//! TRACES: FR-EXP-1 | FR-EXP-2 | FR-EXP-3 | FR-EXP-4 | FR-EXP-6 | FR-EXP-8 | FR-NC-6a
//! Wires [`Settings`] to the Slint settings page.
//!
//! Shaped after [`launch_ui`](crate::launch_ui): the record lives in
//! `dr-types` and is tested headless, [`render`] pushes it into window
//! properties, and [`wire`] connects the callbacks. This module moves values
//! across the boundary and decides nothing about what a setting *means*.
//!
//! # Every edit saves
//!
//! There is no Save button. A settings page with one has to answer what
//! happens when the window closes with the button untouched, and every
//! available answer is bad: discarding silently loses work, prompting turns a
//! preference change into a dialogue, and saving anyway makes the button a
//! decoration. Writing on each edit removes the question — the file is a few
//! hundred bytes, written by rename, and the user's last action is always what
//! is stored.
//!
//! A failed write is surfaced rather than swallowed, because the whole
//! contract of this page is that what it shows is what is saved. If the disk
//! is full or the config directory is unwritable, a page that kept displaying
//! the new value would be lying.

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

use dr_types::settings::budget;
use dr_types::{
    CollisionPolicy, ColourSpace, ExportFormat, ExportTarget, OutputSharpening, Settings,
    SizingMode,
};
use slint::ComponentHandle;

use crate::settings_store::SettingsStore;
use crate::AppWindow;

/// Shared settings state for the running window.
pub struct SettingsController {
    pub settings: RefCell<Settings>,
    pub store: SettingsStore,
    /// Reported by the page when a write fails. Held here rather than pushed
    /// straight to the window so [`render`] stays the single writer of window
    /// properties.
    error: RefCell<Option<String>>,
    /// How much disk the cache is currently using, as a label. Supplied by
    /// whoever owns the catalog — this module has no connection to query.
    usage_label: RefCell<String>,
    /// TRACES: FR-EXP-6
    /// The remote folder picker, while it is open.
    ///
    /// The same [`FolderBrowser`](crate::launch::FolderBrowser) the launch
    /// screen uses to choose a library root, reused rather than reimplemented:
    /// it browses a remote tree and nothing about it is specific to what the
    /// chosen folder is *for*. `None` means the picker is closed, which is
    /// also the only state a device destination ever has — a path on this
    /// machine is typed or chosen by the platform, not walked over WebDAV.
    pub browser: RefCell<Option<crate::launch::FolderBrowser>>,
    /// Polls the folder listing while one is in flight.
    ///
    /// Held here rather than in the function that starts it: a `slint::Timer`
    /// stops the moment it is dropped, so a timer local to `spawn_folder_list`
    /// would be collected before the listing it is waiting on ever arrived.
    /// The same place `LaunchController` keeps its own poll timer.
    poll_timer: RefCell<Option<slint::Timer>>,
}

impl SettingsController {
    pub fn new() -> Rc<Self> {
        let store = SettingsStore::open();
        let settings = store.load();
        Rc::new(Self {
            settings: RefCell::new(settings),
            store,
            error: RefCell::new(None),
            usage_label: RefCell::new(String::new()),
            browser: RefCell::new(None),
            poll_timer: RefCell::new(None),
        })
    }

    /// The current settings, for whoever needs to act on them.
    pub fn snapshot(&self) -> Settings {
        self.settings.borrow().clone()
    }

    /// Adopt a folder chosen in the picker as the export destination.
    ///
    /// Goes through `edit` like every other change, so it is saved the moment
    /// it is chosen — the page has no Save button and a destination that
    /// survived only until the window closed would be the one setting that
    /// behaved differently from all the others.
    pub fn set_destination(&self, path: String) {
        self.edit(|s| s.export.set_active_destination(path));
    }

    /// Report a failure onto the page's error line.
    pub fn set_error(&self, message: impl Into<String>) {
        *self.error.borrow_mut() = Some(message.into());
    }

