//! Semantic similarity discovery: find related entities via vector search.

use std::collections::HashSet;

use rusqlite::Connection;
use serde::Serialize;

use crate::cli::render::{Icons, Theme};
use crate::cli::robot::RobotMeta;
use crate::core::config::Config;
use crate::core::db::create_connection;
use crate::core::error::{LoreError, Result};
use crate::core::paths::get_db_path;
use crate::core::project::resolve_project;
use crate::core::time::ms_to_iso;
use crate::embedding::ollama::{OllamaClient, OllamaConfig};
use crate::search::search_vector;

// ---------------------------------------------------------------------------
// Response types
// ---------------------------------------------------------------------------

#[derive(Debug, Serialize)]
pub struct RelatedResponse {
    pub mode: String,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub source: Option<RelatedSource>,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub query: Option<String>,
    pub results: Vec<RelatedResult>,
    #[serde(skip_serializing_if = "Vec::is_empty")]
    pub warnings: Vec<String>,
}

#[derive(Debug, Serialize)]
pub struct RelatedSource {
    pub source_type: String,
    pub iid: i64,
    pub title: String,
    pub project_path: String,
}

#[derive(Debug, Serialize)]
pub struct RelatedResult {
    pub source_type: String,
    pub iid: i64,
    pub title: String,
    pub url: String,
    pub similarity_score: f64,
    pub project_path: String,
    #[serde(skip_serializing_if = "Vec::is_empty")]
    pub shared_labels: Vec<String>,
    pub author: Option<String>,
    pub updated_at: String,
}

// ---------------------------------------------------------------------------
// Internal row types
// ---------------------------------------------------------------------------

struct DocumentRow {
    id: i64,
    source_type: String,
    source_id: i64,
    #[allow(dead_code)]
    project_id: i64,
    #[allow(dead_code)]
    title: Option<String>,
    url: Option<String>,
    content_text: String,
    label_names: Option<String>,
    author_username: Option<String>,
    updated_at: Option<i64>,
}

struct EntityInfo {
    #[allow(dead_code)]
    iid: i64,
    title: String,
    project_path: String,
}

// ---------------------------------------------------------------------------
// Main entry point
// ---------------------------------------------------------------------------

/// Run the related command.
///
/// Modes:
/// - Entity mode: `lore related issues 42` or `lore related mrs 99`
/// - Query mode: `lore related 'search terms'`
pub async fn run_related(
    config: &Config,
    query_or_type: &str,
    iid: Option<i64>,
    limit: usize,
    project: Option<&str>,
) -> Result<RelatedResponse> {
    let db_path = get_db_path(config.storage.db_path.as_deref());
    let conn = create_connection(&db_path)?;

    // Check if embeddings exist
    let embedding_count: i64 = conn
        .query_row("SELECT COUNT(*) FROM embedding_metadata", [], |row| {
            row.get(0)
        })
        .unwrap_or(0);

    if embedding_count == 0 {
        return Err(LoreError::Other(
            "No embeddings found. Run 'lore embed' first to generate vector embeddings.".into(),
        ));
    }

    // Validate input
    if query_or_type.trim().is_empty() {
        return Err(LoreError::Other(
            "Query cannot be empty. Provide an entity type (issues/mrs) and IID, or a search query.".into(),
        ));
    }

    // Determine mode: entity vs query
    let entity_type = match query_or_type.to_lowercase().as_str() {
        "issues" | "issue" | "i" => Some("issue"),
        "mrs" | "mr" | "m" | "merge_request" => Some("merge_request"),
        _ => None,
    };

    if let Some(etype) = entity_type {
        // Entity mode
        let iid = iid.ok_or_else(|| {
            LoreError::Other("Entity mode requires an IID (e.g., 'lore related issues 42')".into())
        })?;
        run_related_entity(&conn, config, etype, iid, limit, project).await
    } else {
        // Query mode - treat query_or_type as free text
        run_related_query(&conn, config, query_or_type, limit, project).await
    }
}

async fn run_related_entity(
    conn: &Connection,
    config: &Config,
    entity_type: &str,
    iid: i64,
    limit: usize,
    project_filter: Option<&str>,
) -> Result<RelatedResponse> {
    // Find the source document
    let source_doc = find_entity_document(conn, entity_type, iid, project_filter)?;
    let source_info = get_entity_info(conn, entity_type, source_doc.source_id)?;

    // Embed the source content
    let embedding = embed_text(config, &source_doc.content_text).await?;

    // Search for similar documents (limit + 1 to account for filtering self)
    let vector_results = search_vector(conn, &embedding, limit.saturating_add(1))?;

