//! The per-OS text-editing keymap: a keypress and modifiers to an engine [`EditAction`] or a
//! host-side clipboard operation. The Windows/Linux table is the reference's key handler
//! (`0x77b160`: Ctrl+arrows by word, Ctrl+A/C/X/V, Ctrl/Shift+Insert, Shift+Delete).
//! Deviation: macOS takes the Cocoa text-field chords and Ctrl+Backspace/Delete delete a word,
//! because editing follows each OS's own text fields.

use benilla_ui::script::{EditAction, EditUnit};
use bevy::input::keyboard::KeyCode;

/// The modifier snapshot a chord is read against; `sup` is Cmd on macOS, the OS key elsewhere.
#[derive(Clone, Copy, Default)]
pub(crate) struct Mods {
    pub(crate) shift: bool,
    pub(crate) ctrl: bool,
    pub(crate) alt: bool,
    pub(crate) sup: bool,
}

/// What a keypress means for the focused box.
#[derive(Clone, Copy, Debug, PartialEq)]
pub(crate) enum Chord {
    /// A semantic edit for `UiScript::editbox_action`.
    Edit(EditAction),
    /// Copy the selection to the OS clipboard (`UiScript::editbox_copy` + host write).
    Copy,
    /// Copy, then delete the selection.
    Cut,
    /// Paste the OS clipboard (host read + `UiScript::paste`).
    Paste,
}

/// What `key` under `m` means; `None` falls through to character input.
pub(crate) fn chord(key: KeyCode, m: Mods, mac: bool) -> Option<Chord> {
    if mac {
        chord_mac(key, m)
    } else {
        chord_pc(key, m)
    }
}

/// macOS, the Cocoa text-field chords: Option is a word, Cmd the line edge; plain Up/Down recall
/// history. Cocoa's Emacs Ctrl set is left unbound.
fn chord_mac(key: KeyCode, m: Mods) -> Option<Chord> {
    use EditUnit::{Char, Edge, Word};
    let mv = |unit, back| {
        Some(Chord::Edit(EditAction::Move {
            unit,
            back,
            extend: m.shift,
        }))
    };
    let del = |unit, back| Some(Chord::Edit(EditAction::Delete { unit, back }));
    match key {
        KeyCode::ArrowLeft | KeyCode::ArrowRight => {
            let back = key == KeyCode::ArrowLeft;
            if m.sup {
                mv(Edge, back)
            } else if m.alt {
                mv(Word, back)
            } else {
                mv(Char, back)
            }
        }
        // Cmd+Up/Down is the box's start/end; Shift extends there.
        KeyCode::ArrowUp | KeyCode::ArrowDown => {
            let back = key == KeyCode::ArrowUp;
            if m.sup || m.shift {
                mv(Edge, back)
            } else if m.alt || m.ctrl {
                None
            } else if back {
                Some(Chord::Edit(EditAction::HistoryPrev))
            } else {
                Some(Chord::Edit(EditAction::HistoryNext))
            }
        }
        KeyCode::Home => mv(Edge, true),
        KeyCode::End => mv(Edge, false),
        KeyCode::Backspace => {
            if m.sup {
                del(Edge, true)
            } else if m.alt {
                del(Word, true)
            } else {
                del(Char, true)
            }
        }
        KeyCode::Delete => {
            if m.sup {
                del(Edge, false)
            } else if m.alt {
                del(Word, false)
            } else {
                del(Char, false)
            }
        }
        KeyCode::KeyA if m.sup => Some(Chord::Edit(EditAction::SelectAll)),
        KeyCode::KeyC if m.sup => Some(Chord::Copy),
        KeyCode::KeyX if m.sup => Some(Chord::Cut),
        KeyCode::KeyV if m.sup => Some(Chord::Paste),
        _ => None,
    }
}

