use once_cell::sync::Lazy;
use regex::Regex;
use serde_json::json;
use sha2::{Digest, Sha256};
use std::collections::HashMap;
use std::fs;
use std::path::Path;
use std::time::SystemTime;

use crate::state::{atomic_write_json, load_json_with_fallbacks, BACKUP_COUNT};

// ---------------------------------------------------------------------------
// Constants
// ---------------------------------------------------------------------------

/// Current version for Google Fonts metadata (fonts_meta.json).
const GOOGLE_FONTS_META_VERSION: u64 = 7;

/// Current version for Font Awesome metadata (fa_meta.json).
const FA_META_VERSION: u64 = 3;

/// User-Agent header value for HTTP requests.
/// Google Fonts API returns different CSS based on User-Agent; we want woff2.
const USER_AGENT: &str = "Mozilla/5.0";

/// Google Fonts CSS URLs.
const GOOGLE_FONT_URLS: &[(&str, &str)] = &[
    (
        "Sora",
        "https://fonts.googleapis.com/css2?family=Sora:wght@500;600;700;800&display=swap",
    ),
    (
        "Manrope",
        "https://fonts.googleapis.com/css2?family=Manrope:wght@400;500;600;700;800&display=swap",
    ),
    (
        "IBM Plex Mono",
        "https://fonts.googleapis.com/css2?family=IBM+Plex+Mono:wght@400;500;600&display=swap",
    ),
];

/// Font Awesome CSS URL.
const FA_CSS_URL: &str =
    "https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.5.2/css/all.min.css";

/// Base URL for resolving relative Font Awesome webfont URLs.
const FA_WEBFONTS_BASE: &str =
    "https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.5.2/webfonts/";

// ---------------------------------------------------------------------------
// Compiled regex patterns
// ---------------------------------------------------------------------------

/// Regex for extracting woff2 font URLs from Google Fonts CSS.
static GOOGLE_FONT_URL_RE: Lazy<Regex> =
    Lazy::new(|| Regex::new(r#"url\(([^)]+)\)\s*format\(['"]woff2['"]\)"#).unwrap());

/// Regex for extracting all url(...) references from Font Awesome CSS.
static FA_URL_RE: Lazy<Regex> = Lazy::new(|| Regex::new(r"url\(([^)]+)\)").unwrap());

// ---------------------------------------------------------------------------
// 1. safe_filename_from_url
// ---------------------------------------------------------------------------

/// Generate a safe local filename from a URL using SHA-256 hash for uniqueness.
///
/// The filename is `{stem}-{hash}{suffix}` where `hash` is the first 10 hex
/// characters of the SHA-256 digest of the full URL. If the URL path has no
/// extension, `.woff2` is appended.
pub fn safe_filename_from_url(url: &str) -> String {
    // Extract the last path component from the URL
    let base = url
        .split('?')
        .next()
        .unwrap_or(url)
        .split('#')
        .next()
        .unwrap_or(url)
        .rsplit('/')
        .next()
        .unwrap_or("font.woff2");

    let base = if base.is_empty() { "font.woff2" } else { base };

    // Ensure the base has an extension
    let base = if !base.contains('.') {
        format!("{}.woff2", base)
    } else {
        base.to_string()
    };

    // Split into stem and suffix
    let (stem, suffix) = match base.rfind('.') {
        Some(pos) => (&base[..pos], &base[pos..]),
        None => (base.as_str(), ".woff2"),
    };

    // Compute SHA-256 hash of the full URL
    let mut hasher = Sha256::new();
    hasher.update(url.as_bytes());
    let digest = format!("{:x}", hasher.finalize());
    let url_hash = &digest[..10];

    format!("{}-{}{}", stem, url_hash, suffix)
}

// ---------------------------------------------------------------------------
// 2. ensure_google_fonts_local
// ---------------------------------------------------------------------------