    // Filter out self and hydrate results
    let source_labels = parse_label_names(&source_doc.label_names);
    let mut results = Vec::new();
    let mut warnings = Vec::new();

    for vr in vector_results {
        // Skip self
        if vr.document_id == source_doc.id {
            continue;
        }

        if let Some(result) = hydrate_result(conn, vr.document_id, vr.distance, &source_labels)? {
            results.push(result);
        }

        if results.len() >= limit {
            break;
        }
    }

    // Check for low similarity
    if !results.is_empty() && results.iter().all(|r| r.similarity_score < 0.3) {
        warnings.push("No strongly related entities found (all scores < 0.3)".to_string());
    }

    Ok(RelatedResponse {
        mode: "entity".to_string(),
        source: Some(RelatedSource {
            source_type: entity_type.to_string(),
            iid,
            title: source_info.title,
            project_path: source_info.project_path,
        }),
        query: None,
        results,
        warnings,
    })
}

async fn run_related_query(
    conn: &Connection,
    config: &Config,
    query: &str,
    limit: usize,
    project_filter: Option<&str>,
) -> Result<RelatedResponse> {
    let mut warnings = Vec::new();

    // Warn if query is very short
    if query.split_whitespace().count() <= 2 {
        warnings.push("Short queries may produce noisy results".to_string());
    }

    // Embed the query
    let embedding = embed_text(config, query).await?;

    // Search for similar documents (fetch extra to allow for project filtering)
    let vector_results = search_vector(conn, &embedding, limit.saturating_mul(2))?;

    // Filter by project if specified and hydrate
    let project_id = project_filter
        .map(|p| resolve_project(conn, p))
        .transpose()?;

    let mut results = Vec::new();
    let empty_labels: HashSet<String> = HashSet::new();

    for vr in vector_results {
        // Check project filter
        if let Some(pid) = project_id {
            let doc_project_id: Option<i64> = conn
                .query_row(
                    "SELECT project_id FROM documents WHERE id = ?1",
                    [vr.document_id],
                    |row| row.get(0),
                )
                .ok();

            if doc_project_id != Some(pid) {
                continue;
            }
        }

        if let Some(result) = hydrate_result(conn, vr.document_id, vr.distance, &empty_labels)? {
            results.push(result);
        }

        if results.len() >= limit {
            break;
        }
    }

    // Check for low similarity
    if !results.is_empty() && results.iter().all(|r| r.similarity_score < 0.3) {
        warnings.push("No strongly related entities found (all scores < 0.3)".to_string());
    }

    Ok(RelatedResponse {
        mode: "query".to_string(),
        source: None,
        query: Some(query.to_string()),
        results,
        warnings,
    })
}

// ---------------------------------------------------------------------------
// DB helpers
// ---------------------------------------------------------------------------

fn find_entity_document(
    conn: &Connection,
    entity_type: &str,
    iid: i64,
    project_filter: Option<&str>,
) -> Result<DocumentRow> {
    let table = match entity_type {
        "issue" => "issues",
        "merge_request" => "merge_requests",
        _ => {
            return Err(LoreError::Other(format!(
                "Unknown entity type: {entity_type}"
            )));
        }
    };

    let (sql, params): (String, Vec<Box<dyn rusqlite::ToSql>>) = match project_filter {
        Some(project) => {
            let project_id = resolve_project(conn, project)?;
            (
                format!(
                    "SELECT d.id, d.source_type, d.source_id, d.project_id, d.title, d.url,
                            d.content_text, d.label_names, d.author_username, d.updated_at
                     FROM documents d
                     JOIN {table} e ON d.source_id = e.id
                     WHERE d.source_type = ?1 AND e.iid = ?2 AND e.project_id = ?3"
                ),
                vec![
                    Box::new(entity_type.to_string()),
                    Box::new(iid),
                    Box::new(project_id),
                ],
            )
        }
        None => (
            format!(
                "SELECT d.id, d.source_type, d.source_id, d.project_id, d.title, d.url,
                        d.content_text, d.label_names, d.author_username, d.updated_at
                 FROM documents d
                 JOIN {table} e ON d.source_id = e.id
                 WHERE d.source_type = ?1 AND e.iid = ?2"
            ),
            vec![Box::new(entity_type.to_string()), Box::new(iid)],
        ),
    };

    let param_refs: Vec<&dyn rusqlite::ToSql> = params.iter().map(|p| p.as_ref()).collect();

