// Package api is geniusrun's HTTP layer: REST handlers over internal/store,
// internal/garmin, and internal/sync.
package api

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"log"
	"log/slog"
	"net/http"
	"os"
	"path/filepath"
	"strconv"
	"sync"
	"sync/atomic"
	"time"

	"github.com/go-chi/chi/v5"
	"github.com/go-chi/chi/v5/middleware"

	"geniusrun/backend/internal/applog"
	"geniusrun/backend/internal/auth"
	"geniusrun/backend/internal/garmin"
	"geniusrun/backend/internal/store"
	appsync "geniusrun/backend/internal/sync"
)

// Server wires the HTTP handlers to the app's dependencies. garmin.Client
// and sync.Service are per-user (each user might have their own Garmin
// account), built lazily on first use via GarminFactory and cached.
type Server struct {
	DB      *store.DB
	Auth    auth.Verifier
	Session SessionConfig

	// GarminFactory builds a real (or fake, in tests) garmin.Client from a
	// fully-resolved per-user Config. Production wiring passes
	// garmin.NewClient; tests inject a factory returning a shared
	// *mock.Client (see newTestServer in api_test.go).
	GarminFactory func(garmin.Config) garmin.Client
	// GarminBase holds the plumbing shared by every user's garmin.Config
	// (the python interpreter path + the token-store root directory); only
	// GarminEmail/GarminPassword/TokenStorePath vary per user, filled in by
	// garminFor.
	GarminBase garmin.Config
	SyncConfig appsync.Config

	mu              sync.Mutex
	userGarmin      map[int64]garmin.Client
	userSync        map[int64]*appsync.Service
	userAuthStatus  map[int64]garmin.AuthStatus
	userAuthMessage map[int64]string
	userSyncRunning map[int64]bool
	setupGarmin     map[string]*setupSession
}

// NewServer builds a Server.
func NewServer(db *store.DB, garminFactory func(garmin.Config) garmin.Client, garminBase garmin.Config, syncConfig appsync.Config, authVerifier auth.Verifier, session SessionConfig) *Server {
	return &Server{
		DB: db, GarminFactory: garminFactory, GarminBase: garminBase, SyncConfig: syncConfig,
		Auth: authVerifier, Session: session,
		userGarmin:      map[int64]garmin.Client{},
		userSync:        map[int64]*appsync.Service{},
		userAuthStatus:  map[int64]garmin.AuthStatus{},
		userAuthMessage: map[int64]string{},
		userSyncRunning: map[int64]bool{},
		setupGarmin:     map[string]*setupSession{},
	}
}

// setupSession is a temporary, not-yet-persisted Garmin authentication
// attempt made during onboarding, before any users/profile row exists --
// keyed by OIDC subject (the only stable identifier available pre-account)
// rather than a user id. Closed (never promoted into Server.userGarmin) once
// /api/setup/complete actually creates the account -- its Client's
// garmin.Config.TokenStorePath is permanently pinned to the ephemeral
// setup/{hash} directory, so reusing the object after that directory is
// renamed to the permanent {userID} one would respawn against a stale path
// the next time anything closes and restarts its subprocess; a later
// garminFor(ctx, userID) call builds a fresh client with the correct path
// instead. Otherwise evicted lazily (the next setup-endpoint touch for that
// subject checks staleness first) once idle past setupSessionIdleTimeout.
type setupSession struct {
	Client          garmin.Client
	Email, Password string
	Status          garmin.AuthStatus
	Message         string
	LastUsed        time.Time
}

// setupSessionIdleTimeout bounds how long an onboarding Garmin session
// survives without being touched (login, MFA, or complete) before it's
// evicted -- long enough to check email for an MFA code, short enough that
// an abandoned attempt doesn't leave a subprocess running indefinitely.
const setupSessionIdleTimeout = 15 * time.Minute

