mach-tui 0.7.0

//! The task dialog — title, description, due date and subtasks — used for
//! both creating and editing a task.

use std::time::Instant;

use ratatui::layout::Rect;

use crate::description::DescriptionEditor;
use crate::due;
use crate::duepicker::DuePicker;
use crate::image::{GifLoad, GifPlayback, TemporaryImage};
use crate::model::{Block, Category, Label, LabelColor, MAX_LABELS_PER_TASK, MAX_TITLE_LEN, Task};
use crate::text_input::TextInput;
use crate::undo::{EditKind, History};

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Field {
    Title,
    Category,
    Labels,
    Due,
    Importance,
    Description,
}

impl Field {
    /// Tab order follows the layout: title, metadata, then description.
    pub fn next(self) -> Self {
        match self {
            Self::Title => Self::Category,
            Self::Category => Self::Labels,
            Self::Labels => Self::Due,
            Self::Due => Self::Importance,
            Self::Importance => Self::Description,
            Self::Description => Self::Title,
        }
    }

    pub fn prev(self) -> Self {
        match self {
            Self::Title => Self::Description,
            Self::Category => Self::Title,
            Self::Labels => Self::Category,
            Self::Due => Self::Labels,
            Self::Importance => Self::Due,
            Self::Description => Self::Importance,
        }
    }
}

/// Editable content of the category dialog (for undo).
#[derive(Debug, Clone, PartialEq, Eq)]
struct CategorySnap {
    name: TextInput,
    description: DescriptionEditor,
    on_description: bool,
}

/// The category dialog: a name and a text-only description of what it is for.
pub struct CategoryForm {
    pub name: TextInput,
    pub description: DescriptionEditor,
    pub on_description: bool,
    pub error: Option<String>,
    /// The category being edited; `None` when creating one.
    pub editing: Option<String>,
    /// Full modal rectangle from the last frame, including its chrome.
    pub form_area: Rect,
    pub name_area: Rect,
    pub description_area: Rect,
    /// Screen rect of the open description `/` dropdown.
    pub description_menu_area: Option<Rect>,
    history: History<CategorySnap>,
    initial_name: String,
    initial_description: String,
}

impl CategoryForm {
    pub fn new() -> Self {
        Self {
            name: TextInput::new("", crate::model::MAX_CATEGORY_NAME_LEN),
            description: DescriptionEditor::plain(""),
            on_description: false,
            error: None,
            editing: None,
            form_area: Rect::ZERO,
            name_area: Rect::ZERO,
            description_area: Rect::ZERO,
            description_menu_area: None,
            history: History::new(),
            initial_name: String::new(),
            initial_description: String::new(),
        }
    }

    pub fn edit(category: &crate::model::Category) -> Self {
        Self {
            name: TextInput::new(&category.name, crate::model::MAX_CATEGORY_NAME_LEN),
            description: DescriptionEditor::plain(&category.description),
            editing: Some(category.id.clone()),
            initial_name: category.name.clone(),
            initial_description: category.description.clone(),
            ..Self::new()
        }
    }

    pub fn title_text(&self) -> &'static str {
        if self.editing.is_some() {
            "Edit category"
        } else {
            "New category"
        }
    }

    pub fn toggle_field(&mut self) {
        self.set_description_focus(!self.on_description);
    }

    /// Focus a particular field while preserving undo coalescing boundaries.
    pub fn set_description_focus(&mut self, description: bool) {
        if self.on_description != description {
            self.history.break_coalesce();
            self.on_description = description;
        }
    }

    pub fn is_dirty(&self) -> bool {
        self.name.value() != self.initial_name
            || self.description.plain_value() != self.initial_description
    }

    fn snap(&self) -> CategorySnap {
        CategorySnap {
            name: self.name.clone(),
            description: self.description.clone(),
            on_description: self.on_description,
        }
    }

    fn restore(&mut self, s: CategorySnap) {
        self.name = s.name;
        self.description = s.description;
        self.on_description = s.on_description;
        self.error = None;
    }

    /// Snapshot before a content edit.
    pub fn before_edit(&mut self, kind: EditKind) {
        let Self {
            name,
            description,
            on_description,
            history,
            ..
        } = self;
        history.before_edit_with(kind, || CategorySnap {
            name: name.clone(),
            description: description.clone(),
            on_description: *on_description,
        });
    }

    pub fn break_coalesce(&mut self) {
        self.history.break_coalesce();
    }

    pub fn undo(&mut self) -> bool {
        let Some(prev) = self.history.undo(self.snap()) else {
            return false;
        };
        self.restore(prev);
        true
    }

    pub fn redo(&mut self) -> bool {
        let Some(next) = self.history.redo(self.snap()) else {
            return false;
        };
        self.restore(next);
        true
    }

