package redshift

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"strings"
	"time"

	"github.com/hashicorp/errwrap"
	"github.com/hashicorp/go-multierror"
	"github.com/hashicorp/vault/api"
	"github.com/hashicorp/vault/sdk/database/dbplugin"
	"github.com/hashicorp/vault/sdk/database/helper/connutil"
	"github.com/hashicorp/vault/sdk/database/helper/credsutil"
	"github.com/hashicorp/vault/sdk/database/helper/dbutil"
	"github.com/hashicorp/vault/sdk/helper/dbtxn"
	"github.com/hashicorp/vault/sdk/helper/strutil"
	"github.com/lib/pq"
)

const (
	// This is how this plugin will be reflected in middleware
	// such as metrics.
	middlewareTypeName = "redshift"

	// This allows us to use the postgres database driver.
	sqlTypeName = "postgres"

	defaultRenewSQL = `
ALTER USER "{{name}}" VALID UNTIL '{{expiration}}';
`
	defaultRotateRootCredentialsSQL = `
ALTER USER "{{username}}" WITH PASSWORD '{{password}}';
`
)

// lowercaseUsername is the reason we wrote this plugin. Redshift implements (mostly)
// a postgres 8 interface, and part of that is under the hood, it's lowercasing the
// usernames.
func New(lowercaseUsername bool) func() (interface{}, error) {
	return func() (interface{}, error) {
		db := newRedshift(lowercaseUsername)
		// Wrap the plugin with middleware to sanitize errors
		dbType := dbplugin.NewDatabaseErrorSanitizerMiddleware(db, db.SecretValues)
		return dbType, nil
	}
}

func newRedshift(lowercaseUsername bool) *RedShift {
	connProducer := &connutil.SQLConnectionProducer{}
	connProducer.Type = sqlTypeName

	credsProducer := &credsutil.SQLCredentialsProducer{
		DisplayNameLen:    8,
		RoleNameLen:       8,
		UsernameLen:       63,
		Separator:         "-",
		LowercaseUsername: lowercaseUsername,
	}

	db := &RedShift{
		SQLConnectionProducer: connProducer,
		CredentialsProducer:   credsProducer,
	}

	return db
}

// Run instantiates a RedShift object, and runs the RPC server for the plugin
func Run(apiTLSConfig *api.TLSConfig) error {
	dbType, err := New(true)()
	if err != nil {
		return err
	}

	dbplugin.Serve(dbType.(dbplugin.Database), api.VaultPluginTLSProvider(apiTLSConfig))

	return nil
}

type RedShift struct {
	*connutil.SQLConnectionProducer
	credsutil.CredentialsProducer
}

func (r *RedShift) Type() (string, error) {
	return middlewareTypeName, nil
}

// getConnection accepts a context and retuns a new pointer to a sql.DB object.
// It's up to the caller to close the connection or handle reuse logic.
func (r *RedShift) getConnection(ctx context.Context) (*sql.DB, error) {
	db, err := r.Connection(ctx)
	if err != nil {
		return nil, err
	}
	return db.(*sql.DB), nil
}

// SetCredentials uses provided information to set/create a user in the
// database. Unlike CreateUser, this method requires a username be provided and
// uses the name given, instead of generating a name. This is used for creating
// and setting the password of static accounts, as well as rolling back
// passwords in the database in the event an updated database fails to save in
// Vault's storage.
func (r *RedShift) SetCredentials(ctx context.Context, statements dbplugin.Statements, staticUser dbplugin.StaticUserConfig) (username, password string, err error) {
	if len(statements.Rotation) == 0 {
		statements.Rotation = []string{defaultRotateRootCredentialsSQL}
	}

	username = staticUser.Username
	password = staticUser.Password
	if username == "" || password == "" {
		return "", "", errors.New("must provide both username and password")
	}

	// Grab the lock
	r.Lock()
	defer r.Unlock()

	// Get the connection
	db, err := r.getConnection(ctx)
	if err != nil {
		return "", "", err
	}
	defer db.Close()

	// Check if the role exists
	var exists bool
	err = db.QueryRowContext(ctx, "SELECT exists (SELECT usename FROM pg_user WHERE usename=$1);", username).Scan(&exists)
	if err != nil && err != sql.ErrNoRows {
		return "", "", err
	}

	// Vault requires the database user already exist, and that the credentials
	// used to execute the rotation statements has sufficient privileges.
	stmts := statements.Rotation

	// Start a transaction
	tx, err := db.BeginTx(ctx, nil)
	if err != nil {
		return "", "", err
	}
	defer func() {
		tx.Rollback()
	}()

	// Execute each query
	for _, stmt := range stmts {
		for _, query := range strutil.ParseArbitraryStringSlice(stmt, ";") {
			query = strings.TrimSpace(query)
			if len(query) == 0 {
				continue
			}

			m := map[string]string{
				"name":     staticUser.Username,
				"password": password,
			}
			if err := dbtxn.ExecuteTxQuery(ctx, tx, m, query); err != nil {
				return "", "", err
			}
		}
	}

