package server

import (
	"context"
	"encoding/pem"
	"errors"
	"fmt"
	"net"
	"net/http"
	"net/netip"
	"strings"
	"time"

	"jarl/internal/api"
	"jarl/internal/auth"
	"jarl/internal/certs"
	"jarl/internal/encdns"
	"jarl/internal/model"
)

// TLS certificates (docs/certificates.md). Administrators only: a
// certificate's key can impersonate the server.

type certView struct {
	*model.Certificate
	Status  certs.Status `json:"status"`
	NextTry *time.Time   `json:"next_attempt,omitempty"` // acme: when the loop obtains it next
	Files   *certFiles   `json:"files,omitempty"`        // dns use: where named reads it
	Serving bool         `json:"serving,omitempty"`      // jarld serves it now (web use)
	// NamedUse says what of named's configuration uses it: "DNS over TLS
	// on 10.0.10.5 port 853" (list and get only).
	NamedUse []string `json:"named_use,omitempty"`
	// IssuingSince is set while Jarl is obtaining it.
	IssuingSince *time.Time `json:"issuing_since,omitempty"`
	// Owner is the user a certificate for another host belongs to; PulledBy
	// who downloaded it (list and get; an owner who isn't an administrator
	// sees only their own downloads).
	Owner    string                  `json:"owner,omitempty"`
	PulledBy []model.CertificatePull `json:"pulled_by,omitempty"`
}

type certFiles struct {
	Chain string `json:"chain"`
	Key   string `json:"key"`
}

func (s *Server) presentCert(c *model.Certificate) certView {
	m := s.cfg.Certs
	v := certView{Certificate: c, Status: m.StatusOf(c), Serving: m.WebName() == c.Name && c.HasUse(model.CertUseWeb)}
	if c.Source == model.CertSourceACME {
		t := m.Due(c)
		v.NextTry = &t
	}
	if t := m.Issuing(c.Name); !t.IsZero() {
		v.IssuingSince = &t
	}
	if c.HasUse(model.CertUseDNS) && c.NotAfter != nil {
		dir := m.FilesDir(c.Name)
		v.Files = &certFiles{Chain: dir + "/" + certs.ChainFile, Key: dir + "/" + certs.KeyFile}
	}
	return v
}

func (s *Server) certsReady(p *auth.Principal) error {
	if err := requireAdmin(p); err != nil {
		return err
	}
	if s.cfg.Certs == nil {
		return &httpError{http.StatusNotFound, "disabled", "certificates aren't available in this jarld"}
	}
	return nil
}

// certsAccess lets in administrators and users with a certificates grant
// (certificates for other hosts: their own only).
func (s *Server) certsAccess(p *auth.Principal) error {
	if s.cfg.Certs == nil {
		return &httpError{http.StatusNotFound, "disabled", "certificates aren't available in this jarld"}
	}
	if p.IsAdmin() || p.Can(auth.Action{Resource: auth.ResCerts}) {
		return nil
	}
	return forbidden("certificates need an administrator, or a certificates grant for their names (certificates:write names=*.example.com)")
}

// certAllowed reports whether p may see (or, with write, change) c: an
// administrator any; anyone else their own, while their grants cover all
// its names.
func certAllowed(p *auth.Principal, c *model.Certificate, write bool) bool {
	if p.IsAdmin() {
		return true
	}
	if p.User == nil || c.OwnerID == 0 || c.OwnerID != p.User.ID {
		return false
	}
	for _, d := range c.Domains {
		if !p.Can(auth.Action{Resource: auth.ResCerts, Write: write, Name: d}) {
			return false
		}
	}
	return true
}

// certFor returns the certificate in the path, if p may see it (else not
// found, so names of others' certificates don't leak).
func (s *Server) certFor(r *http.Request, p *auth.Principal, write bool) (*model.Certificate, error) {
	c, err := s.cfg.Certs.Get(r.Context(), r.PathValue("name"))
	if err != nil {
		return nil, certErr(err)
	}
	if !certAllowed(p, c, write) {
		if write && certAllowed(p, c, false) {
			return nil, forbidden("you may only download certificate %s", c.Name)
		}
		return nil, notFound("no such certificate")
	}
	return c, nil
}

