use axum::http::HeaderMap;
use loco_rs::prelude::*;
use serde::{Deserialize, Deserializer, Serialize};
use serde_json::Value;
use std::{collections::HashSet, time::Instant};

use crate::{
    controllers::site_settings,
    models::_entities::posts,
    services::{abuse_guard, analytics, content},
};

fn deserialize_boolish_option<'de, D>(
    deserializer: D,
) -> std::result::Result<Option<bool>, D::Error>
where
    D: Deserializer<'de>,
{
    let raw = Option::<String>::deserialize(deserializer)?;

    raw.map(|value| match value.trim().to_ascii_lowercase().as_str() {
        "1" | "true" | "yes" | "on" => Ok(true),
        "0" | "false" | "no" | "off" => Ok(false),
        other => Err(serde::de::Error::custom(format!(
            "invalid boolean value `{other}`"
        ))),
    })
    .transpose()
}

fn normalize_text(value: &str) -> String {
    value
        .split_whitespace()
        .collect::<Vec<_>>()
        .join(" ")
        .trim()
        .to_ascii_lowercase()
}

fn tokenize(value: &str) -> Vec<String> {
    value
        .split(|ch: char| !ch.is_alphanumeric() && ch != '-' && ch != '_')
        .map(normalize_text)
        .filter(|item| !item.is_empty())
        .collect()
}

fn levenshtein_distance(left: &str, right: &str) -> usize {
    if left == right {
        return 0;
    }
    if left.is_empty() {
        return right.chars().count();
    }
    if right.is_empty() {
        return left.chars().count();
    }

    let right_chars = right.chars().collect::<Vec<_>>();
    let mut prev = (0..=right_chars.len()).collect::<Vec<_>>();

    for (i, left_ch) in left.chars().enumerate() {
        let mut curr = vec![i + 1; right_chars.len() + 1];
        for (j, right_ch) in right_chars.iter().enumerate() {
            let cost = usize::from(left_ch != *right_ch);
            curr[j + 1] = (curr[j] + 1).min(prev[j + 1] + 1).min(prev[j] + cost);
        }
        prev = curr;
    }

    prev[right_chars.len()]
}

fn parse_synonym_groups(value: &Option<Value>) -> Vec<Vec<String>> {
    value
        .as_ref()
        .and_then(Value::as_array)
        .cloned()
        .unwrap_or_default()
        .into_iter()
        .filter_map(|item| item.as_str().map(ToString::to_string))
        .map(|item| {
            let normalized = item.replace("=>", ",").replace('|', ",");
            normalized
                .split([',', '，'])
                .map(normalize_text)
                .filter(|token| !token.is_empty())
                .collect::<Vec<_>>()
        })
        .filter(|group| !group.is_empty())
        .collect()
}

fn expand_search_terms(query: &str, synonym_groups: &[Vec<String>]) -> Vec<String> {
    let normalized_query = normalize_text(query);
    let query_tokens = tokenize(query);
    let mut expanded = Vec::new();
    let mut seen = HashSet::new();

    if !normalized_query.is_empty() && seen.insert(normalized_query.clone()) {
        expanded.push(normalized_query.clone());
    }

    for token in &query_tokens {
        if seen.insert(token.clone()) {
            expanded.push(token.clone());
        }
    }

    for group in synonym_groups {
        let matched = group.iter().any(|item| {
            *item == normalized_query
                || query_tokens.iter().any(|token| token == item)
                || normalized_query.contains(item)
        });

        if matched {
            for token in group {
                if seen.insert(token.clone()) {
                    expanded.push(token.clone());
                }
            }
        }
    }

    expanded
}

fn candidate_terms(posts: &[posts::Model]) -> Vec<String> {
    let mut seen = HashSet::new();
    let mut candidates = Vec::new();

    for post in posts {
        for source in [
            post.title.as_deref().unwrap_or_default(),
            post.category.as_deref().unwrap_or_default(),
            &post.slug,
        ] {
            for token in tokenize(source) {
                if token.len() >= 3 && seen.insert(token.clone()) {
                    candidates.push(token);
                }
            }
        }

        if let Some(tags) = post.tags.as_ref().and_then(Value::as_array) {
            for token in tags.iter().filter_map(Value::as_str).flat_map(tokenize) {
                if token.len() >= 2 && seen.insert(token.clone()) {
                    candidates.push(token);
                }
            }
        }
    }

