// Package engine defines the Engine interface and mount registry.
// Phase 1: interface and registry only, no concrete implementations.
package engine

import (
	"context"
	"errors"
	"fmt"
	"sync"

	"git.wntrmute.dev/kyle/metacrypt/internal/barrier"
)

// EngineType identifies a cryptographic engine type.
type EngineType string

const (
	EngineTypeCA      EngineType = "ca"
	EngineTypeSSHCA   EngineType = "sshca"
	EngineTypeTransit EngineType = "transit"
	EngineTypeUser    EngineType = "user"
)

var (
	ErrMountExists   = errors.New("engine: mount already exists")
	ErrMountNotFound = errors.New("engine: mount not found")
	ErrUnknownType   = errors.New("engine: unknown engine type")
)

// Request is a request to an engine.
type Request struct {
	Operation string
	Path      string
	Data      map[string]interface{}
}

// Response is a response from an engine.
type Response struct {
	Data map[string]interface{}
}

// Engine is the interface that all cryptographic engines must implement.
type Engine interface {
	// Type returns the engine type.
	Type() EngineType
	// Initialize sets up the engine for first use.
	Initialize(ctx context.Context, b barrier.Barrier, mountPath string) error
	// Unseal opens the engine using state from the barrier.
	Unseal(ctx context.Context, b barrier.Barrier, mountPath string) error
	// Seal closes the engine and zeroizes key material.
	Seal() error
	// HandleRequest processes a request.
	HandleRequest(ctx context.Context, req *Request) (*Response, error)
}

// Factory creates a new engine instance of a given type.
type Factory func() Engine

// Mount represents a mounted engine instance.
type Mount struct {
	Name       string     `json:"name"`
	Type       EngineType `json:"type"`
	MountPath  string     `json:"mount_path"`
	engine     Engine
}

// Registry manages mounted engine instances.
type Registry struct {
	mu       sync.RWMutex
	mounts   map[string]*Mount
	factories map[EngineType]Factory
	barrier  barrier.Barrier
}

// NewRegistry creates a new engine registry.
func NewRegistry(b barrier.Barrier) *Registry {
	return &Registry{
		mounts:    make(map[string]*Mount),
		factories: make(map[EngineType]Factory),
		barrier:   b,
	}
}

// RegisterFactory registers a factory for the given engine type.
func (r *Registry) RegisterFactory(t EngineType, f Factory) {
	r.mu.Lock()
	defer r.mu.Unlock()
	r.factories[t] = f
}

// Mount creates and initializes a new engine mount.
func (r *Registry) Mount(ctx context.Context, name string, engineType EngineType) error {
	r.mu.Lock()
	defer r.mu.Unlock()

	if _, exists := r.mounts[name]; exists {
		return ErrMountExists
	}

	factory, ok := r.factories[engineType]
	if !ok {
		return fmt.Errorf("%w: %s", ErrUnknownType, engineType)
	}

	eng := factory()
	mountPath := fmt.Sprintf("engine/%s/%s/", engineType, name)

	if err := eng.Initialize(ctx, r.barrier, mountPath); err != nil {
		return fmt.Errorf("engine: initialize %q: %w", name, err)
	}

	r.mounts[name] = &Mount{
		Name:      name,
		Type:      engineType,
		MountPath: mountPath,
		engine:    eng,
	}
	return nil
}

// Unmount removes and seals an engine mount.
func (r *Registry) Unmount(name string) error {
	r.mu.Lock()
	defer r.mu.Unlock()

	mount, exists := r.mounts[name]
	if !exists {
		return ErrMountNotFound
	}

	if err := mount.engine.Seal(); err != nil {
		return fmt.Errorf("engine: seal %q: %w", name, err)
	}

	delete(r.mounts, name)
	return nil
}

// ListMounts returns all current mounts.
func (r *Registry) ListMounts() []Mount {
	r.mu.RLock()
	defer r.mu.RUnlock()

	mounts := make([]Mount, 0, len(r.mounts))
	for _, m := range r.mounts {
		mounts = append(mounts, Mount{
			Name:      m.Name,
			Type:      m.Type,
			MountPath: m.MountPath,
		})
	}
	return mounts
}

// HandleRequest routes a request to the appropriate engine.
func (r *Registry) HandleRequest(ctx context.Context, mountName string, req *Request) (*Response, error) {
	r.mu.RLock()
	mount, exists := r.mounts[mountName]
	r.mu.RUnlock()

	if !exists {
		return nil, ErrMountNotFound
	}

	return mount.engine.HandleRequest(ctx, req)
}

// SealAll seals all mounted engines.
func (r *Registry) SealAll() error {
	r.mu.Lock()
	defer r.mu.Unlock()

	for name, mount := range r.mounts {
		if err := mount.engine.Seal(); err != nil {
			return fmt.Errorf("engine: seal %q: %w", name, err)
		}
	}
	return nil
}