tubular/src/keys.rs

use std::{fmt::Write as _, io};

use ratatui::crossterm::event::{KeyCode, KeyEvent, KeyModifiers};
use ratatui::{
    style::Stylize,
    text::{Line, Span, Text},
};
use toml_edit::{Array, Item};

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
#[repr(usize)]
pub enum Context {
    Normal,
    Info,
    Description,
    CollectionNormal,
    CollectionInfo,
    CollectionDescription,
    SearchInput,
    SelectorNormal,
    SelectorInput,
    TagList,
    TagFilter,
    TagInput,
    CategoryNameInput,
    Help,
}

const ALL: &[Context] = &[
    Context::Normal,
    Context::Info,
    Context::Description,
    Context::CollectionNormal,
    Context::CollectionInfo,
    Context::CollectionDescription,
    Context::SearchInput,
    Context::SelectorNormal,
    Context::SelectorInput,
    Context::TagList,
    Context::TagFilter,
    Context::TagInput,
    Context::CategoryNameInput,
    Context::Help,
];
const VIEW: &[Context] = &[
    Context::Normal,
    Context::Info,
    Context::Description,
    Context::CollectionNormal,
    Context::CollectionInfo,
    Context::CollectionDescription,
];
const COLLECTION: &[Context] = &[
    Context::CollectionNormal,
    Context::CollectionInfo,
    Context::CollectionDescription,
];
const TEXT: &[Context] = &[
    Context::SearchInput,
    Context::SelectorInput,
    Context::TagFilter,
    Context::TagInput,
    Context::CategoryNameInput,
];
const NON_TEXT: &[Context] = &[
    Context::Normal,
    Context::Info,
    Context::Description,
    Context::CollectionNormal,
    Context::CollectionInfo,
    Context::CollectionDescription,
    Context::SelectorNormal,
    Context::TagList,
    Context::Help,
];

struct Definition {
    action: Action,
    name: &'static str,
    description: &'static str,
    contexts: &'static [Context],
    defaults: &'static [&'static str],
}

// The enum order, storage indices, documentation and default TOML all share this registry.
macro_rules! actions {
    ($($action:ident, $name:literal, $description:literal, $contexts:expr, [$($key:literal),*];)*) => {
        #[derive(Clone, Copy, Debug, PartialEq, Eq)]
        #[repr(usize)]
        pub enum Action { $($action),* }

        const DEFINITIONS: &[Definition] = &[
            $(Definition {
                action: Action::$action,
                name: $name,
                description: $description,
                contexts: $contexts,
                defaults: &[$($key),*],
            }),*
        ];
    };
}