    let mut stmt = conn.prepare(&sql)?;
    let rows: Vec<DocumentRow> = stmt
        .query_map(param_refs.as_slice(), |row| {
            Ok(DocumentRow {
                id: row.get(0)?,
                source_type: row.get(1)?,
                source_id: row.get(2)?,
                project_id: row.get(3)?,
                title: row.get(4)?,
                url: row.get(5)?,
                content_text: row.get(6)?,
                label_names: row.get(7)?,
                author_username: row.get(8)?,
                updated_at: row.get(9)?,
            })
        })?
        .collect::<std::result::Result<Vec<_>, _>>()?;

    match rows.len() {
        0 => Err(LoreError::NotFound(format!(
            "{entity_type} #{iid} not found (run 'lore sync' first?)"
        ))),
        1 => Ok(rows.into_iter().next().unwrap()),
        _ => Err(LoreError::Ambiguous(format!(
            "{entity_type} #{iid} exists in multiple projects. Use --project to specify."
        ))),
    }
}

fn get_entity_info(conn: &Connection, entity_type: &str, entity_id: i64) -> Result<EntityInfo> {
    let table = match entity_type {
        "issue" => "issues",
        "merge_request" => "merge_requests",
        _ => {
            return Err(LoreError::Other(format!(
                "Unknown entity type: {entity_type}"
            )));
        }
    };

    let sql = format!(
        "SELECT e.iid, e.title, p.path_with_namespace
         FROM {table} e
         JOIN projects p ON e.project_id = p.id
         WHERE e.id = ?1"
    );

    conn.query_row(&sql, [entity_id], |row| {
        Ok(EntityInfo {
            iid: row.get(0)?,
            title: row.get(1)?,
            project_path: row.get(2)?,
        })
    })
    .map_err(|e| LoreError::NotFound(format!("Entity not found: {e}")))
}

fn hydrate_result(
    conn: &Connection,
    document_id: i64,
    distance: f64,
    source_labels: &HashSet<String>,
) -> Result<Option<RelatedResult>> {
    let doc: Option<DocumentRow> = conn
        .query_row(
            "SELECT d.id, d.source_type, d.source_id, d.project_id, d.title, d.url,
                    d.content_text, d.label_names, d.author_username, d.updated_at
             FROM documents d
             WHERE d.id = ?1",
            [document_id],
            |row| {
                Ok(DocumentRow {
                    id: row.get(0)?,
                    source_type: row.get(1)?,
                    source_id: row.get(2)?,
                    project_id: row.get(3)?,
                    title: row.get(4)?,
                    url: row.get(5)?,
                    content_text: row.get(6)?,
                    label_names: row.get(7)?,
                    author_username: row.get(8)?,
                    updated_at: row.get(9)?,
                })
            },
        )
        .ok();

    let Some(doc) = doc else {
        return Ok(None);
    };

    // Skip discussion/note documents - we want entities only
    if doc.source_type == "discussion" || doc.source_type == "note" {
        return Ok(None);
    }

    // Get IID from the source entity
    let table = match doc.source_type.as_str() {
        "issue" => "issues",
        "merge_request" => "merge_requests",
        _ => return Ok(None),
    };

    // Get IID and title from the source entity - skip gracefully if not found
    // (this handles orphaned documents where the entity was deleted)
    let entity_info: Option<(i64, String, String)> = conn
        .query_row(
            &format!(
                "SELECT e.iid, e.title, p.path_with_namespace
                 FROM {table} e
                 JOIN projects p ON e.project_id = p.id
                 WHERE e.id = ?1"
            ),
            [doc.source_id],
            |row| Ok((row.get(0)?, row.get(1)?, row.get(2)?)),
        )
        .ok();

    let Some((iid, title, project_path)) = entity_info else {
        // Entity not found in database - skip this result
        return Ok(None);
    };

    // Compute shared labels
    let result_labels = parse_label_names(&doc.label_names);
    let shared_labels: Vec<String> = source_labels
        .intersection(&result_labels)
        .cloned()
        .collect();

    Ok(Some(RelatedResult {
        source_type: doc.source_type,
        iid,
        title,
        url: doc.url.unwrap_or_default(),
        similarity_score: distance_to_similarity(distance),
        project_path,
        shared_labels,
        author: doc.author_username,
        updated_at: doc.updated_at.map(ms_to_iso).unwrap_or_default(),
    }))
}

// ---------------------------------------------------------------------------
// Embedding helper
// ---------------------------------------------------------------------------

async fn embed_text(config: &Config, text: &str) -> Result<Vec<f32>> {
    let ollama = OllamaClient::new(OllamaConfig {
        base_url: config.embedding.base_url.clone(),
        model: config.embedding.model.clone(),
        timeout_secs: 60,
    });

    let embeddings = ollama.embed_batch(&[text]).await?;
    embeddings
        .into_iter()
        .next()
        .ok_or_else(|| LoreError::EmbeddingFailed {
            document_id: 0,
            reason: "No embedding returned".to_string(),
        })
}

