<?php declare(strict_types=1);

/*
 * This file is part of Composer.
 *
 * (c) Nils Adermann <naderman@naderman.de>
 *     Jordi Boggiano <j.boggiano@seld.be>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Composer\DependencyResolver;

use Composer\Package\AliasPackage;
use Composer\Package\BasePackage;
use Composer\Package\Version\VersionParser;
use Composer\Semver\CompilingMatcher;
use Composer\Semver\Constraint\ConstraintInterface;
use Composer\Semver\Constraint\Constraint;
use Composer\Semver\Constraint\MultiConstraint;
use Composer\Semver\Intervals;

/**
 * Optimizes a given pool
 *
 * @author Yanick Witschi <yanick.witschi@terminal42.ch>
 */
class PoolOptimizer
{
    /**
     * @var PolicyInterface
     */
    private $policy;

    /**
     * @var array<int, true>
     */
    private $irremovablePackages = array();

    /**
     * @var array<string, array<string, ConstraintInterface>>
     */
    private $requireConstraintsPerPackage = array();

    /**
     * @var array<string, array<string, ConstraintInterface>>
     */
    private $conflictConstraintsPerPackage = array();

    /**
     * @var array<int, true>
     */
    private $packagesToRemove = array();

    /**
     * @var array<int, BasePackage[]>
     */
    private $aliasesPerPackage = array();

    /**
     * @var array<string, array<string, string>>
     */
    private $removedVersionsByPackage = array();

    public function __construct(PolicyInterface $policy)
    {
        $this->policy = $policy;
    }

    /**
     * @return Pool
     */
    public function optimize(Request $request, Pool $pool): Pool
    {
        $this->prepare($request, $pool);

        $this->optimizeByIdenticalDependencies($request, $pool);

        $this->optimizeImpossiblePackagesAway($request, $pool);

        $optimizedPool = $this->applyRemovalsToPool($pool);

        // No need to run this recursively at the moment
        // because the current optimizations cannot provide
        // even more gains when ran again. Might change
        // in the future with additional optimizations.

        $this->irremovablePackages = array();
        $this->requireConstraintsPerPackage = array();
        $this->conflictConstraintsPerPackage = array();
        $this->packagesToRemove = array();
        $this->aliasesPerPackage = array();
        $this->removedVersionsByPackage = array();

        return $optimizedPool;
    }

    /**
     * @return void
     */
    private function prepare(Request $request, Pool $pool): void
    {
        $irremovablePackageConstraintGroups = array();

        // Mark fixed or locked packages as irremovable
        foreach ($request->getFixedOrLockedPackages() as $package) {
            $irremovablePackageConstraintGroups[$package->getName()][] = new Constraint('==', $package->getVersion());
        }

        // Extract requested package requirements
        foreach ($request->getRequires() as $require => $constraint) {
            $constraint = Intervals::compactConstraint($constraint);
            $this->requireConstraintsPerPackage[$require][(string) $constraint] = $constraint;
        }

        // First pass over all packages to extract information and mark package constraints irremovable
        foreach ($pool->getPackages() as $package) {
            // Extract package requirements
            foreach ($package->getRequires() as $link) {
                $constraint = Intervals::compactConstraint($link->getConstraint());
                $this->requireConstraintsPerPackage[$link->getTarget()][(string) $constraint] = $constraint;
            }
            // Extract package conflicts
            foreach ($package->getConflicts() as $link) {
                $constraint = Intervals::compactConstraint($link->getConstraint());
                $this->conflictConstraintsPerPackage[$link->getTarget()][(string) $constraint] = $constraint;
            }

            // Keep track of alias packages for every package so if either the alias or aliased is kept
            // we keep the others as they are a unit of packages really
            if ($package instanceof AliasPackage) {
                $this->aliasesPerPackage[$package->getAliasOf()->id][] = $package;
            }
        }

        $irremovablePackageConstraints = array();
        foreach ($irremovablePackageConstraintGroups as $packageName => $constraints) {
            $irremovablePackageConstraints[$packageName] = 1 === \count($constraints) ? $constraints[0] : new MultiConstraint($constraints, false);
        }
        unset($irremovablePackageConstraintGroups);

        // Mark the packages as irremovable based on the constraints
        foreach ($pool->getPackages() as $package) {
            if (!isset($irremovablePackageConstraints[$package->getName()])) {
                continue;
            }

            if (CompilingMatcher::match($irremovablePackageConstraints[$package->getName()], Constraint::OP_EQ, $package->getVersion())) {
                $this->markPackageIrremovable($package);
            }
        }
    }

    /**
     * @return void
     */
    private function markPackageIrremovable(BasePackage $package): void
    {
        $this->irremovablePackages[$package->id] = true;
        if ($package instanceof AliasPackage) {
            // recursing here so aliasesPerPackage for the aliasOf can be checked
            // and all its aliases marked as irremovable as well
            $this->markPackageIrremovable($package->getAliasOf());
        }
        if (isset($this->aliasesPerPackage[$package->id])) {
            foreach ($this->aliasesPerPackage[$package->id] as $aliasPackage) {
                $this->irremovablePackages[$aliasPackage->id] = true;
            }
        }
    }

