use crate::core::error::Result;
use rusqlite::Connection;

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum FtsQueryMode {
    Safe,
    Raw,
}

#[derive(Debug)]
pub struct FtsResult {
    pub document_id: i64,
    pub bm25_score: f64,
    pub snippet: String,
}

/// Validate an FTS5 query string for safety.
/// Rejects known-dangerous patterns: unbalanced quotes, excessive wildcards,
/// and empty queries. Returns the sanitized query or falls back to Safe mode.
fn sanitize_raw_fts(raw: &str) -> Option<String> {
    let trimmed = raw.trim();
    if trimmed.is_empty() {
        return None;
    }

    // Reject unbalanced double quotes (FTS5 syntax error)
    let quote_count = trimmed.chars().filter(|&c| c == '"').count();
    if quote_count % 2 != 0 {
        return None;
    }

    // Reject leading wildcard-only queries (expensive full-table scan)
    if trimmed == "*" || trimmed.starts_with("* ") {
        return None;
    }

    Some(trimmed.to_string())
}

pub fn to_fts_query(raw: &str, mode: FtsQueryMode) -> String {
    match mode {
        FtsQueryMode::Raw => {
            // Validate raw FTS5 input; fall back to Safe mode if invalid
            match sanitize_raw_fts(raw) {
                Some(sanitized) => sanitized,
                None => to_fts_query(raw, FtsQueryMode::Safe),
            }
        }
        FtsQueryMode::Safe => {
            let trimmed = raw.trim();
            if trimmed.is_empty() {
                return String::new();
            }

            // FTS5 boolean operators are case-sensitive uppercase keywords.
            // Pass them through unquoted so users can write "switch AND health".
            // Note: NEAR is a function NEAR(term1 term2, N), not an infix operator.
            // Users who need NEAR syntax should use FtsQueryMode::Raw.
            const FTS5_OPERATORS: &[&str] = &["AND", "OR", "NOT"];

            let mut result = String::with_capacity(trimmed.len() + 20);
            for (i, token) in trimmed.split_whitespace().enumerate() {
                if i > 0 {
                    result.push(' ');
                }
                if FTS5_OPERATORS.contains(&token) {
                    result.push_str(token);
                } else if let Some(stem) = token.strip_suffix('*')
                    && !stem.is_empty()
                    && stem.chars().all(|c| c.is_alphanumeric() || c == '_')
                {
                    result.push('"');
                    result.push_str(&stem.replace('"', "\"\""));
                    result.push_str("\"*");
                } else {
                    result.push('"');
                    result.push_str(&token.replace('"', "\"\""));
                    result.push('"');
                }
            }
            result
        }
    }
}

pub fn search_fts(
    conn: &Connection,
    query: &str,
    limit: usize,
    mode: FtsQueryMode,
) -> Result<Vec<FtsResult>> {
    let fts_query = to_fts_query(query, mode);
    if fts_query.is_empty() {
        return Ok(Vec::new());
    }

    let sql = r#"
        SELECT d.id, bm25(documents_fts) AS score,
               snippet(documents_fts, 1, '<mark>', '</mark>', '...', 64) AS snip
        FROM documents_fts
        JOIN documents d ON d.id = documents_fts.rowid
        WHERE documents_fts MATCH ?1
        ORDER BY score
        LIMIT ?2
    "#;

    let mut stmt = conn.prepare_cached(sql)?;
    let results = stmt
        .query_map(rusqlite::params![fts_query, limit as i64], |row| {
            Ok(FtsResult {
                document_id: row.get(0)?,
                bm25_score: row.get(1)?,
                snippet: row.get(2)?,
            })
        })?
        .collect::<std::result::Result<Vec<_>, _>>()?;

    Ok(results)
}

pub fn generate_fallback_snippet(content_text: &str, max_chars: usize) -> String {
    // Use char_indices to find the boundary at max_chars in a single pass,
    // short-circuiting early for large strings instead of counting all chars.
    let byte_end = match content_text.char_indices().nth(max_chars) {
        Some((i, _)) => i,
        None => return content_text.to_string(), // content fits within max_chars
    };
    let truncated = &content_text[..byte_end];

    if let Some(last_space) = truncated.rfind(' ') {
        format!("{}...", &truncated[..last_space])
    } else {
        format!("{}...", truncated)
    }
}

pub fn get_result_snippet(fts_snippet: Option<&str>, content_text: &str) -> String {
    match fts_snippet {
        Some(s) if !s.is_empty() => s.to_string(),
        _ => generate_fallback_snippet(content_text, 200),
    }
}