    candidates
}

fn find_spelling_fallback(
    query: &str,
    posts: &[posts::Model],
    synonym_groups: &[Vec<String>],
) -> Vec<String> {
    let primary_token = tokenize(query).into_iter().next().unwrap_or_default();
    if primary_token.len() < 3 {
        return Vec::new();
    }

    let mut nearest = candidate_terms(posts)
        .into_iter()
        .map(|candidate| {
            let distance = levenshtein_distance(&primary_token, &candidate);
            (candidate, distance)
        })
        .filter(|(_, distance)| *distance <= 2)
        .collect::<Vec<_>>();
    nearest.sort_by(|left, right| left.1.cmp(&right.1).then_with(|| left.0.cmp(&right.0)));

    nearest
        .into_iter()
        .take(3)
        .flat_map(|(candidate, _)| expand_search_terms(&candidate, synonym_groups))
        .collect()
}

fn post_has_tag(post: &posts::Model, wanted_tag: &str) -> bool {
    let wanted = normalize_text(wanted_tag);

    post.tags
        .as_ref()
        .and_then(Value::as_array)
        .map(|tags| {
            tags.iter()
                .filter_map(Value::as_str)
                .map(normalize_text)
                .any(|tag| tag == wanted)
        })
        .unwrap_or(false)
}

fn score_post(post: &posts::Model, query: &str, terms: &[String]) -> f64 {
    let normalized_query = normalize_text(query);
    let title = normalize_text(post.title.as_deref().unwrap_or_default());
    let description = normalize_text(post.description.as_deref().unwrap_or_default());
    let content_text = normalize_text(post.content.as_deref().unwrap_or_default());
    let category = normalize_text(post.category.as_deref().unwrap_or_default());
    let slug = normalize_text(&post.slug);
    let tags = post
        .tags
        .as_ref()
        .and_then(Value::as_array)
        .cloned()
        .unwrap_or_default()
        .into_iter()
        .filter_map(|item| item.as_str().map(normalize_text))
        .collect::<Vec<_>>();

    let mut score = 0.0;

    if !normalized_query.is_empty() {
        if title.contains(&normalized_query) {
            score += 6.0;
        }
        if description.contains(&normalized_query) {
            score += 4.0;
        }
        if slug.contains(&normalized_query) {
            score += 4.0;
        }
        if category.contains(&normalized_query) {
            score += 3.0;
        }
        if tags.iter().any(|tag| tag.contains(&normalized_query)) {
            score += 4.0;
        }
        if content_text.contains(&normalized_query) {
            score += 2.0;
        }
    }

    for term in terms {
        if term.is_empty() {
            continue;
        }

        if title.contains(term) {
            score += 3.5;
        }
        if description.contains(term) {
            score += 2.2;
        }
        if slug.contains(term) {
            score += 2.0;
        }
        if category.contains(term) {
            score += 1.8;
        }
        if tags.iter().any(|tag| tag == term) {
            score += 2.5;
        } else if tags.iter().any(|tag| tag.contains(term)) {
            score += 1.5;
        }
        if content_text.contains(term) {
            score += 0.8;
        }
    }

    score
}

fn is_preview_search(query: &SearchQuery, headers: &HeaderMap) -> bool {
    query.preview.unwrap_or(false)
        || headers
            .get("x-termi-search-mode")
            .and_then(|value| value.to_str().ok())
            .map(|value| value.eq_ignore_ascii_case("preview"))
            .unwrap_or(false)
}

fn normalize_search_sort_by(value: Option<&str>) -> String {
    match value
        .map(str::trim)
        .unwrap_or_default()
        .to_ascii_lowercase()
        .as_str()
    {
        "newest" | "created_at" => "newest".to_string(),
        "oldest" => "oldest".to_string(),
        "title" => "title".to_string(),
        _ => "relevance".to_string(),
    }
}

fn normalize_sort_order(value: Option<&str>, sort_by: &str) -> String {
    match value
        .map(str::trim)
        .unwrap_or_default()
        .to_ascii_lowercase()
        .as_str()
    {
        "asc" => "asc".to_string(),
        "desc" => "desc".to_string(),
        _ if sort_by == "title" => "asc".to_string(),
        _ => "desc".to_string(),
    }
}

