//! URL routes and the handler function for each page.
//!
//! URL layout (similar to cgit):
//!
//! | URL                                  | page                          |
//! |--------------------------------------|-------------------------------|
//! | `/`                                  | list of repos                 |
//! | `/{repo}/`                           | summary                       |
//! | `/{repo}/refs`                       | all branches and tags         |
//! | `/{repo}/log?h=branch&ofs=50`        | commit log, 50 per page       |
//! | `/{repo}/commit/{id}`                | one commit with its diff      |
//! | `/{repo}/tree/{path}?h=branch`       | directory listing             |
//! | `/{repo}/blob/{path}?h=branch`       | one file, highlighted         |
//! | `/{repo}/raw/{path}?h=branch`        | one file, raw bytes           |
//! | `/{repo}/info/refs`, `/git-upload-pack` | `git clone` (see smart_http) |
//!
//! `?h=` picks a branch, tag or commit id; without it we use HEAD.

use axum::extract::{DefaultBodyLimit, Path, Query, State};
use axum::http::{header, HeaderMap, HeaderValue, StatusCode};
use axum::response::{Html, IntoResponse, Redirect, Response};
use axum::routing::{get, post};
use axum::{middleware, Router};
use serde::Deserialize;
use std::sync::Arc;

use crate::config::{RepoConfig, Repos, ServerConfig};
use crate::git::{self, PathContent};
use crate::highlight::Highlighter;
use crate::markdown::{self, LinkBase};
use crate::pages::{self, BlobBody, IndexRow, RepoHeader, Tab};
use crate::{smart_http, util};

/// Commits per page on the log view.
pub const LOG_PAGE_SIZE: usize = 50;
/// Files larger than this are not rendered in the blob view.
const MAX_BLOB_DISPLAY: usize = 2 * 1024 * 1024;

const STYLE_CSS: &str = include_str!("../static/style.css");

/// Shared, read-only state handed to every request.
pub struct AppState {
    pub server: ServerConfig,
    pub repos: Repos,
    pub highlighter: Highlighter,
}

pub type Shared = Arc<AppState>;

impl AppState {
    pub fn new(server: ServerConfig, repos: Repos) -> Shared {
        Arc::new(AppState { server, repos, highlighter: Highlighter::new() })
    }

    /// Look up a repo by its URL name. Unknown names are a 404: this is the
    /// check that keeps the server from reading anything that isn't configured.
    pub fn repo(&self, name: &str) -> Result<RepoConfig, AppError> {
        self.repos.get(name).cloned().ok_or_else(|| AppError::not_found("no such repository"))
    }

    /// The URL people should pass to `git clone`.
    fn clone_url(&self, repo: &str, headers: &HeaderMap) -> String {
        let base = match &self.server.clone_base_url {
            Some(b) => b.trim_end_matches('/').to_string(),
            None => {
                let host = headers
                    .get(header::HOST)
                    .and_then(|h| h.to_str().ok())
                    .filter(|h| h.chars().all(|c| c.is_ascii_alphanumeric() || ".:-[]".contains(c)))
                    .unwrap_or(&self.server.listen);
                format!("http://{host}")
            }
        };
        format!("{base}/{repo}")
    }
}

pub fn router(state: Shared) -> Router {
    Router::new()
        .route("/", get(index))
        .route("/static/style.css", get(style_css))
        .route("/static/highlight.css", get(highlight_css))
        .route("/{repo}", get(add_slash))
        .route("/{repo}/", get(summary))
        .route("/{repo}/refs", get(refs))
        .route("/{repo}/log", get(log))
        .route("/{repo}/commit/{id}", get(commit))
        .route("/{repo}/tree", get(tree_root))
        .route("/{repo}/tree/", get(tree_root))
        .route("/{repo}/tree/{*path}", get(tree))
        .route("/{repo}/blob/{*path}", get(blob))
        .route("/{repo}/raw/{*path}", get(raw))
        // git clone over smart HTTP (read-only)
        .route("/{repo}/info/refs", get(smart_http::info_refs))
        .route(
            "/{repo}/git-upload-pack",
            post(smart_http::upload_pack).layer(DefaultBodyLimit::max(smart_http::MAX_REQUEST_BYTES)),
        )
        .route("/{repo}/git-receive-pack", post(smart_http::receive_pack_refused))
        .fallback(|| async { AppError::not_found("page not found") })
        .layer(middleware::map_response(security_headers))
        .with_state(state)
}

