//! One content root, and what a request path resolves to inside it.
//!
//! Containment is enforced twice, independently. `path::clean_path` cannot
//! produce a string that escapes the root; `safe_file` then canonicalises what
//! that string names and requires the result to still be under the root, which
//! is what defeats a symlink pointing outside. There is a residual window
//! between canonicalising and opening a file; for an author-controlled tree that
//! is acceptable, and it is the reason the canonical path is what gets opened.

use std::path::{Path, PathBuf};
use std::sync::Arc;

use crate::cache::StatCache;
use crate::config::{DIR_CONFIG, DirConfig, PageSettings};
use crate::error::Error;
use crate::mime;
use crate::path::{clean_path, url_for};

/// How deep a chain of server-side redirects `resolve_flat` will follow. Every
/// redirect currently points at a directly resolvable document, so one hop is
/// always enough; the cap is there so a future rule cannot loop.
const MAX_FLAT_HOPS: usize = 5;

/// What a request path resolved to.
#[derive(Debug)]
pub enum Resolution {
    Found(Resource),
    /// The resource lives at this canonical root-relative URL.
    Redirect(String),
    NotFound,
}

#[derive(Debug)]
pub enum Resource {
    /// A Markdown document, to be rendered into the format the caller serves.
    Document { url: String, source: PathBuf, settings: PageSettings },
    /// A file served byte for byte.
    Raw { path: PathBuf, media_type: &'static str },
}

pub struct Site {
    root: PathBuf,
    dir_configs: StatCache<DirConfig>,
    /// Shared by every directory without a config of its own, so the common case
    /// allocates nothing.
    built_in: Arc<DirConfig>,
}

impl Site {
    /// Open a content root, canonicalising it so containment checks have a
    /// stable base and a missing root fails now rather than per request.
    pub fn new(root: &Path) -> Result<Self, Error> {
        let root =
            root.canonicalize().map_err(|cause| Error::Io { path: root.to_path_buf(), cause })?;
        if !root.is_dir() {
            return Err(Error::config(format!("{} is not a directory", root.display())));
        }
        Ok(Site { root, dir_configs: StatCache::new(), built_in: Arc::new(DirConfig::default()) })
    }

    pub fn root(&self) -> &Path {
        &self.root
    }

    /// Resolve a request path.
    ///
    /// | Request | Serves |
    /// | --- | --- |
    /// | `/` | `index.md` |
    /// | `/foo` | `foo.md`, else `foo/index.md` |
    /// | `/foo.md` | redirects to `/foo` |
    /// | `/img.png` | the file itself, by media type |
    pub fn resolve(&self, url_path: &str) -> Result<Resolution, Error> {
        let Some(clean) = clean_path(url_path) else { return Ok(Resolution::NotFound) };
        let Some(source) = self.file_for(&clean) else { return Ok(Resolution::NotFound) };

        // `/foo.md` always redirects to its extensionless form, so one
        // root-relative link works identically from every protocol.
        if clean.ends_with(".md") {
            return Ok(match url_for(&self.root, &source) {
                Some(url) => Resolution::Redirect(url),
                None => Resolution::NotFound,
            });
        }

        if source.extension().and_then(|e| e.to_str()) != Some("md") {
            let media_type = mime::media_type(&source);
            return Ok(Resolution::Found(Resource::Raw { path: source, media_type }));
        }

        let Some(url) = url_for(&self.root, &source) else { return Ok(Resolution::NotFound) };
        let settings = self.settings_for(&source)?;
        Ok(Resolution::Found(Resource::Document { url, source, settings }))
    }

    /// Resolve the way [`Site::resolve`] does, but never hand back a redirect.
    ///
    /// Nex and Gopher have no redirect status, so there is nothing to bounce a
    /// client with: the canonical target is resolved here instead and its content
    /// served directly, on the first request.
    pub fn resolve_flat(&self, url_path: &str) -> Result<Resolution, Error> {
        let mut target = url_path.to_string();
        for _ in 0..MAX_FLAT_HOPS {
            match self.resolve(&target)? {
                Resolution::Redirect(location) => target = location,
                settled => return Ok(settled),
            }
        }
        Ok(Resolution::NotFound)
    }

