//! Filesystem Assembly for APT-OSTree
//! 
//! This module implements the filesystem assembly process that combines base filesystem
//! with layered packages using hardlink optimization for efficient storage and proper
//! layering order.

use std::path::{Path, PathBuf};
use std::fs;
use std::os::unix::fs::{MetadataExt, PermissionsExt};
use std::collections::HashMap;
use tracing::{info, warn, debug};
use serde::{Serialize, Deserialize};
use std::pin::Pin;
use std::future::Future;

use crate::error::AptOstreeResult;
use crate::apt_ostree_integration::DebPackageMetadata;

/// Filesystem assembly manager
pub struct FilesystemAssembler {
    base_path: PathBuf,
    staging_path: PathBuf,
    final_path: PathBuf,
}

/// File metadata for deduplication
#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq, Hash)]
pub struct FileMetadata {
    pub size: u64,
    pub mode: u32,
    pub mtime: i64,
    pub inode: u64,
    pub device: u64,
}

/// Assembly configuration
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct AssemblyConfig {
    pub base_filesystem_path: PathBuf,
    pub staging_directory: PathBuf,
    pub final_deployment_path: PathBuf,
    pub enable_hardlinks: bool,
    pub preserve_permissions: bool,
    pub preserve_timestamps: bool,
}

impl Default for AssemblyConfig {
    fn default() -> Self {
        Self {
            base_filesystem_path: PathBuf::from("/var/lib/apt-ostree/base"),
            staging_directory: PathBuf::from("/var/lib/apt-ostree/staging"),
            final_deployment_path: PathBuf::from("/var/lib/apt-ostree/deployments"),
            enable_hardlinks: true,
            preserve_permissions: true,
            preserve_timestamps: true,
        }
    }
}

impl FilesystemAssembler {
    /// Create a new filesystem assembler
    pub fn new(config: AssemblyConfig) -> AptOstreeResult<Self> {
        info!("Creating filesystem assembler with config: {:?}", config);
        
        // Create directories if they don't exist
        fs::create_dir_all(&config.base_filesystem_path)?;
        fs::create_dir_all(&config.staging_directory)?;
        fs::create_dir_all(&config.final_deployment_path)?;
        
        Ok(Self {
            base_path: config.base_filesystem_path,
            staging_path: config.staging_directory,
            final_path: config.final_deployment_path,
        })
    }
    
    /// Assemble filesystem from base and package layers
    pub async fn assemble_filesystem(
        &self,
        base_commit: &str,
        package_commits: &[String],
        target_deployment: &str,
    ) -> AptOstreeResult<()> {
        info!("Assembling filesystem from base {} and {} packages", base_commit, package_commits.len());
        
        // Create staging directory for this assembly
        let staging_dir = self.staging_path.join(target_deployment);
        if staging_dir.exists() {
            fs::remove_dir_all(&staging_dir)?;
        }
        fs::create_dir_all(&staging_dir)?;
        
        // Step 1: Checkout base filesystem with hardlinks
        self.checkout_base_filesystem(base_commit, &staging_dir).await?;
        
        // Step 2: Layer packages in order
        for (index, package_commit) in package_commits.iter().enumerate() {
            info!("Layering package {} ({}/{})", package_commit, index + 1, package_commits.len());
            self.layer_package(package_commit, &staging_dir).await?;
        }
        
        // Step 3: Optimize hardlinks
        if self.should_optimize_hardlinks() {
            self.optimize_hardlinks(&staging_dir).await?;
        }
        
        // Step 4: Create final deployment
        let final_deployment = self.final_path.join(target_deployment);
        if final_deployment.exists() {
            fs::remove_dir_all(&final_deployment)?;
        }
        
        self.create_final_deployment(&staging_dir, &final_deployment).await?;
        
        // Clean up staging
        fs::remove_dir_all(&staging_dir)?;
        
        info!("Filesystem assembly completed: {}", target_deployment);
        Ok(())
    }
    
    /// Checkout base filesystem using hardlinks for efficiency
    async fn checkout_base_filesystem(&self, base_commit: &str, staging_dir: &Path) -> AptOstreeResult<()> {
        info!("Checking out base filesystem from commit: {}", base_commit);
        
        // TODO: Implement actual OSTree checkout
        // For now, create a placeholder base filesystem
        let base_commit_path = self.base_path.join(base_commit);
        
        if base_commit_path.exists() {
            // Copy base filesystem using hardlinks where possible
            self.copy_with_hardlinks(&base_commit_path, staging_dir).await?;
        } else {
            // Create minimal base filesystem structure
            self.create_minimal_base_filesystem(staging_dir).await?;
        }
        
        info!("Base filesystem checkout completed");
        Ok(())
    }
    
    /// Layer a package on top of the current filesystem
    async fn layer_package(&self, package_commit: &str, staging_dir: &Path) -> AptOstreeResult<()> {
        info!("Layering package commit: {}", package_commit);
        
