package oauth

import (
	"context"
	"fmt"
	"net/http"
	"sync"

	"github.com/bluesky-social/indigo/atproto/auth/oauth"
	"github.com/bluesky-social/indigo/atproto/syntax"
)

// SessionCache represents a cached OAuth session
type SessionCache struct {
	Session   *oauth.ClientSession
	SessionID string
}

// Refresher manages OAuth sessions and token refresh for AppView
type Refresher struct {
	app           *App
	sessions      map[string]*SessionCache // Key: DID string
	mu            sync.RWMutex
	refreshLocks  map[string]*sync.Mutex // Per-DID locks for refresh operations
	refreshLockMu sync.Mutex             // Protects refreshLocks map
}

// NewRefresher creates a new session refresher
func NewRefresher(app *App) *Refresher {
	return &Refresher{
		app:          app,
		sessions:     make(map[string]*SessionCache),
		refreshLocks: make(map[string]*sync.Mutex),
	}
}

// GetSession gets a fresh OAuth session for a DID
// Returns cached session if still valid, otherwise resumes from store
func (r *Refresher) GetSession(ctx context.Context, did string) (*oauth.ClientSession, error) {
	// Check cache first (fast path)
	r.mu.RLock()
	cached, ok := r.sessions[did]
	r.mu.RUnlock()

	if ok && cached.Session != nil {
		// Session cached, tokens will auto-refresh if needed
		return cached.Session, nil
	}

	// Session not cached, need to resume from store
	// Get or create per-DID lock to prevent concurrent resume operations
	r.refreshLockMu.Lock()
	didLock, ok := r.refreshLocks[did]
	if !ok {
		didLock = &sync.Mutex{}
		r.refreshLocks[did] = didLock
	}
	r.refreshLockMu.Unlock()

	// Acquire DID-specific lock
	didLock.Lock()
	defer didLock.Unlock()

	// Double-check cache after acquiring lock (another goroutine might have loaded it)
	r.mu.RLock()
	cached, ok = r.sessions[did]
	r.mu.RUnlock()

	if ok && cached.Session != nil {
		return cached.Session, nil
	}

	// Actually resume the session
	return r.resumeSession(ctx, did)
}

// GetAccessToken gets a fresh access token for a DID
// This is a convenience method that extracts the access token from the session
func (r *Refresher) GetAccessToken(ctx context.Context, did string) (string, error) {
	session, err := r.GetSession(ctx, did)
	if err != nil {
		return "", err
	}

	// Get access token and DPoP nonce from session
	accessToken, _ := session.GetHostAccessData()
	return accessToken, nil
}

// GetHTTPClient returns an HTTP client with DPoP authentication for a DID
// The client automatically adds DPoP headers and refreshes tokens as needed
func (r *Refresher) GetHTTPClient(ctx context.Context, did string) (*http.Client, error) {
	session, err := r.GetSession(ctx, did)
	if err != nil {
		return nil, err
	}

	// Get API client from session
	// This client automatically handles DPoP and token refresh
	apiClient := session.APIClient()
	return apiClient.Client, nil
}

// resumeSession loads a session from storage and caches it
func (r *Refresher) resumeSession(ctx context.Context, did string) (*oauth.ClientSession, error) {
	// Parse DID
	accountDID, err := syntax.ParseDID(did)
	if err != nil {
		return nil, fmt.Errorf("failed to parse DID: %w", err)
	}

	// Get all sessions for this DID from store
	fileStore, ok := r.app.clientApp.Store.(*FileStore)
	if !ok {
		return nil, fmt.Errorf("store is not a FileStore")
	}

	// Find a session for this DID
	sessions := fileStore.ListSessions()
	var sessionID string
	for _, sessionData := range sessions {
		if sessionData.AccountDID.String() == did {
			sessionID = sessionData.SessionID
			break
		}
	}

	if sessionID == "" {
		return nil, fmt.Errorf("no session found for DID: %s", did)
	}

	// Resume session
	session, err := r.app.ResumeSession(ctx, accountDID, sessionID)
	if err != nil {
		return nil, fmt.Errorf("failed to resume session: %w", err)
	}

	// Cache the session
	r.mu.Lock()
	r.sessions[did] = &SessionCache{
		Session:   session,
		SessionID: sessionID,
	}
	r.mu.Unlock()

	return session, nil
}

// InvalidateSession removes a cached session for a DID
// This is useful when a new OAuth flow creates a fresh session
func (r *Refresher) InvalidateSession(did string) {
	r.mu.Lock()
	delete(r.sessions, did)
	r.mu.Unlock()
}

// RevokeSession removes a session from both cache and storage
func (r *Refresher) RevokeSession(ctx context.Context, did string) error {
	// Remove from cache
	r.mu.Lock()
	cached, ok := r.sessions[did]
	delete(r.sessions, did)
	r.mu.Unlock()

	if !ok {
		// Not cached, still try to delete from storage
		accountDID, err := syntax.ParseDID(did)
		if err != nil {
			return fmt.Errorf("failed to parse DID: %w", err)
		}

		// Find session ID from store
		fileStore, ok := r.app.clientApp.Store.(*FileStore)
		if !ok {
			return fmt.Errorf("store is not a FileStore")
		}

		sessions := fileStore.ListSessions()
		for _, sessionData := range sessions {
			if sessionData.AccountDID.String() == did {
				return r.app.clientApp.Store.DeleteSession(ctx, accountDID, sessionData.SessionID)
			}
		}

		return fmt.Errorf("no session found for DID: %s", did)
	}

	// Revoke the session via OAuth
	if err := cached.Session.RevokeSession(ctx); err != nil {
		fmt.Printf("WARNING: failed to revoke session for %s: %v\n", did, err)
		// Continue anyway to delete from storage
	}

	// Delete from storage
	accountDID, err := syntax.ParseDID(did)
	if err != nil {
		return fmt.Errorf("failed to parse DID: %w", err)
	}

	return r.app.clientApp.Store.DeleteSession(ctx, accountDID, cached.SessionID)
}

// CleanupExpiredSessions removes expired sessions from cache
// Note: indigo handles token expiry automatically, but we clean up orphaned cache entries
func (r *Refresher) CleanupExpiredSessions(ctx context.Context) {
	r.mu.Lock()
	defer r.mu.Unlock()

	// For each cached session, verify it still exists in storage
	for did, cached := range r.sessions {
		accountDID, err := syntax.ParseDID(did)
		if err != nil {
			delete(r.sessions, did)
			continue
		}

		// Try to get session from store
		_, err = r.app.clientApp.Store.GetSession(ctx, accountDID, cached.SessionID)
		if err != nil {
			// Session no longer exists, remove from cache
			delete(r.sessions, did)
		}
	}
}