//! File input and output without a file system (C2): the browser.
//!
//! The web build has no paths. Open picks a file through the browser's file
//! picker (or takes one dropped on the window) and hands its bytes to
//! `file.open_data`; Save and Export make the bytes with `file.save_data` and
//! `file.export_data` and give them to the user as a download. The pickers and
//! downloads come through [`FileDialogs`](crate::dialogs::FileDialogs) (`is_web`,
//! `pick_web`, `download`), so a test can script them on the desktop too.

use std::cell::RefCell;
use std::rc::Rc;

use serde_json::{json, Value};

use crate::App;

/// A file the user picked or dropped in the browser.
#[derive(Debug, Clone, PartialEq)]
pub struct WebPick {
    pub name: String,
    pub bytes: Vec<u8>,
}

/// What a pick is for: the picker is one dialog, the request says what to do
/// with the file when it arrives.
#[derive(Debug, Clone, PartialEq, Default)]
pub enum WebPurpose {
    /// Open it as the figure.
    #[default]
    Open,
    /// File > Merge.
    Merge,
    /// Picture mode: a picture in the box the user drew.
    PictureBox { rect: [f64; 4], keep_aspect: bool },
    /// Import a picture at the centre of the view.
    PictureImport,
    /// The picture panel's Browse / Relink.
    PictureRelink,
}

/// Where asynchronous picks arrive: the browser's file picker answers some
/// frames after the request. Cloning shares the queue.
#[derive(Clone, Default)]
pub struct WebInbox {
    queue: Rc<RefCell<Vec<(WebPurpose, WebPick)>>>,
    purpose: Rc<RefCell<WebPurpose>>,
    ctx: Rc<RefCell<Option<egui::Context>>>,
}

impl WebInbox {
    /// Remember the context, so an arriving pick wakes the UI (the web app
    /// only draws on events).
    pub fn attach(&self, ctx: &egui::Context) {
        if let Ok(mut c) = self.ctx.try_borrow_mut() {
            if c.is_none() {
                *c = Some(ctx.clone());
            }
        }
    }

    /// What the next pick is for (set just before the picker opens).
    pub fn request(&self, purpose: WebPurpose) {
        if let Ok(mut p) = self.purpose.try_borrow_mut() {
            *p = purpose;
        }
    }

    /// A pick arrived, for what was requested last.
    pub fn push(&self, pick: WebPick) {
        let purpose = self.purpose.try_borrow().map(|p| p.clone()).unwrap_or_default();
        if let Ok(mut q) = self.queue.try_borrow_mut() {
            q.push((purpose, pick));
        }
        if let Ok(c) = self.ctx.try_borrow() {
            if let Some(c) = c.as_ref() {
                c.request_repaint();
            }
        }
    }

    /// Put a pick back to deal with later.
    pub fn requeue(&self, purpose: WebPurpose, pick: WebPick) {
        if let Ok(mut q) = self.queue.try_borrow_mut() {
            q.push((purpose, pick));
        }
    }

    /// The picks that arrived since the last call.
    pub fn take(&self) -> Vec<(WebPurpose, WebPick)> {
        self.queue
            .try_borrow_mut()
            .map(|mut q| std::mem::take(&mut *q))
            .unwrap_or_default()
    }
}

/// The part of `name` after the last `/` or `\`, which is how a browser
/// reports a file (no folders), without control characters.
pub fn base_name(name: &str) -> String {
    let n = name.rsplit(['/', '\\']).next().unwrap_or(name);
    n.chars().filter(|c| !c.is_control()).collect()
}

fn extension(name: &str) -> String {
    name.rsplit_once('.')
        .map(|(_, e)| e.to_ascii_lowercase())
        .unwrap_or_default()
}

/// Open a picked or dropped file as the figure: a Fig or native file, or a
/// PDF, SVG or PNG export with the figure embedded (which opens under a
/// `.fig` name, as on the desktop, so Save never names the export).
pub fn open_pick(app: &mut App, pick: &WebPick) {
    let mut name = base_name(&pick.name);
    if name.is_empty() {
        name = "figure.fig".to_string();
    }
    let embedded = !matches!(extension(&name).as_str(), "fig" | "xfig" | "rustfig");
    if embedded {
        name = match name.rsplit_once('.') {
            Some((stem, _)) if !stem.is_empty() => format!("{stem}.fig"),
            _ => format!("{name}.fig"),
        };
    }
    if app
        .run(
            "file.open_data",
            json!({"base64": rustfig_engine::base64(&pick.bytes), "name": name}),
        )
        .is_some()
    {
        app.engine.set_modified(embedded);
        app.info(format!("Current figure \"{name}\""));
    }
}

/// What a pick that arrived is used for (C2): Merge adds the figure, a
/// picture is kept in memory under its file name (the figure keeps only the
/// name, as on the desktop; the bytes live until the session ends) and placed.
pub fn handle_pick(app: &mut App, purpose: WebPurpose, pick: &WebPick) {
    let name = base_name(&pick.name);
    match purpose {
        WebPurpose::Open => {}
        WebPurpose::Merge => {
            let r = app.run(
                "file.merge_data",
                json!({"base64": rustfig_engine::base64(&pick.bytes)}),
            );
            if r.is_some() {
                app.info(format!("Merged {name}"));
            }
        }
        WebPurpose::PictureBox { rect, keep_aspect } => {
            if keep_picture(app, &name, pick) {
                let [x, y, w, h] = rect;
                app.add_picture(&name, [x, y, w, h], keep_aspect);
            }
        }
        WebPurpose::PictureImport => {
            if keep_picture(app, &name, pick) {
                let c = app.engine.view.visible().center();
                app.run("shape.picture", json!({"path": name, "x": c.x, "y": c.y}));
            }
        }
        WebPurpose::PictureRelink => {
            if keep_picture(app, &name, pick) {
                app.web_relink_name = Some(name);
            }
        }
    }
}

