//! update: compare the installed version with the latest available one and
//! reinstall when an update exists.

use super::*;
use crate::backup;
use crate::events::{Event, EventKind};
use crate::installers;
use crate::runner::{Runner, SystemRunner};
use anyhow::{bail, Result};
use std::cmp::Ordering;
use std::path::PathBuf;

pub fn run(
    app: &App,
    agent_name: Option<&str>,
    all: bool,
    rollback: Option<&str>,
) -> Result<i32> {
    // Issue #64: --rollback restores a pre-update backup instead of updating.
    if rollback.is_some() {
        return rollback_point(app, rollback);
    }

    let runner = SystemRunner::new(app.dry_run(), app.cli.verbose, &app.log);

    let policy = app.config.settings.update_policy.unwrap_or_default();
    if policy == UpdatePolicy::None && all {
        app.log.warn("update policy is 'none'; 'am update --all' is a no-op");
        return Ok(0);
    }

    if let Some(name) = agent_name {
        if policy == UpdatePolicy::None && !app.yes() {
            app.log.warn("update policy is 'none'; use --yes to force a single-agent update");
        }
        return update_one(app, &runner, name);
    }
    if all {
        let entries = app.state.all()?;
        let names: Vec<String> = entries.keys().cloned().collect();
        let mut failed = 0;
        // Issue #64: one snapshot covers the whole batch.
        if !app.dry_run() && !names.is_empty() {
            let info = backup::create_backup(app, "update:--all", &names)?;
            app.log.verbose(&format!("pre-update backup: {}", info.id));
            app.emit(
                &Event::now(EventKind::Backup)
                    .with_args(vec![info.id.clone()])
                    .with_reason("update:--all"),
            );
        }
        for name in names {
            if let Err(e) = update_one(app, &runner, &name) {
                failed += 1;
                app.log.error(&format!("{name}: {e:#}"));
            }
        }
        return Ok(if failed > 0 { 1 } else { 0 });
    }
    bail!("update requires an agent name, or --all");
}

fn update_one(app: &App, runner: &dyn Runner, name: &str) -> Result<i32> {
    let agent = require_agent(app, name)?;

    // Issue #65: honor per-agent pinned version.
    if let Some(pin) = agent.pin_version.as_deref() {
        let current = app
            .state
            .get(&agent.name)
            .ok()
            .flatten()
            .and_then(|e| e.version.clone());
        if current.as_deref() == Some(pin) {
            app.log.success(&format!(
                "{} is pinned to v{pin} and already at that version",
                agent.title()
            ));
        } else {
            app.log.warn(&format!(
                "{} is pinned to v{pin} but currently at {}; update skipped",
                agent.title(),
                current.as_deref().unwrap_or("unknown")
            ));
        }
        return Ok(0);
    }

    let Some(entry) = app.state.get(&agent.name).ok().flatten() else {
        bail!(
            "agent '{}' is not installed by agent-manager — use 'am install {}'",
            agent.name,
            agent.name
        );
    };
    let spec = agent
        .install
        .as_ref()
        .ok_or_else(|| anyhow::anyhow!("agent '{}' has no install definition", agent.name))?;
    let methods = spec.all_methods();
    // Prefer the method that was originally used.
    let method = methods
        .iter()
        .find(|m| m.kind.as_str() == entry.method)
        .copied()
        .unwrap_or(methods[0]);

    let latest = if app.dry_run() {
        None
    } else {
        installers::latest_version(app, agent, method, runner)?
    };
    let current = entry.version.clone().or_else(|| {
        entry
            .bins
            .first()
            .and_then(|b| installers::detect_version(runner, &PathBuf::from(b)))
    });

    match (&latest, &current) {
        (Some(l), Some(c)) => match crate::version::compare(l, c) {
            Some(Ordering::Greater) => {
                app.log.info(&format!("update available: {c} -> {l}"));
            }
            Some(Ordering::Equal) | Some(Ordering::Less) => {
                app.log
                    .success(&format!("{} is up to date (v{c})", agent.title()));
                return Ok(0);
            }
            None => {
                app.log.warn(&format!("cannot compare versions ({c} vs {l}); reinstalling"));
            }
        },
        (Some(l), None) => app.log.info(&format!(
            "latest available: {l} (installed version unknown); reinstalling"
        )),
        (None, Some(c)) => app.log.warn(&format!(
            "cannot determine the latest version (installed: {c}); reinstalling"
        )),
        (None, None) => app.log.warn("cannot determine versions; reinstalling"),
    }

    if app.dry_run() {
        app.log
            .dry(format!("would reinstall {} via {}", agent.name, method.kind));
        return Ok(0);
    }
    // Issue #64: snapshot before the real update so a broken upgrade can be
    // undone with 'am update --rollback'.
    let info = backup::create_backup(app, &format!("update:{}", agent.name), &[agent.name.clone()])?;
    app.log.verbose(&format!("pre-update backup: {}", info.id));
    app.emit(
        &Event::now(EventKind::Backup)
            .with_args(vec![info.id.clone()])
            .with_agent(agent.name.clone())
            .with_reason("pre-update"),
    );
    crate::deps::ensure_deps(app, agent, runner)?;
    let outcome = installers::run_install(app, agent, method, runner)?;
    let mut new_entry = installers::make_entry(agent, method, &outcome, app);
    new_entry.installed_at = entry.installed_at.clone();
    new_entry.updated_at = Some(installers::now_rfc3339());
    let version = new_entry.version.clone().unwrap_or_else(|| "unknown".to_string());
    app.state.set(&new_entry)?;
    app.emit(
        &Event::now(EventKind::Update)
            .with_agent(agent.name.clone())
            .with_args(vec![format!("method={}", method.kind)]),
    );
    crate::hooks::run_hooks(
        app,
        "on_update",
        &std::env::current_dir().unwrap_or_default(),
    );
    app.log.success(&format!(
        "updated {} to v{version}",
        agent.title()
    ));
    Ok(0)
}

/// Issue #64: 'am update --rollback [point]' — restore a pre-update backup.
/// '--rollback list' prints the available backup points.
fn rollback_point(app: &App, point: Option<&str>) -> Result<i32> {
    if point == Some("list") {
        let all = backup::list_backups(app);
        if all.is_empty() {
            app.log.info("no backup found — run an update first to create one");
            return Ok(0);
        }
        println!("pre-update backups ({}):", all.len());
        for b in &all {
            println!(
                "  {}  {}  agents={}{}",
                b.id,
                b.reason,
                if b.agents.is_empty() {
                    "all".to_string()
                } else {
                    b.agents.join(",")
                },
                if b.state && b.config { "  [state+config]" } else { "" }
            );
        }
        println!("\nuse 'am update --rollback <id>' to restore one");
        return Ok(0);
    }
    let info = backup::restore_backup(app, point)?;
    app.emit(
        &Event::now(EventKind::Rollback)
            .with_args(vec![info.id.clone()])
            .with_reason(&info.reason),
    );
    app.log.success(&format!(
        "rolled back to backup {} ({})",
        info.id, info.reason
    ));
    Ok(0)
}