export type GcsimStatement = { text: string; line: number; source: string };

export class GcsimTextError extends Error {
  constructor(message: string, public line: number, public source: string) {
    super(message);
  }
}

function lineDetails(input: string, position: number) {
  const line = input.slice(0, position).split("\n").length;
  return { line, source: input.split(/\r?\n/)[line - 1]?.trim() ?? "" };
}

// Split only at top level: loops, conditionals, functions and action parameters
// must stay intact. Comments are removed without touching quoted strings.
export function splitGcsimStatementsWithLocations(input: string): GcsimStatement[] {
  const originalInput = input;
  const statements: GcsimStatement[] = [];
  const stack: string[] = [];
  // Replacing comments up front also lets a comment appear before an else.
  input = input.replace(/"(?:\\.|[^"\\])*"|'(?:\\.|[^'\\])*'|#[^\n]*|\/\/[^\n]*/g, (match) => match.startsWith("#") || match.startsWith("//") ? " ".repeat(match.length) : match);
  let text = "";
  let start = 0;
  let quote = "";
  let escaped = false;
  const flush = (end: number) => {
    const leadingWhitespace = text.search(/\S/);
    if (leadingWhitespace >= 0) {
      const position = start + leadingWhitespace;
      const { line, source } = lineDetails(originalInput, position);
      statements.push({ text: text.trim(), line, source });
    }
    text = "";
    start = end;
  };
  for (let i = 0; i < input.length; i++) {
    const char = input[i];
    if (quote) {
      text += char;
      if (escaped) escaped = false;
      else if (char === "\\") escaped = true;
      else if (char === quote) quote = "";
      continue;
    }
    if (char === '"' || char === "'") { quote = char; text += char; continue; }
    if ("([{".includes(char)) {
      stack.push(char);
      if (stack.length > 64) {
        const details = lineDetails(originalInput, i);
        throw new GcsimTextError("Config is nested too deeply.", details.line, details.source);
      }
    } else if (")]}".includes(char)) {
      const expected: Record<string, string> = { ")": "(", "]": "[", "}": "{" };
      if (stack.pop() !== expected[char]) {
        const details = lineDetails(originalInput, i);
        throw new GcsimTextError(`Unmatched '${char}' at position ${i + 1}.`, details.line, details.source);
      }
    }
    text += char;
    if (stack.length === 0 && char === ";") flush(i + 1);
    // Keep an else branch attached to its if statement.
    if (stack.length === 0 && char === "}" && !/^\s*else\b/.test(input.slice(i + 1))) flush(i + 1);
  }
  const trailingPosition = start + Math.max(0, text.search(/\S/));
  const trailing = lineDetails(originalInput, trailingPosition);
  if (quote) throw new GcsimTextError("Unclosed quoted string.", trailing.line, trailing.source);
  if (stack.length) throw new GcsimTextError("Unclosed bracket or parenthesis.", trailing.line, trailing.source);
  if (text.trim()) throw new GcsimTextError("Missing ';' at the end of a statement.", trailing.line, trailing.source);
  return statements;
}

export function splitGcsimStatements(input: string): string[] {
  return splitGcsimStatementsWithLocations(input).map((statement) => statement.text);
}