use std::{
    future::Future,
    path::{Path, PathBuf},
    pin::Pin,
};

use chrono::{DateTime, SecondsFormat, Utc};
use sha2::{Digest, Sha256};

use figment::{
    Figment,
    providers::{Format, Toml},
};
use flate2::{Compression, write::GzEncoder};
use miette::{IntoDiagnostic, Result};
use pulldown_cmark::{Options, Parser, html};
use tera::{Context, Tera};
use tracing::warn;

use crate::{changelog::ChangelogExtractor, config::AbbayeConfig, version_extractors::VersionInfo};

const TEMPLATE_ROOT_INDEX: &str = include_str!("templates/root_index.html");
const TEMPLATE_VERSION_INDEX: &str = include_str!("templates/version_index.html");
const ATOM_FEED_FILENAME: &str = "releases.atom";

// ── Types ───────────────────────────────────────────────────────────────────

/// A version entry as passed to Tera templates.
#[derive(serde::Serialize)]
struct VersionEntry {
    /// Version string (e.g. `"1.2.3"`).
    version: String,
    /// ISO-8601 date string (e.g. `"2024-01-15"`) when the release date is known.
    date: Option<String>,
}

impl VersionEntry {
    fn from_info(info: &VersionInfo) -> Self {
        Self {
            version: info.version.clone(),
            date: info.date.map(|dt| dt.format("%Y-%m-%d").to_string()),
        }
    }
}

/// Metadata about a single file-type dist artifact, passed to Tera templates.
#[derive(serde::Serialize)]
struct DistFileInfo {
    /// File name (relative to `dist/`).
    name: String,
    /// Raw byte size of the file.
    size_bytes: u64,
    /// Human-readable size (e.g. "1.4 MB").
    size_human: String,
    /// Lowercase hex-encoded SHA-256 digest of the file contents.
    sha256: String,
}

// ── Public API ────────────────────────────────────────────────────────────────

/// Load the Abbaye2 configuration from the current working directory.
///
/// Looks for `.abbaye.toml` first, then `abbaye.toml`; when both are present
/// `abbaye.toml` takes precedence (last merge wins).
pub fn load_config() -> Result<AbbayeConfig> {
    let cwd = std::env::current_dir().into_diagnostic()?;
    Figment::new()
        .merge(Toml::file(cwd.join(".abbaye.toml")))
        .merge(Toml::file(cwd.join("abbaye.toml")))
        .extract()
        .into_diagnostic()
}

/// Build the full website into `config.output_dir` (defaults to `public/`).
///
/// # Steps
///
/// 1. Extract the current version via the configured [`crate::version_extractors::AnyVersionExtractor`].
/// 2. Run every configured builder and split the resulting [`crate::builders::ArtifactPath`]s
///    into *dist* (regular files) and *docs* (directories).
/// 3. Copy dist artifacts to `<output>/<version>/dist/`.
/// 4. Copy doc directories to `<output>/<version>/docs/<crate>/` and archive
///    the whole `docs/` tree as `docs.tar.gz`.
/// 5. Render `<output>/<version>/index.html` from the project README and the
///    matching changelog section.
/// 6. Re-render the root `<output>/index.html`, listing all known versions
///    (newest first).
/// 7. Update the `<output>/latest` symlink (Unix) or redirect page (other).
pub async fn build_site(config: AbbayeConfig) -> Result<()> {
    let output_dir = config
        .output_dir
        .clone()
        .unwrap_or_else(|| PathBuf::from("public"));

    tokio::fs::create_dir_all(&output_dir)
        .await
        .into_diagnostic()?;

    // ── 1. Version ────────────────────────────────────────────────────────────
    let version_info = config.version_extractor.extract().await?;
    let version = version_info.version.clone();

