use std::{
    io::{Cursor, Read},
    time::Duration,
};

use axum::{
    extract::{DefaultBodyLimit, Path, State},
    http::{header, Method},
    response::{IntoResponse, Redirect, Response},
    routing::{get, post},
    Json, Router,
};
use axum_typed_multipart::{FieldData, TryFromMultipart, TypedMultipart};
use lazy_static::lazy_static;
use revolt_config::{config, report_internal_error};
use revolt_database::{iso8601_timestamp::Timestamp, Database, FileHash, Metadata, User};
use revolt_files::{
    create_thumbnail, decode_image, fetch_from_s3, upload_to_s3, AUTHENTICATION_TAG_SIZE_BYTES,
};
use revolt_result::{create_error, Error, Result};
use serde::{Deserialize, Serialize};
use sha2::Digest;
use tempfile::NamedTempFile;
use tokio::time::Instant;
use tower_http::cors::{AllowHeaders, Any, CorsLayer};
use utoipa::ToSchema;

use crate::{exif::strip_metadata, metadata::generate_metadata, mime_type::determine_mime_type, AppState};

/// Build the API router
pub async fn router() -> Router<AppState> {
    let config = config().await;

    let cors = CorsLayer::new()
        .allow_methods([Method::POST])
        .allow_headers(AllowHeaders::mirror_request())
        .expose_headers(vec![
            "X-RateLimit-Limit".try_into().unwrap(),
            "X-RateLimit-Bucket".try_into().unwrap(),
            "X-RateLimit-Remaining".try_into().unwrap(),
            "X-RateLimit-Reset-After".try_into().unwrap(),
        ])
        .allow_origin(Any);

    Router::new()
        .route("/", get(root))
        .route(
            "/:tag",
            post(upload_file)
                .options(options)
                .layer(DefaultBodyLimit::max(
                    config.features.limits.global.body_limit_size,
                )),
        )
        .route("/:tag/:file_id", get(fetch_preview))
        .route("/:tag/:file_id/:file_name", get(fetch_file))
        .layer(cors)
}

lazy_static! {
    /// Short-lived file cache to allow us to populate different CDN regions without increasing bandwidth to S3 provider
    /// Uploads will also be stored here to prevent immediately queued downloads from doing the entire round-trip
    static ref S3_CACHE: moka::future::Cache<String, Result<Vec<u8>>> = moka::future::Cache::builder()
        .weigher(|_key, value: &Result<Vec<u8>>| -> u32 {
            std::mem::size_of::<Result<Vec<u8>>>() as u32 + if let Ok(vec) = value {
                vec.len().try_into().unwrap_or(u32::MAX)
            } else {
                std::mem::size_of::<Error>() as u32
            }
        })
        // TODO config
        // .max_capacity(1024 * 1024 * 1024) // Cache up to 1GiB in memory
        // .max_capacity(512 * 1024 * 1024) // Cache up to 512MiB in memory
        .max_capacity(2 * 1024 * 1024 * 1024) // Cache up to 2GiB in memory
        .time_to_live(Duration::from_secs(5 * 60)) // For up to 5 minutes
        .build();
}

/// Retrieve hash information and file data by given hash
async fn retrieve_file_by_hash(hash: &FileHash) -> Result<Vec<u8>> {
    if let Some(data) = S3_CACHE.get(&hash.id).await {
        data
    } else {
        let data = fetch_from_s3(&hash.bucket_id, &hash.path, &hash.iv).await;
        S3_CACHE.insert(hash.id.to_owned(), data.clone()).await;
        data
    }
}

/// Successful root response
#[derive(Serialize, Debug, ToSchema)]
pub struct RootResponse {
    autumn: &'static str,
    version: &'static str,
}

/// Capture crate version from Cargo
static CRATE_VERSION: &str = env!("CARGO_PKG_VERSION");

