//! Everything a key can ask for. Views never see raw key presses: the engine
//! turns them into [`Command`]s using the tables in
//! [`bindings`](super::bindings), and each view decides what a command means
//! there. `Move(Left)` goes to the nearest node on the left on the canvas,
//! for example, and to the parent in the outline.
//!
//! [`COMMANDS`] names every command, for `keys.toml`, and says what it does,
//! for which-key and the help.

use crate::model::{Layout, Side};

/// Ways to move the cursor.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum Motion {
    Left,
    Down,
    Up,
    Right,
    Parent,
    FirstChild,
    NextSibling,
    PreviousSibling,
    /// The next node in reading order (in text: the next word).
    Next,
    /// The previous node in reading order (in text: the previous word).
    Previous,
    /// The root (in text: the start).
    First,
    /// The last node (in text: the end).
    Last,
    /// The end of the word (`e`, in text).
    WordEnd,
    /// The start of the line (`0`, in text).
    LineStart,
    /// The line's first character that isn't a space (`^`, in text).
    FirstNonBlank,
    /// The end of the line (`$`, in text).
    LineEnd,
    SearchNext,
    SearchPrevious,
    /// To the next time a character shows up on the line (`f`, in text).
    FindForward(char),
    /// To the previous time a character shows up on the line (`F`).
    FindBackward(char),
    /// To just before the next time a character shows up (`t`).
    TillForward(char),
    /// To just after the previous time a character shows up (`T`).
    TillBackward(char),
    /// The last `f`, `F`, `t` or `T` again (`;`).
    RepeatFind,
    /// The last `f`, `F`, `t` or `T` again, the other way (`,`).
    RepeatFindBackward,
}

/// Keys that wait for a target, like vim's `d`: `dd`, `dab`.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum Operator {
    Delete,
    Yank,
    Change,
    Indent,
    Outdent,
}

impl Operator {
    /// What the operator does, for which-key's title.
    pub fn name(self) -> &'static str {
        match self {
            Operator::Delete => "delete",
            Operator::Yank => "yank",
            Operator::Change => "change",
            Operator::Indent => "indent",
            Operator::Outdent => "outdent",
        }
    }
}

/// What an operator acts on.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum Target {
    /// The operator's own key again (`dd`, `yy`, `>>`): this node, with its
    /// branch (in text: this line).
    Current,
    /// `ab`, around a branch: the node and everything below it.
    Branch,
    /// `ib`, inside a branch: just what's below the node.
    Children,
    /// What's selected (an operator in visual mode).
    Selection,
    /// From the cursor to where a motion goes (`dw`, `dfx`, in text).
    Motion(Motion),
    /// What's inside a piece of text (`iw`, `i"`, `i(`).
    Inside(TextObject),
    /// A piece of text with its edges (`aw`: the word and a space, `a"`:
    /// the quotes too).
    Around(TextObject),
}

/// Pieces of text an operator can act on wherever the cursor is in them, as
/// in vim: `ciw` changes the word under the cursor.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum TextObject {
    Word,
    /// Text in double quotes.
    Quotes,
    /// Text in round brackets.
    Parens,
}

/// Keys that need one more character, typed right after them: `m` then a
/// letter.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum CharKey {
    SetMark,
    JumpToMark,
    FindForward,
    FindBackward,
    TillForward,
    TillBackward,
    /// `r`, in text: the character to put in place of the cursor's.
    Replace,
}

impl CharKey {
    /// The command once the character is known.
    pub fn command(self, c: char) -> Command {
        match self {
            CharKey::SetMark => Command::SetMark(c),
            CharKey::JumpToMark => Command::JumpToMark(c),
            CharKey::FindForward => Command::Move(Motion::FindForward(c)),
            CharKey::FindBackward => Command::Move(Motion::FindBackward(c)),
            CharKey::TillForward => Command::Move(Motion::TillForward(c)),
            CharKey::TillBackward => Command::Move(Motion::TillBackward(c)),
            CharKey::Replace => Command::ReplaceChar(c),
        }
    }

    /// Whether the key moves the cursor (`f`, `t`…), so it can be an
    /// operator's target too: `dfx`.
    pub fn moves(self) -> bool {
        matches!(
            self,
            CharKey::FindForward | CharKey::FindBackward | CharKey::TillForward | CharKey::TillBackward
        )
    }

    /// As the target of an operator, once the character is known (`dfx`).
    /// Only motions can be targets.
    pub fn target(self, c: char) -> Option<Target> {
        match self.command(c) {
            Command::Move(motion) => Some(Target::Motion(motion)),
            _ => None,
        }
    }