    /// Show what the cache is holding. Empty hides the line.
    pub fn set_usage_label(&self, label: String) {
        *self.usage_label.borrow_mut() = label;
    }

    /// Apply an edit and persist it.
    ///
    /// Takes a closure rather than a whole `Settings` so a caller cannot
    /// accidentally write back a stale copy of the fields it was not editing —
    /// with a save on every keystroke, two controls holding their own snapshots
    /// would overwrite each other.
    fn edit(&self, f: impl FnOnce(&mut Settings)) {
        {
            let mut settings = self.settings.borrow_mut();
            f(&mut settings);
            // The page can produce out-of-range values — a typed quality, a
            // pasted number — so the same clamp the file gets on read applies
            // here, before anything is stored or shown.
            settings.sanitise();
        }

        let snapshot = self.settings.borrow().clone();
        match self.store.save(&snapshot) {
            Ok(()) => *self.error.borrow_mut() = None,
            Err(e) => {
                log::warn!("saving settings: {e}");
                *self.error.borrow_mut() = Some(format!(
                    "Could not save to {}: {e}",
                    self.store.path().display()
                ));
            }
        }
    }
}

/// Push the settings into the window's properties.
pub fn render(window: &AppWindow, controller: &SettingsController) {
    let s = controller.settings.borrow();

    // --- cache ---------------------------------------------------------
    window.set_settings_original_budget(budget::label(s.cache.original_budget_bytes).into());
    window.set_settings_original_unlimited(s.cache.original_budget_bytes.is_none());
    window.set_settings_thumbnail_budget(budget::label(s.cache.thumbnail_budget_bytes).into());
    window.set_settings_thumbnail_unlimited(s.cache.thumbnail_budget_bytes.is_none());
    window.set_settings_keep_opened(s.cache.keep_opened_originals);
    window.set_settings_copy_includes_framing(s.develop.copy_includes_framing);
    window.set_settings_cache_usage(controller.usage_label.borrow().clone().into());

    // --- export --------------------------------------------------------
    //
    // Choice rows are sent as labels plus the selected index rather than as a
    // model of structs: the page draws a row of chips from them and nothing
    // else, so a label and an index is the whole of what it needs.
    window.set_settings_format_labels(labels(ExportFormat::ALL.iter().map(|f| f.label())));
    window.set_settings_format_selected(index_of(&ExportFormat::ALL, &s.export.format));

    window.set_settings_quality(s.export.quality as i32);
    // Disabled rather than hidden for a lossless format: a control that
    // vanishes when PNG is picked reads as a bug, where a greyed one explains
    // itself.
    window.set_settings_quality_enabled(s.export.format.is_lossy());

    window.set_settings_colour_labels(labels(ColourSpace::ALL.iter().map(|c| c.label())));
    window.set_settings_colour_selected(index_of(&ColourSpace::ALL, &s.export.colour_space));

    window.set_settings_sizing_labels(labels(SizingMode::CHOICES.iter().map(|m| m.label())));
    // Compared by variant, not by equality: `LongEdge(900)` after the user
    // typed their own number is still the "Long edge" choice, and equality
    // against `CHOICES` would light nothing.
    window.set_settings_sizing_selected(
        SizingMode::CHOICES
            .iter()
            .position(|m| m.same_mode(s.export.sizing))
            .unwrap_or(0) as i32,
    );
    window.set_settings_sizing_value(s.export.sizing.value().unwrap_or(0) as i32);
    // `Original` carries no number, so the field beside the chips has nothing
    // to edit and is hidden rather than shown holding a meaningless zero.
    window.set_settings_sizing_has_value(s.export.sizing.value().is_some());
    window.set_settings_sizing_unit(
        match s.export.sizing {
            SizingMode::Percentage(_) => "%",
            _ => "px",
        }
        .into(),
    );
    window.set_settings_allow_upscaling(s.export.allow_upscaling);

