//! Pure layout logic: split / merge / resize / move_session, nominal and error
//! paths, grid validation, and immutability of the source tree (ARCHITECTURE §7).

mod helpers;

use domain::{
    Direction, GridCell, GridContainer, LayoutError, LayoutNode, LayoutTree, LeafCell,
    SplitContainer, WeightedChild,
};
use domain::ids::AgentId;
use helpers::{node, session};

fn agent_id(n: u128) -> AgentId {
    AgentId::from_uuid(uuid::Uuid::from_u128(n))
}

fn leaf(id: u128, sess: Option<u128>) -> LeafCell {
    LeafCell {
        id: node(id),
        session: sess.map(session),
        agent: None,
    }
}

fn single(id: u128, sess: Option<u128>) -> LayoutTree {
    LayoutTree::single(leaf(id, sess))
}

// ---------------------------------------------------------------------------
// split
// ---------------------------------------------------------------------------

#[test]
fn split_nominal_produces_two_children() {
    let tree = single(1, Some(100));
    let out = tree
        .split(node(1), Direction::Row, leaf(2, None), node(9))
        .unwrap();
    match out.root {
        LayoutNode::Split(s) => {
            assert_eq!(s.id, node(9));
            assert_eq!(s.direction, Direction::Row);
            assert_eq!(s.children.len(), 2);
            assert!(s.children.iter().all(|c| c.weight > 0.0));
        }
        _ => panic!("expected a split at the root"),
    }
}

#[test]
fn split_is_immutable_source_unchanged() {
    let tree = single(1, Some(100));
    let before = tree.clone();
    let _ = tree
        .split(node(1), Direction::Column, leaf(2, None), node(9))
        .unwrap();
    assert_eq!(tree, before, "source tree must not be mutated");
}

#[test]
fn split_missing_target_is_node_not_found() {
    let tree = single(1, None);
    let err = tree
        .split(node(404), Direction::Row, leaf(2, None), node(9))
        .unwrap_err();
    assert_eq!(err, LayoutError::NodeNotFound(node(404)));
}

#[test]
fn split_into_a_session_already_present_elsewhere_is_duplicate() {
    // root leaf 1 holds session 100; we split it adding a NEW leaf that reuses
    // the same session id → duplicate must be rejected by validation.
    let tree = single(1, Some(100));
    let err = tree
        .split(node(1), Direction::Row, leaf(2, Some(100)), node(9))
        .unwrap_err();
    assert_eq!(err, LayoutError::DuplicateSession(session(100)));
}

// ---------------------------------------------------------------------------
// merge
// ---------------------------------------------------------------------------

#[test]
fn merge_keeps_selected_child() {
    let tree = single(1, Some(100))
        .split(node(1), Direction::Row, leaf(2, Some(200)), node(9))
        .unwrap();
    // keep index 1 (the new leaf with session 200).
    let merged = tree.merge(node(9), 1).unwrap();
    assert_eq!(merged.root, LayoutNode::Leaf(leaf(2, Some(200))));
}

#[test]
fn merge_is_immutable() {
    let tree = single(1, Some(100))
        .split(node(1), Direction::Row, leaf(2, None), node(9))
        .unwrap();
    let before = tree.clone();
    let _ = tree.merge(node(9), 0).unwrap();
    assert_eq!(tree, before);
}

#[test]
fn merge_unknown_container_is_node_not_found() {
    let tree = single(1, None)
        .split(node(1), Direction::Row, leaf(2, None), node(9))
        .unwrap();
    let err = tree.merge(node(404), 0).unwrap_err();
    assert_eq!(err, LayoutError::NodeNotFound(node(404)));
}

#[test]
fn merge_index_out_of_range_is_cross_container() {
    let tree = single(1, None)
        .split(node(1), Direction::Row, leaf(2, None), node(9))
        .unwrap();
    let err = tree.merge(node(9), 5).unwrap_err();
    assert_eq!(err, LayoutError::CrossContainer);
}

// ---------------------------------------------------------------------------
// resize
// ---------------------------------------------------------------------------

#[test]
fn resize_nominal_updates_weights() {
    let tree = single(1, None)
        .split(node(1), Direction::Row, leaf(2, None), node(9))
        .unwrap();
    let out = tree.resize(node(9), &[2.0, 3.0]).unwrap();
    match out.root {
        LayoutNode::Split(s) => {
            assert_eq!(s.children[0].weight, 2.0);
            assert_eq!(s.children[1].weight, 3.0);
        }
        _ => panic!("expected split"),
    }
}

