// Cthulhu screen reader.
// Copyright (c) 2026 Storm Dragon
// Authors: Storm Dragon, Angus Kola
//
// 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 (
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"

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

const maxConfigSize = 1024 * 1024

func DefaultPath() (string, error) {
	if dataHome := os.Getenv("XDG_DATA_HOME"); dataHome != "" {
		return filepath.Join(dataHome, "cthulhu", "user-settings-go.toml"), nil
	}
	home, err := os.UserHomeDir()
	if err != nil {
		return "", fmt.Errorf("resolve home directory: %w", err)
	}
	return filepath.Join(home, ".local", "share", "cthulhu", "user-settings-go.toml"), nil
}

// Load reads legacy Python settings or the current versioned schema without
// modifying the file. A present schema marker always selects strict decoding.
func Load(path string) (Settings, error) {
	settings := DefaultSettings()
	if path == "" {
		var err error
		path, err = DefaultPath()
		if err != nil {
			return Settings{}, err
		}
	}
	settings.Path = path

	file, err := os.Open(path)
	if errors.Is(err, os.ErrNotExist) {
		return settings, nil
	}
	if err != nil {
		return Settings{}, fmt.Errorf("open configuration: %w", err)
	}
	defer file.Close()

	contents, err := io.ReadAll(io.LimitReader(file, maxConfigSize+1))
	if err != nil {
		return Settings{}, fmt.Errorf("read configuration: %w", err)
	}
	if len(contents) > maxConfigSize {
		return Settings{}, fmt.Errorf("configuration exceeds %d bytes", maxConfigSize)
	}

	var envelope struct {
		SchemaVersion *int `toml:"schema-version"`
	}
	if err := toml.Unmarshal(contents, &envelope); err != nil {
		return Settings{}, fmt.Errorf("parse configuration: %w", err)
	}
	if envelope.SchemaVersion != nil {
		settings, err := decodeWritable(contents)
		if err != nil {
			return Settings{}, err
		}
		settings.Path = path
		settings.Loaded = true
		return settings, nil
	}

	var parsed document
	if err := toml.Unmarshal(contents, &parsed); err != nil {
		return Settings{}, fmt.Errorf("parse configuration: %w", err)
	}
	apply(&settings, parsed.General)

	profileName := selectedProfile(parsed.General, parsed.Profiles)
	if profileName != "" {
		profile, exists := parsed.Profiles[profileName]
		if !exists {
			return Settings{}, fmt.Errorf("configured profile %q does not exist", profileName)
		}
		apply(&settings, profile)
	}
	settings.ActiveProfile = profileName
	settings.Loaded = true
	if err := validate(settings); err != nil {
		return Settings{}, err
	}
	return settings, nil
}