// Package setup implements SPEC-005: the `/setup` wizard that brings a fresh
// instance to life. The gate is the **config toggle `setup`** (D-045):
//
//   - `setup: true`  → `/setup` serves the wizard at the public domain;
//   - `setup: false` + no admin → the instance is LOCKED: `GET /` and
//     `GET /setup` render a boilerplate telling the operator to enable setup,
//     and every other route is 404 (this state is not publicly claimable);
//   - completion → the wizard writes `setup: false` and creates the admin.
//
// The setup CODE (`setup_code`) is an OPTIONAL second factor (D-044 · D-045):
// when set, `GET /setup` first shows the code form and `POST /setup?do=setup&
// action=unlock` with the correct code grants the unlock (a signed cookie, not
// a session — no user exists yet); when empty, the toggle alone admits.
//
// The wizard walks three steps — (1) the domain / base URL, (2) the top admin
// with TOTP enrollment, (3) mail · locale · timezone — and finishes by
// persisting the settings to `config.yaml` with `setup: false` (D-035) and
// signalling completion (`Actions.Done`), after which `/setup` 404s (delete,
// don't redirect).
//
// Step 2 enrolls TOTP ONLY (D-041): a passkey registered over plain-HTTP
// loopback binds RP ID 127.0.0.1 and is unusable at the public domain. The
// admin adds a passkey at first login on the real origin, via the passkey
// nudge (SPEC-006 §8). It reuses SPEC-006's TOTP ceremony (flow.Actions) —
// no duplication.
//
// The wizard holds no routing of its own — the door (SPEC-003/005) gates it to
// setup mode and verifies the pre-session CSRF token (A15) before invoking any
// action here.
//
// Spec: docs/specs/spec-005-setup-wizard.md.
package setup

import (
	"context"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"net/http"
	"net/url"
	"os"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"

	"git.lohmar.co.uk/cclohmar/NextMyDay/internal/core/audit"
	"git.lohmar.co.uk/cclohmar/NextMyDay/internal/core/auth"
	"git.lohmar.co.uk/cclohmar/NextMyDay/internal/core/config"
	"git.lohmar.co.uk/cclohmar/NextMyDay/internal/core/httpx"
	"git.lohmar.co.uk/cclohmar/NextMyDay/internal/core/users"
)

// adminUserID is the top admin — the first user (D-013, D-021).
const adminUserID int64 = 1

// Users is the narrow slice of the user service the wizard needs.
type Users interface {
	// Count reports how many users exist — the fail-safe setup-mode check
	// (SPEC-005 §3) and the "is the admin already created?" question.
	Count(ctx context.Context) (int, error)
	// Create creates the top admin via the bootstrap path (creatorID == 0).
	Create(ctx context.Context, creatorID int64, email, displayName string, role users.Role) (users.UserID, error)
	// Get loads a user.
	Get(ctx context.Context, id int64) (users.User, error)
}

// Enroller is the SPEC-006 TOTP ceremony, reused so the wizard never
// duplicates the work (SPEC-005 §4). Step 2 enrolls TOTP only (D-041) — the
// wizard never calls the WebAuthn registration actions.
//
// The seam carries no JSON-writing method: the wizard is server-rendered and
// no-JS, so it renders the issued secret and the verify form itself rather than
// delegating to the enroll flow's JSON API (`webauthn.js`'s contract) — the
// exact coupling that stalled the wizard's TOTP step (SPEC-005 §11).
type Enroller interface {
	// IssueTOTP issues (and persists) the TOTP secret and returns the otpauth
	// URL, writing NO response — the caller owns the reply.
	IssueTOTP(ctx context.Context, guid string) (string, error)
	// TOTPVerify verifies a code: it completes the admin's enrollment (the
	// wizard's TOTP-only mode, D-041) and mints the session.
	TOTPVerify(w http.ResponseWriter, r *http.Request, guid string) error
}