	// Commit the transaction
	if err := tx.Commit(); err != nil {
		return "", "", err
	}
	return username, password, nil
}

func (r *RedShift) CreateUser(ctx context.Context, statements dbplugin.Statements, usernameConfig dbplugin.UsernameConfig, expiration time.Time) (username string, password string, err error) {
	statements = dbutil.StatementCompatibilityHelper(statements)

	if len(statements.Creation) == 0 {
		return "", "", dbutil.ErrEmptyCreationStatement
	}

	// Grab the lock
	r.Lock()
	defer r.Unlock()

	username, err = r.GenerateUsername(usernameConfig)
	if err != nil {
		return "", "", err
	}

	password, err = r.GeneratePassword()
	if err != nil {
		return "", "", err
	}

	expirationStr, err := r.GenerateExpiration(expiration)
	if err != nil {
		return "", "", err
	}

	// Get the connection
	db, err := r.getConnection(ctx)
	if err != nil {
		return "", "", err
	}
	defer db.Close()

	// Start a transaction
	tx, err := db.BeginTx(ctx, nil)
	if err != nil {
		return "", "", err

	}
	defer func() {
		tx.Rollback()
	}()

	// Execute each query
	for _, stmt := range statements.Creation {
		for _, query := range strutil.ParseArbitraryStringSlice(stmt, ";") {
			query = strings.TrimSpace(query)
			if len(query) == 0 {
				continue
			}

			m := map[string]string{
				"name":       username,
				"password":   password,
				"expiration": expirationStr,
			}
			if err := dbtxn.ExecuteTxQuery(ctx, tx, m, query); err != nil {
				return "", "", err
			}
		}
	}

	// Commit the transaction
	if err := tx.Commit(); err != nil {
		return "", "", err
	}
	return username, password, nil
}

func (r *RedShift) RenewUser(ctx context.Context, statements dbplugin.Statements, username string, expiration time.Time) error {
	r.Lock()
	defer r.Unlock()

	statements = dbutil.StatementCompatibilityHelper(statements)

	renewStmts := statements.Renewal
	if len(renewStmts) == 0 {
		renewStmts = []string{defaultRenewSQL}
	}

	db, err := r.getConnection(ctx)
	if err != nil {
		return err
	}
	defer db.Close()

	tx, err := db.BeginTx(ctx, nil)
	if err != nil {
		return err
	}
	defer func() {
		tx.Rollback()
	}()

	expirationStr, err := r.GenerateExpiration(expiration)
	if err != nil {
		return err
	}

	for _, stmt := range renewStmts {
		for _, query := range strutil.ParseArbitraryStringSlice(stmt, ";") {
			query = strings.TrimSpace(query)
			if len(query) == 0 {
				continue
			}

			m := map[string]string{
				"name":       username,
				"expiration": expirationStr,
			}
			if err := dbtxn.ExecuteTxQuery(ctx, tx, m, query); err != nil {
				return err
			}
		}
	}

	return tx.Commit()
}

func (r *RedShift) RevokeUser(ctx context.Context, statements dbplugin.Statements, username string) error {
	// Grab the lock
	r.Lock()
	defer r.Unlock()

	statements = dbutil.StatementCompatibilityHelper(statements)

	if len(statements.Revocation) == 0 {
		return r.defaultRevokeUser(ctx, username)
	}

	return r.customRevokeUser(ctx, username, statements.Revocation)
}

func (r *RedShift) customRevokeUser(ctx context.Context, username string, revocationStmts []string) error {
	db, err := r.getConnection(ctx)
	if err != nil {
		return err
	}
	defer db.Close()

	tx, err := db.BeginTx(ctx, nil)
	if err != nil {
		return err
	}
	defer func() {
		tx.Rollback()
	}()

	for _, stmt := range revocationStmts {
		for _, query := range strutil.ParseArbitraryStringSlice(stmt, ";") {
			query = strings.TrimSpace(query)
			if len(query) == 0 {
				continue
			}

			m := map[string]string{
				"name": username,
			}
			if err := dbtxn.ExecuteTxQuery(ctx, tx, m, query); err != nil {
				return err
			}
		}
	}

	return tx.Commit()
}

func (r *RedShift) defaultRevokeUser(ctx context.Context, username string) error {
	db, err := r.getConnection(ctx)
	if err != nil {
		return err
	}
	defer db.Close()

