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import { AggregationComputer, AggregationGroupComputer, IValue, nil, QueryError, _ISelection, _IType, _Transaction } from '../../interfaces-private.ts';import { ExprCall } from 'https://deno.land/x/pgsql_ast_parser@12.0.1/mod.ts';import { buildValue } from '../../parser/expression-builder.ts';import { Types } from '../../datatypes/index.ts';import { nullIsh, sum } from '../../utils.ts';import { withSelection } from '../../parser/context.ts';

class AvgExpr implements AggregationComputer<number> {
    constructor(private exp: IValue) {    }
    get type(): _IType<any> {        return Types.bigint;    }
    createGroup(t: _Transaction): AggregationGroupComputer<number> {        let full: number[] = [];        return {            feedItem: (item) => {                const value = this.exp.get(item, t);                if (!nullIsh(value)) {                    full.push(value);                }            },            finish: () => full.length === 0 ? null : sum(full) / full.length,        }    }}

export function buildAvg(this: void, base: _ISelection, call: ExprCall) {    return withSelection(base, () => {        const args = call.args;        if (args.length !== 1) {            throw new QueryError('AVG expects one argument, given ' + args.length);        }
        const what = buildValue(args[0]);        return new AvgExpr(what);    });}