package api

import (
	"crypto/subtle"
	"encoding/json"
	"errors"
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/kami/hexis/internal/domain"
	"github.com/kami/hexis/internal/execution"
	"github.com/kami/hexis/internal/storage"
	"github.com/kami/hexis/internal/wire"
)

type Handler struct {
	store     storage.Interface
	engine    *execution.Engine
	authToken string
}

// NewHandler builds the HTTP handler. authToken is the shared bearer token
// required on every /api/v1/ request; if it is empty the API refuses all
// /api/v1/ traffic rather than serving it unauthenticated.
func NewHandler(store storage.Interface, engine *execution.Engine, authToken string) *Handler {
	return &Handler{store: store, engine: engine, authToken: authToken}
}

// SupportedAPIVersion is the version this server implements. A request
// carrying X-Hexis-Version set to anything else is rejected — clients that
// don't send the header at all are allowed through unversioned, to avoid
// breaking callers mid-rollout.
const SupportedAPIVersion = "v1"

func (h *Handler) Register(mux *http.ServeMux) {
	mux.HandleFunc("/health", h.health)
	mux.HandleFunc("/ready", h.ready)

	api := http.NewServeMux()
	api.HandleFunc("/api/v1/capabilities", h.handleCapabilities)
	api.HandleFunc("/api/v1/capabilities/", h.handleCapabilityByID)
	api.HandleFunc("/api/v1/execute", h.handleExecute)
	api.HandleFunc("/api/v1/confirmations", h.handleConfirmations)
	api.HandleFunc("/api/v1/executions", h.handleExecutions)
	api.HandleFunc("/api/v1/executions/", h.handleExecutionByID)
	api.HandleFunc("/api/v1/changes", h.handleChanges)

	mux.Handle("/api/v1/", h.requireAuth(versionCheck(api)))
}

// requireAuth enforces the shared bearer token on the whole /api/v1/ surface.
// /health and /ready stay open so probes keep working.
func (h *Handler) requireAuth(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if h.authToken == "" {
			// Fail closed: an unset token must never mean "no auth required".
			writeJSON(w, http.StatusServiceUnavailable, errorResponse("server misconfigured: HEXIS_API_TOKEN is not set"))
			return
		}
		presented, ok := bearerToken(r)
		if !ok || subtle.ConstantTimeCompare([]byte(presented), []byte(h.authToken)) != 1 {
			w.Header().Set("WWW-Authenticate", `Bearer realm="hexis"`)
			writeJSON(w, http.StatusUnauthorized, errorResponse("unauthorized"))
			return
		}
		next.ServeHTTP(w, r)
	})
}

func bearerToken(r *http.Request) (string, bool) {
	h := r.Header.Get("Authorization")
	if h == "" {
		return "", false
	}
	const prefix = "bearer "
	if len(h) <= len(prefix) || !strings.EqualFold(h[:len(prefix)], prefix) {
		return "", false
	}
	return strings.TrimSpace(h[len(prefix):]), true
}

func versionCheck(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if v := r.Header.Get("X-Hexis-Version"); v != "" && v != SupportedAPIVersion {
			writeJSON(w, http.StatusPreconditionFailed, map[string]string{
				"error":             "unsupported API version",
				"requested_version": v,
				"supported_version": SupportedAPIVersion,
			})
			return
		}
		next.ServeHTTP(w, r)
	})
}

func (h *Handler) health(w http.ResponseWriter, r *http.Request) {
	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
}

func (h *Handler) ready(w http.ResponseWriter, r *http.Request) {
	_, err := h.store.LatestSequence()
	if err != nil {
		writeJSON(w, http.StatusServiceUnavailable, map[string]string{"status": "not_ready"})
		return
	}
	writeJSON(w, http.StatusOK, map[string]string{"status": "ready"})
}

func (h *Handler) handleCapabilities(w http.ResponseWriter, r *http.Request) {
	switch r.Method {
	case http.MethodGet:
		h.listCapabilities(w, r)
	case http.MethodPost:
		h.createCapability(w, r)
	default:
		writeJSON(w, http.StatusMethodNotAllowed, errorResponse("method not allowed"))
	}
}

func (h *Handler) listCapabilities(w http.ResponseWriter, r *http.Request) {
	entityID := r.URL.Query().Get("entity_id")
	caps, err := h.store.ListCapabilities(entityID)
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, errorResponse(err.Error()))
		return
	}
	// wire.Capabilities is the single serializer shared with the MCP adapter
	// and pkg/client; it also carries the server-derived `enabled` and
	// `requires_confirmation` fields this endpoint previously omitted.
	writeJSON(w, http.StatusOK, wire.Capabilities(caps))
}