    // ── 2. Tera setup ─────────────────────────────────────────────────────────
    let mut tera = Tera::default();
    tera.add_raw_template("root_index.html", TEMPLATE_ROOT_INDEX)
        .into_diagnostic()?;
    tera.add_raw_template("version_index.html", TEMPLATE_VERSION_INDEX)
        .into_diagnostic()?;

    // ── 3. Builders ───────────────────────────────────────────────────────────
    let mut dist_artifacts = Vec::new();
    let mut doc_artifacts = Vec::new();

    for builder in &config.builders {
        for artifact in builder.build().await? {
            if artifact.path.is_dir() {
                doc_artifacts.push(artifact);
            } else {
                dist_artifacts.push(artifact);
            }
        }
    }

    // ── 4. Lay out dist/ ──────────────────────────────────────────────────────
    let version_dir = output_dir.join(&version);
    let dist_dir = version_dir.join("dist");
    tokio::fs::create_dir_all(&dist_dir)
        .await
        .into_diagnostic()?;

    for artifact in &dist_artifacts {
        tokio::fs::copy(&artifact.path, dist_dir.join(&artifact.name))
            .await
            .into_diagnostic()?;
    }

    // Compute size + SHA-256 for each copied dist artifact.
    let mut dist_file_infos: Vec<DistFileInfo> = Vec::new();
    for artifact in &dist_artifacts {
        let dest = dist_dir.join(&artifact.name);
        let bytes = tokio::fs::read(&dest).await.into_diagnostic()?;
        let size_bytes = bytes.len() as u64;
        let sha256 = hex_sha256(&bytes);
        dist_file_infos.push(DistFileInfo {
            name: artifact.name.clone(),
            size_bytes,
            size_human: human_size(size_bytes),
            sha256,
        });
    }
    let has_dist = !dist_file_infos.is_empty();

    // ── 5. Lay out docs/ ──────────────────────────────────────────────────────
    let has_docs = !doc_artifacts.is_empty();
    let has_docs_tarball;

    if has_docs {
        let docs_dir = version_dir.join("docs");

        for artifact in &doc_artifacts {
            // Copy the complete target/doc tree — this includes the shared
            // rustdoc CSS, JS, fonts and search indices at the root of the
            // directory in addition to the per-crate HTML subdirectories.
            copy_dir_recursive(artifact.path.clone(), docs_dir.clone()).await?;
        }

        // Rustdoc writes index.html at the root for single-crate projects.
        // For workspaces it may be absent; generate a fallback listing then.
        if !docs_dir.join("index.html").exists() {
            let crate_names = find_doc_crates(&docs_dir).await?;
            write_docs_index(&docs_dir, &crate_names).await?;
        }

        let tarball = version_dir.join("docs.tar.gz");
        let docs_dir_c = docs_dir.clone();
        let tarball_c = tarball.clone();
        tokio::task::spawn_blocking(move || archive_dir(&docs_dir_c, &tarball_c))
            .await
            .into_diagnostic()??;

        has_docs_tarball = true;
    } else {
        has_docs_tarball = false;
    }

    // ── 6. README ─────────────────────────────────────────────────────────────
    let readme_path = config
        .site
        .readme
        .as_deref()
        .unwrap_or(Path::new("README.md"));

    let readme_html = match tokio::fs::read_to_string(readme_path).await {
        Ok(content) => render_markdown(&content),
        Err(_) => {
            warn!("README not found at {}", readme_path.display());
            String::new()
        }
    };

    // ── 7. Changelog section ──────────────────────────────────────────────────
    let changelog_html = match ChangelogExtractor
        .section(config.changelog.clone(), &version)
        .await
    {
        Ok(section) => render_markdown(&section),
        Err(_) => {
            warn!("No changelog entry found for version {version}");
            String::new()
        }
    };

