// Board motion animation (P6.1) — a PURELY VISUAL timeline the view plays over
// one player move. The logical model (commit_swap / resolve) stays authoritative:
// `plan_and_commit` commits the move on the real board exactly as before, then
// replays the SAME operations on a value-copy of the pre-move board to record the
// per-step geometry (the swap, each cascade round's matched cells, and each
// round's per-column fall provenance). Because the copy starts from the identical
// cells AND RNG state and runs the identical primitives, its recorded `final`
// board equals the model's settled board gem-for-gem — the animation only ever
// ends ON the already-decided result, never changes it.
//
// Per-gem idle/select/clear gem animations (P6.3) and score popups / particle FX
// (P6.2) are NOT here; this step animates board MOTION only: swap slide, matched
// scale-out, and collapse/refill fall.
#import "modules/std.sx";
#import "modules/math";
#import "modules/ui/types.sx";
#import "board.sx";
#import "board_layout.sx";

// Short, frame-timed durations (seconds) for each timeline segment. Driven by
// the frame loop's delta_time, so they are wall-clock, framerate-independent.
SWAP_ANIM_DUR  :f32: 0.16;
CLEAR_ANIM_DUR :f32: 0.14;
FALL_ANIM_DUR  :f32: 0.22;

// Easing helpers. Slide/fall decelerate into place (ease-out cubic); the clear
// scale-out accelerates as it shrinks (ease-in quad).
ease_out_cubic :: (t: f32) -> f32 { u := t - 1.0; u * u * u + 1.0 }
ease_in_quad :: (t: f32) -> f32 { t * t }

// One recorded cascade round. `before` is the board at the round's start (the
// swapped board for round 0, the previous round's `after` otherwise — never has
// holes). `matched` flags the cells cleared this round (they scale out). `src`
// maps each destination cell to the SOURCE ROW its gem falls from within the same
// column: a non-negative row for a surviving gem that slides down, or a NEGATIVE
// row (above the board) for a freshly-refilled gem dropping in from the top.
// `after` is the board once this round has cleared, collapsed, and refilled.
AnimRound :: struct {
    before: [BOARD_CELLS]Gem;
    matched: MatchMask;
    src: [BOARD_CELLS]s64;
    after: [BOARD_CELLS]Gem;
}

// The full recorded timeline of one move. `legal` mirrors the model's decision:
// a legal swap has >=1 round and `final` is the settled board; an illegal swap
// has zero rounds, `pre == final`, and the view plays a slide-and-return. `a`/`b`
// are the swapped cells; `pre` is the board before the swap (the slide's start).
AnimMove :: struct {
    legal: bool;
    a: Cell;
    b: Cell;
    pre: [BOARD_CELLS]Gem;
    rounds: List(AnimRound);
    final: [BOARD_CELLS]Gem;
}

// Commit the player's swap authoritatively AND record its visual timeline. The
// real board is mutated by `commit_swap` exactly as the non-animated path did;
// the recording runs on a separate value-copy taken BEFORE the commit, so it
// replays the identical cells + RNG stream and its `final` equals `board.cells`.
plan_and_commit :: (board: *Board, a: Cell, b: Cell) -> AnimMove {
    move : AnimMove = ---;
    move.a = a;
    move.b = b;
    move.rounds = List(AnimRound).{};
    move.pre = board.cells;

    // Snapshot the entire model state (cells + RNG + score + moves) before the
    // commit so the replay below is bit-identical to what commit_swap does.
    scratch : Board = board.*;

    mv := commit_swap(board, a, b);
    move.legal = mv.legal;
    if !mv.legal {
        move.final = board.cells;
        return move;
    }

    swap(@scratch, a, b);
    while true {
        m := find_matches(@scratch);
        if m.count() == 0 { break; }

        round : AnimRound = ---;
        round.before = scratch.cells;
        round.matched = m;

        clear_cells(@scratch, @m);

