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

package spellcheck

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

func Exceptions_path(home string) string {
	return filepath.Join(home, ".local/share/stormux/fenrirscreenreader/spelling/exceptions.json")
}

func load_exceptions(path string) (map[string]string, error) {
	words := make(map[string]string)
	file, err := os.Open(path)
	if errors.Is(err, os.ErrNotExist) {
		return words, nil
	}
	if err != nil {
		return nil, err
	}
	defer file.Close()
	data, err := io.ReadAll(io.LimitReader(file, (1<<20)+1))
	if err != nil {
		return nil, err
	}
	if len(data) > 1<<20 {
		return nil, fmt.Errorf("exceptions file exceeds 1 MiB")
	}
	var entries []string
	if err := json.Unmarshal(data, &entries); err != nil {
		return nil, err
	}
	for _, word := range entries {
		if !valid_word(word) {
			return nil, fmt.Errorf("invalid exceptions file")
		}
		words[strings.ToLower(word)] = word
	}
	return words, nil
}

func exception_list(words map[string]string) []string {
	entries := make([]string, 0, len(words))
	for _, word := range words {
		entries = append(entries, word)
	}
	sort.Slice(entries, func(i, j int) bool { return strings.ToLower(entries[i]) < strings.ToLower(entries[j]) })
	return entries
}

// Each edit reloads the latest list while holding a stable, per-file lock.
// Atomic replacement alone cannot protect against another reader's stale copy.
func update_exceptions(ctx context.Context, path string, operation Operation, word string) (map[string]string, error) {
	if err := os.MkdirAll(filepath.Dir(path), 0700); err != nil {
		return nil, err
	}
	lock, err := os.OpenFile(path+".lock", os.O_CREATE|os.O_RDWR|syscall.O_NOFOLLOW|syscall.O_NONBLOCK, 0600)
	if err != nil {
		return nil, err
	}
	defer lock.Close()
	info, err := lock.Stat()
	if err != nil {
		return nil, err
	}
	if !info.Mode().IsRegular() || info.Mode().Perm()&0077 != 0 || info.Sys().(*syscall.Stat_t).Uid != uint32(os.Geteuid()) {
		return nil, fmt.Errorf("exceptions lock must be private and owned by the current account")
	}
	waitCtx, cancel := context.WithTimeout(ctx, 2*time.Second)
	defer cancel()
	for {
		if err := waitCtx.Err(); err != nil {
			return nil, err
		}
		err = syscall.Flock(int(lock.Fd()), syscall.LOCK_EX|syscall.LOCK_NB)
		if err == nil {
			break
		}
		if !errors.Is(err, syscall.EWOULDBLOCK) {
			return nil, err
		}
		timer := time.NewTimer(10 * time.Millisecond)
		select {
		case <-waitCtx.Done():
			timer.Stop()
			return nil, waitCtx.Err()
		case <-timer.C:
		}
	}
	words, err := load_exceptions(path)
	if err != nil {
		return nil, err
	}
	key := strings.ToLower(word)
	if operation == Add {
		words[key] = word
	} else {
		delete(words, key)
	}
	if err := save_exceptions(path, words); err != nil {
		return nil, err
	}
	return words, nil
}

func save_exceptions(path string, words map[string]string) error {
	data, err := json.MarshalIndent(exception_list(words), "", "  ")
	if err != nil {
		return err
	}
	if len(data) > 1<<20 {
		return fmt.Errorf("exceptions file exceeds 1 MiB")
	}
	dir := filepath.Dir(path)
	if err := os.MkdirAll(dir, 0700); err != nil {
		return err
	}
	file, err := os.CreateTemp(dir, ".exceptions-*.json")
	if err != nil {
		return err
	}
	defer os.Remove(file.Name())
	if _, err := file.Write(append(data, '\n')); err != nil {
		file.Close()
		return err
	}
	if err := file.Sync(); err != nil {
		file.Close()
		return err
	}
	if err := file.Close(); err != nil {
		return err
	}
	return os.Rename(file.Name(), path)
}