<?php declare(strict_types = 1);

namespace SlevomatCodingStandard\Sniffs\Variables;

use PHP_CodeSniffer\Files\File;
use PHP_CodeSniffer\Sniffs\Sniff;
use SlevomatCodingStandard\Helpers\FixerHelper;
use SlevomatCodingStandard\Helpers\ScopeHelper;
use SlevomatCodingStandard\Helpers\TokenHelper;
use function array_keys;
use function array_reverse;
use function count;
use function in_array;
use function preg_match;
use function preg_quote;
use function sprintf;
use const T_AND_EQUAL;
use const T_BITWISE_AND;
use const T_CLOSE_CURLY_BRACKET;
use const T_CONCAT_EQUAL;
use const T_DIV_EQUAL;
use const T_DO;
use const T_DOC_COMMENT_CLOSE_TAG;
use const T_DOUBLE_COLON;
use const T_ELSEIF;
use const T_EQUAL;
use const T_FOR;
use const T_FOREACH;
use const T_IF;
use const T_MINUS_EQUAL;
use const T_MOD_EQUAL;
use const T_MUL_EQUAL;
use const T_OPEN_CURLY_BRACKET;
use const T_OPEN_PARENTHESIS;
use const T_OR_EQUAL;
use const T_PLUS_EQUAL;
use const T_POW_EQUAL;
use const T_RETURN;
use const T_SEMICOLON;
use const T_SL_EQUAL;
use const T_SR_EQUAL;
use const T_STATIC;
use const T_STRING;
use const T_SWITCH;
use const T_VARIABLE;
use const T_WHILE;
use const T_XOR_EQUAL;

class UselessVariableSniff implements Sniff
{

	public const CODE_USELESS_VARIABLE = 'UselessVariable';

	/**
	 * @return array<int, (int|string)>
	 */
	public function register(): array
	{
		return [
			T_RETURN,
		];
	}

	/**
	 * @phpcsSuppress SlevomatCodingStandard.TypeHints.ParameterTypeHint.MissingNativeTypeHint
	 * @param int $returnPointer
	 */
	public function process(File $phpcsFile, $returnPointer): void
	{
		$tokens = $phpcsFile->getTokens();

		/** @var int $variablePointer */
		$variablePointer = TokenHelper::findNextEffective($phpcsFile, $returnPointer + 1);
		if ($tokens[$variablePointer]['code'] !== T_VARIABLE) {
			return;
		}

		$returnSemicolonPointer = TokenHelper::findNextEffective($phpcsFile, $variablePointer + 1);
		if ($tokens[$returnSemicolonPointer]['code'] !== T_SEMICOLON) {
			return;
		}

		$variableName = $tokens[$variablePointer]['content'];

		$functionPointer = $this->findFunctionPointer($phpcsFile, $variablePointer);

		if ($functionPointer !== null) {
			if ($this->isReturnedByReference($phpcsFile, $functionPointer)) {
				return;
			}

			if ($this->isStaticVariable($phpcsFile, $functionPointer, $variablePointer, $variableName)) {
				return;
			}

			if ($this->isFunctionParameter($phpcsFile, $functionPointer, $variableName)) {
				return;
			}
		}

		$previousVariablePointer = $this->findPreviousVariablePointer($phpcsFile, $returnPointer, $variableName);
		if ($previousVariablePointer === null) {
			return;
		}

		if (!$this->isAssignmentToVariable($phpcsFile, $previousVariablePointer)) {
			return;
		}

		if ($this->isAssignedInControlStructure($phpcsFile, $previousVariablePointer)) {
			return;
		}

		if ($this->isAssignedInFunctionCall($phpcsFile, $previousVariablePointer)) {
			return;
		}

		if ($this->hasVariableVarAnnotation($phpcsFile, $previousVariablePointer)) {
			return;
		}

		if ($this->hasAnotherAssignmentBefore($phpcsFile, $previousVariablePointer, $variableName)) {
			return;
		}

		if (!$this->areBothPointersNearby($phpcsFile, $previousVariablePointer, $returnPointer)) {
			return;
		}

		$errorParameters = [
			sprintf('Useless variable %s.', $variableName),
			$previousVariablePointer,
			self::CODE_USELESS_VARIABLE,
		];

		$pointerBeforePreviousVariable = TokenHelper::findPreviousEffective($phpcsFile, $previousVariablePointer - 1);

		if (
			!in_array($tokens[$pointerBeforePreviousVariable]['code'], [T_SEMICOLON, T_OPEN_CURLY_BRACKET, T_CLOSE_CURLY_BRACKET], true)
			&& TokenHelper::findNextEffective($phpcsFile, $returnSemicolonPointer + 1) !== null
		) {
			$phpcsFile->addError(...$errorParameters);
			return;
		}

		$fix = $phpcsFile->addFixableError(...$errorParameters);

		if (!$fix) {
			return;
		}

		/** @var int $assignmentPointer */
		$assignmentPointer = TokenHelper::findNextEffective($phpcsFile, $previousVariablePointer + 1);

