use std::{io::Cursor, panic, sync::Arc, time::Duration};

use async_trait::async_trait;
use chrono::Utc;
use diesel::{pg::upsert::excluded, prelude::*};
use image::{
    codecs::png::PngEncoder, ColorType, GenericImageView, ImageEncoder, ImageFormat, ImageReader,
};
use pdfium_render::prelude::*;
use serde::Deserialize;
use serde_json::json;
use tokio::task;
use tracing::{error, info, warn};
use uuid::Uuid;

use crate::{
    jobs::JOB_GENERATE_THUMBNAILS,
    models::{Document, DocumentAsset, DocumentVersion, NewDocumentAsset},
    schema::{document_assets, document_versions, documents},
    state::AppState,
};

use super::{analyze::determine_thumbnail_support, JobExecution, JobHandler};

const THUMBNAIL_WIDTH: u32 = 512;
const THUMBNAIL_HEIGHT: u32 = 512;
const THUMBNAIL_ASSET_TYPE: &str = "thumbnail";

#[derive(Debug, Deserialize)]
struct ThumbnailPayload {
    document_id: Uuid,
    document_version_id: Uuid,
    #[serde(default)]
    force: bool,
}

pub struct GenerateThumbnailsJob;

impl GenerateThumbnailsJob {
    pub fn new() -> Self {
        Self
    }
}

#[async_trait]
impl JobHandler for GenerateThumbnailsJob {
    fn job_type(&self) -> &'static str {
        JOB_GENERATE_THUMBNAILS
    }

    async fn handle(&self, state: Arc<AppState>, job: crate::models::Job) -> JobExecution {
        let payload: ThumbnailPayload = match serde_json::from_value(job.payload.clone()) {
            Ok(p) => p,
            Err(err) => {
                return JobExecution::Failed {
                    error: format!("invalid thumbnail payload: {err}"),
                }
            }
        };

        let state_clone = state.clone();
        let initial =
            match task::spawn_blocking(move || load_thumbnail_context(state_clone, &payload)).await
            {
                Ok(Ok(ctx)) => ctx,
                Ok(Err(err)) => {
                    warn!(job_id = %job.id, error = %err, "thumbnail job will retry");
                    return JobExecution::Retry {
                        delay: Duration::from_secs(30),
                        error: err,
                    };
                }
                Err(join_err) => {
                    error!(job_id = %job.id, error = %join_err, "thumbnail task panicked");
                    return JobExecution::Retry {
                        delay: Duration::from_secs(60),
                        error: format!("worker panicked: {join_err}"),
                    };
                }
            };

        if initial.skip {
            info!(job_id = %job.id, "thumbnails already exist; skipping");
            return JobExecution::Success;
        }

        let bytes = match state.storage.get_object(&initial.version.s3_key).await {
            Ok(bytes) => bytes,
            Err(err) => {
                warn!(job_id = %job.id, error = %err, "thumbnail fetch failed; will retry");
                return JobExecution::Retry {
                    delay: Duration::from_secs(30),
                    error: err.to_string(),
                };
            }
        };

        let generation = match generate_thumbnail(&initial.document, &bytes) {
            Ok(result) => result,
            Err(err) => {
                return JobExecution::Failed { error: err };
            }
        };

        if let Err(err) = state
            .storage
            .put_object(
                &generation.s3_key,
                generation.image_bytes.clone(),
                Some("image/png".into()),
            )
            .await
        {
            warn!(job_id = %job.id, error = %err, "failed to upload thumbnail; retrying");
            return JobExecution::Retry {
                delay: Duration::from_secs(30),
                error: err.to_string(),
            };
        }

        let state_clone = state.clone();
        match task::spawn_blocking(move || {
            persist_thumbnail_metadata(state_clone, &initial, &generation)
        })
        .await
        {
            Ok(Ok(())) => {}
            Ok(Err(err)) => {
                warn!(job_id = %job.id, error = %err, "failed to persist thumbnail metadata; retrying");
                return JobExecution::Retry {
                    delay: Duration::from_secs(30),
                    error: err,
                };
            }
            Err(join_err) => {
                error!(job_id = %job.id, error = %join_err, "thumbnail metadata update panicked");
                return JobExecution::Retry {
                    delay: Duration::from_secs(30),
                    error: format!("metadata update panic: {join_err}"),
                };
            }
        }

        JobExecution::Success
    }
}

struct ThumbnailContext {
    document: Document,
    version: DocumentVersion,
    skip: bool,
}

struct GeneratedThumbnail {
    image_bytes: Vec<u8>,
    width: Option<i32>,
    height: Option<i32>,
    s3_key: String,
}

fn load_thumbnail_context(
    state: Arc<AppState>,
    payload: &ThumbnailPayload,
) -> Result<ThumbnailContext, String> {
    let mut conn = state.db().map_err(|err| format!("{err:?}"))?;

    let version: DocumentVersion = document_versions::table
        .find(payload.document_version_id)
        .first(&mut conn)
        .map_err(|err| format!("{err:?}"))?;

    if version.document_id != payload.document_id {
        return Err("document/version mismatch".into());
    }

    let document: Document = documents::table
        .find(payload.document_id)
        .first(&mut conn)
        .map_err(|err| format!("{err:?}"))?;

    let existing: Option<DocumentAsset> = document_assets::table
        .filter(document_assets::document_version_id.eq(payload.document_version_id))
        .filter(document_assets::asset_type.eq(THUMBNAIL_ASSET_TYPE))
        .first(&mut conn)
        .optional()
        .map_err(|err| format!("{err:?}"))?;

    let (supported, _) = determine_thumbnail_support(&document);
    if !supported {
        return Err("thumbnail generation not supported for this document".into());
    }

    let skip = existing.is_some() && !payload.force;