actions! {
    Interrupt, "app.interrupt", "Exit immediately", ALL, ["ctrl+c"];
    Quit, "app.quit", "Quit the application", &[Context::Normal, Context::Info, Context::Description, Context::CollectionNormal, Context::CollectionInfo, Context::CollectionDescription, Context::Help], ["q"];
    ProviderChoose, "app.provider", "Choose the browsing provider", &[Context::Normal, Context::CollectionNormal], ["p"];
    Help, "help.toggle", "Open or close keyboard help", NON_TEXT, ["?"];
    InputSubmit, "input.submit", "Submit search, browse selector, leave tag filter, stage new tag or save category name", TEXT, ["enter"];
    InputCancel, "input.cancel", "Leave text input without submitting", TEXT, ["escape"];
    DeleteCharacter, "input.delete.character", "Delete the previous character", TEXT, ["backspace"];
    DeleteWord, "input.delete.word", "Delete the previous word", TEXT, ["alt+backspace", "ctrl+w"];
    DeleteLine, "input.delete.line", "Clear the input line", TEXT, ["super+backspace", "ctrl+u", "alt+super+backspace"];
    SearchEdit, "search.edit", "Edit general or current-category search", VIEW, ["i"];
    ViewSearch, "view.search", "Go to general YouTube Search", VIEW, ["/"];
    ViewFeed, "view.feed", "Go to the combined subscription Feed", VIEW, ["F"];
    ViewPrevious, "view.history.previous", "Go back in view history", VIEW, ["-"];
    ViewNext, "view.history.next", "Go forward in view history", VIEW, ["+"];
    ViewTabNext, "view.tab.next", "Select the next view tab", VIEW, ["tab", "ctrl+tab"];
    ViewTabPrevious, "view.tab.previous", "Select the previous view tab", VIEW, ["shift+tab"];
    ViewRefresh, "view.refresh", "Refresh the current view and configuration", VIEW, ["r"];
    VideoPlay, "video.play", "Play checked videos in check order, or the selected video", VIEW, ["enter"];
    VideoEnqueue, "video.enqueue", "Append checked videos in check order, or the selected video, to Terebi's queue", VIEW, ["ctrl+enter"];
    VideoOpen, "video.open", "Open the selected YouTube video in the default browser", VIEW, ["o"];
    VideoCopyUrl, "video.copy_url", "Copy the selected video's URL to the terminal clipboard", VIEW, ["y"];
    VideoNext, "video.select.next", "Select the next video", VIEW, ["j", "down", "ctrl+j"];
    VideoPrevious, "video.select.previous", "Select the previous video", VIEW, ["k", "up", "ctrl+k"];
    VideoFirst, "video.select.first", "Select the first video", VIEW, ["g", "home"];
    VideoLast, "video.select.last", "Select the last video", VIEW, ["G", "end"];
    VideoToggle, "video.select.toggle", "Toggle the selected video's playback check", VIEW, ["space"];
    VideoClear, "video.select.clear", "Discard playback checks in the current view", VIEW, ["escape", "ctrl+space"];
    InfoOverview, "video.info.overview", "Show the video overview", VIEW, ["d"];
    InfoDescription, "video.info.description", "Show the video description", VIEW, ["d"];
    InfoHide, "video.info.hide", "Close the video preview", &[Context::Info, Context::Description, Context::CollectionInfo, Context::CollectionDescription], ["escape"];
    CategoryBrowse, "category.browse", "Browse categories", VIEW, ["c"];
    ChannelBrowse, "channel.browse", "Browse subscribed channels", VIEW, ["u"];
    VideoChannel, "video.channel", "Open the selected video's channel", VIEW, ["U"];
    ChannelTags, "channel.tags", "Edit the selected YouTube channel's or anime show's category tags", VIEW, ["s"];
    CategoryTags, "category.tags", "Edit category tags for all channels in this category", VIEW, ["S"];
    CategoryRename, "category.rename", "Rename the current or selected category", &[Context::Normal, Context::CollectionNormal, Context::SelectorNormal, Context::TagList], ["R"];
    CategorySave, "category.save", "Save the combined category view as a new category", VIEW, ["P"];
    WatchLaterSave, "video.watch_later.save", "Save the selected video to watch later", VIEW, ["w"];
    WatchLaterBrowse, "view.watch_later.browse", "Choose watch later across all categories or one category", VIEW, ["W"];
    WatchLaterBrowseCategory, "view.watch_later.category", "Browse the current category's watch later", VIEW, ["alt+w"];
    WatchLaterFilter, "view.watch_later.filter", "Cycle watch-later filter: all, unwatched, watched", &[Context::Normal, Context::CollectionNormal], ["f"];
