import { execFileSync } from 'node:child_process';
import { readFile } from 'node:fs/promises';
import { join } from 'node:path';

import {
    type CompatibilityDiagnostic,
    getCompatibilityDiagnostics,
} from '../src/lib/cssBrowserCompatibility';

interface PullRequestEvent {
    pull_request: {
        base: { sha: string };
        head: { sha: string };
        number: number;
    };
}

interface PullRequestFile {
    filename: string;
    previous_filename?: string;
    status: 'added' | 'copied' | 'modified' | 'removed' | 'renamed' | 'unchanged';
}

interface ContentResponse {
    content: string;
    encoding: string;
    sha: string;
}

interface GitBlobResponse {
    content: string;
    encoding: string;
}

class GitHubRequestError extends Error {
    constructor(
        readonly status: number,
        message: string
    ) {
        super(message);
    }
}

class GitHubApi {
    constructor(
        private readonly repository: string,
        private readonly token: string
    ) {}

    private async request<T>(path: string, init?: RequestInit): Promise<T> {
        const response = await fetch(`https://api.github.com${path}`, {
            ...init,
            headers: {
                Accept: 'application/vnd.github+json',
                Authorization: `Bearer ${this.token}`,
                'Content-Type': 'application/json',
                'X-GitHub-Api-Version': '2022-11-28',
                ...init?.headers,
            },
        });
        const responseText = await response.text();

        if (!response.ok) {
            throw new GitHubRequestError(
                response.status,
                `${init?.method ?? 'GET'} ${path} failed: ${responseText}`
            );
        }

        return JSON.parse(responseText) as T;
    }

    async listPullRequestFiles(pullRequestNumber: number): Promise<PullRequestFile[]> {
        const files: PullRequestFile[] = [];

        for (let page = 1; ; page += 1) {
            const result = await this.request<PullRequestFile[]>(
                `/repos/${this.repository}/pulls/${pullRequestNumber}/files?per_page=100&page=${page}`
            );
            files.push(...result);
            if (result.length < 100) {
                return files;
            }
        }
    }

    private async getContent(path: string, ref: string): Promise<string> {
        const encodedPath = path.split('/').map(encodeURIComponent).join('/');
        const content = await this.request<ContentResponse>(
            `/repos/${this.repository}/contents/${encodedPath}?ref=${encodeURIComponent(ref)}`
        );
        const response = content.content
            ? content
            : await this.request<GitBlobResponse>(
                  `/repos/${this.repository}/git/blobs/${content.sha}`
              );

        if (response.encoding !== 'base64') {
            throw new Error(
                `Unsupported GitHub content encoding for ${path}: ${response.encoding}`
            );
        }

        return Buffer.from(response.content.replaceAll('\n', ''), 'base64').toString('utf8');
    }

    async getFileAtRef(path: string, ref: string): Promise<string> {
        return this.getContent(path, ref);
    }
}

async function getBrowserslist(api: GitHubApi, headSha: string): Promise<string[]> {
    const packageJson = JSON.parse(
        await api.getFileAtRef('packages/gitbook/package.json', headSha)
    ) as { browserslist?: string[] };

    if (!packageJson.browserslist?.length) {
        throw new Error('packages/gitbook/package.json must define a Browserslist configuration.');
    }

    return packageJson.browserslist;
}

async function getBaseContent(
    api: GitHubApi,
    file: PullRequestFile,
    baseSha: string
): Promise<string> {
    if (file.status === 'added') {
        return '';
    }

    try {
        return await api.getFileAtRef(file.previous_filename ?? file.filename, baseSha);
    } catch (error) {
        if (error instanceof GitHubRequestError && error.status === 404) {
            return '';
        }
        throw error;
    }
}

function report(diagnostics: CompatibilityDiagnostic[]): boolean {
    if (diagnostics.length === 0) {
        console.log('CSS browser compatibility check passed.');
        return true;
    }

    console.error(
        `${diagnostics.length} newly added CSS declaration(s) are not fully supported by the configured Browserslist targets:`
    );
    for (const diagnostic of diagnostics) {
        // Workflow command so the failure is annotated on the PR diff.
        console.error(
            `::error file=${diagnostic.file},line=${diagnostic.line},col=${diagnostic.column}::${diagnostic.property} is not supported by ${diagnostic.unsupportedBrowsers}`
        );
    }
    return false;
}