    window.set_settings_sharpening_labels(labels(OutputSharpening::ALL.iter().map(|x| x.label())));
    window.set_settings_sharpening_selected(index_of(&OutputSharpening::ALL, &s.export.sharpening));

    window.set_settings_filename_template(s.export.filename_template.clone().into());
    window.set_settings_collision_labels(labels(CollisionPolicy::ALL.iter().map(|c| c.label())));
    window.set_settings_collision_selected(index_of(&CollisionPolicy::ALL, &s.export.collision));
    window.set_settings_strip_location(s.export.strip_location);

    // `available()`, not `ALL`: Android cannot write to a device folder, and
    // offering a target that fails at the last step is what made export look
    // broken there rather than absent.
    let targets = ExportTarget::available();
    window.set_settings_target_labels(labels(targets.iter().map(|t| t.label())));
    window.set_settings_target_selected(index_of(targets, &s.export.target));
    window.set_settings_destination(s.export.active_destination().into());
    // Derived from the target itself, never from its position in a list whose
    // length differs by platform.
    window.set_settings_browse_available(s.export.target.is_remote());
    // The field means different things either side of the choice, and a
    // placeholder saying which is cheaper than a paragraph under it.
    // The placeholder names what an empty field *means*, which differs by
    // target: on a filesystem it is a question, on the server it is the
    // library root.
    window.set_settings_destination_hint(s.export.destination_label().into());

    // --- the remote folder picker --------------------------------------
    {
        let browser = controller.browser.borrow();
        window.set_settings_browse_open(browser.is_some());
        match browser.as_ref() {
            Some(b) => {
                // The root is shown as a word rather than as an empty string,
                // which would read as a control that had lost its value.
                window.set_settings_browse_path(
                    if b.path.is_empty() {
                        "Library root".to_string()
                    } else {
                        b.path.clone()
                    }
                    .into(),
                );
                window.set_settings_browse_loading(b.loading);
                window.set_settings_browse_at_root(b.parent_path().is_none());
                window.set_settings_browse_entries(slint::ModelRc::new(slint::VecModel::from(
                    b.entries
                        .iter()
                        .map(|e| slint::SharedString::from(e.as_str()))
                        .collect::<Vec<_>>(),
                )));
            }
            None => {
                window.set_settings_browse_entries(slint::ModelRc::new(slint::VecModel::from(
                    Vec::<slint::SharedString>::new(),
                )));
                window.set_settings_browse_loading(false);
            }
        }
    }

    window.set_settings_error(controller.error.borrow().clone().unwrap_or_default().into());
}

/// A label list as a Slint model.
fn labels<'a>(items: impl Iterator<Item = &'a str>) -> slint::ModelRc<slint::SharedString> {
    let v: Vec<slint::SharedString> = items.map(slint::SharedString::from).collect();
    slint::ModelRc::new(slint::VecModel::from(v))
}

/// Where `value` sits in `all`, as the index the page selects by.
fn index_of<T: PartialEq>(all: &[T], value: &T) -> i32 {
    all.iter().position(|v| v == value).unwrap_or(0) as i32
}

/// Connect the page's callbacks.
///
/// `on_budget_changed` runs when a cache ceiling moves, so the caller can
/// enforce it against the catalog — this module has no connection and must not
/// grow one.
pub fn wire<F>(window: &AppWindow, controller: Rc<SettingsController>, on_budget_changed: F)
where
    F: Fn(&Settings) + 'static,
{
    let on_budget_changed = Rc::new(on_budget_changed);

    // --- opening and closing -------------------------------------------
    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        window.on_settings_open(move || {
            let Some(w) = weak.upgrade() else { return };
            // Re-read from disk on open rather than trusting the copy in
            // memory: another instance of the app may have written the file
            // since, and showing a stale value would let this window save it
            // back over the newer one.
            *ctl.settings.borrow_mut() = ctl.store.load();
            render(&w, &ctl);
            w.set_show_settings(true);
        });
    }

