'use strict';

/* Expose. */
module.exports = factory;

/* Factory. */
function factory(file) {
  var contents = indices(String(file));

  return {
    toPosition: offsetToPositionFactory(contents),
    toOffset: positionToOffsetFactory(contents)
  };
}

/* Factory to get the line and column-based `position` for
 * `offset` in the bound indices. */
function offsetToPositionFactory(indices) {
  return offsetToPosition;

  /* Get the line and column-based `position` for
   * `offset` in the bound indices. */
  function offsetToPosition(offset) {
    var index = -1;
    var length = indices.length;

    if (offset < 0) {
      return {};
    }

    while (++index < length) {
      if (indices[index] > offset) {
        return {
          line: index + 1,
          column: (offset - (indices[index - 1] || 0)) + 1,
          offset: offset
        };
      }
    }

    return {};
  }
}

/* Factory to get the `offset` for a line and column-based
 * `position` in the bound indices. */
function positionToOffsetFactory(indices) {
  return positionToOffset;

  /* Get the `offset` for a line and column-based
   * `position` in the bound indices. */
  function positionToOffset(position) {
    var line = position && position.line;
    var column = position && position.column;

    if (!isNaN(line) && !isNaN(column) && line - 1 in indices) {
      return ((indices[line - 2] || 0) + column - 1) || 0;
    }

    return -1;
  }
}

/* Get indices of line-breaks in `value`. */
function indices(value) {
  var result = [];
  var index = value.indexOf('\n');

  while (index !== -1) {
    result.push(index + 1);
    index = value.indexOf('\n', index + 1);
  }

  result.push(value.length + 1);

  return result;
}