package broker

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"os"
	"regexp"
	"strings"
	"time"
)

// The mesh runs the broker, so there is no chicken-and-egg in a node needing an account before it
// can connect: the account is created when the token is issued, and the one-time secret in that
// token IS the password. A node's first connection is already authenticated, and enrolment is
// what happens over it.
//
// novox/hq ADR 0004's *a node holds its own identity and nothing else* is why the account is per
// node rather than shared. A shared enrolment account would let any node consume another's queue,
// which is the shared-credential fault that record exists to remove, reappearing at the transport.

// ManagementVar holds the broker's management API, credentials included.
const ManagementVar = "MESH_BROKER_MANAGEMENT"

// safeName is what a node may be called at the broker.
//
// The name goes into a URL path and into permission patterns, which are regular expressions. A
// name carrying a `.` or a `*` would silently widen what that node may reach — so it is
// constrained here rather than escaped later, because an escape that is forgotten once is a node
// reading everybody's queues.
var safeName = regexp.MustCompile(`^[a-z0-9][a-z0-9-]{0,62}$`)

// Management is the broker's administrative interface.
type Management struct {
	base   *url.URL
	client *http.Client
}

// ManagementFromEnvironment reads where the management API is, if it is configured.
func ManagementFromEnvironment() (*Management, error) {
	raw := strings.TrimSpace(os.Getenv(ManagementVar))
	if raw == "" {
		return nil, ErrNotConfigured
	}
	base, err := url.Parse(raw)
	if err != nil || base.Host == "" {
		// The value carries a password, so it is not quoted back.
		return nil, fmt.Errorf("%s is not a usable URL", ManagementVar)
	}
	return &Management{base: base, client: &http.Client{Timeout: 15 * time.Second}}, nil
}

// QueueFor is the queue a node consumes from. One per node, named after it.
func QueueFor(node string) string { return "node." + node }

// ExchangeName is where nodes publish what they have to say. One exchange, and the control plane
// is the only consumer behind it (novox/hq ADR 0006 — one consumer, so two cannot silently split
// the traffic between them).
const ExchangeName = "mesh"

// BuildQueueName is where build work waits. Duplicated from `link` rather than imported, for the
// same reason QueueFor above is: this package must not depend on the one that uses it, and a
// constant that differed would be caught by the test that asserts they agree.
const BuildQueueName = "builds"

// CreateNodeAccount gives a node its own broker account, with the token's secret as the password.
//
// Scoped so a node can reach its own queue and the one exchange, and nothing else. The patterns
// are anchored: a node called `laptop` must not be able to read `laptop-of-somebody-else`.
func (m *Management) CreateNodeAccount(ctx context.Context, node, password string) error {
	if !safeName.MatchString(node) {
		return fmt.Errorf(
			"%q cannot be a broker account name: it becomes part of a permission pattern, so it "+
				"is lower-case letters, digits and dashes", node)
	}

	if err := m.put(ctx, "/api/users/"+url.PathEscape(node),
		map[string]string{"password": password, "tags": ""}); err != nil {
		return fmt.Errorf("cannot create the broker account for %s: %w", node, err)
	}

	queue := regexp.QuoteMeta(QueueFor(node))
	if err := m.put(ctx, "/api/permissions/%2f/"+url.PathEscape(node), map[string]string{
		"configure": "^" + queue + "$",
		"write":     "^(" + regexp.QuoteMeta(ExchangeName) + "|" + queue + ")$",
		"read":      "^" + queue + "$",
	}); err != nil {
		return fmt.Errorf("cannot scope the broker account for %s: %w", node, err)
	}
	return nil
}

// CreateBuilderAccount scopes an account to taking build work and answering it.
//
// **A build machine is not a node**, and giving it a node's account would let it read another
// machine's declarations. What it needs is narrower and different: read the build queue, and
// write to the exchange and to whatever temporary queue an asker is waiting on.
//
// The reply queues are the reason `write` is not simply the exchange. `RequestBuild` declares an
// exclusive queue with a generated name and waits on it, so a builder that could not write to it
// could take work and never answer — which is the failure that looks like a builder that is not
// running.
func (m *Management) CreateBuilderAccount(ctx context.Context, name, password string) error {
	if !safeName.MatchString(name) {
		return fmt.Errorf(
			"%q cannot be a broker account name: it becomes part of a permission pattern, so it "+
				"is lower-case letters, digits and dashes", name)
	}

