//! In-app updates (M10.9).
//!
//! Two channels, because two audiences: `stable` follows tagged `v*` releases,
//! `dev` follows every green push. Each reads a `latest.json` published as an asset
//! on a release whose TAG NEVER CHANGES — verified necessary, because Forgejo has no
//! `/releases/latest/download/<asset>` route (it 404s), so "newest" cannot be named
//! in a URL. A fixed tag can.
//!
//! The feed lives on Fabled-Git rather than on a ThoughtSync server, deliberately:
//! this app is usable having never linked a server, and an install that can't reach
//! its own updates because it isn't paired with anything would contradict the whole
//! local-first premise.
//!
//! Updates are signed. The public half is baked into `tauri.conf.json`; the private
//! half exists only as a CI secret, and is generated by the operator — a release
//! signing key that has passed through anyone else's hands is not a signing key.

use serde::{Deserialize, Serialize};
use tauri::State;
use tauri_plugin_updater::UpdaterExt;

use crate::local::{store, Db};

/// Where the manifests live. Fixed tags, so these URLs are permanent.
const FEED_BASE: &str = "https://git.fabledsword.com/bvandeusen/thoughtsync/releases/download";

const CHANNEL_PREF: &str = "update_channel";

#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum Channel {
    Stable,
    Dev,
}

impl Channel {
    fn as_str(self) -> &'static str {
        match self {
            Channel::Stable => "stable",
            Channel::Dev => "dev",
        }
    }

    /// Anything unrecognized reads as `stable`. A corrupted or hand-edited value
    /// must not silently opt someone into pre-release builds.
    fn parse(raw: &str) -> Self {
        match raw.trim() {
            "dev" => Channel::Dev,
            _ => Channel::Stable,
        }
    }

    fn feed_url(self) -> String {
        format!("{FEED_BASE}/{}/latest.json", self.as_str())
    }
}

/// What the UI needs to describe the update situation without a second call.
#[derive(Debug, Serialize)]
pub struct UpdateStatus {
    pub channel: Channel,
    pub current_version: String,
    /// The newer version on offer, or `None` when already up to date.
    pub available: Option<String>,
    pub notes: Option<String>,
    /// False when this install can't apply an update to itself (see
    /// `self_update_blocker`). The UI must not offer a button that cannot work.
    pub can_install: bool,
    /// Why not, in words meant for the person reading them.
    pub blocked_reason: Option<String>,
}

/// Whether this install can replace itself, and if not, why.
///
/// The updater rewrites the running bundle in place, which only works for formats
/// that ARE a single self-contained file. On Linux that means the AppImage and
/// nothing else: a `.deb` or pacman install is owned by the package manager, and
/// silently overwriting files it tracks would corrupt its database. Tauri detects
/// the AppImage case by the `APPIMAGE` env var the runtime sets.
fn self_update_blocker() -> Option<String> {
    if cfg!(target_os = "linux") && std::env::var_os("APPIMAGE").is_none() {
        return Some(
            "This copy was installed by your package manager, so it updates the same \
             way — `apt upgrade`, `pacman -Syu`, or re-running the install script. \
             In-app updates work on the AppImage build."
                .to_string(),
        );
    }
    None
}

fn read_channel(db: &State<'_, Db>) -> Result<Channel, String> {
    let conn = db.0.lock().map_err(|e| e.to_string())?;
    let raw = store::pref(&conn, CHANNEL_PREF).map_err(|e| e.to_string())?;
    Ok(raw
        .as_deref()
        .map(Channel::parse)
        .unwrap_or(Channel::Stable))
}

#[tauri::command]
pub fn update_channel_get(db: State<'_, Db>) -> Result<Channel, String> {
    read_channel(&db)
}

#[tauri::command]
pub fn update_channel_set(channel: Channel, db: State<'_, Db>) -> Result<Channel, String> {
    let conn = db.0.lock().map_err(|e| e.to_string())?;
    store::set_pref(&conn, CHANNEL_PREF, channel.as_str()).map_err(|e| e.to_string())?;
    log::info!("update channel set to {}", channel.as_str());
    Ok(channel)
}

/// Ask the feed whether there's something newer. Never installs anything.
#[tauri::command]
pub async fn update_check(
    app: tauri::AppHandle,
    db: State<'_, Db>,
) -> Result<UpdateStatus, String> {
    let channel = read_channel(&db)?;
    let current_version = app.package_info().version.to_string();
    let blocked_reason = self_update_blocker();

    let url = channel
        .feed_url()
        .parse()
        .map_err(|e| format!("the update feed address is malformed: {e}"))?;
    let updater = app
        .updater_builder()
        .endpoints(vec![url])
        .map_err(|e| e.to_string())?
        .build()
        .map_err(|e| format!("updates aren't configured for this build: {e}"))?;

