/**
 * A word whose value is text with provenance- this literal value appeared in the source
 * code, and was not the result of any backslash, variable, or command substitutions.
 *
 * This provides a level of intentionality that commands can use to distinguish switches:
 *
 * ```tcl
 * puts -stderr text ;# -stderr can be interpreted as a flag and is not part of the message to print
 * puts "-stderr" text ;# -stderr is not a flag, but is part of the message to print
 * puts $var text ;# The value of $var is part of the message to print, even if the value happens to be "-stderr"
 * ```
 */
export type EnchantedWord = {
  enchanted: string;
};

/**
 * A word whose value is plain text, with no special provenance.
 */
export type TextWord = {
  text: string;
};

/**
 * A word whose value is "safe" HTML using allowlisted elements/attributes/styles,
 * suitable for inclusion in HTML output with no escaping.
 */
export type HtmlWord = {
  html: string;
};

export type TextPiece = TextWord;
export type VariablePiece = { variable: string };
export type CommandPiece = { command: unknown };
export type InterpolatedPiece = TextPiece | VariablePiece | CommandPiece;

/**
 * A word whose value needs to be determined by evaluating some combination of variable and command
 * substitutions, and concatenating the results with any literal spans.
 */
export type InterpolatedWord = {
  pieces: InterpolatedPiece[];
};

function IsTextPiece(piece: InterpolatedPiece | undefined): piece is TextPiece {
  return piece ? "text" in piece : false;
}

// safely concatenate text pieces, converting as needed
export function Concat(left: TextPiece, right: TextPiece) {
  return { text: left.text + right.text };
}

export function SimplifyWord(
  pieces: InterpolatedPiece[]
): InterpolatedWord | TextWord {
  const consolidated: InterpolatedPiece[] = [];
  for (const piece of pieces) {
    const top = consolidated[consolidated.length - 1];
    if (IsTextPiece(top) && IsTextPiece(piece)) {
      consolidated[consolidated.length - 1] = Concat(top, piece);
    } else {
      consolidated.push(piece);
    }
  }

  if (consolidated.length == 0) {
    return { text: "" };
  } else if (consolidated.length == 1 && IsTextPiece(consolidated[0])) {
    return consolidated[0];
  } else {
    return { pieces: consolidated };
  }
}

export type Word = EnchantedWord | TextWord | HtmlWord | InterpolatedWord;