    {
        let weak = window.as_weak();
        window.on_settings_close(move || {
            let Some(w) = weak.upgrade() else { return };
            w.set_show_settings(false);
        });
    }

    // --- cache ---------------------------------------------------------
    //
    // A budget arrives as typed text. An unparseable entry leaves the previous
    // value in place and `render` puts the stored one back in the field, so a
    // typo is visibly rejected rather than silently shrinking a cache.
    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        let notify = on_budget_changed.clone();
        window.on_settings_original_budget_changed(move |text| {
            let Some(w) = weak.upgrade() else { return };
            if let Some(bytes) = budget::from_gb(&text) {
                ctl.edit(|s| s.cache.original_budget_bytes = Some(bytes));
                notify(&ctl.snapshot());
            } else {
                log::debug!("ignoring an unusable cache budget: {text:?}");
            }
            render(&w, &ctl);
        });
    }

    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        let notify = on_budget_changed.clone();
        window.on_settings_original_unlimited_toggled(move |unlimited| {
            let Some(w) = weak.upgrade() else { return };
            ctl.edit(|s| {
                s.cache.original_budget_bytes = if unlimited {
                    None
                } else {
                    // Back to the default rather than to whatever it was
                    // before: the previous figure is not kept while unlimited
                    // is on, and inventing one would be a guess. The default is
                    // at least a documented number.
                    Some(dr_types::settings::DEFAULT_ORIGINAL_BUDGET_BYTES)
                };
            });
            notify(&ctl.snapshot());
            render(&w, &ctl);
        });
    }

    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        let notify = on_budget_changed.clone();
        window.on_settings_thumbnail_budget_changed(move |text| {
            let Some(w) = weak.upgrade() else { return };
            if let Some(bytes) = budget::from_gb(&text) {
                ctl.edit(|s| s.cache.thumbnail_budget_bytes = Some(bytes));
                notify(&ctl.snapshot());
            }
            render(&w, &ctl);
        });
    }

    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        let notify = on_budget_changed.clone();
        window.on_settings_thumbnail_unlimited_toggled(move |unlimited| {
            let Some(w) = weak.upgrade() else { return };
            ctl.edit(|s| {
                s.cache.thumbnail_budget_bytes = if unlimited {
                    None
                } else {
                    Some(dr_types::settings::DEFAULT_THUMBNAIL_BUDGET_BYTES)
                };
            });
            notify(&ctl.snapshot());
            render(&w, &ctl);
        });
    }

    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        window.on_settings_keep_opened_toggled(move |on| {
            let Some(w) = weak.upgrade() else { return };
            ctl.edit(|s| s.cache.keep_opened_originals = on);
            render(&w, &ctl);
        });
    }

    // --- export --------------------------------------------------------
    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        window.on_settings_format_picked(move |i| {
            let Some(w) = weak.upgrade() else { return };
            if let Some(f) = ExportFormat::ALL.get(i as usize).copied() {
                ctl.edit(|s| s.export.format = f);
            }
            render(&w, &ctl);
        });
    }

    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        window.on_settings_quality_changed(move |q| {
            let Some(w) = weak.upgrade() else { return };
            // Cast before clamping: a negative from the control would wrap to a
            // large `u8` and land on 100 instead of the floor.
            ctl.edit(|s| s.export.quality = q.clamp(1, 100) as u8);
            render(&w, &ctl);
        });
    }

    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        window.on_settings_colour_picked(move |i| {
            let Some(w) = weak.upgrade() else { return };
            if let Some(c) = ColourSpace::ALL.get(i as usize).copied() {
                ctl.edit(|s| s.export.colour_space = c);
            }
            render(&w, &ctl);
        });
    }

