use std::collections::{HashMap, HashSet};

use futures::future::join_all;
use rusqlite::Connection;
use sha2::{Digest, Sha256};
use tracing::{debug, info, instrument, warn};

use crate::core::error::Result;
use crate::core::shutdown::ShutdownSignal;
use crate::embedding::change_detector::{count_pending_documents, find_pending_documents};
use crate::embedding::chunk_ids::{CHUNK_ROWID_MULTIPLIER, encode_rowid};
use crate::embedding::chunking::{CHUNK_MAX_BYTES, EXPECTED_DIMS, split_into_chunks};
use crate::embedding::ollama::OllamaClient;

const BATCH_SIZE: usize = 32;
const DB_PAGE_SIZE: usize = 500;
pub const DEFAULT_EMBED_CONCURRENCY: usize = 4;

#[derive(Debug, Default)]
pub struct EmbedResult {
    pub chunks_embedded: usize,
    pub docs_embedded: usize,
    pub failed: usize,
    pub skipped: usize,
}

struct ChunkWork {
    doc_id: i64,
    chunk_index: usize,
    total_chunks: usize,
    doc_hash: String,
    chunk_hash: String,
    text: String,
}

#[instrument(skip(conn, client, progress_callback, signal), fields(%model_name, items_processed, items_skipped, errors))]
pub async fn embed_documents(
    conn: &Connection,
    client: &OllamaClient,
    model_name: &str,
    concurrency: usize,
    progress_callback: Option<Box<dyn Fn(usize, usize)>>,
    signal: &ShutdownSignal,
) -> Result<EmbedResult> {
    let total = count_pending_documents(conn, model_name)? as usize;
    let mut result = EmbedResult::default();
    let mut last_id: i64 = 0;
    let mut processed: usize = 0;

    if total == 0 {
        return Ok(result);
    }

    info!(total, "Starting embedding pipeline");

    loop {
        if signal.is_cancelled() {
            info!("Shutdown requested, stopping embedding pipeline");
            break;
        }

        info!(last_id, "Querying pending documents...");
        let pending = find_pending_documents(conn, DB_PAGE_SIZE, last_id, model_name)?;
        if pending.is_empty() {
            break;
        }
        info!(
            count = pending.len(),
            "Found pending documents, starting page"
        );

        conn.execute_batch("SAVEPOINT embed_page")?;
        let page_result = embed_page(
            conn,
            client,
            model_name,
            concurrency,
            &pending,
            &mut result,
            &mut last_id,
            &mut processed,
            total,
            &progress_callback,
            signal,
        )
        .await;
        match page_result {
            Ok(()) if signal.is_cancelled() => {
                let _ = conn.execute_batch("ROLLBACK TO embed_page; RELEASE embed_page");
                info!("Rolled back incomplete page to preserve data integrity");
            }
            Ok(()) => {
                conn.execute_batch("RELEASE embed_page")?;
                let _ = conn.execute_batch("PRAGMA wal_checkpoint(PASSIVE)");
                info!(
                    chunks_embedded = result.chunks_embedded,
                    failed = result.failed,
                    skipped = result.skipped,
                    total,
                    "Page complete"
                );
            }
            Err(e) => {
                let _ = conn.execute_batch("ROLLBACK TO embed_page; RELEASE embed_page");
                return Err(e);
            }
        }
    }

    info!(
        chunks_embedded = result.chunks_embedded,
        failed = result.failed,
        skipped = result.skipped,
        "Embedding pipeline complete"
    );

    tracing::Span::current().record("items_processed", result.chunks_embedded);
    tracing::Span::current().record("items_skipped", result.skipped);
    tracing::Span::current().record("errors", result.failed);

    Ok(result)
}

#[allow(clippy::too_many_arguments)]
async fn embed_page(
    conn: &Connection,
    client: &OllamaClient,
    model_name: &str,
    concurrency: usize,
    pending: &[crate::embedding::change_detector::PendingDocument],
    result: &mut EmbedResult,
    last_id: &mut i64,
    processed: &mut usize,
    total: usize,
    progress_callback: &Option<Box<dyn Fn(usize, usize)>>,
    signal: &ShutdownSignal,
) -> Result<()> {
    let mut all_chunks: Vec<ChunkWork> = Vec::with_capacity(pending.len() * 3);
    let mut page_normal_docs: usize = 0;
    let mut chunks_needed: HashMap<i64, usize> = HashMap::with_capacity(pending.len());
    let mut chunks_stored: HashMap<i64, usize> = HashMap::with_capacity(pending.len());