// ---------------------------------------------------------------------------
// Utilities
// ---------------------------------------------------------------------------

/// Convert L2 distance to a 0-1 similarity score.
/// Uses inverse relationship: closer (lower distance) = higher similarity.
fn distance_to_similarity(distance: f64) -> f64 {
    1.0 / (1.0 + distance)
}

fn parse_label_names(label_names_json: &Option<String>) -> HashSet<String> {
    label_names_json
        .as_deref()
        .and_then(|s| serde_json::from_str::<Vec<String>>(s).ok())
        .unwrap_or_default()
        .into_iter()
        .collect()
}

// ---------------------------------------------------------------------------
// Printers
// ---------------------------------------------------------------------------

pub fn print_related_human(response: &RelatedResponse) {
    // Header
    let header = match &response.source {
        Some(src) => format!("Related to {} #{}: {}", src.source_type, src.iid, src.title),
        None => format!(
            "Related to query: \"{}\"",
            response.query.as_deref().unwrap_or("")
        ),
    };
    println!("{}", Theme::bold().render(&header));
    println!("{}", "-".repeat(header.len().min(70)));
    println!();

    if response.results.is_empty() {
        println!("No related entities found.");
        return;
    }

    for (i, result) in response.results.iter().enumerate() {
        let type_icon = match result.source_type.as_str() {
            "issue" => Icons::issue_opened(),
            "merge_request" => Icons::mr_opened(),
            _ => " ",
        };

        let score_bar_len = (result.similarity_score * 10.0) as usize;
        let score_bar: String = "\u{2588}".repeat(score_bar_len);

        println!(
            "{:>2}. {} {} #{} ({:.0}%) {}",
            i + 1,
            type_icon,
            result.source_type,
            result.iid,
            result.similarity_score * 100.0,
            score_bar
        );
        println!("    {}", result.title);
        println!(
            "    {} | @{}",
            result.project_path,
            result.author.as_deref().unwrap_or("?")
        );

        if !result.shared_labels.is_empty() {
            println!("    Labels shared: {}", result.shared_labels.join(", "));
        }
        println!();
    }

    // Warnings
    for warning in &response.warnings {
        println!("{} {}", Theme::warning().render(Icons::warning()), warning);
    }
}

pub fn print_related_json(response: &RelatedResponse, elapsed_ms: u64) {
    let meta = RobotMeta { elapsed_ms };
    let output = serde_json::json!({
        "ok": true,
        "data": response,
        "meta": meta,
    });
    match serde_json::to_string(&output) {
        Ok(json) => println!("{json}"),
        Err(e) => eprintln!("Error serializing to JSON: {e}"),
    }
}

// ---------------------------------------------------------------------------
// Tests
// ---------------------------------------------------------------------------

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

    #[test]
    fn test_distance_to_similarity_identical() {
        assert!((distance_to_similarity(0.0) - 1.0).abs() < f64::EPSILON);
    }

    #[test]
    fn test_distance_to_similarity_midpoint() {
        assert!((distance_to_similarity(1.0) - 0.5).abs() < f64::EPSILON);
    }

    #[test]
    fn test_distance_to_similarity_large() {
        let sim = distance_to_similarity(2.0);
        assert!(sim > 0.0 && sim < 0.5);
        assert!((sim - 0.333_333_333_333_333_3).abs() < 0.001);
    }

    #[test]
    fn test_distance_to_similarity_range() {
        for d in [0.0, 0.1, 0.5, 1.0, 2.0, 5.0, 10.0] {
            let sim = distance_to_similarity(d);
            assert!(
                sim > 0.0 && sim <= 1.0,
                "score {sim} out of range for distance {d}"
            );
        }
    }

    #[test]
    fn test_parse_label_names_valid() {
        let json = Some(r#"["bug", "priority::high"]"#.to_string());
        let labels = parse_label_names(&json);
        assert!(labels.contains("bug"));
        assert!(labels.contains("priority::high"));
        assert_eq!(labels.len(), 2);
    }

    #[test]
    fn test_parse_label_names_empty() {
        let labels = parse_label_names(&None);
        assert!(labels.is_empty());
    }

    #[test]
    fn test_parse_label_names_invalid_json() {
        let json = Some("not valid json".to_string());
        let labels = parse_label_names(&json);
        assert!(labels.is_empty());
    }

    #[test]
    fn test_parse_label_names_empty_array() {
        let json = Some("[]".to_string());
        let labels = parse_label_names(&json);
        assert!(labels.is_empty());
    }
}