import type {
  GpoAnalysisSnapshot,
  GpoBackupInstance,
  GpoSnapshotCompleteness,
  GpoSnapshotStatus
} from '../domain/gpo-ingestion';
import { gpoBackupCompleteness, gpoBackupInstanceValidationErrors } from '../domain/gpo-ingestion';

export interface GpoSnapshotBuildOptions {
  createdAt: string;
  maximumCollectionSkewMs?: number;
}

function hash(value: string): string {
  let result = 0x811c9dc5;
  for (let index = 0; index < value.length; index += 1) {
    result ^= value.charCodeAt(index);
    result = Math.imul(result, 0x01000193);
  }
  return (result >>> 0).toString(16).padStart(8, '0');
}

function effectiveBackupSetId(instance: GpoBackupInstance): string {
  return instance.backupSet.id ?? 'gpo-backup-set:' + instance.sourceArtifactId;
}

function groupKey(instance: GpoBackupInstance): string {
  const domain = instance.backupSet.scope === 'selected-gpos' && instance.backupSet.evidence === 'user-selection'
    ? 'user-selected-backup-set'
    : instance.domain.status === 'resolved' ? instance.domain.key : `unknown:${instance.id}`;
  const backupSet = effectiveBackupSetId(instance);
  return JSON.stringify([instance.projectId, domain, backupSet]);
}

function setDeclaration(instance: GpoBackupInstance): string {
  return JSON.stringify([
    instance.backupSet.scope,
    instance.backupSet.evidence,
    instance.backupSet.expectedGpoCount ?? null
  ]);
}

function collectionWindow(instances: GpoBackupInstance[]): { from: string; to: string } | undefined {
  if (instances.some(instance => instance.collection.status === 'unknown')) return undefined;
  const times = instances.map(instance => (instance.collection as Extract<GpoBackupInstance['collection'], { status: 'observed' }>).collectedAt)
    .sort((left, right) => Date.parse(left) - Date.parse(right));
  return times.length ? { from: times[0], to: times[times.length - 1] } : undefined;
}

function domainSplits(instances: GpoBackupInstance[]): Set<string> {
  const domainsBySet = new Map<string, Set<string>>();
  instances.forEach(instance => {
    
    const domain = instance.domain.status === 'resolved' ? instance.domain.key : `unknown:${instance.id}`;
    const backupSetId = effectiveBackupSetId(instance);
    const domains = domainsBySet.get(backupSetId) ?? new Set<string>();
    domains.add(domain);
    domainsBySet.set(backupSetId, domains);
  });
  return new Set([...domainsBySet].filter(([, domains]) => domains.size > 1).map(([setId]) => setId));
}

function snapshotForGroup(
  instances: GpoBackupInstance[],
  splitSetIds: ReadonlySet<string>,
  createdAt: string,
  maximumCollectionSkewMs: number
): GpoAnalysisSnapshot {
  const first = instances[0];
  const diagnostics = new Set<string>();
  let inconsistent = false;
  let indeterminate = false;

  if (first.domain.status === 'unknown') {
    diagnostics.add('gpo-domain-unknown');
    indeterminate = true;
  }
  const derivedBackupSet = !first.backupSet.id;
  const backupSetId = effectiveBackupSetId(first);
  const selectedUpload = first.backupSet.scope === 'selected-gpos' && first.backupSet.evidence === 'user-selection';
  const mixedDomains = splitSetIds.has(backupSetId);
  if (derivedBackupSet) diagnostics.add('gpo-backup-set-derived-from-source-artifact');
  if (mixedDomains && selectedUpload) {
    diagnostics.add('gpo-backup-set-domain-mixed');
    indeterminate = true;
  } else if (mixedDomains) {
    diagnostics.add('gpo-backup-set-domain-split');
    inconsistent = true;
  }
  if (new Set(instances.map(setDeclaration)).size > 1) {
    diagnostics.add('gpo-backup-set-declaration-conflict');
    inconsistent = true;
  }
  const resolvedGpoIds = instances.flatMap(instance => instance.identity.status === 'resolved' ? [instance.identity.gpoId] : []);
  if (resolvedGpoIds.length !== new Set(resolvedGpoIds).size) {
    diagnostics.add('gpo-duplicate-identity-in-snapshot');
    inconsistent = true;
  }
  const resolvedBackupIds = instances.flatMap(instance => instance.identity.status === 'resolved' ? [instance.identity.backupId] : []);
  if (resolvedBackupIds.length !== new Set(resolvedBackupIds).size) {
    diagnostics.add('gpo-duplicate-backup-in-snapshot');
    inconsistent = true;
  }
  if (instances.some(instance => instance.identity.status === 'unresolved')) {
    diagnostics.add('gpo-identity-unresolved');
    indeterminate = true;
  }
  if (instances.some(instance => gpoBackupCompleteness(instance) !== 'complete')) {
    diagnostics.add('gpo-backup-instance-incomplete');
    indeterminate = true;
  }

