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

package clipboard

import (
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"
	"syscall"
	"time"
	"unicode/utf8"
)

const maxHistoryBytes = 64 << 20

// Snapshot preserves newest-first order and the selected history entry.
type Snapshot struct {
	Version  int      `json:"version"`
	Entries  []string `json:"entries"`
	Selected int      `json:"selected"`
}

func History_path(home string, terminalMode bool) string {
	if terminalMode {
		return filepath.Join(home, ".local/state/fenrir/clipboard/terminal.json")
	}
	return "/var/lib/fenrir/clipboard/tty.json"
}

func (h *History) Snapshot() Snapshot {
	return Snapshot{Version: 1, Entries: append([]string{}, h.entries...), Selected: h.index}
}

func validate_snapshot(state Snapshot) error {
	if state.Version != 1 || len(state.Entries) > 10000 || state.Selected < 0 || (len(state.Entries) == 0 && state.Selected != 0) || (len(state.Entries) > 0 && state.Selected >= len(state.Entries)) {
		return fmt.Errorf("invalid clipboard history")
	}
	total := 0
	for _, text := range state.Entries {
		if err := Validate_text(text); err != nil {
			return err
		}
		total += len(text)
		if total > maxHistoryBytes {
			return fmt.Errorf("clipboard history exceeds 64 MiB")
		}
	}
	return nil
}

func (h *History) Restore(state Snapshot) error {
	if err := validate_snapshot(state); err != nil {
		return err
	}
	h.entries = append([]string(nil), state.Entries[:min(len(state.Entries), h.limit)]...)
	h.index = min(state.Selected, max(0, len(h.entries)-1))
	return nil
}

func (h *History) Resize(limit int) {
	h.limit = max(1, limit)
	h.entries = h.entries[:min(len(h.entries), h.limit)]
	h.index = min(h.index, max(0, len(h.entries)-1))
}

// A stable lock inode serializes only individual transactions. Closing it
// releases ownership; another reader can immediately read, update or clear.
func acquire_history(path string, create bool) (*os.File, error) {
	if err := private_directory(filepath.Dir(path), create); err != nil {
		if !create && errors.Is(err, os.ErrNotExist) {
			return nil, nil
		}
		return nil, err
	}
	file, err := os.OpenFile(path+".lock", os.O_CREATE|os.O_RDWR|syscall.O_NOFOLLOW|syscall.O_NONBLOCK, 0600)
	if err != nil {
		return nil, err
	}
	info, err := file.Stat()
	if err == nil && (!info.Mode().IsRegular() || info.Mode().Perm()&0077 != 0 || info.Sys().(*syscall.Stat_t).Uid != uint32(os.Geteuid())) {
		err = fmt.Errorf("clipboard history lock must be private and owned by the current account")
	}
	deadline := time.Now().Add(2 * time.Second)
	for err == nil {
		err = syscall.Flock(int(file.Fd()), syscall.LOCK_EX|syscall.LOCK_NB)
		if !errors.Is(err, syscall.EWOULDBLOCK) || time.Now().After(deadline) {
			break
		}
		time.Sleep(10 * time.Millisecond)
		err = nil
	}
	if err == nil {
		err = remove_temporary_history(path)
	}
	if err != nil {
		file.Close()
		return nil, err
	}
	return file, nil
}

func private_directory(path string, create bool) error {
	if create {
		if err := os.MkdirAll(path, 0700); err != nil {
			return err
		}
	}
	info, err := os.Lstat(path)
	if err != nil {
		return err
	}
	if !info.IsDir() || info.Mode().Perm()&0077 != 0 || info.Sys().(*syscall.Stat_t).Uid != uint32(os.Geteuid()) {
		return fmt.Errorf("clipboard history directory must be private and owned by the current account")
	}
	return nil
}

func load_history(path string) (Snapshot, error) {
	empty := Snapshot{Version: 1}
	if err := private_directory(filepath.Dir(path), false); err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return empty, nil
		}
		return empty, err
	}
	file, err := os.OpenFile(path, os.O_RDONLY|syscall.O_NOFOLLOW|syscall.O_NONBLOCK, 0)
	if errors.Is(err, os.ErrNotExist) {
		return empty, nil
	}
	if err != nil {
		return empty, err
	}
	defer file.Close()
	info, err := file.Stat()
	if err != nil {
		return empty, err
	}
	if !info.Mode().IsRegular() || info.Mode().Perm()&0077 != 0 || info.Sys().(*syscall.Stat_t).Uid != uint32(os.Geteuid()) {
		return empty, fmt.Errorf("clipboard history must be a private regular file owned by the current account")
	}
	data, err := io.ReadAll(io.LimitReader(file, maxHistoryBytes+1))
	if err != nil {
		return empty, err
	}
	if len(data) > maxHistoryBytes || !utf8.Valid(data) {
		return empty, fmt.Errorf("invalid or oversized clipboard history")
	}
	var state Snapshot
	if err := json.Unmarshal(data, &state); err != nil {
		return empty, fmt.Errorf("invalid clipboard history JSON")
	}
	if err := validate_snapshot(state); err != nil {
		return empty, err
	}
	return state, nil
}

func save_history(path string, state Snapshot) error {
	if err := validate_snapshot(state); err != nil {
		return err
	}
	data, err := json.Marshal(state)
	if err != nil {
		return err
	}
	if len(data) > maxHistoryBytes {
		return fmt.Errorf("clipboard history exceeds 64 MiB")
	}
	if err := private_directory(filepath.Dir(path), true); err != nil {
		return err
	}
	// Do not replace symlinks, devices or directories supplied at the destination.
	if info, err := os.Lstat(path); err == nil {
		if !info.Mode().IsRegular() {
			return fmt.Errorf("clipboard history must be a regular file")
		}
	} else if !errors.Is(err, os.ErrNotExist) {
		return err
	}
	file, err := os.CreateTemp(filepath.Dir(path), "."+filepath.Base(path)+"-*.tmp")
	if err != nil {
		return err
	}
	defer os.Remove(file.Name())
	_, writeErr := file.Write(data)
	err = errors.Join(writeErr, file.Sync(), file.Close())
	if err != nil {
		return err
	}
	if err := os.Rename(file.Name(), path); err != nil {
		return err
	}
	return sync_directory(filepath.Dir(path))
}

func remove_history(path string) error {
	if err := private_directory(filepath.Dir(path), false); err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return nil
		}
		return err
	}
	err := os.Remove(path)
	if errors.Is(err, os.ErrNotExist) {
		return nil
	}
	if err != nil {
		return err
	}
	return sync_directory(filepath.Dir(path))
}

func sync_directory(path string) error {
	dir, err := os.Open(path)
	if err != nil {
		return err
	}
	return errors.Join(dir.Sync(), dir.Close())
}

// A killed process can leave an atomic-write temporary file. Only clean this
// history's own files after acquiring its lock, including when clearing it.
func remove_temporary_history(path string) error {
	entries, err := os.ReadDir(filepath.Dir(path))
	if err != nil {
		return err
	}
	for _, entry := range entries {
		if !strings.HasPrefix(entry.Name(), "."+filepath.Base(path)+"-") || !strings.HasSuffix(entry.Name(), ".tmp") || !entry.Type().IsRegular() {
			continue
		}
		if err := os.Remove(filepath.Join(filepath.Dir(path), entry.Name())); err != nil {
			return err
		}
	}
	return nil
}