//! TRACES: FR-MRG-1 | FR-MRG-4 | FR-MRG-5 | FR-MRG-7
//! The merge page: the grid's selection to a panorama, with a pause for
//! the photographer in the middle.
//!
//! The job itself is [`crate::merge`] and has no interface in it; this is
//! the wiring, on the import page's model. A press on "Merge to panorama"
//! fetches the selected originals on a worker, hands them to the job, and
//! opens the page; a timer drains the job's events into the page's
//! properties. When the alignment arrives the page shows it and waits.
//! "Merge" sends the decision; "Stop" or "Back" cancels. When the file is
//! staged, the outbox drains and the library rescans, and the composite
//! appears in the grid beside its sources.

use crate::executors::{self, Executor};
use std::cell::{Cell, RefCell};
use std::rc::Rc;
use std::sync::mpsc::{Receiver, Sender};

use slint::ComponentHandle;

use crate::activity::{Activity, ActivityLog, Kind};
use crate::merge::{
    self, AlignmentReport, Cancel, Decision, FillSettings, MergeDestination, MergeEvent,
    MergeInput, MergeRequest,
};
use crate::{AppWindow, Library, MergeFrameRow, Page};

/// How often the page reads the job's channel.
const DRAIN_INTERVAL: std::time::Duration = std::time::Duration::from_millis(120);

/// A running merge, as the page holds it.
struct Job {
    rx: Receiver<MergeEvent>,
    decide: Sender<Decision>,
    cancel: Cancel,
    names: Vec<String>,
    activity: Activity,
}

pub struct MergeController {
    activity: Rc<ActivityLog>,
    job: RefCell<Option<Job>>,
    timer: RefCell<Option<slint::Timer>>,
    /// The projection chip: 0 auto, then the three in `Projection`'s order.
    projection: Cell<i32>,
    /// The border chip: 0 crop, 1 fill (FR-MRG-4).
    border: Cell<i32>,
    /// The fill's knobs, as the page's sliders have them.
    fill: Cell<FillSettings>,
    report: RefCell<Option<AlignmentReport>>,
}

impl MergeController {
    /// The fill to ask for: the knobs if the border chip says fill, else
    /// none.
    fn fill_choice(&self) -> Option<FillSettings> {
        (self.border.get() == 1).then(|| self.fill.get())
    }
}

impl MergeController {
    pub fn new(activity: Rc<ActivityLog>) -> Rc<Self> {
        Rc::new(MergeController {
            activity,
            job: RefCell::new(None),
            timer: RefCell::new(None),
            projection: Cell::new(0),
            border: Cell::new(0),
            fill: Cell::new(FillSettings::default()),
            report: RefCell::new(None),
        })
    }
}

/// What the page needs from the library to start: the account for the
/// fetch, and where the outbox is.
pub struct Context {
    pub conn: dr_sync::Connection,
    pub outbox: std::path::PathBuf,
}

/// Wire the page. `sources` yields the selection as fetchable library
/// sources; `context` the account; `on_done` runs when a composite has
/// been staged, so the caller can drain the outbox and rescan.
pub fn wire<S, C, F>(
    window: &AppWindow,
    ctl: Rc<MergeController>,
    gpu: Option<dr_gpu::GpuContext>,
    sources: S,
    context: C,
    on_done: F,
) where
    S: Fn() -> Vec<crate::export::Source> + 'static,
    C: Fn() -> Option<Context> + 'static,
    F: Fn(&AppWindow) + 'static,
{
    wire_start(window, &ctl, gpu, sources, context, on_done);
    wire_decision(window, &ctl);
    wire_stop_and_leave(window, &ctl);
}

/// Start.
fn wire_start<S, C, F>(
    window: &AppWindow,
    ctl: &Rc<MergeController>,
    gpu: Option<dr_gpu::GpuContext>,
    sources: S,
    context: C,
    on_done: F,
) where
    S: Fn() -> Vec<crate::export::Source> + 'static,
    C: Fn() -> Option<Context> + 'static,
    F: Fn(&AppWindow) + 'static,
{
    let on_done = Rc::new(on_done);
    let gpu_for_start = gpu.clone();