        // TODO: Implement actual package commit checkout
        // For now, simulate package layering
        let package_path = self.staging_path.join("packages").join(package_commit);
        
        if package_path.exists() {
            // Apply package files on top of current filesystem
            self.apply_package_files(&package_path, staging_dir).await?;
        } else {
            warn!("Package commit not found: {}", package_commit);
        }
        
        Ok(())
    }
    
    /// Copy directory using hardlinks where possible
    fn copy_with_hardlinks<'a>(&'a self, src: &'a Path, dst: &'a Path) -> Pin<Box<dyn Future<Output = AptOstreeResult<()>> + 'a>> {
        Box::pin(async move {
            debug!("Copying with hardlinks: {} -> {}", src.display(), dst.display());
            
            if src.is_file() {
                // For files, try to create hardlink, fallback to copy
                if let Err(_) = fs::hard_link(src, dst) {
                    fs::copy(src, dst)?;
                }
            } else if src.is_dir() {
                fs::create_dir_all(dst)?;
                
                for entry in fs::read_dir(src)? {
                    let entry = entry?;
                    let src_path = entry.path();
                    let dst_path = dst.join(entry.file_name());
                    
                    self.copy_with_hardlinks(&src_path, &dst_path).await?;
                }
            }
            
            Ok(())
        })
    }
    
    /// Create minimal base filesystem structure
    pub async fn create_minimal_base_filesystem(&self, staging_dir: &Path) -> AptOstreeResult<()> {
        info!("Creating minimal base filesystem structure");
        
        let dirs = [
            "bin", "boot", "dev", "etc", "home", "lib", "lib64", "media", 
            "mnt", "opt", "proc", "root", "run", "sbin", "srv", "sys", 
            "tmp", "usr", "var"
        ];
        
        for dir in &dirs {
            fs::create_dir_all(staging_dir.join(dir))?;
        }
        
        // Create essential files
        let etc_dir = staging_dir.join("etc");
        fs::write(etc_dir.join("hostname"), "localhost\n")?;
        fs::write(etc_dir.join("hosts"), "127.0.0.1 localhost\n::1 localhost\n")?;
        
        info!("Minimal base filesystem created");
        Ok(())
    }
    
    /// Apply package files to the filesystem
    async fn apply_package_files(&self, package_path: &Path, staging_dir: &Path) -> AptOstreeResult<()> {
        debug!("Applying package files: {} -> {}", package_path.display(), staging_dir.display());
        
        // Read package metadata
        let metadata_path = package_path.join("metadata.json");
        if metadata_path.exists() {
            let metadata_content = fs::read_to_string(&metadata_path)?;
            let metadata: DebPackageMetadata = serde_json::from_str(&metadata_content)?;
            
            info!("Applying package: {} {}", metadata.name, metadata.version);
        }
        
        // Apply files from package
        let files_dir = package_path.join("files");
        if files_dir.exists() {
            self.copy_with_hardlinks(&files_dir, staging_dir).await?;
        }
        
        // Apply scripts if they exist
        let scripts_dir = package_path.join("scripts");
        if scripts_dir.exists() {
            // TODO: Execute scripts in proper order
            info!("Package scripts found, would execute in proper order");
        }
        
        Ok(())
    }
    
    /// Optimize hardlinks for identical files
    async fn optimize_hardlinks(&self, staging_dir: &Path) -> AptOstreeResult<()> {
        info!("Optimizing hardlinks in: {}", staging_dir.display());
        
        let mut file_map: HashMap<FileMetadata, Vec<PathBuf>> = HashMap::new();
        
        // Scan all files and group by metadata
        self.scan_files_for_deduplication(staging_dir, &mut file_map).await?;
        
        // Create hardlinks for identical files
        let mut hardlink_count = 0;
        for (metadata, paths) in file_map {
            if paths.len() > 1 {
                // Use the first path as the source for hardlinks
                let source = &paths[0];
                for target in &paths[1..] {
                    if let Err(_) = fs::hard_link(source, target) {
                        warn!("Failed to create hardlink: {} -> {}", source.display(), target.display());
                    } else {
                        hardlink_count += 1;
                    }
                }
            }
        }
        
        info!("Hardlink optimization completed: {} hardlinks created", hardlink_count);
        Ok(())
    }
    