    // ── 8. Version index.html ─────────────────────────────────────────────────
    let mut version_ctx = Context::new();
    version_ctx.insert("project_name", &config.site.name);
    version_ctx.insert("version", &version);
    version_ctx.insert("readme_html", &readme_html);
    version_ctx.insert("changelog_html", &changelog_html);
    version_ctx.insert("has_docs", &has_docs);
    version_ctx.insert("has_docs_tarball", &has_docs_tarball);
    version_ctx.insert("has_dist", &has_dist);
    version_ctx.insert("dist_files", &dist_file_infos);

    let version_html = tera
        .render("version_index.html", &version_ctx)
        .into_diagnostic()?;
    tokio::fs::write(version_dir.join("index.html"), version_html)
        .await
        .into_diagnostic()?;

    // ── 9. Root index.html + Atom feed ──────────────────────────────────────
    // Collect every known version from the version extractor, ensure the
    // current version is present (handles untagged builds), then sort newest-first.
    let mut all_versions = config.version_extractor.extract_all().await?;
    if !all_versions.iter().any(|v| v.version == version) {
        all_versions.push(version_info.clone());
    }
    all_versions.sort_by(|a, b| compare_versions(&b.version, &a.version));

    // Build the template-friendly list (version string + optional date string).
    let version_entries: Vec<VersionEntry> =
        all_versions.iter().map(VersionEntry::from_info).collect();

    let base_url = config
        .site
        .base_url
        .as_deref()
        .map(|u| u.trim_end_matches('/'));

    let mut root_ctx = Context::new();
    root_ctx.insert("project_name", &config.site.name);
    root_ctx.insert("versions", &version_entries);
    root_ctx.insert("atom_feed", ATOM_FEED_FILENAME);

    let root_html = tera
        .render("root_index.html", &root_ctx)
        .into_diagnostic()?;
    tokio::fs::write(output_dir.join("index.html"), root_html)
        .await
        .into_diagnostic()?;

    // ── 10. Atom feed ─────────────────────────────────────────────────────────
    let atom_xml = generate_atom_feed(&config.site.name, &all_versions, base_url);
    tokio::fs::write(output_dir.join(ATOM_FEED_FILENAME), atom_xml)
        .await
        .into_diagnostic()?;

    // ── 11. `latest` symlink ──────────────────────────────────────────────────
    if let Some(latest) = all_versions.first() {
        update_latest_symlink(&output_dir, &latest.version)?;
    }

    Ok(())
}

// ── Private helpers ───────────────────────────────────────────────────────────

/// Render Markdown to an HTML string.
fn render_markdown(md: &str) -> String {
    let opts = Options::ENABLE_TABLES | Options::ENABLE_STRIKETHROUGH;
    let parser = Parser::new_ext(md, opts);
    let mut buf = String::new();
    html::push_html(&mut buf, parser);
    buf
}

/// Scan `docs_dir` for subdirectories that contain an `index.html` and return
/// their names. Used to build a fallback listing when rustdoc itself did not
/// generate a root `index.html` (typical for multi-crate workspaces).
async fn find_doc_crates(docs_dir: &Path) -> Result<Vec<String>> {
    let mut names = Vec::new();
    let mut entries = tokio::fs::read_dir(docs_dir).await.into_diagnostic()?;
    while let Some(entry) = entries.next_entry().await.into_diagnostic()? {
        let path = entry.path();
        if path.is_dir() && path.join("index.html").exists() {
            names.push(entry.file_name().to_string_lossy().into_owned());
        }
    }
    Ok(names)
}

/// Write a `docs/index.html` that either redirects straight to the single
/// crate's docs (one crate) or lists all crates (multiple crates).
async fn write_docs_index(docs_dir: &Path, crate_names: &[String]) -> Result<()> {
    let html = if crate_names.len() == 1 {
        format!(
            "<!DOCTYPE html><html><head>\
            <meta http-equiv=\"refresh\" content=\"0;url={}/index.html\">\
            </head></html>",
            crate_names[0]
        )
    } else {
        let items = crate_names
            .iter()
            .map(|n| format!("  <li><a href=\"{n}/index.html\">{n}</a></li>"))
            .collect::<Vec<_>>()
            .join("\n");
        format!(
            "<!DOCTYPE html>\n<html><head><meta charset=\"utf-8\">\
            <title>Documentation</title></head>\
            <body><h1>Documentation</h1><ul>\n{items}\n</ul></body></html>"
        )
    };

    tokio::fs::write(docs_dir.join("index.html"), html)
        .await
        .into_diagnostic()
}