/// Keep a picked picture's bytes under its file name for the session.
pub fn keep_picture(app: &mut App, name: &str, pick: &WebPick) -> bool {
    if name.is_empty() {
        app.error("The picture has no file name");
        return false;
    }
    app.run(
        "picture.store",
        json!({"name": name, "base64": rustfig_engine::base64(&pick.bytes)}),
    )
    .is_some()
}

/// Gives `bytes` to the user as a download at once: a Blob, an `<a download>`
/// element, a click (no dialog).
#[cfg(target_arch = "wasm32")]
pub fn browser_download(name: &str, bytes: &[u8]) -> Result<(), String> {
    use wasm_bindgen::JsCast;
    let err = |what: &str| format!("download failed: {what}");
    let array = js_sys::Uint8Array::from(bytes);
    let parts = js_sys::Array::new();
    parts.push(&array);
    let opts = web_sys::BlobPropertyBag::new();
    opts.set_type("application/octet-stream");
    let blob = web_sys::Blob::new_with_u8_array_sequence_and_options(&parts, &opts).map_err(|_| err("blob"))?;
    let url = web_sys::Url::create_object_url_with_blob(&blob).map_err(|_| err("url"))?;
    let document = web_sys::window()
        .and_then(|w| w.document())
        .ok_or_else(|| err("no document"))?;
    let a = document
        .create_element("a")
        .map_err(|_| err("element"))?
        .dyn_into::<web_sys::HtmlAnchorElement>()
        .map_err(|_| err("anchor"))?;
    a.set_href(&url);
    a.set_download(name);
    if let Some(body) = document.body() {
        body.append_child(&a).map_err(|_| err("append"))?;
        a.click();
        body.remove_child(&a).ok(); // the click has already started the download
    } else {
        a.click();
    }
    web_sys::Url::revoke_object_url(&url).ok(); // the browser has the data by now
    Ok(())
}

/// Save: the figure as a download named after the open file (`figure.fig`
/// for a new one; a `.rustfig` name keeps the native format).
pub fn save(app: &mut App) {
    let current = app.engine.path().map(base_name).filter(|n| !n.is_empty());
    let name = current.unwrap_or_else(|| "figure.fig".to_string());
    let format = if extension(&name) == "rustfig" {
        "rustfig"
    } else {
        "fig"
    };
    let Some(r) = app.run("file.save_data", json!({ "format": format })) else {
        return;
    };
    let Some(text) = r.get("data").and_then(Value::as_str) else {
        app.error("Save: no data");
        return;
    };
    match app.file_dialogs.download(&name, text.as_bytes().to_vec()) {
        Ok(()) => {
            app.engine.set_path(Some(name.clone()));
            app.engine.set_modified(false);
            app.info(format!("Saved {name} (downloaded)"));
        }
        Err(e) => app.error(e),
    }
}

/// Export: `file.export_data` with the panel's parameters, each file it
/// produces as a download (`default_name` for the one file, the figure's name
/// with each file's extension for several, as PostScript with PDF).
pub fn export(app: &mut App, params: &Value, default_name: &str) -> bool {
    let mut p = params.clone();
    if let Some(m) = p.as_object_mut() {
        m.remove("path");
    }
    let Some(r) = app.run("file.export_data", p) else {
        return false;
    };
    let mut files: Vec<(String, Vec<u8>)> = Vec::new();
    let mut add = |name: String, v: &Value| {
        if let Some(t) = v.get("data").and_then(Value::as_str) {
            files.push((name, t.as_bytes().to_vec()));
        } else if let Some(b) = v.get("base64").and_then(Value::as_str) {
            files.push((name, rustfig_engine::base64_decode(b)));
        }
    };
    match r.get("files").and_then(Value::as_array) {
        Some(list) => {
            let stem = default_name.rsplit_once('.').map_or(default_name, |(s, _)| s);
            for f in list {
                let ext = f.get("extension").and_then(Value::as_str).unwrap_or("out");
                add(format!("{stem}.{ext}"), f);
            }
        }
        None => add(default_name.to_string(), &r),
    }
    if files.is_empty() {
        app.error("Export: nothing was produced");
        return false;
    }
    let count = files.len();
    for (name, bytes) in files {
        if let Err(e) = app.file_dialogs.download(&name, bytes) {
            app.error(e);
            return false;
        }
    }
    app.info(format!(
        "Exported {default_name} (downloaded{})",
        if count > 1 { ", several files" } else { "" }
    ));
    true
}

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

    #[test]
    fn base_name_strips_folders_and_controls() {
        assert_eq!(base_name("a/b/c.fig"), "c.fig");
        assert_eq!(base_name("C:\\x\\Zeichnung ä.fig"), "Zeichnung ä.fig");
        assert_eq!(base_name("x\n.fig"), "x.fig");
        assert_eq!(base_name(""), "");
    }
}