package alertapi

import (
	"encoding/json"
	"errors"
	"io"
	"net/http"
	"strconv"
	"strings"

	"github.com/itworx/pulse/internal/alert"
	"github.com/itworx/pulse/internal/audit"
	"github.com/itworx/pulse/internal/auth"
	"github.com/itworx/pulse/internal/correlation"
	"github.com/itworx/pulse/internal/metriccatalog"
	"github.com/itworx/pulse/internal/problem"
)

type Handler struct {
	Repository alert.Store
	Registry   metriccatalog.Registry
	Audit      audit.Store
}

func (h Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	principal, ok := auth.PrincipalFromContext(r.Context())
	if !ok {
		fail(w, r, http.StatusUnauthorized, "UNAUTHORIZED", "Authentication required.")
		return
	}
	path := strings.TrimPrefix(r.URL.Path, "/api/v1/alert-rules")
	if path == "" || path == "/" {
		switch r.Method {
		case http.MethodGet:
			h.list(w, r)
		case http.MethodPost:
			if !requireEdit(w, r, principal.Role) {
				return
			}
			h.create(w, r, principal.Subject)
		default:
			fail(w, r, http.StatusMethodNotAllowed, "METHOD_NOT_ALLOWED", "This method is not supported.")
		}
		return
	}
	parts := strings.Split(strings.Trim(path, "/"), "/")
	if len(parts) < 1 || parts[0] == "" || len(parts) > 2 {
		fail(w, r, http.StatusNotFound, "NOT_FOUND", "Alert rule route not found.")
		return
	}
	id := parts[0]
	if len(parts) == 1 && r.Method == http.MethodGet {
		h.get(w, r, id)
		return
	}
	if len(parts) == 2 && parts[1] == "versions" && r.Method == http.MethodGet {
		h.versions(w, r, id)
		return
	}
	if len(parts) == 2 && parts[1] == "test" && r.Method == http.MethodPost {
		if !requireEdit(w, r, principal.Role) {
			return
		}
		h.test(w, r, id)
		return
	}
	if len(parts) == 2 && (parts[1] == "enable" || parts[1] == "disable") && r.Method == http.MethodPost {
		if !requireEdit(w, r, principal.Role) {
			return
		}
		h.setEnabled(w, r, id, principal.Subject, parts[1] == "enable")
		return
	}
	if len(parts) == 1 && r.Method == http.MethodPut {
		if !requireEdit(w, r, principal.Role) {
			return
		}
		h.update(w, r, id, principal.Subject)
		return
	}
	fail(w, r, http.StatusNotFound, "NOT_FOUND", "Alert rule route not found.")
}

func (h Handler) list(w http.ResponseWriter, r *http.Request) {
	limit := 100
	if value := r.URL.Query().Get("limit"); value != "" {
		parsed, err := strconv.Atoi(value)
		if err != nil || parsed < 1 || parsed > 100 {
			fail(w, r, http.StatusBadRequest, "INVALID_LIMIT", "The alert-rule limit must be between 1 and 100.")
			return
		}
		limit = parsed
	}
	items, err := h.Repository.List(r.Context(), limit)
	if err != nil {
		h.repositoryFailure(w, r, err, "Alert rules are unavailable.")
		return
	}
	write(w, http.StatusOK, map[string]any{"items": items})
}

func (h Handler) get(w http.ResponseWriter, r *http.Request, id string) {
	item, err := h.Repository.Get(r.Context(), id)
	if err != nil {
		h.repositoryFailure(w, r, err, "Alert rule not found.")
		return
	}
	write(w, http.StatusOK, map[string]any{"rule": item})
}

func (h Handler) versions(w http.ResponseWriter, r *http.Request, id string) {
	limit := 100
	if value := r.URL.Query().Get("limit"); value != "" {
		parsed, err := strconv.Atoi(value)
		if err != nil || parsed < 1 || parsed > 100 {
			fail(w, r, http.StatusBadRequest, "INVALID_LIMIT", "The version limit must be between 1 and 100.")
			return
		}
		limit = parsed
	}
	items, err := h.Repository.Versions(r.Context(), id, limit)
	if err != nil {
		h.repositoryFailure(w, r, err, "Alert-rule versions are unavailable.")
		return
	}
	write(w, http.StatusOK, map[string]any{"items": items})
}

func (h Handler) create(w http.ResponseWriter, r *http.Request, actor string) {
	var document alert.Document
	if err := decode(r, &document); err != nil {
		fail(w, r, http.StatusBadRequest, "INVALID_RULE", "The alert-rule document is invalid.")
		return
	}
	if document.ID == "" {
		document.ID = alert.NewID()
	}
	rule, version, err := h.Repository.Create(r.Context(), actor, document, "initial version")
	if err != nil {
		h.repositoryFailure(w, r, err, "Alert rule could not be created.")
		return
	}
	if err := h.record(r, actor, "alert_rule.create", rule.ID, nil, map[string]any{"revision": rule.Revision, "version": version.VersionNumber}); err != nil {
		fail(w, r, http.StatusServiceUnavailable, "AUDIT_UNAVAILABLE", "The audit event could not be recorded.")
		return
	}
	write(w, http.StatusCreated, map[string]any{"rule": rule, "version": version})
}