// setupTokenStoreDir returns the token-store directory an ephemeral setup
// session for sub should use -- hashed rather than sub itself, since sub is
// an opaque string from the identity provider and using it verbatim in a
// filesystem path would be a directory-traversal risk if it ever contained
// path separators.
func setupTokenStoreDir(root, sub string) string {
	h := sha256.Sum256([]byte(sub))
	return filepath.Join(root, "setup", hex.EncodeToString(h[:]))
}

// setupSessionFor returns sub's in-progress ephemeral Garmin session, if
// any and not stale. A stale session is closed and evicted first, so the
// caller always either gets a fresh, live session or none.
func (s *Server) setupSessionFor(sub string) (*setupSession, bool) {
	s.mu.Lock()
	defer s.mu.Unlock()
	sess, ok := s.setupGarmin[sub]
	if !ok {
		return nil, false
	}
	if time.Since(sess.LastUsed) > setupSessionIdleTimeout {
		sess.Client.Close()
		delete(s.setupGarmin, sub)
		if s.GarminBase.TokenStorePath != "" {
			os.RemoveAll(setupTokenStoreDir(s.GarminBase.TokenStorePath, sub))
		}
		return nil, false
	}
	return sess, true
}

// replaceSetupSession closes and replaces sub's ephemeral Garmin session
// (if any) with a freshly built one for the given credentials -- same
// "close old, spawn new" semantics as garmin.Client.UpdateCredentials.
func (s *Server) replaceSetupSession(sub, email, password string) *setupSession {
	s.mu.Lock()
	old, ok := s.setupGarmin[sub]
	s.mu.Unlock()
	if ok {
		old.Client.Close()
	}

	cfg := s.GarminBase
	cfg.GarminEmail = email
	cfg.GarminPassword = password
	if cfg.TokenStorePath != "" {
		cfg.TokenStorePath = setupTokenStoreDir(s.GarminBase.TokenStorePath, sub)
	}
	sess := &setupSession{Client: s.GarminFactory(cfg), Email: email, Password: password, LastUsed: time.Now()}

	s.mu.Lock()
	s.setupGarmin[sub] = sess
	s.mu.Unlock()
	return sess
}

// recordSetupAuthResult updates sub's ephemeral session after a login or
// MFA attempt. A no-op if the session is gone (e.g. evicted concurrently).
func (s *Server) recordSetupAuthResult(sub string, res garmin.AuthResult) {
	s.mu.Lock()
	defer s.mu.Unlock()
	if sess, ok := s.setupGarmin[sub]; ok {
		sess.Status = res.Status
		sess.Message = res.Message
		sess.LastUsed = time.Now()
	}
}

// removeSetupSession closes and drops sub's ephemeral Garmin session, if
// any, and best-effort removes its token-store directory. Used when
// abandoning onboarding (logout). handleSetupComplete closes the client the
// same way but keeps (renames) the directory instead of removing it, since
// that's the real, now-permanent session.
func (s *Server) removeSetupSession(sub string) {
	s.mu.Lock()
	sess, ok := s.setupGarmin[sub]
	delete(s.setupGarmin, sub)
	s.mu.Unlock()
	if !ok {
		return
	}
	sess.Client.Close()
	if s.GarminBase.TokenStorePath != "" {
		os.RemoveAll(setupTokenStoreDir(s.GarminBase.TokenStorePath, sub))
	}
}

// garminFor returns userID's garmin.Client, building and caching it (from
// userID's own profile row) on first use.
func (s *Server) garminFor(ctx context.Context, userID int64) (garmin.Client, error) {
	s.mu.Lock()
	if c, ok := s.userGarmin[userID]; ok {
		s.mu.Unlock()
		return c, nil
	}
	s.mu.Unlock()

	profile, err := s.DB.GetProfile(ctx, userID)
	if err != nil {
		return nil, fmt.Errorf("load profile for garmin client (user %d): %w", userID, err)
	}
	cfg := s.GarminBase
	cfg.GarminEmail = profile.GarminEmail
	cfg.GarminPassword = profile.GarminPassword
	if cfg.TokenStorePath != "" {
		cfg.TokenStorePath = filepath.Join(cfg.TokenStorePath, strconv.FormatInt(userID, 10))
	}

	s.mu.Lock()
	defer s.mu.Unlock()
	if c, ok := s.userGarmin[userID]; ok {
		return c, nil // built concurrently by another request between our unlock and re-lock
	}
	client := s.GarminFactory(cfg)
	s.userGarmin[userID] = client
	return client, nil
}