    /**
     * @return Pool Optimized pool
     */
    private function applyRemovalsToPool(Pool $pool): Pool
    {
        $packages = array();
        $removedVersions = array();
        foreach ($pool->getPackages() as $package) {
            if (!isset($this->packagesToRemove[$package->id])) {
                $packages[] = $package;
            } else {
                $removedVersions[$package->getName()][$package->getVersion()] = $package->getPrettyVersion();
            }
        }

        $optimizedPool = new Pool($packages, $pool->getUnacceptableFixedOrLockedPackages(), $removedVersions, $this->removedVersionsByPackage);

        return $optimizedPool;
    }

    /**
     * @return void
     */
    private function optimizeByIdenticalDependencies(Request $request, Pool $pool): void
    {
        $identicalDefinitionsPerPackage = array();
        $packageIdenticalDefinitionLookup = array();

        foreach ($pool->getPackages() as $package) {

            // If that package was already marked irremovable, we can skip
            // the entire process for it
            if (isset($this->irremovablePackages[$package->id])) {
                continue;
            }

            $this->markPackageForRemoval($package->id);

            $dependencyHash = $this->calculateDependencyHash($package);

            foreach ($package->getNames(false) as $packageName) {
                if (!isset($this->requireConstraintsPerPackage[$packageName])) {
                    continue;
                }

                foreach ($this->requireConstraintsPerPackage[$packageName] as $requireConstraint) {
                    $groupHashParts = array();

                    if (CompilingMatcher::match($requireConstraint, Constraint::OP_EQ, $package->getVersion())) {
                        $groupHashParts[] = 'require:' . (string) $requireConstraint;
                    }

                    if ($package->getReplaces()) {
                        foreach ($package->getReplaces() as $link) {
                            if (CompilingMatcher::match($link->getConstraint(), Constraint::OP_EQ, $package->getVersion())) {
                                // Use the same hash part as the regular require hash because that's what the replacement does
                                $groupHashParts[] = 'require:' . (string) $link->getConstraint();
                            }
                        }
                    }

                    if (isset($this->conflictConstraintsPerPackage[$packageName])) {
                        foreach ($this->conflictConstraintsPerPackage[$packageName] as $conflictConstraint) {
                            if (CompilingMatcher::match($conflictConstraint, Constraint::OP_EQ, $package->getVersion())) {
                                $groupHashParts[] = 'conflict:' . (string) $conflictConstraint;
                            }
                        }
                    }

                    if (!$groupHashParts) {
                        continue;
                    }

                    $groupHash = implode('', $groupHashParts);
                    $identicalDefinitionsPerPackage[$packageName][$groupHash][$dependencyHash][] = $package;
                    $packageIdenticalDefinitionLookup[$package->id][$packageName] = array('groupHash' => $groupHash, 'dependencyHash' => $dependencyHash);
                }
            }
        }

        foreach ($identicalDefinitionsPerPackage as $constraintGroups) {
            foreach ($constraintGroups as $constraintGroup) {
                foreach ($constraintGroup as $packages) {
                    // Only one package in this constraint group has the same requirements, we're not allowed to remove that package
                    if (1 === \count($packages)) {
                        $this->keepPackage($packages[0], $identicalDefinitionsPerPackage, $packageIdenticalDefinitionLookup);
                        continue;
                    }

                    // Otherwise we find out which one is the preferred package in this constraint group which is
                    // then not allowed to be removed either
                    $literals = array();

                    foreach ($packages as $package) {
                        $literals[] = $package->id;
                    }

                    foreach ($this->policy->selectPreferredPackages($pool, $literals) as $preferredLiteral) {
                        $this->keepPackage($pool->literalToPackage($preferredLiteral), $identicalDefinitionsPerPackage, $packageIdenticalDefinitionLookup);
                    }
                }
            }
        }
    }

    /**
     * @return string
     */
    private function calculateDependencyHash(BasePackage $package): string
    {
        $hash = '';

        $hashRelevantLinks = array(
            'requires' => $package->getRequires(),
            'conflicts' => $package->getConflicts(),
            'replaces' => $package->getReplaces(),
            'provides' => $package->getProvides(),
        );

        foreach ($hashRelevantLinks as $key => $links) {
            if (0 === \count($links)) {
                continue;
            }

            // start new hash section
            $hash .= $key . ':';

            $subhash = array();

            foreach ($links as $link) {
                // To get the best dependency hash matches we should use Intervals::compactConstraint() here.
                // However, the majority of projects are going to specify their constraints already pretty
                // much in the best variant possible. In other words, we'd be wasting time here and it would actually hurt
                // performance more than the additional few packages that could be filtered out would benefit the process.
                $subhash[$link->getTarget()] = (string) $link->getConstraint();
            }

            // Sort for best result
            ksort($subhash);

            foreach ($subhash as $target => $constraint) {
                $hash .= $target . '@' . $constraint;
            }
        }

        return $hash;
    }

    /**
     * @param int $id
     * @return void
     */
    private function markPackageForRemoval(int $id): void
    {
        // We are not allowed to remove packages if they have been marked as irremovable
        if (isset($this->irremovablePackages[$id])) {
            throw new \LogicException('Attempted removing a package which was previously marked irremovable');
        }