// withOwners adds owners and downloads to views: all of them for an
// administrator, the principal's own downloads for anyone else (who sees
// only their own certificates).
func (s *Server) withOwners(ctx context.Context, p *auth.Principal, views []certView) error {
	pulls, err := s.store.CertificatePulls(ctx)
	if err != nil {
		return err
	}
	if !p.IsAdmin() {
		for i := range views {
			for _, pl := range pulls[views[i].ID] {
				if p.User != nil && pl.UserID == p.User.ID {
					views[i].PulledBy = append(views[i].PulledBy, pl)
				}
			}
			if p.User != nil && views[i].OwnerID != 0 {
				views[i].Owner = p.User.Username
			}
		}
		return nil
	}
	users, err := s.store.ListUsers(ctx)
	if err != nil {
		return err
	}
	names := map[int64]string{}
	for _, u := range users {
		names[u.ID] = u.Username
	}
	for i := range views {
		if id := views[i].OwnerID; id != 0 {
			views[i].Owner = names[id]
			if views[i].Owner == "" {
				views[i].Owner = fmt.Sprintf("deleted user %d", id)
			}
		}
		views[i].PulledBy = pulls[views[i].ID]
	}
	return nil
}

func certErr(err error) error {
	var ie *certs.InputError
	switch {
	case errors.As(err, &ie):
		return badRequest("%s", ie.Msg)
	case errors.Is(err, certs.ErrNotFound):
		return notFound("no such certificate")
	case errors.Is(err, certs.ErrConflict):
		return conflict("a certificate with that name exists")
	case errors.Is(err, certs.ErrTaken):
		return conflict("the certificate name is taken by another user's certificate (or one Jarl uses): choose another name")
	}
	return err
}

// certList: GET /certificates.
func (s *Server) certList(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := s.certsAccess(p); err != nil {
		return err
	}
	all, err := s.cfg.Certs.List(r.Context())
	if err != nil {
		return err
	}
	st, err := s.store.LoadState(r.Context())
	if err != nil {
		return err
	}
	out := []certView{}
	for _, c := range all {
		if !certAllowed(p, c, false) {
			continue
		}
		v := s.presentCert(c)
		v.NamedUse = encdns.CertUses(st, s.cfg.Certs.FilesDir(c.Name))
		out = append(out, v)
	}
	if err := s.withOwners(r.Context(), p, out); err != nil {
		return err
	}
	if !p.IsAdmin() {
		writeJSON(w, http.StatusOK, map[string]any{"certificates": out})
		return nil
	}
	writeJSON(w, http.StatusOK, map[string]any{"certificates": out, "account": s.cfg.Certs.AccountInfo(r.Context())})
	return nil
}

// certGet: GET /certificates/{name}.
func (s *Server) certGet(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := s.certsAccess(p); err != nil {
		return err
	}
	c, err := s.certFor(r, p, false)
	if err != nil {
		return err
	}
	st, err := s.store.LoadState(r.Context())
	if err != nil {
		return err
	}
	v := s.presentCert(c)
	v.NamedUse = encdns.CertUses(st, s.cfg.Certs.FilesDir(c.Name))
	vs := []certView{v}
	if err := s.withOwners(r.Context(), p, vs); err != nil {
		return err
	}
	v = vs[0]
	writeJSON(w, http.StatusOK, v)
	return nil
}

// certRequest: POST /certificates/{name}/request {"domains": [...],
// "key_type": "ec256"}, for jarl cert get: the certificate for another
// host, owned by the caller's user. A new one is created and obtained
// (202 while that runs; poll GET /certificates/{name} until
// issuing_since is gone). An existing one is the caller's, obtained again
// only when its names change; otherwise it is returned as it is (200).
func (s *Server) certRequest(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := s.certsAccess(p); err != nil {
		return err
	}
	if p.User == nil || p.User.ID == 0 {
		return forbidden("certificates for other hosts belong to a user: use an API token, not the local socket as root")
	}
	var in struct {
		Domains []string `json:"domains"`
		KeyType string   `json:"key_type"`
	}
	if err := decodeJSON(r, &in); err != nil {
		return err
	}
	for _, d := range in.Domains {
		d = strings.ToLower(strings.TrimSuffix(strings.TrimSpace(d), "."))
		if !p.Can(auth.Action{Resource: auth.ResCerts, Write: true, Name: d}) {
			return forbidden("you may not get a certificate for %s: that needs certificates:write with a names pattern that matches it", d)
		}
	}
	res, err := s.cfg.Certs.Ensure(r.Context(), r.PathValue("name"), in.Domains, in.KeyType, p)
	if err != nil {
		return certErr(err)
	}
	v := s.presentCert(res.Certificate)
	out := map[string]any{"certificate": v, "created": res.Created, "changed": res.Changed}
	if res.Ignored != "" {
		out["warnings"] = []string{res.Ignored}
	}
	status := http.StatusOK
	if v.IssuingSince != nil {
		status = http.StatusAccepted
	}
	writeJSON(w, status, out)
	return nil
}