// syncFor returns userID's sync.Service, building and caching it on first use.
func (s *Server) syncFor(ctx context.Context, userID int64) (*appsync.Service, error) {
	s.mu.Lock()
	if svc, ok := s.userSync[userID]; ok {
		s.mu.Unlock()
		return svc, nil
	}
	s.mu.Unlock()

	client, err := s.garminFor(ctx, userID)
	if err != nil {
		return nil, err
	}

	s.mu.Lock()
	defer s.mu.Unlock()
	if svc, ok := s.userSync[userID]; ok {
		return svc, nil
	}
	svc := appsync.NewService(client, s.DB, userID, s.SyncConfig, nil)
	s.userSync[userID] = svc
	return svc, nil
}

// removeGarminClient drops userID's cached garmin.Client/sync.Service (if
// any) and every other per-user in-memory entry for userID, terminating the
// client's subprocess and best-effort removing its on-disk token-store
// directory. Called when a user's account has just been deleted from the
// DB, so nothing in memory keeps referencing a userID that no longer
// exists.
func (s *Server) removeGarminClient(userID int64) {
	s.mu.Lock()
	client, ok := s.userGarmin[userID]
	delete(s.userGarmin, userID)
	delete(s.userSync, userID)
	delete(s.userAuthStatus, userID)
	delete(s.userAuthMessage, userID)
	delete(s.userSyncRunning, userID)
	s.mu.Unlock()

	if ok {
		if err := client.Close(); err != nil {
			log.Printf("api: close garmin client for deleted user %d: %v", userID, err)
		}
	}
	if s.GarminBase.TokenStorePath == "" {
		return
	}
	tokenStoreDir := filepath.Join(s.GarminBase.TokenStorePath, strconv.FormatInt(userID, 10))
	if err := os.RemoveAll(tokenStoreDir); err != nil {
		log.Printf("api: remove token store dir for deleted user %d: %v", userID, err)
	}
}

var requestIDCounter atomic.Int64

// requestLoggingMiddleware logs one JSON line per HTTP request (method,
// path, status, duration) and attaches a per-request logger (tagged with a
// request_id) to the request context, so any downstream call this request
// triggers -- e.g. a Garmin wrapper round-trip -- logs with the same
// correlating id (see internal/applog, internal/garmin's roundTrip).
func requestLoggingMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		id := fmt.Sprintf("req-%d", requestIDCounter.Add(1))
		logger := applog.FromContext(r.Context()).With("request_id", id)
		r = r.WithContext(applog.WithLogger(r.Context(), logger))

		ww := middleware.NewWrapResponseWriter(w, r.ProtoMajor)
		start := time.Now()
		next.ServeHTTP(ww, r)

		level := slog.LevelInfo
		if ww.Status() >= 500 {
			level = slog.LevelWarn
		}
		logger.LogAttrs(r.Context(), level, "http request",
			slog.String("method", r.Method),
			slog.String("path", r.URL.Path),
			slog.Int("status", ww.Status()),
			slog.Int64("duration_ms", time.Since(start).Milliseconds()),
		)
	})
}

// Router builds the HTTP routes.
func (s *Server) Router() http.Handler {
	r := chi.NewRouter()
	r.Use(requestLoggingMiddleware)
	r.Use(corsMiddleware)
	r.Route("/api", func(r chi.Router) {
		r.Get("/health", s.handleHealth)

