//! Source page scraper: fetches a source URL and extracts article links.
//!
//! Used in Phase 1 of the generation pipeline to discover articles
//! from user-configured sources before falling back to LLM web search.

use std::sync::Arc;
use crate::errors::AppError;
use crate::services::llm::LlmProvider;
use crate::services::llm::schema::build_link_extraction_schema;
use crate::services::prompts::build_link_extraction_prompt;
use scraper::{Html, Selector};
use url::Url;

/// Patterns in URL paths that indicate non-article pages.
const EXCLUDED_PATH_PATTERNS: &[&str] = &[
    "/tag", "/category", "/author", "/page", "/login", "/signup",
    "/privacy", "/terms", "/search", "/contact", "/about", "/topics", 
    "/archive", "/companies", "/events", "/company", "/event", "/collections",
];

/// File extensions that indicate static assets, not articles.
const EXCLUDED_EXTENSIONS: &[&str] = &[
    ".css", ".js", ".png", ".jpg", ".jpeg", ".gif", ".svg",
    ".pdf", ".zip", ".xml", ".json", ".ico", ".woff", ".woff2",
];

/// Extract article links from a source page.
///
/// Fetches the HTML at `source_url`, extracts all `<a href>` links,
/// filters to same-domain article-like URLs, deduplicates, and returns
/// up to `max_links` candidate URLs.
pub async fn extract_article_links(
    http_client: &reqwest::Client,
    source_url: &str,
    max_links: usize,
) -> Result<Vec<String>, AppError> {
    let base_url = Url::parse(source_url)
        .map_err(|e| AppError::BadRequest(format!("Invalid source URL: {}", e)))?;
    let base_domain = base_url.host_str().unwrap_or("").to_lowercase();

    let response = http_client
        .get(source_url)
        .send()
        .await
        .map_err(|e| {
            tracing::warn!(url = source_url, error = %e, "Failed to fetch source page");
            AppError::Internal(anyhow::anyhow!("Failed to fetch source page"))
        })?;

    if !response.status().is_success() {
        tracing::warn!(url = source_url, status = %response.status(), "Source page returned non-200");
        return Ok(Vec::new());
    }

    let html_text = response.text().await.map_err(|e| {
        AppError::Internal(anyhow::anyhow!("Failed to read source page body: {}", e))
    })?;

    let links = extract_links_from_html(&html_text, &base_url, &base_domain);

    Ok(links.into_iter().take(max_links).collect())
}

/// Extract and filter article links from HTML content.
///
/// This is a pure function (no I/O) for easy testing.
pub fn extract_links_from_html(
    html: &str,
    base_url: &Url,
    base_domain: &str,
) -> Vec<String> {
    let document = Html::parse_document(html);
    let selector = Selector::parse("a[href]").unwrap();
    let mut seen = std::collections::HashSet::new();
    let mut links = Vec::new();

    for element in document.select(&selector) {
        if let Some(href) = element.value().attr("href") {
            let resolved = match base_url.join(href) {
                Ok(u) => u,
                Err(_) => continue,
            };

            if resolved.scheme() != "http" && resolved.scheme() != "https" {
                continue;
            }

            let link_domain = resolved.host_str().unwrap_or("").to_lowercase();
            if link_domain != base_domain {
                continue;
            }

            let path = resolved.path();
            if path.is_empty() || path == "/" {
                continue;
            }

            let path_lower = path.to_lowercase();
            if EXCLUDED_PATH_PATTERNS.iter().any(|p| path_lower.contains(p)) {
                continue;
            }

            if EXCLUDED_EXTENSIONS.iter().any(|ext| path_lower.ends_with(ext)) {
                continue;
            }

            let mut normalized = resolved.clone();
            normalized.set_fragment(None);
            let url_str = normalized.to_string();

            if seen.insert(url_str.clone()) {
                links.push(url_str);
            }
        }
    }

    links
}

/// Extract all links from HTML as (href, anchor_text) pairs for LLM analysis.
///
/// Minimal filtering: same-domain, http/https, non-empty path.
/// No article-pattern filtering — the LLM decides which are articles.
pub fn extract_links_as_pairs(
    html: &str,
    base_url: &Url,
) -> Vec<(String, String)> {
    let base_domain = base_url.host_str().unwrap_or("").to_lowercase();
    let document = Html::parse_document(html);
    let selector = Selector::parse("a[href]").unwrap();
    let mut pairs = Vec::new();

    for element in document.select(&selector) {
        if let Some(href) = element.value().attr("href") {
            let resolved = match base_url.join(href) {
                Ok(u) => u,
                Err(_) => continue,
            };

            if resolved.scheme() != "http" && resolved.scheme() != "https" {
                continue;
            }

            let link_domain = resolved.host_str().unwrap_or("").to_lowercase();
            if link_domain != base_domain {
                continue;
            }

