/**
 * CSV import/export -- hand-written, no library.
 *
 * Export follows RFC 4180: fields containing the delimiter, a double quote, CR
 * or LF are wrapped in double quotes and inner quotes are doubled. Line ending
 * is CRLF, optional UTF-8 BOM for Excel. Delimiter is "," or ";".
 *
 * Import: a small state-machine parser that understands quoted fields with
 * embedded delimiters / newlines, plus delimiter sniffing and de/en locale
 * number normalisation. A leading "=" makes the cell a formula.
 */

import type { DocumentStore } from '../store/document';
import { rawString } from '../store/format';

export type Delimiter = ',' | ';' | '\t';

export interface CsvExportOptions {
  delimiter: Delimiter;
  bom: boolean;
  crlf: boolean;
}

// ---- export --------------------------------------------------------------

function needsQuoting(field: string, delimiter: string): boolean {
  return (
    field.includes(delimiter) ||
    field.includes('"') ||
    field.includes('\n') ||
    field.includes('\r')
  );
}

function quoteField(field: string, delimiter: string): string {
  if (!needsQuoting(field, delimiter)) return field;
  return `"${field.replace(/"/g, '""')}"`;
}

/** Bounding box of the used area of a sheet. */
function usedBounds(cells: Record<string, string>): { rows: number; cols: number } {
  let rows = 0;
  let cols = 0;
  for (const key of Object.keys(cells)) {
    const [c, r] = key.split(',').map(Number);
    if (c + 1 > cols) cols = c + 1;
    if (r + 1 > rows) rows = r + 1;
  }
  return { rows, cols };
}

export function tableToCsv(
  store: DocumentStore,
  tableId: string,
  opts: CsvExportOptions,
): string {
  const table = store.tableById(tableId);
  if (!table) return '';
  const bounds = usedBounds(table.cells);
  const rows = Math.max(bounds.rows, 1);
  const cols = Math.max(bounds.cols, 1);
  const eol = opts.crlf ? '\r\n' : '\n';

  const lines: string[] = [];
  for (let r = 0; r < rows; r++) {
    const fields: string[] = [];
    for (let c = 0; c < cols; c++) {
      const value = rawString(store.cellValue(tableId, c, r));
      fields.push(quoteField(value, opts.delimiter));
    }
    lines.push(fields.join(opts.delimiter));
  }
  return (opts.bom ? '' : '') + lines.join(eol) + eol;
}

// ---- import --------------------------------------------------------------

export function sniffDelimiter(text: string): Delimiter {
  const firstLine = text.slice(0, text.search(/\r?\n/) >>> 0 || text.length);
  const counts: Record<Delimiter, number> = { ',': 0, ';': 0, '\t': 0 };
  let inQuotes = false;
  for (const ch of firstLine) {
    if (ch === '"') inQuotes = !inQuotes;
    else if (!inQuotes && (ch === ',' || ch === ';' || ch === '\t')) counts[ch]++;
  }
  const best = (Object.keys(counts) as Delimiter[]).sort(
    (a, b) => counts[b] - counts[a],
  )[0];
  return counts[best] > 0 ? best : ',';
}

/** RFC-4180-ish parser. Returns a matrix of raw string cells. */
export function parseCsv(text: string, delimiter: Delimiter): string[][] {
  const rows: string[][] = [];
  let row: string[] = [];
  let field = '';
  let inQuotes = false;
  let i = 0;
  const n = text.length;
  // strip BOM
  if (text.charCodeAt(0) === 0xfeff) i = 1;

  const endField = () => {
    row.push(field);
    field = '';
  };
  const endRow = () => {
    endField();
    rows.push(row);
    row = [];
  };

  while (i < n) {
    const ch = text[i];
    if (inQuotes) {
      if (ch === '"') {
        if (text[i + 1] === '"') {
          field += '"';
          i += 2;
          continue;
        }
        inQuotes = false;
        i++;
        continue;
      }
      field += ch;
      i++;
      continue;
    }
    if (ch === '"') {
      inQuotes = true;
      i++;
      continue;
    }
    if (ch === delimiter) {
      endField();
      i++;
      continue;
    }
    if (ch === '\r') {
      if (text[i + 1] === '\n') i++;
      endRow();
      i++;
      continue;
    }
    if (ch === '\n') {
      endRow();
      i++;
      continue;
    }
    field += ch;
    i++;
  }
  // trailing field / row (unless the file ended exactly on a newline)
  if (field !== '' || row.length > 0) endRow();
  return rows;
}

const DE_NUMBER = /^-?\d{1,3}(\.\d{3})+(,\d+)?$|^-?\d+,\d+$/;
const EN_NUMBER = /^-?\d{1,3}(,\d{3})+(\.\d+)?$|^-?\d+\.\d+$/;

/** Normalise a locale-formatted number to a plain JS number literal string. */
export function normalizeNumber(value: string): string {
  const v = value.trim();
  if (v === '' || v.startsWith('=')) return value;
  if (/^-?\d+$/.test(v)) return v;
  if (DE_NUMBER.test(v)) return v.replace(/\./g, '').replace(',', '.');
  if (EN_NUMBER.test(v)) return v.replace(/,/g, '');
  return value;
}

export interface CsvToCellsResult {
  cells: Record<string, string>;
  rows: number;
  cols: number;
}

export function matrixToCells(
  matrix: string[][],
  detectNumbers = true,
): CsvToCellsResult {
  const cells: Record<string, string> = {};
  let cols = 0;
  matrix.forEach((line, r) => {
    if (line.length > cols) cols = line.length;
    line.forEach((cell, c) => {
      let raw = cell;
      if (detectNumbers) raw = normalizeNumber(raw);
      if (raw !== '') cells[`${c},${r}`] = raw;
    });
  });
  return { cells, rows: matrix.length, cols: Math.max(cols, 1) };
}