    CollectionRemoveSelected, "view.collection.remove.selected", "Remove the selected video from the current collection (also in its previews)", COLLECTION, ["x"];
    CollectionRemoveBulk, "view.collection.remove.bulk", "Confirm removal of the current collection subset", COLLECTION, ["X"];
    SavedVideoSave, "video.saved.save", "Save the selected video (also in previews)", VIEW, ["v"];
    SavedVideoBrowse, "view.saved.browse", "Choose saved videos across all categories or one category", VIEW, ["V"];
    SavedVideoBrowseCategory, "view.saved.category", "Browse the current category's saved videos", VIEW, ["alt+v"];
    WatchingBrowse, "view.watching.browse", "Browse started, unfinished videos", VIEW, ["C"];
    WatchStatusWatching, "video.status.watching", "Mark the selected video as watching", VIEW, ["m"];
    WatchStatusWatched, "video.status.watched", "Mark the selected video as watched", VIEW, ["M"];
    SelectorNext, "selector.select.next", "Select the next category or channel", &[Context::SelectorNormal], ["j", "down"];
    SelectorPrevious, "selector.select.previous", "Select the previous category or channel", &[Context::SelectorNormal], ["k", "up"];
    SelectorInputNext, "selector.input.next", "Select the next match while editing the filter", &[Context::SelectorInput], ["down", "ctrl+j"];
    SelectorInputPrevious, "selector.input.previous", "Select the previous match while editing the filter", &[Context::SelectorInput], ["up", "ctrl+k"];
    SelectorEdit, "selector.edit", "Edit the category, channel, or collection filter", &[Context::SelectorNormal], ["i"];
    SelectorOpen, "selector.open", "Open the selected category, channel, or collection", &[Context::SelectorNormal], ["enter"];
    SelectorPin, "selector.pin", "Toggle category pinning (category picker only)", &[Context::SelectorNormal], ["p"];
    SelectorToggle, "selector.toggle", "Check a category for combined browsing (category picker only)", &[Context::SelectorNormal], ["space"];
    SelectorClose, "selector.close", "Close the category, channel, or collection picker", &[Context::SelectorNormal], ["escape"];
    TagNext, "tags.select.next", "Select the next category tag", &[Context::TagList], ["j", "down"];
    TagPrevious, "tags.select.previous", "Select the previous category tag", &[Context::TagList], ["k", "up"];
    TagEdit, "tags.edit", "Edit the category tag filter", &[Context::TagList], ["i"];
    TagInputNext, "tags.input.next", "Select the next tag while editing the filter", &[Context::TagFilter], ["down", "ctrl+j"];
    TagInputPrevious, "tags.input.previous", "Select the previous tag while editing the filter", &[Context::TagFilter], ["up", "ctrl+k"];
    TagToggle, "tags.toggle", "Toggle the selected category tag", &[Context::TagList], ["space"];
    TagNew, "tags.new", "Enter a new category tag name", &[Context::TagList], ["n"];
    TagSave, "tags.save", "Save category tag changes", &[Context::TagList], ["enter"];
    TagCancel, "tags.cancel", "Discard category tag changes and close", &[Context::TagList], ["escape"];
    DescriptionNext, "video.description.scroll.next", "Scroll the description down one line", &[Context::Description, Context::CollectionDescription], ["down", "ctrl+j"];
    DescriptionPrevious, "video.description.scroll.previous", "Scroll the description up one line", &[Context::Description, Context::CollectionDescription], ["up", "ctrl+k"];
    DescriptionPageNext, "video.description.page.next", "Scroll the description down one page", &[Context::Description, Context::CollectionDescription], ["pagedown"];
    DescriptionPagePrevious, "video.description.page.previous", "Scroll the description up one page", &[Context::Description, Context::CollectionDescription], ["pageup"];
    HelpNext, "help.scroll.next", "Scroll help down one line", &[Context::Help], ["j", "down", "ctrl+j"];
    HelpPrevious, "help.scroll.previous", "Scroll help up one line", &[Context::Help], ["k", "up", "ctrl+k"];
    HelpPageNext, "help.page.next", "Scroll help down one page", &[Context::Help], ["pagedown"];
    HelpPagePrevious, "help.page.previous", "Scroll help up one page", &[Context::Help], ["pageup"];
    HelpClose, "help.close", "Close keyboard help", &[Context::Help], ["escape"];
}

