//! Loading and validating the TOML config file.
//!
//! The config is the *only* thing that decides which repositories are served.
//! A request for a repo name that is not listed here gets a 404, so nobody can
//! ask the server to read an arbitrary directory on disk.

use serde::Deserialize;
use std::collections::BTreeMap;
use std::path::{Path, PathBuf};

/// The whole config file, as written by the user.
#[derive(Debug, Clone, Deserialize)]
#[serde(deny_unknown_fields)]
pub struct Config {
    #[serde(default)]
    pub server: ServerConfig,
    /// Each `[[repo]]` table in the TOML file becomes one entry here.
    #[serde(default, rename = "repo")]
    pub repos: Vec<RepoConfig>,
}

#[derive(Debug, Clone, Deserialize)]
#[serde(deny_unknown_fields)]
pub struct ServerConfig {
    /// Address to listen on, e.g. "127.0.0.1:8090".
    #[serde(default = "default_listen")]
    pub listen: String,
    /// Title shown at the top of every page.
    #[serde(default = "default_title")]
    pub site_title: String,
    /// Base URL shown in "git clone ..." hints, e.g. "https://git.example.com".
    /// When unset, the `Host` header of the request is used.
    #[serde(default)]
    pub clone_base_url: Option<String>,
}

impl Default for ServerConfig {
    fn default() -> Self {
        ServerConfig { listen: default_listen(), site_title: default_title(), clone_base_url: None }
    }
}

fn default_listen() -> String {
    "127.0.0.1:8090".to_string()
}

fn default_title() -> String {
    "git".to_string()
}

#[derive(Debug, Clone, Deserialize)]
#[serde(deny_unknown_fields)]
pub struct RepoConfig {
    /// URL name, e.g. "rust-kernel" -> http://host/rust-kernel/
    pub name: String,
    /// Path on disk: a bare repo (`foo.git`) or a normal checkout (`foo/`).
    pub path: PathBuf,
    #[serde(default)]
    pub description: String,
}

/// The validated, ready-to-use set of repos, looked up by name.
#[derive(Debug, Clone)]
pub struct Repos {
    by_name: BTreeMap<String, RepoConfig>,
}

impl Repos {
    pub fn get(&self, name: &str) -> Option<&RepoConfig> {
        // Allow `/name.git/...` as an alias for `/name/...` (people expect it in clone URLs).
        let name = name.strip_suffix(".git").unwrap_or(name);
        self.by_name.get(name)
    }

    /// All repos, sorted by name.
    pub fn iter(&self) -> impl Iterator<Item = &RepoConfig> {
        self.by_name.values()
    }

    pub fn len(&self) -> usize {
        self.by_name.len()
    }

    pub fn is_empty(&self) -> bool {
        self.by_name.is_empty()
    }
}

impl Config {
    /// Parse a config from TOML text.
    pub fn from_toml(text: &str) -> Result<Config, String> {
        toml::from_str(text).map_err(|e| format!("invalid config: {e}"))
    }

    /// Read and parse a config file from disk.
    pub fn load(path: &Path) -> Result<Config, String> {
        let text =
            std::fs::read_to_string(path).map_err(|e| format!("cannot read {}: {e}", path.display()))?;
        Config::from_toml(&text)
    }

    /// Check names and paths, and build the lookup table.
    ///
    /// Paths are canonicalized (symlinks and `..` resolved) once, here, so the
    /// rest of the program only ever deals with fixed absolute paths.
    pub fn validate(&self) -> Result<Repos, String> {
        let mut by_name = BTreeMap::new();
        for repo in &self.repos {
            let name = repo.name.strip_suffix(".git").unwrap_or(&repo.name);
            if !is_valid_repo_name(name) {
                return Err(format!(
                    "repo name {:?} is not allowed (use letters, digits, '-', '_' and '.', not starting with '.')",
                    repo.name
                ));
            }
            let path = std::fs::canonicalize(&repo.path)
                .map_err(|e| format!("repo {name:?}: path {}: {e}", repo.path.display()))?;
            let fixed = RepoConfig { name: name.to_string(), path, description: repo.description.clone() };
            if by_name.insert(name.to_string(), fixed).is_some() {
                return Err(format!("repo name {name:?} is listed twice"));
            }
        }
        Ok(Repos { by_name })
    }
}

/// Repo names end up in URLs, so keep them boring.
pub fn is_valid_repo_name(name: &str) -> bool {
    !name.is_empty()
        && name.len() <= 100
        && !name.starts_with('.')
        && name.chars().all(|c| c.is_ascii_alphanumeric() || c == '-' || c == '_' || c == '.')
}

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

    #[test]
    fn parses_full_config() {
        let cfg = Config::from_toml(
            r#"
            [server]
            listen = "0.0.0.0:9000"
            site_title = "my git"

            [[repo]]
            name = "one"
            path = "/tmp"
            description = "first"
            "#,
        )
        .unwrap();
        assert_eq!(cfg.server.listen, "0.0.0.0:9000");
        assert_eq!(cfg.server.site_title, "my git");
        assert_eq!(cfg.repos.len(), 1);
        assert_eq!(cfg.repos[0].description, "first");
    }

    #[test]
    fn defaults_apply() {
        let cfg = Config::from_toml("").unwrap();
        assert_eq!(cfg.server.listen, "127.0.0.1:8090");
        assert!(cfg.repos.is_empty());
    }

    #[test]
    fn rejects_unknown_keys() {
        assert!(Config::from_toml("bogus = 1").is_err());
    }

    #[test]
    fn repo_names() {
        assert!(is_valid_repo_name("rust-kernel"));
        assert!(is_valid_repo_name("a_b.c"));
        assert!(!is_valid_repo_name(""));
        assert!(!is_valid_repo_name(".."));
        assert!(!is_valid_repo_name(".hidden"));
        assert!(!is_valid_repo_name("a/b"));
        assert!(!is_valid_repo_name("a b"));
        assert!(!is_valid_repo_name("<script>"));
    }

    #[test]
    fn validate_rejects_bad_and_duplicate_names() {
        let bad = Config::from_toml("[[repo]]\nname = \"../x\"\npath = \"/tmp\"").unwrap();
        assert!(bad.validate().is_err());
        let dup = Config::from_toml(
            "[[repo]]\nname = \"x\"\npath = \"/tmp\"\n[[repo]]\nname = \"x.git\"\npath = \"/tmp\"",
        )
        .unwrap();
        assert!(dup.validate().is_err());
        let ok = Config::from_toml("[[repo]]\nname = \"x.git\"\npath = \"/tmp\"").unwrap();
        let repos = ok.validate().unwrap();
        assert!(repos.get("x").is_some());
        assert!(repos.get("x.git").is_some());
        assert!(repos.get("y").is_none());
    }
}