hexis/internal/api/handler.go

package api

import (
	"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"
)

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

func NewHandler(store storage.Interface, engine *execution.Engine) *Handler {
	return &Handler{store: store, engine: engine}
}

// 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.handleExecutionByID)
	api.HandleFunc("/api/v1/changes", h.handleChanges)

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

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
	}
	if caps == nil {
		caps = []*domain.Capability{}
	}

	var apiCaps []map[string]any
	for _, c := range caps {
		apiCaps = append(apiCaps, map[string]any{
			"capability_id":         c.ID,
			"id":                    c.ID,
			"name":                  c.Name,
			"description":           c.Description,
			"target_types":          c.TargetTypes,
			"target_entity_id":      c.TargetEntityID,
			"provider":              c.Provider,
			"operation":             c.Operation,
			"risk":                  c.Risk,
			"read_only":             c.ReadOnly,
			"expected_side_effects": c.ExpectedSideEffects,
		})
	}

	writeJSON(w, http.StatusOK, apiCaps)
}

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"`
		RequiresConfirmation bool           `json:"requires_confirmation,omitempty"`
		Enabled              *bool          `json:"enabled,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
	}

	// Destructive capabilities are disabled by default and must be turned on
	// explicitly (ECOSYSTEM-SPEC.md §4.3).
	enabled := req.Risk != "destructive"
	if req.Enabled != nil {
		enabled = *req.Enabled
	}

	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: req.RequiresConfirmation,
		Enabled:              enabled,
		TimeoutSeconds:       req.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}
}