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

    #[test]
    fn test_safe_query_basic() {
        let result = to_fts_query("auth error", FtsQueryMode::Safe);
        assert_eq!(result, "\"auth\" \"error\"");
    }

    #[test]
    fn test_safe_query_prefix() {
        let result = to_fts_query("auth*", FtsQueryMode::Safe);
        assert_eq!(result, "\"auth\"*");
    }

    #[test]
    fn test_safe_query_special_chars() {
        let result = to_fts_query("C++", FtsQueryMode::Safe);
        assert_eq!(result, "\"C++\"");
    }

    #[test]
    fn test_safe_query_dash() {
        let result = to_fts_query("-DWITH_SSL", FtsQueryMode::Safe);
        assert_eq!(result, "\"-DWITH_SSL\"");
    }

    #[test]
    fn test_safe_query_quotes() {
        let result = to_fts_query("he said \"hello\"", FtsQueryMode::Safe);
        assert_eq!(result, "\"he\" \"said\" \"\"\"hello\"\"\"");
    }

    #[test]
    fn test_raw_mode_passthrough() {
        let result = to_fts_query("auth OR error", FtsQueryMode::Raw);
        assert_eq!(result, "auth OR error");
    }

    #[test]
    fn test_empty_query() {
        let result = to_fts_query("", FtsQueryMode::Safe);
        assert_eq!(result, "");

        let result = to_fts_query("   ", FtsQueryMode::Safe);
        assert_eq!(result, "");
    }

    #[test]
    fn test_prefix_only_alphanumeric() {
        let result = to_fts_query("C++*", FtsQueryMode::Safe);
        assert_eq!(result, "\"C++*\"");

        let result = to_fts_query("auth*", FtsQueryMode::Safe);
        assert_eq!(result, "\"auth\"*");
    }

    #[test]
    fn test_prefix_with_underscore() {
        let result = to_fts_query("jwt_token*", FtsQueryMode::Safe);
        assert_eq!(result, "\"jwt_token\"*");
    }

    #[test]
    fn test_fallback_snippet_short() {
        let result = generate_fallback_snippet("Short content", 200);
        assert_eq!(result, "Short content");
    }

    #[test]
    fn test_fallback_snippet_word_boundary() {
        let content = "This is a moderately long piece of text that should be truncated at a word boundary for readability purposes";
        let result = generate_fallback_snippet(content, 50);
        assert!(result.ends_with("..."));
        assert!(result.len() <= 55);
    }

    #[test]
    fn test_get_result_snippet_prefers_fts() {
        let result = get_result_snippet(Some("FTS <mark>match</mark>"), "full content text");
        assert_eq!(result, "FTS <mark>match</mark>");
    }

    #[test]
    fn test_get_result_snippet_fallback() {
        let result = get_result_snippet(None, "full content text");
        assert_eq!(result, "full content text");
    }

    #[test]
    fn test_get_result_snippet_empty_fts() {
        let result = get_result_snippet(Some(""), "full content text");
        assert_eq!(result, "full content text");
    }

    #[test]
    fn test_raw_mode_valid_fts5_passes_through() {
        let result = to_fts_query("auth OR error", FtsQueryMode::Raw);
        assert_eq!(result, "auth OR error");

        let result = to_fts_query("\"exact phrase\"", FtsQueryMode::Raw);
        assert_eq!(result, "\"exact phrase\"");
    }

    #[test]
    fn test_raw_mode_unbalanced_quotes_falls_back_to_safe() {
        let result = to_fts_query("auth \"error", FtsQueryMode::Raw);
        // Falls back to Safe mode: each token quoted
        assert_eq!(result, "\"auth\" \"\"\"error\"");
    }

    #[test]
    fn test_raw_mode_leading_wildcard_falls_back_to_safe() {
        let result = to_fts_query("* OR auth", FtsQueryMode::Raw);
        // Falls back to Safe mode; OR is an FTS5 operator so it passes through unquoted
        assert_eq!(result, "\"*\" OR \"auth\"");

        let result = to_fts_query("*", FtsQueryMode::Raw);
        assert_eq!(result, "\"*\"");
    }

    #[test]
    fn test_raw_mode_empty_falls_back_to_safe() {
        let result = to_fts_query("", FtsQueryMode::Raw);
        assert_eq!(result, "");

        let result = to_fts_query("   ", FtsQueryMode::Raw);
        assert_eq!(result, "");
    }
}