#[test]
fn resize_is_immutable() {
    let tree = single(1, None)
        .split(node(1), Direction::Row, leaf(2, None), node(9))
        .unwrap();
    let before = tree.clone();
    let _ = tree.resize(node(9), &[2.0, 3.0]).unwrap();
    assert_eq!(tree, before);
}

#[test]
fn resize_nonpositive_weight_rejected() {
    let tree = single(1, None)
        .split(node(1), Direction::Row, leaf(2, None), node(9))
        .unwrap();
    let err = tree.resize(node(9), &[0.0, 1.0]).unwrap_err();
    assert_eq!(err, LayoutError::NonPositiveWeight { weight: 0.0 });

    let err = tree.resize(node(9), &[-1.0, 1.0]).unwrap_err();
    assert_eq!(err, LayoutError::NonPositiveWeight { weight: -1.0 });
}

#[test]
fn resize_wrong_arity_is_cross_container() {
    let tree = single(1, None)
        .split(node(1), Direction::Row, leaf(2, None), node(9))
        .unwrap();
    let err = tree.resize(node(9), &[1.0, 2.0, 3.0]).unwrap_err();
    assert_eq!(err, LayoutError::CrossContainer);
}

#[test]
fn resize_unknown_container_is_node_not_found() {
    let tree = single(1, None)
        .split(node(1), Direction::Row, leaf(2, None), node(9))
        .unwrap();
    let err = tree.resize(node(404), &[1.0, 2.0]).unwrap_err();
    assert_eq!(err, LayoutError::NodeNotFound(node(404)));
}

// ---------------------------------------------------------------------------
// move_session
// ---------------------------------------------------------------------------

fn two_leaves(from_sess: Option<u128>, to_sess: Option<u128>) -> LayoutTree {
    LayoutTree::new(LayoutNode::Split(SplitContainer {
        id: node(9),
        direction: Direction::Row,
        children: vec![
            WeightedChild {
                node: LayoutNode::Leaf(leaf(1, from_sess)),
                weight: 1.0,
            },
            WeightedChild {
                node: LayoutNode::Leaf(leaf(2, to_sess)),
                weight: 1.0,
            },
        ],
    }))
}

/// Looks up the session held by the leaf `id` in a tree (test-only helper that
/// walks the public structure, since the domain's lookup is private).
fn session_for(tree: &LayoutTree, id: domain::NodeId) -> Option<domain::SessionId> {
    fn walk(n: &LayoutNode, id: domain::NodeId) -> Option<Option<domain::SessionId>> {
        match n {
            LayoutNode::Leaf(l) if l.id == id => Some(l.session),
            LayoutNode::Leaf(_) => None,
            LayoutNode::Split(s) => s.children.iter().find_map(|c| walk(&c.node, id)),
            LayoutNode::Grid(g) => g.cells.iter().find_map(|c| walk(&c.node, id)),
        }
    }
    walk(&tree.root, id).flatten()
}

#[test]
fn move_session_nominal() {
    let tree = two_leaves(Some(100), None);
    let out = tree.move_session(node(1), node(2)).unwrap();
    assert_eq!(session_for(&out, node(1)), None);
    assert_eq!(session_for(&out, node(2)), Some(session(100)));
}

#[test]
fn move_session_is_immutable() {
    let tree = two_leaves(Some(100), None);
    let before = tree.clone();
    let _ = tree.move_session(node(1), node(2)).unwrap();
    assert_eq!(tree, before);
}

#[test]
fn move_session_from_empty_rejected() {
    let tree = two_leaves(None, None);
    let err = tree.move_session(node(1), node(2)).unwrap_err();
    assert_eq!(err, LayoutError::CrossContainer);
}

#[test]
fn move_session_to_occupied_rejected() {
    let tree = two_leaves(Some(100), Some(200));
    let err = tree.move_session(node(1), node(2)).unwrap_err();
    assert_eq!(err, LayoutError::CrossContainer);
}