/// Windows/Linux: the reference's chords (`0x77b160`) plus the Ctrl word deletes.
fn chord_pc(key: KeyCode, m: Mods) -> Option<Chord> {
    use EditUnit::{Char, Edge, Word};
    let mv = |unit, back| {
        Some(Chord::Edit(EditAction::Move {
            unit,
            back,
            extend: m.shift,
        }))
    };
    let del = |unit, back| Some(Chord::Edit(EditAction::Delete { unit, back }));
    match key {
        // Ctrl picks the word helper, as the reference forks on its Ctrl test `0x41f8f0(1)`.
        KeyCode::ArrowLeft | KeyCode::ArrowRight => {
            let back = key == KeyCode::ArrowLeft;
            if m.ctrl {
                mv(Word, back)
            } else {
                mv(Char, back)
            }
        }
        // Plain Up/Down only: history recall.
        KeyCode::ArrowUp if !(m.ctrl || m.alt || m.shift || m.sup) => {
            Some(Chord::Edit(EditAction::HistoryPrev))
        }
        KeyCode::ArrowDown if !(m.ctrl || m.alt || m.shift || m.sup) => {
            Some(Chord::Edit(EditAction::HistoryNext))
        }
        KeyCode::Home => mv(Edge, true),
        KeyCode::End => mv(Edge, false),
        // Shift+Delete cuts, as the reference does (`0x77b160`).
        KeyCode::Backspace => {
            if m.ctrl {
                del(Word, true)
            } else {
                del(Char, true)
            }
        }
        KeyCode::Delete => {
            if m.shift && !m.ctrl {
                Some(Chord::Cut)
            } else if m.ctrl {
                del(Word, false)
            } else {
                del(Char, false)
            }
        }
        // The reference's other CUA mirrors: Ctrl+Insert copies, Shift+Insert pastes.
        KeyCode::Insert if m.ctrl => Some(Chord::Copy),
        KeyCode::Insert if m.shift => Some(Chord::Paste),
        // `!m.alt` excludes AltGr, which arrives as Ctrl+Alt and types letters on European
        // layouts (Polish AltGr+A is `ą`); must agree with the char-input branch in `input.rs`.
        KeyCode::KeyA if m.ctrl && !m.alt => Some(Chord::Edit(EditAction::SelectAll)),
        KeyCode::KeyC if m.ctrl && !m.alt => Some(Chord::Copy),
        KeyCode::KeyX if m.ctrl && !m.alt => Some(Chord::Cut),
        KeyCode::KeyV if m.ctrl && !m.alt => Some(Chord::Paste),
        _ => None,
    }
}

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

    const NONE: Mods = Mods {
        shift: false,
        ctrl: false,
        alt: false,
        sup: false,
    };
    const SHIFT: Mods = Mods {
        shift: true,
        ..NONE
    };
    const CTRL: Mods = Mods { ctrl: true, ..NONE };
    const ALT: Mods = Mods { alt: true, ..NONE };
    const SUP: Mods = Mods { sup: true, ..NONE };

    fn edit(c: Option<Chord>) -> EditAction {
        match c {
            Some(Chord::Edit(a)) => a,
            other => panic!("expected an edit action, got {other:?}"),
        }
    }

