import pickBy from "lodash/pickBy";
import type { QueryAnnotation } from "../abstract/QueryAnnotation";
import { QueryBase } from "../abstract/QueryBase";
import type { Schema } from "../abstract/Schema";
import { stringHash, hasKey, inspectCompact } from "../internal/misc";
import type { Hints, Literal, Order, Row, SelectInput, Table } from "../types";
import { escapeLiteral } from "./helpers/escapeLiteral";
import { RAW_PREPEND_HINT } from "./internal/buildHintQueries";
import { escapeString } from "./internal/escapeString";
import type { PgClient } from "./PgClient";
import { PgRunner } from "./PgRunner";

/**
 * This is mostly to do hacks in PostgreSQL queries. Not even exposed by Ent
 * framework, but can be used by PG-dependent code.
 */
export type SelectInputCustom =
  | {
      ctes?: Literal[];
      joins?: Literal[];
      from?: Literal;
      hints?: Hints;
    }
  | undefined;

const ALLOWED_ORDER = [
  "ASC",
  "ASC NULLS LAST",
  "ASC NULLS FIRST",
  "DESC",
  "DESC NULLS LAST",
  "DESC NULLS FIRST",
];

export class PgQuerySelect<TTable extends Table> extends QueryBase<
  TTable,
  SelectInput<TTable>,
  Array<Row<TTable>>,
  PgClient
> {
  /** @ignore */
  readonly RUNNER_CLASS = PgRunnerSelect;

  override async run(
    client: PgClient,
    annotation: QueryAnnotation,
  ): Promise<Array<Row<TTable>>> {
    const custom = this.input.custom as SelectInputCustom;
    const disableBatching = !!custom?.hints?.[RAW_PREPEND_HINT];
    return client
      .batcher(
        this.constructor,
        this.schema,
        JSON.stringify(custom?.hints) || "",
        disableBatching,
        () => new this.RUNNER_CLASS(this.schema, client),
      )
      .run(this.input, annotation);
  }
}

class PgRunnerSelect<TTable extends Table> extends PgRunner<
  TTable,
  SelectInput<TTable>,
  Array<Row<TTable>>
> {
  static override readonly IS_WRITE = false;
  private prefix = this.fmt("SELECT %SELECT_FIELDS FROM %T ");
  private prefixUnion = this.fmt("SELECT ");
  private midfixUnion = this.fmt(" AS _key, %SELECT_FIELDS FROM %T ");
  private builder;

  readonly op = "SELECT";
  readonly maxBatchSize = 10; // PG crashes on large queries with lots of UNION ALL, so we keep this value low.
  readonly default = []; // We just need something here.

  constructor(schema: Schema<TTable>, client: PgClient) {
    super(schema, client);
    this.builder = this.createWhereBuilder({
      prefix: this.fmt(""),
      suffix: this.fmt(""),
    });
  }

  override key(input: SelectInput<TTable>): string {
    // Coalesce equal select queries.
    const json = JSON.stringify(input);
    return stringHash(json);
  }

  async runSingle(
    input: SelectInput<TTable>,
    annotations: QueryAnnotation[],
  ): Promise<Array<Row<TTable>>> {
    const { sql, hints } = this.buildCustom(
      input,
      this.prefix +
        this.builder.prefix +
        this.builder.func(input.where) +
        this.builder.suffix +
        this.buildOptionalOrder(input.order) +
        this.buildLimit(input.limit),
    );
    return this.clientQuery<Row<TTable>>(sql, annotations, 1, hints);
  }

  async runBatch(
    inputs: Map<string, SelectInput<TTable>>,
    annotations: QueryAnnotation[],
  ): Promise<Map<string, Array<Row<TTable>>>> {
    // SELECT '...' AS _key, ... FROM ... WHERE ...
    //    UNION ALL
    // SELECT '...' AS _key, ... FROM ... WHERE ...
    const pieces: string[] = [];
    let allHints: Hints = {};
    for (const [key, input] of inputs.entries()) {
      const { sql, hints } = this.buildCustom(
        input,
        this.prefixUnion +
          escapeString(key) +
          this.midfixUnion +
          this.builder.prefix +
          this.builder.func(input.where) +
          this.builder.suffix +
          this.buildOptionalOrder(input.order) +
          this.buildLimit(input.limit),
      );
      pieces.push("(" + sql + ")");
      allHints = { ...allHints, ...pickBy(hints, (v) => v !== undefined) };
    }

    const unionRows = await this.clientQuery<{ _key: string } & Row<TTable>>(
      pieces.join("\n  UNION ALL\n"),
      annotations,
      inputs.size,
      Object.keys(allHints).length > 0 ? allHints : undefined,
    );

    const outputs = new Map<string, Array<Row<TTable>>>();
    for (const { _key: key, ...row } of unionRows) {
      let rows = outputs.get(key);
      if (!rows) {
        rows = [];
        outputs.set(key, rows);
      }

      rows.push(row as Row<TTable>);
    }

    return outputs;
  }

  private buildCustom(
    input: SelectInput<TTable>,
    sql: string,
  ): {
    sql: string;
    hints: Hints | undefined;
  } {
    const custom = input.custom as SelectInputCustom;
    if (custom?.joins?.length) {
      sql = sql.replace(
        / FROM \S+\s+/,
        (m) =>
          m +
          "\n" +
          custom.joins!.map((join) => escapeLiteral(join)).join("\n") +
          "\n",
      );
    } else if (custom?.from?.length) {
      sql = sql.replace(
        / FROM \S+/,
        () => " FROM " + escapeLiteral(custom.from!),
      );
    }

    if (custom?.ctes?.length) {
      sql =
        "WITH\n  " +
        custom.ctes.map((cte) => escapeLiteral(cte)).join(",\n  ") +
        "\n" +
        sql;
    }

    return { sql, hints: custom?.hints };
  }

  private buildOptionalOrder(order: Order<TTable> | undefined): string {
    if (!order) {
      return "";
    }

    // TS tuples support is unfortunately weak: it has hard time treating arrays
    // as tuples, and also treating strings as literal strings. E.g. we can't do:
    //   [["field", "ASC"], ...]
    // in the caller code and have Order<TType> to be tuple-based; the only
    // work-around would be
    //   [tuple("field" as const, "ASC" as const), ...]
    // which is ugly. So we use object-based order specifiers and lots of run-time
    // checks around the data passed.
    const pieces: string[] = [];
    for (const item of order) {
      if (hasKey("$literal", item)) {
        if (Object.keys(item).length > 1) {
          throw Error(
            "Invalid order specification - $literal must be the only key: " +
              inspectCompact(item),
          );
        }

        pieces.push(escapeLiteral(item.$literal));
      } else {
        for (const [field, dir] of Object.entries(item)) {
          if (!ALLOWED_ORDER.includes("" + dir)) {
            throw Error(
              `Invalid order specifier: ${dir}; allowed specifiers: ` +
                ALLOWED_ORDER.join(", "),
            );
          }

          pieces.push(`${this.escapeField(field)} ${dir}`);
        }
      }
    }

    return pieces.length > 0 ? " ORDER BY " + pieces.join(", ") : "";
  }

  private buildLimit(limit: number): string {
    return " LIMIT " + (parseInt("" + limit) || 0);
  }
}