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

package app

import (
	"strings"
	"unicode/utf8"

	"git.stormux.org/storm/cthulhu/internal/atspi"
)

// textSelection tracks only the focused text object. Its cached content is
// bounded by the native snapshot and is retired when focus changes.
type textSelection struct {
	id         atspi.ObjectID
	start, end int
	text       string
}

const selectionFragmentLimit = 120
const lineSelectionFragmentLimit = 4096

func (selection *textSelection) reset(snapshot atspi.Snapshot) {
	selection.id = snapshot.ID()
	selection.start, selection.end = snapshot.SelectionStart, snapshot.SelectionEnd
	selection.text = snapshot.SelectionText
}

func (selection *textSelection) changed(snapshot atspi.Snapshot) string {
	return selection.changedWithLimit(snapshot, selectionFragmentLimit)
}

func (selection *textSelection) changedWithLimit(snapshot atspi.Snapshot, fragmentLimit int) string {
	start, end := snapshot.SelectionStart, snapshot.SelectionEnd
	if selection.id != snapshot.ID() {
		selection.reset(snapshot)
		return ""
	}
	oldStart, oldEnd, oldText := selection.start, selection.end, selection.text
	selection.reset(snapshot)
	if start == oldStart && end == oldEnd && oldText == snapshot.SelectionText {
		return ""
	}
	if end <= start {
		if oldEnd > oldStart {
			return "selection removed"
		}
		return ""
	}
	if oldEnd <= oldStart {
		return selectionFragment(snapshot.SelectionText, "selected", fragmentLimit)
	}
	var changes []string
	if start > oldStart {
		changes = append(changes, selectionFragment(selectionSlice(oldText, 0, min(oldEnd, start)-oldStart), "unselected", fragmentLimit))
	}
	if end < oldEnd {
		changes = append(changes, selectionFragment(selectionSlice(oldText, max(oldStart, end)-oldStart, oldEnd-oldStart), "unselected", fragmentLimit))
	}
	if start < oldStart {
		changes = append(changes, selectionFragment(selectionSlice(snapshot.SelectionText, 0, min(end, oldStart)-start), "selected", fragmentLimit))
	}
	if end > oldEnd {
		changes = append(changes, selectionFragment(selectionSlice(snapshot.SelectionText, max(start, oldEnd)-start, end-start), "selected", fragmentLimit))
	}
	if len(changes) == 0 {
		return "selection changed"
	}
	return strings.Join(changes, ", ")
}

func selectionSlice(value string, start, end int) string {
	runes := []rune(value)
	if start < 0 || end > len(runes) || start >= end {
		return ""
	}
	return string(runes[start:end])
}

func selectionFragment(value, change string, limit int) string {
	if utf8.RuneCountInString(value) > limit {
		return change
	}
	value = strings.Join(strings.Fields(value), " ")
	if value == "" {
		return change
	}
	return value + " " + change
}