    {
        let weak = window.as_weak();
        let ctl = ctl.clone();
        let on_done = on_done.clone();
        window
            .global::<Library>()
            .on_library_merge_selection(move || {
                let Some(w) = weak.upgrade() else { return };
                if ctl.job.borrow().is_some() {
                    w.global::<Library>()
                        .set_library_status("A panorama is already being merged".into());
                    return;
                }
                let Some(gpu) = gpu.clone() else {
                    w.global::<Library>().set_library_status(
                        "No GPU: a panorama cannot be merged on this device".into(),
                    );
                    return;
                };
                let Some(context) = context() else {
                    w.global::<Library>()
                        .set_library_status("Open a library first".into());
                    return;
                };
                // The selection, in library order. The catalog's order is the
                // grid's, which is capture time — the order a sweep was shot.
                let sources: Vec<(String, Option<crate::library::CacheContext>)> = sources()
                    .into_iter()
                    .filter_map(|s| match s {
                        crate::export::Source::Library { path, cache } => Some((path, cache)),
                        crate::export::Source::Rendered { .. } => None,
                    })
                    .collect();
                if sources.len() < 2 {
                    w.global::<Library>()
                        .set_library_status("Select at least two frames to merge".into());
                    return;
                }

                // Where the composite goes: beside its sources, through the
                // outbox (FR-MRG-3). The sources' folder, relative to the root.
                let root = context.conn.account.root.trim_matches('/').to_string();
                let first_dir = std::path::Path::new(&sources[0].0)
                    .parent()
                    .map(|p| p.to_string_lossy().trim_matches('/').to_string())
                    .unwrap_or_default();
                let remote_dir = first_dir
                    .strip_prefix(&root)
                    .map(|s| s.trim_start_matches('/').to_string())
                    .unwrap_or(first_dir);
                let destination = MergeDestination::Outbox {
                    outbox: context.outbox,
                    remote_dir,
                };

                let names: Vec<String> = sources
                    .iter()
                    .map(|(p, _)| {
                        std::path::Path::new(p)
                            .file_name()
                            .map(|n| n.to_string_lossy().into_owned())
                            .unwrap_or_else(|| p.clone())
                    })
                    .collect();

                // The fetch, on the job's own thread before the job: every
                // original comes down in turn — sequential so twelve downloads
                // do not halve each other's bandwidth — and the job then takes
                // bytes, which keeps it free of the library.
                let conn = context.conn.clone();
                let fetch_names = names.clone();
                let fetch =
                    move |tx: &Sender<MergeEvent>, cancel: &Cancel| -> Option<Vec<MergeInput>> {
                        let mut frames = Vec::with_capacity(sources.len());
                        for (i, (path, cache)) in sources.into_iter().enumerate() {
                            if cancel.is_cancelled() {
                                let _ = tx.send(MergeEvent::Cancelled);
                                return None;
                            }
                            let _ = tx.send(MergeEvent::Progress {
                                stage: "Fetching",
                                done: i,
                                total: fetch_names.len(),
                            });
                            let rx =
                                crate::library::spawn_full_fetch(conn.clone(), path.clone(), cache);
                            let bytes = match rx.recv() {
                                Ok(Ok(bytes)) => bytes,
                                Ok(Err(e)) => {
                                    let _ = tx.send(MergeEvent::Failed(format!(
                                        "{}: {}",
                                        fetch_names[i], e.message
                                    )));
                                    return None;
                                }
                                Err(_) => {
                                    let _ = tx.send(MergeEvent::Failed(format!(
                                        "{}: the download ended without answering",
                                        fetch_names[i]
                                    )));
                                    return None;
                                }
                            };
                            frames.push(MergeInput {
                                name: fetch_names[i].clone(),
                                bytes: std::sync::Arc::new(bytes),
                            });
                        }
                        Some(frames)
                    };
                start(&w, &ctl, gpu, names, destination, fetch, &on_done);
            });
    }