    /// `(name, description)` once there is a name to save.
    pub fn submit(&mut self) -> Option<(String, String)> {
        self.submit_with(|_, _| Ok(()))
    }

    /// Validate and submit through a caller-provided uniqueness/policy hook.
    /// The hook receives the normalized name and the edited category id.
    pub fn submit_with<F>(&mut self, validate_name: F) -> Option<(String, String)>
    where
        F: FnOnce(&str, Option<&str>) -> Result<(), String>,
    {
        let name = self.name.value().trim().to_string();
        if name.is_empty() {
            self.error = Some("A name is required".to_string());
            self.on_description = false;
            return None;
        }
        if let Err(error) = validate_name(&name, self.editing.as_deref()) {
            self.error = Some(error);
            self.on_description = false;
            return None;
        }
        self.error = None;
        Some((name, self.description.plain_value()))
    }
}

impl Default for CategoryForm {
    fn default() -> Self {
        Self::new()
    }
}

/// Where each field's box landed in the last frame, so a click can find
/// the field under the pointer.
#[derive(Debug, Default, Clone, Copy)]
pub struct FieldAreas {
    pub title: Rect,
    pub category: Rect,
    pub labels: Rect,
    pub due: Rect,
    pub importance: Rect,
    pub description: Rect,
}

impl FieldAreas {
    pub fn field_at(&self, x: u16, y: u16) -> Option<Field> {
        let pos = ratatui::layout::Position { x, y };
        if self.title.contains(pos) {
            Some(Field::Title)
        } else if self.category.contains(pos) {
            Some(Field::Category)
        } else if self.labels.contains(pos) {
            Some(Field::Labels)
        } else if self.due.contains(pos) {
            Some(Field::Due)
        } else if self.importance.contains(pos) {
            Some(Field::Importance)
        } else if self.description.contains(pos) {
            Some(Field::Description)
        } else {
            None
        }
    }

    pub fn rect(&self, field: Field) -> Rect {
        match field {
            Field::Title => self.title,
            Field::Category => self.category,
            Field::Labels => self.labels,
            Field::Due => self.due,
            Field::Importance => self.importance,
            Field::Description => self.description,
        }
    }
}

/// The values a submitted form hands back to the app.
#[derive(Debug, Clone, Default, PartialEq)]
pub struct TaskDraft {
    pub title: String,
    /// Real category UUID, or `None` for Uncategorized.
    pub category_id: Option<String>,
    /// Stable label IDs, kept in the global label order.
    pub label_ids: Vec<String>,
    pub due: String,
    pub importance: u8,
    pub description: Vec<Block>,
}

impl TaskDraft {
    pub fn new(title: &str) -> Self {
        Self {
            title: title.to_string(),
            ..Self::default()
        }
    }

    pub(crate) fn resolved_title_and_due(&self) -> (String, String) {
        let (inline_due, title) = due::parse(self.title.trim());
        let due = if self.due.is_empty() {
            inline_due
        } else {
            self.due.clone()
        };
        (title, due)
    }
}

/// Editable content of the task dialog (for undo). UI chrome is excluded.
#[derive(Debug, Clone, PartialEq, Eq)]
struct TaskSnap {
    title: TextInput,
    category_id: Option<String>,
    label_ids: Vec<String>,
    due: TextInput,
    importance: u8,
    description: DescriptionEditor,
    field: Field,
}

#[derive(Debug, Clone, PartialEq, Eq)]
struct CategoryChoice {
    id: Option<String>,
    name: String,
}

