ebook-rs 0.16.1

use crate::cfi::Cfi;
use crate::section::Section;
use serde::{Deserialize, Serialize};

/// A single search result item.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct SearchResult {
    pub spine_index: usize,
    pub snippet: String,
    pub cfi: String,
    pub char_offset: usize,
}

/// Full-text search engine across chapter sections.
pub struct SearchEngine;

impl SearchEngine {
    /// Perform full-text search over a slice of sections.
    /// P4 Fix: Reuses pre-computed section.plain_text_lower for zero-allocation searching.
    pub fn search(sections: &[Section], query: &str, case_sensitive: bool) -> Vec<SearchResult> {
        if query.trim().is_empty() {
            return Vec::new();
        }

        #[cfg(feature = "parallel")]
        {
            use rayon::prelude::*;
            sections
                .par_iter()
                .flat_map(|section| Self::search_section(section, query, case_sensitive))
                .collect()
        }

        #[cfg(not(feature = "parallel"))]
        {
            let mut results = Vec::new();
            for section in sections {
                results.extend(Self::search_section(section, query, case_sensitive));
            }
            results
        }
    }

    /// Search a single section safely without cross-string offset mismatch panics.
    pub fn search_section(
        section: &Section,
        query: &str,
        case_sensitive: bool,
    ) -> Vec<SearchResult> {
        let mut results = Vec::new();
        if query.trim().is_empty() || section.plain_text.is_empty() {
            return results;
        }

        let query_lower = if case_sensitive {
            query.to_string()
        } else {
            query.to_lowercase()
        };

        let target_text = if case_sensitive {
            &section.plain_text
        } else {
            &section.plain_text_lower
        };

        let finder = memchr::memmem::Finder::new(query_lower.as_bytes());
        let is_ascii = target_text.is_ascii();

        for match_byte_idx in finder.find_iter(target_text.as_bytes()) {
            let char_offset = if is_ascii {
                match_byte_idx
            } else {
                target_text[..match_byte_idx].chars().count()
            };

            let match_len = query_lower.len();

            let (before, matched, after, has_prefix, has_suffix) =
                extract_zero_alloc_snippet(&section.plain_text, match_byte_idx, match_len);

            let prefix = if has_prefix { "..." } else { "" };
            let suffix = if has_suffix { "..." } else { "" };

            let snippet = format!(
                "{}{}<mark>{}</mark>{}{}",
                prefix,
                html_escape(before),
                html_escape(matched),
                html_escape(after),
                suffix
            );

            let cfi = Cfi::from_spine_index(section.index, None, char_offset).to_string();

            results.push(SearchResult {
                spine_index: section.index,
                snippet,
                cfi,
                char_offset,
            });
        }

        results
    }

    /// Perform full-text regex pattern search across chapter sections.
    pub fn search_regex(sections: &[Section], pattern: &str) -> Result<Vec<SearchResult>, String> {
        let re = regex::Regex::new(pattern)
            .map_err(|e| format!("Invalid regex pattern '{}': {}", pattern, e))?;
        let mut results = Vec::new();

        for section in sections {
            for m in re.find_iter(&section.plain_text) {
                let abs_idx = m.start();
                let match_str = m.as_str();

                let text_chars: Vec<char> = section.plain_text.chars().collect();
                let char_idx = section.plain_text[..abs_idx.min(section.plain_text.len())]
                    .chars()
                    .count();
                let q_char_len = match_str.chars().count();

                let start_c = char_idx.saturating_sub(40);
                let end_c = (char_idx + q_char_len + 40).min(text_chars.len());

                let match_end = (char_idx + q_char_len).min(text_chars.len());
                let before: String = text_chars[start_c..char_idx].iter().collect();
                let matched: String = text_chars[char_idx..match_end].iter().collect();
                let after: String = text_chars[match_end..end_c].iter().collect();

                let prefix = if start_c > 0 { "..." } else { "" };
                let suffix = if end_c < text_chars.len() { "..." } else { "" };

                let snippet = format!(
                    "{}{}<mark>{}</mark>{}{}",
                    prefix,
                    html_escape(&before),
                    html_escape(&matched),
                    html_escape(&after),
                    suffix
                );
                let cfi = Cfi::from_spine_index(section.index, None, char_idx).to_string();

                results.push(SearchResult {
                    spine_index: section.index,
                    snippet,
                    cfi,
                    char_offset: char_idx,
                });
            }
        }