// certPEM: GET /certificates/{name}/pem?part=fullchain|cert|key|bundle,
// the certificate as PEM for use elsewhere: the chain (default), the
// certificate alone, the private key, or the key followed by the chain
// (one file, as HAProxy wants). Anything with the key is audited.
func (s *Server) certPEM(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := s.certsAccess(p); err != nil {
		return err
	}
	if _, err := s.certFor(r, p, false); err != nil {
		return err
	}
	part := r.URL.Query().Get("part")
	if part == "" {
		part = "fullchain"
	}
	if part == "key" || part == "bundle" {
		if ok, why := s.keyTransport(r); !ok {
			return &httpError{http.StatusForbidden, "https_required", "a private key is only handed out over HTTPS (or to this server itself), and this request came by " + why}
		}
	}
	c, chain, key, err := s.cfg.Certs.PEM(r.Context(), r.PathValue("name"))
	if err != nil {
		return certErr(err)
	}
	var out []byte
	file := c.Name + "-" + part + ".pem"
	switch part {
	case "fullchain":
		out = chain
	case "cert":
		if b, _ := pem.Decode(chain); b != nil {
			out = pem.EncodeToMemory(b)
		}
	case "key":
		out = key
	case "bundle":
		out = append(append(append([]byte{}, key...), '\n'), chain...)
	default:
		return badRequest("part must be fullchain, cert, key or bundle")
	}
	if len(out) == 0 {
		return badRequest("certificate %s has no %s", c.Name, part)
	}
	if part == "key" || part == "bundle" {
		s.eng.Audit(r.Context(), p, "certificate.export_key", "certificate", c.ID, c.Name, "success", "exported the private key ("+part+")")
	}
	pull := &model.CertificatePull{CertID: c.ID, Who: pullWho(p), Serial: c.Serial, IP: s.clientIP(r), At: time.Now().UTC()}
	if p.User != nil {
		pull.UserID = p.User.ID
	}
	if p.Token != nil {
		pull.TokenID = p.Token.ID
	}
	if err := s.store.RecordCertificatePull(r.Context(), pull); err != nil {
		s.log.Warn("recording a certificate download failed", "certificate", c.Name, "err", err)
	}
	w.Header().Set("Content-Type", "application/x-pem-file")
	w.Header().Set("Content-Disposition", `attachment; filename="`+file+`"`)
	w.Header().Set("Cache-Control", "no-store")
	_, err = w.Write(out)
	return err
}

// certCreate: POST /certificates. With "issue": true (the default for
// certificates Jarl obtains) it is obtained before the answer.
func (s *Server) certCreate(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := s.certsReady(p); err != nil {
		return err
	}
	var in struct {
		certs.Input
		Issue *bool `json:"issue"`
	}
	if err := decodeJSON(r, &in); err != nil {
		return err
	}
	c, err := s.cfg.Certs.Create(r.Context(), in.Input, p)
	if err != nil {
		return certErr(err)
	}
	if c.Source == model.CertSourceACME && (in.Issue == nil || *in.Issue) {
		return s.writeIssue(w, r, c.Name, p, http.StatusCreated)
	}
	if c.Source == model.CertSourceACME {
		s.cfg.Certs.Kick()
	}
	writeJSON(w, http.StatusCreated, map[string]any{"certificate": s.presentCert(c)})
	return nil
}

// certUpdate: PATCH /certificates/{name}.
func (s *Server) certUpdate(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := s.certsReady(p); err != nil {
		return err
	}
	var in certs.Input
	if err := decodeJSON(r, &in); err != nil {
		return err
	}
	c, err := s.cfg.Certs.Update(r.Context(), r.PathValue("name"), in, p)
	if err != nil {
		return certErr(err)
	}
	writeJSON(w, http.StatusOK, map[string]any{"certificate": s.presentCert(c)})
	return nil
}