    // A missing manifest is the ordinary state of a channel nobody has published to
    // yet — report it as "nothing available" rather than as a failure to act on.
    // Matched on the message rather than an error variant so this doesn't break on a
    // plugin minor that renames one.
    let found = match updater.check().await {
        Ok(found) => found,
        Err(e) => {
            let detail = e.to_string();
            if is_missing_manifest(&detail) {
                None
            } else {
                return Err(describe_check_error(&detail));
            }
        }
    };

    Ok(UpdateStatus {
        channel,
        current_version,
        available: found.as_ref().map(|u| u.version.clone()),
        notes: found.as_ref().and_then(|u| u.body.clone()),
        can_install: found.is_some() && blocked_reason.is_none(),
        blocked_reason,
    })
}

/// Download, verify and apply the update, then relaunch.
///
/// Refuses up front on an install that can't replace itself, rather than failing
/// halfway through with a permissions error nobody can interpret.
#[tauri::command]
pub async fn update_install(app: tauri::AppHandle, db: State<'_, Db>) -> Result<(), String> {
    if let Some(reason) = self_update_blocker() {
        return Err(reason);
    }
    let channel = read_channel(&db)?;
    let url = channel
        .feed_url()
        .parse()
        .map_err(|e| format!("the update feed address is malformed: {e}"))?;
    let updater = app
        .updater_builder()
        .endpoints(vec![url])
        .map_err(|e| e.to_string())?
        .build()
        .map_err(|e| format!("updates aren't configured for this build: {e}"))?;

    let found = updater
        .check()
        .await
        .map_err(|e| describe_check_error(&e.to_string()))?;
    let Some(update) = found else {
        return Err("There's no update to install — this is already the newest build.".to_string());
    };

    log::info!(
        "installing update {} over {} ({} channel)",
        update.version,
        app.package_info().version,
        channel.as_str()
    );
    update
        .download_and_install(|_chunk, _total| {}, || {})
        .await
        .map_err(|e| format!("the update couldn't be installed: {e}"))?;

    // Only reached if the install succeeded. `restart` diverges, so it's the tail.
    log::info!("update installed; restarting");
    app.restart()
}

/// Whether a check failure just means "this channel has nothing published yet".
fn is_missing_manifest(detail: &str) -> bool {
    let lower = detail.to_lowercase();
    lower.contains("404") || lower.contains("not found")
}

/// Turn a check failure into something worth reading. The default rendering of a
/// transport error names the URL and nothing else, which tells a user nothing about
/// what they could do next.
fn describe_check_error(detail: &str) -> String {
    let lower = detail.to_lowercase();
    if lower.contains("error sending request") || lower.contains("dns") || lower.contains("connect")
    {
        return "Couldn't reach the update server — check your connection.".to_string();
    }
    format!("Couldn't check for updates: {detail}")
}

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

    #[test]
    fn each_channel_has_its_own_fixed_feed() {
        assert!(Channel::Stable.feed_url().ends_with("/stable/latest.json"));
        assert!(Channel::Dev.feed_url().ends_with("/dev/latest.json"));
        assert_ne!(Channel::Stable.feed_url(), Channel::Dev.feed_url());
    }

    #[test]
    fn the_feed_is_https() {
        // The manifest names the URL and signature of a binary that is about to
        // replace this one. The signature is what actually protects it, but there's
        // no reason to hand an attacker the manifest to tamper with in the first place.
        assert!(Channel::Stable.feed_url().starts_with("https://"));
        assert!(Channel::Dev.feed_url().starts_with("https://"));
    }

    #[test]
    fn an_unknown_channel_falls_back_to_stable() {
        // A corrupted or hand-edited pref must never silently opt someone into
        // pre-release builds — the safe default is the conservative one.
        assert_eq!(Channel::parse("dev"), Channel::Dev);
        assert_eq!(Channel::parse("stable"), Channel::Stable);
        assert_eq!(Channel::parse("nightly"), Channel::Stable);
        assert_eq!(Channel::parse(""), Channel::Stable);
    }

    #[test]
    fn an_unpublished_channel_is_not_reported_as_a_failure() {
        // Before the first publish, or on a channel nobody uses, the feed simply
        // isn't there. That's "you're up to date", not something to alarm anyone with.
        assert!(is_missing_manifest("http status: 404 Not Found"));
        assert!(is_missing_manifest("Release Not Found"));
        assert!(!is_missing_manifest("invalid signature"));
    }

    #[test]
    fn an_unreachable_server_reads_as_a_connection_problem() {
        let msg = describe_check_error("error sending request for url (https://…)");
        assert!(msg.contains("connection"), "got {msg}");
        // Anything unrecognized still surfaces its detail rather than being swallowed.
        assert!(describe_check_error("invalid signature").contains("invalid signature"));
    }

    #[test]
    fn the_channel_name_round_trips() {
        for channel in [Channel::Stable, Channel::Dev] {
            assert_eq!(Channel::parse(channel.as_str()), channel);
        }
    }
}