		$assignmentFixerMapping = [
			T_PLUS_EQUAL => '+',
			T_MINUS_EQUAL => '-',
			T_MUL_EQUAL => '*',
			T_DIV_EQUAL => '/',
			T_POW_EQUAL => '**',
			T_MOD_EQUAL => '%',
			T_AND_EQUAL => '&',
			T_OR_EQUAL => '|',
			T_XOR_EQUAL => '^',
			T_SL_EQUAL => '<<',
			T_SR_EQUAL => '>>',
			T_CONCAT_EQUAL => '.',
		];

		$previousVariableSemicolonPointer = $this->findSemicolon($phpcsFile, $previousVariablePointer);

		$phpcsFile->fixer->beginChangeset();

		if ($tokens[$assignmentPointer]['code'] === T_EQUAL) {
			FixerHelper::change($phpcsFile, $previousVariablePointer, $assignmentPointer, 'return');
		} else {
			FixerHelper::addBefore($phpcsFile, $previousVariablePointer, 'return ');
			FixerHelper::replace($phpcsFile, $assignmentPointer, $assignmentFixerMapping[$tokens[$assignmentPointer]['code']]);
		}

		FixerHelper::removeBetweenIncluding($phpcsFile, $previousVariableSemicolonPointer + 1, $returnSemicolonPointer);

		$phpcsFile->fixer->endChangeset();
	}

	private function findPreviousVariablePointer(File $phpcsFile, int $pointer, string $variableName): ?int
	{
		$tokens = $phpcsFile->getTokens();

		for ($i = $pointer - 1; $i >= 0; $i--) {
			if (
				in_array($tokens[$i]['code'], TokenHelper::FUNCTION_TOKEN_CODES, true)
				&& ScopeHelper::isInSameScope($phpcsFile, $tokens[$i]['scope_opener'] + 1, $pointer)
			) {
				return null;
			}

			if ($tokens[$i]['code'] !== T_VARIABLE) {
				continue;
			}

			if ($tokens[$i]['content'] !== $variableName) {
				continue;
			}

			$previousPointer = TokenHelper::findPreviousEffective($phpcsFile, $i - 1);
			if ($tokens[$previousPointer]['code'] === T_DOUBLE_COLON) {
				continue;
			}

			if (!ScopeHelper::isInSameScope($phpcsFile, $i, $pointer)) {
				continue;
			}

			return $i;
		}

		return null;
	}

	private function isAssignedInControlStructure(File $phpcsFile, int $pointer): bool
	{
		$controlStructure = TokenHelper::findPrevious($phpcsFile, [
			T_WHILE,
			T_FOR,
			T_FOREACH,
			T_SWITCH,
			T_IF,
			T_ELSEIF,
		], $pointer - 1);

		if ($controlStructure === null) {
			return false;
		}

		$tokens = $phpcsFile->getTokens();

		return $tokens[$controlStructure]['parenthesis_opener'] < $pointer && $pointer < $tokens[$controlStructure]['parenthesis_closer'];
	}

	private function isAssignedInFunctionCall(File $phpcsFile, int $pointer): bool
	{
		$possibleFunctionNamePointer = TokenHelper::findPrevious($phpcsFile, T_STRING, $pointer - 1);

		if ($possibleFunctionNamePointer === null) {
			return false;
		}

		$tokens = $phpcsFile->getTokens();

		$parenthesisOpenerPointer = TokenHelper::findNextEffective($phpcsFile, $possibleFunctionNamePointer + 1);
		if ($tokens[$parenthesisOpenerPointer]['code'] !== T_OPEN_PARENTHESIS) {
			return false;
		}

		return $parenthesisOpenerPointer < $pointer && $pointer < $tokens[$parenthesisOpenerPointer]['parenthesis_closer'];
	}

	private function isAssignmentToVariable(File $phpcsFile, int $pointer): bool
	{
		$assignmentPointer = TokenHelper::findNextEffective($phpcsFile, $pointer + 1);
		return in_array($phpcsFile->getTokens()[$assignmentPointer]['code'], [
			T_EQUAL,
			T_PLUS_EQUAL,
			T_MINUS_EQUAL,
			T_MUL_EQUAL,
			T_DIV_EQUAL,
			T_POW_EQUAL,
			T_MOD_EQUAL,
			T_AND_EQUAL,
			T_OR_EQUAL,
			T_XOR_EQUAL,
			T_SL_EQUAL,
			T_SR_EQUAL,
			T_CONCAT_EQUAL,
		], true);
	}

	private function findFunctionPointer(File $phpcsFile, int $pointer): ?int
	{
		$tokens = $phpcsFile->getTokens();

		foreach (array_reverse($tokens[$pointer]['conditions'], true) as $conditionPointer => $conditionTokenCode) {
			if (in_array($conditionTokenCode, TokenHelper::FUNCTION_TOKEN_CODES, true)) {
				return $conditionPointer;
			}
		}

		return null;
	}

	private function isStaticVariable(File $phpcsFile, int $functionPointer, int $variablePointer, string $variableName): bool
	{
		$tokens = $phpcsFile->getTokens();

		for ($i = $tokens[$functionPointer]['scope_opener'] + 1; $i < $variablePointer; $i++) {
			if ($tokens[$i]['code'] !== T_VARIABLE) {
				continue;
			}
			if ($tokens[$i]['content'] !== $variableName) {
				continue;
			}