#[derive(Debug, Clone, PartialEq, Eq)]
struct LabelChoice {
    id: String,
    name: String,
    color: LabelColor,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct LabelPicker {
    pub index: usize,
    area: Rect,
    start: usize,
}

impl CategoryChoice {
    fn uncategorized() -> Self {
        Self {
            id: None,
            name: "Uncategorized".to_string(),
        }
    }
}

pub struct TaskForm {
    pub title: TextInput,
    category_id: Option<String>,
    category_choices: Vec<CategoryChoice>,
    label_ids: Vec<String>,
    label_choices: Vec<LabelChoice>,
    pub due: TextInput,
    pub importance: u8,
    pub description: DescriptionEditor,
    pub field: Field,
    pub error: Option<String>,
    /// The task being edited; `None` when creating a new one.
    pub editing: Option<String>,
    /// Filled in while drawing; used to hit-test clicks.
    pub areas: FieldAreas,
    /// Full editor rectangle from the last frame, including its chrome.
    pub form_area: Rect,
    /// Whether the description's image is shown full size.
    pub preview: bool,
    /// Decoded GIF for preview, keyed by path (kept after close for fast reopen).
    pub gif: Option<(std::path::PathBuf, GifPlayback)>,
    /// GIF decode in progress; polled by the normal animation tick.
    pub gif_pending: Option<GifLoad>,
    /// The calendar, while a due date is being picked.
    pub picker: Option<DuePicker>,
    /// The bounded multi-select list, while Labels is being edited.
    pub label_picker: Option<LabelPicker>,
    /// Last description click (line index), for double-click to open a picture.
    pub last_description_click: Option<(Instant, usize)>,
    /// Description scroll after last paint — scroll changes need the same protocol
    /// drop as menu close so pictures that shrink/move do not ghost.
    pub description_scroll: usize,
    /// Screen rect of the open description `/` dropdown (for mouse hit-testing).
    pub description_menu_area: Option<Rect>,
    /// Where each description picture was drawn last frame: `(line index, screen rect)`.
    /// Clicks only select a picture when they land inside this rect — not the
    /// full-width letterbox gutter.
    pub image_hits: Vec<(usize, Rect)>,
    /// Overlay rectangles that occluded description images last frame.
    /// Changes require graphics placements to be emitted again.
    pub(crate) image_occlusions: Vec<Rect>,
    pub(crate) image_layout: Vec<(std::path::PathBuf, u16, u16)>,
    history: History<TaskSnap>,
    initial: TaskDraft,
    temporary_images: Vec<TemporaryImage>,
}

impl TaskForm {
    pub fn new() -> Self {
        Self::new_with_images(crate::image::default_images_root(), &[])
    }

    pub fn new_with_images(
        image_root: std::path::PathBuf,
        attachments: &[crate::store::Attachment],
    ) -> Self {
        Self::with_description(DescriptionEditor::new_with_images(
            &[],
            image_root,
            attachments,
        ))
    }

    fn with_description(description: DescriptionEditor) -> Self {
        Self {
            title: TextInput::new("", MAX_TITLE_LEN),
            category_id: None,
            category_choices: vec![CategoryChoice::uncategorized()],
            label_ids: Vec::new(),
            label_choices: Vec::new(),
            due: TextInput::new("", 32),
            importance: 0,
            description,
            field: Field::Title,
            error: None,
            editing: None,
            areas: FieldAreas::default(),
            form_area: Rect::ZERO,
            preview: false,
            gif: None,
            gif_pending: None,
            picker: None,
            label_picker: None,
            last_description_click: None,
            description_scroll: 0,
            description_menu_area: None,
            image_hits: Vec::new(),
            image_occlusions: Vec::new(),
            image_layout: Vec::new(),
            history: History::new(),
            initial: TaskDraft::default(),
            temporary_images: Vec::new(),
        }
    }

    pub fn edit(task: &Task) -> Self {
        Self::edit_with_images(task, crate::image::default_images_root(), &[])
    }

    pub fn edit_with_images(
        task: &Task,
        image_root: std::path::PathBuf,
        attachments: &[crate::store::Attachment],
    ) -> Self {
        let description =
            DescriptionEditor::new_with_images(&task.description, image_root, attachments);
        let initial_description = description.value();
        let mut form = Self::with_description(description);
        form.title = TextInput::new(&task.title, MAX_TITLE_LEN);
        form.category_id = task.category_id.clone();
        form.label_ids = task.label_ids.clone();
        form.due = TextInput::new(&task.due, 32);
        form.importance = task.importance;
        form.editing = Some(task.id.clone());
        form.initial = TaskDraft {
            title: task.title.clone(),
            category_id: task.category_id.clone(),
            label_ids: task.label_ids.clone(),
            due: task.due.clone(),
            importance: task.importance,
            description: initial_description,
        };
        form
    }