/// Recursively copy the contents of `src` into `dst`.
///
/// Uses explicit boxing to satisfy the compiler for the async recursive call.
fn copy_dir_recursive(
    src: PathBuf,
    dst: PathBuf,
) -> Pin<Box<dyn Future<Output = Result<()>> + Send>> {
    Box::pin(async move {
        tokio::fs::create_dir_all(&dst).await.into_diagnostic()?;
        let mut entries = tokio::fs::read_dir(&src).await.into_diagnostic()?;
        while let Some(entry) = entries.next_entry().await.into_diagnostic()? {
            let src_path = entry.path();
            let dst_path = dst.join(entry.file_name());
            if src_path.is_dir() {
                copy_dir_recursive(src_path, dst_path).await?;
            } else {
                tokio::fs::copy(&src_path, &dst_path)
                    .await
                    .into_diagnostic()?;
            }
        }
        Ok(())
    })
}

/// Pack `src` directory into a `.tar.gz` archive at `dest`.
///
/// The top-level entry inside the archive is named after the source directory.
fn archive_dir(src: &Path, dest: &Path) -> Result<()> {
    let dir_name = src
        .file_name()
        .map(|n| n.to_string_lossy().into_owned())
        .unwrap_or_else(|| "docs".to_owned());

    let file = std::fs::File::create(dest).into_diagnostic()?;
    let enc = GzEncoder::new(file, Compression::default());
    let mut archive = tar::Builder::new(enc);
    archive.append_dir_all(&dir_name, src).into_diagnostic()?;
    archive
        .into_inner()
        .into_diagnostic()?
        .finish()
        .into_diagnostic()?;
    Ok(())
}

/// Compare two version strings, preferring semver ordering and falling back
/// to lexicographic comparison for non-semver strings (e.g. git describe output).
fn strip_v(s: &str) -> &str {
    s.strip_prefix('v').unwrap_or(s)
}

fn compare_versions(a: &str, b: &str) -> std::cmp::Ordering {
    match (
        semver::Version::parse(strip_v(a)),
        semver::Version::parse(strip_v(b)),
    ) {
        (Ok(va), Ok(vb)) => va.cmp(&vb),
        _ => a.cmp(b),
    }
}

/// Compute a lowercase hex-encoded SHA-256 digest of `data`.
fn hex_sha256(data: &[u8]) -> String {
    let mut hasher = Sha256::new();
    hasher.update(data);
    hasher
        .finalize()
        .iter()
        .map(|b| format!("{b:02x}"))
        .collect()
}

/// Format a byte count as a human-readable string (e.g. "1.4 MB").
fn human_size(bytes: u64) -> String {
    const KIB: u64 = 1024;
    const MIB: u64 = KIB * 1024;
    const GIB: u64 = MIB * 1024;
    if bytes >= GIB {
        format!("{:.1} GB", bytes as f64 / GIB as f64)
    } else if bytes >= MIB {
        format!("{:.1} MB", bytes as f64 / MIB as f64)
    } else if bytes >= KIB {
        format!("{:.1} KB", bytes as f64 / KIB as f64)
    } else {
        format!("{bytes} B")
    }
}

/// Escape the five XML predefined characters in a string.
fn xml_escape(s: &str) -> String {
    s.replace('&', "&amp;")
        .replace('<', "&lt;")
        .replace('>', "&gt;")
        .replace('"', "&quot;")
        .replace('\'', "&apos;")
}

