use chrono::DateTime;
use chrono::Duration;
use chrono::Utc;
use serde::Deserialize;
use serde::Serialize;
use std::path::Path;
use std::path::PathBuf;

use codex_core::config::Config;
use codex_core::default_client::create_client;

use crate::version::CODEX_CLI_VERSION;

pub fn get_upgrade_version(config: &Config) -> Option<String> {
    let version_file = version_filepath(config);
    let info = read_version_info(&version_file).ok();

    if match &info {
        None => true,
        Some(info) => info.last_checked_at < Utc::now() - Duration::hours(20),
    } {
        // Refresh the cached latest version in the background so TUI startup
        // isn’t blocked by a network call. The UI reads the previously cached
        // value (if any) for this run; the next run shows the banner if needed.
        tokio::spawn(async move {
            check_for_update(&version_file)
                .await
                .inspect_err(|e| tracing::error!("Failed to update version: {e}"))
        });
    }

    info.and_then(|info| {
        if is_newer(&info.latest_version, CODEX_CLI_VERSION).unwrap_or(false) {
            Some(info.latest_version)
        } else {
            None
        }
    })
}

#[derive(Serialize, Deserialize, Debug, Clone)]
struct VersionInfo {
    latest_version: String,
    // ISO-8601 timestamp (RFC3339)
    last_checked_at: DateTime<Utc>,
    #[serde(default)]
    dismissed_version: Option<String>,
}

#[derive(Deserialize, Debug, Clone)]
struct ReleaseInfo {
    tag_name: String,
}

const VERSION_FILENAME: &str = "version.json";
const LATEST_RELEASE_URL: &str = "https://api.github.com/repos/openai/codex/releases/latest";

fn version_filepath(config: &Config) -> PathBuf {
    config.codex_home.join(VERSION_FILENAME)
}

fn read_version_info(version_file: &Path) -> anyhow::Result<VersionInfo> {
    let contents = std::fs::read_to_string(version_file)?;
    Ok(serde_json::from_str(&contents)?)
}

async fn check_for_update(version_file: &Path) -> anyhow::Result<()> {
    let ReleaseInfo {
        tag_name: latest_tag_name,
    } = create_client()
        .get(LATEST_RELEASE_URL)
        .send()
        .await?
        .error_for_status()?
        .json::<ReleaseInfo>()
        .await?;

    // Preserve any previously dismissed version if present.
    let prev_info = read_version_info(version_file).ok();
    let info = VersionInfo {
        latest_version: latest_tag_name
            .strip_prefix("rust-v")
            .ok_or_else(|| anyhow::anyhow!("Failed to parse latest tag name '{latest_tag_name}'"))?
            .into(),
        last_checked_at: Utc::now(),
        dismissed_version: prev_info.and_then(|p| p.dismissed_version),
    };

    let json_line = format!("{}\n", serde_json::to_string(&info)?);
    if let Some(parent) = version_file.parent() {
        tokio::fs::create_dir_all(parent).await?;
    }
    tokio::fs::write(version_file, json_line).await?;
    Ok(())
}

fn is_newer(latest: &str, current: &str) -> Option<bool> {
    match (parse_version(latest), parse_version(current)) {
        (Some(l), Some(c)) => Some(l > c),
        _ => None,
    }
}

/// Returns the latest version to show in a popup, if it should be shown.
/// This respects the user's dismissal choice for the current latest version.
pub fn get_upgrade_version_for_popup(config: &Config) -> Option<String> {
    let version_file = version_filepath(config);
    let latest = get_upgrade_version(config)?;
    // If the user dismissed this exact version previously, do not show the popup.
    if let Ok(info) = read_version_info(&version_file)
        && info.dismissed_version.as_deref() == Some(latest.as_str())
    {
        return None;
    }
    Some(latest)
}