func (h *Handler) createCapability(w http.ResponseWriter, r *http.Request) {
	var req struct {
		Name                string         `json:"name"`
		Description         string         `json:"description,omitempty"`
		TargetTypes         []string       `json:"target_types"`
		TargetEntityID      string         `json:"target_entity_id,omitempty"`
		Provider            string         `json:"provider"`
		Operation           string         `json:"operation"`
		Risk                string         `json:"risk,omitempty"`
		ReadOnly            bool           `json:"read_only"`
		ExpectedSideEffects string         `json:"expected_side_effects,omitempty"`
		TimeoutSeconds      int            `json:"timeout_seconds,omitempty"`
		Attributes          map[string]any `json:"attributes,omitempty"`
	}
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeJSON(w, http.StatusBadRequest, errorResponse("invalid JSON"))
		return
	}
	if req.Name == "" || req.Provider == "" || req.Operation == "" {
		writeJSON(w, http.StatusBadRequest, errorResponse("name, provider, and operation are required"))
		return
	}

	// `enabled` and `requires_confirmation` are derived server-side from the
	// risk tier and are deliberately NOT settable from the request body — a
	// caller-supplied override would make the ECOSYSTEM-SPEC.md §4.3 guards
	// opt-out for the untrusted caller they exist to constrain.
	enabled := domain.EnabledForRisk(req.Risk)
	requiresConfirmation := domain.RequiresConfirmationForRisk(req.Risk)

	timeoutSeconds := req.TimeoutSeconds
	if timeoutSeconds <= 0 {
		timeoutSeconds = domain.DefaultCapabilityTimeoutSeconds
	}

	now := time.Now().UTC()
	cap := &domain.Capability{
		ID:                   domain.NewCapabilityID(),
		Name:                 req.Name,
		Description:          req.Description,
		TargetTypes:          req.TargetTypes,
		TargetEntityID:       req.TargetEntityID,
		Provider:             req.Provider,
		Operation:            req.Operation,
		Risk:                 req.Risk,
		ReadOnly:             req.ReadOnly,
		ExpectedSideEffects:  req.ExpectedSideEffects,
		RequiresConfirmation: requiresConfirmation,
		Enabled:              enabled,
		TimeoutSeconds:       timeoutSeconds,
		Attributes:           req.Attributes,
		CreatedAt:            now,
		UpdatedAt:            now,
		Version:              1,
	}
	if cap.TargetTypes == nil {
		cap.TargetTypes = []string{}
	}
	if cap.Attributes == nil {
		cap.Attributes = map[string]any{}
	}

	if err := h.store.CreateCapability(cap); err != nil {
		writeJSON(w, http.StatusInternalServerError, errorResponse(err.Error()))
		return
	}

	h.store.AppendEvent(&domain.Event{
		ID:        domain.NewEventID(),
		Type:      domain.EventCapabilityRegistered,
		Timestamp: now,
		Payload:   map[string]any{"capability_id": cap.ID, "name": cap.Name},
	})

	writeJSON(w, http.StatusCreated, cap)
}

func (h *Handler) handleCapabilityByID(w http.ResponseWriter, r *http.Request) {
	id := strings.TrimPrefix(r.URL.Path, "/api/v1/capabilities/")
	if id == "" {
		writeJSON(w, http.StatusBadRequest, errorResponse("id required"))
		return
	}

	switch r.Method {
	case http.MethodGet:
		h.getCapability(w, r, id)
	case http.MethodDelete:
		h.deleteCapability(w, r, id)
	default:
		writeJSON(w, http.StatusMethodNotAllowed, errorResponse("method not allowed"))
	}
}

func (h *Handler) getCapability(w http.ResponseWriter, r *http.Request, id string) {
	cap, err := h.store.GetCapability(id)
	if err != nil {
		writeJSON(w, http.StatusNotFound, errorResponse(err.Error()))
		return
	}
	writeJSON(w, http.StatusOK, cap)
}

func (h *Handler) deleteCapability(w http.ResponseWriter, r *http.Request, id string) {
	if err := h.store.DeleteCapability(id); err != nil {
		writeJSON(w, http.StatusNotFound, errorResponse(err.Error()))
		return
	}
	writeJSON(w, http.StatusOK, map[string]string{"status": "deleted"})
}