    /// What the character is for, for which-key: the keys, and what they do.
    pub fn hints(self) -> &'static [(&'static str, &'static str)] {
        match self {
            CharKey::SetMark => &[("a–z", "mark this node"), ("A–Z", "mark it, across documents")],
            CharKey::JumpToMark => {
                &[("a–z A–Z", "go to that mark"), ("'", "back to where you were before the last jump")]
            }
            CharKey::Replace => &[("any key", "the character to put in its place")],
            _ => &[("any key", "the character to go to")],
        }
    }
}

/// Where text goes and comes from with yank and paste: `"a` before a
/// command picks register `a`.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum Register {
    /// The usual one, when no register is named.
    Unnamed,
    /// `"a` to `"z` (capitals name the same registers).
    Named(char),
    /// `"+` (or `"*`): the system clipboard.
    Clipboard,
    /// `"_`: nowhere, for deleting without keeping a copy.
    BlackHole,
}

impl Register {
    /// The register a character names after `"`, if it names one.
    pub fn named(c: char) -> Option<Register> {
        match c {
            '"' => Some(Register::Unnamed),
            'a'..='z' => Some(Register::Named(c)),
            'A'..='Z' => Some(Register::Named(c.to_ascii_lowercase())),
            '+' | '*' => Some(Register::Clipboard),
            '_' => Some(Register::BlackHole),
            _ => None,
        }
    }

    /// The registers, for which-key after `"`.
    pub const HINTS: &[(&str, &str)] = &[
        ("a–z", "a named register"),
        ("+", "the system clipboard"),
        ("_", "nowhere (delete without a copy)"),
    ];
}

/// Everything a key sequence can ask for.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum Command {
    /// Move the cursor.
    Move(Motion),
    /// An operator with its target: `dd`, `yab`.
    Operate(Operator, Target),
    /// Mark the cursor's node with a letter (`ma`).
    SetMark(char),
    /// Go to a marked node (`'a`).
    JumpToMark(char),

    // Jumping around.
    Search,
    JumpBack,
    JumpForward,
    FollowPortal,
    FollowLink,
    /// `gu`: up to where the document is reached from (the portals that
    /// lead to it).
    GoUp,
    /// Enter: edit the title, or go through a portal.
    Activate,

    // The view.
    Center,
    ScrollDown,
    ScrollUp,
    ScrollLeft,
    ScrollRight,
    HalfPageDown,
    HalfPageUp,
    ZoomIn,
    ZoomOut,
    ToggleFold,
    OpenFold,
    CloseFold,
    AutoFold,
    OpenAllFolds,
    CloseAllFolds,
    ToggleFocus,
    ShowBody,
    /// The outline: every body under its title, or none.
    ToggleBodies,

    // Creating and editing.
    AddBelow,
    AddAbove,
    AddChild,
    EditTitle,
    EditTitleAtStart,
    RetypeTitle,
    /// In the K card: type in the body, at its end.
    EditBody,
    /// In the K card: type in the body, at its start.
    EditBodyAtStart,
    /// `x`: delete just this node; its children move up.
    DeleteNode,
    /// Inside text: paste after the text cursor.
    PasteAfter,
    /// Inside text: paste before the text cursor.
    PasteBefore,
    /// `p` on nodes: paste as the node's last children.
    PasteAsChild,
    /// `P` on nodes: paste as the node's next siblings.
    PasteAsSibling,
    Undo,
    Redo,
    Repeat,

    // Vim keys inside text.
    /// `i`: type before the cursor.
    InsertBefore,
    /// `a`: type after the cursor.
    InsertAfter,
    /// `I`: type at the start of the line.
    InsertAtStart,
    /// `A`: type at the end of the line.
    InsertAtEnd,
    /// `r`: this character in place of the cursor's.
    ReplaceChar(char),
    /// `~`: upper case to lower case and back.
    SwitchCase,
    /// `J`: the next line joins this one.
    JoinLines,

    // Typing.
    /// Backspace.
    DeleteBefore,
    /// Delete.
    DeleteAfter,
    /// `Ctrl-w`.
    DeleteWordBefore,
    /// `Ctrl-u`.
    DeleteLineBefore,

    // Arranging.
    /// Lay the cursor's branch out (or each selected one).
    Tidy(Layout),
    /// Line the selected nodes up.
    Align(Side),

