"use strict";

const debug = require("debug")("srap:backend:postgresql:query:get-task-stream");
const simpleSource = require("@promistream/simple-source");

const query = `
	WITH
		dependency_tasks AS (
			SELECT * FROM
				json_to_recordset(:dependencyTaskDefinitions) AS x(task text, task_version text)
		),
		matching_items AS (
			SELECT
				DISTINCT ON (srap_items.id)
				srap_items.*,
				results.updated_at AS result_date,
				results.task_version,
				(
					results.is_successful = TRUE
					AND (
						results.expires_at < NOW()
						OR results.is_invalidated = TRUE
					)
				) AS is_candidate
			FROM srap_items
				INNER JOIN srap_tags
					ON srap_tags.item_id = srap_items.id
					AND srap_tags.name = ANY(:tags)
				LEFT JOIN srap_task_results AS results
					ON results.item_id = srap_items.id
					AND results.task = :task
				WHERE
					NOT EXISTS (
						SELECT FROM srap_tasks_in_progress AS pr WHERE pr.item_id = srap_items.id
					)
		),
		candidates AS (
			SELECT * FROM matching_items
				WHERE result_date IS NULL
			UNION
			SELECT * FROM matching_items
				WHERE is_candidate = TRUE
				OR NOT (task_version = :taskVersion)
		)
	(
		SELECT
			*
		FROM
			candidates
		WHERE
			NOT EXISTS (
				SELECT
					results.*
				FROM dependency_tasks
					LEFT JOIN srap_task_results AS results
						ON dependency_tasks.task = results.task
						AND dependency_tasks.task_version = results.task_version
						AND results.item_id = candidates.id
				WHERE
					results.is_successful IS NULL
					OR results.is_successful = FALSE
					OR (
						results.is_successful = TRUE
						AND (
							results.expires_at < NOW()
							OR results.is_invalidated = TRUE
						)
					)
			)
	) LIMIT :resultLimit;
`;

module.exports = function ({ metrics, backendSettings }) {
	return function (tx, { task }) {
		return simpleSource(() => {
			let startTime = Date.now();
			
			return Promise.try(() => {
				return tx.raw(query, {
					tags: task.tags,
					task: task.name,
					taskVersion: task.version,
					resultLimit: backendSettings.taskBatchSize,
					dependencyTaskDefinitions: JSON.stringify(task.dependencies.map((dependency) => {
						// Case-mapping for SQL compatibility
						return { task_version: dependency.version, task: dependency.name };
					}))
				});
			}).then((result) => {
				let timeElapsed = Date.now() - startTime;
	
				metrics.taskFetchTime.labels({ task: task.name }).set(timeElapsed / 1000);
				metrics.taskFetchResults.labels({ task: task.name }).set(result.rowCount);
	
				debug(`Task retrieval query for '${task.name}' took ${timeElapsed}ms and produced ${result.rowCount} results`);
	
				if (result.rowCount > 0) {
					return result.rows;
				} else {
					// TODO: Consider using LISTEN/NOTIFY instead?
					return Promise.resolve([]).delay(backendSettings.taskBatchDelay);
				}
			});
		});
	};
}