//! Named snapshots and the undo/redo stack.
use dr_pipeline::Edit;

use crate::labels;

use super::session::DevelopSession;

impl DevelopSession {
    // ---- named snapshots ---------------------------------------------------

    /// TRACES: FR-DEV-5
    /// Hand the session the snapshots its sidecar holds. Called once, on
    /// open, beside [`Self::apply_version`].
    pub fn set_snapshots(&mut self, snapshots: Vec<dr_pipeline::Version>) {
        self.snapshots = snapshots;
        self.removed_snapshots.clear();
    }

    /// The snapshots as they stand, oldest first.
    pub fn snapshots(&self) -> &[dr_pipeline::Version] {
        &self.snapshots
    }

    /// The ids deleted this sitting, for the save.
    pub fn removed_snapshots(&self) -> &[String] {
        &self.removed_snapshots
    }

    /// TRACES: FR-DEV-5
    /// Name the state the photograph is in, and keep it. Returns the id.
    ///
    /// Not a history step: taking a snapshot changes nothing about the edit,
    /// and an undo that removed one would be undoing a decision to remember
    /// rather than a change to the photograph. Deleting one is the same.
    ///
    /// The id is stamped with the second and a per-process random word
    /// rather than counted, because two devices can each take a snapshot of
    /// the same photograph and both have to survive the merge — which keys
    /// on this id, and would fold two `snap-3`s into one.
    pub fn take_snapshot(&mut self, name: &str) -> String {
        use std::hash::{BuildHasher, Hasher};
        let now = std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .map(|d| d.as_secs() as i64)
            .unwrap_or(0);
        let salt = std::collections::hash_map::RandomState::new()
            .build_hasher()
            .finish();
        let id = format!("snap-{now}-{:08x}", salt as u32);

        let name = name.trim();
        let name = if name.is_empty() {
            format!("Snapshot {}", self.snapshots.len() + 1)
        } else {
            name.to_string()
        };
        let mut version = dr_pipeline::Version::from_graph(id.clone(), name, &self.graph);
        // The stack with the model's coverage folded in, for the reason the
        // save uses it: a subject layer stored by identity alone renders as
        // nothing until a model is run, and a snapshot restored on the other
        // device, or in a batch export, never gets one.
        version.masks = self.masks_for_storage();
        version.modified = now;
        self.snapshots.push(version);
        id
    }

    /// TRACES: FR-DEV-5
    /// Put the photograph back the way a snapshot has it. One history step,
    /// so it is undoable as a whole, exactly as a paste is.
    pub fn restore_snapshot(&mut self, id: &str) -> bool {
        let Some(version) = self.snapshots.iter().find(|v| v.uuid == id).cloned() else {
            return false;
        };
        let rebake = version.apply(&mut self.graph);
        self.pay_film_debt(&rebake);
        self.history
            .record(&self.graph, Edit::Action(labels::step::SNAPSHOT_RESTORED));
        true
    }

    /// TRACES: FR-DEV-5
    pub fn rename_snapshot(&mut self, id: &str, name: &str) {
        let name = name.trim();
        if name.is_empty() {
            return;
        }
        if let Some(v) = self.snapshots.iter_mut().find(|v| v.uuid == id) {
            v.name = name.to_string();
        }
    }

    /// TRACES: FR-DEV-5
    /// Forget a snapshot. Remembered as a deletion so the save takes it out
    /// of the file rather than merely not putting it back.
    pub fn delete_snapshot(&mut self, id: &str) {
        let before = self.snapshots.len();
        self.snapshots.retain(|v| v.uuid != id);
        if self.snapshots.len() != before {
            self.removed_snapshots.push(id.to_string());
        }
        if self.compared_snapshot.as_deref() == Some(id) {
            self.compared_snapshot = None;
        }
    }

    /// TRACES: FR-DEV-7
    /// Hold a comparison against a snapshot, or let it go. Returns whether
    /// anything changed, so a repeat costs no render.
    pub fn compare_snapshot(&mut self, id: Option<&str>) -> bool {
        let id = id.filter(|id| self.snapshots.iter().any(|v| v.uuid == *id));
        if self.compared_snapshot.as_deref() == id {
            return false;
        }
        self.compared_snapshot = id.map(str::to_string);
        true
    }

    /// The snapshot being held against the edit, if one is.
    pub fn compared_snapshot(&self) -> Option<&str> {
        self.compared_snapshot.as_deref()
    }

