// Package config loads embedded defaults and optionally merges a user
// overlay from ~/.config/archduino/overlay.yaml.
package config

import (
	_ "embed"
	"fmt"
	"os"
	"path/filepath"

	"gopkg.in/yaml.v3"
)

//go:embed defaults.yaml
var defaultsYAML []byte

// Config is the fully-resolved runtime configuration.
type Config struct {
	Version         int               `yaml:"version"`
	ExtraPackages   []string          `yaml:"extra_packages"`
	DisabledModules []string          `yaml:"disabled_modules"`
	ThemeOverrides  map[string]string `yaml:"theme_overrides"`
}

const currentVersion = 1

// Load returns defaults merged with the overlay at overlayPath (if present).
// If overlayPath is "", the default location (~/.config/archduino/overlay.yaml)
// is used. A missing overlay is not an error.
func Load(overlayPath string) (Config, error) {
	var cfg Config
	if err := yaml.Unmarshal(defaultsYAML, &cfg); err != nil {
		return Config{}, fmt.Errorf("parse embedded defaults: %w", err)
	}

	if overlayPath == "" {
		home, err := os.UserHomeDir()
		if err != nil {
			return cfg, nil
		}
		overlayPath = filepath.Join(home, ".config", "archduino", "overlay.yaml")
	}

	data, err := os.ReadFile(overlayPath)
	if err != nil {
		if os.IsNotExist(err) {
			return cfg, nil
		}
		return Config{}, fmt.Errorf("read overlay %s: %w", overlayPath, err)
	}

	var overlay Config
	if err := yaml.Unmarshal(data, &overlay); err != nil {
		return Config{}, fmt.Errorf("parse overlay %s: %w", overlayPath, err)
	}
	if overlay.Version != 0 && overlay.Version != currentVersion {
		return Config{}, fmt.Errorf("overlay %s: unsupported version %d (want %d)", overlayPath, overlay.Version, currentVersion)
	}

	return merge(cfg, overlay), nil
}

func merge(base, over Config) Config {
	out := base
	if len(over.ExtraPackages) > 0 {
		out.ExtraPackages = append(append([]string{}, base.ExtraPackages...), over.ExtraPackages...)
	}
	if len(over.DisabledModules) > 0 {
		out.DisabledModules = append(append([]string{}, base.DisabledModules...), over.DisabledModules...)
	}
	if len(over.ThemeOverrides) > 0 {
		merged := make(map[string]string, len(base.ThemeOverrides)+len(over.ThemeOverrides))
		for k, v := range base.ThemeOverrides {
			merged[k] = v
		}
		for k, v := range over.ThemeOverrides {
			merged[k] = v
		}
		out.ThemeOverrides = merged
	}
	return out
}