// Copyright 2017-2018 New Vector Ltd
// Copyright 2019-2020 The Matrix.org Foundation C.I.C.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package postgres

import (
	"context"
	"database/sql"

	"github.com/matrix-org/dendrite/internal"
	"github.com/matrix-org/dendrite/internal/sqlutil"
	"github.com/matrix-org/dendrite/roomserver/storage/tables"
	"github.com/matrix-org/dendrite/roomserver/types"
)

const eventJSONSchema = `
-- Stores the JSON for each event. This kept separate from the main events
-- table to keep the rows in the main events table small.
CREATE TABLE IF NOT EXISTS roomserver_event_json (
    -- Local numeric ID for the event.
    event_nid BIGINT NOT NULL PRIMARY KEY,
    -- The JSON for the event.
    -- Stored as TEXT because this should be valid UTF-8.
    -- Not stored as a JSONB because we always just pull the entire event
    -- so there is no point in postgres parsing it.
    -- Not stored as JSON because we already validate the JSON in the server
    -- so there is no point in postgres validating it.
    -- TODO: Should we be compressing the events with Snappy or DEFLATE?
    event_json TEXT NOT NULL
);
`

const insertEventJSONSQL = "" +
	"INSERT INTO roomserver_event_json (event_nid, event_json) VALUES ($1, $2)" +
	" ON CONFLICT (event_nid) DO UPDATE SET event_json=$2"

// Bulk event JSON lookup by numeric event ID.
// Sort by the numeric event ID.
// This means that we can use binary search to lookup by numeric event ID.
const bulkSelectEventJSONSQL = "" +
	"SELECT event_nid, event_json FROM roomserver_event_json" +
	" WHERE event_nid = ANY($1)" +
	" ORDER BY event_nid ASC"

const purgeEventJSONSQL = `
	DELETE FROM roomserver_event_json WHERE event_nid = ANY(
		SELECT event_nid FROM roomserver_events WHERE room_nid = $1
	)
`

type eventJSONStatements struct {
	insertEventJSONStmt     *sql.Stmt
	bulkSelectEventJSONStmt *sql.Stmt
	purgeEventJSONStmt      *sql.Stmt
}

func CreateEventJSONTable(db *sql.DB) error {
	_, err := db.Exec(eventJSONSchema)
	return err
}

func PrepareEventJSONTable(db *sql.DB) (tables.EventJSON, error) {
	s := &eventJSONStatements{}

	return s, sqlutil.StatementList{
		{&s.insertEventJSONStmt, insertEventJSONSQL},
		{&s.bulkSelectEventJSONStmt, bulkSelectEventJSONSQL},
		{&s.purgeEventJSONStmt, purgeEventJSONSQL},
	}.Prepare(db)
}

func (s *eventJSONStatements) InsertEventJSON(
	ctx context.Context, txn *sql.Tx, eventNID types.EventNID, eventJSON []byte,
) error {
	stmt := sqlutil.TxStmt(txn, s.insertEventJSONStmt)
	_, err := stmt.ExecContext(ctx, int64(eventNID), eventJSON)
	return err
}

func (s *eventJSONStatements) BulkSelectEventJSON(
	ctx context.Context, txn *sql.Tx, eventNIDs []types.EventNID,
) ([]tables.EventJSONPair, error) {
	stmt := sqlutil.TxStmt(txn, s.bulkSelectEventJSONStmt)
	rows, err := stmt.QueryContext(ctx, eventNIDsAsArray(eventNIDs))
	if err != nil {
		return nil, err
	}
	defer internal.CloseAndLogIfError(ctx, rows, "bulkSelectEventJSON: rows.close() failed")

	// We know that we will only get as many results as event NIDs
	// because of the unique constraint on event NIDs.
	// So we can allocate an array of the correct size now.
	// We might get fewer results than NIDs so we adjust the length of the slice before returning it.
	results := make([]tables.EventJSONPair, len(eventNIDs))
	i := 0
	var eventNID int64
	for ; rows.Next(); i++ {
		result := &results[i]
		if err := rows.Scan(&eventNID, &result.EventJSON); err != nil {
			return nil, err
		}
		result.EventNID = types.EventNID(eventNID)
	}
	return results[:i], rows.Err()
}

func (s *eventJSONStatements) PurgeEventJSONs(
	ctx context.Context, txn *sql.Tx, roomNID types.RoomNID,
) error {
	_, err := sqlutil.TxStmt(txn, s.purgeEventJSONStmt).ExecContext(ctx, roomNID)
	return err
}