    /// The source file a cleaned path names, if one exists and is contained.
    fn file_for(&self, clean: &str) -> Option<PathBuf> {
        if clean.is_empty() {
            return self.safe_file(&self.root.join("index.md"));
        }

        // A name that already carries an extension resolves literally: `.md` is
        // never appended to a file that was asked for by name.
        let named = Path::new(clean).file_name()?.to_str()?;
        if named.contains('.') {
            return self.safe_file(&self.root.join(clean));
        }

        self.safe_file(&self.root.join(format!("{clean}.md")))
            .or_else(|| self.safe_file(&self.root.join(clean).join("index.md")))
    }

    /// The canonical path of a file inside the root, or `None`.
    ///
    /// Canonicalising first and testing `is_file` on the *result* is what stops a
    /// symlink to a directory, or to anything outside the root, from passing.
    fn safe_file(&self, path: &Path) -> Option<PathBuf> {
        let resolved = path.canonicalize().ok()?;
        (resolved.starts_with(&self.root) && resolved.is_file()).then_some(resolved)
    }

    fn settings_for(&self, source: &Path) -> Result<PageSettings, Error> {
        let Some(name) = source.file_name().and_then(|n| n.to_str()) else {
            return Ok(PageSettings::default());
        };
        let dir = source.parent().unwrap_or(&self.root);
        Ok(self.dir_config(dir)?.settings_for(name))
    }

    fn dir_config(&self, dir: &Path) -> Result<Arc<DirConfig>, Error> {
        let path = dir.join(DIR_CONFIG);
        if !path.is_file() {
            return Ok(self.built_in.clone());
        }
        self.dir_configs.get_or_insert_with(&path, || DirConfig::load(&path))
    }
}

#[cfg(test)]
mod tests {
    use std::fs;

    use super::*;

    /// Mirrors smolweb's `tests/conftest.py` fixture, so its assertions port
    /// across directly.
    fn fixture() -> (tempfile::TempDir, Site) {
        let dir = tempfile::tempdir().unwrap();
        let root = dir.path();
        fs::write(root.join("index.md"), "# Home\n\nHello.\n").unwrap();
        fs::write(root.join("about.md"), "# About\n\nBody.\n").unwrap();
        fs::write(root.join("img.png"), b"\x89PNG\r\n\x1a\nfake").unwrap();
        fs::create_dir(root.join("dir")).unwrap();
        fs::write(root.join("dir/index.md"), "# Nested\n\nNested body.\n").unwrap();
        fs::write(root.join(".secret.md"), "# Hidden\n").unwrap();
        let site = Site::new(root).unwrap();
        (dir, site)
    }

    #[track_caller]
    fn document(site: &Site, path: &str) -> (String, PathBuf, PageSettings) {
        match site.resolve(path).unwrap() {
            Resolution::Found(Resource::Document { url, source, settings }) => {
                (url, source, settings)
            }
            other => panic!("expected a document at {path}, got {other:?}"),
        }
    }

    /// Force a modification time change: filesystem granularity is coarse
    /// enough that two writes in one test can share a timestamp.
    fn bump_mtime(path: &Path) {
        let later = std::time::SystemTime::now() + std::time::Duration::from_secs(5);
        fs::File::options()
            .write(true)
            .open(path)
            .unwrap()
            .set_times(fs::FileTimes::new().set_accessed(later).set_modified(later))
            .unwrap();
    }

    #[track_caller]
    fn assert_not_found(site: &Site, path: &str) {
        match site.resolve(path).unwrap() {
            Resolution::NotFound => {}
            other => panic!("expected nothing at {path}, got {other:?}"),
        }
    }

    // -- Ported from TestPathTraversal ------------------------------------

    #[test]
    fn traversal_attempts_are_refused() {
        let (_dir, site) = fixture();
        for path in [
            "/../../etc/passwd",
            "/../../../../../../etc/passwd",
            "/foo/../../etc/passwd",
            // Percent-decoded to ".." before normalising, then clamped.
            "/%2e%2e/etc/passwd",
        ] {
            assert_not_found(&site, path);
        }
    }

