import type { SourceKind } from './worker/onenote.client.js';

export const MAX_SOURCE_FILE_BYTES = 512 * 1024 * 1024;
export const MAX_SOURCE_PARTS = 256;

export interface SourceFileDescriptor {
  name: string;
  size: number;
}

interface SourceFileSelectionFailure {
  ok: false;
  title: string;
  message: string;
}

export type SourceFileSelection<T extends SourceFileDescriptor> =
  | {
      ok: true;
      kind: 'one';
      source: T;
      cabinetParts: [];
    }
  | {
      ok: true;
      kind: 'onepkg';
      source: T;
      cabinetParts: T[];
    }
  | SourceFileSelectionFailure;

export function sourceKindFromFileName(fileName: string): SourceKind | null {
  const normalized = fileName.toLocaleLowerCase('en-US');
  if (normalized.endsWith('.onepkg')) return 'onepkg';
  if (normalized.endsWith('.one')) return 'one';
  return null;
}

export function isCabinetPartFileName(fileName: string): boolean {
  return fileName.toLocaleLowerCase('en-US').endsWith('.cab');
}

export function selectSourceFiles<T extends SourceFileDescriptor>(
  files: readonly T[]
): SourceFileSelection<T> {
  if (files.length === 0) {
    return invalidSelection();
  }
  if (files.length > MAX_SOURCE_PARTS) {
    return {
      ok: false,
      title: 'Too many package parts',
      message: `Choose at most ${MAX_SOURCE_PARTS} files for one cabinet set.`,
    };
  }

  const sections: T[] = [];
  const packages: T[] = [];
  const cabinetParts: T[] = [];
  for (const file of files) {
    const kind = sourceKindFromFileName(file.name);
    if (kind === 'one') sections.push(file);
    else if (kind === 'onepkg') packages.push(file);
    else if (isCabinetPartFileName(file.name)) cabinetParts.push(file);
    else {
      return {
        ok: false,
        title: 'Unsupported file name',
        message:
          'Choose one .one file, or one .onepkg file together with its .cab parts.',
      };
    }
  }

  const validSection =
    sections.length === 1 && packages.length === 0 && cabinetParts.length === 0;
  const validPackage = sections.length === 0 && packages.length === 1;
  if (!validSection && !validPackage) return invalidSelection();

  const seenNames = new Set<string>();
  let totalSize = 0;
  for (const file of files) {
    const nameKey = file.name.normalize('NFC').toLocaleLowerCase('en-US');
    if (seenNames.has(nameKey)) {
      return {
        ok: false,
        title: 'Duplicate file name',
        message: `The selection contains more than one file named ${file.name}.`,
      };
    }
    seenNames.add(nameKey);
    if (!Number.isSafeInteger(file.size) || file.size < 0) {
      return {
        ok: false,
        title: 'Invalid file size',
        message: `The browser reported an invalid size for ${file.name}.`,
      };
    }
    if (file.size > MAX_SOURCE_FILE_BYTES) {
      return {
        ok: false,
        title: 'File is too large',
        message: `${file.name} exceeds the current 512 MiB safety limit.`,
      };
    }
    totalSize += file.size;
    if (!Number.isSafeInteger(totalSize) || totalSize > MAX_SOURCE_FILE_BYTES) {
      return {
        ok: false,
        title: 'Package set is too large',
        message:
          'The selected .onepkg and .cab files exceed the combined 512 MiB safety limit.',
      };
    }
  }

  if (validSection) {
    return { ok: true, kind: 'one', source: sections[0]!, cabinetParts: [] };
  }
  return {
    ok: true,
    kind: 'onepkg',
    source: packages[0]!,
    cabinetParts,
  };
}

function invalidSelection(): SourceFileSelectionFailure {
  return {
    ok: false,
    title: 'Choose one OneNote source',
    message:
      'Choose one .one file, or one .onepkg file together with its .cab parts.',
  };
}