func (h *Handler) handleExecute(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		writeJSON(w, http.StatusMethodNotAllowed, errorResponse("method not allowed"))
		return
	}

	var req domain.ExecuteRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeJSON(w, http.StatusBadRequest, errorResponse("invalid JSON"))
		return
	}
	if req.CapabilityID == "" || req.TargetEntityID == "" {
		writeJSON(w, http.StatusBadRequest, errorResponse("capability_id and target_entity_id are required"))
		return
	}
	if req.CorrelationID == "" {
		req.CorrelationID = r.Header.Get("X-Correlation-ID")
	}
	if req.CausationID == "" {
		req.CausationID = r.Header.Get("X-Causation-ID")
	}

	result, err := h.engine.Execute(&req)
	if err != nil {
		writeJSON(w, executeErrorStatus(err), errorResponse(err.Error()))
		return
	}

	writeJSON(w, http.StatusOK, result.Execution)
}

func executeErrorStatus(err error) int {
	switch {
	case errors.Is(err, domain.ErrExecutionInFlight):
		return http.StatusConflict
	case errors.Is(err, domain.ErrCapabilityNotFound):
		return http.StatusNotFound
	case errors.Is(err, domain.ErrConfirmationRequired),
		errors.Is(err, domain.ErrConfirmationInvalid),
		errors.Is(err, domain.ErrConfirmationExpired),
		errors.Is(err, domain.ErrConfirmationConsumed),
		errors.Is(err, domain.ErrConfirmationNotFound),
		errors.Is(err, domain.ErrCapabilityDisabled),
		errors.Is(err, domain.ErrCapabilityNotBound):
		return http.StatusForbidden
	default:
		return http.StatusBadRequest
	}
}

func (h *Handler) handleConfirmations(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		writeJSON(w, http.StatusMethodNotAllowed, errorResponse("method not allowed"))
		return
	}

	var req struct {
		CapabilityID   string         `json:"capability_id"`
		TargetEntityID string         `json:"target_entity_id"`
		Arguments      map[string]any `json:"arguments,omitempty"`
		Requester      string         `json:"requester,omitempty"`
	}
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeJSON(w, http.StatusBadRequest, errorResponse("invalid JSON"))
		return
	}
	if req.CapabilityID == "" || req.TargetEntityID == "" {
		writeJSON(w, http.StatusBadRequest, errorResponse("capability_id and target_entity_id are required"))
		return
	}

	conf, err := h.engine.CreateConfirmation(req.CapabilityID, req.TargetEntityID, req.Requester, req.Arguments)
	if err != nil {
		status := http.StatusBadRequest
		if errors.Is(err, domain.ErrCapabilityNotFound) {
			status = http.StatusNotFound
		} else if errors.Is(err, domain.ErrCapabilityNotBound) {
			status = http.StatusForbidden
		}
		writeJSON(w, status, errorResponse(err.Error()))
		return
	}

	writeJSON(w, http.StatusCreated, conf)
}

func (h *Handler) handleExecutionByID(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		writeJSON(w, http.StatusMethodNotAllowed, errorResponse("method not allowed"))
		return
	}

	id := strings.TrimPrefix(r.URL.Path, "/api/v1/executions/")
	if id == "" {
		writeJSON(w, http.StatusBadRequest, errorResponse("id required"))
		return
	}

	exec, err := h.store.GetExecution(id)
	if err != nil {
		writeJSON(w, http.StatusNotFound, errorResponse(err.Error()))
		return
	}
	writeJSON(w, http.StatusOK, exec)
}

func (h *Handler) handleChanges(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		writeJSON(w, http.StatusMethodNotAllowed, errorResponse("method not allowed"))
		return
	}

	seqStr := r.URL.Query().Get("since")
	var since int64
	if seqStr != "" {
		parsed, err := strconv.ParseInt(seqStr, 10, 64)
		if err != nil {
			writeJSON(w, http.StatusBadRequest, errorResponse("since must be an integer sequence"))
			return
		}
		since = parsed
	}

	events, err := h.store.EventsAfter(since, 100)
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, errorResponse(err.Error()))
		return
	}
	if events == nil {
		events = []*domain.Event{}
	}
	writeJSON(w, http.StatusOK, events)
}

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	json.NewEncoder(w).Encode(v)
}

func errorResponse(msg string) map[string]string {
	return map[string]string{"error": msg}
}