//! Self-update mechanism.
//!
//! Checks the hosted herdr.dev update manifest for newer versions and downloads the binary.
//! Uses `curl` as a subprocess for HTTP — no additional Rust HTTP dependencies.
//! JSON parsing uses serde_json (already in deps for persistence).

use std::collections::BTreeMap;
use std::env;
use std::fs;
use std::process::Command;

use serde::Deserialize;

const UPDATE_MANIFEST_URL: &str = "https://herdr.dev/latest.json";
const CURRENT_VERSION: &str = env!("CARGO_PKG_VERSION");
const FAKE_UPDATE_VERSION_ENV: &str = "HERDR_FAKE_UPDATE_VERSION";

fn fake_release_notes_body(version: &str) -> String {
    format!(
        "### Changed\n- Test update v{version} for local UI validation.\n\n### Notes\n- This is stub release-notes content generated by {FAKE_UPDATE_VERSION_ENV}."
    )
}

// ---------------------------------------------------------------------------
// Version
// ---------------------------------------------------------------------------

/// Parsed semver version for comparison.
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
pub struct Version {
    pub major: u32,
    pub minor: u32,
    pub patch: u32,
}

impl Version {
    pub fn parse(s: &str) -> Option<Self> {
        let s = s.strip_prefix('v').unwrap_or(s);
        let parts: Vec<&str> = s.split('.').collect();
        if parts.len() != 3 {
            return None;
        }
        Some(Self {
            major: parts[0].parse().ok()?,
            minor: parts[1].parse().ok()?,
            patch: parts[2].parse().ok()?,
        })
    }

    pub fn current() -> Self {
        Self::parse(CURRENT_VERSION).expect("invalid CARGO_PKG_VERSION")
    }
}

impl std::fmt::Display for Version {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{}.{}.{}", self.major, self.minor, self.patch)
    }
}

// ---------------------------------------------------------------------------
// Update manifest
// ---------------------------------------------------------------------------

#[derive(Deserialize)]
struct UpdateManifest {
    version: String,
    notes: String,
    assets: BTreeMap<String, String>,
}

impl UpdateManifest {
    fn download_url_for(&self, os: &str, arch: &str) -> Option<String> {
        self.assets.get(&format!("{os}-{arch}")).cloned()
    }

    fn notes_body(&self) -> String {
        self.notes.trim().to_string()
    }
}

// ---------------------------------------------------------------------------
// Release info
// ---------------------------------------------------------------------------

/// Information about an available update.
struct ReleaseInfo {
    version: Version,
    download_url: String,
    notes_body: String,
}

/// Check the hosted update manifest for the latest release. Returns release info if newer.
fn check_latest() -> Result<Option<ReleaseInfo>, String> {
    let current = Version::current();

    let output = Command::new("curl")
        .args([
            "-sfL",
            "--retry",
            "3",
            "--connect-timeout",
            "10",
            "--max-time",
            "20",
            UPDATE_MANIFEST_URL,
        ])
        .output()
        .map_err(|e| format!("curl failed: {e}"))?;

    if !output.status.success() {
        return Err("failed to fetch update manifest".into());
    }

    let manifest: UpdateManifest = serde_json::from_slice(&output.stdout)
        .map_err(|e| format!("failed to parse update manifest JSON: {e}"))?;

    let latest = Version::parse(&manifest.version)
        .ok_or_else(|| format!("invalid version in update manifest: {}", manifest.version))?;

    if latest <= current {
        return Ok(None); // up to date
    }

    let notes_body = manifest.notes_body();
    if notes_body.is_empty() {
        return Err("update manifest notes are empty".into());
    }

    let (os, arch) = platform_target();
    let download_url = manifest
        .download_url_for(os, arch)
        .ok_or_else(|| format!("no binary for {os}-{arch} in update manifest"))?;

    Ok(Some(ReleaseInfo {
        version: latest,
        download_url,
        notes_body,
    }))
}

// ---------------------------------------------------------------------------
// Download + install
// ---------------------------------------------------------------------------

/// Download and install a release. Returns the installed version.
fn download_and_install(release: &ReleaseInfo) -> Result<(), String> {
    let current_exe = env::current_exe().map_err(|e| format!("can't find current binary: {e}"))?;

    let parent = current_exe.parent().ok_or("can't find binary directory")?;