    debug!(count = pending.len(), "Starting chunking loop");
    for doc in pending {
        *last_id = doc.document_id;

        if doc.content_text.is_empty() {
            record_embedding_error(
                conn,
                doc.document_id,
                0,
                &doc.content_hash,
                "empty",
                model_name,
                "Document has empty content",
            )?;
            result.skipped += 1;
            *processed += 1;
            continue;
        }

        if page_normal_docs.is_multiple_of(50) {
            debug!(
                doc_id = doc.document_id,
                doc_num = page_normal_docs,
                content_bytes = doc.content_text.len(),
                "Chunking document"
            );
        }
        if page_normal_docs.is_multiple_of(100) {
            info!(
                doc_id = doc.document_id,
                content_bytes = doc.content_text.len(),
                docs_so_far = page_normal_docs,
                "Chunking document"
            );
        }
        let chunks = split_into_chunks(&doc.content_text);
        debug!(
            doc_id = doc.document_id,
            chunk_count = chunks.len(),
            "Chunked"
        );
        let total_chunks = chunks.len();

        if total_chunks as i64 > CHUNK_ROWID_MULTIPLIER {
            warn!(
                doc_id = doc.document_id,
                chunk_count = total_chunks,
                max = CHUNK_ROWID_MULTIPLIER,
                "Document produces too many chunks, skipping to prevent rowid collision"
            );
            record_embedding_error(
                conn,
                doc.document_id,
                0,
                &doc.content_hash,
                "overflow-sentinel",
                model_name,
                &format!(
                    "Document produces {} chunks, exceeding max {}",
                    total_chunks, CHUNK_ROWID_MULTIPLIER
                ),
            )?;
            result.skipped += 1;
            *processed += 1;
            if let Some(cb) = progress_callback {
                cb(*processed, total);
            }
            continue;
        }

        chunks_needed.insert(doc.document_id, total_chunks);

        for (chunk_index, text) in chunks {
            all_chunks.push(ChunkWork {
                doc_id: doc.document_id,
                chunk_index,
                total_chunks,
                doc_hash: doc.content_hash.clone(),
                chunk_hash: sha256_hash(&text),
                text,
            });
        }

        page_normal_docs += 1;
    }

    debug!(total_chunks = all_chunks.len(), "Chunking loop done");

    let mut cleared_docs: HashSet<i64> = HashSet::with_capacity(pending.len());
    let mut embed_buf: Vec<u8> = Vec::with_capacity(EXPECTED_DIMS * 4);

    // Split chunks into batches, then process batches in concurrent groups
    let batches: Vec<&[ChunkWork]> = all_chunks.chunks(BATCH_SIZE).collect();
    debug!(
        batches = batches.len(),
        concurrency, "Starting Ollama requests"
    );
    info!(
        chunks = all_chunks.len(),
        batches = batches.len(),
        docs = page_normal_docs,
        "Chunking complete, starting Ollama requests"
    );

    info!(
        batches = batches.len(),
        concurrency, "About to start Ollama request loop"
    );
    for (group_idx, concurrent_group) in batches.chunks(concurrency).enumerate() {
        debug!(group_idx, "Starting concurrent group");
        if signal.is_cancelled() {
            info!("Shutdown requested during embedding, stopping mid-page");
            break;
        }

        // Phase 1: Collect texts (must outlive the futures)
        let batch_texts: Vec<Vec<&str>> = concurrent_group
            .iter()
            .map(|batch| batch.iter().map(|c| c.text.as_str()).collect())
            .collect();

        // Phase 2: Fire concurrent HTTP requests to Ollama
        let futures: Vec<_> = batch_texts
            .iter()
            .map(|texts| client.embed_batch(texts))
            .collect();
        let api_results = join_all(futures).await;
        debug!(
            group_idx,
            results = api_results.len(),
            "Ollama group complete"
        );

        // Phase 3: Serial DB writes for each batch result
        for (batch, api_result) in concurrent_group.iter().zip(api_results) {
            match api_result {
                Ok(embeddings) => {
                    for (i, embedding) in embeddings.iter().enumerate() {
                        if i >= batch.len() {
                            break;
                        }
                        let chunk = &batch[i];