/// Extra headers on every response. The Content-Security-Policy tells the
/// browser to never run scripts on our pages, as a second line of defence
/// behind HTML escaping.
async fn security_headers(mut res: Response) -> Response {
    let h = res.headers_mut();
    h.insert(
        header::CONTENT_SECURITY_POLICY,
        HeaderValue::from_static("default-src 'none'; style-src 'self'; img-src 'self' https:; frame-ancestors 'none'; base-uri 'none'; form-action 'none'"),
    );
    h.insert(header::X_CONTENT_TYPE_OPTIONS, HeaderValue::from_static("nosniff"));
    h.insert(header::REFERRER_POLICY, HeaderValue::from_static("same-origin"));
    res
}

// ------------------------------------------------------------ errors --

/// An error page. Handlers return `Result<_, AppError>` and `?` does the rest.
#[derive(Debug)]
pub struct AppError {
    pub status: StatusCode,
    pub message: String,
}

impl AppError {
    pub fn not_found(msg: &str) -> AppError {
        AppError { status: StatusCode::NOT_FOUND, message: msg.to_string() }
    }
}

impl From<git::Error> for AppError {
    fn from(e: git::Error) -> Self {
        match e {
            git::Error::NotFound(m) => AppError { status: StatusCode::NOT_FOUND, message: m },
            git::Error::Git(e) => {
                eprintln!("git error: {e}");
                AppError {
                    status: StatusCode::INTERNAL_SERVER_ERROR,
                    message: "internal error reading repository".into(),
                }
            }
        }
    }
}

impl IntoResponse for AppError {
    fn into_response(self) -> Response {
        let page = pages::error("RustForge", self.status.as_u16(), &self.message);
        (self.status, Html(page.into_string())).into_response()
    }
}

/// libgit2 calls block the thread, so run them on tokio's blocking pool
/// instead of stalling the async web server.
async fn blocking<T: Send + 'static>(
    f: impl FnOnce() -> Result<T, AppError> + Send + 'static,
) -> Result<T, AppError> {
    tokio::task::spawn_blocking(f).await.map_err(|_| AppError {
        status: StatusCode::INTERNAL_SERVER_ERROR,
        message: "internal error".into(),
    })?
}

#[derive(Deserialize, Default)]
pub struct RevQuery {
    /// branch / tag / commit id
    pub h: Option<String>,
    /// log offset
    pub ofs: Option<usize>,
}

impl RevQuery {
    fn rev(&self) -> Option<&str> {
        self.h.as_deref().filter(|s| !s.is_empty())
    }
}

// ---------------------------------------------------------- handlers --

async fn style_css() -> impl IntoResponse {
    ([(header::CONTENT_TYPE, "text/css; charset=utf-8")], STYLE_CSS)
}

async fn highlight_css(State(st): State<Shared>) -> impl IntoResponse {
    ([(header::CONTENT_TYPE, "text/css; charset=utf-8")], st.highlighter.css.clone())
}

async fn add_slash(State(st): State<Shared>, Path(repo): Path<String>) -> Result<Redirect, AppError> {
    let rc = st.repo(&repo)?;
    Ok(Redirect::permanent(&format!("/{}/", rc.name)))
}

