// Package registry provides a global registry of package-format frontends.
//
// Frontends self-register via init() from their own packages, so a future
// format (e.g. Gentoo ebuild, void-src) only needs a new package that imports
// this one — nothing else changes.
package registry

import (
	"fmt"
	"sort"
	"sync"
)

// Options carries per-conversion settings shared by all frontends.
type Options struct {
	Output string // directory to write converted output into
	Repo   string // repository base URL (binary frontend)
	Arch   string // target architecture (source frontend)
}

// Frontend converts one input of a specific package format to Zeta.
type Frontend interface {
	// Name returns the frontend's CLI subcommand name.
	Name() string
	// Convert converts input into Zeta format under opts.Output.
	Convert(input string, opts Options) error
}

var (
	mu        sync.RWMutex
	frontends = make(map[string]Frontend)
)

// Register adds f to the global registry. It panics if a frontend with the
// same Name is already registered.
func Register(f Frontend) {
	mu.Lock()
	defer mu.Unlock()
	name := f.Name()
	if name == "" {
		panic("registry: frontend with empty name")
	}
	if _, dup := frontends[name]; dup {
		panic(fmt.Sprintf("registry: duplicate frontend %q", name))
	}
	frontends[name] = f
}

// List returns the names of all registered frontends, sorted.
func List() []string {
	mu.RLock()
	defer mu.RUnlock()
	names := make([]string, 0, len(frontends))
	for name := range frontends {
		names = append(names, name)
	}
	sort.Strings(names)
	return names
}

// Get returns the frontend registered under name.
func Get(name string) (Frontend, bool) {
	mu.RLock()
	defer mu.RUnlock()
	f, ok := frontends[name]
	return f, ok
}