    // A way to land on the page at startup with local files, for looking
    // at it without a mouse: `DARKROOM_START_MERGE=a.CR2,b.CR2`. The same
    // job, the same page; only the fetch is a read. Off unless set.
    if let Some(list) = std::env::var_os("DARKROOM_START_MERGE") {
        let paths: Vec<std::path::PathBuf> = list
            .to_string_lossy()
            .split(',')
            .filter(|p| !p.is_empty())
            .map(std::path::PathBuf::from)
            .collect();
        if let (Some(gpu), Some(first)) = (gpu_for_start.clone(), paths.first()) {
            let names: Vec<String> = paths
                .iter()
                .map(|p| {
                    p.file_name()
                        .map(|n| n.to_string_lossy().into_owned())
                        .unwrap_or_default()
                })
                .collect();
            let dir = first
                .parent()
                .map(std::path::Path::to_path_buf)
                .unwrap_or_default();
            let read_paths = paths.clone();
            let fetch = move |tx: &Sender<MergeEvent>, _: &Cancel| -> Option<Vec<MergeInput>> {
                let mut frames = Vec::new();
                for p in &read_paths {
                    match MergeInput::read(p) {
                        Ok(f) => frames.push(f),
                        Err(e) => {
                            let _ = tx.send(MergeEvent::Failed(e));
                            return None;
                        }
                    }
                }
                Some(frames)
            };
            start(
                window,
                ctl,
                gpu,
                names,
                MergeDestination::Local(dir),
                fetch,
                &on_done,
            );
            // `DARKROOM_START_MERGE_FILL=1` opens it with the fill chosen,
            // to look at the knobs; the preview fills once the alignment
            // is in, as a chip pick would have it.
            if std::env::var_os("DARKROOM_START_MERGE_FILL").is_some() {
                ctl.border.set(1);
                window.set_merge_border_selected(1);
                if let Some(job) = ctl.job.borrow().as_ref() {
                    let _ = job.decide.send(Decision::Preview {
                        projection: None,
                        fill: ctl.fill_choice(),
                    });
                }
            }
        }
    }
}

/// The decision.
fn wire_decision(window: &AppWindow, ctl: &Rc<MergeController>) {
    {
        let weak = window.as_weak();
        let ctl = ctl.clone();
        window.on_merge_confirm(move || {
            let Some(w) = weak.upgrade() else { return };
            let projection = chip_projection(ctl.projection.get());
            let fill = ctl.fill_choice();
            if let Some(job) = ctl.job.borrow().as_ref() {
                let _ = job.decide.send(Decision::Merge { projection, fill });
                job.activity.detail("merging");
            }
            w.set_merge_running(true);
            w.set_merge_stage("Merging".into());
            w.set_merge_status("".into());
        });
    }
    {
        let weak = window.as_weak();
        let ctl = ctl.clone();
        window.on_merge_projection_picked(move |i| {
            let Some(w) = weak.upgrade() else { return };
            ctl.projection.set(i);
            w.set_merge_projection_selected(i);
            // Show it: the job redraws the preview on that surface and
            // reports again, and the drain puts the new picture up.
            if let Some(job) = ctl.job.borrow().as_ref() {
                let _ = job.decide.send(Decision::Preview {
                    projection: chip_projection(i),
                    fill: ctl.fill_choice(),
                });
            }
        });
    }
    {
        let weak = window.as_weak();
        let ctl = ctl.clone();
        window.on_merge_border_picked(move |i| {
            let Some(w) = weak.upgrade() else { return };
            ctl.border.set(i);
            w.set_merge_border_selected(i);
            // The fill is shown before it is chosen for good: the job
            // redraws the preview with the border filled, or not.
            if let Some(job) = ctl.job.borrow().as_ref() {
                let _ = job.decide.send(Decision::Preview {
                    projection: chip_projection(ctl.projection.get()),
                    fill: ctl.fill_choice(),
                });
            }
            w.set_merge_running(true);
            w.set_merge_stage(
                if i == 1 {
                    "Filling the preview"
                } else {
                    "Drawing the preview"
                }
                .into(),
            );
        });
    }

