID returns the UUID passed as first argument if non-empty,
// otherwise generates and returns a new random UUID (v4).
func makeUUID(u string) string {
	if u != "" {
		return u
	}
	return uuid.New().String()
}

// batch represents objects sent to the /batch/ endpoint with pre-serialized messages.
// Messages are pre-serialized as json.RawMessage for efficient batch building -
// json.Marshal embeds them directly without re-encoding.
type batch struct {
	ApiKey              string            `json:"api_key"`
	HistoricalMigration bool              `json:"historical_migration,omitempty"`
	Messages            []json.RawMessage `json:"batch"`
}

// APIMessage is a wire-format message produced by Message.APIfy and passed to callbacks.
type APIMessage any

// prepareForSend creates the API message and serializes it to JSON.
// Returns pre-serialized JSON for efficient batch building, the original
// APIMessage for callbacks, and any serialization error.
// Size is derived from len(json.RawMessage) when needed - O(1) operation.
func prepareForSend(msg Message) (json.RawMessage, APIMessage, error) {
	apiMsg := msg.APIfy()
	data, err := json.Marshal(apiMsg)
	if err != nil {
		return nil, apiMsg, err
	}
	return json.RawMessage(data), apiMsg, nil
}

const (
	maxBatchBytes   = 500000
	maxMessageBytes = 500000
)