#[test]
fn move_session_missing_leaf_is_node_not_found() {
    let tree = two_leaves(Some(100), None);
    assert_eq!(
        tree.move_session(node(404), node(2)).unwrap_err(),
        LayoutError::NodeNotFound(node(404))
    );
    assert_eq!(
        tree.move_session(node(1), node(404)).unwrap_err(),
        LayoutError::NodeNotFound(node(404))
    );
}

// ---------------------------------------------------------------------------
// validate(): grid invariants & duplicate sessions
// ---------------------------------------------------------------------------

fn grid(col_w: Vec<f32>, row_w: Vec<f32>, cells: Vec<GridCell>) -> LayoutTree {
    LayoutTree::new(LayoutNode::Grid(GridContainer {
        id: node(50),
        col_weights: col_w,
        row_weights: row_w,
        cells,
    }))
}

fn gcell(id: u128, row: u16, col: u16, rs: u16, cs: u16) -> GridCell {
    GridCell {
        node: LayoutNode::Leaf(leaf(id, None)),
        row,
        col,
        row_span: rs,
        col_span: cs,
    }
}

#[test]
fn grid_fully_covered_2x2_ok() {
    let cells = vec![
        gcell(1, 0, 0, 1, 1),
        gcell(2, 0, 1, 1, 1),
        gcell(3, 1, 0, 1, 1),
        gcell(4, 1, 1, 1, 1),
    ];
    let t = grid(vec![1.0, 1.0], vec![1.0, 1.0], cells);
    assert!(t.validate().is_ok());
}

#[test]
fn grid_merged_span_full_coverage_ok() {
    // one cell spanning the whole top row + two cells on the bottom row.
    let cells = vec![
        gcell(1, 0, 0, 1, 2), // top row merged
        gcell(2, 1, 0, 1, 1),
        gcell(3, 1, 1, 1, 1),
    ];
    let t = grid(vec![1.0, 1.0], vec![1.0, 1.0], cells);
    assert!(t.validate().is_ok());
}

#[test]
fn grid_overlap_rejected() {
    let cells = vec![
        gcell(1, 0, 0, 1, 2),
        gcell(2, 0, 1, 1, 1), // overlaps column 1 of the spanning cell
        gcell(3, 1, 0, 1, 1),
        gcell(4, 1, 1, 1, 1),
    ];
    let t = grid(vec![1.0, 1.0], vec![1.0, 1.0], cells);
    assert!(matches!(
        t.validate().unwrap_err(),
        LayoutError::OverlappingCells { .. }
    ));
}

#[test]
fn grid_uncovered_surface_rejected() {
    // 2x2 grid but only one cell → three cells uncovered.
    let t = grid(vec![1.0, 1.0], vec![1.0, 1.0], vec![gcell(1, 0, 0, 1, 1)]);
    assert!(matches!(
        t.validate().unwrap_err(),
        LayoutError::UncoveredCell { .. }
    ));
}

#[test]
fn grid_span_out_of_bounds_rejected() {
    let t = grid(vec![1.0], vec![1.0], vec![gcell(1, 0, 0, 2, 1)]);
    assert!(matches!(
        t.validate().unwrap_err(),
        LayoutError::SpanOutOfBounds { .. }
    ));
}

#[test]
fn grid_zero_span_rejected() {
    let t = grid(vec![1.0], vec![1.0], vec![gcell(1, 0, 0, 0, 1)]);
    assert_eq!(t.validate().unwrap_err(), LayoutError::InvalidSpan);
}

#[test]
fn grid_nonpositive_weight_rejected() {
    let t = grid(vec![0.0], vec![1.0], vec![gcell(1, 0, 0, 1, 1)]);
    assert_eq!(
        t.validate().unwrap_err(),
        LayoutError::NonPositiveWeight { weight: 0.0 }
    );
}

#[test]
fn duplicate_session_across_leaves_rejected() {
    let tree = two_leaves(Some(100), Some(100));
    assert_eq!(
        tree.validate().unwrap_err(),
        LayoutError::DuplicateSession(session(100))
    );
}

#[test]
fn empty_split_rejected() {
    let t = LayoutTree::new(LayoutNode::Split(SplitContainer {
        id: node(9),
        direction: Direction::Row,
        children: vec![],
    }));
    assert_eq!(t.validate().unwrap_err(), LayoutError::EmptySplit);
}