    /// Whether `(x, y)` sits on the drawn picture for description line `line`.
    pub fn image_hit_at(&self, line: usize, x: u16, y: u16) -> bool {
        use ratatui::layout::Position;
        self.image_hits
            .iter()
            .any(|(i, r)| *i == line && r.contains(Position { x, y }))
    }

    pub fn set_image_root(&mut self, image_root: std::path::PathBuf) {
        self.description.set_image_root(image_root);
    }

    pub fn set_attachments(&mut self, attachments: &[crate::store::Attachment]) {
        self.description.set_attachments(attachments);
    }

    /// Install the real categories available to this form and select the
    /// task's starting category. `All tasks` is a view, not a destination;
    /// Uncategorized is always the first choice.
    ///
    /// Call this once when opening the form, before the user edits it. The
    /// selected value becomes part of the dirty-state baseline.
    pub fn set_categories(&mut self, categories: &[Category], selected_id: Option<&str>) {
        self.category_choices.clear();
        self.category_choices.push(CategoryChoice::uncategorized());
        self.category_choices
            .extend(
                categories
                    .iter()
                    .filter(|category| !category.is_all())
                    .map(|category| CategoryChoice {
                        id: Some(category.id.clone()),
                        name: category.name.clone(),
                    }),
            );
        self.category_id = selected_id
            .filter(|id| {
                self.category_choices
                    .iter()
                    .any(|choice| choice.id.as_deref() == Some(*id))
            })
            .map(str::to_string);
        self.initial.category_id = self.category_id.clone();
    }

    pub fn category_id(&self) -> Option<&str> {
        self.category_id.as_deref()
    }

    pub fn category_label(&self) -> &str {
        self.category_choices
            .iter()
            .find(|choice| choice.id.as_deref() == self.category_id.as_deref())
            .map(|choice| choice.name.as_str())
            .unwrap_or("Uncategorized")
    }

    /// Select the previous/next category, wrapping at either end.
    pub fn cycle_category(&mut self, delta: i32) {
        let len = self.category_choices.len();
        if len <= 1 {
            return;
        }
        let current = self
            .category_choices
            .iter()
            .position(|choice| choice.id.as_deref() == self.category_id.as_deref())
            .unwrap_or_default();
        let next = (current as i32 + delta).rem_euclid(len as i32) as usize;
        if next == current {
            return;
        }
        self.before_edit(EditKind::Atomic);
        self.category_id = self.category_choices[next].id.clone();
    }

    pub fn clear_category(&mut self) {
        if self.category_id.is_none() {
            return;
        }
        self.before_edit(EditKind::Atomic);
        self.category_id = None;
    }

    /// Install the global label vocabulary and canonicalize this task's
    /// selected IDs into that same order. Call once when opening the form.
    pub fn set_labels(&mut self, labels: &[Label], selected_ids: &[String]) {
        self.label_choices = labels
            .iter()
            .map(|label| LabelChoice {
                id: label.id.clone(),
                name: label.name.clone(),
                color: label.color,
            })
            .collect();
        self.label_ids = self
            .label_choices
            .iter()
            .filter(|choice| selected_ids.contains(&choice.id))
            .map(|choice| choice.id.clone())
            .collect();
        self.initial.label_ids = self.label_ids.clone();
    }

    /// Refresh the global vocabulary without discarding this form's draft or
    /// undo history. Deleted IDs are removed and surviving IDs follow global
    /// label order in every snapshot.
    pub fn refresh_labels(&mut self, labels: &[Label]) {
        self.label_choices = labels
            .iter()
            .map(|label| LabelChoice {
                id: label.id.clone(),
                name: label.name.clone(),
                color: label.color,
            })
            .collect();
        let order = self
            .label_choices
            .iter()
            .map(|choice| choice.id.clone())
            .collect::<Vec<_>>();
        let canonicalize = |ids: &mut Vec<String>| {
            *ids = order
                .iter()
                .filter(|id| ids.contains(id))
                .cloned()
                .collect();
        };
        canonicalize(&mut self.label_ids);
        canonicalize(&mut self.initial.label_ids);
        self.history
            .for_each_mut(|snapshot| canonicalize(&mut snapshot.label_ids));
    }

    pub fn label_ids(&self) -> &[String] {
        &self.label_ids
    }

    pub fn selected_labels(&self) -> Vec<(&str, LabelColor)> {
        self.label_choices
            .iter()
            .filter(|choice| self.label_ids.contains(&choice.id))
            .map(|choice| (choice.name.as_str(), choice.color))
            .collect()
    }

