use std::collections::HashSet;

use rusqlite::Connection;
use sha2::{Digest, Sha256};
use tracing::{info, instrument, warn};

use crate::core::error::Result;
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;

#[derive(Debug, Default)]
pub struct EmbedResult {
    pub 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), fields(%model_name, items_processed, items_skipped, errors))]
pub async fn embed_documents(
    conn: &Connection,
    client: &OllamaClient,
    model_name: &str,
    progress_callback: Option<Box<dyn Fn(usize, usize)>>,
) -> 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 {
        let pending = find_pending_documents(conn, DB_PAGE_SIZE, last_id, model_name)?;
        if pending.is_empty() {
            break;
        }

        conn.execute_batch("SAVEPOINT embed_page")?;
        let page_result = embed_page(
            conn,
            client,
            model_name,
            &pending,
            &mut result,
            &mut last_id,
            &mut processed,
            total,
            &progress_callback,
        )
        .await;
        match page_result {
            Ok(()) => {
                conn.execute_batch("RELEASE embed_page")?;
            }
            Err(e) => {
                let _ = conn.execute_batch("ROLLBACK TO embed_page; RELEASE embed_page");
                return Err(e);
            }
        }
    }

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

    tracing::Span::current().record("items_processed", result.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,
    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)>>,
) -> Result<()> {
    let mut all_chunks: Vec<ChunkWork> = Vec::with_capacity(pending.len() * 3);
    let mut page_normal_docs: usize = 0;

    for doc in pending {
        *last_id = doc.document_id;

        if doc.content_text.is_empty() {
            result.skipped += 1;
            *processed += 1;
            continue;
        }

        let chunks = split_into_chunks(&doc.content_text);
        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;
        }

        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;
    }

    let mut cleared_docs: HashSet<i64> = HashSet::with_capacity(pending.len());

    for batch in all_chunks.chunks(BATCH_SIZE) {
        let texts: Vec<&str> = batch.iter().map(|c| c.text.as_str()).collect();

        match client.embed_batch(&texts).await {
            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,
                    )?;
                    result.embedded += 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,
                                )?;
                                result.embedded += 1;
                            }
                            _ => {
                                warn!(
                                    doc_id = chunk.doc_id,
                                    chunk_index = chunk.chunk_index,
                                    chunk_bytes = chunk.text.len(),
                                    "Chunk too large for model context window"
                                );
                                record_embedding_error(
                                    conn,
                                    chunk.doc_id,
                                    chunk.chunk_index,
                                    &chunk.doc_hash,
                                    &chunk.chunk_hash,
                                    model_name,
                                    "Chunk exceeds model context window",
                                )?;
                                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;
                    }
                }
            }
        }
    }

    *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.execute(
        "DELETE FROM embedding_metadata WHERE document_id = ?1",
        [document_id],
    )?;

    let start_rowid = encode_rowid(document_id, 0);
    let end_rowid = encode_rowid(document_id + 1, 0);
    conn.execute(
        "DELETE FROM embeddings WHERE rowid >= ?1 AND rowid < ?2",
        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,
) -> Result<()> {
    let rowid = encode_rowid(doc_id, chunk_index as i64);

    let mut embedding_bytes = Vec::with_capacity(embedding.len() * 4);
    for f in embedding {
        embedding_bytes.extend_from_slice(&f.to_le_bytes());
    }

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

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

    let now = chrono::Utc::now().timestamp_millis();
    conn.execute(
        "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)",
        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(())
}

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.execute(
        "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",
        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())
}