// Deps assembles the wizard's dependencies.
type Deps struct {
	// Config is the startup configuration; the wizard persists a copy of it
	// (with `setup: false` and the new settings) to ConfigPath.
	Config *config.Config
	// ConfigPath is where the settings are persisted to (usually config.yaml,
	// never the committed example).
	ConfigPath string
	// Code is the OPTIONAL setup code (D-044 · D-045). When blank the toggle
	// alone admits and the wizard is served directly; when set, the wizard
	// requires it (a second factor). The startup banner prints it only when set
	// (`Actions.Code`).
	Code string
	// Users creates and inspects the top admin.
	Users Users
	// Identities mints and resolves the admin's identity.
	Identities auth.Identities
	// Enroll is the SPEC-006 ceremony (flow.Actions).
	Enroll Enroller
	// Audit receives the bootstrap events (A11).
	Audit audit.Audit
	// CSRF issues and verifies the anonymous double-submit token (A15).
	CSRF *httpx.PreSessionCSRF
	// Logger receives structured logs. Defaults to slog.Default().
	Logger *slog.Logger
	// Printout receives the rendered config when the file is not writable.
	// Defaults to os.Stdout.
	Printout io.Writer
	// WriteFile writes the config file (tests inject a failing writer to
	// exercise the "print the values" path). Defaults to os.WriteFile 0600.
	WriteFile func(path string, data []byte) error
}

// Actions is the /setup wizard.
type Actions struct {
	d     Deps
	gate  *Gate
	mu    sync.Mutex
	draft draft
	// done signals that the bootstrap is complete. The live config is treated
	// as an immutable startup snapshot (D-035: the FILE is the source of
	// truth), so completion is a concurrency-safe flag here rather than a
	// mutation of config.Setup — the door reads it on every request.
	done atomic.Bool
}

// Done reports whether the wizard has completed — the door's "setup is over"
// signal (SPEC-005 §5). It is safe for concurrent use.
func (a *Actions) Done() bool { return a.done.Load() }

// draft is the small amount of wizard state that is not yet in the database or
// the config: the base URL captured in step 1 (empty = step 1 unanswered).
type draft struct {
	domain string
}

// New validates and builds the wizard.
func New(d Deps) (*Actions, error) {
	switch {
	case d.Config == nil:
		return nil, errors.New("setup: Config is required")
	case d.Users == nil:
		return nil, errors.New("setup: Users is required")
	case d.Identities == nil:
		return nil, errors.New("setup: Identities is required")
	case d.Enroll == nil:
		return nil, errors.New("setup: Enroll is required")
	case d.CSRF == nil:
		return nil, errors.New("setup: CSRF is required")
	}
	if strings.TrimSpace(d.ConfigPath) == "" {
		return nil, errors.New("setup: ConfigPath is required")
	}
	if d.Logger == nil {
		d.Logger = slog.Default()
	}
	if d.Printout == nil {
		d.Printout = os.Stdout
	}
	if d.WriteFile == nil {
		d.WriteFile = writeFile0600
	}
	// D-044: the first-run gate — the OPTIONAL setup code + the signed unlock
	// cookie. A blank code means no code is required (D-045).
	gate, err := NewGate(d.Code, d.CSRF, d.Logger)
	if err != nil {
		return nil, err
	}
	return &Actions{d: d, gate: gate}, nil
}

// Code returns the setup code to print in the startup banner, or "" when no
// code is required (D-045) — there is nothing to print in that case.
func (a *Actions) Code() string { return a.gate.Code() }

// CodeRequired reports whether the wizard requires a code (D-045: `setup_code`
// is set). The startup banner prints the code only when it does.
func (a *Actions) CodeRequired() bool { return a.gate.Required() }

// Gate exposes the first-run gate so the door can ask whether a request is
// unlocked and render the first-run pages (D-044/D-045). The wizard itself
// never parses a path — the door decides.
func (a *Actions) Gate() *Gate { return a.gate }