    pub fn label_choices(&self) -> impl Iterator<Item = (&str, &str, LabelColor, bool)> {
        self.label_choices.iter().map(|choice| {
            (
                choice.id.as_str(),
                choice.name.as_str(),
                choice.color,
                self.label_ids.contains(&choice.id),
            )
        })
    }

    pub fn label_picker_open(&self) -> bool {
        self.label_picker.is_some()
    }

    pub fn open_label_picker(&mut self) {
        self.history.break_coalesce();
        self.field = Field::Labels;
        self.picker = None;
        self.description.close_menu();
        let index = self
            .label_choices
            .iter()
            .position(|choice| self.label_ids.contains(&choice.id))
            .unwrap_or_default();
        self.label_picker = Some(LabelPicker {
            index,
            area: Rect::default(),
            start: 0,
        });
    }

    pub fn close_label_picker(&mut self) {
        self.label_picker = None;
    }

    pub(crate) fn set_label_picker_layout(&mut self, area: Rect, start: usize) {
        if let Some(picker) = &mut self.label_picker {
            picker.area = area;
            picker.start = start;
        }
    }

    pub fn label_picker_area(&self) -> Option<Rect> {
        self.label_picker.as_ref().map(|picker| picker.area)
    }

    pub(crate) fn label_picker_row_at(&self, x: u16, y: u16) -> Option<usize> {
        let picker = self.label_picker.as_ref()?;
        if !picker.area.contains(ratatui::layout::Position { x, y })
            || y <= picker.area.y
            || y >= picker.area.bottom().saturating_sub(1)
        {
            return None;
        }
        let index = picker.start + usize::from(y - picker.area.y - 1);
        (index <= self.label_choices.len()).then_some(index)
    }

    pub(crate) fn select_label_picker(&mut self, index: usize) {
        if let Some(picker) = &mut self.label_picker
            && index <= self.label_choices.len()
        {
            picker.index = index;
        }
    }

    pub fn label_picker_manage_selected(&self) -> bool {
        self.label_picker
            .as_ref()
            .is_some_and(|picker| picker.index == self.label_choices.len())
    }

    pub fn move_label_picker(&mut self, delta: isize) {
        let count = self.label_choices.len().saturating_add(1);
        let Some(picker) = &mut self.label_picker else {
            return;
        };
        if count > 0 {
            picker.index = (picker.index as isize + delta).clamp(0, count as isize - 1) as usize;
        }
    }

    pub fn select_first_label(&mut self) {
        if let Some(picker) = &mut self.label_picker {
            picker.index = 0;
        }
    }

    pub fn select_last_label(&mut self) {
        if let Some(picker) = &mut self.label_picker {
            picker.index = self.label_choices.len();
        }
    }

    pub fn toggle_current_label(&mut self) -> Result<(), &'static str> {
        let Some(index) = self.label_picker.as_ref().map(|picker| picker.index) else {
            return Ok(());
        };
        let Some(id) = self
            .label_choices
            .get(index)
            .map(|choice| choice.id.clone())
        else {
            return Ok(());
        };
        self.toggle_label(&id)
    }

    pub fn toggle_label(&mut self, id: &str) -> Result<(), &'static str> {
        if self.label_ids.iter().any(|selected| selected == id) {
            self.before_edit(EditKind::Atomic);
            self.label_ids.retain(|selected| selected != id);
            return Ok(());
        }
        if self.label_ids.len() >= MAX_LABELS_PER_TASK {
            return Err("This task already has the maximum number of labels");
        }
        if !self.label_choices.iter().any(|choice| choice.id == id) {
            return Ok(());
        }
        self.before_edit(EditKind::Atomic);
        self.label_ids.push(id.to_string());
        self.canonicalize_label_ids();
        Ok(())
    }

    pub fn clear_labels(&mut self) {
        if self.label_ids.is_empty() {
            return;
        }
        self.before_edit(EditKind::Atomic);
        self.label_ids.clear();
    }

    fn canonicalize_label_ids(&mut self) {
        self.label_ids = self
            .label_choices
            .iter()
            .filter(|choice| self.label_ids.contains(&choice.id))
            .map(|choice| choice.id.clone())
            .collect();
    }