                        if embedding.len() != EXPECTED_DIMS {
                            warn!(
                                doc_id = chunk.doc_id,
                                chunk_index = chunk.chunk_index,
                                got_dims = embedding.len(),
                                expected = EXPECTED_DIMS,
                                "Dimension mismatch, skipping"
                            );
                            record_embedding_error(
                                conn,
                                chunk.doc_id,
                                chunk.chunk_index,
                                &chunk.doc_hash,
                                &chunk.chunk_hash,
                                model_name,
                                &format!(
                                    "Dimension mismatch: got {}, expected {}",
                                    embedding.len(),
                                    EXPECTED_DIMS
                                ),
                            )?;
                            result.failed += 1;
                            continue;
                        }

                        if !cleared_docs.contains(&chunk.doc_id) {
                            clear_document_embeddings(conn, chunk.doc_id)?;
                            cleared_docs.insert(chunk.doc_id);
                        }

                        store_embedding(
                            conn,
                            chunk.doc_id,
                            chunk.chunk_index,
                            &chunk.doc_hash,
                            &chunk.chunk_hash,
                            model_name,
                            embedding,
                            chunk.total_chunks,
                            &mut embed_buf,
                        )?;
                        result.chunks_embedded += 1;
                        *chunks_stored.entry(chunk.doc_id).or_insert(0) += 1;
                    }

                    // Record errors for chunks that Ollama silently dropped
                    if embeddings.len() < batch.len() {
                        warn!(
                            returned = embeddings.len(),
                            expected = batch.len(),
                            "Ollama returned fewer embeddings than inputs"
                        );
                        for chunk in &batch[embeddings.len()..] {
                            record_embedding_error(
                                conn,
                                chunk.doc_id,
                                chunk.chunk_index,
                                &chunk.doc_hash,
                                &chunk.chunk_hash,
                                model_name,
                                &format!(
                                    "Batch mismatch: got {} of {} embeddings",
                                    embeddings.len(),
                                    batch.len()
                                ),
                            )?;
                            result.failed += 1;
                        }
                    }
                }
                Err(e) => {
                    let err_str = e.to_string();
                    let err_lower = err_str.to_lowercase();
                    let is_context_error = err_lower.contains("context length")
                        || err_lower.contains("too long")
                        || err_lower.contains("maximum context")
                        || err_lower.contains("token limit")
                        || err_lower.contains("exceeds")
                        || (err_lower.contains("413") && err_lower.contains("http"));

                    if is_context_error && batch.len() > 1 {
                        warn!(
                            "Batch failed with context length error, retrying chunks individually"
                        );
                        for chunk in *batch {
                            match client.embed_batch(&[chunk.text.as_str()]).await {
                                Ok(embeddings)
                                    if !embeddings.is_empty()
                                        && embeddings[0].len() == EXPECTED_DIMS =>
                                {
                                    if !cleared_docs.contains(&chunk.doc_id) {
                                        clear_document_embeddings(conn, chunk.doc_id)?;
                                        cleared_docs.insert(chunk.doc_id);
                                    }

                                    store_embedding(
                                        conn,
                                        chunk.doc_id,
                                        chunk.chunk_index,
                                        &chunk.doc_hash,
                                        &chunk.chunk_hash,
                                        model_name,
                                        &embeddings[0],
                                        chunk.total_chunks,
                                        &mut embed_buf,
                                    )?;
                                    result.chunks_embedded += 1;
                                    *chunks_stored.entry(chunk.doc_id).or_insert(0) += 1;
                                }
                                Ok(embeddings) => {
                                    let got_dims = embeddings.first().map_or(0, std::vec::Vec::len);
                                    let reason = format!(
                                        "Retry failed: got {} embeddings, first has {} dims (expected {})",
                                        embeddings.len(),
                                        got_dims,
                                        EXPECTED_DIMS
                                    );
                                    warn!(
                                        doc_id = chunk.doc_id,
                                        chunk_index = chunk.chunk_index,
                                        %reason,
                                        "Chunk retry returned unexpected result"
                                    );
                                    record_embedding_error(
                                        conn,
                                        chunk.doc_id,
                                        chunk.chunk_index,
                                        &chunk.doc_hash,
                                        &chunk.chunk_hash,
                                        model_name,
                                        &reason,
                                    )?;
                                    result.failed += 1;
                                }
                                Err(retry_err) => {
                                    let reason = format!("Retry failed: {}", retry_err);
                                    warn!(
                                        doc_id = chunk.doc_id,
                                        chunk_index = chunk.chunk_index,
                                        chunk_bytes = chunk.text.len(),
                                        error = %retry_err,
                                        "Chunk retry request failed"
                                    );
                                    record_embedding_error(
                                        conn,
                                        chunk.doc_id,
                                        chunk.chunk_index,
                                        &chunk.doc_hash,
                                        &chunk.chunk_hash,
                                        model_name,
                                        &reason,
                                    )?;
                                    result.failed += 1;
                                }
                            }
                        }
                    } else {
                        warn!(error = %e, "Batch embedding failed");
                        for chunk in *batch {
                            record_embedding_error(
                                conn,
                                chunk.doc_id,
                                chunk.chunk_index,
                                &chunk.doc_hash,
                                &chunk.chunk_hash,
                                model_name,
                                &e.to_string(),
                            )?;
                            result.failed += 1;
                        }
                    }
                }
            }
        }
    }