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
struct Key {
    code: KeyCode,
    modifiers: KeyModifiers,
}

impl Key {
    fn normalized(mut self) -> Self {
        if self.code == KeyCode::BackTab {
            self.code = KeyCode::Tab;
            self.modifiers.insert(KeyModifiers::SHIFT);
        }
        if let KeyCode::Char(character) = self.code
            && !character.is_control()
            && self.modifiers.contains(KeyModifiers::SHIFT)
        {
            // Terminals usually report the already-shifted character. A single-character
            // uppercase mapping also accepts synthetic shift+i as I without allocating.
            let mut uppercase = character.to_uppercase();
            if let Some(first) = uppercase.next()
                && uppercase.next().is_none()
            {
                self.code = KeyCode::Char(first);
            }
            self.modifiers.remove(KeyModifiers::SHIFT);
        }
        self
    }

    fn parse(description: &str) -> Result<Self, String> {
        let mut remaining = description;
        let mut modifiers = KeyModifiers::NONE;
        loop {
            if remaining.chars().count() == 1 {
                break;
            }
            let Some((modifier, key)) = remaining.split_once('+') else {
                break;
            };
            let flag = match modifier.to_ascii_lowercase().as_str() {
                "ctrl" | "control" => KeyModifiers::CONTROL,
                "alt" | "option" => KeyModifiers::ALT,
                "super" | "cmd" | "command" => KeyModifiers::SUPER,
                "shift" => KeyModifiers::SHIFT,
                _ => {
                    return Err(format!(
                        "unknown modifier {modifier:?}; use ctrl, alt, super or shift"
                    ));
                }
            };
            if modifiers.contains(flag) {
                return Err(format!("repeated modifier {modifier:?}"));
            }
            modifiers.insert(flag);
            remaining = key;
        }
        let mut characters = remaining.chars();
        let code = match (characters.next(), characters.next()) {
            (Some(character), None) if !character.is_control() => KeyCode::Char(character),
            _ => match remaining.to_ascii_lowercase().as_str() {
                "escape" | "esc" => KeyCode::Esc,
                "enter" | "return" => KeyCode::Enter,
                "tab" => KeyCode::Tab,
                "backtab" => KeyCode::BackTab,
                "up" => KeyCode::Up,
                "down" => KeyCode::Down,
                "left" => KeyCode::Left,
                "right" => KeyCode::Right,
                "home" => KeyCode::Home,
                "end" => KeyCode::End,
                "pageup" => KeyCode::PageUp,
                "pagedown" => KeyCode::PageDown,
                "backspace" => KeyCode::Backspace,
                "delete" => KeyCode::Delete,
                "space" => KeyCode::Char(' '),
                name => {
                    let function = name
                        .strip_prefix('f')
                        .and_then(|number| number.parse::<u8>().ok());
                    match function {
                        Some(number @ 1..=24) => KeyCode::F(number),
                        _ => {
                            return Err(format!(
                                "unknown key {remaining:?}; use one character, a named key or f1..f24"
                            ));
                        }
                    }
                }
            },
        };
        Ok(Self { code, modifiers }.normalized())
    }

    fn label(self) -> String {
        let mut text = String::new();
        for (flag, name) in [
            (KeyModifiers::CONTROL, "Ctrl+"),
            (KeyModifiers::ALT, "Alt+"),
            (KeyModifiers::SUPER, "Super+"),
            (KeyModifiers::SHIFT, "Shift+"),
        ] {
            if self.modifiers.contains(flag) {
                text.push_str(name);
            }
        }
        match self.code {
            KeyCode::Char(' ') => text.push_str("Space"),
            KeyCode::Char(character) => text.push(character),
            KeyCode::F(number) => {
                let _ = write!(text, "F{number}");
            }
            code => text.push_str(match code {
                KeyCode::Esc => "Esc",
                KeyCode::Enter => "Enter",
                KeyCode::Tab => "Tab",
                KeyCode::Up => "↑",
                KeyCode::Down => "↓",
                KeyCode::Left => "←",
                KeyCode::Right => "→",
                KeyCode::Home => "Home",
                KeyCode::End => "End",
                KeyCode::PageUp => "PgUp",
                KeyCode::PageDown => "PgDn",
                KeyCode::Backspace => "Backspace",
                KeyCode::Delete => "Del",
                _ => unreachable!("only supported normalized keys have labels"),
            }),
        }
        text
    }
}

