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

// Package i3ipc observes i3 without issuing window-management commands.
package i3ipc

import (
	"encoding/binary"
	"encoding/json"
	"errors"
	"io"
)

const (
	workspaces            = 1
	subscribe             = 2
	tree                  = 4
	eventBit       uint32 = 1 << 31
	workspaceEvent        = eventBit
	modeEvent             = eventBit | 2
	windowEvent           = eventBit | 3
	// A corrupt peer cannot cause an unbounded allocation or event backlog.
	maxPayload = 16 << 20
	maxPending = 256
)

type message struct {
	kind uint32
	body []byte
}

func readMessage(r io.Reader) (message, error) {
	var header [14]byte
	if _, err := io.ReadFull(r, header[:]); err != nil {
		return message{}, err
	}
	if string(header[:6]) != "i3-ipc" {
		return message{}, errors.New("invalid i3 magic")
	}
	size := binary.NativeEndian.Uint32(header[6:10])
	if size > maxPayload {
		return message{}, errors.New("i3 payload too large")
	}
	body := make([]byte, int(size))
	if _, err := io.ReadFull(r, body); err != nil {
		return message{}, err
	}
	if len(body) != 0 && !json.Valid(body) {
		return message{}, errors.New("invalid i3 JSON")
	}
	return message{binary.NativeEndian.Uint32(header[10:]), body}, nil
}

func writeMessage(w io.Writer, kind uint32, body []byte) error {
	if len(body) > maxPayload {
		return errors.New("i3 payload too large")
	}
	var header [14]byte
	copy(header[:], "i3-ipc")
	binary.NativeEndian.PutUint32(header[6:10], uint32(len(body)))
	binary.NativeEndian.PutUint32(header[10:], kind)
	for _, part := range [][]byte{header[:], body} {
		for len(part) > 0 {
			n, err := w.Write(part)
			if err != nil {
				return err
			}
			if n == 0 {
				return io.ErrShortWrite
			}
			part = part[n:]
		}
	}
	return nil
}