//! Version scanner for available agent binaries
//!
//! Scans a downloads directory for agent binaries and parses version info
//! from filenames in the format: gururmm-agent-{os}-{arch}-{version}[.exe]

use std::collections::HashMap;
use std::path::{Path, PathBuf};
use std::sync::Arc;

use anyhow::Result;
use semver::Version;
use tokio::sync::RwLock;
use tracing::{debug, error, info, warn};

/// Information about an available agent version
#[derive(Debug, Clone)]
pub struct AvailableVersion {
    /// Semantic version
    pub version: Version,
    /// Operating system (linux, windows)
    pub os: String,
    /// Architecture (amd64, arm64)
    pub arch: String,
    /// Filename on disk
    pub filename: String,
    /// Full download URL
    pub download_url: String,
    /// SHA256 checksum
    pub checksum_sha256: String,
    /// File size in bytes
    pub file_size: u64,
}

/// Manages available agent versions
pub struct UpdateManager {
    /// Directory containing agent binaries
    downloads_dir: PathBuf,
    /// Base URL for downloads
    base_url: String,
    /// Cached available versions, keyed by "os-arch"
    versions: Arc<RwLock<HashMap<String, Vec<AvailableVersion>>>>,
    /// Whether auto-updates are enabled
    pub auto_update_enabled: bool,
    /// Update timeout in seconds
    pub update_timeout_secs: u64,
}

impl UpdateManager {
    /// Create a new UpdateManager
    pub fn new(
        downloads_dir: PathBuf,
        base_url: String,
        auto_update_enabled: bool,
        update_timeout_secs: u64,
    ) -> Self {
        Self {
            downloads_dir,
            base_url,
            versions: Arc::new(RwLock::new(HashMap::new())),
            auto_update_enabled,
            update_timeout_secs,
        }
    }

    /// Scan the downloads directory for available agent binaries
    pub async fn scan_versions(&self) -> Result<()> {
        let mut versions: HashMap<String, Vec<AvailableVersion>> = HashMap::new();

        if !self.downloads_dir.exists() {
            warn!("Downloads directory does not exist: {:?}", self.downloads_dir);
            return Ok(());
        }

        let entries = std::fs::read_dir(&self.downloads_dir)?;

        for entry in entries.flatten() {
            let path = entry.path();
            if !path.is_file() {
                continue;
            }

            let filename = match path.file_name().and_then(|n| n.to_str()) {
                Some(name) => name.to_string(),
                None => continue,
            };

            // Skip checksum files
            if filename.ends_with(".sha256") {
                continue;
            }

            // Try to parse as agent binary
            if let Some((os, arch, version)) = Self::parse_filename(&filename) {
                // Read checksum from companion file
                let checksum = self.read_checksum(&path).await.unwrap_or_default();

                if checksum.is_empty() {
                    warn!("No checksum found for {}, skipping", filename);
                    continue;
                }

                // Get file size
                let file_size = std::fs::metadata(&path).map(|m| m.len()).unwrap_or(0);

                let download_url = format!("{}/{}", self.base_url.trim_end_matches('/'), filename);

                let available = AvailableVersion {
                    version,
                    os: os.clone(),
                    arch: arch.clone(),
                    filename: filename.clone(),
                    download_url,
                    checksum_sha256: checksum,
                    file_size,
                };

                let key = format!("{}-{}", os, arch);
                debug!("Found agent binary: {} (v{})", filename, available.version);
                versions.entry(key).or_default().push(available);
            }
        }

        // Sort each list by version descending (newest first)
        for list in versions.values_mut() {
            list.sort_by(|a, b| b.version.cmp(&a.version));
        }

        let total: usize = versions.values().map(|v| v.len()).sum();
        info!("Scanned {} agent binaries across {} platform/arch combinations", total, versions.len());

        *self.versions.write().await = versions;
        Ok(())
    }

    /// Parse a filename to extract OS, architecture, and version
    ///
    /// Expected format: gururmm-agent-{os}-{arch}-{version}[.exe]
    /// Examples:
    /// - gururmm-agent-linux-amd64-0.2.0
    /// - gururmm-agent-windows-amd64-0.2.0.exe
    fn parse_filename(filename: &str) -> Option<(String, String, Version)> {
        // Remove .exe extension if present
        let name = filename.strip_suffix(".exe").unwrap_or(filename);

        // Split by dashes
        let parts: Vec<&str> = name.split('-').collect();

        // Expected: ["gururmm", "agent", "linux", "amd64", "0", "2", "0"]
        // or: ["gururmm", "agent", "linux", "amd64", "0.2.0"]
        if parts.len() < 5 || parts[0] != "gururmm" || parts[1] != "agent" {
            return None;
        }

        let os = parts[2].to_string();
        let arch = parts[3].to_string();

