//! Connect mode (`C`): the cursor goes to another node, a line follows it
//! there, and Enter links the two (DESIGN.md, "Keys"). On the way, `d`
//! removes the line already there (a branch between a parent and its child
//! is cut, and the child comes loose), `>` puts the node under the other
//! one, and the `<Space>` keys style the line, branch or link, as you watch.
//! Everything connect mode changes is one undo step, which Esc takes back;
//! when it's done, the cursor goes back to where it started (the user's
//! pick in part 8d).
//!
//! From visual mode, every selected node connects to the one you go to.

use ratatui::style::Color;

use super::action::{self, Action, AppAction, DocAction, Message};
use super::mode::Connect;
use super::popup::{LinePick, PickKind};
use crate::config::theme_file::{ARROWS, STROKES};
use crate::input::command::Command;
use crate::input::engine::Typed;
use crate::model::{EditOp, Label, LineLook, LineRef, Link, NodeId, Spot};
use crate::ui::theme::LineStyle;
use crate::view::ViewContext;

/// Connect mode's answer to a command, or `None` for the ones that move the
/// cursor as usual.
pub fn command(typed: &Typed, connect: &Connect, ctx: &ViewContext<'_>) -> Option<Vec<Action>> {
    let actions = match typed.command {
        Command::Confirm => link(connect, ctx),
        Command::RemoveLink => remove(connect, ctx),
        Command::AttachAsChild => attach(connect, ctx),
        Command::CycleArrows => cycle_arrows(connect, ctx),
        Command::CycleLine => cycle_line(connect, ctx),
        Command::PickColor => picker(connect, ctx, LinePick::Color),
        Command::PickStyle => picker(connect, ctx, LinePick::Style),
        Command::EditLabel => picker(connect, ctx, LinePick::Label),
        Command::Escape => cancel(connect),
        // The other end is in this document.
        Command::FollowPortal | Command::JumpBack | Command::JumpForward | Command::GoUp => {
            say(Message::info("connect mode stays in this document: Enter or Esc first"))
        }
        Command::SetMark(name) | Command::JumpToMark(name) if name.is_ascii_uppercase() => {
            say(Message::info("connect mode stays in this document: Enter or Esc first"))
        }
        Command::Search => {
            say(Message::info("n and N find the last search again here: / starts one in normal mode"))
        }
        _ => return None,
    };
    Some(actions)
}

/// The nodes being connected to `target`: the sources, but not the target
/// itself.
pub fn others(connect: &Connect, target: NodeId) -> Vec<NodeId> {
    connect.sources.iter().copied().filter(|&id| id != target).collect()
}

/// What's being connected to what: `Raised beds → Watering`.
pub fn ends(connect: &Connect, ctx: &ViewContext<'_>) -> String {
    let target = ctx.cursor;
    match others(connect, target).as_slice() {
        [] => format!("{} → ?", what(ctx, &connect.sources)),
        sources => format!("{} → {}", what(ctx, sources), title(ctx, target)),
    }
}

/// What the status bar says in connect mode, in place of the breadcrumb:
/// what's being connected to what, and what joins them already.
pub fn status(connect: &Connect, ctx: &ViewContext<'_>) -> String {
    let target = ctx.cursor;
    let sources = others(connect, target);
    let mut text = ends(connect, ctx);
    if sources.is_empty() {
        text.push_str(" · go to the node to connect");
    }
    if let [source] = sources.as_slice() {
        match ctx.doc.line_between(*source, target) {
            Some(LineRef::Link(_)) => text.push_str(" · linked"),
            Some(LineRef::Branch(child)) if child == target => text.push_str(" · its child"),
            Some(LineRef::Branch(_)) => text.push_str(" · its parent"),
            None => {}
        }
    }
    text
}

/// The lines from each node being connected to the cursor's, changed by
/// `change`: a line that isn't there yet is made, as a link with that look.
pub fn restyle(connect: &Connect, ctx: &ViewContext<'_>, change: impl Fn(&mut LineLook)) -> Vec<Action> {
    let target = ctx.cursor;
    others(connect, target)
        .into_iter()
        .filter_map(|source| {
            let op = match ctx.doc.line_between(source, target) {
                Some(line) => {
                    let mut look = ctx.doc.line_look(line).cloned().unwrap_or_default();
                    change(&mut look);
                    EditOp::SetLine { line, look }
                }
                None => {
                    let mut link = Link::new(source, target)?;
                    change(&mut link.look);
                    EditOp::Link(link)
                }
            };
            Some(Action::edit_in(op, connect.group))
        })
        .collect()
}

