// Package dex creates Dex local-password accounts by writing
// passwords.dex.coreos.com custom resources directly against the in-cluster
// Kubernetes API. This is the write side of the invite flow: a recipient sets a
// password on /invite/{token}, Tapir bcrypt-hashes it and POSTs a Password CR into
// the auth namespace, and Dex (configured with kubernetes storage) then serves
// local-password login for that email.
//
// Why the raw API and not kubectl/client-go: the deployed pod already carries a
// service-account token and the cluster CA at the well-known mount paths, so a
// single net/http POST needs no extra dependency and no shelling out. Standalone /
// dev has no such mount — NewPasswordClient returns ErrNotInCluster and the web
// handler degrades gracefully (account creation only works in the deployed env).
package dex

import (
	"bytes"
	"context"
	"crypto/tls"
	"crypto/x509"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"os"
	"strings"
	"time"
)

// Sentinel errors let the web handler turn API outcomes into clear user messages.
var (
	// ErrNotInCluster means the service-account token mount is absent, so there is
	// no in-cluster API to talk to (local dev / tests). Construction-time only.
	ErrNotInCluster = errors.New("dex: not running in-cluster (no service-account token)")
	// ErrPasswordExists maps the API's 409 Conflict — a Password CR for this email
	// already exists. The handler treats it as a benign "log in instead".
	ErrPasswordExists = errors.New("dex: password already exists")
	// ErrForbidden maps 401/403 — the tapir ServiceAccount lacks create/get on
	// passwords.dex.coreos.com in the auth namespace (RBAC not applied).
	ErrForbidden = errors.New("dex: forbidden — missing RBAC for passwords.dex.coreos.com")
)

// Well-known in-cluster service-account mount paths (projected by kubelet).
const (
	saTokenPath = "/var/run/secrets/kubernetes.io/serviceaccount/token" //nolint:gosec // path, not a secret
	saCAPath    = "/var/run/secrets/kubernetes.io/serviceaccount/ca.crt"
	// apiServer is the in-cluster API endpoint; its TLS is validated against the
	// mounted cluster CA.
	apiServer = "https://kubernetes.default.svc"
	// passwordsPath is the Dex Password collection in the auth namespace.
	passwordsPath = "/apis/dex.coreos.com/v1/namespaces/auth/passwords"
)

// PasswordClient writes Dex Password CRs against the in-cluster API. Construct it
// with NewPasswordClient; the zero value is not usable.
type PasswordClient struct {
	server string
	token  string
	http   *http.Client
}

// NewPasswordClient reads the service-account token and cluster CA from the
// well-known mount paths and returns a client that authenticates as the pod's
// ServiceAccount. It returns ErrNotInCluster when the token mount is absent (dev /
// tests / standalone), so callers can detect "no Dex available" and degrade.
func NewPasswordClient() (*PasswordClient, error) {
	token, err := os.ReadFile(saTokenPath)
	if errors.Is(err, os.ErrNotExist) {
		return nil, ErrNotInCluster
	}
	if err != nil {
		return nil, fmt.Errorf("dex: read service-account token: %w", err)
	}

	caPEM, err := os.ReadFile(saCAPath)
	if err != nil {
		return nil, fmt.Errorf("dex: read cluster CA: %w", err)
	}
	pool := x509.NewCertPool()
	if !pool.AppendCertsFromPEM(caPEM) {
		return nil, errors.New("dex: cluster CA is not valid PEM")
	}

	hc := &http.Client{
		Timeout: 10 * time.Second,
		Transport: &http.Transport{
			TLSClientConfig: &tls.Config{RootCAs: pool, MinVersion: tls.VersionTLS12},
		},
	}
	return newClient(apiServer, strings.TrimSpace(string(token)), hc), nil
}

// newClient is the injectable constructor shared by NewPasswordClient and tests
// (which point server at an httptest.Server and pass its TLS client).
func newClient(server, token string, hc *http.Client) *PasswordClient {
	return &PasswordClient{server: server, token: token, http: hc}
}

// password is the wire form of a Dex Password CR. The hash field is a plain
// bcrypt string (e.g. "$2a$12$..."). Dex v2.41+ stores and compares it as-is —
// it does NOT base64-decode the field. Earlier code base64-encoded the hash
// based on a misread of Dex's internal []byte type; that caused every dynamic
// invite login to fail with "Invalid credentials" while static passwords (set as
// plain strings in the configmap) worked fine.
type password struct {
	APIVersion string            `json:"apiVersion"`
	Kind       string            `json:"kind"`
	Metadata   map[string]string `json:"metadata"`
	Email      string            `json:"email"`
	Hash       string            `json:"hash"`
	Username   string            `json:"username"`
	UserID     string            `json:"userID"`
}

// CreatePassword creates a Dex local-password account for email with the given
// bcrypt hash and Dex user id. The CR name is derived from the email so it is a
// valid, stable, idempotent Kubernetes object name. Returns ErrPasswordExists on
// 409 (the account already exists) and ErrForbidden on 401/403 (RBAC missing).
func (c *PasswordClient) CreatePassword(ctx context.Context, email, bcryptHash, userID string) error {
	body, err := json.Marshal(password{
		APIVersion: "dex.coreos.com/v1",
		Kind:       "Password",
		Metadata:   map[string]string{"name": passwordName(email), "namespace": "auth"},
		Email:      email,
		Hash:       bcryptHash, // raw bcrypt string — Dex compares it directly
		Username:   email,
		UserID:     userID,
	})
	if err != nil {
		return fmt.Errorf("dex: marshal password: %w", err)
	}

	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.server+passwordsPath, bytes.NewReader(body))
	if err != nil {
		return fmt.Errorf("dex: build request: %w", err)
	}
	req.Header.Set("Authorization", "Bearer "+c.token)
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Accept", "application/json")

	resp, err := c.http.Do(req)
	if err != nil {
		return fmt.Errorf("dex: create password: %w", err)
	}
	defer func() { _ = resp.Body.Close() }()

	switch resp.StatusCode {
	case http.StatusCreated, http.StatusOK:
		return nil
	case http.StatusConflict:
		return ErrPasswordExists
	case http.StatusUnauthorized, http.StatusForbidden:
		return ErrForbidden
	default:
		snippet, _ := io.ReadAll(io.LimitReader(resp.Body, 512))
		return fmt.Errorf("dex: create password: unexpected status %d: %s", resp.StatusCode, strings.TrimSpace(string(snippet)))
	}
}

// passwordName maps an email to the Kubernetes object name Dex uses internally
// when looking up a Password CR by email (Dex storage/kubernetes passwordID()).
// Dex maps every character that is not [a-z0-9-] to '-' — it does NOT use
// human-readable substitutions like '-at-' or '-dot-'. Using a different scheme
// creates a name mismatch: Tapir writes the CR under one name, Dex looks it up
// under another, and every login returns "Invalid credentials".
func passwordName(email string) string {
	n := strings.ToLower(strings.TrimSpace(email))
	var b strings.Builder
	for _, r := range n {
		if (r >= 'a' && r <= 'z') || (r >= '0' && r <= '9') || r == '-' {
			b.WriteRune(r)
		} else {
			b.WriteRune('-')
		}
	}
	result := strings.Trim(b.String(), "-")
	if result == "" {
		return "user"
	}
	return result
}