		// Unprotected: these two ARE the login flow, so they can't require
		// a session yet.
		r.Get("/session/login", s.handleSessionLogin)
		r.Get("/session/callback", s.handleSessionCallback)

		r.Group(func(r chi.Router) {
			r.Use(auth.RequireSession(s.Session.Secret))
			r.Use(s.resolveUser)

			r.Get("/session/me", s.handleSessionMe)
			r.Post("/session/logout", s.handleSessionLogout)
			r.Route("/setup", func(r chi.Router) {
				r.Post("/complete", s.handleSetupComplete)
				r.Route("/garmin", func(r chi.Router) {
					r.Post("/login", s.handleSetupGarminLogin)
					r.Post("/mfa", s.handleSetupGarminMFA)
				})
			})

			r.Group(func(r chi.Router) {
				r.Use(requireProvisionedUser)

				r.Route("/profile", func(r chi.Router) {
					r.Get("/", s.handleGetProfile)
					r.Put("/", s.handleUpdateProfile)
					r.Delete("/", s.handleDeleteProfile)
				})

				r.Route("/auth", func(r chi.Router) {
					r.Post("/login", s.handleAuthLogin)
					r.Post("/mfa", s.handleAuthMFA)
					r.Get("/status", s.handleAuthStatus)
				})

				r.Route("/sync", func(r chi.Router) {
					r.Post("/run", s.handleSyncRun)
					r.Post("/reset", s.handleSyncReset)
					r.Get("/runs", s.handleSyncRuns)
					r.Get("/status", s.handleSyncStatus)
				})

				r.Route("/activities", func(r chi.Router) {
					r.Get("/", s.handleListActivities)
					r.Post("/{activityID}/assign", s.handleAssignActivity)
					r.Post("/{activityID}/unlock", s.handleUnlockActivity)
					r.Post("/{activityID}/unassign", s.handleUnassignActivity)
				})

				r.Route("/workout-kinds", func(r chi.Router) {
					r.Get("/", s.handleListWorkoutKinds)
					r.Get("/{id}", s.handleGetWorkoutKind)
					r.Put("/{id}", s.handleUpdateWorkoutKind)
				})

				r.Post("/reclassify", s.handleReclassifyAll)

				r.Get("/progression/{kindID}", s.handleProgression)
			})
		})
	})
	return r
}

// corsMiddleware allows the frontend dev server (a different port) to call
// this API. Reflecting any origin back is safe even with credentials
// enabled: this remains a single-operator app whose real access control is
// the OIDC login gate (internal/auth), not origin-based CSRF defense.
func corsMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if origin := r.Header.Get("Origin"); origin != "" {
			w.Header().Set("Access-Control-Allow-Origin", origin)
			w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS")
			w.Header().Set("Access-Control-Allow-Headers", "Content-Type")
			w.Header().Set("Access-Control-Allow-Credentials", "true")
		}
		if r.Method == http.MethodOptions {
			w.WriteHeader(http.StatusNoContent)
			return
		}
		next.ServeHTTP(w, r)
	})
}

func (s *Server) handleHealth(w http.ResponseWriter, r *http.Request) {
	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
}

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	if err := json.NewEncoder(w).Encode(v); err != nil {
		log.Printf("api: encode response: %v", err)
	}
}

func writeError(w http.ResponseWriter, status int, msg string) {
	writeJSON(w, status, map[string]string{"error": msg})
}

// backgroundSync runs fn in a goroutine with a fresh context, guarded so
// only one sync operation per userID runs at a time. Returns false if one
// is already in progress for that user.
func (s *Server) backgroundSync(userID int64, fn func(ctx context.Context) error) bool {
	s.mu.Lock()
	if s.userSyncRunning[userID] {
		s.mu.Unlock()
		return false
	}
	s.userSyncRunning[userID] = true
	s.mu.Unlock()

	go func() {
		defer func() {
			s.mu.Lock()
			s.userSyncRunning[userID] = false
			s.mu.Unlock()
		}()
		if err := fn(context.Background()); err != nil {
			log.Printf("api: background sync error (user %d): %v", userID, err)
		}
	}()
	return true
}