    Ok(ThumbnailContext {
        document,
        version,
        skip,
    })
}

fn generate_thumbnail(document: &Document, bytes: &[u8]) -> Result<GeneratedThumbnail, String> {
    let is_pdf = document
        .content_type
        .as_deref()
        .map(|mime| mime == "application/pdf")
        .unwrap_or_else(|| {
            document
                .original_name
                .rsplit('.')
                .next()
                .map(|ext| ext.eq_ignore_ascii_case("pdf"))
                .unwrap_or(false)
        });

    let (png_bytes, width, height) = if is_pdf {
        generate_pdf_thumbnail(bytes)?
    } else {
        generate_image_thumbnail(bytes)?
    };

    let s3_key = format!("thumbnails/{}/{}.png", document.id, Uuid::new_v4());

    Ok(GeneratedThumbnail {
        image_bytes: png_bytes,
        width,
        height,
        s3_key,
    })
}

fn generate_image_thumbnail(bytes: &[u8]) -> Result<(Vec<u8>, Option<i32>, Option<i32>), String> {
    let reader = ImageReader::new(Cursor::new(bytes))
        .with_guessed_format()
        .map_err(|err| err.to_string())?;
    let mut image = reader.decode().map_err(|err| err.to_string())?;
    if image.width() > THUMBNAIL_WIDTH || image.height() > THUMBNAIL_HEIGHT {
        image = image.thumbnail(THUMBNAIL_WIDTH, THUMBNAIL_HEIGHT);
    }

    let (width, height) = image.dimensions();
    let mut cursor = Cursor::new(Vec::new());
    image
        .write_to(&mut cursor, ImageFormat::Png)
        .map_err(|err| err.to_string())?;
    let buffer = cursor.into_inner();
    Ok((buffer, Some(width as i32), Some(height as i32)))
}

fn generate_pdf_thumbnail(bytes: &[u8]) -> Result<(Vec<u8>, Option<i32>, Option<i32>), String> {
    let pdfium = panic::catch_unwind(|| Pdfium::default())
        .map_err(|_| "failed to initialize PDFium".to_string())?;

    let document = pdfium
        .load_pdf_from_byte_slice(bytes, None)
        .map_err(|err| format!("load pdf: {err}"))?;

    let page = document
        .pages()
        .get(0)
        .map_err(|err| format!("load first page: {err}"))?;

    let render_config = PdfRenderConfig::new()
        .set_target_width(THUMBNAIL_WIDTH as i32)
        .set_maximum_height(THUMBNAIL_HEIGHT as i32)
        .render_form_data(true)
        .rotate_if_landscape(PdfPageRenderRotation::None, true);

    let bitmap = page
        .render_with_config(&render_config)
        .map_err(|err| format!("render pdf page: {err}"))?;

    let image = bitmap.as_image().to_rgb8();
    let (width, height) = image.dimensions();
    let mut cursor = Cursor::new(Vec::new());
    PngEncoder::new(&mut cursor)
        .write_image(image.as_raw(), width, height, ColorType::Rgb8.into())
        .map_err(|err| format!("encode pdf thumbnail: {err}"))?;

    Ok((cursor.into_inner(), Some(width as i32), Some(height as i32)))
}

fn persist_thumbnail_metadata(
    state: Arc<AppState>,
    context: &ThumbnailContext,
    generated: &GeneratedThumbnail,
) -> Result<(), String> {
    let mut conn = state.db().map_err(|err| format!("{err:?}"))?;

    let new_asset = NewDocumentAsset {
        id: Uuid::new_v4(),
        document_version_id: context.version.id,
        asset_type: THUMBNAIL_ASSET_TYPE.to_string(),
        s3_key: generated.s3_key.clone(),
        mime_type: "image/png".to_string(),
        width: generated.width,
        height: generated.height,
        metadata: json!({
            "generated_at": Utc::now().to_rfc3339(),
        }),
    };

    diesel::insert_into(document_assets::table)
        .values(&new_asset)
        .on_conflict((
            document_assets::document_version_id,
            document_assets::asset_type,
        ))
        .do_update()
        .set((
            document_assets::s3_key.eq(excluded(document_assets::s3_key)),
            document_assets::mime_type.eq(excluded(document_assets::mime_type)),
            document_assets::width.eq(excluded(document_assets::width)),
            document_assets::height.eq(excluded(document_assets::height)),
            document_assets::metadata.eq(excluded(document_assets::metadata)),
        ))
        .execute(&mut conn)
        .map_err(|err| format!("{err:?}"))?;

    Ok(())
}