    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        window.on_settings_sizing_picked(move |i| {
            let Some(w) = weak.upgrade() else { return };
            if let Some(mode) = SizingMode::CHOICES.get(i as usize).copied() {
                // Keeps the number the user already typed when they move
                // between two sized modes: switching long edge to short edge
                // at 900px means 900 on the other axis, not back to 1600.
                ctl.edit(|s| {
                    s.export.sizing = match s.export.sizing.value() {
                        Some(v) => mode.with_value(v),
                        None => mode,
                    };
                });
            }
            render(&w, &ctl);
        });
    }

    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        window.on_settings_sizing_value_changed(move |text| {
            let Some(w) = weak.upgrade() else { return };
            match text.trim().parse::<u32>() {
                Ok(v) if v > 0 => ctl.edit(|s| s.export.sizing = s.export.sizing.with_value(v)),
                _ => log::debug!("ignoring an unusable export size: {text:?}"),
            }
            render(&w, &ctl);
        });
    }

    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        window.on_settings_upscaling_toggled(move |on| {
            let Some(w) = weak.upgrade() else { return };
            ctl.edit(|s| s.export.allow_upscaling = on);
            render(&w, &ctl);
        });
    }

    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        window.on_settings_sharpening_picked(move |i| {
            let Some(w) = weak.upgrade() else { return };
            if let Some(x) = OutputSharpening::ALL.get(i as usize).copied() {
                ctl.edit(|s| s.export.sharpening = x);
            }
            render(&w, &ctl);
        });
    }

    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        window.on_settings_template_changed(move |text| {
            let Some(w) = weak.upgrade() else { return };
            ctl.edit(|s| s.export.filename_template = text.to_string());
            render(&w, &ctl);
        });
    }

    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        window.on_settings_collision_picked(move |i| {
            let Some(w) = weak.upgrade() else { return };
            if let Some(c) = CollisionPolicy::ALL.get(i as usize).copied() {
                ctl.edit(|s| s.export.collision = c);
            }
            render(&w, &ctl);
        });
    }

    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        window.on_settings_strip_location_toggled(move |on| {
            let Some(w) = weak.upgrade() else { return };
            ctl.edit(|s| s.export.strip_location = on);
            render(&w, &ctl);
        });
    }

    // TRACES: FR-DEV-6
    // Whether a copied edit carries the crop. Off by default — see
    // `DevelopSettings::copy_includes_framing` for why that is the safe
    // direction rather than merely the conservative one.
    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        window.on_settings_copy_includes_framing_toggled(move |on| {
            let Some(w) = weak.upgrade() else { return };
            ctl.edit(|s| s.develop.copy_includes_framing = on);
            render(&w, &ctl);
        });
    }

    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        window.on_settings_destination_changed(move |text| {
            let Some(w) = weak.upgrade() else { return };
            ctl.edit(|s| s.export.set_active_destination(text.to_string()));
            render(&w, &ctl);
        });
    }

    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        window.on_settings_target_changed(move |i| {
            let Some(w) = weak.upgrade() else { return };
            if let Some(&t) = ExportTarget::available().get(i.max(0) as usize) {
                // Nothing is cleared. Each target keeps its own destination
                // (see `ExportSettings::remote_destination`), so switching to
                // look at the other option no longer throws away the one
                // already set — which is what made this setting appear not to
                // stick.
                ctl.edit(|s| s.export.target = t);
            }
            render(&w, &ctl);
        });
    }

    // --- reset ---------------------------------------------------------
    {
        let weak = window.as_weak();
        let ctl = controller.clone();
        let notify = on_budget_changed.clone();
        window.on_settings_reset(move || {
            let Some(w) = weak.upgrade() else { return };
            ctl.edit(|s| *s = Settings::default());
            notify(&ctl.snapshot());
            render(&w, &ctl);
        });
    }
}