#[derive(Clone, Debug, PartialEq, Eq)]
pub struct Bindings {
    labels: Vec<Vec<String>>,
    contexts: [Vec<(Key, Action)>; ALL.len()],
}

impl Default for Bindings {
    fn default() -> Self {
        Self::build(default_keys()).expect("the default key registry must be valid")
    }
}

fn default_keys() -> Vec<Vec<Key>> {
    DEFINITIONS
        .iter()
        .map(|definition| {
            definition
                .defaults
                .iter()
                .map(|key| Key::parse(key).expect("default key descriptions must be valid"))
                .collect()
        })
        .collect()
}

fn invalid(message: impl Into<String>) -> io::Error {
    io::Error::new(io::ErrorKind::InvalidData, message.into())
}

impl Bindings {
    pub fn from_toml(item: Option<&Item>) -> io::Result<Self> {
        let mut keys = default_keys();
        if let Some(item) = item {
            let mut overridden = vec![false; DEFINITIONS.len()];
            Self::read_overrides(item, "", &mut keys, &mut overridden)?;
        }
        Self::build(keys)
    }

    fn read_overrides(
        item: &Item,
        path: &str,
        keys: &mut [Vec<Key>],
        overridden: &mut [bool],
    ) -> io::Result<()> {
        if let Some(definition) = DEFINITIONS
            .iter()
            .find(|definition| definition.name == path)
        {
            if std::mem::replace(&mut overridden[definition.action as usize], true) {
                return Err(invalid(format!(
                    "keys.{path}: duplicate action override; use only one quoted or nested dotted path for this action"
                )));
            }
            let mut aliases = Vec::new();
            let mut add = |description: &str| -> io::Result<()> {
                let key = Key::parse(description).map_err(|error| {
                    invalid(format!(
                        "keys.{path}: invalid binding {description:?}: {error}"
                    ))
                })?;
                if !aliases.contains(&key) {
                    aliases.push(key);
                }
                Ok(())
            };
            if let Some(description) = item.as_str() {
                add(description)?;
            } else if let Some(array) = item.as_array() {
                for (index, value) in array.iter().enumerate() {
                    let description = value.as_str().ok_or_else(|| {
                        invalid(format!(
                            "keys.{path}[{index}]: expected a key description string"
                        ))
                    })?;
                    add(description)?;
                }
            } else {
                return Err(invalid(format!(
                    "keys.{path}: expected a string or array of strings; use [] to disable"
                )));
            }
            keys[definition.action as usize] = aliases;
            return Ok(());
        }
        if !path.is_empty()
            && !DEFINITIONS.iter().any(|definition| {
                definition
                    .name
                    .strip_prefix(path)
                    .is_some_and(|suffix| suffix.starts_with('.'))
            })
        {
            return Err(invalid(format!(
                "keys.{path}: unknown action or action group; consult --default-config for valid paths"
            )));
        }
        let table = item.as_table_like().ok_or_else(|| {
            invalid(format!(
                "keys{}: expected a table of action bindings",
                if path.is_empty() {
                    String::new()
                } else {
                    format!(".{path}")
                }
            ))
        })?;
        for (name, value) in table.iter() {
            let child = if path.is_empty() {
                name.to_owned()
            } else {
                format!("{path}.{name}")
            };
            Self::read_overrides(value, &child, keys, overridden)?;
        }
        Ok(())
    }

    fn build(keys: Vec<Vec<Key>>) -> io::Result<Self> {
        let mut contexts: [Vec<(Key, Action)>; ALL.len()] = std::array::from_fn(|_| Vec::new());
        for definition in DEFINITIONS {
            for &context in definition.contexts {
                let entries = &mut contexts[context as usize];
                for &key in &keys[definition.action as usize] {
                    if let Some((_, previous)) = entries.iter_mut().find(|(bound, _)| *bound == key)
                    {
                        *previous = overlap_winner(context, *previous, definition.action).ok_or_else(|| {
                            invalid(format!(
                                "keys: binding {} collides in {context:?} between {} and {}; rebind or disable one action",
                                key.label(), DEFINITIONS[*previous as usize].name, definition.name,
                            ))
                        })?;
                    } else {
                        entries.push((key, definition.action));
                    }
                }
            }
        }
        Ok(Self {
            labels: keys
                .into_iter()
                .map(|aliases| aliases.into_iter().map(Key::label).collect())
                .collect(),
            contexts,
        })
    }