/// Download and cache Google Fonts (Sora, Manrope, IBM Plex Mono) locally.
///
/// The `fonts_dir` is the directory where `fonts.css`, `fonts_meta.json`, and
/// individual `.woff2` files are stored.
///
/// If already cached (version matches, ok=true, CSS file exists), this is a
/// no-op. Otherwise, downloads each font family's CSS from the Google Fonts
/// API, extracts woff2 URLs, downloads each font file, rewrites the CSS to
/// use local paths, and writes the combined CSS and metadata.
pub async fn ensure_google_fonts_local(fonts_dir: &Path) -> Result<(), String> {
    fs::create_dir_all(fonts_dir).map_err(|e| format!("Failed to create fonts dir: {}", e))?;

    let meta_path = fonts_dir.join("fonts_meta.json");
    let css_path = fonts_dir.join("fonts.css");

    // Check if already cached
    if let Some(meta) = load_json_with_fallbacks(&meta_path, BACKUP_COUNT) {
        if let Some(obj) = meta.as_object() {
            let version_ok = obj
                .get("version")
                .and_then(|v| v.as_u64())
                .map(|v| v == GOOGLE_FONTS_META_VERSION)
                .unwrap_or(false);
            let ok_flag = obj
                .get("ok")
                .and_then(|v| v.as_bool())
                .unwrap_or(false);

            if version_ok && ok_flag && css_path.exists() {
                return Ok(());
            }
        }
    }

    let client = reqwest::Client::builder()
        .user_agent(USER_AGENT)
        .build()
        .map_err(|e| format!("Failed to build HTTP client: {}", e))?;

    let mut all_css_parts: Vec<String> = Vec::new();
    let mut downloaded_files: Vec<String> = Vec::new();
    let mut errors: Vec<String> = Vec::new();

    for (family, css_url) in GOOGLE_FONT_URLS {
        // Download the CSS for this font family
        let css_text = match client.get(*css_url).send().await {
            Ok(resp) => match resp.text().await {
                Ok(text) => text,
                Err(e) => {
                    errors.push(format!("Failed to read CSS for {}: {}", family, e));
                    continue;
                }
            },
            Err(e) => {
                errors.push(format!("Failed to download CSS for {}: {}", family, e));
                continue;
            }
        };

        // Find all woff2 url(...) references and download each font file
        let mut rewritten_css = css_text.clone();
        let mut replacements: Vec<(String, String)> = Vec::new();

        for cap in GOOGLE_FONT_URL_RE.captures_iter(&css_text) {
            let raw_url = cap[1].trim().trim_matches('\'').trim_matches('"');

            let safe_name = safe_filename_from_url(raw_url);
            let local_path = fonts_dir.join(&safe_name);

            // Download the font file
            match client.get(raw_url).send().await {
                Ok(resp) => match resp.bytes().await {
                    Ok(bytes) => {
                        if let Err(e) = fs::write(&local_path, &bytes) {
                            errors.push(format!("Failed to write {}: {}", safe_name, e));
                            continue;
                        }
                        downloaded_files.push(safe_name.clone());
                    }
                    Err(e) => {
                        errors.push(format!("Failed to read bytes for {}: {}", safe_name, e));
                        continue;
                    }
                },
                Err(e) => {
                    errors.push(format!("Failed to download {}: {}", raw_url, e));
                    continue;
                }
            }

            // Record the replacement: original url(...) content -> local path
            let replacement_url = format!("/fonts/{}", safe_name);
            replacements.push((cap[1].to_string(), replacement_url));
        }

        // Apply all URL replacements to the CSS
        for (original, replacement) in &replacements {
            let old = format!("url({}) format", original);
            let new = format!("url({}) format", replacement);
            rewritten_css = rewritten_css.replace(&old, &new);
        }

        all_css_parts.push(rewritten_css);
    }

    // Write combined CSS
    let combined_css = all_css_parts.join("\n");
    fs::write(&css_path, &combined_css)
        .map_err(|e| format!("Failed to write fonts.css: {}", e))?;

    // Write metadata
    let timestamp = SystemTime::now()
        .duration_since(SystemTime::UNIX_EPOCH)
        .map(|d| d.as_secs())
        .unwrap_or(0);

    let ok = errors.is_empty();
    let meta = json!({
        "version": GOOGLE_FONTS_META_VERSION,
        "ok": ok,
        "timestamp": timestamp,
        "downloaded": downloaded_files,
        "errors": errors,
    });

    atomic_write_json(&meta_path, &meta, BACKUP_COUNT);

    if ok {
        Ok(())
    } else {
        Err(format!(
            "Google Fonts download completed with errors: {}",
            errors.join("; ")
        ))
    }
}

