use futures::future::join_all;
use just_progress::progress;
use log::{error, info, trace};
use memmap2::Mmap;
use std::path::PathBuf;
use tokio::{fs::File, io::AsyncWriteExt};

use crate::{
    chunker::{
        constants::{BUTCK_INDEX_FILE_SUFFIX, BUTCK_INDEX_MAGIC},
        context::ButckContext,
        rw::error::{ButckRWError, ButckRWErrorKind},
        rw::storage,
    },
    utils::size_display::size_display,
};

pub async fn build(ctx: ButckContext) -> Result<(), ButckRWError> {
    if ctx.storage_path.is_none() {
        return Err(ButckRWErrorKind::NoButckStorageFound.pack(ctx));
    }
    if ctx.file_paths.is_empty() {
        return Err(
            ButckRWErrorKind::RebuildFailed("No bidx files specified".to_string()).pack(ctx),
        );
    }

    let tasks: Vec<_> = ctx
        .file_paths
        .iter()
        .map(|bidx_path| async {
            trace!(
                "Preparing to rebuild from bidx file `{}`",
                bidx_path.display()
            );
            rebuild_from_bidx(bidx_path, &ctx).await
        })
        .collect();

    let results = join_all(tasks).await;

    for result in results {
        if let Err(e) = result {
            return Err(e.pack(ctx));
        }
    }

    Ok(())
}

async fn rebuild_from_bidx(
    bidx_path: &PathBuf,
    ctx: &ButckContext,
) -> Result<(), ButckRWErrorKind> {
    // Validate file extension
    if let Some(ext) = bidx_path.extension()
        && ext != BUTCK_INDEX_FILE_SUFFIX
    {
        return Err(ButckRWErrorKind::InvalidBidxFormat);
    }

    info!("Rebuilding from bidx file: {}", bidx_path.display());

    // Read bidx file content
    let bidx_content = if ctx.memmap_read {
        let file = File::open(bidx_path).await?;
        let mmap = unsafe { Mmap::map(&file)? };
        mmap.to_vec()
    } else {
        tokio::fs::read(bidx_path).await?
    };

    // Verify file size includes at least the header
    if bidx_content.len() < 6 {
        return Err(ButckRWErrorKind::InvalidBidxFormat);
    }

    // Validate MAGIC bytes
    if bidx_content[0..4] != BUTCK_INDEX_MAGIC {
        return Err(ButckRWErrorKind::InvalidBidxFormat);
    }

    // Read filename
    let filename_len = u16::from_le_bytes([bidx_content[4], bidx_content[5]]) as usize;
    if bidx_content.len() < 6 + filename_len {
        return Err(ButckRWErrorKind::InvalidBidxFormat);
    }
    let filename_bytes = &bidx_content[6..6 + filename_len];
    let original_filename = String::from_utf8(filename_bytes.to_vec())
        .map_err(|_| ButckRWErrorKind::InvalidBidxFormat)?;

    trace!("Original filename from bidx: {}", original_filename);

    let hash_data_start = 6 + filename_len;
    let hash_data = &bidx_content[hash_data_start..];

    // Verify that hash data size is a multiple of 32 bytes
    if hash_data.len() % 32 != 0 {
        return Err(ButckRWErrorKind::InvalidBidxFormat);
    }

    let chunk_count = hash_data.len() / 32;
    info!("Found {} chunks in bidx file", chunk_count);

    let mut chunk_hashes = Vec::with_capacity(chunk_count);
    for i in 0..chunk_count {
        let start = i * 32;
        let end = start + 32;
        let hash_bytes: [u8; 32] = hash_data[start..end]
            .try_into()
            .map_err(|_| ButckRWErrorKind::InvalidBidxFormat)?;
        chunk_hashes.push(hash_bytes);
    }

    trace!("Parsed {} chunk hashes", chunk_hashes.len());

