package server

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"strconv"
	"strings"
	"time"

	"jarl/internal/api"
	"jarl/internal/auth"
	"jarl/internal/model"
	"jarl/internal/store"
)

func (s *Server) whoami(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	se, _ := r.Context().Value(keySession).(*model.Session)
	writeJSON(w, http.StatusOK, s.whoamiOf(p, se))
	return nil
}

func (s *Server) changeOwnPassword(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if p.Token != nil {
		return forbidden("passwords can't be changed with an API token; log in to the web UI")
	}
	var in api.PasswordChange
	if err := decodeJSON(r, &in); err != nil {
		return err
	}
	u, err := s.store.GetUser(r.Context(), p.User.ID)
	if err != nil {
		return err
	}
	if u.PasswordHash != "" && !auth.CheckPassword(u.PasswordHash, in.Current) {
		s.eng.Audit(r.Context(), p, "user.password", "user", u.ID, u.Username, "failure", "wrong current password")
		return &httpError{http.StatusForbidden, "wrong_password", "the current password is wrong"}
	}
	hash, err := auth.HashPassword(in.Password)
	if err != nil {
		return badRequest("%v", err)
	}
	u.PasswordHash = hash
	if err := s.store.UpdateUser(r.Context(), u); err != nil {
		return err
	}
	// Log out other sessions.
	keep := ""
	if se, ok := r.Context().Value(keySession).(*model.Session); ok {
		keep = se.IDHash
	}
	s.store.DeleteUserSessions(r.Context(), u.ID, keep)
	s.eng.Audit(r.Context(), p, "user.password", "user", u.ID, u.Username, "success", "")
	w.WriteHeader(http.StatusNoContent)
	return nil
}

// grantsFrom builds the grant list from structured grants, compact
// strings or a role template.
func grantsFrom(grants *[]model.Grant, strs *[]string, role string) ([]model.Grant, bool, error) {
	var out []model.Grant
	set := false
	if role != "" {
		t, ok := auth.RoleTemplates[role]
		if !ok {
			var names []string
			for n := range auth.RoleTemplates {
				names = append(names, n)
			}
			return nil, false, badRequest("unknown role %q (known: %s)", role, strings.Join(names, ", "))
		}
		out = append(out, t...)
		set = true
	}
	if grants != nil {
		for _, g := range *grants {
			if err := auth.ValidateGrant(&g); err != nil {
				return nil, false, badRequest("%v", err)
			}
			out = append(out, g)
		}
		set = true
	}
	if strs != nil {
		for _, gs := range *strs {
			g, err := auth.ParseGrant(gs)
			if err != nil {
				return nil, false, badRequest("grant %q: %v", gs, err)
			}
			out = append(out, g)
		}
		set = true
	}
	if set && out == nil {
		out = []model.Grant{}
	}
	return out, set, nil
}

func parseExpiry(in api.TokenInput) (*time.Time, error) {
	if in.ExpiresAt != nil {
		if in.ExpiresAt.Before(time.Now()) {
			return nil, badRequest("expires_at is in the past")
		}
		return in.ExpiresAt, nil
	}
	if in.ExpiresIn == "" {
		return nil, nil
	}
	d, err := parseDays(in.ExpiresIn)
	if err != nil || d <= 0 {
		return nil, badRequest("invalid expires_in %q (use e.g. 90d or 720h)", in.ExpiresIn)
	}
	t := time.Now().Add(d)
	return &t, nil
}

// parseDays parses a duration in Go syntax ("720h", "15m") or in days
// ("90d").
func parseDays(v string) (time.Duration, error) {
	v = strings.TrimSpace(v)
	if n, ok := strings.CutSuffix(v, "d"); ok {
		days, err := strconv.Atoi(n)
		if err != nil || days < 0 {
			return 0, fmt.Errorf("invalid duration %q", v)
		}
		return time.Duration(days) * 24 * time.Hour, nil
	}
	return time.ParseDuration(v)
}

