export type OptimizationElements =
	| 'leave-balances'
	| 'public-holiday-weeks'
	| 'time-off-periods'
	| 'work-sequences'
	| 'leave-placements';
export type OptimizationCondition =
	| 'at-risk'
	| 'complete'
	| 'internal'
	| 'non-empty'
	| 'supporting';
export type OptimizationMeasure =
	| 'unplaced-quantity'
	| 'public-holiday-week-value'
	| 'non-working-day-gain'
	| 'work-sequence-length'
	| 'work-sequence-deficit'
	| 'placement-count';
export type OptimizationAggregation = 'sum' | 'count' | 'maximum';
export type OptimizationDirection = 'minimize' | 'maximize';
export type OptimizationUnit = 'working-days' | 'calendar-days' | 'count';

interface OptimizationConfigurationBase {
	elements: OptimizationElements;
	conditions: readonly OptimizationCondition[];
	aggregation: OptimizationAggregation;
	direction: OptimizationDirection;
}

export type OptimizationConfiguration = OptimizationConfigurationBase &
	(
		| { measure: 'work-sequence-deficit'; thresholdDays: number }
		| { measure: Exclude<OptimizationMeasure, 'work-sequence-deficit'>; thresholdDays?: never }
	);

/** Each row accepts any subset of its conditions and both comparison directions. */
export const OPTIMIZATION_CATALOG = [
	{
		elements: 'leave-balances',
		measure: 'unplaced-quantity',
		conditions: ['at-risk'],
		aggregations: ['sum', 'count', 'maximum'],
		unit: 'working-days',
	},
	{
		elements: 'public-holiday-weeks',
		measure: 'public-holiday-week-value',
		conditions: ['complete'],
		aggregations: ['sum', 'count', 'maximum'],
		unit: 'calendar-days',
	},
	{
		elements: 'time-off-periods',
		measure: 'non-working-day-gain',
		conditions: [],
		aggregations: ['sum', 'count', 'maximum'],
		unit: 'calendar-days',
	},
	{
		elements: 'work-sequences',
		measure: 'work-sequence-length',
		conditions: ['internal', 'non-empty'],
		aggregations: ['sum', 'count', 'maximum'],
		unit: 'working-days',
	},
	{
		elements: 'work-sequences',
		measure: 'work-sequence-deficit',
		conditions: ['internal', 'non-empty'],
		aggregations: ['sum', 'count', 'maximum'],
		unit: 'working-days',
	},
	{
		elements: 'leave-placements',
		measure: 'placement-count',
		conditions: ['supporting'],
		aggregations: ['sum', 'count', 'maximum'],
		unit: 'count',
	},
] as const;

export type OptimizationValidation =
	| { valid: true; configuration: OptimizationConfiguration }
	| {
			valid: false;
			code: 'invalid-optimization-configuration' | 'unsupported-optimization-configuration';
			message: string;
	  };

export function validateOptimizationConfiguration(value: unknown): OptimizationValidation {
	const invalid = (message: string): OptimizationValidation => ({
		valid: false,
		code: 'invalid-optimization-configuration',
		message,
	});
	const unsupported = (message: string): OptimizationValidation => ({
		valid: false,
		code: 'unsupported-optimization-configuration',
		message,
	});
	if (!value || typeof value !== 'object' || Array.isArray(value))
		return invalid('An optimization configuration must be an object.');
	const config = value as Record<string, unknown>;
	const fields = [
		'elements',
		'conditions',
		'measure',
		'aggregation',
		'direction',
		'thresholdDays',
	];
	if (Object.keys(config).some((key) => !fields.includes(key)))
		return unsupported('The optimization configuration contains an unsupported field.');
	if (config['direction'] !== 'minimize' && config['direction'] !== 'maximize')
		return invalid('The optimization direction must be minimize or maximize.');
	if (
		!Array.isArray(config['conditions']) ||
		[...config['conditions']].some((condition) => typeof condition !== 'string') ||
		new Set(config['conditions']).size !== config['conditions'].length
	)
		return invalid('Optimization conditions must be a list of distinct conditions.');
	const row = OPTIMIZATION_CATALOG.find(
		(item) => item.elements === config['elements'] && item.measure === config['measure'],
	);
	if (!row) return unsupported('The planning elements and measure are not compatible.');
	const conditions: readonly string[] = row.conditions;
	if (config['conditions'].some((condition) => !conditions.includes(condition)))
		return unsupported('A condition is not supported for these planning elements.');
	const aggregations: readonly string[] = row.aggregations;
	if (typeof config['aggregation'] !== 'string' || !aggregations.includes(config['aggregation']))
		return unsupported('The aggregation is not supported for this measure.');
	if (config['measure'] === 'work-sequence-deficit') {
		if (!Number.isSafeInteger(config['thresholdDays']) || Number(config['thresholdDays']) <= 0)
			return invalid('The deficit threshold must be a positive integer in working days.');
	} else if ('thresholdDays' in config)
		return unsupported('Only the work-sequence deficit accepts a working-day threshold.');
	return { valid: true, configuration: value as OptimizationConfiguration };
}

