//! Finding out what a machine can run, rather than being told.
//!
//! The phone adds a machine by giving connection details; this asks the machine
//! itself which of the known programs it has, and the answer becomes its
//! providers. That is a security property, not a convenience: **no route accepts
//! a command from the phone.** If it did, the enrolled token could introduce
//! arbitrary programs to run on every machine a setup names.
//!
//! It is also the better interface: nobody wants to type an absolute path on a
//! phone keyboard, and a machine that has moved its binaries answers correctly
//! on the next probe.
//!
//! The cost is that a program somewhere unusual is invisible. The escape hatch
//! is editing `config.ron` on the backend, which is exactly the authority the
//! phone is not being given.

use anyhow::Result;

use crate::config::{DriverKind, ProviderConfig};
use crate::session::transport::{Launch, Transport};

/// What is looked for, and what finding it makes. Extending this is how a new
/// driver becomes discoverable -- one row, not a branch anywhere. The name is
/// what the provider gets called, so it is what the phone shows and what a
/// session stores.
const PROBES: &[(&str, &str, DriverKind)] = &[
    ("claude-cli", "claude", DriverKind::ClaudeCli),
    ("local-llama", "llama-server", DriverKind::LlamaCpp),
];

/// Models offered for a discovered Claude CLI. A shortcut list for the spawn
/// screen, not a restriction -- the field stays free text.
const CLAUDE_MODELS: &[&str] = &["fable", "opus", "sonnet", "haiku"];

/// Asks `transport`'s machine which of [`PROBES`] it has.
///
/// One round trip rather than one per program: over ssh each would be a separate
/// connection and handshake. `command -v` is POSIX and a shell builtin, so it
/// works whatever is installed -- and `|| true` keeps a missing program from
/// ending the loop, since the caller wants the whole answer.
pub async fn discover(transport: &Transport) -> Result<Vec<ProviderConfig>> {
    let wanted: Vec<&str> = PROBES.iter().map(|(_, binary, _)| *binary).collect();
    let script = format!(
        "for p in {}; do command -v \"$p\" || true; done",
        wanted.join(" ")
    );
    let launch = Launch::new("sh", vec!["-c".to_string(), script], None);
    let found = transport.capture(&launch).await.map_err(explain)?;

    let mut providers = Vec::new();
    // Echo runs inside this server, so it exists exactly where this server does
    // and nowhere else. Offering it on a remote machine would be a choice that
    // changes nothing.
    if matches!(transport, Transport::Here) {
        providers.push(ProviderConfig {
            name: crate::config::ECHO_PROVIDER.to_string(),
            kind: DriverKind::Echo,
            command: None,
            models: Vec::new(),
        });
    }
    for (name, binary, kind) in PROBES {
        let path = found
            .lines()
            .map(str::trim)
            .find(|line| line.rsplit('/').next() == Some(*binary));
        let Some(path) = path else {
            continue;
        };
        providers.push(ProviderConfig {
            name: (*name).to_string(),
            kind: *kind,
            // The resolved path rather than the bare name: PATH under a
            // non-interactive ssh session is not the one a person sees when they
            // log in, so "it is on my PATH" is not enough.
            command: Some(path.to_string()),
            models: match kind {
                DriverKind::ClaudeCli => CLAUDE_MODELS.iter().map(|m| (*m).to_string()).collect(),
                _ => Vec::new(),
            },
        });
    }
    Ok(providers)
}

/// Adds what to do to failures whose own wording does not say.
///
/// ssh's messages are written for someone at a terminal on the backend, which is
/// exactly who is not reading this one. Host key verification is the case that
/// matters: **every** machine fails it the first time, so without this, adding a
/// machine from the phone looks broken rather than unfinished.
///
/// Deliberately not fixed by relaxing the check. `StrictHostKeyChecking` stays
/// at its default, so a first connection is a decision somebody makes on the
/// backend with the key in front of them.
fn explain(err: anyhow::Error) -> anyhow::Error {
    let message = format!("{err:#}");
    if message.contains("Host key verification failed") {
        return anyhow::anyhow!(
            "{message} This machine has not been connected to before, so its key is not \
             trusted yet. Ssh to it once from the backend -- that is where the decision to \
             trust a key belongs -- and try again.",
        );
    }
    if message.contains("Permission denied") {
        return anyhow::anyhow!(
            "{message} The key named here has to be authorized on that machine, and the path \
             is read on the backend rather than on the phone.",
        );
    }
    err
}

