use clap::Clap;
use controller::Controller;
use git2::Commit;
use git2::ObjectType;
use git2::Oid;
use git2::Repository;
use git2::Signature;
use git2::Tree;
use hyper::header;
use hyper::http::request::Parts;
use hyper::http::response::Builder;
use hyper::service::{make_service_fn, service_fn};
use hyper::Method;
use hyper::StatusCode;
use hyper::{Body, Server};
use percent_encoding::percent_decode_str;
use pulldown_cmark::html;
use pulldown_cmark::Options;
use pulldown_cmark::Parser;
use serde::Deserialize;
use sputnik::html_escape;
use sputnik::mime;
use sputnik::request::SputnikParts;
use sputnik::response::SputnikBuilder;
use std::convert::Infallible;
use std::env;
use std::path::Component;
use std::path::Path;
use std::path::PathBuf;
use std::str::FromStr;
use std::sync::Arc;
use url::Url;

#[cfg(unix)]
use {
    hyperlocal::UnixServerExt, std::fs, std::fs::Permissions,
    std::os::unix::prelude::PermissionsExt,
};

use crate::controller::MultiUserController;
use crate::controller::SoloController;
use crate::error::Error;

mod controller;
mod diff;
mod error;
mod forms;
mod get_routes;
mod post_routes;
mod shares;

pub enum Response {
    Raw(HyperResponse),
    Page(Page),
}

impl From<Page> for Response {
    fn from(page: Page) -> Self {
        Self::Page(page)
    }
}

impl From<HyperResponse> for Response {
    fn from(resp: HyperResponse) -> Self {
        Self::Raw(resp)
    }
}

pub(crate) type HyperResponse = hyper::Response<hyper::Body>;
pub(crate) type Request = hyper::Request<hyper::Body>;

#[derive(Clap, Debug)]
#[clap(name = "gitpad")]
struct Args {
    /// Enable mutliuser mode (requires a reverse-proxy that handles
    /// authentication and sets the Username header)
    #[clap(short)]
    multiuser: bool,

    #[clap(short, default_value = "8000")]
    port: u16,

    /// e.g. https://example.com (used to enforce Host and Origin headers)
    #[clap(long)]
    origin: Option<HttpOrigin>,

    /// Serve via the given Unix domain socket path.
    #[cfg(unix)]
    #[clap(long)]
    socket: Option<String>,
}

#[tokio::main]
async fn main() {
    let args = Args::parse();
    let repo = Repository::open_bare(env::current_dir().unwrap())
        .expect("expected current directory to be a bare Git repository");

    if args.multiuser {
        serve(MultiUserController::new(&repo), args).await;
    } else {
        serve(
            SoloController(Branch(
                repo.find_reference("HEAD")
                    .unwrap()
                    .symbolic_target()
                    .unwrap()
                    .strip_prefix("refs/heads/")
                    .unwrap()
                    .to_owned(),
            )),
            args,
        )
        .await;
    }
}

#[derive(Clone, Debug)]
struct HttpOrigin {
    origin: String,
    host_idx: usize,
}

impl HttpOrigin {
    /// Returns the Host header value (e.g. `example.com` for the origin `https://example.com`).
    fn host(&self) -> &str {
        &self.origin[self.host_idx..]
    }
}

impl FromStr for HttpOrigin {
    type Err = &'static str;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let url = Url::parse(s).map_err(|_| "invalid URL")?;
        if url.scheme() != "http" && url.scheme() != "https" {
            return Err("expected http:// or https:// scheme");
        }
        if url.path() != "/" {
            return Err("path must be /".into());
        }
        Ok(HttpOrigin {
            origin: url.origin().ascii_serialization(),
            host_idx: url.scheme().len() + "://".len(),
        })
    }
}

async fn serve<C: Controller + Send + Sync + 'static>(controller: C, args: Args) {
    let controller = Arc::new(controller);

    #[cfg(unix)]
    if let Some(socket_path) = &args.socket {
        let origin: &'static HttpOrigin = Box::leak(Box::new(
            args.origin
                .expect("if you use --socket, you must specify an --origin"),
        ));