    {
        let weak = window.as_weak();
        let ctl = ctl.clone();
        window.on_merge_fill_knob(move |name, value| {
            let Some(w) = weak.upgrade() else { return };
            let mut f = ctl.fill.get();
            let v = value.round().max(0.0) as usize;
            match name.as_str() {
                "scale" => f.scale = (v as u32).clamp(1, 8),
                "erosion" => f.erosion = v,
                "coarse" => f.params.coarse = v.max(1),
                "band" => f.params.band = v.max(8),
                "mirror" => f.params.mirror_depth = v,
                "feather" => f.params.feather = v,
                _ => return,
            }
            ctl.fill.set(f);
            show_fill_knobs(&w, &f);
            // A knob turned while the fill is chosen redraws the preview
            // with it; turned under the crop it waits for the chip.
            if ctl.border.get() != 1 {
                return;
            }
            if let Some(job) = ctl.job.borrow().as_ref() {
                let _ = job.decide.send(Decision::Preview {
                    projection: chip_projection(ctl.projection.get()),
                    fill: Some(f),
                });
            }
            w.set_merge_running(true);
            w.set_merge_stage("Filling the preview".into());
        });
    }
}

/// Stopping and leaving.
fn wire_stop_and_leave(window: &AppWindow, ctl: &Rc<MergeController>) {
    {
        let weak = window.as_weak();
        let ctl = ctl.clone();
        window.on_merge_abandon(move || {
            let Some(w) = weak.upgrade() else { return };
            if let Some(job) = ctl.job.borrow().as_ref() {
                job.cancel.cancel();
                let _ = job.decide.send(Decision::Abandon);
            }
            w.set_merge_status("Stopping…".into());
        });
    }
    {
        let weak = window.as_weak();
        let ctl = ctl.clone();
        window.on_merge_close(move || {
            let Some(w) = weak.upgrade() else { return };
            // Leaving is abandoning: the page is the only thing that can
            // confirm the merge, so a job left waiting behind it would wait
            // for ever. A merge that is already writing is stopped too — the
            // page is where it reports, and a file finishing unseen would be
            // a composite the photographer did not confirm seeing.
            if let Some(job) = ctl.job.borrow_mut().take() {
                job.cancel.cancel();
                let _ = job.decide.send(Decision::Abandon);
                job.activity.finish_quietly();
            }
            *ctl.timer.borrow_mut() = None;
            w.set_active_page(Page::None);
        });
    }
}

/// Start a job: `fetch` runs first on the job's thread and hands back the
/// frames (or reports why not and returns `None`); the job follows on the
/// same thread. The page opens clean, and a timer drains the events.
fn start<Fetch>(
    window: &AppWindow,
    ctl: &Rc<MergeController>,
    gpu: dr_gpu::GpuContext,
    names: Vec<String>,
    destination: MergeDestination,
    fetch: Fetch,
    on_done: &Rc<impl Fn(&AppWindow) + 'static>,
) where
    Fetch: FnOnce(&Sender<MergeEvent>, &Cancel) -> Option<Vec<MergeInput>> + Send + 'static,
{
    let (tx, rx) = std::sync::mpsc::channel();
    let (decide, decision) = std::sync::mpsc::channel();
    let cancel = Cancel::default();
    let activity = ctl.activity.begin(Kind::Download, "Panorama");
    activity.total(names.len());

    {
        let cancel = cancel.clone();
        let tx = tx.clone();
        executors::spawn(Executor::GpuSubmit, "merge", move || {
            let Some(frames) = fetch(&tx, &cancel) else {
                return;
            };
            let mut request = MergeRequest::new(frames, destination);
            request.inpaint_model = crate::library::inpaint_model();
            merge::run(gpu, request, tx, decision, cancel);
        });
    }