    pub fn resolve(&self, context: Context, event: KeyEvent) -> Option<Action> {
        let key = Key {
            code: event.code,
            modifiers: event.modifiers,
        }
        .normalized();
        self.contexts[context as usize]
            .iter()
            .find_map(|(bound, action)| (*bound == key).then_some(*action))
    }

    pub fn label(&self, action: Action) -> &str {
        self.labels[action as usize]
            .first()
            .map_or("unbound", String::as_str)
    }

    pub fn help_text(&self) -> Text<'static> {
        use Action::*;
        type Row = (&'static [Action], &'static str);
        let sections: &[(&str, &[Row])] = &[
            (
                "VIEWS AND VIDEOS",
                &[
                    (&[VideoNext, VideoPrevious], "Select next / previous video"),
                    (
                        &[VideoPlay],
                        "Play checked videos in check order, or the selected video",
                    ),
                    (
                        &[VideoEnqueue],
                        "Append checked videos in check order, or the selected video, to Terebi's queue",
                    ),
                    (
                        &[VideoToggle],
                        "Check / uncheck the selected video for playback",
                    ),
                    (&[VideoClear], "Clear playback checks in the current view"),
                    (
                        &[VideoOpen],
                        "Open the selected YouTube video in the default browser",
                    ),
                    (&[VideoCopyUrl], "Copy the selected video's URL"),
                    (
                        &[WatchStatusWatching],
                        "Mark selected as watching (clear watched)",
                    ),
                    (
                        &[WatchStatusWatched],
                        "Mark selected as watched (leave watching)",
                    ),
                    (&[SearchEdit], "Edit general or current-category search"),
                    (&[ViewSearch], "Go to general YouTube Search"),
                    (&[ViewFeed], "Go to the combined subscription Feed"),
                    (
                        &[InfoOverview, InfoDescription],
                        "Info → full description → info",
                    ),
                    (&[VideoChannel], "Browse the selected video's channel"),
                    (&[ChannelBrowse], "Choose a saved channel"),
                    (&[CategoryBrowse], "Choose a saved category"),
                    (&[ChannelTags], "Edit the selected channel's tags"),
                    (&[CategoryTags], "Edit all channels in a category"),
                    (
                        &[CategoryRename],
                        "Rename the current category (including scoped collections)",
                    ),
                    (
                        &[CategorySave],
                        "Save a combined category view as a new category",
                    ),
                    (&[ViewTabNext, ViewTabPrevious], "Cycle visible tabs"),
                    (&[ViewPrevious], "Back (preview close takes priority)"),
                    (&[ViewNext], "Forward after going back"),
                    (&[VideoFirst], "First loaded video"),
                    (&[VideoLast], "Last loaded video"),
                    (&[ViewRefresh], "Reload config and refresh"),
                    (
                        &[ProviderChoose],
                        "Choose the browsing provider (NORMAL only)",
                    ),
                    (&[Help], "Open / close this reference"),
                    (&[Quit, Interrupt], "Quit"),
                ],
            ),
            (
                "WATCH LATER",
                &[
                    (&[WatchLaterSave], "Save the selected video"),
                    (
                        &[WatchLaterBrowse],
                        "Choose all-categories or category watch later",
                    ),
                    (
                        &[WatchLaterBrowseCategory],
                        "Browse current category's watch later",
                    ),
                    (&[WatchLaterFilter], "Cycle all / unwatched / watched"),
                ],
            ),
            (
                "SAVED VIDEOS",
                &[
                    (
                        &[SavedVideoSave],
                        "Save the selected video (also in previews)",
                    ),
                    (
                        &[SavedVideoBrowse],
                        "Choose all-categories or category saved videos",
                    ),
                    (
                        &[SavedVideoBrowseCategory],
                        "Browse current category's saved videos",
                    ),
                ],
            ),
            (
                "CURRENTLY WATCHING",
                &[(&[WatchingBrowse], "Browse started, unfinished videos")],
            ),
            (
                "COLLECTION LISTS",
                &[
                    (
                        &[CollectionRemoveSelected],
                        "Remove selected from the current collection only",