    // Check write permissions early
    let test_path = parent.join(".herdr-write-test");
    if let Err(e) = fs::write(&test_path, b"") {
        let _ = fs::remove_file(&test_path);
        return Err(format!(
            "install directory not writable: {} ({}). Try running with appropriate permissions.",
            parent.display(),
            e
        ));
    }
    let _ = fs::remove_file(&test_path);

    // Unique temp file (avoids races with concurrent instances)
    let tmp_path = parent.join(format!(".herdr-update-{}.tmp", std::process::id()));

    // Download the exact asset URL (pinned to the release we checked)
    let status = Command::new("curl")
        .args(["-sfL", "--max-time", "120", "-o"])
        .arg(&tmp_path)
        .arg(&release.download_url)
        .status()
        .map_err(|e| format!("download failed: {e}"))?;

    if !status.success() {
        let _ = fs::remove_file(&tmp_path);
        return Err("download failed".into());
    }

    // Make executable
    #[cfg(unix)]
    {
        use std::os::unix::fs::PermissionsExt;
        if let Err(e) = fs::set_permissions(&tmp_path, fs::Permissions::from_mode(0o755)) {
            let _ = fs::remove_file(&tmp_path);
            return Err(format!("chmod failed: {e}"));
        }
    }

    // Atomic replace — rename over the current binary.
    // On Linux, the running process keeps its fd to the old inode.
    // Next launch picks up the new file.
    if let Err(e) = fs::rename(&tmp_path, &current_exe) {
        let _ = fs::remove_file(&tmp_path);
        return Err(format!("failed to replace binary: {e}"));
    }

    Ok(())
}

// ---------------------------------------------------------------------------
// Public API
// ---------------------------------------------------------------------------

/// Manual self-update command (`herdr update`).
pub fn self_update() -> Result<Version, String> {
    eprintln!("checking for updates...");

    let current = Version::current();

    let release = match check_latest()? {
        Some(r) => r,
        None => {
            eprintln!("already up to date (v{current})");
            return Ok(current);
        }
    };

    eprintln!("downloading v{}...", release.version);
    if let Err(e) =
        crate::release_notes::save_pending(&release.version.to_string(), &release.notes_body)
    {
        tracing::warn!("failed to save pending release notes: {e}");
    }
    download_and_install(&release)?;
    eprintln!("updated to v{}", release.version);

    Ok(release.version)
}

/// Background auto-update: check, download, install, notify TUI.
/// Runs in a background thread at startup.
pub fn auto_update(events: tokio::sync::mpsc::Sender<crate::events::AppEvent>) {
    if let Ok(version) = env::var(FAKE_UPDATE_VERSION_ENV) {
        let version = version.trim();
        if !version.is_empty() {
            tracing::info!(
                env = FAKE_UPDATE_VERSION_ENV,
                version,
                "using fake update version for local testing"
            );
            if let Err(e) =
                crate::release_notes::save_pending(version, &fake_release_notes_body(version))
            {
                tracing::warn!("failed to save fake pending release notes: {e}");
            }
            let _ = events.blocking_send(crate::events::AppEvent::UpdateReady {
                version: version.to_string(),
            });
        }
        return;
    }

    let release = match check_latest() {
        Ok(Some(r)) => r,
        _ => return, // up to date or failed — silently do nothing
    };

    tracing::info!(
        "new version v{} available, downloading from {}",
        release.version,
        release.download_url
    );

    if let Err(e) =
        crate::release_notes::save_pending(&release.version.to_string(), &release.notes_body)
    {
        tracing::warn!("failed to save pending release notes: {e}");
    }

    if let Err(e) = download_and_install(&release) {
        tracing::warn!("auto-update failed: {e}");
        return;
    }

    tracing::info!(
        "auto-update: v{} installed, restart to use",
        release.version
    );

    // Notify the TUI — blocking_send is safe from a std::thread
    let _ = events.blocking_send(crate::events::AppEvent::UpdateReady {
        version: release.version.to_string(),
    });
}

// ---------------------------------------------------------------------------
// Helpers
// ---------------------------------------------------------------------------

fn platform_target() -> (&'static str, &'static str) {
    let os = if cfg!(target_os = "linux") {
        "linux"
    } else if cfg!(target_os = "macos") {
        "macos"
    } else {
        "unknown"
    };

    let arch = if cfg!(target_arch = "x86_64") {
        "x86_64"
    } else if cfg!(target_arch = "aarch64") {
        "aarch64"
    } else {
        "unknown"
    };