/// Persist a dismissal for the current latest version so we don't show
/// the update popup again for this version.
pub async fn dismiss_version(config: &Config, version: &str) -> anyhow::Result<()> {
    let version_file = version_filepath(config);
    let mut info = match read_version_info(&version_file) {
        Ok(info) => info,
        Err(_) => return Ok(()),
    };
    info.dismissed_version = Some(version.to_string());
    let json_line = format!("{}\n", serde_json::to_string(&info)?);
    if let Some(parent) = version_file.parent() {
        tokio::fs::create_dir_all(parent).await?;
    }
    tokio::fs::write(version_file, json_line).await?;
    Ok(())
}

fn parse_version(v: &str) -> Option<(u64, u64, u64)> {
    let mut iter = v.trim().split('.');
    let maj = iter.next()?.parse::<u64>().ok()?;
    let min = iter.next()?.parse::<u64>().ok()?;
    let pat = iter.next()?.parse::<u64>().ok()?;
    Some((maj, min, pat))
}

/// Update action the CLI should perform after the TUI exits.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum UpdateAction {
    /// Update via `npm install -g @openai/codex@latest`.
    NpmGlobalLatest,
    /// Update via `bun install -g @openai/codex@latest`.
    BunGlobalLatest,
    /// Update via `brew upgrade codex`.
    BrewUpgrade,
}

#[cfg(any(not(debug_assertions), test))]
pub(crate) fn get_update_action() -> Option<UpdateAction> {
    let exe = std::env::current_exe().unwrap_or_default();
    let managed_by_npm = std::env::var_os("CODEX_MANAGED_BY_NPM").is_some();
    let managed_by_bun = std::env::var_os("CODEX_MANAGED_BY_BUN").is_some();
    if managed_by_npm {
        Some(UpdateAction::NpmGlobalLatest)
    } else if managed_by_bun {
        Some(UpdateAction::BunGlobalLatest)
    } else if cfg!(target_os = "macos")
        && (exe.starts_with("/opt/homebrew") || exe.starts_with("/usr/local"))
    {
        Some(UpdateAction::BrewUpgrade)
    } else {
        None
    }
}

impl UpdateAction {
    /// Returns the list of command-line arguments for invoking the update.
    pub fn command_args(self) -> (&'static str, &'static [&'static str]) {
        match self {
            UpdateAction::NpmGlobalLatest => ("npm", &["install", "-g", "@openai/codex@latest"]),
            UpdateAction::BunGlobalLatest => ("bun", &["install", "-g", "@openai/codex@latest"]),
            UpdateAction::BrewUpgrade => ("brew", &["upgrade", "--cask", "codex"]),
        }
    }

    /// Returns string representation of the command-line arguments for invoking the update.
    pub fn command_str(self) -> String {
        let (command, args) = self.command_args();
        let args_str = args.join(" ");
        format!("{command} {args_str}")
    }
}

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

    #[test]
    fn prerelease_version_is_not_considered_newer() {
        assert_eq!(is_newer("0.11.0-beta.1", "0.11.0"), None);
        assert_eq!(is_newer("1.0.0-rc.1", "1.0.0"), None);
    }

    #[test]
    fn plain_semver_comparisons_work() {
        assert_eq!(is_newer("0.11.1", "0.11.0"), Some(true));
        assert_eq!(is_newer("0.11.0", "0.11.1"), Some(false));
        assert_eq!(is_newer("1.0.0", "0.9.9"), Some(true));
        assert_eq!(is_newer("0.9.9", "1.0.0"), Some(false));
    }

    #[test]
    fn whitespace_is_ignored() {
        assert_eq!(parse_version(" 1.2.3 \n"), Some((1, 2, 3)));
        assert_eq!(is_newer(" 1.2.3 ", "1.2.2"), Some(true));
    }

    #[test]
    fn test_get_update_action() {
        let prev = std::env::var_os("CODEX_MANAGED_BY_NPM");

        // First: no npm var -> expect None (we do not run from brew in CI)
        unsafe { std::env::remove_var("CODEX_MANAGED_BY_NPM") };
        assert_eq!(get_update_action(), None);

        // Then: with npm var -> expect NpmGlobalLatest
        unsafe { std::env::set_var("CODEX_MANAGED_BY_NPM", "1") };
        assert_eq!(get_update_action(), Some(UpdateAction::NpmGlobalLatest));

        // Restore prior value to avoid leaking state
        if let Some(v) = prev {
            unsafe { std::env::set_var("CODEX_MANAGED_BY_NPM", v) };
        } else {
            unsafe { std::env::remove_var("CODEX_MANAGED_BY_NPM") };
        }
    }
}