// ---------------------------------------------------------------------------
// 3. ensure_fontawesome_local
// ---------------------------------------------------------------------------

/// Clean and resolve a Font Awesome URL reference.
///
/// Strips whitespace and quotes, resolves relative URLs against the FA
/// webfonts base URL. Returns the URL unchanged if it is a `data:` URI.
fn clean_fa_url(u: &str) -> String {
    let u = u.trim().trim_matches('\'').trim_matches('"');

    if u.starts_with("data:") {
        return u.to_string();
    }
    if u.starts_with("//") {
        return format!("https:{}", u);
    }
    if u.starts_with("http://") || u.starts_with("https://") {
        return u.to_string();
    }

    // Relative URL: strip leading "./" and "../" then join with base
    let cleaned = u
        .trim_start_matches("./")
        .replace("../", "");
    format!("{}{}", FA_WEBFONTS_BASE, cleaned)
}

/// Download and cache Font Awesome 6.5.2 locally.
///
/// The `fa_dir` is the directory where `fa.css` and `fa_meta.json` live.
/// The `fa_dir/webfonts/` subdirectory holds individual webfont files.
///
/// If already cached (version matches, ok=true, CSS file exists), this is a
/// no-op. Otherwise, downloads the Font Awesome CSS, extracts all `url(...)`
/// references, downloads each font file (skipping `data:` URIs), rewrites
/// the CSS to use local paths, and writes the CSS and metadata.
pub async fn ensure_fontawesome_local(fa_dir: &Path) -> Result<(), String> {
    fs::create_dir_all(fa_dir).map_err(|e| format!("Failed to create fa dir: {}", e))?;

    let webfonts_dir = fa_dir.join("webfonts");
    fs::create_dir_all(&webfonts_dir)
        .map_err(|e| format!("Failed to create webfonts dir: {}", e))?;

    let meta_path = fa_dir.join("fa_meta.json");
    let css_path = fa_dir.join("fa.css");

    // Check if already cached
    if let Some(meta) = load_json_with_fallbacks(&meta_path, BACKUP_COUNT) {
        if let Some(obj) = meta.as_object() {
            let version_ok = obj
                .get("version")
                .and_then(|v| v.as_u64())
                .map(|v| v == FA_META_VERSION)
                .unwrap_or(false);
            let ok_flag = obj
                .get("ok")
                .and_then(|v| v.as_bool())
                .unwrap_or(false);

            if version_ok && ok_flag && css_path.exists() {
                return Ok(());
            }
        }
    }

    let client = reqwest::Client::builder()
        .user_agent(USER_AGENT)
        .build()
        .map_err(|e| format!("Failed to build HTTP client: {}", e))?;

    // Download the Font Awesome CSS
    let css_text = client
        .get(FA_CSS_URL)
        .send()
        .await
        .map_err(|e| format!("Failed to download FA CSS: {}", e))?
        .text()
        .await
        .map_err(|e| format!("Failed to read FA CSS: {}", e))?;

    let mut downloaded_files: Vec<String> = Vec::new();
    let mut errors: Vec<String> = Vec::new();
    let mut replacements: HashMap<String, String> = HashMap::new();

    for cap in FA_URL_RE.captures_iter(&css_text) {
        let raw_url = &cap[1];
        let resolved = clean_fa_url(raw_url);

        // Skip data: URIs
        if resolved.starts_with("data:") {
            continue;
        }

        // Determine the filename from the resolved URL
        let filename = resolved
            .split('?')
            .next()
            .unwrap_or(&resolved)
            .split('#')
            .next()
            .unwrap_or(&resolved)
            .rsplit('/')
            .next()
            .unwrap_or("font.woff2")
            .to_string();

        if filename.is_empty() {
            continue;
        }

        let local_path = webfonts_dir.join(&filename);