    /// Open the full-size image viewer. GIF frames decode asynchronously;
    /// the still-image cache can paint a placeholder in the meantime.
    pub fn open_image_preview(&mut self) -> Option<String> {
        // Only the image under the cursor — never fall back to "first in description".
        let Some(path) = self.description.selected_image() else {
            self.preview = false;
            return Some("No image to preview".into());
        };
        self.preview = true;
        if crate::image::is_gif(&path) {
            // Keep a decoded GIF across close/reopen while this form is open.
            if matches!(&self.gif, Some((p, _)) if p == &path) {
                return None;
            }
            if self
                .gif_pending
                .as_ref()
                .is_none_or(|pending| pending.path() != path)
            {
                self.gif = None;
                self.gif_pending = Some(GifLoad::start(path));
            }
        } else {
            // Different still — drop any previous GIF cache.
            if !matches!(&self.gif, Some((p, _)) if p == &path) {
                self.gif = None;
            }
            self.gif_pending = None;
        }
        None
    }

    pub fn close_image_preview(&mut self) {
        self.preview = false;
        // Keep `gif` so reopening the same animation is instant.
    }

    pub fn gif_playing(&self) -> bool {
        self.preview
            && (self.gif_pending.is_some()
                || (!crate::theme::reduced_motion()
                    && self
                        .gif
                        .as_ref()
                        .is_some_and(|(_, g)| g.is_animated() && !g.is_paused())))
    }

    /// Advance GIF animation; returns true when the frame changed.
    pub fn tick_gif(&mut self) -> bool {
        if let Some(result) = self.gif_pending.as_ref().and_then(GifLoad::poll) {
            let path = self
                .gif_pending
                .take()
                .expect("a polled GIF load is still pending")
                .path()
                .to_path_buf();
            match result {
                Ok(gif) => self.gif = Some((path, gif)),
                Err(error) => {
                    self.gif = None;
                    self.error = Some(error);
                }
            }
            return true;
        }
        if crate::theme::reduced_motion() {
            return false;
        }
        if let Some((_, gif)) = &mut self.gif {
            return gif.tick();
        }
        false
    }

    /// Click while preview is open: pause/resume an animated GIF.
    /// Static images ignore the click (Esc still closes).
    pub fn preview_click(&mut self) {
        if crate::theme::reduced_motion() {
            return;
        }
        if let Some((_, gif)) = &mut self.gif {
            gif.toggle_pause();
        }
    }

    pub fn is_edit(&self) -> bool {
        self.editing.is_some()
    }

    pub fn is_dirty(&self) -> bool {
        self.content() != self.initial
    }

    fn content(&self) -> TaskDraft {
        TaskDraft {
            title: self.title.value(),
            category_id: self.category_id.clone(),
            label_ids: self.label_ids.clone(),
            due: self.due.value(),
            importance: self.importance,
            description: self.description.value(),
        }
    }

    pub fn title_text(&self) -> &'static str {
        if self.is_edit() {
            "Edit task"
        } else {
            "New task"
        }
    }

    fn snap(&self) -> TaskSnap {
        TaskSnap {
            title: self.title.clone(),
            category_id: self.category_id.clone(),
            label_ids: self.label_ids.clone(),
            due: self.due.clone(),
            importance: self.importance,
            description: self.description.clone(),
            field: self.field,
        }
    }

    fn restore(&mut self, s: TaskSnap) {
        self.title = s.title;
        self.category_id = s.category_id;
        self.label_ids = s.label_ids;
        self.due = s.due;
        self.importance = s.importance;
        self.description = s.description;
        self.field = s.field;
        self.error = None;
        // Overlays are not part of content history.
        self.picker = None;
        self.label_picker = None;
        self.preview = false;
        self.gif_pending = None;
        self.description.close_menu();
    }

    /// Snapshot before a content edit (call before mutating).
    pub fn before_edit(&mut self, kind: EditKind) {
        let Self {
            title,
            category_id,
            label_ids,
            due,
            importance,
            description,
            field,
            history,
            ..
        } = self;
        history.before_edit_with(kind, || TaskSnap {
            title: title.clone(),
            category_id: category_id.clone(),
            label_ids: label_ids.clone(),
            due: due.clone(),
            importance: *importance,
            description: description.clone(),
            field: *field,
        });
    }

    pub fn break_coalesce(&mut self) {
        self.history.break_coalesce();
    }

    pub fn undo(&mut self) -> bool {
        let Some(prev) = self.history.undo(self.snap()) else {
            return false;
        };
        self.restore(prev);
        true
    }

    pub fn redo(&mut self) -> bool {
        let Some(next) = self.history.redo(self.snap()) else {
            return false;
        };
        self.restore(next);
        true
    }

    pub(crate) fn insert_temporary_image(&mut self, image: TemporaryImage) -> bool {
        let reference = image.path().to_string_lossy().into_owned();
        if !self.description.insert_block(Block::image(&reference)) {
            return false;
        }
        self.temporary_images.push(image);
        true
    }

