package adapter

import (
	"context"
	"fmt"
	"io"

	"github.com/edgeai/gateway/pkg/api"
)

// ModelAdapter is the interface that all inference engine adapters must implement.
type ModelAdapter interface {
	// Name returns the adapter name (e.g., "ollama", "vllm").
	Name() string

	// ChatCompletion sends a non-streaming chat completion request.
	ChatCompletion(ctx context.Context, req *ChatRequest) (*ChatResponse, error)

	// ChatCompletionStream sends a streaming chat completion request.
	ChatCompletionStream(ctx context.Context, req *ChatRequest) (<-chan StreamChunk, error)

	// ListModels returns available models from the engine.
	ListModels(ctx context.Context) ([]ModelInfo, error)

	// HealthCheck checks if the engine is reachable.
	HealthCheck(ctx context.Context) error

	// Cancel cancels an in-progress request by request ID.
	Cancel(requestID string) error
}

// ChatRequest is the internal request sent to an adapter.
type ChatRequest struct {
	RequestID     string
	Model         string // actual model name
	Messages      []api.Message
	MaxTokens     int
	Temperature   *float64
	TopP          *float64
	Stream        bool
	CancelCh      <-chan struct{}
}

// ChatResponse is the internal response from an adapter.
type ChatResponse struct {
	Content       string
	FinishReason  string
	InputTokens   int
	OutputTokens  int
	ActualModel   string
}

// StreamChunk represents a single chunk in a streaming response.
type StreamChunk struct {
	Delta         string
	FinishReason  string
	InputTokens   int
	OutputTokens  int
	Error         error
	Done          bool
}

// ModelInfo describes a model available in the engine.
type ModelInfo struct {
	Name          string
	ContextWindow int
}

// Registry manages model adapters by provider name.
type Registry struct {
	adapters map[string]ModelAdapter
}

func NewRegistry() *Registry {
	return &Registry{adapters: make(map[string]ModelAdapter)}
}

func (r *Registry) Register(name string, adapter ModelAdapter) {
	r.adapters[name] = adapter
}

func (r *Registry) Get(name string) (ModelAdapter, error) {
	a, ok := r.adapters[name]
	if !ok {
		return nil, fmt.Errorf("adapter not found: %s", name)
	}
	return a, nil
}

func (r *Registry) Names() []string {
	names := make([]string, 0, len(r.adapters))
	for n := range r.adapters {
		names = append(names, n)
	}
	return names
}

// Ensure io is imported for future use (streaming readers).
var _ = io.EOF