/// Root response from service
#[utoipa::path(
    get,
    path = "/",
    responses(
        (status = 200, description = "Echo response", body = RootResponse)
    )
)]
async fn root() -> Json<RootResponse> {
    Json(RootResponse {
        autumn: "Hello, I am a file server!",
        version: CRATE_VERSION,
    })
}

/// Empty handler for OPTIONS routes
async fn options() {}

/// Available tags to upload to
#[derive(Clone, Deserialize, Debug, ToSchema, strum_macros::IntoStaticStr)]
#[allow(non_camel_case_types)]
pub enum Tag {
    attachments,
    avatars,
    backgrounds,
    icons,
    banners,
    emojis,
}

/// Request body for upload
#[derive(ToSchema, TryFromMultipart)]
pub struct UploadPayload {
    #[schema(format = Binary)]
    #[allow(dead_code)]
    #[form_data(limit = "unlimited")] // handled by axum
    file: FieldData<NamedTempFile>,
}

/// Successful upload response
#[derive(Serialize, Debug, ToSchema)]
pub struct UploadResponse {
    /// ID to attach uploaded file to object
    id: String,
}

/// Upload a file
///
/// Available tags and restrictions:
///
/// | Tag | Size | Resolution | Type |
/// | :-: | --: | :-- | :-: |
/// | attachments | 20 MB | - | Any |
/// | avatars | 4 MB | 40 MP or 10,000px | Image |
/// | backgrounds | 6 MB | 40 MP or 10,000px | Image |
/// | icons | 2.5 MB | 40 MP or 10,000px | Image |
/// | banners | 6 MB | 40 MP or 10,000px | Image |
/// | emojis | 500 KB | 40 MP or 10,000px | Image |
#[utoipa::path(
    post,
    path = "/{tag}",
    responses(
        (status = 200, description = "Upload was successful", body = UploadResponse)
    ),
    params(
        ("tag" = Tag, Path, description = "Tag to upload to (e.g. attachments, icons, ...)")
    ),
    request_body(content_type = "multipart/form-data", content = UploadPayload),
    security(
        ("session_token" = []),
        ("bot_token" = [])
    )
)]
async fn upload_file(
    State(db): State<Database>,
    user: User,
    Path(tag): Path<Tag>,
    TypedMultipart(UploadPayload { mut file }): TypedMultipart<UploadPayload>,
) -> Result<Json<UploadResponse>> {
    // Fetch configuration
    let config = config().await;

    // Keep track of processing time
    let now = Instant::now();

    // Extract the filename, or give it a generic name
    let filename = file.metadata.file_name.unwrap_or("unnamed-file".to_owned());

    // Load file to memory
    let mut buf = Vec::<u8>::new();
    report_internal_error!(file.contents.read_to_end(&mut buf))?;

    // Take note of original file size
    let original_file_size = buf.len();

    // Ensure the file is not empty
    if original_file_size < config.files.limit.min_file_size {
        return Err(create_error!(FileTooSmall));
    }

    // Get user's file upload limits
    let limits = user.limits().await;
    let size_limit = *limits
        .file_upload_size_limit
        .get(tag.clone().into())
        .expect("size limit");

    if original_file_size > size_limit {
        return Err(create_error!(FileTooLarge { max: size_limit }));
    }

    // Generate sha256 hash
    let original_hash = {
        let mut hasher = sha2::Sha256::new();
        hasher.update(&buf);
        hasher.finalize()
    };

    // Generate an ID for this file
    let id = if matches!(tag, Tag::emojis) {
        ulid::Ulid::new().to_string()
    } else {
        nanoid::nanoid!(42)
    };

    // Determine the mime type for the file
    let mime_type = determine_mime_type(&mut file.contents, &buf, &filename);

    // Check blocklist for mime type
    if config
        .files
        .blocked_mime_types
        .iter()
        .any(|m| m == mime_type)
    {
        return Err(create_error!(FileTypeNotAllowed));
    }

    // Determine metadata for the file
    let metadata = generate_metadata(&file.contents, mime_type);