/// TRACES: FR-EXP-6
/// List the folders under `path`, for the export destination picker.
///
/// A near-twin of `launch_ui::spawn_folder_list` and deliberately not shared
/// with it. That one reaches into the `LaunchController` for its session and
/// reports failures onto the launch screen's error line; this one is handed
/// credentials and writes to the settings page. Factoring them together would
/// mean a function taking both controllers, or a trait implemented twice to
/// abstract two call sites — more machinery than the twenty lines it saves.
///
/// The *model* is shared, which is the part that matters: both drive a
/// [`FolderBrowser`](crate::launch::FolderBrowser), so navigation behaves
/// identically in both places.
pub fn spawn_folder_list(
    weak: slint::Weak<AppWindow>,
    ctl: Rc<SettingsController>,
    creds: dr_sync_nextcloud::AppCredentials,
    user_id: String,
    path: String,
) {
    use dr_sync::{RemoteBackend, RemotePath};
    use dr_sync_nextcloud::NextcloudBackend;

    let (tx, rx) = std::sync::mpsc::channel::<Result<Vec<String>, String>>();

    std::thread::spawn(move || {
        // Multi-thread, for the reason the login worker records: a
        // current-thread runtime left reqwest's connection future unpolled on
        // Android, and the await never resolved.
        let rt = tokio::runtime::Builder::new_multi_thread()
            .worker_threads(1)
            .enable_io()
            .enable_time()
            .build();
        let Ok(rt) = rt else {
            let _ = tx.send(Err("runtime".into()));
            return;
        };
        rt.block_on(async {
            match NextcloudBackend::new(&creds, &user_id) {
                Ok(b) => match b.list(&RemotePath::new(&path), None).await {
                    Ok(entries) => {
                        let mut dirs: Vec<String> = entries
                            .iter()
                            .filter(|e| e.kind == dr_sync::EntryKind::Directory)
                            .map(|e| e.path.name().to_string())
                            .collect();
                        dirs.sort_by_key(|d| d.to_ascii_lowercase());
                        let _ = tx.send(Ok(dirs));
                    }
                    Err(e) => {
                        let _ = tx.send(Err(e.to_string()));
                    }
                },
                Err(e) => {
                    let _ = tx.send(Err(e.to_string()));
                }
            }
        });
    });

    let timer = slint::Timer::default();
    let ctl_cb = ctl.clone();
    timer.start(
        slint::TimerMode::Repeated,
        std::time::Duration::from_millis(150),
        move || {
            let Some(w) = weak.upgrade() else { return };
            match rx.try_recv() {
                Ok(Ok(dirs)) => {
                    if let Some(b) = ctl_cb.browser.borrow_mut().as_mut() {
                        b.entries = dirs;
                        b.loading = false;
                    }
                    render(&w, &ctl_cb);
                }
                Ok(Err(e)) => {
                    // The picker stays open showing the folder it was on. A
                    // listing that failed is not a reason to discard where the
                    // user had navigated to.
                    if let Some(b) = ctl_cb.browser.borrow_mut().as_mut() {
                        b.loading = false;
                    }
                    *ctl_cb.error.borrow_mut() = Some(format!("Could not list folders: {e}"));
                    render(&w, &ctl_cb);
                }
                Err(std::sync::mpsc::TryRecvError::Empty) => return,
                Err(std::sync::mpsc::TryRecvError::Disconnected) => {
                    if let Some(b) = ctl_cb.browser.borrow_mut().as_mut() {
                        b.loading = false;
                    }
                    render(&w, &ctl_cb);
                }
            }
            // The channel has delivered, so there is nothing left to poll
            // for. Stopping it here rather than leaving it running is what
            // keeps a page opened and closed twenty times from accumulating
            // twenty timers.
            if let Some(t) = ctl_cb.poll_timer.borrow().as_ref() {
                t.stop();
            }
        },
    );
    *ctl.poll_timer.borrow_mut() = Some(timer);
}