	if err := m.put(ctx, "/api/users/"+url.PathEscape(name),
		map[string]string{"password": password, "tags": ""}); err != nil {
		return fmt.Errorf("cannot create the broker account for %s: %w", name, err)
	}

	builds := regexp.QuoteMeta(BuildQueueName)
	if err := m.put(ctx, "/api/permissions/%2f/"+url.PathEscape(name), map[string]string{
		// It declares the build queue, because whichever builder starts first must be able to —
		// and a queue nobody may declare is a queue that exists only if the control plane has
		// already run, which makes the order they start in matter.
		"configure": "^" + builds + "$",
		// The exchange, and nothing else. **Not the default exchange**: permission there is
		// granted per exchange rather than per queue, so a builder allowed to use it could
		// publish into any node's queue — the privilege a build machine most obviously should
		// not have. Answers go through the exchange, which is why they can.
		"write": "^" + regexp.QuoteMeta(ExchangeName) + "$",
		// The build queue and nothing else. Not another machine's declarations.
		"read": "^" + builds + "$",
	}); err != nil {
		return fmt.Errorf("cannot scope the broker account for %s: %w", name, err)
	}
	return nil
}

// RemoveNodeAccount withdraws a node's access.
func (m *Management) RemoveNodeAccount(ctx context.Context, node string) error {
	if !safeName.MatchString(node) {
		return fmt.Errorf("%q is not a broker account name", node)
	}
	return m.do(ctx, http.MethodDelete, "/api/users/"+url.PathEscape(node), nil)
}

// Accounts lists the broker's users, so a picture can be read from the system rather than assumed
// (novox/hq ADR 0018).
func (m *Management) Accounts(ctx context.Context) ([]string, error) {
	body, err := m.get(ctx, "/api/users")
	if err != nil {
		return nil, err
	}
	var users []struct {
		Name string `json:"name"`
	}
	if err := json.Unmarshal(body, &users); err != nil {
		return nil, err
	}
	names := make([]string, 0, len(users))
	for _, u := range users {
		names = append(names, u.Name)
	}
	return names, nil
}

func (m *Management) put(ctx context.Context, path string, body any) error {
	return m.do(ctx, http.MethodPut, path, body)
}

func (m *Management) get(ctx context.Context, path string) ([]byte, error) {
	request, err := m.request(ctx, http.MethodGet, path, nil)
	if err != nil {
		return nil, err
	}
	response, err := m.client.Do(request)
	if err != nil {
		return nil, err
	}
	defer response.Body.Close()
	if response.StatusCode >= 300 {
		return nil, fmt.Errorf("the broker's management API answered %s to GET %s",
			response.Status, path)
	}
	return io.ReadAll(io.LimitReader(response.Body, 1<<20))
}

func (m *Management) do(ctx context.Context, method, path string, body any) error {
	request, err := m.request(ctx, method, path, body)
	if err != nil {
		return err
	}
	response, err := m.client.Do(request)
	if err != nil {
		return err
	}
	defer response.Body.Close()
	if response.StatusCode >= 300 {
		detail, _ := io.ReadAll(io.LimitReader(response.Body, 4096))
		return fmt.Errorf("the broker's management API answered %s to %s %s: %s",
			response.Status, method, path, strings.TrimSpace(string(detail)))
	}
	return nil
}

func (m *Management) request(ctx context.Context, method, path string, body any) (*http.Request, error) {
	var payload io.Reader
	if body != nil {
		raw, err := json.Marshal(body)
		if err != nil {
			return nil, err
		}
		payload = bytes.NewReader(raw)
	}

	// Path joined by hand rather than through url.Parse: %2f is the default vhost and must reach
	// the broker still encoded. Parsing would decode it to a slash and address a different route.
	target := strings.TrimSuffix(m.base.String(), "/")
	if user := m.base.User; user != nil {
		target = strings.TrimSuffix(m.base.Scheme+"://"+m.base.Host, "/")
	}
	request, err := http.NewRequestWithContext(ctx, method, target+path, payload)
	if err != nil {
		return nil, err
	}
	if user := m.base.User; user != nil {
		password, _ := user.Password()
		request.SetBasicAuth(user.Username(), password)
	}
	if body != nil {
		request.Header.Set("Content-Type", "application/json")
	}
	return request, nil
}