//! `HuggingFace` Hub integration for model downloading

use crate::error::{CandleError, Result};
use serde::{Deserialize, Serialize};
use std::path::{Path, PathBuf};
use tracing::{debug, info};

/// Configuration for `HuggingFace` Hub access
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct HubConfig {
    /// `HuggingFace` API token (optional, for private models)
    pub token: Option<String>,
    /// Cache directory for downloaded models
    pub cache_dir: PathBuf,
    /// Revision/branch to download (default: "main")
    pub revision: String,
    /// Prefer safetensors format
    pub prefer_safetensors: bool,
}

impl Default for HubConfig {
    fn default() -> Self {
        let cache_dir = dirs::cache_dir()
            .unwrap_or_else(|| PathBuf::from("."))
            .join("rtx-candle")
            .join("models");

        Self {
            token: std::env::var("HF_TOKEN").ok(),
            cache_dir,
            revision: "main".to_string(),
            prefer_safetensors: true,
        }
    }
}

impl HubConfig {
    /// Set the API token
    pub fn with_token(mut self, token: impl Into<String>) -> Self {
        self.token = Some(token.into());
        self
    }

    /// Set the cache directory
    pub fn with_cache_dir(mut self, dir: impl Into<PathBuf>) -> Self {
        self.cache_dir = dir.into();
        self
    }

    /// Set the revision
    pub fn with_revision(mut self, revision: impl Into<String>) -> Self {
        self.revision = revision.into();
        self
    }
}

/// Model file information
#[derive(Debug, Clone)]
pub struct ModelFile {
    /// File name
    pub name: String,
    /// File size in bytes
    pub size: u64,
    /// File type
    pub file_type: ModelFileType,
}

/// Type of model file
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ModelFileType {
    /// `SafeTensors` weights
    SafeTensors,
    /// `PyTorch` weights
    PyTorch,
    /// GGUF quantized weights
    Gguf,
    /// Tokenizer config
    TokenizerConfig,
    /// Model config
    ModelConfig,
    /// Other file
    Other,
}

impl ModelFileType {
    /// Detect file type from name
    pub fn from_filename(name: &str) -> Self {
        if name.ends_with(".safetensors") {
            Self::SafeTensors
        } else if name.ends_with(".bin") || name.ends_with(".pt") || name.ends_with(".pth") {
            Self::PyTorch
        } else if name.ends_with(".gguf") {
            Self::Gguf
        } else if name.contains("tokenizer") && name.ends_with(".json") {
            Self::TokenizerConfig
        } else if name == "config.json" {
            Self::ModelConfig
        } else {
            Self::Other
        }
    }
}

/// Download a model from `HuggingFace` Hub
///
/// Returns the path to the downloaded model directory.
pub fn download_model(model_id: &str, config: &HubConfig) -> Result<PathBuf> {
    info!("Downloading model from HuggingFace Hub: {}", model_id);

    // Sanitize model ID for directory name
    let model_dir_name = model_id.replace('/', "--");
    let model_dir = config
        .cache_dir
        .join(&model_dir_name)
        .join(&config.revision);

    // Check if already cached
    if model_dir.exists() {
        debug!("Model already cached at: {}", model_dir.display());
        return Ok(model_dir);
    }

    // Create cache directory
    std::fs::create_dir_all(&model_dir)?;

    // In a real implementation, this would:
    // 1. Query HuggingFace API for model files
    // 2. Download weight files (preferring safetensors)
    // 3. Download config.json and tokenizer files
    // 4. Cache everything locally

    // For now, return placeholder path
    // Real implementation would use hf-hub crate or direct API calls
    info!("Model would be downloaded to: {}", model_dir.display());

    // Placeholder: create marker file
    let marker = model_dir.join(".downloading");
    std::fs::write(&marker, model_id)?;

    Err(CandleError::hub(format!(
        "Hub download not implemented. Would download {} to {}",
        model_id,
        model_dir.display()
    )))
}

/// Get the path to a cached model
pub fn get_cached_model(model_id: &str, config: &HubConfig) -> Option<PathBuf> {
    let model_dir_name = model_id.replace('/', "--");
    let model_dir = config
        .cache_dir
        .join(&model_dir_name)
        .join(&config.revision);

    if model_dir.exists() {
        Some(model_dir)
    } else {
        None
    }
}

/// List all cached models
pub fn list_cached_models(config: &HubConfig) -> Result<Vec<String>> {
    let mut models = Vec::new();

    if !config.cache_dir.exists() {
        return Ok(models);
    }

    for entry in std::fs::read_dir(&config.cache_dir)? {
        let entry = entry?;
        if entry.file_type()?.is_dir() {
            let name = entry.file_name().to_string_lossy().replace("--", "/");
            models.push(name);
        }
    }

    Ok(models)
}

/// Clear the model cache
pub fn clear_cache(config: &HubConfig) -> Result<()> {
    if config.cache_dir.exists() {
        std::fs::remove_dir_all(&config.cache_dir)?;
        info!("Cleared model cache: {}", config.cache_dir.display());
    }
    Ok(())
}

/// Get cache size in bytes
pub fn cache_size(config: &HubConfig) -> Result<u64> {
    if !config.cache_dir.exists() {
        return Ok(0);
    }

    let mut total = 0;
    for entry in walkdir(config.cache_dir.as_path())? {
        let metadata = entry.metadata()?;
        if metadata.is_file() {
            total += metadata.len();
        }
    }

    Ok(total)
}

/// Simple directory walker
fn walkdir(path: &Path) -> Result<Vec<std::fs::DirEntry>> {
    let mut entries = Vec::new();

    fn walk_recursive(path: &Path, entries: &mut Vec<std::fs::DirEntry>) -> std::io::Result<()> {
        for entry in std::fs::read_dir(path)? {
            let entry = entry?;
            let entry_path = entry.path();
            entries.push(entry);
            if entry_path.is_dir() {
                walk_recursive(&entry_path, entries)?;
            }
        }
        Ok(())
    }

    walk_recursive(path, &mut entries)?;
    Ok(entries)
}

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

    #[test]
    fn test_hub_config_default() {
        let config = HubConfig::default();
        assert_eq!(config.revision, "main");
        assert!(config.prefer_safetensors);
    }

    #[test]
    fn test_hub_config_builder() {
        let config = HubConfig::default()
            .with_token("test_token")
            .with_revision("v1.0");

        assert_eq!(config.token, Some("test_token".to_string()));
        assert_eq!(config.revision, "v1.0");
    }

    #[test]
    fn test_model_file_type() {
        assert_eq!(
            ModelFileType::from_filename("model.safetensors"),
            ModelFileType::SafeTensors
        );
        assert_eq!(
            ModelFileType::from_filename("pytorch_model.bin"),
            ModelFileType::PyTorch
        );
        assert_eq!(
            ModelFileType::from_filename("model.gguf"),
            ModelFileType::Gguf
        );
        assert_eq!(
            ModelFileType::from_filename("config.json"),
            ModelFileType::ModelConfig
        );
    }

    #[test]
    fn test_get_cached_model_not_exists() {
        let config = HubConfig {
            cache_dir: PathBuf::from("/nonexistent"),
            ..Default::default()
        };

        assert!(get_cached_model("test/model", &config).is_none());
    }
}