    #[test]
    fn a_symlink_escaping_the_root_is_refused() {
        let dir = tempfile::tempdir().unwrap();
        let outside = dir.path().join("outside");
        fs::create_dir(&outside).unwrap();
        fs::write(outside.join("secret.md"), "# Secret\n").unwrap();
        let root = dir.path().join("root");
        fs::create_dir(&root).unwrap();
        std::os::unix::fs::symlink(outside.join("secret.md"), root.join("escape.md")).unwrap();

        let site = Site::new(&root).unwrap();
        assert_not_found(&site, "/escape");
        // The literal form is refused on the same grounds, not redirected.
        assert_not_found(&site, "/escape.md");
    }

    #[test]
    fn a_symlink_to_a_directory_outside_the_root_is_refused() {
        let dir = tempfile::tempdir().unwrap();
        let outside = dir.path().join("outside");
        fs::create_dir(&outside).unwrap();
        fs::write(outside.join("index.md"), "# Secret\n").unwrap();
        let root = dir.path().join("root");
        fs::create_dir(&root).unwrap();
        std::os::unix::fs::symlink(&outside, root.join("link")).unwrap();

        let site = Site::new(&root).unwrap();
        assert_not_found(&site, "/link");
    }

    #[test]
    fn dotfile_paths_are_refused() {
        let (_dir, site) = fixture();
        assert_not_found(&site, "/.secret");
        assert_not_found(&site, "/.secret.md");
    }

    #[test]
    fn the_per_directory_config_is_never_served() {
        let (dir, site) = fixture();
        fs::write(dir.path().join(DIR_CONFIG), "[defaults]\ncache_control = 60\n").unwrap();
        // It is not a dotfile by accident: without that rule it carries a dot in
        // its name and so would resolve literally, like img.png does.
        assert_not_found(&site, "/.itsybitsy.toml");
    }

    // -- Ported from TestResolutionRules ----------------------------------

    #[test]
    fn root_serves_index() {
        let (dir, site) = fixture();
        let (url, source, _) = document(&site, "/");
        assert_eq!(url, "/");
        assert_eq!(source, dir.path().canonicalize().unwrap().join("index.md"));
    }

    #[test]
    fn an_extensionless_path_serves_the_md_file() {
        let (_dir, site) = fixture();
        let (url, source, _) = document(&site, "/about");
        assert_eq!(url, "/about");
        assert_eq!(source.file_name().unwrap(), "about.md");
    }

    #[test]
    fn a_directory_serves_its_index() {
        let (_dir, site) = fixture();
        // Both forms resolve to the same page, and neither is redirected to the
        // other. That is the behaviour being ported, not an oversight.
        for path in ["/dir", "/dir/"] {
            let (url, source, _) = document(&site, path);
            assert_eq!(url, "/dir/");
            assert!(source.ends_with("dir/index.md"), "{source:?}");
        }
    }

    #[test]
    fn an_md_extension_redirects_to_the_canonical_url() {
        let (_dir, site) = fixture();
        match site.resolve("/about.md").unwrap() {
            Resolution::Redirect(location) => assert_eq!(location, "/about"),
            other => panic!("expected a redirect, got {other:?}"),
        }
        match site.resolve("/dir/index.md").unwrap() {
            Resolution::Redirect(location) => assert_eq!(location, "/dir/"),
            other => panic!("expected a redirect, got {other:?}"),
        }
    }

    #[test]
    fn a_missing_md_file_is_not_found() {
        let (_dir, site) = fixture();
        assert_not_found(&site, "/nonexistent.md");
    }

    #[test]
    fn a_raw_file_is_served_with_its_media_type() {
        let (_dir, site) = fixture();
        match site.resolve("/img.png").unwrap() {
            Resolution::Found(Resource::Raw { path, media_type }) => {
                assert_eq!(media_type, "image/png");
                assert_eq!(path.file_name().unwrap(), "img.png");
            }
            other => panic!("expected a raw file, got {other:?}"),
        }
    }

    #[test]
    fn a_missing_path_is_not_found() {
        let (_dir, site) = fixture();
        assert_not_found(&site, "/nope");
    }