async fn index(State(st): State<Shared>) -> Result<Html<String>, AppError> {
    blocking(move || {
        let now = util::now_unix();
        let rows: Vec<IndexRow> = st
            .repos
            .iter()
            .map(|rc| IndexRow {
                name: rc.name.clone(),
                description: rc.description.clone(),
                idle: git::open(&rc.path).ok().and_then(|r| git::last_change(&r)).map(|t| util::age(now - t)),
            })
            .collect();
        Ok(Html(pages::index(&st.server.site_title, &rows).into_string()))
    })
    .await
}

fn header<'a>(st: &'a AppState, rc: &'a RepoConfig, tab: Tab, rev: Option<&'a str>) -> RepoHeader<'a> {
    RepoHeader { site_title: &st.server.site_title, name: &rc.name, description: &rc.description, tab, rev }
}

async fn summary(
    State(st): State<Shared>,
    Path(repo): Path<String>,
    headers: HeaderMap,
) -> Result<Html<String>, AppError> {
    let rc = st.repo(&repo)?;
    let clone_url = st.clone_url(&rc.name, &headers);
    blocking(move || {
        let r = git::open(&rc.path)?;
        let mut branches = git::branches(&r)?;
        let mut tags = git::tags(&r)?;
        branches.truncate(10);
        tags.truncate(10);
        let (commits, readme) = match git::resolve(&r, None) {
            Ok(head) => {
                let (commits, _) = git::log(&r, head, 0, 10)?;
                let base_links = format!("/{}/tree/", rc.name);
                let base_images = format!("/{}/raw/", rc.name);
                let base = LinkBase { links: &base_links, images: &base_images };
                let readme = git::readme(&r, head).map(|(name, text)| {
                    let html = if name.ends_with(".md") || name.ends_with(".markdown") {
                        markdown::render(&text, Some(&base))
                    } else {
                        format!("<pre>{}</pre>", crate::highlight::escape(&text))
                    };
                    (name, html)
                });
                (commits, readme)
            }
            Err(_) => (Vec::new(), None), // empty repo
        };
        let s = pages::Summary { clone_url, branches: &branches, tags: &tags, commits: &commits, readme };
        Ok(Html(pages::summary(&header(&st, &rc, Tab::Summary, None), &s).into_string()))
    })
    .await
}

async fn refs(State(st): State<Shared>, Path(repo): Path<String>) -> Result<Html<String>, AppError> {
    let rc = st.repo(&repo)?;
    blocking(move || {
        let r = git::open(&rc.path)?;
        let page = pages::refs(&header(&st, &rc, Tab::Refs, None), &git::branches(&r)?, &git::tags(&r)?);
        Ok(Html(page.into_string()))
    })
    .await
}

async fn log(
    State(st): State<Shared>,
    Path(repo): Path<String>,
    Query(q): Query<RevQuery>,
) -> Result<Html<String>, AppError> {
    let rc = st.repo(&repo)?;
    blocking(move || {
        let r = git::open(&rc.path)?;
        let start = git::resolve(&r, q.rev())?;
        let ofs = q.ofs.unwrap_or(0);
        let (commits, more) = git::log(&r, start, ofs, LOG_PAGE_SIZE)?;
        let page = pages::log(&header(&st, &rc, Tab::Log, q.rev()), &commits, ofs, LOG_PAGE_SIZE, more);
        Ok(Html(page.into_string()))
    })
    .await
}

async fn commit(
    State(st): State<Shared>,
    Path((repo, id)): Path<(String, String)>,
) -> Result<Html<String>, AppError> {
    let rc = st.repo(&repo)?;
    blocking(move || {
        let r = git::open(&rc.path)?;
        let oid = git::resolve(&r, Some(&id))?;
        let info = git::commit(&r, oid)?;
        let diff = git::commit_diff(&r, oid)?;
        Ok(Html(pages::commit(&header(&st, &rc, Tab::Commit, None), &info, &diff).into_string()))
    })
    .await
}

async fn tree_root(
    State(st): State<Shared>,
    Path(repo): Path<String>,
    Query(q): Query<RevQuery>,
) -> Result<Response, AppError> {
    show_path(st, repo, String::new(), q).await
}

async fn tree(
    State(st): State<Shared>,
    Path((repo, path)): Path<(String, String)>,
    Query(q): Query<RevQuery>,
) -> Result<Response, AppError> {
    show_path(st, repo, path, q).await
}

async fn blob(
    State(st): State<Shared>,
    Path((repo, path)): Path<(String, String)>,
    Query(q): Query<RevQuery>,
) -> Result<Response, AppError> {
    show_path(st, repo, path, q).await
}