    /// Opens the calendar on whatever the field already reads.
    pub fn open_due_picker(&mut self) {
        self.history.break_coalesce();
        self.field = Field::Due;
        self.label_picker = None;
        self.picker = Some(DuePicker::new(self.due.value().trim()));
    }

    /// Writes the picked day back into the field.
    pub fn take_due_picker(&mut self) {
        let Some(picker) = self.picker.take() else {
            return;
        };
        self.before_edit(EditKind::Atomic);
        self.due = TextInput::new(&picker.value(), 32);
    }

    /// Steps importance up, wrapping back to none after three.
    pub fn cycle_importance(&mut self) {
        let next = crate::model::next_importance(self.importance);
        self.set_importance(next);
    }

    pub fn set_importance(&mut self, importance: u8) {
        let next = importance.min(crate::model::MAX_IMPORTANCE);
        if next == self.importance {
            return;
        }
        self.before_edit(EditKind::Atomic);
        self.importance = next;
    }

    pub fn clear_due(&mut self) {
        if self.due.is_empty() && self.picker.is_none() {
            return;
        }
        self.before_edit(EditKind::Atomic);
        self.picker = None;
        self.label_picker = None;
        self.due = TextInput::new("", 32);
    }

    pub fn focus_next(&mut self) {
        self.history.break_coalesce();
        self.picker = None;
        self.label_picker = None;
        self.description.close_menu();
        self.field = self.field.next();
    }

    pub fn focus_prev(&mut self) {
        self.history.break_coalesce();
        self.picker = None;
        self.label_picker = None;
        self.description.close_menu();
        self.field = self.field.prev();
    }

    /// Move focus; dismiss the calendar and slash menu when leaving
    /// the fields that own them.
    pub fn set_field(&mut self, field: Field) {
        self.history.break_coalesce();
        if field != Field::Due {
            self.picker = None;
        }
        if field != Field::Labels {
            self.label_picker = None;
        }
        if field != Field::Description {
            self.description.close_menu();
        }
        self.field = field;
    }

    /// Validates the form. On success returns the draft; on failure sets
    /// `error` and focuses the offending field.
    pub fn submit(&mut self) -> Option<TaskDraft> {
        self.error = None;

        let title = self.title.value().trim().to_string();
        if title.is_empty() {
            self.error = Some("A title is required".to_string());
            self.field = Field::Title;
            return None;
        }

        let due_text = self.due.value().trim().to_string();
        if !due::is_valid(&due_text) {
            self.error = Some(format!("'{due_text}' is not a date mach understands"));
            self.field = Field::Due;
            return None;
        }

        // A `[date]` typed into the title still works, and fills the due
        // field when it was left empty. It gets the same check the Due
        // field does — otherwise it is a way around it.
        let (inline_due, title) = due::parse(&title);
        if title.is_empty() {
            self.error = Some("A title is required".to_string());
            self.field = Field::Title;
            return None;
        }
        if !due::is_valid(&inline_due) {
            self.error = Some(format!("'{inline_due}' is not a date mach understands"));
            self.field = Field::Title;
            return None;
        }

        Some(TaskDraft {
            title,
            category_id: self.category_id.clone(),
            label_ids: self.label_ids.clone(),
            due: if due_text.is_empty() {
                inline_due
            } else {
                due_text
            },
            importance: self.importance,
            description: self.description.value(),
        })
    }
}

impl Default for TaskForm {
    fn default() -> Self {
        Self::new()
    }
}

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

    #[test]
    fn requires_a_title() {
        let mut form = TaskForm::new();
        assert!(form.submit().is_none());
        assert_eq!(form.field, Field::Title);
        assert!(form.error.is_some());
    }

    #[test]
    fn rejects_an_unparsable_date() {
        let mut form = TaskForm::new();
        form.title = TextInput::new("something", MAX_TITLE_LEN);
        form.due = TextInput::new("next tuesday", 32);
        assert!(form.submit().is_none());
        assert_eq!(form.field, Field::Due);
    }