/// The labels of the links from each node being connected to the cursor's
/// (made if they aren't there yet). A branch has no label: it's left alone.
pub fn relabel(connect: &Connect, ctx: &ViewContext<'_>, label: &Option<Label>) -> Vec<Action> {
    let target = ctx.cursor;
    others(connect, target)
        .into_iter()
        .filter_map(|source| {
            let op = match ctx.doc.line_between(source, target) {
                Some(LineRef::Link(key)) => EditOp::SetLabel { key, label: label.clone() },
                Some(LineRef::Branch(_)) => return None,
                None => {
                    let mut link = Link::new(source, target)?;
                    link.label = label.clone();
                    EditOp::Link(link)
                }
            };
            Some(Action::edit_in(op, connect.group))
        })
        .collect()
}

/// The line connect mode works on first: from the first node being
/// connected to the cursor's, if anything joins them.
pub fn first_line(connect: &Connect, ctx: &ViewContext<'_>) -> Option<LineRef> {
    let target = ctx.cursor;
    let source = *others(connect, target).first()?;
    ctx.doc.line_between(source, target)
}

/// Enter: links each node to the cursor's, unless a line joins them
/// already, and connect mode is done.
fn link(connect: &Connect, ctx: &ViewContext<'_>) -> Vec<Action> {
    let target = ctx.cursor;
    let sources = others(connect, target);
    if sources.is_empty() {
        return aim_first();
    }
    let links: Vec<Link> = sources
        .iter()
        .filter(|&&source| ctx.doc.line_between(source, target).is_none())
        .filter_map(|&source| Link::new(source, target))
        .collect();
    let mut actions: Vec<Action> =
        links.iter().map(|link| Action::edit_in(EditOp::Link(link.clone()), connect.group)).collect();
    actions.extend(done(connect));
    if !links.is_empty() {
        let from: Vec<NodeId> = links.iter().map(Link::start).collect();
        let text = format!("linked {} → {}", what(ctx, &from), title(ctx, target));
        actions.push(Action::say(Message::done(text)));
    }
    actions
}

/// `d`: removes each line between a node and the cursor's. A link goes; a
/// branch is cut, and the child comes loose with its own branch.
fn remove(connect: &Connect, ctx: &ViewContext<'_>) -> Vec<Action> {
    let target = ctx.cursor;
    let sources = others(connect, target);
    if sources.is_empty() {
        return aim_first();
    }
    let (mut ops, mut loose) = (Vec::new(), Vec::new());
    for &source in &sources {
        match ctx.doc.line_between(source, target) {
            Some(LineRef::Link(key)) => ops.push(EditOp::Unlink(vec![key])),
            Some(LineRef::Branch(child)) => {
                ops.push(EditOp::MoveTo { id: child, spot: Spot::Loose });
                loose.push(child);
            }
            None => {}
        }
    }
    let text = match (ops.len(), loose.as_slice()) {
        (0, _) => {
            let text =
                format!("nothing joins {} and {}: Enter links them", what(ctx, &sources), title(ctx, target));
            return say(Message::info(text));
        }
        (1, [child]) => format!("cut the branch: {} is a loose node now", title(ctx, *child)),
        (1, _) => format!("unlinked {} and {}", what(ctx, &sources), title(ctx, target)),
        (count, _) => format!("removed {count} lines"),
    };
    let mut actions: Vec<Action> = ops.into_iter().map(|op| Action::edit_in(op, connect.group)).collect();
    actions.extend(done(connect));
    actions.push(Action::say(Message::done(text)));
    actions
}

/// `>`: puts each node under the cursor's, as its last child, with its
/// branch. It stays where it is on the canvas, and a link between the two
/// goes: the branch takes its place.
fn attach(connect: &Connect, ctx: &ViewContext<'_>) -> Vec<Action> {
    let (doc, target) = (ctx.doc, ctx.cursor);
    let sources = others(connect, target);
    if sources.is_empty() {
        return aim_first();
    }
    if sources.contains(&doc.root()) {
        return say(Message::problem(
            "the root stays at the top: C on the other node puts that one under it",
        ));
    }
    if let Some(&holder) = sources.iter().find(|&&source| doc.is_inside(target, source)) {
        let text = format!(
            "{} is in {}'s branch, and a branch can't go inside itself",
            title(ctx, target),
            title(ctx, holder)
        );
        return say(Message::problem(text));
    }
    let moving: Vec<NodeId> =
        sources.into_iter().filter(|&source| doc.parent(source) != Some(target)).collect();
    if moving.is_empty() {
        return say(Message::info(format!("it's under {} already", title(ctx, target))));
    }
    let mut actions = Vec::new();
    for &source in &moving {
        if let Some(LineRef::Link(key)) = doc.line_between(source, target) {
            actions.push(Action::edit_in(EditOp::Unlink(vec![key]), connect.group));
        }
        let op = EditOp::MoveTo { id: source, spot: Spot::LastChildOf(target) };
        actions.push(Action::edit_in(op, connect.group));
    }
    actions.extend(done(connect));
    let verb = if moving.len() == 1 { "is" } else { "are" };
    let text = format!("{} {verb} under {} now", what(ctx, &moving), title(ctx, target));
    actions.push(Action::say(Message::done(text)));
    actions
}