        // Only download each file once
        if !replacements.contains_key(raw_url) {
            match client.get(&resolved).send().await {
                Ok(resp) => match resp.bytes().await {
                    Ok(bytes) => {
                        if let Err(e) = fs::write(&local_path, &bytes) {
                            errors.push(format!("Failed to write {}: {}", filename, e));
                            continue;
                        }
                        downloaded_files.push(filename.clone());
                    }
                    Err(e) => {
                        errors.push(format!("Failed to read bytes for {}: {}", filename, e));
                        continue;
                    }
                },
                Err(e) => {
                    errors.push(format!("Failed to download {}: {}", resolved, e));
                    continue;
                }
            }

            let replacement = format!("/fa/webfonts/{}", filename);
            replacements.insert(raw_url.to_string(), replacement);
        }
    }

    // Rewrite CSS with local paths
    let mut rewritten_css = css_text.clone();
    for (original, replacement) in &replacements {
        let old = format!("url({})", original);
        let new = format!("url({})", replacement);
        rewritten_css = rewritten_css.replace(&old, &new);
    }

    // Write rewritten CSS
    fs::write(&css_path, &rewritten_css)
        .map_err(|e| format!("Failed to write fa.css: {}", e))?;

    // Write metadata
    let timestamp = SystemTime::now()
        .duration_since(SystemTime::UNIX_EPOCH)
        .map(|d| d.as_secs())
        .unwrap_or(0);

    let ok = errors.is_empty();
    let meta = json!({
        "version": FA_META_VERSION,
        "ok": ok,
        "timestamp": timestamp,
        "downloaded": downloaded_files,
        "errors": errors,
    });

    atomic_write_json(&meta_path, &meta, BACKUP_COUNT);

    if ok {
        Ok(())
    } else {
        Err(format!(
            "Font Awesome download completed with errors: {}",
            errors.join("; ")
        ))
    }
}

// ===========================================================================
// Tests
// ===========================================================================

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

    // -- safe_filename_from_url -----------------------------------------------

    #[test]
    fn test_safe_filename_from_url_basic() {
        let url = "https://fonts.gstatic.com/s/sora/v12/abc123.woff2";
        let result = safe_filename_from_url(url);

        // Should contain the original stem
        assert!(result.starts_with("abc123-"));
        // Should end with .woff2
        assert!(result.ends_with(".woff2"));
        // Should contain a 10-char hash between stem and extension
        let parts: Vec<&str> = result.rsplitn(2, '.').collect();
        let before_ext = parts[1]; // "abc123-{hash}"
        let hash_part = before_ext.rsplit('-').next().unwrap();
        assert_eq!(hash_part.len(), 10);
    }

    #[test]
    fn test_safe_filename_from_url_no_extension() {
        let url = "https://example.com/fontfile";
        let result = safe_filename_from_url(url);

        // Should have .woff2 appended
        assert!(result.ends_with(".woff2"));
        assert!(result.starts_with("fontfile-"));
    }

    #[test]
    fn test_safe_filename_from_url_deterministic() {
        let url = "https://fonts.gstatic.com/s/sora/v12/abc.woff2";
        let result1 = safe_filename_from_url(url);
        let result2 = safe_filename_from_url(url);
        assert_eq!(result1, result2);
    }

    #[test]
    fn test_safe_filename_different_urls() {
        let url1 = "https://fonts.gstatic.com/s/sora/v12/abc.woff2";
        let url2 = "https://fonts.gstatic.com/s/manrope/v14/def.woff2";
        let result1 = safe_filename_from_url(url1);
        let result2 = safe_filename_from_url(url2);
        assert_ne!(result1, result2);
    }

    // -- clean_fa_url ---------------------------------------------------------

    #[test]
    fn test_clean_fa_url_data() {
        let result = clean_fa_url("data:font/woff2;base64,abc");
        assert_eq!(result, "data:font/woff2;base64,abc");
    }

    #[test]
    fn test_clean_fa_url_protocol_relative() {
        let result = clean_fa_url("//example.com/font.woff2");
        assert_eq!(result, "https://example.com/font.woff2");
    }