    /// TRACES: FR-DEV-7
    /// Render the photograph as a snapshot has it, without becoming it.
    ///
    /// The same suspension [`Self::render_original`] uses — borrow the graph
    /// for one render and hand it back — because it is the same question
    /// about a different reference point: "the version I liked twenty
    /// minutes ago" instead of the file. Nothing is recorded and nothing is
    /// marked modified. A held comparison against a snapshot that has since
    /// been deleted falls back to the edit itself, which is what is on
    /// screen anyway.
    pub fn render_compared(&mut self, width: u32, height: u32) -> Result<slint::Image, String> {
        let Some(version) = self
            .compared_snapshot
            .as_deref()
            .and_then(|id| self.snapshots.iter().find(|v| v.uuid == id))
            .cloned()
        else {
            return self.render(width, height);
        };
        let saved = self.graph.state();
        let debt = version.apply(&mut self.graph);
        self.pay_film_debt(&debt);
        let rendered = self.render(width, height);
        let debt = self.graph.set_state(&saved);
        self.pay_film_debt(&debt);
        rendered
    }

    /// TRACES: FR-DEV-5
    /// The snapshot list as the panel draws it, oldest first.
    pub fn snapshot_rows(&self) -> Vec<crate::SnapshotRow> {
        self.snapshots
            .iter()
            .map(|v| crate::SnapshotRow {
                id: v.uuid.as_str().into(),
                name: v.name.as_str().into(),
                comparing: self.compared_snapshot.as_deref() == Some(v.uuid.as_str()),
            })
            .collect()
    }

    /// TRACES: FR-DEV-5
    /// [`Self::pay_film_debt`] for a history step, when the step went
    /// anywhere.
    ///
    /// The guard is the whole difference between the two: a step that found
    /// nowhere to go left the graph alone, and clearing the film because
    /// undo hit the floor would take the picture's stock off it.
    pub(super) fn settle(&mut self, step: &dr_pipeline::Step) {
        if let dr_pipeline::Step::Took(rebake) = step {
            self.pay_film_debt(rebake);
        }
    }

    /// TRACES: FR-DEV-5
    /// Step the edit back one, returning whether anything moved.
    ///
    /// The panel must be rebuilt from [`Self::rows`] afterwards, for the same
    /// reason a paste must: this moves values the controls are showing and
    /// nothing here pushes them.
    pub fn undo(&mut self) -> bool {
        let step = self.history.undo(&mut self.graph);
        self.settle(&step);
        step.moved()
    }

    /// TRACES: FR-DEV-5
    /// Step the edit forward one, returning whether anything moved.
    pub fn redo(&mut self) -> bool {
        let step = self.history.redo(&mut self.graph);
        self.settle(&step);
        step.moved()
    }

    pub fn can_undo(&self) -> bool {
        self.history.can_undo()
    }

    pub fn can_redo(&self) -> bool {
        self.history.can_redo()
    }

    /// TRACES: FR-DEV-5 | FR-DEV-7
    /// Every step this photograph has been through, newest first.
    ///
    /// Newest first because the list is consulted to take back something just
    /// done, not browsed chronologically — the order `dr_catalog::trash`
    /// settled on for the same question. It also keeps the interesting end
    /// against the heading, so a stack sixty-four deep does not put the step
    /// the photographer is looking for at the bottom of a long scroll.
    ///
    /// The reversal happens here rather than in the core, which returns the
    /// stack in stack order and stamps each row with its own index — so
    /// nothing on this side does arithmetic to turn a row back into a step.
    pub fn history_rows(&self) -> Vec<crate::HistoryRow> {
        let mut rows: Vec<_> = self
            .history
            .entries(&self.graph)
            .into_iter()
            .map(|entry| crate::HistoryRow {
                index: entry.index as i32,
                label: labels::resolve(entry.label.0).into(),
                current: entry.current,
                // Everything past the mark is a future the photographer
                // stepped out of. Still listed, because it is still reachable
                // by redo and hiding it would make redo arrive somewhere the
                // panel never mentioned — but drawn as the branch it is.
                undone: entry.index > self.history.cursor(),
            })
            .collect();
        rows.reverse();
        rows
    }

    /// TRACES: FR-DEV-5 | FR-DEV-7
    /// Step straight to one row of [`Self::history_rows`].
    ///
    /// Takes the row's own `index`, not its position in that list.
    /// TRACES: FR-DEV-5
    /// A number that changes exactly when [`Self::history_rows`] would.
    ///
    /// The panel is rebuilt off this rather than every redraw: a drag ends in
    /// a redraw per frame and changes no row, and pushing a fresh model makes
    /// the toolkit tear down and recreate every one of them.
    pub fn history_revision(&self) -> u64 {
        self.history.revision()
    }

    pub fn go_to_history(&mut self, index: i32) -> bool {
        let Ok(index) = usize::try_from(index) else {
            return false;
        };
        let step = self.history.go_to(&mut self.graph, index);
        self.settle(&step);
        step.moved()
    }