                    ),
                    (
                        &[CollectionRemoveBulk],
                        "Confirm removal of current list / category / filtered subset",
                    ),
                    (
                        &[],
                        "Previews inherit their underlying collection's removal scope",
                    ),
                    (
                        &[],
                        "Bulk confirmation: y / Enter confirms; n / Esc cancels",
                    ),
                ],
            ),
            (
                "FULL DESCRIPTION",
                &[
                    (&[DescriptionNext, DescriptionPrevious], "Scroll lines"),
                    (
                        &[DescriptionPageNext, DescriptionPagePrevious],
                        "Scroll pages",
                    ),
                    (&[VideoNext, VideoPrevious], "Change the selected video"),
                    (&[InfoOverview], "Return to video info"),
                    (&[InfoHide], "Close the preview"),
                ],
            ),
            (
                "CHANNEL / CATEGORY / COLLECTION SELECTOR",
                &[
                    (&[SelectorNext, SelectorPrevious], "Move in NORMAL mode"),
                    (&[SelectorEdit], "Enter filter INSERT mode"),
                    (
                        &[SelectorInputNext, SelectorInputPrevious],
                        "Move while filtering",
                    ),
                    (
                        &[SelectorOpen, InputSubmit],
                        "Browse checked categories, or the selected match",
                    ),
                    (
                        &[SelectorToggle],
                        "Check categories for a combined feed (NORMAL only)",
                    ),
                    (
                        &[SelectorPin],
                        "Pin / unpin a category (category picker only)",
                    ),
                    (
                        &[CategoryRename],
                        "Rename the selected category, not combined / channel rows",
                    ),
                    (&[InputCancel, SelectorClose], "INSERT → NORMAL → close"),
                ],
            ),
            (
                "CHANNEL TAGS",
                &[
                    (&[TagNext, TagPrevious], "Move between tags"),
                    (&[TagEdit], "Enter filter INSERT mode"),
                    (&[TagInputNext, TagInputPrevious], "Move while filtering"),
                    (
                        &[InputSubmit, InputCancel],
                        "Leave tag filter without saving",
                    ),
                    (&[TagToggle], "Toggle a tag"),
                    (&[TagNew], "Enter a new tag name"),
                    (
                        &[CategoryRename],
                        "Rename a tag; existing category renames save immediately",
                    ),
                    (&[TagSave], "Save tags"),
                    (&[InputSubmit], "Stage a new tag name"),
                    (&[TagCancel], "Cancel tag changes"),
                    (&[InputCancel], "Abandon a new tag name"),
                ],
            ),
            (
                "TEXT INPUT",
                &[
                    (
                        &[InputSubmit],
                        "Submit search / stage tag / save category name",
                    ),
                    (
                        &[InputCancel],
                        "Leave INSERT / abandon tag or category name",
                    ),
                    (&[DeleteCharacter], "Delete one character"),
                    (&[DeleteWord], "Delete previous word"),
                    (&[DeleteLine], "Clear the line"),
                ],
            ),
            (
                "HELP WINDOW",
                &[
                    (&[HelpNext, HelpPrevious], "Scroll lines"),
                    (&[HelpPageNext, HelpPagePrevious], "Scroll pages"),
                    (&[Help, HelpClose], "Close help without changing view"),
                    (&[Interrupt], "Quit from any mode or popup"),
                ],
            ),
        ];
        let mut text = Text::default();
        for &(heading, rows) in sections {
            text.push_line("");
            text.push_line(Line::from(Span::raw(heading).bold()));
            text.push_line("");
            for &(actions, description) in rows {
                if actions == [InfoOverview, InfoDescription]
                    && self.labels[InfoOverview as usize] != self.labels[InfoDescription as usize]
                {
                    for (action, description) in [
                        (InfoOverview, "Open video info"),
                        (InfoDescription, "Open the full description"),
                    ] {
                        text.push_line(format!(
                            "{:<18} {}",
                            self.help_keys(&[action]),
                            description
                        ));
                    }
                } else {
                    text.push_line(format!("{:<18} {}", self.help_keys(actions), description));
                }
            }
        }
        text
    }

