// TRACES: FR-DEV-5 | FR-DEV-7
// The steps this photograph has been through, and the way back to any of them.
//
// **Nothing here names an operation, and nothing here names a step.** The rows
// arrive already resolved — Rust turns each step's localisation key into a
// display string against the UI's catalogue — so an operation added to the
// pipeline as a YAML declaration appears in this list under a sensible name
// with no change to this file, on the same terms it appears in the panel
// (FR-DEV-3c).
//
// **Why a list and not just the two buttons.** Undo answers "take back the
// last thing", which is the question a photographer asks about the mistake
// they have just noticed. It is the wrong instrument for the one they notice
// six adjustments later: eight presses, each changing the picture, with no way
// to see how far back the mistake was without passing through it. A step is a
// whole state in `dr-pipeline`, so arriving at one from six away costs what
// arriving from one does — which is what makes a row worth making clickable
// rather than decorative.

import { Theme } from "theme.slint";
import { Develop } from "session.slint";
import { PanelHeading, Caption, Label, Value, Button } from "widgets.slint";

// One step, flattened for Slint's model system.
export struct HistoryRow {
    // Routing back to the core: this step's position in the stack. **Not** its
    // position in this list, which runs the other way — see `history-rows` in
    // `develop.rs` for why the two are deliberately different numbers.
    index: int,

    // Resolved in Rust against the UI's catalogue; the core deals in keys.
    label: string,

    // The state the photograph is in right now. Exactly one row carries it.
    current: bool,

    // A step the photographer has stepped back *out* of, still reachable by
    // redo. Listed rather than hidden — redo would otherwise arrive somewhere
    // this panel never mentioned — but drawn as the branch it is.
    undone: bool,
}

component StepRow inherits Rectangle {
    in property <HistoryRow> data;
    in property <bool> enabled: true;
    callback picked();

    height: Theme.row-height;
    background: root.data.current
        ? Theme.selected
        : (touch.has-hover ? Theme.hover : transparent);

    touch := TouchArea {
        width: 100%;
        height: max(parent.height, Theme.touch-target);
        y: (parent.height - self.height) / 2;
        enabled: root.enabled;
        mouse-cursor: root.enabled ? MouseCursor.pointer : MouseCursor.default;
        clicked => { root.picked(); }
    }

    HorizontalLayout {
        // Small, because the panel around this already pads. The row's
        // background is the highlight for the current step, so it wants to be
        // a band the width of the column rather than a chip inset from it.
        padding-left: Theme.gap-sm;
        padding-right: Theme.gap-sm;
        spacing: Theme.gap-sm;

        // The mark for where the photograph stands. A filled bar against the
        // leading edge rather than a tick beside the name: the eye finds one
        // edge down a column of forty rows, and a glyph in the text column
        // would have to be read.
        Rectangle {
            width: 2px;
            height: parent.height;
            background: root.data.current ? Theme.active : transparent;
        }

        Label {
            text: root.data.label;
            emphasised: root.data.current || touch.has-hover;
            horizontal-stretch: 1;
            overflow: elide;
            // Dimmed rather than removed: this step is a future the
            // photographer stepped out of, and it is still where redo goes.
            opacity: root.data.undone ? 0.45 : 1.0;
        }
    }
}

/// TRACES: FR-DEV-5
/// The edit as a stack of steps, and the two ways of moving through it.
///
/// A global rather than five properties and three callbacks on the panel — see
/// `session.slint` for the argument. The status strip and the keyboard reach
/// the same two actions; before this all three spellings went through the
/// window root and had to be kept in step by hand.
///
/// Rust owns whether there is anywhere to step, because "anywhere" is a
/// position in a stack of snapshots this side never sees. A whole drag is one
/// step; the coalescing that makes it so lives in `dr-pipeline`.
export global Steps {
    /// Every step, newest first. Rust owns the order and stamps each row with
    /// its own position in the stack, so nothing here does arithmetic to turn
    /// a row back into a step.
    in property <[HistoryRow]> rows;
    in property <bool> can-undo: false;
    in property <bool> can-redo: false;
    /// What undo would take back, already resolved. Empty when there is
    /// nowhere to go.
    in property <string> undo-label: "";

    callback undo();
    callback redo();
    /// A row's own `index`, not its position in `rows`.
    callback picked(int);
}

export component HistoryPanel inherits Rectangle {
    background: Theme.surface;

    // **Flat, deliberately** — `MaskPanel` carries the long version of this
    // and it applies here unchanged: a nested layout under-reports its height,
    // so what follows it gets drawn on top of what came before, which is
    // invisible in the source and obvious the moment anyone opens the panel.
    // Every element is a direct child of the one layout that measures them,
    // and the ones that come and go carry their own condition rather than
    // being grouped inside a wrapper.
    //
    // No explicit height either, for the same reason `AdjustPanel` and
    // `MaskPanel` declare none: the row count changes as the photographer
    // works, and a height pinned to a layout's preferred size is one more
    // thing that has to keep up with a repeater.
    layout := VerticalLayout {
        padding: Theme.gap;
        spacing: Theme.gap-sm;
        alignment: start;

        // A heading, not a collapsible. `ComposePanel` carries the argument
        // and it holds here: the list is last in the column, so what a lid
        // would save is scrolling past nothing.
        HorizontalLayout {
            PanelHeading { text: "HISTORY"; }
            Rectangle { horizontal-stretch: 1; }
            if Develop.enabled && Steps.rows.length > 1: Value {
                text: Steps.rows.length - 1 + (Steps.rows.length == 2 ? " step" : " steps");
            }
        }

        if !Develop.enabled: Caption { text: "No image"; }

        // The pair, here as well as in the status strip. The strip's copy is
        // the one that survives the column being put away; this one sits
        // against the list that says what it will do, which is the pairing
        // that makes either of them legible.
        if Develop.enabled: HorizontalLayout {
            spacing: Theme.gap-sm;

            Button {
                text: "Undo";
                enabled: Steps.can-undo;
                horizontal-stretch: 1;
                clicked => { Steps.undo(); }
            }

            Button {
                text: "Redo";
                enabled: Steps.can-redo;
                horizontal-stretch: 1;
                clicked => { Steps.redo(); }
            }
        }

        // What the left-hand button would take back, spelled out.
        //
        // On a caption rather than on the button, because `Button` sizes to
        // its label and does not elide: "Undo Highlights & Shadows" is most of
        // a 280px column on its own, and two of those would lever the column
        // open — `MaskPanel` has the same note about an unwrapped sentence.
        //
        // Undo only. Redo's destination is the row directly above the mark in
        // the list below, where it can be seen; the step undo takes back is
        // the one the photographer is standing on and stopped tracking after a
        // run of small adjustments, which is the moment they are least willing
        // to press a button to find out.
        if Develop.enabled && Steps.can-undo: Caption {
            text: "Undo: " + Steps.undo-label;
            overflow: elide;
        }

        if Develop.enabled && Steps.rows.length > 0: Rectangle {
            height: 1px;
            background: Theme.rule;
        }

        // Newest first. The list is consulted to take back something just
        // done rather than browsed from the beginning — the order
        // `dr_catalog::trash` settled on for the same question — and it keeps
        // the end being worked at against the heading rather than sixty-four
        // rows below it.
        for row in Steps.rows: StepRow {
            data: row;
            enabled: Develop.enabled;
            picked => { Steps.picked(row.index); }
        }
    }
}