// ---------------------------------------------------------------------------
// set_session (L4: cell ↔ terminal binding bridge)
// ---------------------------------------------------------------------------

#[test]
fn set_session_attaches_to_leaf() {
    let tree = single(1, None);
    let out = tree.set_session(node(1), Some(session(100))).unwrap();
    match out.root {
        LayoutNode::Leaf(l) => {
            assert_eq!(l.id, node(1));
            assert_eq!(l.session, Some(session(100)));
        }
        _ => panic!("expected a leaf at the root"),
    }
}

#[test]
fn set_session_detaches_with_none() {
    let tree = single(1, Some(100));
    let out = tree.set_session(node(1), None).unwrap();
    match out.root {
        LayoutNode::Leaf(l) => assert_eq!(l.session, None),
        _ => panic!("expected a leaf at the root"),
    }
}

#[test]
fn set_session_is_immutable_source_unchanged() {
    let tree = single(1, None);
    let before = tree.clone();
    let _ = tree.set_session(node(1), Some(session(100))).unwrap();
    assert_eq!(tree, before, "source tree must not be mutated");
}

#[test]
fn set_session_reaches_nested_leaf() {
    // Attach onto the second leaf of a split, leaving the first empty.
    let tree = two_leaves(None, None);
    let out = tree.set_session(node(2), Some(session(7))).unwrap();
    match out.root {
        LayoutNode::Split(s) => match &s.children[1].node {
            LayoutNode::Leaf(l) => assert_eq!(l.session, Some(session(7))),
            _ => panic!("expected a leaf child"),
        },
        _ => panic!("expected a split root"),
    }
}

#[test]
fn set_session_missing_leaf_is_node_not_found() {
    let tree = single(1, None);
    let err = tree.set_session(node(404), Some(session(100))).unwrap_err();
    assert_eq!(err, LayoutError::NodeNotFound(node(404)));
}

#[test]
fn set_session_duplicate_across_leaves_rejected() {
    // Leaf 1 already hosts session 100; attaching the same session to leaf 2
    // must fail validation rather than producing a duplicate.
    let tree = two_leaves(Some(100), None);
    let err = tree.set_session(node(2), Some(session(100))).unwrap_err();
    assert_eq!(err, LayoutError::DuplicateSession(session(100)));
}

// ---------------------------------------------------------------------------
// set_cell_agent (#3: per-cell agent)
// ---------------------------------------------------------------------------

#[test]
fn set_cell_agent_attaches_agent_to_leaf() {
    let tree = single(1, None);
    let out = tree.set_cell_agent(node(1), Some(agent_id(42))).unwrap();
    match out.root {
        LayoutNode::Leaf(l) => {
            assert_eq!(l.id, node(1));
            assert_eq!(l.agent, Some(agent_id(42)));
        }
        _ => panic!("expected a leaf at root"),
    }
}

#[test]
fn set_cell_agent_detaches_with_none() {
    // First attach, then detach.
    let tree = single(1, None);
    let with_agent = tree.set_cell_agent(node(1), Some(agent_id(42))).unwrap();
    let out = with_agent.set_cell_agent(node(1), None).unwrap();
    match out.root {
        LayoutNode::Leaf(l) => assert_eq!(l.agent, None),
        _ => panic!("expected a leaf at root"),
    }
}

#[test]
fn set_cell_agent_is_immutable_source_unchanged() {
    let tree = single(1, None);
    let before = tree.clone();
    let _ = tree.set_cell_agent(node(1), Some(agent_id(99))).unwrap();
    assert_eq!(tree, before, "source tree must not be mutated");
}

#[test]
fn set_cell_agent_missing_leaf_is_node_not_found() {
    let tree = single(1, None);
    let err = tree.set_cell_agent(node(404), Some(agent_id(1))).unwrap_err();
    assert_eq!(err, LayoutError::NodeNotFound(node(404)));
}

#[test]
fn set_cell_agent_preserves_session() {
    // Session must survive an agent attachment.
    let tree = single(1, Some(100));
    let out = tree.set_cell_agent(node(1), Some(agent_id(7))).unwrap();
    match out.root {
        LayoutNode::Leaf(l) => {
            assert_eq!(l.session, Some(session(100)));
            assert_eq!(l.agent, Some(agent_id(7)));
        }
        _ => panic!("expected leaf"),
    }
}