    // Looks, tags, portals.
    PickColor,
    PickStyle,
    PickBorder,
    EditTags,
    NewPortal,
    Capture,

    // Modes.
    Visual,
    VisualBranches,
    MoveMode,
    ConnectMode,
    CommandLine,
    Escape,

    // In visual, move and connect modes.
    SwapEnds,
    FarLeft,
    FarDown,
    FarUp,
    FarRight,
    ToggleWhole,
    Confirm,
    RemoveLink,
    AttachAsChild,
    CycleArrows,
    CycleLine,
    EditLabel,

    // Panes and documents.
    SplitVertical,
    SplitHorizontal,
    FocusLeft,
    FocusDown,
    FocusUp,
    FocusRight,
    NextPane,
    ClosePane,
    OnlyPane,
    EqualizePanes,
    NextDocument,
    PreviousDocument,
    PickDocument,
    ShowCanvas,
    ShowOutline,
    ShowNote,

    // Help and the app.
    Help,
    ToggleWhichKey,
    /// `ZZ`: close the pane (everything is saved already).
    Close,
}

/// What a key sequence is bound to.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum Bound {
    /// A command, run as soon as its keys are typed.
    Command(Command),
    /// An operator: it waits for a target.
    Operator(Operator),
    /// A key that waits for one more character.
    WithChar(CharKey),
}

/// What a key sequence typed after an operator means.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum TargetBound {
    Target(Target),
    WithChar(CharKey),
}

/// A command's name in `keys.toml`, and what it does.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct CommandInfo {
    pub name: &'static str,
    pub bound: Bound,
    pub help: &'static str,
}

const fn info(name: &'static str, command: Command, help: &'static str) -> CommandInfo {
    CommandInfo { name, bound: Bound::Command(command), help }
}

const fn motion(name: &'static str, motion: Motion, help: &'static str) -> CommandInfo {
    info(name, Command::Move(motion), help)
}

const fn operator(name: &'static str, operator: Operator, help: &'static str) -> CommandInfo {
    CommandInfo { name, bound: Bound::Operator(operator), help }
}

const fn with_char(name: &'static str, key: CharKey, help: &'static str) -> CommandInfo {
    CommandInfo { name, bound: Bound::WithChar(key), help }
}

use Command as C;
use Motion as M;
use Operator as Op;