/// `<Space>a`: the next arrowheads (off, end, start, both), after the ones
/// the first line has now, on every line.
fn cycle_arrows(connect: &Connect, ctx: &ViewContext<'_>) -> Vec<Action> {
    if others(connect, ctx.cursor).is_empty() {
        return aim_first();
    }
    let now = drawn(ctx, first_line(connect, ctx)).arrows;
    let at = ARROWS.iter().position(|&(_, arrows)| arrows == now).map_or(0, |at| (at + 1) % ARROWS.len());
    let (name, next) = ARROWS[at];
    let mut actions = restyle(connect, ctx, |look| look.arrows = Some(next));
    actions.push(Action::say(Message::info(format!("arrowheads: {name}"))));
    actions
}

/// `<Space>l`: the next kind of line (solid, dashed, dotted, thick,
/// double), after the one the first line has now, on every line.
fn cycle_line(connect: &Connect, ctx: &ViewContext<'_>) -> Vec<Action> {
    if others(connect, ctx.cursor).is_empty() {
        return aim_first();
    }
    let now = drawn(ctx, first_line(connect, ctx)).stroke;
    let at = STROKES.iter().position(|&(_, stroke)| stroke == now).map_or(0, |at| (at + 1) % STROKES.len());
    let (name, next) = STROKES[at];
    let mut actions = restyle(connect, ctx, |look| look.line = Some(next));
    actions.push(Action::say(Message::info(format!("line: {name}"))));
    actions
}

/// How a line is drawn now (one that isn't there yet: as a new link would
/// be).
fn drawn(ctx: &ViewContext<'_>, line: Option<LineRef>) -> LineStyle {
    let (theme, default) = (ctx.theme, LineLook::default());
    let look = line.and_then(|line| ctx.doc.line_look(line)).unwrap_or(&default);
    match line {
        Some(LineRef::Branch(_)) => theme.branch_style(look, Color::Reset),
        Some(LineRef::Link(_)) | None => theme.link_style(look, Color::Reset),
    }
}

/// `<Space>c`, `<Space>s` and `<Space>t`: a picker for the line, which
/// comes back to connect mode.
fn picker(connect: &Connect, ctx: &ViewContext<'_>, what: LinePick) -> Vec<Action> {
    let target = ctx.cursor;
    let sources = others(connect, target);
    if sources.is_empty() {
        return aim_first();
    }
    let branches = sources
        .iter()
        .all(|&source| matches!(ctx.doc.line_between(source, target), Some(LineRef::Branch(_))));
    if what == LinePick::Label && branches {
        return say(Message::info("a branch line has no label: links do"));
    }
    vec![Action::App(AppAction::OpenPicker(PickKind::Line(what)))]
}

/// Esc: everything connect mode changed is taken back.
pub fn cancel(connect: &Connect) -> Vec<Action> {
    let mut actions = vec![Action::Doc(DocAction::Cancel(connect.group))];
    actions.extend(done(connect));
    actions
}

/// Back to normal mode, with the cursor where `C` was typed.
fn done(connect: &Connect) -> Vec<Action> {
    vec![Action::App(AppAction::LeaveMode), Action::cursor(connect.start)]
}

fn aim_first() -> Vec<Action> {
    say(Message::info("go to the other node first (hjkl…), then Enter links them"))
}

/// A node's title, for messages.
fn title(ctx: &ViewContext<'_>, id: NodeId) -> String {
    ctx.doc.node(id).map(|node| node.title().to_string()).unwrap_or_default()
}

/// Some nodes, for messages: the title of one, or how many.
fn what(ctx: &ViewContext<'_>, ids: &[NodeId]) -> String {
    match ids {
        [id] => title(ctx, *id),
        _ => action::nodes(ids.len()),
    }
}

fn say(message: Message) -> Vec<Action> {
    vec![Action::say(message)]
}