            let path = resolved.path();
            if path.is_empty() || path == "/" {
                continue;
            }

            let anchor_text: String = element.text().collect::<Vec<_>>().join(" ");
            let anchor_text = anchor_text.trim().to_string();

            pairs.push((resolved.to_string(), anchor_text));
        }
    }

    pairs
}

/// Format link pairs as a text list for the LLM prompt.
/// Caps at 200 links to limit token usage.
fn format_links_for_llm(pairs: &[(String, String)]) -> String {
    pairs
        .iter()
        .take(200)
        .map(|(href, text)| {
            if text.is_empty() {
                format!("- {}", href)
            } else {
                format!("- {} | \"{}\"", href, text)
            }
        })
        .collect::<Vec<_>>()
        .join("\n")
}

/// Extract article links using LLM analysis of the page HTML.
///
/// Falls back to heuristic extraction if the LLM call fails or returns empty.
#[allow(clippy::too_many_arguments)]
pub async fn extract_article_links_with_llm(
    http_client: &reqwest::Client,
    source_url: &str,
    max_links: usize,
    provider: &Arc<dyn LlmProvider>,
    model: &str,
    pool: Option<&sqlx::PgPool>,
    user_id: Option<uuid::Uuid>,
    job_id: Option<uuid::Uuid>,
) -> Result<Vec<String>, AppError> {
    let base_url = Url::parse(source_url)
        .map_err(|e| AppError::BadRequest(format!("Invalid source URL: {}", e)))?;
    let base_domain = base_url.host_str().unwrap_or("").to_lowercase();

    let response = http_client.get(source_url).send().await.map_err(|e| {
        tracing::warn!(url = source_url, error = %e, "Failed to fetch source page");
        AppError::Internal(anyhow::anyhow!("Failed to fetch source page"))
    })?;

    if !response.status().is_success() {
        tracing::warn!(url = source_url, status = %response.status(), "Source page returned non-200");
        return Ok(Vec::new());
    }

    let html_text = response.text().await.map_err(|e| {
        AppError::Internal(anyhow::anyhow!("Failed to read source page body: {}", e))
    })?;

    let pairs = extract_links_as_pairs(&html_text, &base_url);
    let links_text = format_links_for_llm(&pairs);
    let (system, user) = build_link_extraction_prompt(&links_text);
    let schema = build_link_extraction_schema();

    let llm_start = std::time::Instant::now();
    let llm_result = provider.call_llm(model, &system, &user, &schema).await;
    let llm_duration = llm_start.elapsed().as_millis() as u64;

    // Log the LLM call if pool/user_id/job_id are provided
    if let (Some(pool), Some(uid), Some(jid)) = (pool, user_id, job_id) {
        let response_str = match &llm_result {
            Ok(resp) => serde_json::to_string_pretty(resp).unwrap_or_default(),
            Err(e) => format!("Error: {}", e),
        };
        crate::db::llm_call_log::insert(
            pool, uid, jid, "link_extraction", model,
            &system, &user, &response_str, llm_duration as i32,
            None,
        ).await.ok();
    }

    match llm_result {
        Ok(llm_response) => {
            let urls: Vec<String> = llm_response
                .get("urls")
                .and_then(|u| u.as_array())
                .map(|arr| {
                    arr.iter()
                        .filter_map(|v| v.as_str())
                        .filter_map(|href| {
                            let resolved = base_url.join(href).ok()?;
                            if resolved.scheme() != "http" && resolved.scheme() != "https" {
                                return None;
                            }
                            if resolved.host_str()?.to_lowercase() != base_domain {
                                return None;
                            }
                            Some(resolved.to_string())
                        })
                        .collect()
                })
                .unwrap_or_default();

            if urls.is_empty() {
                tracing::warn!(url = source_url, "LLM returned no links, falling back to heuristic");
                let fallback = extract_links_from_html(&html_text, &base_url, &base_domain);
                Ok(fallback.into_iter().take(max_links).collect())
            } else {
                let mut seen = std::collections::HashSet::new();
                let deduped: Vec<String> = urls.into_iter().filter(|u| seen.insert(u.clone())).collect();
                Ok(deduped.into_iter().take(max_links).collect())
            }
        }
        Err(e) => {
            tracing::warn!(url = source_url, error = %e, "LLM link extraction failed, falling back to heuristic");
            let fallback = extract_links_from_html(&html_text, &base_url, &base_domain);
            Ok(fallback.into_iter().take(max_links).collect())
        }
    }
}

