// Fenrir console screen reader.
// Copyright (c) 2026 Storm Dragon
// SPDX-License-Identifier: GPL-3.0-or-later
//
// This program is free software: you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by the Free
// Software Foundation, either version 3 of the License, or (at your option)
// any later version.
//
// This program is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
// more details.
//
// You should have received a copy of the GNU General Public License along with
// this program. If not, see <https://www.gnu.org/licenses/gpl-3.0.html>.

// Package clipboard owns text history and asynchronous clipboard transfers.
package clipboard

import (
	"fmt"
	"unicode/utf8"
)

// MaxBytes bounds individual entries and file/helper messages.
const MaxBytes = 4 << 20

// History belongs to the application loop. New entries select the newest item;
// navigation wraps, matching Python Fenrir. Clear removes the entire history.
type History struct {
	entries []string
	index   int
	limit   int
}

func New_history(limit int) *History { return &History{limit: max(1, limit)} }

func Validate_text(text string) error {
	if len(text) > MaxBytes || !utf8.ValidString(text) {
		return fmt.Errorf("clipboard text must be valid UTF-8 and at most 4 MiB")
	}
	return nil
}

func (h *History) Add(text string) error {
	if err := Validate_text(text); err != nil {
		return err
	}
	h.entries = append([]string{text}, h.entries[:min(len(h.entries), h.limit-1)]...)
	h.index = 0
	return nil
}

func (h *History) Current() (string, bool) {
	if len(h.entries) == 0 {
		return "", false
	}
	return h.entries[h.index], true
}

func (h *History) Move(delta int) {
	if len(h.entries) > 0 {
		h.index = (h.index + delta + len(h.entries)) % len(h.entries)
	}
}
func (h *History) First()         { h.index = 0 }
func (h *History) Last()          { h.index = max(0, len(h.entries)-1) }
func (h *History) At_first() bool { return len(h.entries) > 0 && h.index == 0 }
func (h *History) At_last() bool  { return len(h.entries) > 0 && h.index == len(h.entries)-1 }
func (h *History) Clear()         { h.entries, h.index = nil, 0 }

// Refresh adopts shared entries while retaining this reader's selected copy.
// Count duplicates from the oldest end so a new identical copy stays distinct.
func (h *History) Refresh(state Snapshot) error {
	text, selected := h.Current()
	occurrence := 0
	if selected {
		for _, entry := range h.entries[h.index:] {
			if entry == text {
				occurrence++
			}
		}
	}
	if err := h.Restore(state); err != nil {
		return err
	}
	if selected {
		for i := len(h.entries) - 1; i >= 0; i-- {
			if h.entries[i] == text {
				occurrence--
				if occurrence == 0 {
					h.index = i
					break
				}
			}
		}
	}
	return nil
}