    *ctl.job.borrow_mut() = Some(Job {
        rx,
        decide,
        cancel,
        names,
        activity,
    });
    *ctl.report.borrow_mut() = None;
    ctl.projection.set(0);
    ctl.border.set(0);
    ctl.fill.set(FillSettings::default());
    show_fill_knobs(window, &FillSettings::default());

    // The page, from a clean slate.
    window.set_merge_stage("Fetching".into());
    window.set_merge_running(true);
    window.set_merge_fraction(0.0);
    window.set_merge_status("".into());
    window.set_merge_error("".into());
    window.set_merge_aligned(false);
    window.set_merge_complete(false);
    window.set_merge_summary("".into());
    window.set_merge_frames(slint::ModelRc::new(slint::VecModel::from(Vec::<
        MergeFrameRow,
    >::new())));
    window.set_merge_preview(slint::Image::default());
    window.set_merge_projection_selected(0);
    window.set_merge_border_selected(0);
    window.set_merge_fill_available(false);
    window.set_merge_fill_note("".into());
    window.set_merge_preview_filled(false);
    window.set_merge_done(false);
    window.set_active_page(Page::Merge);

    let timer = slint::Timer::default();
    {
        let weak = window.as_weak();
        let ctl = ctl.clone();
        let on_done = on_done.clone();
        timer.start(slint::TimerMode::Repeated, DRAIN_INTERVAL, move || {
            let Some(w) = weak.upgrade() else { return };
            drain(&w, &ctl, &on_done);
        });
    }
    *ctl.timer.borrow_mut() = Some(timer);
}

/// The projection a chip index names; 0 is "Auto".
fn chip_projection(i: i32) -> Option<dr_pano::Projection> {
    match i {
        1 => Some(dr_pano::Projection::Perspective),
        2 => Some(dr_pano::Projection::Cylindrical),
        3 => Some(dr_pano::Projection::Spherical),
        _ => None,
    }
}

/// Take everything the job has said and reflect it on the page.
fn drain(window: &AppWindow, ctl: &Rc<MergeController>, on_done: &Rc<impl Fn(&AppWindow)>) {
    let (events, gone) = {
        let job = ctl.job.borrow();
        let Some(job) = job.as_ref() else { return };
        merge::drain(&job.rx)
    };
    // The worker is the only sender, so a closed channel with nothing final
    // said is a worker that died without saying anything — the one way
    // `merge::run` cannot report, since reporting is what it was doing.
    // Without this the page stayed on "Stop" for ever.
    let mut events = events;
    if gone && !events.iter().any(MergeEvent::is_final) {
        events.push(MergeEvent::Failed(
            "the merge stopped unexpectedly; the log has the reason".into(),
        ));
    }
    if events.is_empty() {
        return;
    }
    let mut finished = false;
    for event in events {
        match event {
            MergeEvent::Progress { stage, done, total } => {
                window.set_merge_stage(stage.into());
                window.set_merge_running(true);
                window.set_merge_fraction(if total > 0 {
                    done as f32 / total as f32
                } else {
                    0.0
                });
                if let Some(job) = ctl.job.borrow().as_ref() {
                    job.activity.detail(stage.to_lowercase());
                    job.activity.progress(done, total.max(1));
                }
            }
            MergeEvent::Aligned(report) => {
                let names = ctl
                    .job
                    .borrow()
                    .as_ref()
                    .map(|j| j.names.clone())
                    .unwrap_or_default();
                show_report(window, &report, &names);
                window.set_merge_running(false);
                window.set_merge_stage("".into());
                window.set_merge_fraction(0.0);
                window.set_merge_status(if report.frames.iter().all(Result::is_ok) {
                    "Check the alignment, then press Merge.".into()
                } else {
                    "Not every frame could be placed. Remove the ones named and try again.".into()
                });
                *ctl.report.borrow_mut() = Some(report);
            }
            MergeEvent::Done {
                path,
                staged,
                width,
                height,
            } => {
                let name = path
                    .file_name()
                    .map(|n| n.to_string_lossy().into_owned())
                    .unwrap_or_default();
                window.set_merge_running(false);
                window.set_merge_stage("".into());
                window.set_merge_done(true);
                window.set_merge_status(
                    if staged {
                        format!("{name} ({width}×{height}) is queued to go beside its sources.")
                    } else {
                        format!("{name} ({width}×{height}) written to {}.", path.display())
                    }
                    .into(),
                );
                if let Some(job) = ctl.job.borrow().as_ref() {
                    job.activity.finish(format!("{name} merged"));
                }
                finished = true;
                on_done(window);
            }
            MergeEvent::Failed(e) => {
                window.set_merge_running(false);
                window.set_merge_stage("".into());
                window.set_merge_error(e.clone().into());
                if let Some(job) = ctl.job.borrow().as_ref() {
                    job.activity.fail(e);
                }
                finished = true;
            }
            MergeEvent::Cancelled => {
                window.set_merge_running(false);
                window.set_merge_stage("".into());
                window.set_merge_status("Stopped. Nothing was written.".into());
                if let Some(job) = ctl.job.borrow().as_ref() {
                    job.activity.finish_quietly();
                }
                finished = true;
            }
        }
    }
    if finished {
        *ctl.job.borrow_mut() = None;
        *ctl.timer.borrow_mut() = None;
    }
}

