package server

import (
	"errors"
	"fmt"
	"net/http"
	"strings"
	"time"

	"cc.tiredsysadmin.keeporg/internal/blob"
	"cc.tiredsysadmin.keeporg/internal/kdbx"
	"cc.tiredsysadmin.keeporg/internal/secret"
	"cc.tiredsysadmin.keeporg/internal/store"
)

// MinVaultPasswordLen is the shortest vault password the server will create
// a vault with. It guards an organization's whole password database.
const MinVaultPasswordLen = 12

var errNoKeyring = errors.New(
	"this server has no master key, so it cannot hold vault keys: set " +
		secret.MasterKeyEnv + " or master_key_file and restart")

// createVault makes a new, empty KDBX database, encrypts it with the given
// vault password and stores it as version 1. When the strategy needs the
// key, the password is wrapped under the server's master key and kept; for
// every other strategy it is used once and forgotten.
func (s *Server) createVault(u *store.User, name, groupID string, strategy store.Strategy,
	password string) (dbView, error) {
	name = strings.TrimSpace(name)
	switch {
	case name == "":
		return dbView{}, errors.New("the vault needs a name")
	case len(password) < MinVaultPasswordLen:
		return dbView{}, fmt.Errorf("the vault password must be at least %d characters",
			MinVaultPasswordLen)
	case !strategy.Valid():
		return dbView{}, errors.New("unknown merge strategy")
	case strategy.NeedsKey() && s.keyring == nil:
		return dbView{}, errNoKeyring
	}

	// Build the empty database before touching any state, so a failure here
	// leaves nothing behind.
	db := kdbx.New(name, s.cfg.VaultKDF)
	data, err := db.Marshal(password)
	if err != nil {
		return dbView{}, fmt.Errorf("creating the vault file: %w", err)
	}

	id := secret.ID()
	wrapped := ""
	if strategy.NeedsKey() {
		if wrapped, err = s.keyring.Wrap(id, password); err != nil {
			return dbView{}, err
		}
	}
	if err := s.blobs.Put(id, 1, data); err != nil {
		return dbView{}, err
	}

	var out dbView
	err = s.st.Update(func(st *store.State) error {
		if st.Groups[groupID] == nil {
			return errors.New("unknown owner group")
		}
		if !st.IsGroupAdmin(u.ID, groupID) {
			return errForbidden
		}
		rec := &store.Database{
			ID: id, Name: name, OwnerGroupID: groupID, MergeStrategy: strategy,
			WrappedKey: wrapped, Version: 1, SHA256: blob.SHA256(data),
			Size: int64(len(data)), UpdatedAt: time.Now(), UpdatedBy: u.Username,
		}
		st.Databases[id] = rec
		out = toView(rec, store.PermAdmin)
		return nil
	})
	if err != nil {
		if rerr := s.blobs.Forget(id); rerr != nil {
			s.log.Printf("rolling back vault %s: %v", id, rerr)
		}
		return dbView{}, err
	}
	s.notifyList(id)
	s.log.Printf("%s created vault %q (%s), strategy %s", u.Username, name, id, strategy)
	return out, nil
}

// handleCreateVault is the API behind the web form: it creates the database
// record and its first, empty KDBX version in one step.
func (s *Server) handleCreateVault(w http.ResponseWriter, r *http.Request, u *store.User) {
	var req struct {
		Name          string         `json:"name"`
		OwnerGroupID  string         `json:"owner_group_id"`
		MergeStrategy store.Strategy `json:"merge_strategy"`
		Password      string         `json:"password"`
	}
	if !readJSON(w, r, &req) {
		return
	}
	if req.MergeStrategy == "" {
		req.MergeStrategy = store.StrategyMerge
	}
	out, err := s.createVault(u, req.Name, req.OwnerGroupID, req.MergeStrategy, req.Password)
	if err != nil {
		deny(w, err)
		return
	}
	writeJSON(w, http.StatusCreated, out)
}

// handleSetVaultKey stores, replaces or removes the key the server keeps for
// a database, which is what lets an existing database start being merged.
// The password is checked against the stored file before it is accepted.
func (s *Server) handleSetVaultKey(w http.ResponseWriter, r *http.Request, u *store.User) {
	id := r.PathValue("id")
	var req struct {
		Password string `json:"password"`
		Forget   bool   `json:"forget"`
	}
	if !readJSON(w, r, &req) {
		return
	}
	var (
		version int64
		perm    store.Perm
	)
	s.st.Read(func(st *store.State) {
		perm = st.DatabasePerm(u.ID, id)
		if d := st.Databases[id]; d != nil {
			version = d.Version
		}
	})
	if perm != store.PermAdmin {
		deny(w, errForbidden)
		return
	}
	if !req.Forget {
		if s.keyring == nil {
			deny(w, errNoKeyring)
			return
		}
		if version == 0 {
			deny(w, errors.New("this database has no content yet, so the password cannot be checked"))
			return
		}
		data, err := s.blobs.Get(id, version)
		if err != nil {
			deny(w, err)
			return
		}
		if _, err := kdbx.Open(data, req.Password); err != nil {
			deny(w, fmt.Errorf("that password does not open the stored vault: %w", err))
			return
		}
	}
	wrapped := ""
	if !req.Forget {
		var err error
		if wrapped, err = s.keyring.Wrap(id, req.Password); err != nil {
			deny(w, err)
			return
		}
	}
	err := s.st.Update(func(st *store.State) error {
		d := st.Databases[id]
		if d == nil {
			return errors.New("no such database")
		}
		if req.Forget && d.MergeStrategy == store.StrategyMerge {
			return errors.New("switch the merge strategy away from merge before removing the key")
		}
		d.WrappedKey = wrapped
		return nil
	})
	if err != nil {
		deny(w, err)
		return
	}
	writeJSON(w, http.StatusOK, map[string]bool{"key_stored": wrapped != ""})
}

// vaultPassword unwraps the stored key for a database.
func (s *Server) vaultPassword(id, wrapped string) (string, error) {
	if wrapped == "" {
		return "", errors.New("no vault key is stored for this database")
	}
	if s.keyring == nil {
		return "", errNoKeyring
	}
	return s.keyring.Unwrap(id, wrapped)
}