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

    fn base_url(s: &str) -> Url {
        Url::parse(s).unwrap()
    }

    #[test]
    fn extracts_article_links_from_html() {
        let html = r#"
        <html><body>
            <a href="/blog/article-1">Article 1</a>
            <a href="/blog/article-2">Article 2</a>
            <a href="/">Home</a>
        </body></html>"#;
        let base = base_url("https://example.com/blog");
        let links = extract_links_from_html(html, &base, "example.com");
        assert_eq!(links.len(), 2);
        assert!(links[0].contains("/blog/article-1"));
        assert!(links[1].contains("/blog/article-2"));
    }

    #[test]
    fn filters_external_links() {
        let html = r#"<a href="https://other.com/article">External</a>"#;
        let base = base_url("https://example.com");
        let links = extract_links_from_html(html, &base, "example.com");
        assert!(links.is_empty());
    }

    #[test]
    fn filters_non_article_patterns() {
        let html = r#"
        <a href="/tag/ai">Tag</a>
        <a href="/category/tech">Category</a>
        <a href="/author/john">Author</a>
        <a href="/login">Login</a>
        "#;
        let base = base_url("https://example.com");
        let links = extract_links_from_html(html, &base, "example.com");
        assert!(links.is_empty());
    }

    #[test]
    fn filters_static_assets() {
        let html = r#"
        <a href="/style.css">CSS</a>
        <a href="/script.js">JS</a>
        <a href="/logo.png">Image</a>
        "#;
        let base = base_url("https://example.com");
        let links = extract_links_from_html(html, &base, "example.com");
        assert!(links.is_empty());
    }

    #[test]
    fn deduplicates_links() {
        let html = r#"
        <a href="/article">Link 1</a>
        <a href="/article">Link 2</a>
        <a href="/article#section">Link 3</a>
        "#;
        let base = base_url("https://example.com");
        let links = extract_links_from_html(html, &base, "example.com");
        assert_eq!(links.len(), 1);
    }

    #[test]
    fn resolves_relative_urls() {
        let html = r#"<a href="my-post">Relative</a>"#;
        let base = base_url("https://example.com/blog/");
        let links = extract_links_from_html(html, &base, "example.com");
        assert_eq!(links.len(), 1);
        assert!(links[0].contains("/blog/my-post"));
    }

    #[test]
    fn allows_single_segment_paths() {
        let html = r#"<a href="/my-great-article">Article</a>"#;
        let base = base_url("https://example.com");
        let links = extract_links_from_html(html, &base, "example.com");
        assert_eq!(links.len(), 1);
    }

    #[test]
    fn empty_html_returns_empty() {
        let links = extract_links_from_html("", &base_url("https://example.com"), "example.com");
        assert!(links.is_empty());
    }

    #[test]
    fn extract_pairs_returns_href_and_text() {
        let html = r#"
        <html><body>
            <a href="/blog/article-1">Breaking AI News</a>
            <a href="/blog/article-2">GPT-6 Released</a>
        </body></html>"#;
        let base = base_url("https://example.com/blog");
        let pairs = extract_links_as_pairs(html, &base);
        assert_eq!(pairs.len(), 2);
        assert!(pairs[0].0.contains("/blog/article-1"));
        assert_eq!(pairs[0].1, "Breaking AI News");
        assert!(pairs[1].0.contains("/blog/article-2"));
        assert_eq!(pairs[1].1, "GPT-6 Released");
    }

    #[test]
    fn extract_pairs_filters_external_links() {
        let html = r#"<a href="https://other.com/article">External</a>"#;
        let base = base_url("https://example.com");
        let pairs = extract_links_as_pairs(html, &base);
        assert!(pairs.is_empty());
    }

    #[test]
    fn extract_pairs_filters_root_path() {
        let html = r#"<a href="/">Home</a>"#;
        let base = base_url("https://example.com");
        let pairs = extract_links_as_pairs(html, &base);
        assert!(pairs.is_empty());
    }

    #[test]
    fn extract_pairs_handles_empty_anchor_text() {
        let html = r#"<a href="/article"><img src="pic.jpg"/></a>"#;
        let base = base_url("https://example.com");
        let pairs = extract_links_as_pairs(html, &base);
        assert_eq!(pairs.len(), 1);
        assert_eq!(pairs[0].1, "");
    }

    #[test]
    fn format_links_for_llm_formats_correctly() {
        let pairs = vec![
            ("https://example.com/a".to_string(), "Article One".to_string()),
            ("https://example.com/b".to_string(), "".to_string()),
        ];
        let result = format_links_for_llm(&pairs);
        assert!(result.contains("- https://example.com/a | \"Article One\""));
        assert!(result.contains("- https://example.com/b"));
        assert!(!result.contains("| \"\""));
    }

    #[test]
    fn format_links_for_llm_caps_at_200() {
        let pairs: Vec<(String, String)> = (0..300)
            .map(|i| (format!("https://example.com/{}", i), format!("Link {}", i)))
            .collect();
        let result = format_links_for_llm(&pairs);
        let line_count = result.lines().count();
        assert_eq!(line_count, 200);
    }
}