// ============================================================================
// 2048 — slide-and-merge a single row (the core move primitive)
// ============================================================================
//
// slide_left() compacts a row toward the left, merging equal adjacent tiles
// exactly once per move (left-to-right), and reports the points scored (sum of
// merged tiles). A full board move is four row slides; this is that primitive.
//
// Run:  soma run game_2048.cell --signal demo
// Test: soma test game_2048.cell

cell Game2048 {
    face {
        signal compact(row: List) -> List
        signal slide_left(row: List) -> Map
        signal demo() -> Map
    }

    // Drop zeros, preserving order of non-zero tiles.
    on compact(row: List) {
        let out = []
        for v in row {
            if v != 0 { out = push(out, v) }
        }
        return out
    }

    on slide_left(row: List) {
        let tiles = compact(row)
        let merged = []
        let score = 0
        let i = 0
        while i < len(tiles) {
            if i + 1 < len(tiles) && tiles[i] == tiles[i + 1] {
                let v = tiles[i] * 2
                merged = push(merged, v)
                score = score + v
                i = i + 2
            } else {
                merged = push(merged, tiles[i])
                i = i + 1
            }
        }
        // pad back to the original width with zeros
        while len(merged) < len(row) {
            merged = push(merged, 0)
        }
        return map("row", merged, "score", score)
    }

    on demo() {
        // [2,2,4,0] → [4,4,0,0] scoring 4
        return slide_left([2, 2, 4, 0])
    }
}

cell test Game2048Tests {
    rules {
        // basic merge of the leading pair
        assert slide_left([2, 2, 4, 0]).row[0] == 4
        assert slide_left([2, 2, 4, 0]).row[1] == 4
        assert slide_left([2, 2, 4, 0]).score == 4
        // a tile only merges once: [2,2,2,2] → [4,4,0,0] scoring 8
        assert slide_left([2, 2, 2, 2]).row[0] == 4
        assert slide_left([2, 2, 2, 2]).row[1] == 4
        assert slide_left([2, 2, 2, 2]).row[2] == 0
        assert slide_left([2, 2, 2, 2]).score == 8
        // gaps collapse, no merge
        assert slide_left([0, 4, 0, 2]).row[0] == 4
        assert slide_left([0, 4, 0, 2]).row[1] == 2
        assert slide_left([0, 4, 0, 2]).score == 0
        // already-merged trailing pair: [4,2,2,0] → [4,4,0,0]
        assert slide_left([4, 2, 2, 0]).score == 4
        assert compact([0, 0, 8, 0])[0] == 8
    }
}