	// Check if the role exists
	var exists bool
	err = db.QueryRowContext(ctx, "SELECT exists (SELECT usename FROM pg_user WHERE usename=$1);", username).Scan(&exists)
	if err != nil && err != sql.ErrNoRows {
		return err
	}

	if !exists {
		return nil
	}

	// Query for permissions; we need to revoke permissions before we can drop
	// the role
	// This isn't done in a transaction because even if we fail along the way,
	// we want to remove as much access as possible
	stmt, err := db.PrepareContext(ctx, "SELECT DISTINCT table_schema FROM information_schema.role_column_grants WHERE grantee=$1;")
	if err != nil {
		return err
	}
	defer stmt.Close()

	rows, err := stmt.QueryContext(ctx, username)
	if err != nil {
		return err
	}
	defer rows.Close()

	const initialNumRevocations = 16
	revocationStmts := make([]string, 0, initialNumRevocations)
	for rows.Next() {
		var schema string
		err = rows.Scan(&schema)
		if err != nil {
			// keep going; remove as many permissions as possible right now
			continue
		}
		revocationStmts = append(revocationStmts, fmt.Sprintf(
			`REVOKE ALL PRIVILEGES ON ALL TABLES IN SCHEMA %s FROM %s;`,
			pq.QuoteIdentifier(schema),
			pq.QuoteIdentifier(username)))

		revocationStmts = append(revocationStmts, fmt.Sprintf(
			`REVOKE USAGE ON SCHEMA %s FROM %s;`,
			pq.QuoteIdentifier(schema),
			pq.QuoteIdentifier(username)))
	}

	// for good measure, revoke all privileges and usage on schema public
	revocationStmts = append(revocationStmts, fmt.Sprintf(
		`REVOKE ALL PRIVILEGES ON ALL TABLES IN SCHEMA public FROM %s;`,
		pq.QuoteIdentifier(username)))

	revocationStmts = append(revocationStmts, fmt.Sprintf(
		"REVOKE USAGE ON SCHEMA public FROM %s;",
		pq.QuoteIdentifier(username)))

	// get the current database name so we can issue a REVOKE CONNECT for
	// this username
	var dbname sql.NullString
	if err := db.QueryRowContext(ctx, "SELECT current_database();").Scan(&dbname); err != nil {
		return err
	}

	if dbname.Valid {
		/*
			We create this stored procedure to ensure we can durably revoke users on Redshift. We do not
			clean up since that can cause race conditions with other instances of Vault attempting to use
			this SP at the same time.
		*/
		revocationStmts = append(revocationStmts, `CREATE OR REPLACE PROCEDURE terminateloop(dbusername varchar(100))
LANGUAGE plpgsql
AS $$
DECLARE
  currentpid int;
  loopvar int;
  qtyconns int;
BEGIN
SELECT COUNT(process) INTO qtyconns FROM stv_sessions WHERE user_name=dbusername;
  FOR loopvar IN 1..qtyconns LOOP
    SELECT INTO currentpid process FROM stv_sessions WHERE user_name=dbusername ORDER BY process ASC LIMIT 1;
    SELECT pg_terminate_backend(currentpid);
  END LOOP;
END
$$;`)

		revocationStmts = append(revocationStmts, fmt.Sprintf(`call terminateloop('%s');`, username))
	}

	// again, here, we do not stop on error, as we want to remove as
	// many permissions as possible right now
	var lastStmtError *multierror.Error //error
	for _, query := range revocationStmts {
		if err := dbtxn.ExecuteDBQuery(ctx, db, nil, query); err != nil {
			lastStmtError = multierror.Append(lastStmtError, err)
		}
	}

	// can't drop if not all privileges are revoked
	if rows.Err() != nil {
		return errwrap.Wrapf("could not generate revocation statements for all rows: {{err}}", rows.Err())
	}
	if lastStmtError != nil {
		return errwrap.Wrapf("could not perform all revocation statements: {{err}}", lastStmtError)
	}

	// Drop this user
	stmt, err = db.PrepareContext(ctx, fmt.Sprintf(
		`DROP USER IF EXISTS %s;`, pq.QuoteIdentifier(username)))
	if err != nil {
		return err
	}
	defer stmt.Close()
	if _, err := stmt.ExecContext(ctx); err != nil {
		return err
	}

	return nil
}

func (r *RedShift) RotateRootCredentials(ctx context.Context, statements []string) (map[string]interface{}, error) {
	r.Lock()
	defer r.Unlock()

	if len(r.Username) == 0 || len(r.Password) == 0 {
		return nil, errors.New("username and password are required to rotate")
	}

	rotateStatements := statements
	if len(rotateStatements) == 0 {
		rotateStatements = []string{defaultRotateRootCredentialsSQL}
	}

	db, err := r.getConnection(ctx)
	if err != nil {
		return nil, err
	}
	defer db.Close()

	tx, err := db.BeginTx(ctx, nil)
	if err != nil {
		return nil, err
	}
	defer func() {
		tx.Rollback()
	}()

	password, err := r.GeneratePassword()
	if err != nil {
		return nil, err
	}

	for _, stmt := range rotateStatements {
		for _, query := range strutil.ParseArbitraryStringSlice(stmt, ";") {
			query = strings.TrimSpace(query)
			if len(query) == 0 {
				continue
			}
			m := map[string]string{
				"username": r.Username,
				"password": password,
			}
			if err := dbtxn.ExecuteTxQuery(ctx, tx, m, query); err != nil {
				return nil, err
			}
		}
	}

	if err := tx.Commit(); err != nil {
		return nil, err
	}

	r.RawConfig["password"] = password
	return r.RawConfig, nil
}