package protocol

import (
	"encoding/json"
	"fmt"
)

// MaximumCommandBatchSize bounds the ordered commands in one publication.
const MaximumCommandBatchSize = 256

// BatchPayload holds 2 through 256 commands for one device. IDs and targets are
// distinct. Array order is operation order. Each member keeps its own expiry,
// correlation, and causation. There is no combined result.
type BatchPayload struct {
	Commands []BatchCommand
}

// MarshalJSON inserts each command's schema without caller-built envelopes.
func (b BatchPayload) MarshalJSON() ([]byte, error) {
	commands := make([]batchWireCommand, 0, len(b.Commands))

	for _, command := range b.Commands {
		commands = append(commands, batchWireCommand{
			Schema:     Schema,
			Metadata:   command.Metadata,
			Capability: command.Capability,
			Payload:    command.Payload,
		})
	}

	data, err := json.Marshal(batchWirePayload{Commands: commands})
	if err != nil {
		return nil, fmt.Errorf("encode batch members: %w", err)
	}

	return data, nil
}

// UnmarshalJSON rejects unknown fields and unsupported member schemas.
func (b *BatchPayload) UnmarshalJSON(data []byte) error {
	var wire batchWirePayload

	err := decodeObject(data, &wire)
	if err != nil {
		return fmt.Errorf("decode batch members: %w", err)
	}

	commands := make([]BatchCommand, 0, len(wire.Commands))

	for _, command := range wire.Commands {
		if command.Schema != Schema {
			return fmt.Errorf("unsupported batch member schema %d", command.Schema)
		}

		commands = append(commands, BatchCommand{
			Metadata:   command.Metadata,
			Capability: command.Capability,
			Payload:    command.Payload,
		})
	}

	b.Commands = commands

	return nil
}

// BatchCommand holds one complete request without a topic or schema field. The
// outer batch message ID equals the first member's message ID.
type BatchCommand struct {
	Metadata
	Capability string
	Payload    ValuePayload
}

type batchWirePayload struct {
	Commands []batchWireCommand `json:"commands"`
}

type batchWireCommand struct {
	Schema int `json:"schema"`
	Metadata
	Capability string       `json:"capability"`
	Payload    ValuePayload `json:"payload"`
}