fn sort_search_results(items: &mut [SearchResult], sort_by: &str, sort_order: &str) {
    items.sort_by(|left, right| {
        let ordering = match sort_by {
            "newest" => right.created_at.cmp(&left.created_at),
            "oldest" => left.created_at.cmp(&right.created_at),
            "title" => left
                .title
                .as_deref()
                .unwrap_or(&left.slug)
                .to_ascii_lowercase()
                .cmp(
                    &right
                        .title
                        .as_deref()
                        .unwrap_or(&right.slug)
                        .to_ascii_lowercase(),
                ),
            _ => right
                .rank
                .partial_cmp(&left.rank)
                .unwrap_or(std::cmp::Ordering::Equal)
                .then_with(|| right.created_at.cmp(&left.created_at)),
        };

        if sort_by == "relevance" || sort_by == "newest" || sort_by == "oldest" {
            return ordering;
        }

        let ordering = if sort_order == "asc" {
            ordering
        } else {
            ordering.reverse()
        };
        ordering.then_with(|| left.slug.cmp(&right.slug))
    });
}

#[derive(Clone, Debug, Default, Deserialize)]
pub struct SearchQuery {
    pub q: Option<String>,
    pub limit: Option<u64>,
    pub category: Option<String>,
    pub tag: Option<String>,
    #[serde(alias = "type")]
    pub post_type: Option<String>,
    #[serde(default, deserialize_with = "deserialize_boolish_option")]
    pub preview: Option<bool>,
}

#[derive(Clone, Debug, Default, Deserialize)]
pub struct SearchPageQuery {
    #[serde(flatten)]
    pub search: SearchQuery,
    pub page: Option<u64>,
    #[serde(alias = "page_size")]
    pub page_size: Option<u64>,
    pub sort_by: Option<String>,
    pub sort_order: Option<String>,
}

#[derive(Clone, Debug, Serialize)]
pub struct SearchResult {
    pub id: i32,
    pub title: Option<String>,
    pub slug: String,
    pub description: Option<String>,
    pub content: Option<String>,
    pub category: Option<String>,
    pub tags: Option<Value>,
    pub post_type: Option<String>,
    pub image: Option<String>,
    pub pinned: Option<bool>,
    pub created_at: chrono::DateTime<chrono::Utc>,
    pub updated_at: chrono::DateTime<chrono::Utc>,
    pub rank: f64,
}

#[derive(Clone, Debug, Serialize)]
pub struct PagedSearchResponse {
    pub query: String,
    pub items: Vec<SearchResult>,
    pub page: u64,
    pub page_size: u64,
    pub total: usize,
    pub total_pages: u64,
    pub sort_by: String,
    pub sort_order: String,
}

async fn build_search_results(
    ctx: &AppContext,
    query: &SearchQuery,
    headers: &HeaderMap,
) -> Result<(String, bool, Vec<SearchResult>)> {
    let preview_search = is_preview_search(query, headers);

    let q = query.q.clone().unwrap_or_default().trim().to_string();
    if q.is_empty() {
        return Ok((q, preview_search, Vec::new()));
    }

    if !preview_search {
        abuse_guard::enforce_public_scope(
            "search",
            abuse_guard::detect_client_ip(headers).as_deref(),
            Some(&q),
        )?;
    }

    let settings = site_settings::load_current(ctx).await.ok();
    let synonym_groups = settings
        .as_ref()
        .map(|item| parse_synonym_groups(&item.search_synonyms))
        .unwrap_or_default();

    let mut all_posts = posts::Entity::find()
        .all(&ctx.db)
        .await?
        .into_iter()
        .filter(|post| {
            preview_search
                || content::is_post_listed_publicly(post, chrono::Utc::now().fixed_offset())
        })
        .collect::<Vec<_>>();

    if let Some(category) = query
        .category
        .as_deref()
        .map(str::trim)
        .filter(|value| !value.is_empty())
    {
        all_posts.retain(|post| {
            post.category
                .as_deref()
                .map(|value| value.eq_ignore_ascii_case(category))
                .unwrap_or(false)
        });
    }

    if let Some(tag) = query
        .tag
        .as_deref()
        .map(str::trim)
        .filter(|value| !value.is_empty())
    {
        all_posts.retain(|post| post_has_tag(post, tag));
    }

    if let Some(post_type) = query
        .post_type
        .as_deref()
        .map(str::trim)
        .filter(|value| !value.is_empty())
    {
        all_posts.retain(|post| {
            post.post_type
                .as_deref()
                .map(|value| value.eq_ignore_ascii_case(post_type))
                .unwrap_or(false)
        });
    }

