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

package config

import (
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
)

// WriteGreeterSettings installs the effective saved profile at path. The caller
// must run as the destination account; no privileged filesystem writes are needed.
func WriteGreeterSettings(path string, settings Settings) error {
	contents, err := GreeterSettings(settings)
	if err != nil {
		return err
	}
	if settings.Path != "" {
		sourcePath, err := filepath.Abs(settings.Path)
		if err != nil {
			return err
		}
		targetPath, err := filepath.Abs(path)
		if err != nil {
			return err
		}
		source, sourceErr := os.Stat(settings.Path)
		target, targetErr := os.Stat(path)
		if sourcePath == targetPath || sourceErr == nil && targetErr == nil && os.SameFile(source, target) {
			return errors.New("greeter copy cannot replace the source settings")
		}
	}
	if err := os.MkdirAll(filepath.Dir(path), 0o700); err != nil {
		return fmt.Errorf("create greeter settings directory: %w", err)
	}
	temporary, err := os.CreateTemp(filepath.Dir(path), ".greeter-settings-*.toml")
	if err != nil {
		return fmt.Errorf("create greeter settings copy: %w", err)
	}
	defer os.Remove(temporary.Name())
	if _, err := temporary.Write(contents); err != nil {
		temporary.Close()
		return err
	}
	if err := temporary.Sync(); err != nil {
		temporary.Close()
		return err
	}
	if err := temporary.Close(); err != nil {
		return err
	}
	if err := os.Rename(temporary.Name(), path); err != nil {
		return fmt.Errorf("replace greeter settings copy: %w", err)
	}
	return syncDirectory(filepath.Dir(path))
}

// GreeterSettings encodes a complete active profile without application mappings
// or other profiles. Tentacle registries are stored separately and are not copied.
func GreeterSettings(settings Settings) ([]byte, error) {
	if err := validate(settings); err != nil {
		return nil, err
	}
	return encodeDocument(writableDocument{
		SchemaVersion: CurrentSchemaVersion,
		ActiveProfile: "greeter",
		Profiles:      map[string]writableProfile{"greeter": profileFromSettings(settings)},
	})
}

// ReadGreeterSettings reads the bounded snapshot from an already-open pipe.
// Reopening /dev/stdin after switching users can fail its ownership checks.
func ReadGreeterSettings(reader io.Reader) (Settings, error) {
	contents, err := io.ReadAll(io.LimitReader(reader, maxConfigSize+1))
	if err != nil {
		return Settings{}, fmt.Errorf("read greeter settings: %w", err)
	}
	if len(contents) > maxConfigSize {
		return Settings{}, fmt.Errorf("greeter settings exceed %d bytes", maxConfigSize)
	}
	return decodeWritable(contents)
}