// ── the first-run gate (D-044) ──────────────────────────────────────────────

// Unlock is the D-044 code gate: `POST /setup?do=setup&action=unlock` carrying
// the setup code. The door has already verified the pre-session CSRF token
// (A15) and rate-limited the request (A3); here we check the code, grant the
// unlock for this browser, and send the operator on to the wizard
// (post/redirect/get).
//
// When no code is required (D-045) the action is a no-op that simply lands on
// the wizard. A wrong or absent code gets a GENERIC answer — the same page and
// message either way, so the form is no oracle — and is audited (no code value
// logged).
func (a *Actions) Unlock(w http.ResponseWriter, r *http.Request) error {
	if a.done.Load() {
		writeError(w, http.StatusNotFound, "not found")
		return nil
	}
	if !a.gate.Required() {
		redirect(w, r, "/setup")
		return nil
	}
	if !a.gate.Accept(r.FormValue("code")) {
		a.recordSetup(r.Context(), "setup.unlock", "refused")
		return a.gate.codeFormError(w, r)
	}
	a.gate.SetUnlockCookie(w, r)
	a.recordSetup(r.Context(), "setup.unlock", "unlocked")
	redirect(w, r, "/setup")
	return nil
}

// ── the wizard page ─────────────────────────────────────────────────────────

// Page renders the wizard at its current step (GET /setup).
func (a *Actions) Page(w http.ResponseWriter, r *http.Request) error {
	st, err := a.step(r.Context())
	if err != nil {
		return err
	}
	token, err := a.d.CSRF.Ensure(w, r)
	if err != nil {
		return err
	}
	return renderHTML(w, http.StatusOK, wizardPage(st, token, a.draftDomain()))
}

// ── step 1 · the domain ─────────────────────────────────────────────────────

// DomainSave records the base URL (step 1) and advances to step 2.
func (a *Actions) DomainSave(w http.ResponseWriter, r *http.Request) error {
	if a.done.Load() {
		writeError(w, http.StatusNotFound, "not found")
		return nil
	}
	base := strings.TrimSpace(r.FormValue("base_url"))
	if base == "" {
		writeError(w, http.StatusBadRequest, "a base URL is required")
		return nil
	}
	if u, err := url.Parse(base); err != nil || u.Scheme == "" || u.Host == "" {
		writeError(w, http.StatusBadRequest, "invalid base URL")
		return nil
	}
	a.mu.Lock()
	a.draft.domain = base
	a.mu.Unlock()
	redirect(w, r, "/setup")
	return nil
}

// ── step 2 · the top admin ──────────────────────────────────────────────────

// AdminCreate creates `user_id = 1` (role admin) and mints its identity. Only
// one admin may ever exist (SPEC-004 AC-6) — a second attempt is refused.
func (a *Actions) AdminCreate(w http.ResponseWriter, r *http.Request) error {
	ctx := r.Context()
	if a.done.Load() {
		writeError(w, http.StatusNotFound, "not found")
		return nil
	}
	n, err := a.d.Users.Count(ctx)
	if err != nil {
		return err
	}
	if n > 0 {
		// The admin may already exist. Refuse a SECOND admin (AC-5), but repair
		// a first one left without an identity (a crash after Create, before
		// Mint) — otherwise the wizard could never be resumed.
		repaired, err := a.ensureAdminIdentity(ctx)
		if err != nil {
			return err
		}
		if !repaired {
			writeError(w, http.StatusConflict, "an admin already exists")
			return nil
		}
		redirect(w, r, "/setup")
		return nil
	}

	name := strings.TrimSpace(r.FormValue("display_name"))
	email := strings.TrimSpace(r.FormValue("email"))
	if name == "" || email == "" {
		writeError(w, http.StatusBadRequest, "a display name and an email are required")
		return nil
	}