    let mut expanded_terms = expand_search_terms(&q, &synonym_groups);
    let mut results = all_posts
        .iter()
        .map(|post| (post, score_post(post, &q, &expanded_terms)))
        .filter(|(_, rank)| *rank > 0.0)
        .map(|(post, rank)| SearchResult {
            id: post.id,
            title: post.title.clone(),
            slug: post.slug.clone(),
            description: post.description.clone(),
            content: post.content.clone(),
            category: post.category.clone(),
            tags: post.tags.clone(),
            post_type: post.post_type.clone(),
            image: post.image.clone(),
            pinned: post.pinned,
            created_at: post.created_at.into(),
            updated_at: post.updated_at.into(),
            rank,
        })
        .collect::<Vec<_>>();

    if results.is_empty() {
        expanded_terms = find_spelling_fallback(&q, &all_posts, &synonym_groups);
        if !expanded_terms.is_empty() {
            results = all_posts
                .iter()
                .map(|post| (post, score_post(post, &q, &expanded_terms)))
                .filter(|(_, rank)| *rank > 0.0)
                .map(|(post, rank)| SearchResult {
                    id: post.id,
                    title: post.title.clone(),
                    slug: post.slug.clone(),
                    description: post.description.clone(),
                    content: post.content.clone(),
                    category: post.category.clone(),
                    tags: post.tags.clone(),
                    post_type: post.post_type.clone(),
                    image: post.image.clone(),
                    pinned: post.pinned,
                    created_at: post.created_at.into(),
                    updated_at: post.updated_at.into(),
                    rank,
                })
                .collect::<Vec<_>>();
        }
    }

    sort_search_results(&mut results, "relevance", "desc");
    Ok((q, preview_search, results))
}

#[debug_handler]
pub async fn search(
    Query(query): Query<SearchQuery>,
    State(ctx): State<AppContext>,
    headers: HeaderMap,
) -> Result<Response> {
    let started_at = Instant::now();
    let limit = query.limit.unwrap_or(20).clamp(1, 100) as usize;
    let (q, preview_search, mut results) = build_search_results(&ctx, &query, &headers).await?;
    if q.is_empty() {
        return format::json(Vec::<SearchResult>::new());
    }
    results.truncate(limit);

    if !preview_search {
        analytics::record_search_event(
            &ctx,
            &q,
            results.len(),
            &headers,
            started_at.elapsed().as_millis() as i64,
        )
        .await;
    }

    format::json(results)
}

#[debug_handler]
pub async fn search_page(
    Query(query): Query<SearchPageQuery>,
    State(ctx): State<AppContext>,
    headers: HeaderMap,
) -> Result<Response> {
    let started_at = Instant::now();
    let page_size = query.page_size.unwrap_or(20).clamp(1, 100);
    let sort_by = normalize_search_sort_by(query.sort_by.as_deref());
    let sort_order = normalize_sort_order(query.sort_order.as_deref(), &sort_by);
    let (q, preview_search, mut results) =
        build_search_results(&ctx, &query.search, &headers).await?;

    if q.is_empty() {
        return format::json(PagedSearchResponse {
            query: q,
            items: Vec::new(),
            page: 1,
            page_size,
            total: 0,
            total_pages: 1,
            sort_by,
            sort_order,
        });
    }

    sort_search_results(&mut results, &sort_by, &sort_order);

    let total = results.len();
    let total_pages = std::cmp::max(1, ((total as u64) + page_size - 1) / page_size);
    let page = query.page.unwrap_or(1).clamp(1, total_pages);
    let start = ((page - 1) * page_size) as usize;
    let end = std::cmp::min(start + page_size as usize, total);
    let items = if start >= total {
        Vec::new()
    } else {
        results[start..end].to_vec()
    };

    if !preview_search {
        analytics::record_search_event(
            &ctx,
            &q,
            total,
            &headers,
            started_at.elapsed().as_millis() as i64,
        )
        .await;
    }

    format::json(PagedSearchResponse {
        query: q,
        items,
        page,
        page_size,
        total,
        total_pages,
        sort_by,
        sort_order,
    })
}

pub fn routes() -> Routes {
    Routes::new()
        .prefix("api/search/")
        .add("page", get(search_page))
        .add("/", get(search))
}