        // Fall provenance, read off the just-cleared (holed) board — mirrors
        // `collapse`'s packing exactly: scanning a column bottom-to-top, each
        // surviving gem lands at the descending write cursor `w`, so dest row `w`
        // came from source row `r`. The rows left above the survivors (0..w) are
        // refilled, so they drop in from above: a dest row `j` there starts at
        // `j - n_refill`, i.e. stacked just off the top edge.
        for 0..BOARD_COLS: (col) {
            w := BOARD_ROWS - 1;
            r := BOARD_ROWS - 1;
            while r >= 0 {
                if scratch.at(col, r) != .empty {
                    round.src[Board.idx(col, w)] = r;
                    w -= 1;
                }
                r -= 1;
            }
            n_refill := w + 1;
            j := 0;
            while j <= w {
                round.src[Board.idx(col, j)] = j - n_refill;
                j += 1;
            }
        }

        collapse(@scratch);
        refill(@scratch);
        round.after = scratch.cells;
        move.rounds.append(round);
    }

    move.final = scratch.cells;
    move
}

// Which segment of the timeline is playing, and the local 0..1 progress within
// it. `round` indexes `AnimMove.rounds` for clear/fall.
AnimPhaseKind :: enum { swap; clear; fall; done; }

AnimPhase :: struct {
    kind: AnimPhaseKind;
    round: s64;
    t: f32;
}

// Live timeline state for the in-flight move. Heap-allocated (like BoardSelection
// / DragInput) so it survives BoardView's per-frame rebuild; `tick` advances it
// by the frame's delta_time and the view reads `phase` to render the right slice.
BoardAnim :: struct {
    active: bool;
    elapsed: f32;
    move: AnimMove;

    init :: (self: *BoardAnim) {
        self.active = false;
        self.elapsed = 0.0;
        self.move.legal = false;
        self.move.rounds = List(AnimRound).{};
    }

    begin :: (self: *BoardAnim, m: AnimMove) {
        self.move = m;
        self.elapsed = 0.0;
        self.active = true;
    }

    // Total wall-clock length: the swap segment plus a clear+fall pair per round.
    total :: (self: *BoardAnim) -> f32 {
        SWAP_ANIM_DUR + cast(f32) self.move.rounds.len * (CLEAR_ANIM_DUR + FALL_ANIM_DUR)
    }

    tick :: (self: *BoardAnim, dt: f32) {
        if !self.active { return; }
        self.elapsed += dt;
        if self.elapsed >= self.total() { self.active = false; }
    }

    // Resolve `elapsed` to the active segment by walking swap → (clear, fall)*.
    phase :: (self: *BoardAnim) -> AnimPhase {
        e := self.elapsed;
        if e < SWAP_ANIM_DUR {
            return AnimPhase.{ kind = .swap, round = 0, t = e / SWAP_ANIM_DUR };
        }
        e -= SWAP_ANIM_DUR;
        for 0..self.move.rounds.len: (k) {
            if e < CLEAR_ANIM_DUR {
                return AnimPhase.{ kind = .clear, round = k, t = e / CLEAR_ANIM_DUR };
            }
            e -= CLEAR_ANIM_DUR;
            if e < FALL_ANIM_DUR {
                return AnimPhase.{ kind = .fall, round = k, t = e / FALL_ANIM_DUR };
            }
            e -= FALL_ANIM_DUR;
        }
        AnimPhase.{ kind = .done, round = 0, t = 1.0 }
    }
}

// Input gate: the board accepts a new swipe/tap gesture only when no move
// animation is in flight. The view checks this at gesture START (mouse_down),
// not at commit (mouse_up), so a gesture begun while a timeline is playing never
// latches a drag and so cannot commit when the animation later settles. Input
// resumes once `tick` clears `active` at the end of the timeline. A null anim
// (no animation layer wired) always accepts.
accepts_input :: (anim: *BoardAnim) -> bool {
    anim == null or !anim.active
}