/** Same check as CI, but against a local `git diff` instead of the GitHub API. */
async function runLocal(baseRef: string): Promise<boolean> {
    const git = (...args: string[]) =>
        execFileSync('git', args, { encoding: 'utf8', maxBuffer: 64 * 1024 * 1024 });
    const root = git('rev-parse', '--show-toplevel').trim();
    const mergeBase = git('merge-base', baseRef, 'HEAD').trim();
    const browsers = (
        JSON.parse(await readFile(join(root, 'packages/gitbook/package.json'), 'utf8')) as {
            browserslist?: string[];
        }
    ).browserslist;

    if (!browsers?.length) {
        throw new Error('packages/gitbook/package.json must define a Browserslist configuration.');
    }

    // Working tree, so uncommitted changes are checked too.
    const changes = git(
        'diff',
        '--name-status',
        '--find-renames',
        '--diff-filter=ACMR',
        mergeBase,
        '--',
        '*.css'
    )
        .split('\n')
        .filter(Boolean)
        .map((line) => {
            const [status, ...paths] = line.split('\t');
            const previousPath = paths.length > 1 ? paths[0] : undefined;
            const path = paths.at(-1) as string;
            return { added: status?.startsWith('A'), path, previousPath };
        });

    const diagnostics: CompatibilityDiagnostic[] = [];
    for (const change of changes) {
        let base = '';
        if (!change.added) {
            try {
                base = git('show', `${mergeBase}:${change.previousPath ?? change.path}`);
            } catch {
                base = '';
            }
        }
        diagnostics.push(
            ...(await getCompatibilityDiagnostics({
                base,
                browsers,
                file: change.path,
                head: await readFile(join(root, change.path), 'utf8'),
            }))
        );
    }

    console.log(`Checked ${changes.length} changed CSS file(s) against ${baseRef}.`);
    return report(diagnostics);
}

async function run(): Promise<boolean> {
    const token = process.env.GITHUB_TOKEN;
    const repository = process.env.GITHUB_REPOSITORY;
    const eventPath = process.env.GITHUB_EVENT_PATH;

    if (!token || !repository || !eventPath) {
        throw new Error('GITHUB_TOKEN, GITHUB_REPOSITORY, and GITHUB_EVENT_PATH are required.');
    }

    const event = JSON.parse(await readFile(eventPath, 'utf8')) as PullRequestEvent;
    const pullRequest = event.pull_request;
    if (!pullRequest) {
        throw new Error('This script must run from a pull request event.');
    }

    const api = new GitHubApi(repository, token);
    const browsers = await getBrowserslist(api, pullRequest.head.sha);
    const files = (await api.listPullRequestFiles(pullRequest.number)).filter(
        (file) => file.status !== 'removed' && file.filename.endsWith('.css')
    );
    const diagnostics: CompatibilityDiagnostic[] = [];

    for (const file of files) {
        const [base, head] = await Promise.all([
            getBaseContent(api, file, pullRequest.base.sha),
            api.getFileAtRef(file.filename, pullRequest.head.sha),
        ]);
        diagnostics.push(
            ...(await getCompatibilityDiagnostics({
                base,
                browsers,
                file: file.filename,
                head,
            }))
        );
    }

    return report(diagnostics);
}

const localFlagIndex = process.argv.indexOf('--local');

try {
    let success: boolean;
    if (localFlagIndex === -1) {
        success = await run();
    } else {
        success = await runLocal(process.argv[localFlagIndex + 1] ?? 'origin/main');
    }
    process.exitCode = success ? 0 : 1;
} catch (error) {
    console.error(error);
    process.exitCode = 1;
}