// 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 config

import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"os"
	"reflect"
	"slices"
	"strings"
	"syscall"

	"github.com/pelletier/go-toml/v2"
	"github.com/pelletier/go-toml/v2/unstable"
)

// Document retains file identity and table order for an isolated edit. Version
// is metadata, not a UI tab. Omitted tables follow in schema order.
type Document struct {
	Settings          Settings
	Order             []string
	path              string
	original          []byte
	existed           bool
	applicationBase   *Settings
	applicationFields map[string]bool
}

func read_document(path string) ([]byte, error) {
	// Remote SAVEAS can name an arbitrary destination. A FIFO must not
	// block opening before we can establish that it is a regular file.
	file, err := os.OpenFile(path, os.O_RDONLY|syscall.O_NONBLOCK, 0)
	if err != nil {
		return nil, err
	}
	defer file.Close()
	info, err := file.Stat()
	if err != nil {
		return nil, err
	}
	if !info.Mode().IsRegular() {
		return nil, fmt.Errorf("settings destination is not a regular file")
	}
	data, err := io.ReadAll(io.LimitReader(file, (1<<20)+1))
	if err == nil && len(data) > 1<<20 {
		err = fmt.Errorf("settings file exceeds 1 MiB")
	}
	return data, err
}

func Open_document(path string, fallback Settings) (*Document, error) {
	doc := &Document{Settings: fallback, path: path}
	data, err := read_document(path)
	if !errors.Is(err, os.ErrNotExist) {
		if err != nil {
			return nil, err
		}
		doc.Settings, err = Decode(data)
		if err != nil {
			return nil, err
		}
		doc.original, doc.existed = data, true
		var parser unstable.Parser
		parser.Reset(data)
		seen := make(map[string]bool)
		sectionIDs := make(map[string]bool)
		var collect func([]Section)
		collect = func(sections []Section) {
			for _, section := range sections {
				sectionIDs[section.ID] = true
				collect(section.Sections)
			}
		}
		collect(Sections())
		record := func(parts []string) {
			// Map old table order to the migrated hierarchy, preserving sibling order.
			if len(parts) > 0 && (parts[0] == "speech" || parts[0] == "sound") {
				parts = append([]string{"presentation"}, parts...)
			}
			for count := 1; count <= len(parts); count++ {
				name := strings.Join(parts[:count], ".")
				if sectionIDs[name] && !seen[name] {
					doc.Order = append(doc.Order, name)
					seen[name] = true
				}
			}
		}
		var visit func(*unstable.Node, []string)
		visit = func(node *unstable.Node, prefix []string) {
			parts := append([]string(nil), prefix...)
			keys := node.Key()
			for keys.Next() {
				parts = append(parts, string(keys.Node().Data))
			}
			record(parts)
			if node.Kind == unstable.KeyValue && node.Value().Kind == unstable.InlineTable {
				children := node.Value().Children()
				for children.Next() {
					visit(children.Node(), parts)
				}
			}
		}
		var tablePath []string
		for parser.NextExpression() {
			node := parser.Expression()
			switch node.Kind {
			case unstable.Table:
				tablePath = nil
				keys := node.Key()
				for keys.Next() {
					tablePath = append(tablePath, string(keys.Node().Data))
				}
				record(tablePath)
			case unstable.KeyValue:
				visit(node, tablePath)
			}
		}
		if err := parser.Error(); err != nil {
			return nil, err
		}
	}
	return doc, nil
}

// Save checks for external edits made since the menu opened before writing.
// Atomic replacement uses the same system/private permissions policy as Save.
func (d *Document) Save(settings Settings) error {
	data, err := read_document(d.path)
	if d.existed {
		if err != nil {
			return err
		}
		if !bytes.Equal(data, d.original) {
			return fmt.Errorf("settings changed since the menu opened")
		}
	} else if err == nil {
		return fmt.Errorf("settings created since the menu opened")
	} else if !errors.Is(err, os.ErrNotExist) {
		return err
	}
	if err := settings.Validate(); err != nil {
		return err
	}
	if d.applicationBase != nil {
		return d.save_application(settings)
	}
	// The same schema drives persistence and the form, including nested groups.
	var output bytes.Buffer
	fmt.Fprintf(&output, "version = %d\n", settings.Version)
	var encode func([]Section) error
	encode = func(sections []Section) error {
		for _, section := range Ordered_sections(sections, d.Order) {
			value := setting_value(reflect.ValueOf(settings), section.ID)
			fields := make(map[string]any)
			for index := range value.NumField() {
				if value.Field(index).Kind() != reflect.Struct {
					tag := strings.Split(value.Type().Field(index).Tag.Get("toml"), ",")
					if slices.Contains(tag[1:], "omitempty") && value.Field(index).IsZero() {
						continue
					}
					fields[tag[0]] = value.Field(index).Interface()
				}
			}
			if len(fields) > 0 {
				encoded, err := toml.Marshal(fields)
				if err != nil {
					return err
				}
				fmt.Fprintf(&output, "\n[%s]\n", section.ID)
				output.Write(encoded)
			}
			if err := encode(section.Sections); err != nil {
				return err
			}
		}
		return nil
	}
	if err := encode(Sections()); err != nil {
		return err
	}
	return save_data(d.path, output.Bytes())
}