#!/usr/bin/env php
<?php

/**
 * Usage: git close-pull-request
 *
 * Run this from a branch which has an upstream remote branch, and an associated
 * pull request.
 *
 * The script will merge the branch into master, push master (which will
 * automatically close the pull request), and delete both the local and remote
 * branches.
 *
 * Based on a script by @christoomey. Translated into PHP.
 */

class ClosesPullRequests
{
    private $targetBranch;
    private $localBranch;
    private $remoteBranch;

    private const CI_ERROR = 'error';
    private const CI_PENDING = 'pending';
    private const CI_SUCCESS = 'success';

    public function __construct()
    {
        $this->localBranch = exec('git rev-parse --abbrev-ref HEAD');

        $this->targetBranch = getenv('TARGET_BRANCH');
        if (!$this->targetBranch) {
            die('No target branch specified. Aborting.');
        }

        $this->remoteBranch = exec('git rev-parse --abbrev-ref --symbolic-full-name @{u}');
        $this->remoteBranch = str_replace('origin/', '', $this->remoteBranch);
    }

    public function __invoke(): void
    {
        $this->confirmCiStatusIsPassing();
        // TODO: Check that the current branch has a tracking branch.
        $this->fetchOrigin();
        $this->ensureFeatureBranchInSync();
        $this->ensureTargetBranchInSync();
        $this->checkoutTargetBranch();
        $this->mergeLocalBranch();
        $this->pushTargetBranch();
        $this->deleteRemoteBranch();
        $this->deleteLocalBranch();
    }

    private function confirmCiStatusIsPassing(): void
    {
        echo 'Confirming ci-status on PR is green...' . PHP_EOL;

        // TODO: Check for failures, or skip if there is no CI.
        $errors = [
            self::CI_ERROR => 'Aborting: CI error',
            self::CI_PENDING => 'Aborting: CI pending',
        ];

        if (array_key_exists($status = exec('hub ci-status'), $errors)) {
            die($errors[$status]);
        }
    }

    private function fetchOrigin(): void
    {
        print 'Fetching origin to confirm local and remote in sync...'
            . PHP_EOL;
        exec("git fetch origin");
    }

    private function ensureTargetBranchInSync(): void
    {
        $this->ensureBranchInSyncWithUpstream(
            $this->targetBranch,
            $this->targetBranch
        );
    }

    private function ensureFeatureBranchInSync(): void
    {
        $this->ensureBranchInSyncWithUpstream(
            $this->localBranch,
            $this->remoteBranch
        );
    }

    private function ensureBranchInSyncWithUpstream(
        string $localBranch,
        string $remoteBranch
    ): void {
        echo sprintf(
            'Ensuring that %s is in sync with its upstream...',
            $localBranch
        ) . PHP_EOL;

        $localCommitTip = $this->tipCommitOfBranch($localBranch);
        $remoteCommitTip = $this->tipCommitOfBranch(sprintf(
            'origin/%s',
            $remoteBranch
        ));

        if ($localCommitTip != $remoteCommitTip) {
            die(sprintf(
                'Branch %s was out of date, needs rebasing. Aborting.',
                $localBranch
            ));
        }
    }

    private function tipCommitOfBranch(string $branchName): string
    {
        return exec(sprintf('git rev-parse %s', $branchName));
    }

    private function checkoutTargetBranch(): void
    {
        print sprintf('Checking out %s...' . PHP_EOL, $this->targetBranch);
        exec(sprintf('git checkout %s', $this->targetBranch));
    }

    private function mergeLocalBranch(): void
    {
        echo sprintf(
            'Merging %s into %s...' . PHP_EOL,
            $this->localBranch,
            $this->targetBranch
        );

        exec(sprintf('git merge --ff-only %s', $this->localBranch));
    }

    public function pushTargetBranch(): void
    {
        print(sprintf('Pushing updated %s branch...', $this->targetBranch));
        exec(sprintf('git push origin %s', $this->targetBranch));
    }

    public function deleteRemoteBranch(): void
    {
        echo 'Deleting remote branch...' . PHP_EOL;
        exec(sprintf('git push origin :%s', $this->remoteBranch));
    }

    public function deleteLocalBranch(): void
    {
        echo 'Deleting local branch...' . PHP_EOL;
        exec(sprintf('git branch -d %s', $this->localBranch));
    }
}

(new ClosesPullRequests())->__invoke();