	userID, err := a.d.Users.Create(ctx, 0, email, name, users.RoleAdmin)
	if err != nil {
		switch {
		case errors.Is(err, users.ErrBootstrapClosed), errors.Is(err, users.ErrOneAdmin),
			errors.Is(err, users.ErrDuplicateEmail):
			writeError(w, http.StatusConflict, "cannot create the admin")
		case errors.Is(err, users.ErrEmailRequired), errors.Is(err, users.ErrNameRequired),
			errors.Is(err, users.ErrInvalidRole), errors.Is(err, users.ErrBootstrapAdmin):
			writeError(w, http.StatusBadRequest, "bad request")
		default:
			return err
		}
		return nil
	}
	if _, _, err := a.d.Identities.Mint(ctx, userID); err != nil {
		return err
	}
	a.record(ctx, "setup.admin", fmt.Sprintf("user:%d", userID))
	redirect(w, r, "/setup")
	return nil
}

// ensureAdminIdentity mints the top admin's identity when the user exists but
// has none (a crash between Create and Mint). It reports repaired=false when an
// identity already exists — the caller then refuses a second admin (AC-5).
func (a *Actions) ensureAdminIdentity(ctx context.Context) (repaired bool, err error) {
	if _, err := a.d.Identities.ByUserID(ctx, adminUserID); err == nil {
		return false, nil
	} else if !errors.Is(err, auth.ErrIdentityNotFound) {
		return false, err
	}
	u, err := a.d.Users.Get(ctx, adminUserID)
	if err != nil {
		return false, err
	}
	if u.Role != users.RoleAdmin {
		return false, nil
	}
	if _, _, err := a.d.Identities.Mint(ctx, adminUserID); err != nil {
		return false, err
	}
	a.record(ctx, "setup.admin", fmt.Sprintf("user:%d", adminUserID))
	return true, nil
}

// TOTPBegin issues the admin's TOTP secret and renders the wizard's TOTP page:
// the otpauth URL with its human-readable secret and the verify form (SPEC-005
// §4). The wizard is server-rendered and works with no JavaScript, so it does
// NOT answer with the enroll flow's JSON (`webauthn.js`'s contract) — it issues
// the secret through the write-free IssueTOTP seam and renders the page itself.
func (a *Actions) TOTPBegin(w http.ResponseWriter, r *http.Request) error {
	ctx := r.Context()
	guid, ok, err := a.pendingGUID(ctx)
	if err != nil {
		return err
	}
	if !ok {
		writeError(w, http.StatusConflict, "no admin is awaiting enrollment")
		return nil
	}
	url, err := a.d.Enroll.IssueTOTP(ctx, guid)
	if err != nil {
		return err
	}
	token, err := a.d.CSRF.Ensure(w, r)
	if err != nil {
		return err
	}
	return renderHTML(w, http.StatusOK, totpPage(token, url))
}

// TOTPVerify verifies the code, activating the identity and minting a session
// (the ceremony lives in SPEC-006).
func (a *Actions) TOTPVerify(w http.ResponseWriter, r *http.Request) error {
	guid, ok, err := a.pendingGUID(r.Context())
	if err != nil {
		return err
	}
	if !ok {
		writeError(w, http.StatusConflict, "no admin is awaiting enrollment")
		return nil
	}
	return a.d.Enroll.TOTPVerify(w, r, guid)
}

// ── step 3 · settings & finish ──────────────────────────────────────────────

// Finish persists the mail/locale/timezone settings (a copy of the startup
// config with `setup: false`), signals completion (`Done`) and lands the freshly
// enrolled admin on their dashboard.
//
// If `config.yaml` is not writable the values are PRINTED for the operator
// (SPEC-005 §4) and setup still completes.
func (a *Actions) Finish(w http.ResponseWriter, r *http.Request) error {
	ctx := r.Context()
	if a.done.Load() {
		writeError(w, http.StatusNotFound, "not found")
		return nil
	}
	st, err := a.step(ctx)
	if err != nil {
		return err
	}
	if st != stepSettings {
		writeError(w, http.StatusConflict, "the admin is not enrolled yet")
		return nil
	}