/// Every command keys can be bound to, by name. A name in `keys.toml` is
/// one of these.
pub const COMMANDS: &[CommandInfo] = &[
    // Moving the cursor.
    motion("left", M::Left, "left"),
    motion("down", M::Down, "down"),
    motion("up", M::Up, "up"),
    motion("right", M::Right, "right"),
    motion("parent", M::Parent, "the parent"),
    motion("first-child", M::FirstChild, "the first child"),
    motion("next-sibling", M::NextSibling, "the next sibling"),
    motion("previous-sibling", M::PreviousSibling, "the previous sibling"),
    motion("next", M::Next, "the next node, in reading order"),
    motion("previous", M::Previous, "the previous node, in reading order"),
    motion("first", M::First, "the root"),
    motion("last", M::Last, "the last node"),
    motion("word-end", M::WordEnd, "the end of the word"),
    motion("line-start", M::LineStart, "the start of the line"),
    motion("first-non-blank", M::FirstNonBlank, "the first character of the line that isn't a space"),
    motion("line-end", M::LineEnd, "the end of the line"),
    motion("repeat-find", M::RepeatFind, "the last f / t again"),
    motion("repeat-find-backward", M::RepeatFindBackward, "the last f / t again, the other way"),
    motion("search-next", M::SearchNext, "the next match"),
    motion("search-previous", M::SearchPrevious, "the previous match"),
    with_char("find-forward", CharKey::FindForward, "to a character"),
    with_char("find-backward", CharKey::FindBackward, "back to a character"),
    with_char("till-forward", CharKey::TillForward, "up to a character"),
    with_char("till-backward", CharKey::TillBackward, "back up to a character"),
    with_char("set-mark", CharKey::SetMark, "mark this node"),
    with_char("jump-to-mark", CharKey::JumpToMark, "go to a mark"),
    info("search", C::Search, "search"),
    info("jump-back", C::JumpBack, "jump back"),
    info("jump-forward", C::JumpForward, "jump forward"),
    info("follow-portal", C::FollowPortal, "through the portal"),
    info("follow-link", C::FollowLink, "follow a cross-link"),
    info("go-up", C::GoUp, "up to the portals that lead here"),
    info("activate", C::Activate, "edit the title, or go through a portal"),
    // The view.
    info("center", C::Center, "center the view"),
    info("scroll-down", C::ScrollDown, "scroll down"),
    info("scroll-up", C::ScrollUp, "scroll up"),
    info("scroll-left", C::ScrollLeft, "scroll left"),
    info("scroll-right", C::ScrollRight, "scroll right"),
    info("half-page-down", C::HalfPageDown, "half a screen down"),
    info("half-page-up", C::HalfPageUp, "half a screen up"),
    info("zoom-in", C::ZoomIn, "zoom in"),
    info("zoom-out", C::ZoomOut, "zoom out"),
    info("fold-toggle", C::ToggleFold, "fold or unfold"),
    info("fold-open", C::OpenFold, "unfold"),
    info("fold-close", C::CloseFold, "fold"),
    info("fold-auto", C::AutoFold, "fold automatically (open while inside)"),
    info("fold-open-all", C::OpenAllFolds, "unfold everything"),
    info("fold-close-all", C::CloseAllFolds, "fold everything"),
    info("focus", C::ToggleFocus, "focus: fold the other branches"),
    info("show-body", C::ShowBody, "show the body"),
    info("toggle-bodies", C::ToggleBodies, "show every body under its title, or none"),
    // Creating and editing.
    info("add-below", C::AddBelow, "new sibling below"),
    info("add-above", C::AddAbove, "new sibling above"),
    info("add-child", C::AddChild, "new child"),
    info("edit-title", C::EditTitle, "edit the title"),
    info("edit-title-start", C::EditTitleAtStart, "edit the title from its start"),
    info("retype-title", C::RetypeTitle, "retype the title"),
    info("edit-body", C::EditBody, "edit the body"),
    info("edit-body-start", C::EditBodyAtStart, "edit the body from its start"),
    info("delete-node", C::DeleteNode, "delete just this node (children move up)"),
    operator("delete", Op::Delete, "delete…"),
    operator("yank", Op::Yank, "yank (copy)…"),
    operator("change", Op::Change, "change…"),
    operator("indent", Op::Indent, "indent…"),
    operator("outdent", Op::Outdent, "outdent…"),
    info("delete-branch", C::Operate(Op::Delete, Target::Branch), "delete the branch"),
    info("delete-children", C::Operate(Op::Delete, Target::Children), "delete the children"),
    info("yank-branch", C::Operate(Op::Yank, Target::Branch), "yank the branch"),
    info("yank-children", C::Operate(Op::Yank, Target::Children), "yank the children"),
    info("delete-selection", C::Operate(Op::Delete, Target::Selection), "delete the selection"),
    info("yank-selection", C::Operate(Op::Yank, Target::Selection), "yank the selection"),
    info("indent-selection", C::Operate(Op::Indent, Target::Selection), "indent the selection"),
    info("outdent-selection", C::Operate(Op::Outdent, Target::Selection), "outdent the selection"),
    info("paste-after", C::PasteAfter, "paste after"),
    info("paste-before", C::PasteBefore, "paste before"),
    info("paste-as-child", C::PasteAsChild, "paste as children"),
    info("paste-as-sibling", C::PasteAsSibling, "paste as siblings below"),
    info("undo", C::Undo, "undo"),
    info("redo", C::Redo, "redo"),
    info("repeat", C::Repeat, "repeat the last change"),
    info("indent-node", C::Operate(Op::Indent, Target::Current), "under the node above"),
