package grpc

import (
	"context"
	"fmt"
	"os"
	"sync"

	"google.golang.org/grpc"
	"google.golang.org/grpc/metadata"
)

// TokenManager reads auth credentials from environment variables and attaches
// them as gRPC metadata on every call. It also handles automatic token refresh
// by reading new tokens from response headers.
type TokenManager struct {
	mu           sync.RWMutex
	accessToken  string
	refreshToken string
	sandboxID    string
	upstream     string // only set when YAO_GRPC_TAI=enable
	taiMode      bool
}

// NewTokenManagerFromEnv creates a TokenManager from environment variables.
// Returns an error if required variables are missing.
func NewTokenManagerFromEnv() (*TokenManager, error) {
	tm := &TokenManager{
		accessToken:  os.Getenv("YAO_TOKEN"),
		refreshToken: os.Getenv("YAO_REFRESH_TOKEN"),
		sandboxID:    os.Getenv("YAO_SANDBOX_ID"),
	}

	if os.Getenv("YAO_GRPC_TAI") == "enable" {
		tm.taiMode = true
		tm.upstream = os.Getenv("YAO_GRPC_UPSTREAM")
		if tm.upstream == "" {
			return nil, fmt.Errorf("YAO_GRPC_TAI=enable but YAO_GRPC_UPSTREAM is not set")
		}
	}

	return tm, nil
}

// NewTokenManager creates a TokenManager with explicit values (for testing).
func NewTokenManager(accessToken, refreshToken, sandboxID, upstream string) *TokenManager {
	return &TokenManager{
		accessToken:  accessToken,
		refreshToken: refreshToken,
		sandboxID:    sandboxID,
		upstream:     upstream,
		taiMode:      upstream != "",
	}
}

// AttachMetadata returns a context with auth credentials in gRPC metadata.
func (tm *TokenManager) AttachMetadata(ctx context.Context) context.Context {
	tm.mu.RLock()
	defer tm.mu.RUnlock()

	pairs := []string{}
	if tm.accessToken != "" {
		pairs = append(pairs, "authorization", "Bearer "+tm.accessToken)
	}
	if tm.refreshToken != "" {
		pairs = append(pairs, "x-refresh-token", tm.refreshToken)
	}
	if tm.sandboxID != "" {
		pairs = append(pairs, "x-sandbox-id", tm.sandboxID)
	}
	if tm.taiMode && tm.upstream != "" {
		pairs = append(pairs, "x-grpc-upstream", tm.upstream)
	}

	if len(pairs) == 0 {
		return ctx
	}
	return metadata.AppendToOutgoingContext(ctx, pairs...)
}

// HandleResponseHeaders reads new tokens from response headers and updates
// the in-memory credentials. Call after each gRPC response.
func (tm *TokenManager) HandleResponseHeaders(header metadata.MD) {
	if header == nil {
		return
	}

	tm.mu.Lock()
	defer tm.mu.Unlock()

	if vals := header.Get("x-access-token"); len(vals) > 0 && vals[0] != "" {
		tm.accessToken = vals[0]
	}
	if vals := header.Get("x-refresh-token"); len(vals) > 0 && vals[0] != "" {
		tm.refreshToken = vals[0]
	}
}

// UnaryInterceptor returns a gRPC unary client interceptor that attaches
// auth metadata and handles token refresh from response headers.
func (tm *TokenManager) UnaryInterceptor() grpc.UnaryClientInterceptor {
	return func(ctx context.Context, method string, req, reply any,
		cc *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {

		ctx = tm.AttachMetadata(ctx)

		var header metadata.MD
		opts = append(opts, grpc.Header(&header))

		err := invoker(ctx, method, req, reply, cc, opts...)
		tm.HandleResponseHeaders(header)
		return err
	}
}

// StreamInterceptor returns a gRPC stream client interceptor that attaches
// auth metadata. Token refresh from stream headers is handled by the caller
// via stream.Header().
func (tm *TokenManager) StreamInterceptor() grpc.StreamClientInterceptor {
	return func(ctx context.Context, desc *grpc.StreamDesc, cc *grpc.ClientConn,
		method string, streamer grpc.Streamer, opts ...grpc.CallOption) (grpc.ClientStream, error) {

		ctx = tm.AttachMetadata(ctx)
		stream, err := streamer(ctx, desc, cc, method, opts...)
		if err != nil {
			return nil, err
		}

		if header, hErr := stream.Header(); hErr == nil {
			tm.HandleResponseHeaders(header)
		}

		return stream, nil
	}
}

// AccessToken returns the current access token (for testing/debugging).
func (tm *TokenManager) AccessToken() string {
	tm.mu.RLock()
	defer tm.mu.RUnlock()
	return tm.accessToken
}

// IsTaiMode returns whether the client is configured for Tai relay mode.
func (tm *TokenManager) IsTaiMode() bool {
	return tm.taiMode
}