import type {Invoke, ScanRequest} from './repm-invoker.js';

import type {JSONValue} from './json.js';

import {throwIfClosed} from './transaction-closed-error.js';

import {ScanOptions, toRPC} from './scan-options.js';

interface IdCloser {

close(): void;

closed: boolean;

id: number;

}

const VALUE = 0;

const KEY = 1;

const ENTRY = 2;

type ScanIterableKind = typeof VALUE | typeof KEY | typeof ENTRY;

type Args = [

options: ScanOptions | undefined,

invoke: Invoke,

getTransaction: () => Promise<IdCloser> | IdCloser,

shouldCloseTransaction: boolean,

];

export class ScanResult<K> implements AsyncIterable<JSONValue> {

private readonly _args: Args;

constructor(...args: Args) {

this._args = args;

}

[Symbol.asyncIterator](): AsyncIterableIterator<JSONValue> {

return this.values();

}

values(): AsyncIterableIterator<JSONValue> {

return this._newIterator(VALUE);

}

keys(): AsyncIterableIterator<K> {

return this._newIterator(KEY);

}

entries(): AsyncIterableIterator<[K, JSONValue]> {

return this._newIterator(ENTRY);

}

private _newIterator<V>(kind: ScanIterableKind): AsyncIterableIterator<V> {

return scanIterator(kind, ...this._args);

}

}

async function* scanIterator<V>(

kind: ScanIterableKind,

options: ScanOptions | undefined,

invoke: Invoke,

getTransaction: () => Promise<IdCloser> | IdCloser,

shouldCloseTransaction: boolean,

): AsyncGenerator<V> {

const transaction = await getTransaction();

throwIfClosed(transaction);

const items = await load<V>(kind, options, transaction.id, invoke);

try {

for (const item of items) {

yield item;

}

} finally {

if (shouldCloseTransaction && !transaction.closed) {

transaction.close();

}

}

}

async function load<V>(

kind: ScanIterableKind,

options: ScanOptions | undefined,

transactionID: number,

invoke: Invoke,

): Promise<V[]> {

const items: V[] = [];

const decoder = new TextDecoder();

const parse = (v: Uint8Array) => JSON.parse(decoder.decode(v));

type MaybeIndexName = {indexName?: string};

const key = (primaryKey: string, secondaryKey: string | null) =>

(options as MaybeIndexName)?.indexName !== undefined

? [secondaryKey, primaryKey]

: primaryKey;

const receiver = (

primaryKey: string,

secondaryKey: string | null,

value: Uint8Array,

) => {

switch (kind) {

case VALUE:

items.push(parse(value));

return;

case KEY:

items.push((key(primaryKey, secondaryKey) as unknown) as V);

return;

case ENTRY:

items.push(([

key(primaryKey, secondaryKey),

parse(value),

] as unknown) as V);

}

};

const args: ScanRequest = {

transactionId: transactionID,

opts: toRPC(options),

receiver,

};

await invoke('scan', args);

return items;

}