    /// Scan files for deduplication
    fn scan_files_for_deduplication<'a>(
        &'a self,
        dir: &'a Path,
        file_map: &'a mut HashMap<FileMetadata, Vec<PathBuf>>,
    ) -> Pin<Box<dyn Future<Output = AptOstreeResult<()>> + 'a>> {
        Box::pin(async move {
            for entry in fs::read_dir(dir)? {
                let entry = entry?;
                let path = entry.path();
                
                if path.is_file() {
                    let metadata = fs::metadata(&path)?;
                    let file_metadata = FileMetadata {
                        size: metadata.size(),
                        mode: metadata.mode(),
                        mtime: metadata.mtime(),
                        inode: metadata.ino(),
                        device: metadata.dev(),
                    };
                    
                    file_map.entry(file_metadata).or_insert_with(Vec::new).push(path);
                } else if path.is_dir() {
                    self.scan_files_for_deduplication(&path, file_map).await?;
                }
            }
            
            Ok(())
        })
    }
    
    /// Create final deployment
    async fn create_final_deployment(&self, staging_dir: &Path, final_dir: &Path) -> AptOstreeResult<()> {
        info!("Creating final deployment: {} -> {}", staging_dir.display(), final_dir.display());
        
        // Copy staging to final location
        self.copy_with_hardlinks(staging_dir, final_dir).await?;
        
        // Set proper permissions
        self.set_deployment_permissions(final_dir).await?;
        
        info!("Final deployment created: {}", final_dir.display());
        Ok(())
    }
    
    /// Set proper permissions for deployment
    async fn set_deployment_permissions(&self, deployment_dir: &Path) -> AptOstreeResult<()> {
        debug!("Setting deployment permissions: {}", deployment_dir.display());
        
        // Set directory permissions
        let metadata = fs::metadata(deployment_dir)?;
        let mut permissions = metadata.permissions();
        permissions.set_mode(0o755);
        fs::set_permissions(deployment_dir, permissions)?;
        
        // Recursively set permissions for subdirectories
        self.set_recursive_permissions(deployment_dir).await?;
        
        Ok(())
    }
    
    /// Set recursive permissions
    fn set_recursive_permissions<'a>(&'a self, dir: &'a Path) -> Pin<Box<dyn Future<Output = AptOstreeResult<()>> + 'a>> {
        Box::pin(async move {
            for entry in fs::read_dir(dir)? {
                let entry = entry?;
                let path = entry.path();
                
                let metadata = fs::metadata(&path)?;
                let mut permissions = metadata.permissions();
                
                if path.is_dir() {
                    permissions.set_mode(0o755);
                    fs::set_permissions(&path, permissions)?;
                    self.set_recursive_permissions(&path).await?;
                } else if path.is_file() {
                    // Check if file is executable
                    let mode = metadata.mode();
                    if mode & 0o111 != 0 {
                        permissions.set_mode(0o755);
                    } else {
                        permissions.set_mode(0o644);
                    }
                    fs::set_permissions(&path, permissions)?;
                }
            }
            
            Ok(())
        })
    }
    
    /// Check if hardlink optimization should be enabled
    fn should_optimize_hardlinks(&self) -> bool {
        // TODO: Make this configurable
        true
    }
}

/// Package layering order manager
pub struct PackageLayeringManager {
    assembler: FilesystemAssembler,
}

impl PackageLayeringManager {
    /// Create a new package layering manager
    pub fn new(assembler: FilesystemAssembler) -> Self {
        Self { assembler }
    }
    
    /// Determine optimal layering order for packages
    pub fn determine_layering_order(&self, packages: &[DebPackageMetadata]) -> Vec<String> {
        info!("Determining layering order for {} packages", packages.len());
        
        // Simple dependency-based ordering
        // TODO: Implement proper dependency resolution
        let mut ordered_packages = Vec::new();
        let mut processed = std::collections::HashSet::new();
        
        for package in packages {
            if !processed.contains(&package.name) {
                ordered_packages.push(package.name.clone());
                processed.insert(package.name.clone());
            }
        }
        
        info!("Layering order determined: {:?}", ordered_packages);
        ordered_packages
    }
    
    /// Assemble filesystem with proper package ordering
    pub async fn assemble_with_ordering(
        &self,
        base_commit: &str,
        packages: &[DebPackageMetadata],
        target_deployment: &str,
    ) -> AptOstreeResult<()> {
        info!("Assembling filesystem with proper package ordering");
        
        // Determine layering order
        let ordered_package_names = self.determine_layering_order(packages);
        
        // Convert package names to commit IDs (simplified)
        let package_commits: Vec<String> = ordered_package_names
            .iter()
            .map(|name| format!("pkg_{}", name.replace("-", "_")))
            .collect();
        
        // Assemble filesystem
        self.assembler.assemble_filesystem(base_commit, &package_commits, target_deployment).await?;
        
        info!("Filesystem assembly with ordering completed");
        Ok(())
    }
} 