/// A short, stable, filename-safe id derived from a label. Derived once when a
/// setup is added and then fixed, so the label stays editable. Collisions are
/// resolved by the caller, which is the only place that knows what exists.
pub fn id_from(label: &str) -> String {
    let slug: String = label
        .chars()
        .map(|c| {
            if c.is_ascii_alphanumeric() {
                c.to_ascii_lowercase()
            } else {
                '-'
            }
        })
        .collect();
    let slug = slug.trim_matches('-').replace("--", "-");
    if slug.is_empty() {
        crate::session::random_hex()
    } else {
        slug.chars().take(32).collect()
    }
}

/// Normalises what a phone keyboard produced: trims, drops blanks, and
/// expands a leading `~` the way a shell would.
pub fn tidy(value: &str) -> Option<String> {
    let value = value.trim();
    if value.is_empty() {
        return None;
    }
    Some(match value.strip_prefix("~/") {
        Some(rest) => match std::env::home_dir() {
            Some(home) => home.join(rest).to_string_lossy().into_owned(),
            None => value.to_string(),
        },
        None => value.to_string(),
    })
}

/// The inverse of [`tidy`]'s expansion: an absolute path under this machine's
/// home, written back as `~/…`, so that a working directory reads on a phone the
/// way it is written by hand.
///
/// Applied only to paths on **this** machine. `$HOME` here says nothing about
/// the home directory of a machine reached over ssh, so a remote path is stored
/// exactly as it was typed and the remote shell is what expands it.
pub fn shorten_home(path: &str) -> String {
    let Some(home) = std::env::home_dir() else {
        return path.to_string();
    };
    let home = home.to_string_lossy();
    // The separator has to be part of the match, or `/home/bobby` would be read
    // as a path inside `/home/bob`.
    match path.strip_prefix(home.as_ref()) {
        Some("") => "~".to_string(),
        Some(rest) if rest.starts_with('/') => format!("~{rest}"),
        _ => path.to_string(),
    }
}

/// Runs a launch to completion and returns its stdout as text.
///
/// The common case of [`Transport::capture_with_input`]: nothing on stdin, a
/// failure reported as the machine's own words (ssh's "Permission denied" is the
/// useful half of why a setup cannot be reached), and the output read as text
/// because every caller here is asking a question whose answer is words.
impl Transport {
    pub async fn capture(&self, launch: &Launch) -> Result<String> {
        let captured = self
            .capture_with_input(launch, super::session::transport::Input::None)
            .await?;
        Ok(String::from_utf8_lossy(&captured.ok()?).into_owned())
    }
}

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

    /// The two halves of a home-relative path, which have to be inverses: what
    /// is stored is what the phone draws, and what the phone sends back is what
    /// a process is started in.
    #[test]
    fn a_home_path_shortens_and_expands_back() {
        let Some(home) = std::env::home_dir() else {
            return;
        };
        let full = home.join("repos/ai-app-2");
        let full = full.to_string_lossy();
        assert_eq!(shorten_home(&full), "~/repos/ai-app-2");
        assert_eq!(shorten_home(&home.to_string_lossy()), "~");
        assert_eq!(tidy("~/repos/ai-app-2").as_deref(), Some(full.as_ref()));

        // Not a prefix match on the characters: a sibling directory whose name
        // merely starts with the home directory's is not inside it.
        let sibling = format!("{}-backup/notes", home.to_string_lossy());
        assert_eq!(shorten_home(&sibling), sibling);
        assert_eq!(shorten_home("/etc/hosts"), "/etc/hosts");
    }
}