func (s *Server) createTokenFor(w http.ResponseWriter, r *http.Request, p *auth.Principal, u *model.User) error {
	var in api.TokenInput
	if err := decodeJSON(r, &in); err != nil {
		return err
	}
	if strings.TrimSpace(in.Name) == "" {
		return badRequest("a token needs a name")
	}
	grants, set, err := grantsFrom(in.Grants, in.GrantStrings, in.Role)
	if err != nil {
		return err
	}
	exp, err := parseExpiry(in)
	if err != nil {
		return err
	}
	// A restricted token can only create tokens that are no wider than
	// itself.
	if p.Token != nil && p.Token.Grants != nil {
		if !set {
			grants = p.Token.Grants
		} else if !narrower(grants, p.Token.Grants) {
			return forbidden("a restricted token can only create tokens with a subset of its own grants")
		}
	}
	secret, pid, hash := auth.NewToken()
	t := &model.Token{UserID: u.ID, Name: strings.TrimSpace(in.Name), PublicID: pid, SecretHash: hash, ExpiresAt: exp}
	if set {
		t.Grants = grants
	}
	if err := s.store.CreateToken(r.Context(), t); err != nil {
		return err
	}
	t.Username = u.Username
	s.eng.Audit(r.Context(), p, "token.create", "token", t.ID, u.Username+"/"+t.Name, "success", "")
	out := presentToken(t)
	out.Secret = secret
	writeJSON(w, http.StatusCreated, out)
	return nil
}

// narrower reports whether every grant in a is covered by a grant in b
// (a conservative check: identical or b is unfiltered for the resource).
func narrower(a, b []model.Grant) bool {
	for _, g := range a {
		ok := false
		for _, h := range b {
			if (h.Resource == auth.ResAll || h.Resource == g.Resource) && (h.Access == auth.Write || g.Access == auth.Read) &&
				len(h.Zones) == 0 && len(h.Views) == 0 && len(h.Names) == 0 && len(h.Types) == 0 {
				ok = true
				break
			}
			if auth.FormatGrant(g) == auth.FormatGrant(h) {
				ok = true
				break
			}
		}
		if !ok {
			return false
		}
	}
	return true
}

func (s *Server) createOwnToken(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	return s.createTokenFor(w, r, p, p.User)
}

func (s *Server) listTokens(w http.ResponseWriter, r *http.Request, userID int64) error {
	ts, err := s.store.ListTokens(r.Context(), userID)
	if err != nil {
		return err
	}
	out := []api.Token{}
	for _, t := range ts {
		if t.RevokedAt != nil && !queryBool(r, "all") {
			continue
		}
		out = append(out, presentToken(t))
	}
	writeJSON(w, http.StatusOK, out)
	return nil
}

func (s *Server) listOwnTokens(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	return s.listTokens(w, r, p.User.ID)
}

func (s *Server) listAllTokens(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := requireAdmin(p); err != nil {
		return err
	}
	return s.listTokens(w, r, 0)
}

func (s *Server) revokeToken(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	id, err := pathID(r, "id")
	if err != nil {
		return err
	}
	t, err := s.store.GetToken(r.Context(), id)
	if err != nil {
		return err
	}
	if t.UserID != p.User.ID && !p.IsAdmin() {
		return notFound("token %d not found", id)
	}
	if err := s.store.RevokeToken(r.Context(), id); err != nil {
		if errors.Is(err, store.ErrNotFound) {
			return conflict("token %d is already revoked", id)
		}
		return err
	}
	s.eng.Audit(r.Context(), p, "token.revoke", "token", t.ID, t.Username+"/"+t.Name, "success", "")
	w.WriteHeader(http.StatusNoContent)
	return nil
}

// maxRotationGrace is the longest an old secret may keep working.
const maxRotationGrace = 7 * 24 * time.Hour