        // TODO: get rid of code duplication
        // we somehow need to specify the closure type or it gets too specific
        let service = make_service_fn(move |_| {
            let controller = controller.clone();

            async move {
                Ok::<_, hyper::Error>(service_fn(move |req| {
                    service(origin, controller.clone(), req)
                }))
            }
        });
        let path = Path::new(&socket_path);
        if path.exists() {
            fs::remove_file(path).unwrap();
        }
        let server = Server::bind_unix(path).unwrap();

        if fs::metadata(path.parent().unwrap())
            .unwrap()
            .permissions()
            .mode()
            & 0o001
            != 0
        {
            eprintln!("socket parent directory must not have x permission for others");
            std::process::exit(1);
        }

        fs::set_permissions(path, Permissions::from_mode(0o777))
            .expect("failed to set socket permissions");

        println!("Listening on unix socket {}", socket_path);
        server.serve(service).await.expect("server error");
        return;
    }

    eprint!(
        "[warning] Serving GitPad over a TCP socket. \
    If you use a reverse-proxy for access control, \
    it can be circumvented by anybody with a system account."
    );
    #[cfg(unix)]
    eprint!(
        " Use a Unix domain socket (with --socket) to restrict \
    access based on the socket parent directory permissions."
    );
    eprintln!();

    let addr = ([127, 0, 0, 1], args.port).into();
    let url = format!("http://{}", addr);
    let origin: &'static HttpOrigin = Box::leak(Box::new(
        args.origin.unwrap_or_else(|| url.parse().unwrap()),
    ));

    let service = make_service_fn(move |_| {
        let controller = controller.clone();

        async move {
            Ok::<_, hyper::Error>(service_fn(move |req| {
                service(&origin, controller.clone(), req)
            }))
        }
    });
    let server = Server::bind(&addr).serve(service);
    println!("Listening on {}", url);
    server.await.expect("server error");
}

async fn service<C: Controller>(
    origin: &HttpOrigin,
    controller: Arc<C>,
    request: Request,
) -> Result<HyperResponse, Infallible> {
    let (mut parts, body) = request.into_parts();

    let mut script_csp = "'none'".into();
    let mut frame_csp = "'none'".into();

    let mut resp = build_response(origin, &*controller, &mut parts, body)
        .await
        .map(|resp| match resp {
            Response::Raw(resp) => resp,
            Response::Page(page) => {
                if !page.script_src.is_empty() {
                    script_csp = page.script_src.join(" ");
                }
                if let Some(src) = page.frame_src {
                    frame_csp = src;
                }
                Builder::new()
                    .content_type(mime::TEXT_HTML)
                    .body(render_page(&page, &*controller, &parts).into())
                    .unwrap()
            }
        })
        .unwrap_or_else(|err| err.into());

    // we rely on CSP to thwart XSS attacks, all modern browsers support it
    resp.headers_mut()
        .entry(header::CONTENT_SECURITY_POLICY)
        .or_insert_with(|| {
            format!(
                "default-src 'self'; frame-src {}; script-src {}; style-src {}",
                frame_csp,
                script_csp,
                include_str!("static/style.css.sha"),
            )
            .parse()
            .unwrap()
        });
    Ok(resp)
}

#[derive(Default)]
pub struct Page {
    title: String,
    header: String,
    body: String,
    /// will be embedded as inline <script> tags
    scripts: Vec<&'static str>,
    /// for the Content Security Policy
    script_src: Vec<&'static str>,

    /// for the Content Security Policy
    frame_src: Option<&'static str>,
}

fn render_page<C: Controller>(page: &Page, controller: &C, parts: &Parts) -> String {
    let mut out = String::new();
    out.push_str("<!doctype html><html><head><meta charset=utf-8>");
    out.push_str(&format!("<title>{}</title>", html_escape(&page.title)));
    out.push_str("<meta name=viewport content=\"width=device-width, initial-scale=1\"><style>");
    out.push_str(include_str!("static/style.css"));
    out.push_str("</style></head><body><header id=header>");
    out.push_str(&page.header);
    out.push_str(
        &controller
            .user_info_html(parts)
            .map(|h| format!("<div class=user-info>{}</div>", h))
            .unwrap_or_default(),
    );
    out.push_str("</header>");
    out.push_str(&page.body);
    for script in &page.scripts {
        out.push_str(&format!("<script>{}</script>", script));
    }
    out.push_str("</body></html>");
    out
}