	port := 0
	if v := strings.TrimSpace(r.FormValue("mail.port")); v != "" {
		p, err := strconv.Atoi(v)
		if err != nil || p < 0 || p > 65535 {
			writeError(w, http.StatusBadRequest, "invalid mail port")
			return nil
		}
		port = p
	}

	c := *a.d.Config // a copy: the live config stays the startup snapshot (D-035)
	c.Setup = false
	c.Mail = config.Mail{
		Host:     strings.TrimSpace(r.FormValue("mail.host")),
		Port:     port,
		Username: strings.TrimSpace(r.FormValue("mail.username")),
		Password: r.FormValue("mail.password"),
		From:     strings.TrimSpace(r.FormValue("mail.from")),
	}
	c.App = config.App{
		Locale:   strings.TrimSpace(r.FormValue("app.locale")),
		Timezone: strings.TrimSpace(r.FormValue("app.timezone")),
	}
	if d := a.draftDomain(); d != "" {
		c.Server.BaseURL = d
	}

	// R-6: a first boot from config.example.yaml must persist a VIABLE config.
	// Any secret that is still empty or a placeholder is replaced with a
	// strong, freshly generated value before it is written.
	if _, err := a.generateSecrets(&c); err != nil {
		return err
	}

	if err := a.persist(&c); err != nil {
		return err
	}
	a.done.Store(true)
	a.gate.Clear() // retire the setup code + every outstanding unlock (D-044)
	a.record(ctx, "setup.complete", "bootstrap finished")

	target := "/home"
	if guid, err := a.adminGUID(ctx); err == nil && guid != "" {
		target = "/" + guid + "/home"
	}
	redirect(w, r, target)
	return nil
}

// generateSecrets replaces any empty or placeholder secret with a strong,
// cryptographically-random value (R-6), so a copy of config.example.yaml boots
// straight into productive mode after the wizard. It reports whether it changed
// anything.
//
// The TOTP encryption key feeds AES-256-GCM, whose key must be EXACTLY 32
// bytes (SPEC-003 D-2), so it is base64url of 24 random bytes = 32 printable
// characters. The other three are signing keys and only need >= 32 bytes.
func (a *Actions) generateSecrets(c *config.Config) (bool, error) {
	changed := false
	for _, s := range []struct {
		name string
		dst  *string
		n    int
	}{
		{"secrets.cookie_secret", &c.Secrets.CookieSecret, 32},
		{"secrets.csrf_key", &c.Secrets.CSRFKey, 32},
	} {
		if !config.SecretIsPlaceholder(*s.dst) {
			continue
		}
		v, err := randomString(s.n)
		if err != nil {
			return false, err
		}
		*s.dst = v
		changed = true
		a.d.Logger.Info("setup: generated a strong secret", "name", s.name)
	}
	if config.SecretIsPlaceholder(c.Secrets.TOTPEncryptionKey) {
		v, err := randomString(24) // 24 bytes -> 32 base64url chars
		if err != nil {
			return false, err
		}
		c.Secrets.TOTPEncryptionKey = v
		changed = true
		a.d.Logger.Info("setup: generated a strong secret", "name", "secrets.totp_encryption_key")
	}
	return changed, nil
}

// randomString returns n cryptographically-random bytes, base64url-encoded.
// It delegates to config.GenerateSecret so the wizard and the startup path (the
// TOTP key, R-6) mint secrets the same way.
func randomString(n int) (string, error) { return config.GenerateSecret(n) }

// persist writes the config to disk; when it cannot, it prints the values and
// instructs the operator (SPEC-005 §4). It is complete either way.
func (a *Actions) persist(c *config.Config) error {
	data, err := config.Marshal(c)
	if err != nil {
		return err
	}
	if err := a.d.WriteFile(a.d.ConfigPath, data); err != nil {
		a.printValues(data, err)
		return nil
	}
	a.d.Logger.Info("setup: settings persisted", "path", a.d.ConfigPath)
	return nil
}