    #[test]
    fn mac_table() {
        use EditAction::*;
        use EditUnit::*;
        assert_eq!(
            edit(chord(KeyCode::ArrowLeft, NONE, true)),
            Move {
                unit: Char,
                back: true,
                extend: false
            }
        );
        assert_eq!(
            edit(chord(KeyCode::ArrowRight, ALT, true)),
            Move {
                unit: Word,
                back: false,
                extend: false
            }
        );
        assert_eq!(
            edit(chord(KeyCode::ArrowLeft, SUP, true)),
            Move {
                unit: Edge,
                back: true,
                extend: false
            }
        );
        assert_eq!(
            edit(chord(
                KeyCode::ArrowRight,
                Mods { shift: true, ..ALT },
                true
            )),
            Move {
                unit: Word,
                back: false,
                extend: true
            }
        );
        assert_eq!(edit(chord(KeyCode::ArrowUp, NONE, true)), HistoryPrev);
        assert_eq!(edit(chord(KeyCode::ArrowDown, NONE, true)), HistoryNext);
        assert_eq!(
            edit(chord(KeyCode::ArrowUp, SHIFT, true)),
            Move {
                unit: Edge,
                back: true,
                extend: true
            }
        );
        assert_eq!(
            edit(chord(KeyCode::ArrowDown, SUP, true)),
            Move {
                unit: Edge,
                back: false,
                extend: false
            }
        );
        assert_eq!(
            edit(chord(KeyCode::Backspace, SUP, true)),
            Delete {
                unit: Edge,
                back: true
            }
        );
        assert_eq!(
            edit(chord(KeyCode::Backspace, ALT, true)),
            Delete {
                unit: Word,
                back: true
            }
        );
        assert_eq!(
            edit(chord(KeyCode::Delete, ALT, true)),
            Delete {
                unit: Word,
                back: false
            }
        );
        assert_eq!(edit(chord(KeyCode::KeyA, SUP, true)), SelectAll);
        assert_eq!(chord(KeyCode::KeyC, SUP, true), Some(Chord::Copy));
        assert_eq!(chord(KeyCode::KeyX, SUP, true), Some(Chord::Cut));
        assert_eq!(chord(KeyCode::KeyV, SUP, true), Some(Chord::Paste));
        assert_eq!(chord(KeyCode::KeyA, CTRL, true), None);
        assert_eq!(chord(KeyCode::KeyA, NONE, true), None);
    }

    #[test]
    fn pc_table() {
        use EditAction::*;
        use EditUnit::*;
        assert_eq!(
            edit(chord(KeyCode::ArrowLeft, CTRL, false)),
            Move {
                unit: Word,
                back: true,
                extend: false
            }
        );
        assert_eq!(
            edit(chord(KeyCode::ArrowRight, SHIFT, false)),
            Move {
                unit: Char,
                back: false,
                extend: true
            }
        );
        assert_eq!(edit(chord(KeyCode::ArrowUp, NONE, false)), HistoryPrev);
        assert_eq!(chord(KeyCode::ArrowUp, SHIFT, false), None);
        assert_eq!(
            edit(chord(KeyCode::End, SHIFT, false)),
            Move {
                unit: Edge,
                back: false,
                extend: true
            }
        );
        assert_eq!(
            edit(chord(KeyCode::Backspace, CTRL, false)),
            Delete {
                unit: Word,
                back: true
            }
        );
        assert_eq!(
            edit(chord(KeyCode::Delete, CTRL, false)),
            Delete {
                unit: Word,
                back: false
            }
        );
        assert_eq!(edit(chord(KeyCode::KeyA, CTRL, false)), SelectAll);
        assert_eq!(chord(KeyCode::KeyC, CTRL, false), Some(Chord::Copy));
        assert_eq!(chord(KeyCode::KeyV, CTRL, false), Some(Chord::Paste));
        assert_eq!(chord(KeyCode::Insert, CTRL, false), Some(Chord::Copy));
        assert_eq!(chord(KeyCode::Insert, SHIFT, false), Some(Chord::Paste));
        assert_eq!(chord(KeyCode::Delete, SHIFT, false), Some(Chord::Cut));
        assert_eq!(chord(KeyCode::KeyA, SUP, false), None);
    }

    /// AltGr arrives as Ctrl+Alt and types letters on European layouts (Polish `ą`, `ć`, `ź`).
    #[test]
    fn altgr_letters_are_not_clipboard_chords() {
        const ALTGR: Mods = Mods {
            ctrl: true,
            alt: true,
            ..NONE
        };
        for key in [KeyCode::KeyA, KeyCode::KeyC, KeyCode::KeyX, KeyCode::KeyV] {
            assert_eq!(
                chord(key, ALTGR, false),
                None,
                "AltGr+{key:?} must reach character input, not act as a clipboard chord"
            );
        }
        assert_eq!(
            edit(chord(KeyCode::KeyA, CTRL, false)),
            EditAction::SelectAll
        );
        assert_eq!(chord(KeyCode::KeyC, CTRL, false), Some(Chord::Copy));
        assert_eq!(chord(KeyCode::KeyX, CTRL, false), Some(Chord::Cut));
        assert_eq!(chord(KeyCode::KeyV, CTRL, false), Some(Chord::Paste));
    }
}