    // Block non-images for non-attachment uploads
    if !matches!(tag, Tag::attachments) && !matches!(metadata, Metadata::Image { .. }) {
        return Err(create_error!(FileTypeNotAllowed));
    }

    // Find an existing hash and use that if possible
    let file_hash_exists = if let Ok(file_hash) = db
        .fetch_attachment_hash(&format!("{original_hash:02x}"))
        .await
    {
        if !file_hash.iv.is_empty() {
            let tag: &'static str = tag.into();
            db.insert_attachment(&file_hash.into_file(
                id.clone(),
                tag.to_owned(),
                filename,
                user.id,
            ))
            .await?;

            return Ok(Json(UploadResponse { id }));
        }

        true
    } else {
        false
    };

    // Strip metadata
    let (buf, metadata) = strip_metadata(file.contents, buf, metadata, mime_type).await?;

    // Virus scan files if ClamAV is configured
    if matches!(metadata, Metadata::File)
        && (config.files.scan_mime_types.is_empty()
            || config.files.scan_mime_types.iter().any(|v| v == mime_type))
        && crate::clamav::is_malware(&buf).await?
    {
        return Err(create_error!(InternalError));
    }

    // Print file information for debug purposes
    let new_file_size = buf.len() + AUTHENTICATION_TAG_SIZE_BYTES;
    let processed_hash = {
        let mut hasher = sha2::Sha256::new();
        hasher.update(&buf);
        hasher.finalize()
    };
    let process_ratio = new_file_size as f32 / original_file_size as f32;
    let time_to_process = Instant::now() - now;

    tracing::info!("Received file {filename}\nOriginal hash: {original_hash:02x}\nOriginal size: {original_file_size} bytes\nMime type: {mime_type}\nMetadata: {metadata:?}\nProcessed file size: {new_file_size} bytes ({:.2}%).\nProcessed hash: {processed_hash:02x}\nProcessing took {time_to_process:?}", process_ratio * 100.0);

    // Create hash entry in database
    let file_hash = FileHash {
        id: format!("{original_hash:02x}"),
        processed_hash: format!("{processed_hash:02x}"),

        created_at: Timestamp::now_utc(),

        bucket_id: config.files.s3.default_bucket,
        path: format!("{original_hash:02x}"),
        iv: String::new(), // indicates file is not uploaded yet

        metadata,
        content_type: mime_type.to_owned(),
        size: new_file_size as isize,
    };

    // Add attachment hash if it doesn't exist
    if !file_hash_exists {
        db.insert_attachment_hash(&file_hash).await?;
    }

    // Upload the file to S3 and commit nonce to database
    let upload_start = Instant::now();
    let nonce = upload_to_s3(&file_hash.bucket_id, &file_hash.id, &buf).await?;
    db.set_attachment_hash_nonce(&file_hash.id, &nonce).await?;

    // Debug information
    let time_to_upload = Instant::now() - upload_start;
    tracing::info!("Took {time_to_upload:?} to upload {new_file_size} bytes to S3.");

    // Finally, create the file and return its ID
    let tag: &'static str = tag.into();
    db.insert_attachment(&file_hash.into_file(id.clone(), tag.to_owned(), filename, user.id))
        .await?;

    Ok(Json(UploadResponse { id }))
}

/// Header value used for cache control
pub static CACHE_CONTROL: &str = "public, max-age=604800, must-revalidate";

