//! Simple APT transaction implementation
//! 
//! Provides a DNF-like transaction interface for APT operations.

use std::process::Command;
use anyhow::{Result, anyhow};
use std::collections::HashMap;

/// Simple APT transaction that mimics DNF's imperative model
pub struct AptTransaction {
    packages: Vec<String>,
    before_versions: HashMap<String, String>,  // package -> version before
    after_versions: HashMap<String, String>,   // package -> version after
}

impl AptTransaction {
    /// Create a new transaction
    pub fn new() -> Result<Self> {
        Ok(Self {
            packages: Vec::new(),
            before_versions: HashMap::new(),
            after_versions: HashMap::new(),
        })
    }
    
    /// Add a package to the transaction
    pub fn add_package(&mut self, name: &str) -> Result<()> {
        // Verify package exists
        let output = Command::new("apt")
            .args(&["show", name])
            .output()?;
        
        if !output.status.success() {
            return Err(anyhow!("Package not found: {}", name));
        }
        
        self.packages.push(name.to_string());
        Ok(())
    }
    
    /// Resolve dependencies (APT handles this automatically)
    pub fn resolve(&self) -> Result<()> {
        // APT handles dependency resolution automatically
        // Just validate all packages are available
        for package in &self.packages {
            let output = Command::new("apt")
                .args(&["show", package])
                .output()?;
            
            if !output.status.success() {
                return Err(anyhow!("Package unavailable: {}", package));
            }
        }
        Ok(())
    }
    
    /// Commit the transaction
    pub fn commit(&mut self) -> Result<()> {
        if self.packages.is_empty() {
            return Ok(());
        }
        
        // Get current versions before installation
        self.before_versions = self.get_package_versions()?;
        
        // Run apt install with all packages
        let output = Command::new("apt")
            .args(&["install", "-y"])
            .args(&self.packages)
            .output()?;
        
        if !output.status.success() {
            let error = String::from_utf8_lossy(&output.stderr);
            return Err(anyhow!("APT installation failed: {}", error));
        }
        
        // Get versions after installation
        self.after_versions = self.get_package_versions()?;
        
        Ok(())
    }
    
    /// Rollback the transaction by restoring previous versions
    pub fn rollback(&self) -> Result<()> {
        if self.before_versions.is_empty() {
            return Ok(());
        }
        
        // Build list of packages to restore to previous versions
        let mut packages_to_restore = Vec::new();
        
        for (package, before_version) in &self.before_versions {
            if let Some(after_version) = self.after_versions.get(package) {
                // Only rollback if version changed
                if before_version != after_version {
                    packages_to_restore.push(format!("{}={}", package, before_version));
                }
            } else {
                // Package was newly installed, remove it
                packages_to_restore.push(format!("{}", package));
            }
        }
        
        if packages_to_restore.is_empty() {
            return Ok(());
        }
        
        // Restore previous versions or remove newly installed packages
        let output = Command::new("apt")
            .args(&["install", "-y"])
            .args(&packages_to_restore)
            .output()?;
        
        if !output.status.success() {
            let error = String::from_utf8_lossy(&output.stderr);
            return Err(anyhow!("APT rollback failed: {}", error));
        }
        
        Ok(())
    }
    
    /// Get current package versions
    fn get_package_versions(&self) -> Result<HashMap<String, String>> {
        let output = Command::new("dpkg")
            .args(&["-l"])
            .output()?;
        
        if !output.status.success() {
            return Err(anyhow!("Failed to get package versions"));
        }
        
        let mut versions = HashMap::new();
        let output_str = String::from_utf8_lossy(&output.stdout);
        
        for line in output_str.lines() {
            if line.starts_with("ii") {
                let parts: Vec<&str> = line.split_whitespace().collect();
                if parts.len() >= 3 {
                    let package_name = parts[1];
                    let version = parts[2];
                    versions.insert(package_name.to_string(), version.to_string());
                }
            }
        }
        
        Ok(versions)
    }
    
    /// Get list of packages in transaction
    pub fn packages(&self) -> &[String] {
        &self.packages
    }
    
    /// Check if transaction is empty
    pub fn is_empty(&self) -> bool {
        self.packages.is_empty()
    }
    
    /// Get list of packages that were changed by this transaction
    pub fn changed_packages(&self) -> Vec<String> {
        let mut changed = Vec::new();
        
        for (package, before_version) in &self.before_versions {
            if let Some(after_version) = self.after_versions.get(package) {
                if before_version != after_version {
                    changed.push(format!("{}: {} -> {}", package, before_version, after_version));
                }
            } else {
                changed.push(format!("{}: removed", package));
            }
        }
        
        // Add newly installed packages
        for package in &self.packages {
            if !self.before_versions.contains_key(package) {
                if let Some(after_version) = self.after_versions.get(package) {
                    changed.push(format!("{}: installed {}", package, after_version));
                }
            }
        }
        
        changed
    }
}