    #[test]
    fn takes_a_date_typed_into_the_title() {
        let mut form = TaskForm::new();
        form.title = TextInput::new("pay rent [2030-01-02]", MAX_TITLE_LEN);
        let draft = form.submit().expect("valid");
        assert_eq!(draft.title, "pay rent");
        assert_eq!(draft.due, "2030-01-02");
    }

    #[test]
    fn an_explicit_date_wins_over_the_inline_one() {
        let mut form = TaskForm::new();
        form.title = TextInput::new("pay rent [2030-01-02]", MAX_TITLE_LEN);
        form.due = TextInput::new("09:00", 32);
        let draft = form.submit().expect("valid");
        assert_eq!(draft.due, "09:00");
    }

    #[test]
    fn undo_restores_title_and_description() {
        let mut form = TaskForm::new();
        form.before_edit(EditKind::Typing);
        form.title = TextInput::new("hello", MAX_TITLE_LEN);
        form.before_edit(EditKind::Atomic);
        form.description.insert_str("note");
        assert!(form.undo());
        assert!(form.description.is_empty() || form.description.plain_value().is_empty());
        assert_eq!(form.title.value(), "hello");
        assert!(form.undo());
        assert_eq!(form.title.value(), "");
        assert!(form.redo());
        assert_eq!(form.title.value(), "hello");
    }

    #[test]
    fn undo_restores_importance() {
        let mut form = TaskForm::new();
        form.set_importance(2);
        assert_eq!(form.importance, 2);
        assert!(form.undo());
        assert_eq!(form.importance, 0);
        assert!(form.redo());
        assert_eq!(form.importance, 2);
    }

    #[test]
    fn dirty_state_tracks_content_not_focus() {
        let mut task = TaskForm::new();
        task.focus_next();
        assert!(!task.is_dirty());
        task.title.insert('x');
        assert!(task.is_dirty());

        let mut category = CategoryForm::new();
        category.set_description_focus(true);
        assert!(!category.is_dirty());
        category.name.insert('x');
        assert!(category.is_dirty());
    }

    #[test]
    fn category_submit_exposes_a_shared_name_policy_hook() {
        let mut form = CategoryForm::new();
        form.name.insert_str("Work");
        assert!(
            form.submit_with(|name, _| {
                (name != "Work")
                    .then_some(())
                    .ok_or_else(|| "A category with that name already exists".to_string())
            })
            .is_none()
        );
        assert_eq!(
            form.error.as_deref(),
            Some("A category with that name already exists")
        );
    }

    #[test]
    fn opening_a_gif_never_decodes_on_the_input_path() {
        let path = std::env::temp_dir().join(format!("mach-async-{}.gif", std::process::id()));
        std::fs::write(&path, b"not a real gif").unwrap();
        let mut task = Task::new("gif", 0, None, "");
        task.description = vec![Block::Image {
            attachment_id: path.display().to_string(),
        }];
        let mut form = TaskForm::edit(&task);

        assert!(form.open_image_preview().is_none());
        assert!(form.gif.is_none());
        assert!(form.gif_pending.is_some());
    }

    #[test]
    fn category_selector_includes_uncategorized_and_is_part_of_the_draft() {
        let categories = [
            crate::model::Category::all_tasks(),
            crate::model::Category {
                id: "work".into(),
                name: "Work".into(),
                description: String::new(),
            },
        ];
        let mut form = TaskForm::new();
        form.set_categories(&categories, Some("work"));

        assert_eq!(form.category_id(), Some("work"));
        assert_eq!(form.category_label(), "Work");
        assert!(!form.is_dirty());

        form.cycle_category(1);
        assert_eq!(form.category_id(), None);
        assert_eq!(form.category_label(), "Uncategorized");
        assert!(form.is_dirty());

        form.title.insert_str("portable task");
        assert_eq!(form.submit().expect("valid draft").category_id, None);
        assert!(form.undo());
        assert_eq!(form.category_id(), Some("work"));
    }

    #[test]
    fn editing_a_task_keeps_its_category_in_the_dirty_baseline() {
        let mut task = Task::new("move me", 0, Some("work".into()), "");
        task.id = "task".into();
        let categories = [crate::model::Category {
            id: "work".into(),
            name: "Work".into(),
            description: String::new(),
        }];
        let mut form = TaskForm::edit(&task);
        form.set_categories(&categories, task.category_id.as_deref());

        assert_eq!(form.category_id(), Some("work"));
        assert!(!form.is_dirty());
        assert_eq!(
            form.submit().expect("valid draft").category_id.as_deref(),
            Some("work")
        );
    }
}