    info("outdent-node", C::Operate(Op::Outdent, Target::Current), "out from under its parent"),
    // Vim keys inside text.
    info("insert", C::InsertBefore, "type before the cursor"),
    info("append", C::InsertAfter, "type after the cursor"),
    info("insert-at-start", C::InsertAtStart, "type at the start of the line"),
    info("append-at-end", C::InsertAtEnd, "type at the end of the line"),
    with_char("replace-char", CharKey::Replace, "replace the character"),
    info("switch-case", C::SwitchCase, "switch upper and lower case"),
    info("join-lines", C::JoinLines, "join the next line to this one"),
    // Typing.
    info("delete-before", C::DeleteBefore, "delete the character before the cursor"),
    info("delete-after", C::DeleteAfter, "delete the character after the cursor"),
    info("delete-word-before", C::DeleteWordBefore, "delete the word before the cursor"),
    info("delete-line-before", C::DeleteLineBefore, "delete back to the start of the line"),
    // Arranging.
    info("tidy-map", C::Tidy(Layout::Map), "tidy: a mind map"),
    info("tidy-chart", C::Tidy(Layout::Chart), "tidy: an org chart"),
    info("tidy-grid", C::Tidy(Layout::Grid), "tidy: a grid beside it"),
    info("align-left", C::Align(Side::Left), "left edges in a line"),
    info("align-right", C::Align(Side::Right), "right edges in a line"),
    info("align-top", C::Align(Side::Top), "top edges in a line"),
    info("align-bottom", C::Align(Side::Bottom), "bottom edges in a line"),
    info("align-center", C::Align(Side::Center), "middles in a column"),
    // Looks, tags, portals.
    info("pick-color", C::PickColor, "color…"),
    info("pick-style", C::PickStyle, "style…"),
    info("pick-border", C::PickBorder, "border…"),
    info("edit-tags", C::EditTags, "tags…"),
    info("new-portal", C::NewPortal, "new portal…"),
    info("capture", C::Capture, "capture an idea to the inbox…"),
    // Modes.
    info("visual", C::Visual, "select"),
    info("visual-branches", C::VisualBranches, "select whole branches"),
    info("move-mode", C::MoveMode, "move mode"),
    info("connect-mode", C::ConnectMode, "connect mode"),
    info("command-line", C::CommandLine, "command line"),
    info("escape", C::Escape, "cancel"),
    // In visual, move and connect modes.
    info("swap-ends", C::SwapEnds, "the other end of the selection"),
    info("far-left", C::FarLeft, "left by five"),
    info("far-down", C::FarDown, "down by five"),
    info("far-up", C::FarUp, "up by five"),
    info("far-right", C::FarRight, "right by five"),
    info("toggle-whole", C::ToggleWhole, "the whole branch, or just this node"),
    info("confirm", C::Confirm, "confirm"),
    info("remove-link", C::RemoveLink, "remove the link"),
    info("attach-as-child", C::AttachAsChild, "attach as a child here"),
    info("cycle-arrows", C::CycleArrows, "arrowheads"),
    info("cycle-line", C::CycleLine, "line kind"),
    info("edit-label", C::EditLabel, "label…"),
    // Panes and documents.
    info("split-vertical", C::SplitVertical, "split side by side"),
    info("split-horizontal", C::SplitHorizontal, "split above and below"),
    info("focus-left", C::FocusLeft, "the pane on the left"),
    info("focus-down", C::FocusDown, "the pane below"),
    info("focus-up", C::FocusUp, "the pane above"),
    info("focus-right", C::FocusRight, "the pane on the right"),
    info("next-pane", C::NextPane, "the next pane"),
    info("close-pane", C::ClosePane, "close the pane"),
    info("only-pane", C::OnlyPane, "close the other panes"),
    info("equalize-panes", C::EqualizePanes, "even out the panes"),
    info("next-document", C::NextDocument, "the next document"),
    info("previous-document", C::PreviousDocument, "the previous document"),
    info("pick-document", C::PickDocument, "documents…"),
    info("show-canvas", C::ShowCanvas, "canvas"),
    info("show-outline", C::ShowOutline, "outline"),
    info("show-note", C::ShowNote, "note"),
    // Help and the app.
    info("help", C::Help, "help: every key"),
    info("toggle-which-key", C::ToggleWhichKey, "key hints on or off"),
    info("close", C::Close, "close the pane"),
];

/// The command with this name in `keys.toml`.
pub fn by_name(name: &str) -> Option<&'static CommandInfo> {
    COMMANDS.iter().find(|info| info.name == name)
}

/// What a binding does, in words (for which-key and the help).
pub fn help_for(bound: Bound) -> &'static str {
    COMMANDS.iter().find(|info| info.bound == bound).map_or("", |info| info.help)
}

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

    #[test]
    fn names_are_unique_kebab_case() {
        for (index, info) in COMMANDS.iter().enumerate() {
            assert!(info.name.chars().all(|c| c.is_ascii_lowercase() || c == '-'), "{}", info.name);
            assert!(COMMANDS[index + 1..].iter().all(|other| other.name != info.name), "{} twice", info.name);
            assert!(
                COMMANDS[index + 1..].iter().all(|other| other.bound != info.bound),
                "{:?} twice",
                info.bound
            );
        }
    }

    #[test]
    fn registers_by_name() {
        assert_eq!(Register::named('A'), Some(Register::Named('a')));
        assert_eq!(Register::named('*'), Some(Register::Clipboard));
        assert_eq!(Register::named('1'), None);
    }
}