    (os, arch)
}

// ---------------------------------------------------------------------------
// Tests
// ---------------------------------------------------------------------------

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

    #[test]
    fn parse_version_basic() {
        assert_eq!(
            Version::parse("1.2.3"),
            Some(Version {
                major: 1,
                minor: 2,
                patch: 3
            })
        );
    }

    #[test]
    fn parse_version_with_v_prefix() {
        assert_eq!(
            Version::parse("v0.1.0"),
            Some(Version {
                major: 0,
                minor: 1,
                patch: 0
            })
        );
    }

    #[test]
    fn parse_version_invalid() {
        assert_eq!(Version::parse("1.2"), None);
        assert_eq!(Version::parse("abc"), None);
        assert_eq!(Version::parse(""), None);
    }

    #[test]
    fn fake_release_notes_include_version_and_context() {
        let body = fake_release_notes_body("9.4.9");
        assert!(body.contains("v9.4.9"));
        assert!(body.contains("local UI validation"));
        assert!(body.contains(FAKE_UPDATE_VERSION_ENV));
    }

    #[test]
    fn version_ordering() {
        let v010 = Version::parse("0.1.0").unwrap();
        let v011 = Version::parse("0.1.1").unwrap();
        let v020 = Version::parse("0.2.0").unwrap();
        let v100 = Version::parse("1.0.0").unwrap();

        assert!(v010 < v011);
        assert!(v011 < v020);
        assert!(v020 < v100);
        assert!(v010 == Version::parse("0.1.0").unwrap());
    }

    #[test]
    fn version_display() {
        let v = Version {
            major: 0,
            minor: 1,
            patch: 0,
        };
        assert_eq!(v.to_string(), "0.1.0");
    }

    #[test]
    fn current_version_parses() {
        let v = Version::current();
        assert!(v.major < 100);
    }

    #[test]
    fn platform_target_is_known() {
        let (os, arch) = platform_target();
        assert!(os == "linux" || os == "macos", "os: {os}");
        assert!(arch == "x86_64" || arch == "aarch64", "arch: {arch}");
    }

    #[test]
    fn update_manifest_deserializes() {
        let json = "{\n\
            \"version\": \"0.2.0\",\n\
            \"notes\": \"### Changed\\n- One\",\n\
            \"assets\": {\n\
                \"linux-x86_64\": \"https://example.com/herdr-linux-x86_64\",\n\
                \"macos-aarch64\": \"https://example.com/herdr-macos-aarch64\"\n\
            }\n\
        }";
        let manifest: UpdateManifest = serde_json::from_str(json).unwrap();
        assert_eq!(manifest.version, "0.2.0");
        assert_eq!(manifest.assets.len(), 2);
        assert_eq!(manifest.notes_body(), "### Changed\n- One");
        assert_eq!(
            manifest.download_url_for("linux", "x86_64").as_deref(),
            Some("https://example.com/herdr-linux-x86_64")
        );
    }

    #[test]
    fn update_manifest_requires_notes_field() {
        let json = r#"{
            "version": "0.2.0",
            "assets": {
                "linux-x86_64": "https://example.com/herdr-linux-x86_64"
            }
        }"#;

        assert!(serde_json::from_str::<UpdateManifest>(json).is_err());
    }

    #[test]
    fn checked_in_website_manifest_matches_update_schema() {
        let manifest: UpdateManifest = serde_json::from_str(include_str!("../website/latest.json"))
            .expect("website/latest.json should match updater schema");

        assert!(!manifest.notes_body().is_empty());
        assert_eq!(manifest.assets.len(), 4);

        for target in [
            "linux-x86_64",
            "linux-aarch64",
            "macos-x86_64",
            "macos-aarch64",
        ] {
            let url = manifest
                .assets
                .get(target)
                .unwrap_or_else(|| panic!("missing asset URL for {target}"));
            assert!(
                url.contains(&format!("/releases/download/v{}/", manifest.version)),
                "unexpected release URL for {target}: {url}"
            );
            assert!(
                url.ends_with(&format!("herdr-{target}")),
                "unexpected asset name for {target}: {url}"
            );
        }
    }
}