    #[test]
    fn test_clean_fa_url_absolute() {
        let result = clean_fa_url("https://example.com/font.woff2");
        assert_eq!(result, "https://example.com/font.woff2");
    }

    #[test]
    fn test_clean_fa_url_relative() {
        let result = clean_fa_url("../webfonts/fa-solid-900.woff2");
        assert_eq!(
            result,
            "https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.5.2/webfonts/webfonts/fa-solid-900.woff2"
        );
    }

    #[test]
    fn test_clean_fa_url_relative_dot_slash() {
        let result = clean_fa_url("./webfonts/fa-solid-900.woff2");
        assert_eq!(
            result,
            "https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.5.2/webfonts/webfonts/fa-solid-900.woff2"
        );
    }

    #[test]
    fn test_clean_fa_url_strips_quotes() {
        let result = clean_fa_url("'https://example.com/font.woff2'");
        assert_eq!(result, "https://example.com/font.woff2");
    }

    // -- Integration tests (require network) ----------------------------------

    #[tokio::test]
    #[ignore]
    async fn test_google_fonts_download() {
        let dir = tempfile::tempdir().unwrap();
        let fonts_dir = dir.path().join("fonts");

        let result = ensure_google_fonts_local(&fonts_dir).await;
        assert!(result.is_ok(), "Google Fonts download failed: {:?}", result);

        // Verify fonts.css was created
        let css_path = fonts_dir.join("fonts.css");
        assert!(css_path.exists(), "fonts.css should exist");

        let css_content = fs::read_to_string(&css_path).unwrap();
        assert!(!css_content.is_empty(), "fonts.css should not be empty");
        // CSS should contain rewritten local paths
        assert!(
            css_content.contains("/fonts/"),
            "CSS should contain /fonts/ local paths"
        );

        // Verify metadata was created
        let meta_path = fonts_dir.join("fonts_meta.json");
        assert!(meta_path.exists(), "fonts_meta.json should exist");

        let meta = load_json_with_fallbacks(&meta_path, BACKUP_COUNT).unwrap();
        assert_eq!(meta["version"], GOOGLE_FONTS_META_VERSION);
        assert_eq!(meta["ok"], true);
        assert!(
            meta["downloaded"].as_array().unwrap().len() > 0,
            "Should have downloaded at least one font file"
        );

        // Second call should be a no-op (cached)
        let result2 = ensure_google_fonts_local(&fonts_dir).await;
        assert!(result2.is_ok());
    }

    #[tokio::test]
    #[ignore]
    async fn test_fontawesome_download() {
        let dir = tempfile::tempdir().unwrap();
        let fa_dir = dir.path().join("fa");

        let result = ensure_fontawesome_local(&fa_dir).await;
        assert!(
            result.is_ok(),
            "Font Awesome download failed: {:?}",
            result
        );

        // Verify fa.css was created
        let css_path = fa_dir.join("fa.css");
        assert!(css_path.exists(), "fa.css should exist");

        let css_content = fs::read_to_string(&css_path).unwrap();
        assert!(!css_content.is_empty(), "fa.css should not be empty");
        // CSS should contain rewritten local paths
        assert!(
            css_content.contains("/fa/webfonts/"),
            "CSS should contain /fa/webfonts/ local paths"
        );

        // Verify webfonts directory has files
        let webfonts_dir = fa_dir.join("webfonts");
        assert!(webfonts_dir.exists(), "webfonts dir should exist");

        let webfont_files: Vec<_> = fs::read_dir(&webfonts_dir)
            .unwrap()
            .filter_map(|e| e.ok())
            .collect();
        assert!(
            !webfont_files.is_empty(),
            "Should have downloaded at least one webfont file"
        );

        // Verify metadata was created
        let meta_path = fa_dir.join("fa_meta.json");
        assert!(meta_path.exists(), "fa_meta.json should exist");

        let meta = load_json_with_fallbacks(&meta_path, BACKUP_COUNT).unwrap();
        assert_eq!(meta["version"], FA_META_VERSION);
        assert_eq!(meta["ok"], true);

        // Second call should be a no-op (cached)
        let result2 = ensure_fontawesome_local(&fa_dir).await;
        assert!(result2.is_ok());
    }
}