  const collectionRange = collectionWindow(instances);
  if (!collectionRange) {
    diagnostics.add('gpo-collection-time-unknown');
    indeterminate = true;
  } else if (Date.parse(collectionRange.to) - Date.parse(collectionRange.from) > maximumCollectionSkewMs) {
    diagnostics.add('gpo-collection-range-exceeded');
    inconsistent = true;
  }
  if (instances.some(instance => instance.collection.status === 'observed'
    && instance.collection.evidence !== 'collection-manifest')) {
    diagnostics.add('gpo-collection-time-not-manifest-backed');
    indeterminate = true;
  }

  let completeness: GpoSnapshotCompleteness;
  if (inconsistent) completeness = 'inconsistent';
  else if (first.backupSet.scope === 'selected-gpos' || derivedBackupSet) completeness = 'selected-subset';
  else if (first.backupSet.scope !== 'complete-domain-export') completeness = 'unknown';
  else {
    const expected = first.backupSet.expectedGpoCount ?? 0;
    const observed = new Set(resolvedGpoIds).size;
    if (observed > expected) {
      diagnostics.add('gpo-backup-set-count-conflict');
      completeness = 'inconsistent';
      inconsistent = true;
    } else if (observed < expected) {
      diagnostics.add('gpo-backup-set-incomplete');
      completeness = 'unknown';
      indeterminate = true;
    } else completeness = 'complete';
  }

  const status: GpoSnapshotStatus = inconsistent ? 'inconsistent' : indeterminate ? 'indeterminate' : 'consistent';
  const instanceIds = instances.map(instance => instance.id).sort();
  return {
    version: 1,
    id: `gpo-snapshot-${hash(JSON.stringify([groupKey(first), instanceIds]))}`,
    projectId: first.projectId,
    domain: mixedDomains && selectedUpload ? { status: 'unknown' } : first.domain,
    backupSetId,
    collectionWindow: collectionRange,
    instanceIds,
    status,
    completeness,
    permitsSetAbsenceConclusions: status === 'consistent' && completeness === 'complete',
    diagnosticCodes: [...diagnostics].sort(),
    createdAt
  };
}

export function buildGpoAnalysisSnapshots(
  values: GpoBackupInstance[],
  options: GpoSnapshotBuildOptions
): GpoAnalysisSnapshot[] {
  if (!Number.isFinite(Date.parse(options.createdAt))) throw new Error('Der Snapshot-Erstellungszeitpunkt ist ungültig.');
  const maximumCollectionSkewMs = options.maximumCollectionSkewMs ?? 15 * 60 * 1000;
  if (!Number.isInteger(maximumCollectionSkewMs) || maximumCollectionSkewMs < 0 || maximumCollectionSkewMs > 24 * 60 * 60 * 1000) {
    throw new Error('Das zulässige Erhebungszeitfenster ist ungültig.');
  }
  const ids = new Set<string>();
  values.forEach(instance => {
    const errors = gpoBackupInstanceValidationErrors(instance);
    if (errors.length) throw new Error(`Ungültige GPO-Backupinstanz ${instance.id || '<ohne ID>'}: ${errors.join(' ')}`);
    if (ids.has(instance.id)) throw new Error(`Doppelte GPO-Backupinstanz-ID: ${instance.id}.`);
    ids.add(instance.id);
  });
  const sorted = [...values].sort((left, right) => left.id.localeCompare(right.id));
  const grouped = new Map<string, GpoBackupInstance[]>();
  sorted.forEach(instance => {
    const key = groupKey(instance);
    grouped.set(key, [...(grouped.get(key) ?? []), instance]);
  });
  const splitSetIds = domainSplits(sorted);
  return [...grouped.values()]
    .map(group => snapshotForGroup(group, splitSetIds, options.createdAt, maximumCollectionSkewMs))
    .sort((left, right) => left.id.localeCompare(right.id));
}