export function optimizationUnit(configuration: OptimizationConfiguration): OptimizationUnit {
	return configuration.aggregation === 'count'
		? 'count'
		: OPTIMIZATION_CATALOG.find(
				(row) =>
					row.elements === configuration.elements &&
					row.measure === configuration.measure,
			)!.unit;
}

export const OPTIMIZATION_PRESETS = {
	unplacedAtRisk: {
		elements: 'leave-balances',
		conditions: ['at-risk'],
		measure: 'unplaced-quantity',
		aggregation: 'sum',
		direction: 'minimize',
	},
	holidayWeekValue: {
		elements: 'public-holiday-weeks',
		conditions: ['complete'],
		measure: 'public-holiday-week-value',
		aggregation: 'sum',
		direction: 'maximize',
	},
	nonWorkingDayGain: {
		elements: 'time-off-periods',
		conditions: [],
		measure: 'non-working-day-gain',
		aggregation: 'sum',
		direction: 'maximize',
	},
	longestWorkSequence: {
		elements: 'work-sequences',
		conditions: [],
		measure: 'work-sequence-length',
		aggregation: 'maximum',
		direction: 'minimize',
	},
	shortSequenceDeficit: {
		elements: 'work-sequences',
		conditions: ['internal', 'non-empty'],
		measure: 'work-sequence-deficit',
		thresholdDays: 5,
		aggregation: 'sum',
		direction: 'minimize',
	},
	supportingPlacements: {
		elements: 'leave-placements',
		conditions: ['supporting'],
		measure: 'placement-count',
		aggregation: 'count',
		direction: 'minimize',
	},
} as const satisfies Record<string, OptimizationConfiguration>;

/** Concrete observations from one plan; they carry no rule identity or display name. */
export interface OptimizationObservations {
	leaveBalances: readonly { unplacedQuantity: number; atRisk: boolean }[];
	publicHolidayWeeks: readonly { value: number; complete: boolean }[];
	timeOffPeriods: readonly { nonWorkingDates: readonly string[] }[];
	workSequences: readonly { length: number; internal: boolean }[];
	leavePlacements: readonly { supporting: boolean }[];
}

// Calendar geometry reuses frozen date arrays across candidate plans.
const nonWorkingDateCounts = new WeakMap<readonly string[], number>();

export function evaluateOptimization(
	configuration: OptimizationConfiguration,
	observations: OptimizationObservations,
): number {
	const validation = validateOptimizationConfiguration(configuration);
	if (!validation.valid) throw new Error(`${validation.code}: ${validation.message}`);
	const selected = (condition: OptimizationCondition) =>
		configuration.conditions.includes(condition);
	let values: number[];
	switch (configuration.elements) {
		case 'leave-balances':
			values = observations.leaveBalances
				.filter((balance) => !selected('at-risk') || balance.atRisk)
				.map((balance) => balance.unplacedQuantity);
			break;
		case 'public-holiday-weeks':
			values = observations.publicHolidayWeeks
				.filter((week) => !selected('complete') || week.complete)
				.map((week) => week.value);
			break;
		case 'time-off-periods':
			values = observations.timeOffPeriods.map(({ nonWorkingDates }) => {
				const cached = nonWorkingDateCounts.get(nonWorkingDates);
				if (cached !== undefined) return cached;
				const count = new Set(nonWorkingDates).size;
				if (Object.isFrozen(nonWorkingDates))
					nonWorkingDateCounts.set(nonWorkingDates, count);
				return count;
			});
			break;
		case 'work-sequences':
			values = observations.workSequences
				.filter(
					(sequence) =>
						(!selected('internal') || sequence.internal) &&
						(!selected('non-empty') || sequence.length > 0),
				)
				.map((sequence) =>
					configuration.measure === 'work-sequence-deficit'
						? sequence.length > 0
							? Math.max(0, configuration.thresholdDays - sequence.length)
							: 0
						: sequence.length,
				);
			break;
		case 'leave-placements':
			values = observations.leavePlacements
				.filter((placement) => !selected('supporting') || placement.supporting)
				.map(() => 1);
	}
	switch (configuration.aggregation) {
		case 'count':
			return values.length;
		case 'sum':
			return values.reduce((total, value) => total + value, 0);
		case 'maximum':
			return values.reduce((maximum, value) => Math.max(maximum, value), 0);
	}
}

export interface ComparableObjective {
	id: string;
	direction: OptimizationDirection;
	value: number | string;
}

/** Negative means the left candidate is preferred. Strings retain lexical tie-break ordering. */
export function compareObjectiveValues(
	direction: OptimizationDirection,
	left: number | string,
	right: number | string,
): number {
	if (left === right) return 0;
	const difference =
		typeof left === 'number' && typeof right === 'number'
			? left - right
			: left < right
				? -1
				: left > right
					? 1
					: 0;
	return direction === 'minimize' ? difference : -difference;
}

export function firstDifferentObjective(
	left: readonly ComparableObjective[],
	right: readonly ComparableObjective[],
): number {
	return left.findIndex((objective, index) => objective.value !== right[index]?.value);
}

export function compareObjectiveLists(
	left: readonly ComparableObjective[],
	right: readonly ComparableObjective[],
): number {
	const index = firstDifferentObjective(left, right);
	return index < 0
		? 0
		: compareObjectiveValues(left[index].direction, left[index].value, right[index].value);
}