			$pointerBeforeParameter = TokenHelper::findPreviousEffective($phpcsFile, $i - 1);
			if ($tokens[$pointerBeforeParameter]['code'] === T_STATIC) {
				return true;
			}
		}

		return false;
	}

	private function isFunctionParameter(File $phpcsFile, int $functionPointer, string $variableName): bool
	{
		$tokens = $phpcsFile->getTokens();

		for ($i = $tokens[$functionPointer]['parenthesis_opener'] + 1; $i < $tokens[$functionPointer]['parenthesis_closer']; $i++) {
			if ($tokens[$i]['code'] !== T_VARIABLE) {
				continue;
			}
			if ($tokens[$i]['content'] !== $variableName) {
				continue;
			}

			return true;
		}

		return false;
	}

	private function isReturnedByReference(File $phpcsFile, int $functionPointer): bool
	{
		$tokens = $phpcsFile->getTokens();

		$referencePointer = TokenHelper::findNextEffective($phpcsFile, $functionPointer + 1);
		return $tokens[$referencePointer]['code'] === T_BITWISE_AND;
	}

	private function hasVariableVarAnnotation(File $phpcsFile, int $variablePointer): bool
	{
		$tokens = $phpcsFile->getTokens();

		$pointerBeforeVariable = TokenHelper::findPreviousNonWhitespace($phpcsFile, $variablePointer - 1);
		if ($tokens[$pointerBeforeVariable]['code'] !== T_DOC_COMMENT_CLOSE_TAG) {
			return false;
		}

		$docCommentContent = TokenHelper::getContent($phpcsFile, $tokens[$pointerBeforeVariable]['comment_opener'], $pointerBeforeVariable);
		return preg_match(
			'~@(?:(?:phpstan|psalm)-)?var\\s+.+\\s+' . preg_quote($tokens[$variablePointer]['content'], '~') . '(?:\\s|$)~',
			$docCommentContent,
		) !== 0;
	}

	private function hasAnotherAssignmentBefore(File $phpcsFile, int $variablePointer, string $variableName): bool
	{
		$previousVariablePointer = $this->findPreviousVariablePointer($phpcsFile, $variablePointer, $variableName);
		if ($previousVariablePointer === null) {
			return false;
		}

		if (!$this->isAssignmentToVariable($phpcsFile, $previousVariablePointer)) {
			return false;
		}

		return $this->areBothVariablesNearby($phpcsFile, $previousVariablePointer, $variablePointer);
	}

	private function areBothPointersNearby(File $phpcsFile, int $firstPointer, int $secondPointer): bool
	{
		$firstVariableSemicolonPointer = $this->findSemicolon($phpcsFile, $firstPointer);
		$pointerAfterFirstVariableSemicolon = TokenHelper::findNextEffective($phpcsFile, $firstVariableSemicolonPointer + 1);

		return $pointerAfterFirstVariableSemicolon === $secondPointer;
	}

	private function areBothVariablesNearby(File $phpcsFile, int $firstVariablePointer, int $secondVariablePointer): bool
	{
		if ($this->areBothPointersNearby($phpcsFile, $firstVariablePointer, $secondVariablePointer)) {
			return true;
		}

		$tokens = $phpcsFile->getTokens();

		$lastConditionPointer = array_reverse(array_keys($tokens[$firstVariablePointer]['conditions']))[0];
		$lastConditionScopeCloserPointer = $tokens[$lastConditionPointer]['scope_closer'];
		if ($tokens[$lastConditionPointer]['code'] === T_DO) {
			$lastConditionScopeCloserPointer = TokenHelper::findNext($phpcsFile, T_SEMICOLON, $lastConditionScopeCloserPointer + 1);
		}

		return TokenHelper::findNextEffective($phpcsFile, $lastConditionScopeCloserPointer + 1) === $secondVariablePointer;
	}

	private function findSemicolon(File $phpcsFile, int $pointer): int
	{
		$tokens = $phpcsFile->getTokens();

		$semicolonPointer = null;
		for ($i = $pointer + 1; $i < count($tokens) - 1; $i++) {
			if ($tokens[$i]['code'] !== T_SEMICOLON) {
				continue;
			}

			if (!ScopeHelper::isInSameScope($phpcsFile, $pointer, $i)) {
				continue;
			}

			$semicolonPointer = $i;
			break;
		}

		/** @var int $semicolonPointer */
		$semicolonPointer = $semicolonPointer;
		return $semicolonPointer;
	}

}