<?php
namespace Psalm\Checker\Statements\Block;

use PhpParser;
use Psalm\Checker\ScopeChecker;
use Psalm\Checker\StatementsChecker;
use Psalm\Checker\Statements\ExpressionChecker;
use Psalm\CodeLocation;
use Psalm\Context;
use Psalm\Issue\ContinueOutsideLoop;
use Psalm\IssueBuffer;
use Psalm\Type;

class SwitchChecker
{
    /**
     * @param   StatementsChecker               $statements_checker
     * @param   PhpParser\Node\Stmt\Switch_     $stmt
     * @param   Context                         $context
     * @param   Context|null                    $loop_context
     * @return  false|null
     */
    public static function check(
        StatementsChecker $statements_checker,
        PhpParser\Node\Stmt\Switch_ $stmt,
        Context $context,
        Context $loop_context = null
    ) {
        $type_candidate_var = null;

        if (ExpressionChecker::check($statements_checker, $stmt->cond, $context) === false) {
            return false;
        }

        if (isset($stmt->cond->inferredType) && array_values($stmt->cond->inferredType->types)[0] instanceof Type\T) {
            /** @var Type\T */
            $type_type = array_values($stmt->cond->inferredType->types)[0];
            $type_candidate_var = $type_type->typeof;
        }

        $original_context = clone $context;

        /** @var array<string,Type\Union>|null */
        $new_vars_in_scope = null;

        /** @var array<string,bool> */
        $new_vars_possibly_in_scope = [];

        /** @var array<string,Type\Union>|null */
        $redefined_vars = null;

        // the last statement always breaks, by default
        $last_case_exit_type = 'break';

        $case_exit_types = new \SplFixedArray(count($stmt->cases));

        $has_default = false;

        // create a map of case statement -> ultimate exit type
        for ($i = count($stmt->cases) - 1; $i >= 0; $i--) {
            $case = $stmt->cases[$i];

            if (ScopeChecker::doesAlwaysReturnOrThrow($case->stmts)) {
                $last_case_exit_type = 'return_throw';
            } elseif (ScopeChecker::doesAlwaysBreakOrContinue($case->stmts, true)) {
                $last_case_exit_type = 'continue';
            } elseif (ScopeChecker::doesAlwaysBreakOrContinue($case->stmts)) {
                $last_case_exit_type = 'break';
            }

            $case_exit_types[$i] = $last_case_exit_type;
        }

        $leftover_statements = [];

        for ($i = count($stmt->cases) - 1; $i >= 0; $i--) {
            $case = $stmt->cases[$i];
            /** @var string */
            $case_exit_type = $case_exit_types[$i];
            $case_type = null;

            if ($case->cond) {
                if (ExpressionChecker::check($statements_checker, $case->cond, $context) === false) {
                    return false;
                }

                if ($type_candidate_var && $case->cond instanceof PhpParser\Node\Scalar\String_) {
                    $case_type = $case->cond->value;
                }
            }

            $switch_vars = $type_candidate_var && $case_type
                            ? [$type_candidate_var => Type::parseString($case_type)]
                            : [];

            $case_context = clone $original_context;

            $case_context->vars_in_scope = array_merge($case_context->vars_in_scope, $switch_vars);
            $case_context->vars_possibly_in_scope = array_merge($case_context->vars_possibly_in_scope, $switch_vars);

            $old_case_context = clone $case_context;

            $case_stmts = $case->stmts;

            // has a return/throw at end
            $has_ending_statements = ScopeChecker::doesAlwaysReturnOrThrow($case_stmts);
            $has_leaving_statements = ScopeChecker::doesAlwaysBreakOrContinue($case_stmts);

            if (!$case_stmts || (!$has_ending_statements && !$has_leaving_statements)) {
                $case_stmts = array_merge($case_stmts, $leftover_statements);
                $has_ending_statements = ScopeChecker::doesAlwaysReturnOrThrow($case_stmts);
            } else {
                $leftover_statements = [];
            }

            $statements_checker->check($case_stmts, $case_context, $loop_context);

            // has a return/throw at end
            $has_ending_statements = ScopeChecker::doesAlwaysReturnOrThrow($case_stmts);

            if ($case_exit_type !== 'return_throw') {
                $vars = array_diff_key(
                    $case_context->vars_possibly_in_scope,
                    $original_context->vars_possibly_in_scope
                );

                // if we're leaving this block, add vars to outer for loop scope
                if ($case_exit_type === 'continue') {
                    if ($loop_context) {
                        $loop_context->vars_possibly_in_scope = array_merge(
                            $vars,
                            $loop_context->vars_possibly_in_scope
                        );
                    } else {
                        if (IssueBuffer::accepts(
                            new ContinueOutsideLoop(
                                'Continue called when not in loop',
                                new CodeLocation($statements_checker->getSource(), $case)
                            )
                        )) {
                            return false;
                        }
                    }
                } else {
                    $case_redefined_vars = Context::getRedefinedVars($original_context, $case_context);

                    Type::redefineGenericUnionTypes($case_redefined_vars, $context);

                    if ($redefined_vars === null) {
                        $redefined_vars = $case_redefined_vars;
                    } else {
                        foreach ($redefined_vars as $redefined_var => $type) {
                            if (!isset($case_redefined_vars[$redefined_var])) {
                                unset($redefined_vars[$redefined_var]);
                            }
                        }
                    }

                    if ($new_vars_in_scope === null) {
                        $new_vars_in_scope = array_diff_key($case_context->vars_in_scope, $context->vars_in_scope);
                        $new_vars_possibly_in_scope = array_diff_key(
                            $case_context->vars_possibly_in_scope,
                            $context->vars_possibly_in_scope
                        );
                    } else {
                        foreach ($new_vars_in_scope as $new_var => $type) {
                            if (!isset($case_context->vars_in_scope[$new_var])) {
                                unset($new_vars_in_scope[$new_var]);
                            }
                        }

                        $new_vars_possibly_in_scope = array_merge(
                            array_diff_key(
                                $case_context->vars_possibly_in_scope,
                                $context->vars_possibly_in_scope
                            ),
                            $new_vars_possibly_in_scope
                        );
                    }
                }
            }

            if ($case->stmts) {
                $leftover_statements = array_merge($leftover_statements, $case->stmts);
            }

            if (!$case->cond) {
                $has_default = true;
            }
        }

        // only update vars if there is a default
        // if that default has a throw/return/continue, that should be handled above
        if ($has_default) {
            if ($new_vars_in_scope) {
                $context->vars_in_scope = array_merge($context->vars_in_scope, $new_vars_in_scope);
            }

            if ($redefined_vars) {
                $context->vars_in_scope = array_merge($context->vars_in_scope, $redefined_vars);
            }
        }

        $context->vars_possibly_in_scope = array_merge($context->vars_possibly_in_scope, $new_vars_possibly_in_scope);
        return null;
    }
}