/// Shared by tree and blob: a directory shows a listing, a file shows its
/// contents, whichever URL was used.
async fn show_path(st: Shared, repo: String, raw_path: String, q: RevQuery) -> Result<Response, AppError> {
    let rc = st.repo(&repo)?;
    let path = util::clean_repo_path(&raw_path).ok_or_else(|| AppError::not_found("invalid path"))?;
    blocking(move || {
        let r = git::open(&rc.path)?;
        let commit = git::resolve(&r, q.rev())?;
        let content = git::path_content(&r, commit, &path)?;
        let page = match content {
            PathContent::Dir(entries) => pages::tree(&header(&st, &rc, Tab::Tree, q.rev()), &path, &entries),
            PathContent::File { data, .. } => {
                let file_name = path.rsplit('/').next().unwrap_or(&path);
                let body = if data.len() > MAX_BLOB_DISPLAY {
                    BlobBody::TooLarge
                } else if git::is_binary(&data) {
                    BlobBody::Binary
                } else {
                    let text = String::from_utf8_lossy(&data);
                    BlobBody::Text {
                        html: st.highlighter.highlight(file_name, &text),
                        lines: text.lines().count(),
                    }
                };
                pages::blob(&header(&st, &rc, Tab::Tree, q.rev()), &path, data.len(), &body)
            }
        };
        Ok(Html(page.into_string()).into_response())
    })
    .await
}

async fn raw(
    State(st): State<Shared>,
    Path((repo, path)): Path<(String, String)>,
    Query(q): Query<RevQuery>,
) -> Result<Response, AppError> {
    let rc = st.repo(&repo)?;
    let path = util::clean_repo_path(&path).ok_or_else(|| AppError::not_found("invalid path"))?;
    blocking(move || {
        let r = git::open(&rc.path)?;
        let commit = git::resolve(&r, q.rev())?;
        match git::path_content(&r, commit, &path)? {
            PathContent::Dir(_) => Err(AppError::not_found("that path is a directory")),
            PathContent::File { data, .. } => {
                let ctype = raw_content_type(&path, &data);
                let mut res = (StatusCode::OK, data).into_response();
                res.headers_mut().insert(header::CONTENT_TYPE, HeaderValue::from_static(ctype));
                if ctype == "application/octet-stream" {
                    res.headers_mut()
                        .insert(header::CONTENT_DISPOSITION, HeaderValue::from_static("attachment"));
                }
                Ok(res)
            }
        }
    })
    .await
}

/// Raw files are served as plain text, a few safe image types, or a download.
/// Never as text/html or SVG, which a browser would execute.
pub fn raw_content_type(path: &str, data: &[u8]) -> &'static str {
    let ext = path.rsplit('.').next().unwrap_or("").to_ascii_lowercase();
    match ext.as_str() {
        "png" => "image/png",
        "jpg" | "jpeg" => "image/jpeg",
        "gif" => "image/gif",
        "webp" => "image/webp",
        _ if !git::is_binary(data) && std::str::from_utf8(data).is_ok() => "text/plain; charset=utf-8",
        _ => "application/octet-stream",
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn raw_types() {
        assert_eq!(raw_content_type("a.png", b"\x89PNG\0"), "image/png");
        assert_eq!(raw_content_type("index.html", b"<script>"), "text/plain; charset=utf-8");
        assert_eq!(raw_content_type("x.svg", b"<svg onload=x>"), "text/plain; charset=utf-8");
        assert_eq!(raw_content_type("bin", b"\0\x01"), "application/octet-stream");
    }
}