// Copyright (c) 2026 Storm Dragon
// SPDX-License-Identifier: GPL-3.0-or-later

package tentaclewire

import (
	"bytes"
	"encoding/json"
	"unicode"
	"unicode/utf8"
)

const MaxPresentationBytes = 8192 // Per channel, measured in UTF-8 bytes.

// Presentation is a command result, never an unsolicited announcement. Empty
// channels are omitted; neither channel supplies positions or routing targets.
type Presentation struct {
	Speech          string `json:"speech,omitempty"`
	Braille         string `json:"braille,omitempty"`
	Uninterruptible bool   `json:"uninterruptible,omitempty"`
}

func DecodePresentation(data []byte) (Presentation, error) {
	var value Presentation
	if err := DecodeStrict(data, &value); err != nil {
		return value, err
	}
	var fields map[string]json.RawMessage
	if json.Unmarshal(data, &fields) != nil || fields == nil || len(fields) == 0 {
		return value, ErrProtocol
	}
	for _, field := range fields {
		if bytes.Equal(field, []byte("null")) {
			return value, ErrProtocol
		}
	}
	if value.Speech == "" && value.Braille == "" {
		return value, ErrProtocol
	}
	if value.Uninterruptible && value.Speech == "" {
		return value, ErrProtocol
	}
	for _, text := range []string{value.Speech, value.Braille} {
		if len(text) > MaxPresentationBytes {
			return value, ErrLimit
		}
		if !utf8.ValidString(text) {
			return value, ErrProtocol
		}
		for _, char := range text {
			if unicode.IsControl(char) && char != '\n' && char != '\t' {
				return value, ErrProtocol
			}
		}
	}
	return value, nil
}

// The experimental optional API is additive to the command-only handshake.
func ValidAPIs(apis, capabilities []string) bool {
	if len(apis) != len(capabilities) || len(apis) < 1 || len(apis) > 3 || apis[0] != "commands" {
		return false
	}
	if len(apis) >= 2 && apis[1] != "presentation" || len(apis) == 3 && apis[2] != "interaction" {
		return false
	}
	for index := range apis {
		if apis[index] != capabilities[index] {
			return false
		}
	}
	return true
}