<?php

namespace Program;

use RuntimeException;

class ProgramParser
{
	public function parseFile(string $filename): Program
	{
		$lines = explode(PHP_EOL, file_get_contents($filename));
		$lines = array_filter($lines);

		return $this->parse($lines);
	}


	public function parse(array $lines): Program
	{
		// In the first parsing stage, all words are parsed from the file.
		/** @var Word[] $words */
		$words = [];
		foreach ($lines as $line) {
			$characters = str_split(trim($line) . ' ');
			$state = 'NONE';
			$wordBuffer = [];
			foreach ($characters as $character) {
				if ('READING' === $state) {
					if ('-' === $character || is_numeric($character)) {
						$wordBuffer['value'] .= $character;
						continue;
					}
					// Word is finished
					$words[] = new Word($wordBuffer['register'], $wordBuffer['value']);
					$wordBuffer = [];
					$state = 'NONE';
					continue;
				}

				if ('NONE' === $state && ctype_alpha($character)) {
					$state = 'READING';
					$wordBuffer = ['register' => $character, 'value' => ''];
					continue;
				}

				if (stripos($line, 'EOF') !== false) {
					break 2; // End of program reached
				}

				if (';' === $character) {
					break; // Rest of line is a comment
				}
			}
		}

		// In the second stage, the words are ordered by N numbers
		// and shaped into a program
		$firstWord = array_shift($words);
		if (!preg_match('/^N9\d\d\d$/i', $firstWord)) {
			throw new RuntimeException('Expected program number, got ' . $firstWord);
		}
		$program = new Program($firstWord->value);
		$lineBuffer = null;
		foreach ($words as $word) {
			if ($word->register === 'N') {
				if (!is_null($lineBuffer)) {
					$program->addBlock($lineBuffer);
				}
				$lineBuffer = new Block($word->value);
				continue;
			}
			$lineBuffer->addWord($word);
		}

		return $program;
	}
}