// rotateToken: POST /tokens/{id}/rotate gives a token a new secret. The
// token keeps its ID, name, user and grants, so nothing needs to be set up
// again; only the clients that use it need the new secret. The old secret
// stops working at once, or after the grace period. A token that expires
// gets the same lifetime again, counted from now, unless expires_in or
// expires_at says otherwise.
func (s *Server) rotateToken(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	id, err := pathID(r, "id")
	if err != nil {
		return err
	}
	var in api.TokenRotation
	body, err := readBody(r)
	if err != nil {
		return err
	}
	if body != nil {
		dec := json.NewDecoder(bytes.NewReader(body))
		dec.DisallowUnknownFields()
		if err := dec.Decode(&in); err != nil {
			return badRequest("invalid JSON: %v", err)
		}
	}
	t, err := s.store.GetToken(r.Context(), id)
	if err != nil {
		if errors.Is(err, store.ErrNotFound) {
			return notFound("token %d not found", id)
		}
		return err
	}
	if t.UserID != p.User.ID && !p.IsAdmin() {
		return notFound("token %d not found", id)
	}
	// A restricted token may rotate itself, and tokens no wider than
	// itself, but not a wider token of the same user: it would learn that
	// token's new secret.
	if !p.IsAdmin() && p.Token != nil && p.Token.Grants != nil && p.Token.ID != t.ID && (t.Grants == nil || !narrower(t.Grants, p.Token.Grants)) {
		return forbidden("a restricted token can only rotate itself and tokens with a subset of its own grants")
	}
	if t.RevokedAt != nil {
		return conflict("token %d is revoked; create a new one", id)
	}
	now := time.Now()
	var exp *time.Time
	switch {
	case in.ExpiresIn != "" || in.ExpiresAt != nil:
		if in.NoExpiry {
			return badRequest("no_expiry can't be combined with expires_in or expires_at")
		}
		if exp, err = parseExpiry(api.TokenInput{ExpiresIn: in.ExpiresIn, ExpiresAt: in.ExpiresAt}); err != nil {
			return err
		}
	case in.NoExpiry:
	case t.ExpiresAt != nil:
		life := t.ExpiresAt.Sub(t.IssuedAt())
		if life <= 0 {
			return badRequest("can't tell the token's lifetime; give expires_in")
		}
		e := now.Add(life)
		exp = &e
	}
	var prevUntil *time.Time
	if in.Grace != "" {
		g, err := parseDays(in.Grace)
		if err != nil || g < 0 || g > maxRotationGrace {
			return badRequest("invalid grace %q: use a duration up to 7d, e.g. 30m, 24h or 2d", in.Grace)
		}
		until := now.Add(g)
		if t.ExpiresAt != nil && t.ExpiresAt.Before(until) {
			until = *t.ExpiresAt // the old secret never outlives its token
		}
		if g > 0 && until.After(now) {
			prevUntil = &until
		}
	}
	secret, hash := auth.RotateToken(t.PublicID)
	if err := s.store.RotateToken(r.Context(), t.ID, hash, exp, prevUntil); err != nil {
		if errors.Is(err, store.ErrNotFound) {
			return conflict("token %d is revoked; create a new one", id)
		}
		return err
	}
	t, err = s.store.GetToken(r.Context(), id)
	if err != nil {
		return err
	}
	detail := "old secret stops working now"
	if prevUntil != nil {
		detail = "old secret works until " + prevUntil.UTC().Format(time.RFC3339)
	}
	if t.ExpiresAt != nil {
		detail += "; expires " + t.ExpiresAt.UTC().Format(time.RFC3339)
	}
	s.eng.Audit(r.Context(), p, "token.rotate", "token", t.ID, t.Username+"/"+t.Name, "success", detail)
	out := presentToken(t)
	out.Secret = secret
	writeJSON(w, http.StatusOK, out)
	return nil
}

func (s *Server) listUsers(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := requireAdmin(p); err != nil {
		return err
	}
	us, err := s.store.ListUsers(r.Context())
	if err != nil {
		return err
	}
	out := []api.User{}
	for _, u := range us {
		out = append(out, presentUser(u))
	}
	writeJSON(w, http.StatusOK, out)
	return nil
}

func validUsername(n string) error {
	if len(n) < 1 || len(n) > 64 {
		return badRequest("usernames must be 1 to 64 characters")
	}
	for _, c := range n {
		if !(c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z' || c >= '0' && c <= '9' || strings.ContainsRune("._-@", c)) {
			return badRequest("usernames may contain letters, digits, '.', '_', '-' and '@'")
		}
	}
	return nil
}

func (s *Server) createUser(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := requireAdmin(p); err != nil {
		return err
	}
	var in api.UserInput
	if err := decodeJSON(r, &in); err != nil {
		return err
	}
	if in.Username == nil {
		return badRequest("a user needs a username")
	}
	u := &model.User{Username: strings.TrimSpace(*in.Username)}
	if err := validUsername(u.Username); err != nil {
		return err
	}
	if err := applyUserInput(u, &in); err != nil {
		return err
	}
	if err := s.store.CreateUser(r.Context(), u); err != nil {
		if errors.Is(err, store.ErrConflict) {
			return conflict("user %s already exists", u.Username)
		}
		return err
	}
	s.eng.Audit(r.Context(), p, "user.create", "user", u.ID, u.Username, "success", strings.Join(presentUser(u).GrantStrings, "; "))
	writeJSON(w, http.StatusCreated, presentUser(u))
	return nil
}