/// Generate an Atom 1.0 feed listing all known releases.
///
/// - `base_url`: when provided (already stripped of trailing `/`), used to
///   build `<link>` and `<id>` elements with absolute URLs.  When absent,
///   a `urn:` based ID is used and no `<link>` elements are emitted.
fn generate_atom_feed(
    project_name: &str,
    versions: &[VersionInfo],
    base_url: Option<&str>,
) -> String {
    let now: DateTime<Utc> = Utc::now();

    // The feed's <updated> is the most-recent entry date, or now as fallback.
    let feed_updated = versions.iter().filter_map(|v| v.date).max().unwrap_or(now);

    let feed_updated_str = feed_updated.to_rfc3339_opts(SecondsFormat::Secs, true);

    // Feed-level <id> and self-link.
    let feed_id = match base_url {
        Some(base) => format!("{base}/{ATOM_FEED_FILENAME}"),
        None => format!("urn:abbaye:feed:{}", xml_escape(project_name)),
    };

    let self_link = match base_url {
        Some(base) => format!(
            "  <link rel=\"self\" href=\"{}/{ATOM_FEED_FILENAME}\"/>\n",
            xml_escape(base)
        ),
        None => String::new(),
    };
    let alt_link = match base_url {
        Some(base) => format!("  <link href=\"{}\"/>\n", xml_escape(base)),
        None => String::new(),
    };

    let entries: String = versions
        .iter()
        .map(|vi| {
            let entry_date = vi.date.unwrap_or(now);
            let entry_date_str = entry_date.to_rfc3339_opts(SecondsFormat::Secs, true);
            let v_escaped = xml_escape(&vi.version);

            let entry_id = match base_url {
                Some(base) => format!("{base}/{v_escaped}/"),
                None => format!(
                    "urn:abbaye:release:{}:{v_escaped}",
                    xml_escape(project_name)
                ),
            };

            let entry_link = match base_url {
                Some(base) => format!("    <link href=\"{base}/{v_escaped}/\"/>\n"),
                None => String::new(),
            };

            format!(
                "  <entry>\n\
                 \x20   <title>{v_escaped}</title>\n\
                 \x20   <id>{entry_id}</id>\n\
                 \x20   <updated>{entry_date_str}</updated>\n\
                 {entry_link}\
                 \x20 </entry>"
            )
        })
        .collect::<Vec<_>>()
        .join("\n");

    format!(
        "<?xml version=\"1.0\" encoding=\"utf-8\"?>\n\
         <feed xmlns=\"http://www.w3.org/2005/Atom\">\n\
         \x20 <title>{name} Releases</title>\n\
         {self_link}\
         {alt_link}\
         \x20 <updated>{feed_updated_str}</updated>\n\
         \x20 <id>{feed_id}</id>\n\
         {entries}\n\
         </feed>\n",
        name = xml_escape(project_name),
    )
}

/// Create or replace the `latest` symlink in `output_dir`, pointing to
/// `version_dir_name`.
///
/// On non-Unix platforms a meta-refresh redirect page is written instead.
fn update_latest_symlink(output_dir: &Path, version_dir_name: &str) -> Result<()> {
    let link = output_dir.join("latest");

    #[cfg(unix)]
    {
        // Remove any stale symlink or file before (re-)creating it.
        if link.exists() || link.is_symlink() {
            std::fs::remove_file(&link).into_diagnostic()?;
        }
        std::os::unix::fs::symlink(version_dir_name, &link).into_diagnostic()?;
    }

    #[cfg(not(unix))]
    {
        std::fs::create_dir_all(&link).into_diagnostic()?;
        std::fs::write(
            link.join("index.html"),
            format!(
                "<!DOCTYPE html><html><head>\
                <meta http-equiv=\"refresh\" content=\"0;url=../{version_dir_name}/\">\
                </head></html>"
            ),
        )
        .into_diagnostic()?;
    }

    Ok(())
}