//! LLaMA summarization using llama-cpp-2.

use llama_cpp_2::context::params::LlamaContextParams;
use llama_cpp_2::llama_backend::LlamaBackend;
use llama_cpp_2::llama_batch::LlamaBatch;
use llama_cpp_2::model::params::LlamaModelParams;
use llama_cpp_2::model::LlamaModel;
use llama_cpp_2::sampling::LlamaSampler;
use std::num::NonZeroU32;
use std::path::Path;
use thiserror::Error;
use tracing::{debug, info};

#[derive(Error, Debug)]
pub enum SummarizerError {
    #[error("Failed to initialize LLaMA backend: {0}")]
    BackendError(String),
    #[error("Failed to load LLaMA model: {0}")]
    ModelLoadError(String),
    #[error("Failed to create context: {0}")]
    ContextError(String),
    #[error("Summarization failed: {0}")]
    SummarizationError(String),
    #[error("Model not loaded")]
    ModelNotLoaded,
}

/// LLaMA summarizer using llama-cpp-2 bindings.
pub struct LlamaSummarizer {
    backend: Option<LlamaBackend>,
    model: Option<LlamaModel>,
    model_path: Option<String>,
}

impl LlamaSummarizer {
    /// Create a new summarizer instance (without loading a model).
    pub fn new() -> Result<Self, SummarizerError> {
        let backend = LlamaBackend::init()
            .map_err(|e| SummarizerError::BackendError(e.to_string()))?;

        Ok(Self {
            backend: Some(backend),
            model: None,
            model_path: None,
        })
    }

    /// Load a LLaMA model from the given path.
    pub fn load_model(&mut self, model_path: &Path) -> Result<(), SummarizerError> {
        info!("Loading LLaMA model from: {}", model_path.display());

        let backend = self.backend.as_ref()
            .ok_or(SummarizerError::BackendError("Backend not initialized".to_string()))?;

        let model_params = LlamaModelParams::default();

        let model = LlamaModel::load_from_file(backend, model_path, &model_params)
            .map_err(|e| SummarizerError::ModelLoadError(e.to_string()))?;

        self.model = Some(model);
        self.model_path = Some(model_path.to_string_lossy().to_string());

        info!("LLaMA model loaded successfully");
        Ok(())
    }

    /// Check if a model is loaded.
    pub fn is_loaded(&self) -> bool {
        self.model.is_some()
    }

    /// Generate a meeting summary from the transcript.
    pub fn summarize(&self, transcript: &str) -> Result<String, SummarizerError> {
        self.summarize_with_progress(transcript, |_| {})
    }

    /// Generate a meeting summary with progress callback.
    pub fn summarize_with_progress<F>(&self, transcript: &str, mut progress_fn: F) -> Result<String, SummarizerError>
    where
        F: FnMut(f64),
    {
        let model = self
            .model
            .as_ref()
            .ok_or(SummarizerError::ModelNotLoaded)?;

        let prompt = format!(
            "<|begin_of_text|><|start_header_id|>system<|end_header_id|>\n\n\
             You are a helpful assistant that creates structured meeting summaries. \
             Format your response using the following template:\n\n\
             **Title:** A concise, descriptive title for the meeting (5-10 words max).\n\n\
             **Summary:** A high level overview of the meeting.\n\n\
             **Key decisions:** Any important resolutions that the meeting reached.\n\n\
             **Action Items:**\n\
             - list of things that must be addressed\n\n\
             **Discussion points:**\n\
             - a list of each topic/argument/counterpoint brought up in the meeting.\n\n\
             Be concise but comprehensive. Focus on capturing all important information.<|eot_id|><|start_header_id|>user<|end_header_id|>\n\n\
             Please summarize this meeting transcript:\n\n\
             {}<|eot_id|><|start_header_id|>assistant<|end_header_id|>\n\n",
            transcript
        );

        debug!("Generating summary for {} character transcript", transcript.len());

        // Report initial progress
        progress_fn(0.0);

        // Create context for inference
        let ctx_params = LlamaContextParams::default()
            .with_n_ctx(NonZeroU32::new(8192));

        let mut ctx = model
            .new_context(self.backend.as_ref().unwrap(), ctx_params)
            .map_err(|e| SummarizerError::ContextError(e.to_string()))?;

        // Report progress after context creation
        progress_fn(0.1);

        // Tokenize the prompt
        let tokens = model
            .str_to_token(&prompt, llama_cpp_2::model::AddBos::Always)
            .map_err(|e| SummarizerError::SummarizationError(e.to_string()))?;

        debug!("Prompt tokenized to {} tokens", tokens.len());

        // Report progress after tokenization
        progress_fn(0.2);

        // Create batch and add tokens
        let mut batch = LlamaBatch::new(tokens.len(), 1);

        for (i, token) in tokens.iter().enumerate() {
            let is_last = i == tokens.len() - 1;
            batch.add(*token, i as i32, &[0], is_last)
                .map_err(|e| SummarizerError::SummarizationError(e.to_string()))?;
        }

        // Decode the prompt
        ctx.decode(&mut batch)
            .map_err(|e| SummarizerError::SummarizationError(e.to_string()))?;

        // Report progress after prompt decode
        progress_fn(0.3);

        // Generate response tokens
        let mut output_tokens = Vec::new();
        let max_tokens = 1024;
        let mut n_cur = tokens.len();

        // Create sampler for token selection
        let mut sampler = LlamaSampler::chain_simple([
            LlamaSampler::temp(0.7),
            LlamaSampler::top_p(0.9, 1),
            LlamaSampler::dist(42),
        ]);

        for i in 0..max_tokens {
            // Sample the next token using the sampler
            // The sampler.sample() takes context and the index of the last token in the batch
            let token = sampler.sample(&ctx, (batch.n_tokens() - 1) as i32);

            // Check for end of generation
            if model.is_eog_token(token) {
                break;
            }

            output_tokens.push(token);

            // Report progress during generation (from 30% to 90%)
            let generation_progress = i as f64 / max_tokens as f64;
            progress_fn(0.3 + (generation_progress * 0.6));

            // Prepare next batch
            batch.clear();
            batch.add(token, n_cur as i32, &[0], true)
                .map_err(|e| SummarizerError::SummarizationError(e.to_string()))?;

            n_cur += 1;

            // Decode
            ctx.decode(&mut batch)
                .map_err(|e| SummarizerError::SummarizationError(e.to_string()))?;
        }

        // Convert tokens to string
        let output_text = output_tokens
            .iter()
            .filter_map(|t| model.token_to_str(*t, llama_cpp_2::model::Special::Tokenize).ok())
            .collect::<String>();

        // Report completion
        progress_fn(1.0);

        info!("Summary generated: {} characters", output_text.len());
        Ok(output_text.trim().to_string())
    }
}

impl Default for LlamaSummarizer {
    fn default() -> Self {
        Self::new().expect("Failed to create summarizer")
    }
}

/// Get the expected model filename for a given size.
pub fn get_model_filename(model_size: &str) -> String {
    format!("Llama-3.2-{}-Instruct-Q4_K_M.gguf", model_size)
}

/// Check if a LLaMA model exists at the given path.
pub fn model_exists(models_dir: &Path, model_size: &str) -> bool {
    let model_path = models_dir.join(get_model_filename(model_size));
    model_path.exists()
}

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

    #[test]
    fn test_get_model_filename() {
        assert_eq!(
            get_model_filename("3B"),
            "Llama-3.2-3B-Instruct-Q4_K_M.gguf"
        );
    }
}