func applyUserInput(u *model.User, in *api.UserInput) error {
	role := ""
	if in.Role != nil {
		role = *in.Role
	}
	grants, set, err := grantsFrom(in.Grants, in.GrantStrings, role)
	if err != nil {
		return err
	}
	if set {
		u.Grants = grants
	}
	if in.Admin != nil {
		u.Admin = *in.Admin
	}
	if in.Disabled != nil {
		u.Disabled = *in.Disabled
	}
	if in.Comment != nil {
		u.Comment = *in.Comment
	}
	if in.Password != nil {
		if *in.Password == "" {
			u.PasswordHash = "" // service account: tokens only
		} else {
			h, err := auth.HashPassword(*in.Password)
			if err != nil {
				return badRequest("%v", err)
			}
			u.PasswordHash = h
		}
	}
	return nil
}

func (s *Server) userByPath(r *http.Request) (*model.User, error) {
	id, err := pathID(r, "id")
	if err != nil {
		return nil, err
	}
	u, err := s.store.GetUser(r.Context(), id)
	if errors.Is(err, store.ErrNotFound) {
		return nil, notFound("user %d not found", id)
	}
	return u, err
}

func (s *Server) getUser(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	u, err := s.userByPath(r)
	if err != nil {
		return err
	}
	if u.ID != p.User.ID && !p.IsAdmin() {
		return forbidden("only administrators can see other users")
	}
	writeJSON(w, http.StatusOK, presentUser(u))
	return nil
}

func (s *Server) updateUser(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := requireAdmin(p); err != nil {
		return err
	}
	u, err := s.userByPath(r)
	if err != nil {
		return err
	}
	var in api.UserInput
	if err := decodeJSON(r, &in); err != nil {
		return err
	}
	wasAdmin := u.Admin && !u.Disabled
	if in.Username != nil {
		u.Username = strings.TrimSpace(*in.Username)
		if err := validUsername(u.Username); err != nil {
			return err
		}
	}
	if err := applyUserInput(u, &in); err != nil {
		return err
	}
	if wasAdmin && (!u.Admin || u.Disabled) {
		if n, err := s.store.CountAdmins(r.Context()); err == nil && n <= 1 {
			return conflict("%s is the last administrator; make someone else an administrator first", u.Username)
		}
	}
	if err := s.store.UpdateUser(r.Context(), u); err != nil {
		if errors.Is(err, store.ErrConflict) {
			return conflict("user %s already exists", u.Username)
		}
		return err
	}
	if u.Disabled || in.Password != nil {
		s.store.DeleteUserSessions(r.Context(), u.ID, "")
	}
	s.eng.Audit(r.Context(), p, "user.update", "user", u.ID, u.Username, "success", strings.Join(presentUser(u).GrantStrings, "; "))
	writeJSON(w, http.StatusOK, presentUser(u))
	return nil
}

func (s *Server) deleteUser(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := requireAdmin(p); err != nil {
		return err
	}
	u, err := s.userByPath(r)
	if err != nil {
		return err
	}
	if u.ID == p.User.ID {
		return conflict("you can't delete yourself")
	}
	if u.Admin && !u.Disabled {
		if n, err := s.store.CountAdmins(r.Context()); err == nil && n <= 1 {
			return conflict("%s is the last administrator", u.Username)
		}
	}
	if err := s.store.DeleteUser(r.Context(), u.ID); err != nil {
		return err
	}
	s.eng.Audit(r.Context(), p, "user.delete", "user", u.ID, u.Username, "success", "")
	w.WriteHeader(http.StatusNoContent)
	return nil
}

func (s *Server) listUserTokens(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	u, err := s.userByPath(r)
	if err != nil {
		return err
	}
	if u.ID != p.User.ID && !p.IsAdmin() {
		return forbidden("only administrators can see other users' tokens")
	}
	return s.listTokens(w, r, u.ID)
}

func (s *Server) createUserToken(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	u, err := s.userByPath(r)
	if err != nil {
		return err
	}
	if u.ID != p.User.ID && !p.IsAdmin() {
		return forbidden("only administrators can create tokens for other users")
	}
	return s.createTokenFor(w, r, p, u)
}