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

package clipboard

/*
#include "watch.h"
*/
import "C"

import (
	"bufio"
	"context"
	"encoding/json"
	"errors"
	"io"
	"runtime"
	"time"
)

type WatchSettings struct {
	Enabled bool
	Epoch   uint64
}

type TextChange struct {
	Text      string
	Epoch     uint64
	Timestamp uint32
	Ready     bool
}

// WatchText keeps a GTK selection connection warm so successive clipboard
// changes are captured asynchronously and emitted in arrival order. Disabled
// applications never request clipboard targets or contents.
func WatchText(ctx context.Context, input io.Reader, output io.Writer) error {
	runtime.LockOSThread()
	defer runtime.UnlockOSThread()
	ctx, cancel := context.WithCancel(ctx)
	defer cancel()
	settings := make(chan WatchSettings, 1)
	inputDone := make(chan error, 1)
	go func() {
		scanner := bufio.NewScanner(input)
		scanner.Buffer(make([]byte, 1024), 4096)
		for scanner.Scan() {
			var request WatchSettings
			if err := json.Unmarshal(scanner.Bytes(), &request); err != nil {
				inputDone <- err
				return
			}
			select {
			case settings <- request:
			case <-ctx.Done():
				return
			}
		}
		inputDone <- scanner.Err()
	}()
	if C.clipboard_watch_init() == 0 {
		return errors.New("cannot watch clipboard on this display")
	}
	encoder := json.NewEncoder(output)
	if err := encoder.Encode(TextChange{Ready: true}); err != nil {
		return err
	}
	ticker := time.NewTicker(time.Millisecond)
	defer ticker.Stop()
	for {
		select {
		case <-ctx.Done():
			return ctx.Err()
		case err := <-inputDone:
			return err
		case request := <-settings:
			enabled := C.int(0)
			if request.Enabled {
				enabled = 1
			}
			C.clipboard_watch_enable(enabled, C.ulonglong(request.Epoch))
			if err := encoder.Encode(TextChange{Ready: true, Epoch: request.Epoch}); err != nil {
				return err
			}
		case <-ticker.C:
			C.clipboard_watch_iterate()
			for {
				change := C.clipboard_watch_next()
				if change == nil {
					break
				}
				value := TextChange{Text: C.GoString(change.text), Epoch: uint64(change.epoch), Timestamp: uint32(change.timestamp)}
				C.clipboard_watch_free(change)
				if err := encoder.Encode(value); err != nil {
					return err
				}
			}
		}
	}
}