    /// TRACES: FR-DEV-5
    /// What undo would take back, and what redo would put back.
    ///
    /// Named on the buttons rather than left to the bare verb. "Undo" asks the
    /// photographer to remember what they last did, which after a run of small
    /// adjustments is exactly what they have stopped tracking — and it is the
    /// moment they are least willing to press a button and find out.
    ///
    /// Empty when there is nowhere to go, so the caller falls back to the verb
    /// alone rather than printing a label for a disabled control.
    pub fn undo_label(&self) -> String {
        // Undo takes back the step the graph is *standing on*, so the row to
        // name is the current one — not the one it will land on.
        self.step_name(self.history.cursor(), self.history.can_undo())
    }

    /// TRACES: FR-DEV-5
    pub fn redo_label(&self) -> String {
        self.step_name(self.history.cursor() + 1, self.history.can_redo())
    }

    pub(super) fn step_name(&self, index: usize, offered: bool) -> String {
        if !offered {
            return String::new();
        }
        self.history
            .entries(&self.graph)
            .into_iter()
            .find(|e| e.index == index)
            .map(|e| labels::resolve(e.label.0))
            .unwrap_or_default()
    }
}

#[cfg(test)]
mod tests {
    use crate::develop::test_support::*;

    /// TRACES: FR-DEV-5
    /// A snapshot is a state the photographer named: taking one changes
    /// nothing, going back to it is one step, and undo takes the whole of
    /// that step back.
    #[test]
    fn a_snapshot_is_restored_as_one_step_and_undone_as_one() {
        let Some(ctx) = headless() else { return };
        let (mut session, _) = grey_session(&ctx);

        let rows = session.rows();
        let row = rows
            .iter()
            .find(|row| {
                session.set_param(row.op_index, row.param_index, row.maximum);
                !session.is_neutral()
            })
            .expect("some control in the panel moves the picture")
            .clone();
        let liked = session.copy_settings();
        let steps_before = session.history_rows().len();

        let id = session.take_snapshot("Liked this");
        assert_eq!(session.snapshots().len(), 1);
        assert_eq!(session.snapshots()[0].name, "Liked this");
        assert_eq!(
            session.history_rows().len(),
            steps_before,
            "naming a state is not a change to the photograph"
        );

        // Move on, then go back.
        session.set_param(row.op_index, row.param_index, row.minimum);
        let moved_on = session.copy_settings();
        assert_ne!(moved_on, liked, "the premise: the edit has moved");
        let steps_moved = session.history_rows().len();

        assert!(session.restore_snapshot(&id));
        assert_eq!(session.copy_settings(), liked, "back to the named state");
        assert_eq!(
            session.history_rows().len(),
            steps_moved + 1,
            "restoring is one step"
        );

        assert!(session.undo());
        assert_eq!(
            session.copy_settings(),
            moved_on,
            "and undo takes the whole restore back"
        );

        // A name nobody typed is numbered rather than blank.
        session.take_snapshot("  ");
        assert_eq!(session.snapshots()[1].name, "Snapshot 2");

        session.delete_snapshot(&id);
        assert_eq!(session.snapshots().len(), 1);
        assert_eq!(session.removed_snapshots(), [id.as_str()]);
    }

    /// TRACES: FR-DEV-7 | FR-DEV-5
    /// Holding a snapshot against the edit is the same bargain as holding
    /// the original: the picture changes, and nothing else does.
    #[test]
    fn comparing_against_a_snapshot_leaves_the_edit_exactly_as_it_was() {
        let Some(ctx) = headless() else { return };
        let (mut session, _) = grey_session(&ctx);

        let rows = session.rows();
        let row = rows
            .iter()
            .find(|row| {
                session.set_param(row.op_index, row.param_index, row.maximum);
                !session.is_neutral()
            })
            .expect("some control in the panel moves the picture")
            .clone();
        let id = session.take_snapshot("Bright");
        session.set_param(row.op_index, row.param_index, row.minimum);
        let edit = session.copy_settings();
        let steps = session.history_rows().len();

        assert!(session.compare_snapshot(Some(&id)), "the hold began");
        assert!(
            !session.compare_snapshot(Some(&id)),
            "a repeat of the same hold is not a change"
        );
        assert_eq!(session.compared_snapshot(), Some(id.as_str()));
        session
            .render_compared(64, 64)
            .expect("render the snapshot");

        assert_eq!(session.copy_settings(), edit, "every parameter comes back");
        assert_eq!(session.history_rows().len(), steps, "looking is not a step");

        assert!(session.compare_snapshot(None), "and letting go is one");
        assert!(session.compared_snapshot().is_none());
        assert!(
            !session.compare_snapshot(Some("nothing-by-this-name")),
            "a snapshot that does not exist cannot be held"
        );
    }
}