//! Chapter content sync — fetch a logged-in chapter page, extract its
//! image URLs in `pageN` order, download each to storage, and atomically
//! persist a `pages` row per image plus the chapter's `page_count`.
//!
//! Only chapters belonging to a manga someone has bookmarked are
//! candidates. The crawler scans bookmarks at the start of each run and
//! enqueues unfetched chapters; the API also enqueues at bookmark-time
//! so users get instant feedback. Both feed into the same queue and
//! dedup by chapter id.

// Implementation lands in the next commits in this branch. Module is
// declared so other crates can `use crawler::content` without breaking
// builds while iteration is in progress.

use anyhow::Context;
use sqlx::PgPool;
use uuid::Uuid;

use crate::crawler::detect::PageError;
use crate::crawler::rate_limit::HostRateLimiters;
use crate::crawler::session;
use crate::storage::Storage;

/// Parse the chapter page DOM and return the page images in `pageN`
/// order. Filters out the loader `<img class="loading">` and any
/// `<img>` without a numeric `id="pageN"`.
///
/// Reader pages don't render the site's `#logo` element, so the
/// universal logo-sentinel can't apply here — instead we assert
/// `a#pic_container` is present. Its absence means the response is the
/// transient broken-page response (or a redirect to some other layout)
/// and the caller should retry.
pub fn parse_chapter_pages(html: &str) -> Result<Vec<ChapterImage>, PageError> {
    let doc = scraper::Html::parse_document(html);
    let container_sel = scraper::Selector::parse("a#pic_container").unwrap();
    if doc.select(&container_sel).next().is_none() {
        return Err(PageError::transient("reader: a#pic_container missing"));
    }
    let sel = scraper::Selector::parse("a#pic_container img:not(.loading)").unwrap();
    let mut pages: Vec<ChapterImage> = doc
        .select(&sel)
        .filter_map(|img| {
            let id = img.value().id()?;
            let n: i32 = id.strip_prefix("page")?.parse().ok()?;
            let src = img.value().attr("src")?.trim().to_string();
            if src.is_empty() {
                return None;
            }
            Some(ChapterImage { page_number: n, url: src })
        })
        .collect();
    pages.sort_by_key(|p| p.page_number);
    Ok(pages)
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct ChapterImage {
    pub page_number: i32,
    pub url: String,
}

/// Outcome of a single chapter sync — surfaced to callers for logging
/// and exit-code decisions.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum SyncOutcome {
    /// All images downloaded and stored, chapter row updated.
    Fetched { pages: usize },
    /// `page_count > 0` already — no-op unless force_refetch is set.
    Skipped,
    /// Session probe failed mid-sync (avatar selector missing on the
    /// chapter page). Caller should abort the whole crawler run.
    SessionExpired,
}

/// Fetch all images for one chapter and persist them atomically. On
/// any error after the first storage put, the DB transaction rolls
/// back so the chapter stays at `page_count = 0` and is retried on the
/// next run. Bytes already written to storage become orphans; a future
/// reaper sweeps them.
#[allow(clippy::too_many_arguments)]
pub async fn sync_chapter_content(
    browser: &chromiumoxide::Browser,
    db: &PgPool,
    storage: &dyn Storage,
    http: &reqwest::Client,
    rate: &HostRateLimiters,
    chapter_id: Uuid,
    manga_id: Uuid,
    source_url: &str,
    force_refetch: bool,
) -> anyhow::Result<SyncOutcome> {
    // Skip if already fetched, unless caller explicitly forces.
    if !force_refetch {
        let (page_count,): (i32,) =
            sqlx::query_as("SELECT page_count FROM chapters WHERE id = $1")
                .bind(chapter_id)
                .fetch_one(db)
                .await
                .context("read chapter page_count")?;
        if page_count > 0 {
            return Ok(SyncOutcome::Skipped);
        }
    }

    // Nav to chapter page (rate-limited per host).
    rate.wait_for(source_url).await?;
    let page = browser
        .new_page(source_url)
        .await
        .with_context(|| format!("open chapter page {source_url}"))?;
    page.wait_for_navigation().await.context("wait for chapter nav")?;

    // Session probe: avatar present == still logged in. Missing means
    // PHPSESSID expired; bail the entire crawler run.
    if page.find_element("#avatar_menu").await.is_err() {
        page.close().await.ok();
        return Ok(SyncOutcome::SessionExpired);
    }

    let html = page.content().await.context("read chapter html")?;
    page.close().await.ok();

    let images = parse_chapter_pages(&html)
        .with_context(|| format!("parse chapter pages at {source_url}"))?;
    if images.is_empty() {
        anyhow::bail!("no page images parsed from {source_url}");
    }

    // Resolve image URLs against the chapter URL (they may be relative).
    let base = reqwest::Url::parse(source_url).context("parse chapter URL")?;