        $this->packagesToRemove[$id] = true;
    }

    /**
     * @param array<string, array<string, array<string, list<BasePackage>>>> $identicalDefinitionsPerPackage
     * @param array<int, array<string, array{groupHash: string, dependencyHash: string}>> $packageIdenticalDefinitionLookup
     * @return void
     */
    private function keepPackage(BasePackage $package, array $identicalDefinitionsPerPackage, array $packageIdenticalDefinitionLookup): void
    {
        unset($this->packagesToRemove[$package->id]);

        if ($package instanceof AliasPackage) {
            // recursing here so aliasesPerPackage for the aliasOf can be checked
            // and all its aliases marked to be kept as well
            $this->keepPackage($package->getAliasOf(), $identicalDefinitionsPerPackage, $packageIdenticalDefinitionLookup);
        }

        // record all the versions of the package group so we can list them later in Problem output
        foreach ($package->getNames(false) as $name) {
            if (isset($packageIdenticalDefinitionLookup[$package->id][$name])) {
                $packageGroupPointers = $packageIdenticalDefinitionLookup[$package->id][$name];
                $packageGroup = $identicalDefinitionsPerPackage[$name][$packageGroupPointers['groupHash']][$packageGroupPointers['dependencyHash']];
                foreach ($packageGroup as $pkg) {
                    if ($pkg instanceof AliasPackage && $pkg->getPrettyVersion() === VersionParser::DEFAULT_BRANCH_ALIAS) {
                        $pkg = $pkg->getAliasOf();
                    }
                    $this->removedVersionsByPackage[spl_object_hash($package)][$pkg->getVersion()] = $pkg->getPrettyVersion();
                }
            }
        }

        if (isset($this->aliasesPerPackage[$package->id])) {
            foreach ($this->aliasesPerPackage[$package->id] as $aliasPackage) {
                unset($this->packagesToRemove[$aliasPackage->id]);

                // record all the versions of the package group so we can list them later in Problem output
                foreach ($aliasPackage->getNames(false) as $name) {
                    if (isset($packageIdenticalDefinitionLookup[$aliasPackage->id][$name])) {
                        $packageGroupPointers = $packageIdenticalDefinitionLookup[$aliasPackage->id][$name];
                        $packageGroup = $identicalDefinitionsPerPackage[$name][$packageGroupPointers['groupHash']][$packageGroupPointers['dependencyHash']];
                        foreach ($packageGroup as $pkg) {
                            if ($pkg instanceof AliasPackage && $pkg->getPrettyVersion() === VersionParser::DEFAULT_BRANCH_ALIAS) {
                                $pkg = $pkg->getAliasOf();
                            }
                            $this->removedVersionsByPackage[spl_object_hash($aliasPackage)][$pkg->getVersion()] = $pkg->getPrettyVersion();
                        }
                    }
                }
            }
        }
    }

    /**
     * Use the list of locked packages to constrain the loaded packages
     * This will reduce packages with significant numbers of historical versions to a smaller number
     * and reduce the resulting rule set that is generated
     *
     * @return void
     */
    private function optimizeImpossiblePackagesAway(Request $request, Pool $pool): void
    {
        if (count($request->getLockedPackages()) === 0) {
            return;
        }

        $packageIndex = array();

        foreach ($pool->getPackages() as $package) {
            $id = $package->id;

            // Do not remove irremovable packages
            if (isset($this->irremovablePackages[$id])) {
                continue;
            }
            // Do not remove a package aliased by another package, nor aliases
            if (isset($this->aliasesPerPackage[$id]) || $package instanceof AliasPackage) {
                continue;
            }
            // Do not remove locked packages
            if ($request->isFixedPackage($package) || $request->isLockedPackage($package)) {
                continue;
            }

            $packageIndex[$package->getName()][$package->id] = $package;
        }

        foreach ($request->getLockedPackages() as $package) {
            // If this locked package is no longer required by root or anything in the pool, it may get uninstalled so do not apply its requirements
            // In a case where a requirement WERE to appear in the pool by a package that would not be used, it would've been unlocked and so not filtered still
            $isUnusedPackage = true;
            foreach ($package->getNames(false) as $packageName) {
                if (isset($this->requireConstraintsPerPackage[$packageName])) {
                    $isUnusedPackage = false;
                    break;
                }
            }

            if ($isUnusedPackage) {
                continue;
            }

            foreach ($package->getRequires() as $link) {
                $require = $link->getTarget();
                if (!isset($packageIndex[$require])) {
                    continue;
                }

                $linkConstraint = $link->getConstraint();
                foreach ($packageIndex[$require] as $id => $requiredPkg) {
                    if (false === CompilingMatcher::match($linkConstraint, Constraint::OP_EQ, $requiredPkg->getVersion())) {
                        $this->markPackageForRemoval($id);
                        unset($packageIndex[$require][$id]);
                    }
                }
            }
        }
    }
}