/// Fetch preview of file
///
/// This route will only return image content. <br>
/// For all other file types, please use the fetch route (you will receive a redirect if you try to use this route anyways!).
///
/// Depending on the given tag, the file will be re-processed to fit the criteria:
///
/// | Tag | Image Resolution <sup>†</sup> | Animations stripped by preview <sup>‡</sup> |
/// | :-: | --- | :-: |
/// | attachments | Up to 1280px on any axis | ❌ |
/// | avatars | Up to 128px on any axis | ✅ |
/// | backgrounds | Up to 1280x720px | ❌ |
/// | icons | Up to 128px on any axis | ✅ |
/// | banners | Up to 480px on any axis | ❌ |
/// | emojis | Up to 128px on any axis | ❌ |
///
/// <sup>†</sup> aspect ratio will always be preserved
///
/// <sup>‡</sup> to fetch animated variant, suffix `/{file_name}` or `/original` to the path
#[utoipa::path(
    get,
    path = "/{tag}/{file_id}",
    responses(
        (status = 200, description = "Generated preview", body = Vec<u8>)
    ),
    params(
        ("tag" = Tag, Path, description = "Tag to fetch from (e.g. attachments, icons, ...)"),
        ("file_id" = String, Path, description = "File identifier")
    ),
)]
async fn fetch_preview(
    State(db): State<Database>,
    Path((tag, file_id)): Path<(Tag, String)>,
) -> Result<Response> {
    let tag_str: &'static str = tag.clone().into();
    let file = db.fetch_attachment(tag_str, &file_id).await?;

    // Ignore deleted files
    if file.deleted.is_some_and(|v| v) {
        return Err(create_error!(NotFound));
    }

    // Ignore files that haven't been attached
    if file.used_for.is_none() {
        return Err(create_error!(NotFound));
    }

    let hash = file.as_hash(&db).await?;

    let is_animated = matches!(hash.metadata, Metadata::Image { animated: true, .. });

    // Only process image files and don't process GIFs if not avatar or icon
    if !matches!(hash.metadata, Metadata::Image { .. })
        || (is_animated && !matches!(tag, Tag::avatars | Tag::icons))
    {
        return Ok(
            Redirect::permanent(&format!("/{tag_str}/{file_id}/{}", file.filename)).into_response(),
        );
    }

    // Original image data
    let data = retrieve_file_by_hash(&hash).await?;

    // Read image and create thumbnail
    let data = create_thumbnail(
        decode_image(&mut Cursor::new(data), &file.content_type)?,
        tag_str,
    )
    .await;

    Ok((
        [
            (header::CONTENT_TYPE, "image/webp"),
            (header::CONTENT_DISPOSITION, "inline"),
            (header::CACHE_CONTROL, CACHE_CONTROL),
        ],
        data,
    )
        .into_response())
}

/// Fetch original file
///
/// Content disposition header will be set to 'attachment' to prevent browser from rendering anything.
///
/// Using `original` as the file name parameter will redirect you to the original file.
#[utoipa::path(
    get,
    path = "/{tag}/{file_id}/{file_name}",
    responses(
        (status = 200, description = "Original file", body = Vec<u8>)
    ),
    params(
        ("tag" = Tag, Path, description = "Tag to fetch from (e.g. attachments, icons, ...)"),
        ("file_id" = String, Path, description = "File identifier"),
        ("file_name" = String, Path, description = "File name")
    ),
)]
async fn fetch_file(
    State(db): State<Database>,
    Path((tag, file_id, file_name)): Path<(Tag, String, String)>,
) -> Result<Response> {
    let tag: &'static str = tag.clone().into();
    let file = db.fetch_attachment(tag, &file_id).await?;

    // Ignore deleted files
    if file.deleted.is_some_and(|v| v) {
        return Err(create_error!(NotFound));
    }

    // Ignore files that haven't been attached
    if file.used_for.is_none() {
        return Err(create_error!(NotFound));
    }

    // Ensure filename is correct
    if file_name != file.filename {
        if file_name == "original" {
            return Ok(
                Redirect::permanent(&format!("/{tag}/{file_id}/{}", file.filename)).into_response(),
            );
        }

        return Err(create_error!(NotFound));
    }

    let hash = file.as_hash(&db).await?;
    retrieve_file_by_hash(&hash).await.map(|data| {
        (
            [
                (header::CONTENT_TYPE, hash.content_type),
                (header::CONTENT_DISPOSITION, "attachment".to_owned()),
                (header::CACHE_CONTROL, CACHE_CONTROL.to_owned()),
            ],
            data,
        )
            .into_response()
    })
}