func (h Handler) update(w http.ResponseWriter, r *http.Request, id, actor string) {
	expected, err := revision(r)
	if err != nil {
		fail(w, r, http.StatusBadRequest, "INVALID_REVISION", "A valid If-Match or revision value is required.")
		return
	}
	var document alert.Document
	if err := decode(r, &document); err != nil {
		fail(w, r, http.StatusBadRequest, "INVALID_RULE", "The alert-rule document is invalid.")
		return
	}
	updated, err := h.Repository.Update(r.Context(), id, actor, expected, document, "rule update")
	if err != nil {
		h.repositoryFailure(w, r, err, "Alert rule update failed.")
		return
	}
	if err := h.record(r, actor, "alert_rule.update", id, map[string]any{"revision": expected}, map[string]any{"revision": updated.Revision, "version": updated.CurrentVersion}); err != nil {
		fail(w, r, http.StatusServiceUnavailable, "AUDIT_UNAVAILABLE", "The audit event could not be recorded.")
		return
	}
	write(w, http.StatusOK, map[string]any{"rule": updated})
}

func (h Handler) setEnabled(w http.ResponseWriter, r *http.Request, id, actor string, enabled bool) {
	expected, err := revision(r)
	if err != nil {
		fail(w, r, http.StatusBadRequest, "INVALID_REVISION", "A valid If-Match or revision value is required.")
		return
	}
	updated, err := h.Repository.SetEnabled(r.Context(), id, expected, enabled)
	if err != nil {
		h.repositoryFailure(w, r, err, "Alert rule state update failed.")
		return
	}
	action := "alert_rule.disable"
	if enabled {
		action = "alert_rule.enable"
	}
	if err := h.record(r, actor, action, id, map[string]any{"enabled": !enabled, "revision": expected}, map[string]any{"enabled": enabled, "revision": updated.Revision}); err != nil {
		fail(w, r, http.StatusServiceUnavailable, "AUDIT_UNAVAILABLE", "The audit event could not be recorded.")
		return
	}
	write(w, http.StatusOK, map[string]any{"rule": updated})
}

func (h Handler) test(w http.ResponseWriter, r *http.Request, id string) {
	var request struct {
		Rule    *alert.Document `json:"rule"`
		Value   any             `json:"value"`
		Unknown bool            `json:"unknown"`
	}
	if err := decode(r, &request); err != nil {
		fail(w, r, http.StatusBadRequest, "INVALID_PREVIEW", "The alert-rule preview request is invalid.")
		return
	}
	document := request.Rule
	if document == nil {
		current, err := h.Repository.Get(r.Context(), id)
		if err != nil {
			h.repositoryFailure(w, r, err, "Alert rule preview is unavailable.")
			return
		}
		document = &current.Document
	}
	result, err := alert.Preview(*document, alert.PreviewRequest{Value: request.Value, Unknown: request.Unknown}, h.Registry)
	if err != nil {
		h.repositoryFailure(w, r, err, "The alert-rule preview is invalid.")
		return
	}
	write(w, http.StatusOK, map[string]any{"preview": result})
}

func (h Handler) record(r *http.Request, actor, action, resourceID string, before, after map[string]any) error {
	if h.Audit == nil {
		return nil
	}
	return h.Audit.Append(r.Context(), audit.Event{Actor: actor, Action: action, ResourceType: "alert_rule", ResourceID: resourceID, Result: "success", CorrelationID: correlation.FromContext(r.Context()), Before: before, After: after})
}

func (h Handler) repositoryFailure(w http.ResponseWriter, r *http.Request, err error, fallback string) {
	switch {
	case errors.Is(err, alert.ErrInvalidRule):
		fail(w, r, http.StatusBadRequest, "INVALID_RULE", fallback)
	case errors.Is(err, alert.ErrConflict):
		fail(w, r, http.StatusConflict, "REVISION_CONFLICT", "The alert rule was changed by another request.")
	case errors.Is(err, alert.ErrNotFound):
		fail(w, r, http.StatusNotFound, "NOT_FOUND", fallback)
	case errors.Is(err, alert.ErrUnavailable):
		fail(w, r, http.StatusServiceUnavailable, "DATABASE_UNAVAILABLE", fallback)
	default:
		fail(w, r, http.StatusInternalServerError, "ALERT_RULE_REQUEST_FAILED", fallback)
	}
}

func requireEdit(w http.ResponseWriter, r *http.Request, role auth.Role) bool {
	if auth.Allows(role, auth.PermissionEdit) {
		return true
	}
	fail(w, r, http.StatusForbidden, "FORBIDDEN", "Alert-rule editing is not allowed for this role.")
	return false
}

func decode(r *http.Request, target any) error {
	contentType := strings.ToLower(strings.TrimSpace(strings.Split(r.Header.Get("Content-Type"), ";")[0]))
	if contentType != "" && contentType != "application/json" {
		return errors.New("unsupported content type")
	}
	body, err := io.ReadAll(io.LimitReader(r.Body, 2<<20+1))
	if err != nil {
		return err
	}
	defer r.Body.Close()
	if len(body) > 2<<20 {
		return errors.New("request too large")
	}
	decoder := json.NewDecoder(strings.NewReader(string(body)))
	decoder.DisallowUnknownFields()
	if err := decoder.Decode(target); err != nil {
		return err
	}
	var extra any
	if err := decoder.Decode(&extra); err != io.EOF {
		return errors.New("multiple JSON values")
	}
	return nil
}

func revision(r *http.Request) (int64, error) {
	value := r.Header.Get("If-Match")
	if value == "" {
		value = r.URL.Query().Get("revision")
	}
	return strconv.ParseInt(strings.Trim(value, "\""), 10, 64)
}

func fail(w http.ResponseWriter, r *http.Request, status int, code, detail string) {
	problem.Write(w, r, status, code, http.StatusText(status), detail, nil)
}

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