    fn help_keys(&self, actions: &[Action]) -> String {
        use Action::*;
        let matches = |action: Action, expected: &[&str]| {
            self.labels[action as usize]
                .iter()
                .map(String::as_str)
                .eq(expected.iter().copied())
        };
        let movement = match actions {
            [VideoNext, VideoPrevious] | [HelpNext, HelpPrevious] => {
                matches(actions[0], &["j", "↓", "Ctrl+j"])
                    && matches(actions[1], &["k", "↑", "Ctrl+k"])
            }
            [SelectorNext, SelectorPrevious] | [TagNext, TagPrevious] => {
                matches(actions[0], &["j", "↓"]) && matches(actions[1], &["k", "↑"])
            }
            _ => false,
        };
        if movement {
            return if actions == [HelpNext, HelpPrevious] {
                "j/k ↑/↓ Ctrl-J/K".into()
            } else {
                "j / k or arrows".into()
            };
        }
        if matches!(
            actions,
            [DescriptionNext, DescriptionPrevious]
                | [SelectorInputNext, SelectorInputPrevious]
                | [TagInputNext, TagInputPrevious]
        ) && matches(actions[0], &["↓", "Ctrl+j"])
            && matches(actions[1], &["↑", "Ctrl+k"])
        {
            return "↑/↓, Ctrl-J/K".into();
        }
        if actions == [ViewTabNext, ViewTabPrevious]
            && matches(ViewTabNext, &["Tab", "Ctrl+Tab"])
            && matches(ViewTabPrevious, &["Shift+Tab"])
        {
            return "Tab / Shift-Tab".into();
        }
        let mut groups = Vec::new();
        for &action in actions {
            let labels = &self.labels[action as usize];
            let group = if labels.is_empty() {
                "unbound".into()
            } else {
                labels.join(", ")
            };
            if !groups.contains(&group) {
                groups.push(group);
            }
        }
        groups.join(" / ")
    }
}

fn overlap_winner(context: Context, first: Action, second: Action) -> Option<Action> {
    use Action::*;
    let pair = |a, b| (first == a && second == b) || (first == b && second == a);
    if first == second {
        return Some(first);
    }
    if pair(InfoOverview, InfoDescription) && VIEW.contains(&context) {
        return Some(
            if matches!(context, Context::Info | Context::CollectionInfo) {
                InfoDescription
            } else {
                InfoOverview
            },
        );
    }
    if (pair(InfoHide, ViewPrevious) || pair(InfoHide, VideoClear))
        && matches!(
            context,
            Context::Info
                | Context::Description
                | Context::CollectionInfo
                | Context::CollectionDescription
        )
    {
        return Some(InfoHide);
    }
    if matches!(
        context,
        Context::Description | Context::CollectionDescription
    ) {
        if pair(DescriptionNext, VideoNext) {
            return Some(DescriptionNext);
        }
        if pair(DescriptionPrevious, VideoPrevious) {
            return Some(DescriptionPrevious);
        }
    }
    None
}

pub fn default_config() -> String {
    let mut text = String::from(
        "[settings]\npinned_categories = []\n\n[channels]\n\n[categories]\n\n[keys]\n",
    );
    for definition in DEFINITIONS {
        let mut aliases = Array::new();
        for &key in definition.defaults {
            aliases.push(key);
        }
        let _ = writeln!(text, "# {}", definition.description);
        let _ = writeln!(text, "{} = {}", definition.name, aliases);
    }
    text
}

#[cfg(test)]
#[path = "../tests/unit/keys.rs"]
mod tests;