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

    /// A controller writing to a scratch file, with no window attached.
    ///
    /// The edit-and-persist path is what is worth testing here and it needs no
    /// display server; `render` and `wire` are the parts that need a window,
    /// and they only move values.
    fn controller(name: &str) -> Rc<SettingsController> {
        let dir = std::env::temp_dir().join(format!(
            "dr-settings-ui-{name}-{}-{:?}",
            std::process::id(),
            std::thread::current().id()
        ));
        let _ = std::fs::remove_dir_all(&dir);
        std::fs::create_dir_all(&dir).unwrap();

        let store = SettingsStore::open_at(dir.join("settings.json"));
        Rc::new(SettingsController {
            settings: RefCell::new(store.load()),
            store,
            error: RefCell::new(None),
            usage_label: RefCell::new(String::new()),
            browser: RefCell::new(None),
            poll_timer: RefCell::new(None),
        })
    }

    #[test]
    fn an_edit_reaches_the_file_without_a_save_button() {
        let ctl = controller("autosave");
        ctl.edit(|s| s.export.quality = 60);
        assert_eq!(ctl.store.load().export.quality, 60);
    }

    #[test]
    fn an_edit_is_sanitised_before_it_is_stored() {
        let ctl = controller("sanitise");
        ctl.edit(|s| s.export.quality = 200);
        assert_eq!(ctl.snapshot().export.quality, 100);
        assert_eq!(ctl.store.load().export.quality, 100);
    }

    #[test]
    fn two_edits_do_not_overwrite_each_other() {
        // The reason `edit` takes a closure: a caller holding a whole
        // `Settings` would write back its own stale copy of every other field.
        let ctl = controller("independent");
        ctl.edit(|s| s.export.quality = 70);
        ctl.edit(|s| s.export.format = ExportFormat::Png);

        let stored = ctl.store.load();
        assert_eq!(stored.export.quality, 70);
        assert_eq!(stored.export.format, ExportFormat::Png);
    }

    #[test]
    fn a_reset_restores_the_defaults_and_persists_them() {
        let ctl = controller("reset");
        ctl.edit(|s| {
            s.export.quality = 10;
            s.cache.original_budget_bytes = None;
        });
        ctl.edit(|s| *s = Settings::default());

        assert_eq!(ctl.store.load(), Settings::default());
    }

    #[test]
    fn switching_between_sized_modes_keeps_the_typed_number() {
        let ctl = controller("sizing");
        ctl.edit(|s| s.export.sizing = SizingMode::LongEdge(900));
        // What `on_settings_sizing_picked` does for a sized target.
        ctl.edit(|s| {
            s.export.sizing = match s.export.sizing.value() {
                Some(v) => SizingMode::ShortEdge(0).with_value(v),
                None => SizingMode::ShortEdge(1600),
            }
        });
        assert_eq!(ctl.snapshot().export.sizing, SizingMode::ShortEdge(900));
    }

    #[test]
    fn a_write_failure_is_recorded_rather_than_swallowed() {
        // The page's contract is that what it shows is saved, so a failed
        // write has to be visible.
        let ctl = controller("unwritable");
        // A path whose parent is a *file* cannot be created as a directory.
        let blocker = ctl.store.path().with_file_name("blocker");
        std::fs::write(&blocker, b"not a directory").unwrap();
        let broken = SettingsController {
            settings: RefCell::new(Settings::default()),
            store: SettingsStore::open_at(blocker.join("settings.json")),
            error: RefCell::new(None),
            usage_label: RefCell::new(String::new()),
            browser: RefCell::new(None),
            poll_timer: RefCell::new(None),
        };

        broken.edit(|s| s.export.quality = 50);
        assert!(broken.error.borrow().is_some(), "the failure was silent");
    }

    #[test]
    fn a_successful_write_clears_an_earlier_error() {
        let ctl = controller("clears");
        *ctl.error.borrow_mut() = Some("stale".to_string());
        ctl.edit(|s| s.export.quality = 80);
        assert_eq!(*ctl.error.borrow(), None);
    }
}