#[derive(Deserialize)]
struct ActionParam {
    #[serde(default = "default_action")]
    action: String,
}

fn default_action() -> String {
    "view".into()
}

#[derive(Eq, PartialEq, Hash, Clone)]
pub struct Branch(String);

impl Branch {
    fn rev_str(&self) -> String {
        format!("refs/heads/{}", self.0)
    }
}

async fn build_response<C: Controller>(
    origin: &HttpOrigin,
    controller: &C,
    parts: &mut Parts,
    body: Body,
) -> Result<Response, Error> {
    let host = parts
        .headers
        .get("Host")
        .ok_or_else(|| Error::BadRequest("Host header required".into()))?
        .to_str()
        .unwrap();
    if host != origin.host() {
        // We enforce an exact Host header to prevent DNS rebinding attacks.
        return Err(Error::BadRequest(format!("<h1>Bad Request: Unknown Host header</h1>\
        Received the header <pre>Host: {}</pre>
        But expected the header <pre>Host: {}</pre> \
        <p>If you want to serve GitPad under a different hostname you need to specify it on startup with <code>--origin</code>.</p>",
        html_escape(host), html_escape(origin.host()))));
    }

    let unsanitized_path = percent_decode_str(parts.uri.path())
        .decode_utf8()
        .map_err(|_| Error::BadRequest("failed to percent-decode path as UTF-8".into()))?
        .into_owned();

    let repo = Repository::open_bare(env::current_dir().unwrap()).unwrap();

    let (rev, unsanitized_path) = match controller.parse_url_path(&unsanitized_path, &parts, &repo)
    {
        Ok(parsed) => parsed,
        Err(res) => return res,
    };

    let mut comps = Vec::new();

    // prevent directory traversal attacks
    for comp in Path::new(&*unsanitized_path).components() {
        match comp {
            Component::Normal(name) => comps.push(name),
            Component::ParentDir => {
                return Err(Error::Forbidden("path traversal is forbidden".into()))
            }
            _ => {}
        }
    }

    let params: ActionParam = parts.query::<ActionParam>().unwrap();

    let url_path: PathBuf = comps.iter().collect();

    let ctx = Context {
        repo,
        path: url_path,
        branch: rev,
    };

    if !controller.may_read_path(&ctx, parts) {
        return Err(Error::Unauthorized(
            "you are not authorized to view this file".into(),
        ));
    }

    if parts.method == Method::POST {
        return post_routes::build_response(origin, &params, controller, ctx, body, parts).await;
    }

    let mut tree = ctx
        .repo
        .revparse_single(&ctx.branch.rev_str())
        .map(|r| r.into_commit().unwrap().tree().unwrap());

    if ctx.path.components().next().is_some() {
        let entr = match tree.and_then(|t| t.get_path(&ctx.path)) {
            Ok(entr) => entr,
            Err(_) => {
                if unsanitized_path.ends_with('/') {
                    return Err(Error::NotFound("directory not found".into()));
                }

                if controller.may_write_path(&ctx, parts) {
                    if params.action == "edit" {
                        return Ok(forms::edit_text_form(
                            &forms::EditForm::default(),
                            None,
                            controller,
                            &ctx,
                            parts,
                        )
                        .into());
                    } else if params.action == "upload" {
                        return Ok(forms::upload_form(false, controller, &ctx, parts).into());
                    } else {
                        return Err(Error::NotFound(
                            "file not found, but <a href=?action=edit>you can write it</a> or <a href=?action=upload>upload it</a>".into(),
                        ));
                    }
                } else {
                    return Err(Error::NotFound("file not found".into()));
                }
            }
        };