    // Fetch every image bytes-first into memory before writing
    // anything. Lets us bail the whole chapter cleanly if any image
    // fails — DB stays at page_count=0, no partial rows persisted.
    let mut fetched: Vec<(i32, Vec<u8>, &'static str)> = Vec::with_capacity(images.len());
    for img in &images {
        let url = base.join(&img.url).with_context(|| {
            format!("join image URL {} onto {source_url}", img.url)
        })?;
        rate.wait_for(url.as_str()).await?;
        let resp = http
            .get(url.clone())
            // Source CDNs commonly check Referer. Set it to the
            // chapter page — matches what the browser would send.
            .header(reqwest::header::REFERER, source_url)
            .send()
            .await
            .with_context(|| format!("GET {url}"))?
            .error_for_status()
            .with_context(|| format!("non-2xx for {url}"))?;
        let bytes = resp.bytes().await.context("read image body")?.to_vec();
        let ext = infer::get(&bytes).map(|k| k.extension()).unwrap_or("bin");
        fetched.push((img.page_number, bytes, ext));
    }

    // Atomic write: storage puts + page row inserts + page_count
    // update, all in one transaction. If anything fails, rollback +
    // the chapter is retried next run. Storage orphans the bytes; a
    // reaper sweeps them later.
    let mut tx = db.begin().await.context("open chapter sync tx")?;
    for (page_number, bytes, ext) in &fetched {
        let key = format!(
            "mangas/{manga_id}/chapters/{chapter_id}/pages/{:04}.{ext}",
            page_number
        );
        storage
            .put(&key, bytes)
            .await
            .with_context(|| format!("put {key}"))?;
        // (chapter_id, page_number) is unique — re-runs idempotent.
        sqlx::query(
            "INSERT INTO pages (chapter_id, page_number, storage_key, content_type)
             VALUES ($1, $2, $3, $4)
             ON CONFLICT (chapter_id, page_number) DO UPDATE
             SET storage_key = EXCLUDED.storage_key,
                 content_type = EXCLUDED.content_type",
        )
        .bind(chapter_id)
        .bind(page_number)
        .bind(&key)
        .bind(format!("image/{ext}"))
        .execute(&mut *tx)
        .await
        .with_context(|| format!("insert page row {page_number}"))?;
    }
    sqlx::query("UPDATE chapters SET page_count = $1 WHERE id = $2")
        .bind(fetched.len() as i32)
        .bind(chapter_id)
        .execute(&mut *tx)
        .await
        .context("update page_count")?;
    tx.commit().await.context("commit chapter sync")?;

    Ok(SyncOutcome::Fetched { pages: fetched.len() })
}

// Suppress unused-import warning for `session` until the bin/crawler
// wiring lands in this branch and uses it through this module.
#[allow(dead_code)]
fn _keep_session_in_scope() {
    let _ = session::registrable_domain;
}

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

    #[test]
    fn parse_chapter_pages_skips_loader_and_sorts_by_id() {
        // Loader image, two real pages out of order, and one with no id.
        let html = r#"
          <html><body id="body"><a id="pic_container">
            <img class="loading" src="/images/ajax-loader2.gif">
            <img id="page2" class="page2" src="https://cdn/2.jpg">
            <img id="page1" class="page1" src="https://cdn/1.jpg">
            <img src="https://cdn/orphan.jpg">
            <img id="not-a-page" src="https://cdn/not-a-page.jpg">
          </a></body></html>
        "#;
        let pages = parse_chapter_pages(html).expect("parse");
        assert_eq!(pages.len(), 2);
        assert_eq!(pages[0].page_number, 1);
        assert_eq!(pages[0].url, "https://cdn/1.jpg");
        assert_eq!(pages[1].page_number, 2);
        assert_eq!(pages[1].url, "https://cdn/2.jpg");
    }

    #[test]
    fn parse_chapter_pages_drops_images_without_src() {
        let html = r#"
          <a id="pic_container">
            <img id="page1" src="">
            <img id="page2" src="https://cdn/2.jpg">
          </a>
        "#;
        let pages = parse_chapter_pages(html).expect("parse");
        assert_eq!(pages.len(), 1);
        assert_eq!(pages[0].page_number, 2);
    }

    #[test]
    fn parse_chapter_pages_handles_three_digit_page_ids() {
        let html = r#"
          <a id="pic_container">
            <img id="page126" src="https://cdn/126.jpg">
            <img id="page9" src="https://cdn/9.jpg">
            <img id="page50" src="https://cdn/50.jpg">
          </a>
        "#;
        let pages = parse_chapter_pages(html).expect("parse");
        assert_eq!(
            pages.iter().map(|p| p.page_number).collect::<Vec<_>>(),
            vec![9, 50, 126]
        );
    }

    #[test]
    fn parse_chapter_pages_returns_transient_when_container_missing() {
        // Reader doesn't render #logo, so the universal logo sentinel
        // can't be used here — a#pic_container is the reader-specific
        // marker. Broken-page response trips this.
        let html = "<html><body>\
            <p>we're sorry, the request file are not found.</p>\
            </body></html>";
        let err = parse_chapter_pages(html).expect_err("expected Transient");
        assert!(err.is_transient(), "got non-transient: {err}");
    }
}