/// The alignment onto the page: the summary, the table, the preview.
fn show_report(window: &AppWindow, report: &AlignmentReport, names: &[String]) {
    let rows: Vec<MergeFrameRow> = report
        .frames
        .iter()
        .enumerate()
        .map(|(k, f)| {
            let name = names
                .get(k)
                .cloned()
                .unwrap_or_else(|| format!("frame {k}"));
            match f {
                Ok((yaw, pitch)) => MergeFrameRow {
                    name: name.into(),
                    detail: format!("yaw {yaw:.1}° · pitch {pitch:.1}°").into(),
                    aligned: true,
                },
                Err(why) => MergeFrameRow {
                    name: name.into(),
                    detail: why.clone().into(),
                    aligned: false,
                },
            }
        })
        .collect();
    let complete = report.frames.iter().all(Result::is_ok);
    window.set_merge_frames(slint::ModelRc::new(slint::VecModel::from(rows)));
    window.set_merge_aligned(true);
    window.set_merge_complete(complete);
    window.set_merge_summary(
        format!(
            "{} frames, {} overlaps · {:.0} mm equivalent · {:?} · {}×{} px · fit {:.1} px",
            report.frames.len(),
            report.links,
            report.focal_mm,
            report.projection,
            report.width,
            report.height,
            report.rms_px
        )
        .into(),
    );
    if let Some((w, h, rgba)) = &report.preview {
        let buffer = slint::SharedPixelBuffer::<slint::Rgba8Pixel>::clone_from_slice(rgba, *w, *h);
        window.set_merge_preview(slint::Image::from_rgba8(buffer));
    }
    window.set_merge_preview_filled(report.filled);
    match &report.filler {
        Ok(rung) => {
            window.set_merge_fill_available(true);
            window.set_merge_fill_note(format!("runs on {rung}").into());
        }
        Err(why) => {
            window.set_merge_fill_available(false);
            window.set_merge_fill_note(format!("The border can only be cropped: {why}.").into());
        }
    }
}

/// The sliders, from the settings.
fn show_fill_knobs(window: &AppWindow, f: &FillSettings) {
    window.set_merge_fill_scale(f.scale as f32);
    window.set_merge_fill_erosion(f.erosion as f32);
    window.set_merge_fill_coarse(f.params.coarse as f32);
    window.set_merge_fill_band(f.params.band as f32);
    window.set_merge_fill_mirror(f.params.mirror_depth as f32);
    window.set_merge_fill_feather(f.params.feather as f32);
}