        if entr.kind().unwrap() == ObjectType::Blob {
            if unsanitized_path.ends_with('/') {
                return Ok(Builder::new()
                    .status(StatusCode::FOUND)
                    .header(
                        "location",
                        controller
                            .build_url_path(&ctx.branch, unsanitized_path.trim_end_matches('/')),
                    )
                    .body("redirecting".into())
                    .unwrap()
                    .into());
            }
            return get_routes::get_blob(entr, params, controller, ctx, &parts);
        }

        tree = ctx.repo.find_tree(entr.id());
        if !unsanitized_path.ends_with('/') {
            return Err(Error::MissingTrailingSlash(parts.uri.path().to_owned()));
        }
    }

    get_routes::view_tree(tree, controller, &ctx, &parts)
}

fn render_link(name: &str, label: &str, active_action: &str) -> String {
    format!(
        " <a {}{}>{}</a>",
        if name == active_action {
            "class=active".into()
        } else {
            format!("href=?action={}", name)
        },
        if name != label {
            format!(" title='{}'", name)
        } else {
            "".into()
        },
        label
    )
}

fn action_links<C: Controller>(
    active_action: &str,
    controller: &C,
    ctx: &Context,
    parts: &Parts,
) -> String {
    let mut out = String::new();

    out.push_str("<a href=. title='list parent directory'>ls</a>");
    out.push_str(&render_link("view", "view", active_action));
    if controller.may_write_path(ctx, parts) {
        out.push_str(&render_link("edit", "edit", active_action));
    }
    out.push_str(&render_link("log", "log", active_action));
    out.push_str(&render_link("raw", "raw", active_action));
    if controller.may_move_path(ctx, parts) {
        out.push_str(&render_link("move", "mv", active_action));
        out.push_str(&render_link("remove", "rm", active_action));
    }
    out
}

pub struct Context {
    repo: Repository,
    branch: Branch,
    path: PathBuf,
}

impl Context {
    fn branch_head(&self) -> Result<Commit, Error> {
        self.repo
            .revparse_single(&self.branch.rev_str())
            .map_err(|_| Error::NotFound("branch not found".into()))?
            .into_commit()
            .map_err(|_| Error::NotFound("branch not found".into()))
    }

    fn commit(
        &self,
        signature: &Signature,
        msg: &str,
        tree: &Tree,
        parent_commits: &[&Commit],
    ) -> Result<Oid, git2::Error> {
        self.repo.commit(
            Some(&self.branch.rev_str()),
            signature,
            signature,
            msg,
            tree,
            parent_commits,
        )
    }

    fn file_name(&self) -> Option<&str> {
        self.path.file_name().and_then(|x| x.to_str())
    }
}

#[derive(PartialEq)]
enum RenderMode {
    View,
    Preview,
}

fn render_markdown(input: &str, page: &mut Page, _mode: RenderMode) {
    let parser = Parser::new_ext(input, Options::all());
    page.body.push_str("<div class=markdown-output>");
    html::push_html(&mut page.body, parser);
    page.body.push_str("</div>");
}

fn embed_html_as_iframe(input: &str, page: &mut Page, mode: RenderMode) {
    if mode == RenderMode::View {
        page.body.push_str("<iframe src='?action=run'></iframe>");
        page.frame_src = Some("'self'");
    } else {
        page.body
            .push_str("<div class=note>Note that JavaScript does not work in the preview.</div>");
        // sandbox=allow-scripts wouldn't work because the strict parent page CSP still applies

        // The sandbox attribute makes browsers treat the embedded page as a unique origin.
        page.body.push_str(&format!(
            "<iframe srcdoc='{}' sandbox></iframe>",
            html_escape(input)
        ));
    }
}

fn get_renderer(path: &Path) -> Option<fn(&str, &mut Page, RenderMode)> {
    match path.extension().map(|e| e.to_str().unwrap()) {
        Some("md") => Some(render_markdown),
        Some("html") => Some(embed_html_as_iframe),
        _ => None,
    }
}