    // Count docs where all chunks were successfully stored
    for (doc_id, needed) in &chunks_needed {
        if chunks_stored.get(doc_id).copied().unwrap_or(0) == *needed {
            result.docs_embedded += 1;
        }
    }

    *processed += page_normal_docs;
    if let Some(cb) = progress_callback {
        cb(*processed, total);
    }

    Ok(())
}

fn clear_document_embeddings(conn: &Connection, document_id: i64) -> Result<()> {
    conn.prepare_cached("DELETE FROM embedding_metadata WHERE document_id = ?1")?
        .execute([document_id])?;

    let start_rowid = encode_rowid(document_id, 0);
    let end_rowid = encode_rowid(document_id + 1, 0);
    conn.prepare_cached("DELETE FROM embeddings WHERE rowid >= ?1 AND rowid < ?2")?
        .execute(rusqlite::params![start_rowid, end_rowid])?;

    Ok(())
}

#[allow(clippy::too_many_arguments)]
fn store_embedding(
    conn: &Connection,
    doc_id: i64,
    chunk_index: usize,
    doc_hash: &str,
    chunk_hash: &str,
    model_name: &str,
    embedding: &[f32],
    total_chunks: usize,
    embed_buf: &mut Vec<u8>,
) -> Result<()> {
    let rowid = encode_rowid(doc_id, chunk_index as i64);

    embed_buf.clear();
    embed_buf.reserve(embedding.len() * 4);
    for f in embedding {
        embed_buf.extend_from_slice(&f.to_le_bytes());
    }

    conn.prepare_cached("INSERT OR REPLACE INTO embeddings (rowid, embedding) VALUES (?1, ?2)")?
        .execute(rusqlite::params![rowid, &embed_buf[..]])?;

    let chunk_count: Option<i64> = if chunk_index == 0 {
        Some(total_chunks as i64)
    } else {
        None
    };

    let now = chrono::Utc::now().timestamp_millis();
    conn.prepare_cached(
        "INSERT OR REPLACE INTO embedding_metadata
         (document_id, chunk_index, model, dims, document_hash, chunk_hash,
          created_at, attempt_count, last_error, chunk_max_bytes, chunk_count)
         VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7, 1, NULL, ?8, ?9)",
    )?
    .execute(rusqlite::params![
        doc_id,
        chunk_index as i64,
        model_name,
        EXPECTED_DIMS as i64,
        doc_hash,
        chunk_hash,
        now,
        CHUNK_MAX_BYTES as i64,
        chunk_count
    ])?;

    Ok(())
}

pub(crate) fn record_embedding_error(
    conn: &Connection,
    doc_id: i64,
    chunk_index: usize,
    doc_hash: &str,
    chunk_hash: &str,
    model_name: &str,
    error: &str,
) -> Result<()> {
    let now = chrono::Utc::now().timestamp_millis();
    conn.prepare_cached(
        "INSERT INTO embedding_metadata
         (document_id, chunk_index, model, dims, document_hash, chunk_hash,
          created_at, attempt_count, last_error, last_attempt_at, chunk_max_bytes)
         VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7, 1, ?8, ?7, ?9)
         ON CONFLICT(document_id, chunk_index) DO UPDATE SET
           attempt_count = embedding_metadata.attempt_count + 1,
           last_error = ?8,
           last_attempt_at = ?7,
           chunk_max_bytes = ?9",
    )?
    .execute(rusqlite::params![
        doc_id,
        chunk_index as i64,
        model_name,
        EXPECTED_DIMS as i64,
        doc_hash,
        chunk_hash,
        now,
        error,
        CHUNK_MAX_BYTES as i64
    ])?;
    Ok(())
}

fn sha256_hash(input: &str) -> String {
    let mut hasher = Sha256::new();
    hasher.update(input.as_bytes());
    format!("{:x}", hasher.finalize())
}