    #[test]
    fn a_bare_unresolvable_segment_resolves_to_nothing() {
        // Regression carried over from smolweb: the Python reached this path
        // through `rpartition("/")`, where a bare top-level segment yields an
        // empty parent that must not be read as the root index.
        let (_dir, site) = fixture();
        assert_not_found(&site, "/totally-unresolvable-segment");
    }

    #[test]
    fn a_subpath_of_an_existing_document_is_not_found() {
        // `/about/whatever` is not a sub-resource of about.md just because
        // about.md exists. A format that invents sub-URLs claims them later.
        let (_dir, site) = fixture();
        assert_not_found(&site, "/about/whatever");
    }

    #[test]
    fn a_directory_without_an_index_is_not_found() {
        let (dir, site) = fixture();
        fs::create_dir(dir.path().join("empty")).unwrap();
        assert_not_found(&site, "/empty");
    }

    // -- Ported from TestResolveFlat --------------------------------------

    #[test]
    fn a_canonical_redirect_is_resolved_not_bounced() {
        let (_dir, site) = fixture();
        match site.resolve_flat("/about.md").unwrap() {
            Resolution::Found(Resource::Document { url, .. }) => assert_eq!(url, "/about"),
            other => panic!("expected the document itself, got {other:?}"),
        }
    }

    #[test]
    fn resolve_flat_still_reports_a_missing_path() {
        let (_dir, site) = fixture();
        match site.resolve_flat("/nope").unwrap() {
            Resolution::NotFound => {}
            other => panic!("expected nothing, got {other:?}"),
        }
    }

    #[test]
    fn resolve_flat_passes_a_raw_file_straight_through() {
        let (_dir, site) = fixture();
        match site.resolve_flat("/img.png").unwrap() {
            Resolution::Found(Resource::Raw { media_type, .. }) => {
                assert_eq!(media_type, "image/png");
            }
            other => panic!("expected a raw file, got {other:?}"),
        }
    }

    // -- Per-directory settings -------------------------------------------

    #[test]
    fn settings_come_from_the_documents_own_directory() {
        let (dir, site) = fixture();
        let root = dir.path();
        fs::write(
            root.join(DIR_CONFIG),
            "[defaults]\ncache_control = 3600\n\n[page.\"about.md\"]\ntitle = \"About Us\"\n",
        )
        .unwrap();

        let (_, _, about) = document(&site, "/about");
        assert_eq!(about.title.as_deref(), Some("About Us"));
        assert_eq!(about.cache_control, Some(3600));

        // index.md shares the directory defaults but has no title configured.
        let (_, _, index) = document(&site, "/");
        assert_eq!(index.title, None);
        assert_eq!(index.cache_control, Some(3600));

        // The subdirectory does not inherit: it has no config of its own.
        let (_, _, nested) = document(&site, "/dir");
        assert_eq!(nested, PageSettings::default());
    }

    #[test]
    fn an_edited_directory_config_takes_effect() {
        let (dir, site) = fixture();
        let path = dir.path().join(DIR_CONFIG);
        fs::write(&path, "[defaults]\ncache_control = 60\n").unwrap();
        assert_eq!(document(&site, "/about").2.cache_control, Some(60));

        fs::write(&path, "[defaults]\ncache_control = 120\n").unwrap();
        bump_mtime(&path);

        assert_eq!(document(&site, "/about").2.cache_control, Some(120));
    }

    #[test]
    fn a_broken_directory_config_surfaces_as_an_error() {
        let (dir, site) = fixture();
        fs::write(dir.path().join(DIR_CONFIG), "[defaults]\ncache_control = \"soon\"\n").unwrap();
        // Not a silent fall back to defaults: that is how a typo ships.
        assert!(matches!(site.resolve("/about"), Err(Error::Toml { .. })));
    }

    #[test]
    fn a_missing_root_is_rejected_at_construction() {
        let dir = tempfile::tempdir().unwrap();
        assert!(matches!(Site::new(&dir.path().join("absent")), Err(Error::Io { .. })));
    }

    #[test]
    fn a_file_as_a_root_is_rejected() {
        let dir = tempfile::tempdir().unwrap();
        let file = dir.path().join("not-a-dir");
        fs::write(&file, "x").unwrap();
        assert!(matches!(Site::new(&file), Err(Error::Config { .. })));
    }
}