        // Version could be either:
        // - A single part with dots: "0.2.0"
        // - Multiple parts joined: "0", "2", "0"
        let version_str = if parts.len() == 5 {
            // Single part with dots
            parts[4].to_string()
        } else {
            // Multiple parts, join with dots
            parts[4..].join(".")
        };

        let version = Version::parse(&version_str).ok()?;
        Some((os, arch, version))
    }

    /// Read checksum from companion .sha256 file
    async fn read_checksum(&self, binary_path: &Path) -> Result<String> {
        let checksum_path = PathBuf::from(format!("{}.sha256", binary_path.display()));

        if !checksum_path.exists() {
            return Err(anyhow::anyhow!("Checksum file not found"));
        }

        let content = tokio::fs::read_to_string(&checksum_path).await?;

        // Checksum file format: "<hash> <filename>" or just "<hash>"
        let checksum = content
            .split_whitespace()
            .next()
            .ok_or_else(|| anyhow::anyhow!("Empty checksum file"))?
            .to_lowercase();

        // Validate it looks like a SHA256 hash (64 hex chars)
        if checksum.len() != 64 || !checksum.chars().all(|c| c.is_ascii_hexdigit()) {
            return Err(anyhow::anyhow!("Invalid checksum format"));
        }

        Ok(checksum)
    }

    /// Get the latest version available for a given OS/arch
    pub async fn get_latest_version(&self, os: &str, arch: &str) -> Option<AvailableVersion> {
        let versions = self.versions.read().await;
        let key = format!("{}-{}", os, arch);
        versions.get(&key).and_then(|list| list.first().cloned())
    }

    /// Check if an agent with the given version needs an update
    /// Returns the available update if one exists
    pub async fn needs_update(
        &self,
        current_version: &str,
        os: &str,
        arch: &str,
    ) -> Option<AvailableVersion> {
        if !self.auto_update_enabled {
            return None;
        }

        let current = match Version::parse(current_version) {
            Ok(v) => v,
            Err(e) => {
                warn!("Failed to parse current version '{}': {}", current_version, e);
                return None;
            }
        };

        let latest = self.get_latest_version(os, arch).await?;

        if latest.version > current {
            info!(
                "Agent needs update: {} -> {} ({}-{})",
                current, latest.version, os, arch
            );
            Some(latest)
        } else {
            None
        }
    }

    /// Get all available versions (for dashboard display)
    pub async fn get_all_versions(&self) -> HashMap<String, Vec<AvailableVersion>> {
        self.versions.read().await.clone()
    }

    /// Spawn a background task to periodically rescan versions
    pub fn spawn_scanner(&self, interval_secs: u64) -> tokio::task::JoinHandle<()> {
        let downloads_dir = self.downloads_dir.clone();
        let base_url = self.base_url.clone();
        let versions = self.versions.clone();
        let auto_update_enabled = self.auto_update_enabled;
        let update_timeout_secs = self.update_timeout_secs;

        tokio::spawn(async move {
            let manager = UpdateManager {
                downloads_dir,
                base_url,
                versions,
                auto_update_enabled,
                update_timeout_secs,
            };

            let mut interval = tokio::time::interval(std::time::Duration::from_secs(interval_secs));

            loop {
                interval.tick().await;
                if let Err(e) = manager.scan_versions().await {
                    error!("Failed to scan versions: {}", e);
                }
            }
        })
    }
}

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

    #[test]
    fn test_parse_filename_linux() {
        let result = UpdateManager::parse_filename("gururmm-agent-linux-amd64-0.2.0");
        assert!(result.is_some());
        let (os, arch, version) = result.unwrap();
        assert_eq!(os, "linux");
        assert_eq!(arch, "amd64");
        assert_eq!(version, Version::new(0, 2, 0));
    }

    #[test]
    fn test_parse_filename_windows() {
        let result = UpdateManager::parse_filename("gururmm-agent-windows-amd64-0.2.0.exe");
        assert!(result.is_some());
        let (os, arch, version) = result.unwrap();
        assert_eq!(os, "windows");
        assert_eq!(arch, "amd64");
        assert_eq!(version, Version::new(0, 2, 0));
    }

    #[test]
    fn test_parse_filename_arm64() {
        let result = UpdateManager::parse_filename("gururmm-agent-linux-arm64-1.0.0");
        assert!(result.is_some());
        let (os, arch, version) = result.unwrap();
        assert_eq!(os, "linux");
        assert_eq!(arch, "arm64");
        assert_eq!(version, Version::new(1, 0, 0));
    }

    #[test]
    fn test_parse_filename_invalid() {
        assert!(UpdateManager::parse_filename("random-file.txt").is_none());
        assert!(UpdateManager::parse_filename("gururmm-server-linux-amd64-0.1.0").is_none());
        assert!(UpdateManager::parse_filename("gururmm-agent-linux").is_none());
    }
}