        Ok(results)
    }

    /// Format search results into Readium Standard Search Collection JSON (application/vnd.readium.search+json).
    pub fn to_readium_search_json(results: &[SearchResult], query: &str) -> Result<String, String> {
        let locators: Vec<serde_json::Value> = results
            .iter()
            .map(|r| {
                serde_json::json!({
                    "href": format!("section_{}.html", r.spine_index),
                    "type": "application/xhtml+xml",
                    "locations": {
                        "cfi": r.cfi,
                        "position": r.char_offset / 1000 + 1
                    },
                    "text": {
                        "snippet": r.snippet
                    }
                })
            })
            .collect();

        let collection = serde_json::json!({
            "@context": "http://readium.org/webpub-manifest/context.jsonld",
            "metadata": {
                "numberOfResults": results.len(),
                "query": query
            },
            "locators": locators
        });

        serde_json::to_string_pretty(&collection)
            .map_err(|e| format!("Failed to serialize Readium Search JSON: {}", e))
    }
}

/// Extract snippet window surrounding a match without converting the entire string to a Vec<char>.
fn extract_zero_alloc_snippet(
    text: &str,
    byte_offset: usize,
    match_bytes_len: usize,
) -> (&str, &str, &str, bool, bool) {
    if text.is_ascii() {
        let start_b = byte_offset.saturating_sub(40);
        let end_match_b = (byte_offset + match_bytes_len).min(text.len());
        let end_b = (end_match_b + 40).min(text.len());

        let prefix = start_b > 0;
        let suffix = end_b < text.len();

        let before = &text[start_b..byte_offset];
        let matched = &text[byte_offset..end_match_b];
        let after = &text[end_match_b..end_b];

        (before, matched, after, prefix, suffix)
    } else {
        let safe_byte_offset = byte_offset.min(text.len());
        let before_slice = &text[..safe_byte_offset];
        let mut start_b = 0;
        let mut count = 0;
        for (idx, _) in before_slice.char_indices().rev() {
            count += 1;
            if count == 40 {
                start_b = idx;
                break;
            }
        }

        let end_match_b = (safe_byte_offset + match_bytes_len).min(text.len());
        let after_slice = &text[end_match_b..];
        let mut end_b = text.len();
        let mut count = 0;
        for (idx, c) in after_slice.char_indices() {
            count += 1;
            if count == 40 {
                end_b = end_match_b + idx + c.len_utf8();
                break;
            }
        }

        let prefix = start_b > 0;
        let suffix = end_b < text.len();

        let before = &text[start_b..safe_byte_offset];
        let matched = &text[safe_byte_offset..end_match_b];
        let after = &text[end_match_b..end_b];

        (before, matched, after, prefix, suffix)
    }
}

/// Helper function to HTML-escape arbitrary text strings to prevent stored XSS attacks.
pub fn html_escape(s: &str) -> String {
    s.replace('&', "&amp;")
        .replace('<', "&lt;")
        .replace('>', "&gt;")
        .replace('"', "&quot;")
        .replace('\'', "&#39;")
}

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

    #[test]
    fn test_search() {
        let sec = Section {
            index: 0,
            idref: "ch1".to_string(),
            href: "ch1.xhtml".to_string(),
            full_path: "OEBPS/ch1.xhtml".to_string(),
            raw_html: "<p>Hello Rust Reader</p>".to_string(),
            processed_html: "<p>Hello Rust Reader</p>".to_string(),
            plain_text: "Hello Rust Reader".to_string(),
            plain_text_lower: "hello rust reader".to_string(),
            char_count: 17,
            viewport_width: None,
            viewport_height: None,
        };

        let results = SearchEngine::search(&[sec], "Rust", false);
        assert_eq!(results.len(), 1);
        assert_eq!(results[0].spine_index, 0);
        assert!(results[0].snippet.contains("Rust"));
    }
}