// certDelete: DELETE /certificates/{name}.
func (s *Server) certDelete(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := s.certsAccess(p); err != nil {
		return err
	}
	if _, err := s.certFor(r, p, true); err != nil {
		return err
	}
	if err := s.cfg.Certs.Delete(r.Context(), r.PathValue("name"), p); err != nil {
		return certErr(err)
	}
	writeJSON(w, http.StatusOK, map[string]any{"ok": true})
	return nil
}

// certIssue: POST /certificates/{name}/issue starts obtaining it now
// (202), or rereads the files of a file-source certificate (200).
func (s *Server) certIssue(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := s.certsReady(p); err != nil {
		return err
	}
	return s.writeIssue(w, r, r.PathValue("name"), p, http.StatusOK)
}

// writeIssue starts obtaining the certificate (it takes a while: poll
// GET /certificates/{name} until issuing_since is gone).
func (s *Server) writeIssue(w http.ResponseWriter, r *http.Request, name string, p *auth.Principal, status int) error {
	c, err := s.cfg.Certs.IssueAsync(r.Context(), name, p)
	if c == nil {
		return certErr(err)
	}
	if c.Source == model.CertSourceACME && status == http.StatusOK {
		status = http.StatusAccepted
	}
	out := map[string]any{"certificate": s.presentCert(c)}
	if err != nil {
		out["error"] = err.Error()
	}
	writeJSON(w, status, out)
	return nil
}

// certCheck: POST /certificates/{name}/check (or POST /certificates/check
// with a certificate's fields) says where each challenge would go, without
// asking the CA for anything.
func (s *Server) certCheck(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := s.certsReady(p); err != nil {
		return err
	}
	var c *model.Certificate
	if name := r.PathValue("name"); name != "" {
		var err error
		if c, err = s.cfg.Certs.Get(r.Context(), name); err != nil {
			return certErr(err)
		}
	} else {
		var in certs.Input
		if err := decodeJSON(r, &in); err != nil {
			return err
		}
		if in.Name == nil {
			in.Name = model.Ptr("check")
		}
		var err error
		if c, err = s.cfg.Certs.Preview(in); err != nil {
			return certErr(err)
		}
	}
	routes, err := s.cfg.Certs.Check(r.Context(), c)
	if err != nil {
		return certErr(err)
	}
	ok := true
	for _, rt := range routes {
		ok = ok && rt.Error == ""
	}
	writeJSON(w, http.StatusOK, map[string]any{"ok": ok, "routes": routes, "account": s.cfg.Certs.AccountInfo(r.Context())})
	return nil
}

// certSummary sums up the certificates for the dashboard (nil without any).
func (s *Server) certSummary(ctx context.Context) *api.CertSummary {
	if s.cfg.Certs == nil {
		return nil
	}
	all, err := s.cfg.Certs.List(ctx)
	if err != nil || len(all) == 0 {
		return nil
	}
	out := &api.CertSummary{Total: len(all), Problems: []api.CertProblem{}, Serving: s.cfg.Certs.WebName()}
	for _, c := range all {
		if st := s.cfg.Certs.StatusOf(c); st.State != "ok" && st.State != "pending" {
			out.Problems = append(out.Problems, api.CertProblem{Name: c.Name, State: st.State, Message: st.Message})
		}
		if c.NotAfter != nil && (out.NextAfter == nil || c.NotAfter.Before(*out.NextAfter)) {
			out.Next, out.NextAfter = c.Name, c.NotAfter
		}
	}
	return out
}

// keyTransport reports whether a private key may go back over r: HTTPS
// (also through a trusted proxy), the local socket, or loopback.
func (s *Server) keyTransport(r *http.Request) (bool, string) {
	https, why := s.transport(r)
	if https {
		return true, why
	}
	host, _, _ := net.SplitHostPort(r.RemoteAddr)
	if a, err := netip.ParseAddr(host); err == nil && a.Unmap().IsLoopback() && !s.trusted(a.Unmap()) {
		return true, "plain HTTP from this server"
	}
	return false, why
}

// pullWho names a downloader: its token (and user), or the user.
func pullWho(p *auth.Principal) string {
	switch {
	case p.Token != nil:
		return "token " + p.Token.Name + " (" + p.Name() + ")"
	case p.User != nil && p.Method != "":
		return p.Method + " " + p.Name()
	}
	return p.Name()
}