    // Determine output file path
    let output_path = if let Some(output_file) = &ctx.output_file {
        output_file.clone()
    } else {
        // Use the original filename read from the bidx file
        storage::generate_unique_path(&ctx.output_dir, &original_filename)
    };

    info!("Rebuilding file to: {}", output_path.display());

    let progress_name = format!("Rebuild `{}`", output_path.display());
    progress::update_progress(progress_name.as_str(), 0.0);
    let step = 1.0 / chunk_count as f64;

    let mut tasks = Vec::with_capacity(chunk_count);

    for (index, hash_bytes) in chunk_hashes.iter().enumerate() {
        let hash_hex = hex::encode(hash_bytes);
        tasks.push(read_chunk(
            progress_name.as_str(),
            step,
            hash_hex,
            &ctx.output_dir,
            index,
        ));
    }

    trace!("Starting parallel read of {} chunks", tasks.len());
    let results = join_all(tasks).await;
    trace!("All read tasks completed");

    // Collect chunk data and verify order
    let mut chunk_data_list = Vec::with_capacity(chunk_count);
    let mut success_count = 0;

    for (index, result) in results.into_iter().enumerate() {
        match result {
            Ok(chunk_data) => {
                let chunk_size = chunk_data.len();
                success_count += 1;
                chunk_data_list.push((index, chunk_data));
                trace!(
                    "Chunk {} read successfully, size: {} bytes",
                    index, chunk_size
                );
            }
            Err(e) => {
                error!("Failed to read chunk {}: {:?}", index, e);
                return Err(e);
            }
        }
    }

    if success_count != chunk_count {
        return Err(ButckRWErrorKind::ChunkNotFound(format!(
            "Only {}/{} chunks found in storage",
            success_count, chunk_count
        )));
    }

    info!("All {} chunks read successfully", success_count);

    // Sort by index and concatenate files
    chunk_data_list.sort_by_key(|(index, _)| *index);

    // Calculate total size
    let total_size: usize = chunk_data_list.iter().map(|(_, data)| data.len()).sum();
    let (total_value, total_unit) = size_display(total_size);
    info!(
        "Rebuilding file: {} chunks, total size: {:.2} {} ({} bytes)",
        chunk_count, total_value, total_unit, total_size
    );

    // Write to output file
    trace!("Writing to output file: {}", output_path.display());
    let mut output_file = File::create(&output_path).await?;

    for (index, chunk_data) in chunk_data_list {
        trace!("Writing chunk {} ({} bytes)", index, chunk_data.len());
        output_file.write_all(&chunk_data).await?;
        progress::increase(progress_name.as_str(), step as f32);
    }

    output_file.flush().await?;

    info!("File successfully rebuilt: {}", output_path.display());
    progress::complete(progress_name.as_str());

    Ok(())
}

/// Read a single chunk from storage
async fn read_chunk(
    progress_name: &str,
    step: f64,
    hash_hex: String,
    storage_dir: &PathBuf,
    chunk_index: usize,
) -> Result<Vec<u8>, ButckRWErrorKind> {
    trace!("read_chunk[{}]: Starting, hash: {}", chunk_index, hash_hex);

    // Build chunk file path
    let file_path = storage::get_chunk_path(storage_dir, &hash_hex);

    trace!(
        "read_chunk[{}]: Looking for file at: {}",
        chunk_index,
        file_path.display()
    );

    // Read chunk file
    match tokio::fs::read(&file_path).await {
        Ok(data) => {
            trace!(
                "read_chunk[{}]: Read {} bytes successfully",
                chunk_index,
                data.len()
            );
            progress::increase(progress_name, step as f32);
            Ok(data)
        }
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
            trace!("read_chunk[{}]: File not found", chunk_index);
            Err(ButckRWErrorKind::ChunkNotFound(format!(
                "Chunk {} (hash: {}) not found in storage",
                chunk_index, hash_hex
            )))
        }
        Err(e) => {
            trace!("read_chunk[{}]: Read failed: {:?}", chunk_index, e);
            Err(ButckRWErrorKind::IOError(e))
        }
    }
}