// printValues is the operator fallback when config.yaml is not writable: the
// values go to stdout with an instruction, and setup still completes.
func (a *Actions) printValues(data []byte, cause error) {
	a.d.Logger.Warn("setup: config file is not writable — printing the values for the operator",
		"path", a.d.ConfigPath, "error", cause)
	fmt.Fprintf(a.d.Printout,
		"\n# MyDay setup could not write %s: %v\n"+
			"# Write the following to that path by hand, then restart MyDay:\n\n%s\n",
		a.d.ConfigPath, cause, data)
}

// ── state ───────────────────────────────────────────────────────────────────

// step is the wizard's position.
type step int

const (
	stepDomain   step = iota // 1 · the domain / base URL
	stepAdmin                // 2a · the admin's details
	stepEnroll               // 2b · TOTP enrollment (D-041: no passkey)
	stepSettings             // 3 · mail · locale · timezone
)

// step derives the current step from the database and the in-memory draft.
func (a *Actions) step(ctx context.Context) (step, error) {
	n, err := a.d.Users.Count(ctx)
	if err != nil {
		return 0, err
	}
	if n == 0 {
		if a.draftDomain() != "" {
			return stepAdmin, nil
		}
		return stepDomain, nil
	}

	idn, err := a.d.Identities.ByUserID(ctx, adminUserID)
	if err != nil {
		if errors.Is(err, auth.ErrIdentityNotFound) {
			// A user exists but has no live identity — restart step 2.
			return stepAdmin, nil
		}
		return 0, err
	}
	if idn.Status == auth.StatusPendingEnrollment {
		return stepEnroll, nil
	}
	return stepSettings, nil
}

// draftDomain returns the base URL captured in step 1, if any.
func (a *Actions) draftDomain() string {
	a.mu.Lock()
	defer a.mu.Unlock()
	return a.draft.domain
}

// adminGUID returns the admin's current GUID.
func (a *Actions) adminGUID(ctx context.Context) (string, error) {
	idn, err := a.d.Identities.ByUserID(ctx, adminUserID)
	if err != nil {
		return "", err
	}
	return idn.GUID, nil
}

// pendingGUID returns the admin's GUID when its identity still awaits
// enrollment — pending AND inside its bounded enrollment window (SPEC-004 §4,
// A1). ok=false means there is nothing to enroll: no identity, another status,
// or the window has closed.
func (a *Actions) pendingGUID(ctx context.Context) (guid string, ok bool, err error) {
	idn, err := a.d.Identities.ByUserID(ctx, adminUserID)
	if err != nil {
		if errors.Is(err, auth.ErrIdentityNotFound) {
			return "", false, nil
		}
		return "", false, err
	}
	if idn.Status != auth.StatusPendingEnrollment {
		return "", false, nil
	}
	inWindow, err := a.d.Identities.WithinEnrollmentWindow(ctx, adminUserID)
	if err != nil {
		return "", false, err
	}
	if !inWindow {
		return "", false, nil
	}
	return idn.GUID, true, nil
}

// record writes one bootstrap audit row (A11).
func (a *Actions) record(ctx context.Context, action, detail string) {
	if a.d.Audit == nil {
		return
	}
	a.d.Audit.Record(ctx, audit.Event{
		Action:  action,
		Subject: fmt.Sprintf("user:%d", adminUserID),
		Detail:  detail,
	})
}

// recordSetup writes an audit row for an event that happens BEFORE the admin
// exists (the D-044 unlock). The subject is anonymous — there is no user yet.
func (a *Actions) recordSetup(ctx context.Context, action, detail string) {
	if a.d.Audit == nil {
		return
	}
	a.d.Audit.Record(ctx, audit.Event{
		Action:  action,
		Subject: "anonymous",
		Detail:  detail,
	})
}

// writeFile0600 is the default persister: the config holds secrets, so it is
// written owner-only.
func writeFile0600(path string, data []byte) error {
	return os.WriteFile(path, data, 0o600)
}