return `${glyphs.slice(0, Math.max(1, width - 1)).join("")}…`;

}

/**

 * The face the splash writes CODER in, drawn by hand in block glyphs.

 *

 * Hand-drawn because this interface renders with no dependencies, and a figlet

 * package to say one word would be the first. Six rows, because shorter art

 * stops reading as a wordmark and taller art crowds a small terminal.

 */

const SPLASH_WORD = [

  " ██████╗ ██████╗ ██████╗ ███████╗██████╗ ",

  "██╔════╝██╔═══██╗██╔══██╗██╔════╝██╔══██╗",

  "██║     ██║   ██║██║  ██║█████╗  ██████╔╝",

  "██║     ██║   ██║██║  ██║██╔══╝  ██╔══██╗",

  "╚██████╗╚██████╔╝██████╔╝███████╗██║  ██║",

  " ╚═════╝ ╚═════╝ ╚═════╝ ╚══════╝╚═╝  ╚═╝",

];

/** What the splash asks for. The status line already names the workspace. */

const SPLASH_HINT = "type a prompt below to begin";

/**

 * One cell of the splash's binary texture.

 *

 * Seeded from the cell's own position rather than from a random source, so the

 * same viewport always shows the same field. The paint loop diffs rows against

 * the last frame, and texture that shifted on every repaint would rewrite the

 * whole block each time and read as static rather than as a backdrop.

 */

function splashBit(row: number, column: number): string {

  // Two multiply-xor rounds, because one leaves the low bits of neighbouring

  // columns correlated and the field visibly striped.

  let hash = (Math.imul(row + 1, 2654435761) ^ Math.imul(column + 1, 0x9e3779b9)) >>> 0;

  hash = Math.imul(hash ^ (hash >>> 16), 0x45d9f3b) >>> 0;

  return ((hash ^ (hash >>> 16)) & 1) === 0 ? "0" : "1";

}

/** A full row of that texture, one digit per column. */

function splashTexture(row: number, width: number): string {

  let cells = "";

  for (let column = 0; column < width; column += 1) cells += splashBit(row, column);

  return cells;

}

/**

 * What the transcript's viewport shows before the first entry exists.

 *

 * A session opens onto nothing — no banner, by the note at the bottom of this

 * file — and nineteen blank rows read as a program that has not started. The

 * splash is not state and not a lifecycle: it is only what an empty transcript

 * looks like, so the first entry replaces it the way any frame replaces the

 * one before, and it never comes back. Same size in, same rows out, because

 * the renderer repaints on state changes and resize and nothing else.

 *

 * Each size gets the largest rendering that fits whole: the wordmark in a

 * frame with the binary field, a one-line box, or the bare word. Nothing here

 * may emit a row wider than the viewport — the terminal would wrap it, which

 * shifts every row below and leaves text nothing will erase.

 */

function splashLines(width: number, height: number): ReadonlyArray<string> {

  const wordWidth = [...(SPLASH_WORD[0] ?? "")].length;

  /** Wrap inner rows in the frame and center the block in the viewport. */

  const framed = (inner: ReadonlyArray<string>, innerWidth: number): ReadonlyArray<string> => {

    const rows = [

      `${DIM}┌${"─".repeat(innerWidth)}┐${RESET}`,

      ...inner,

      `${DIM}└${"─".repeat(innerWidth)}┘${RESET}`,

    ];

    const left = " ".repeat(Math.max(0, Math.floor((width - innerWidth - 2) / 2)));

    const above = Math.max(0, Math.floor((height - rows.length) / 2));

    return [...Array.from({ length: above }, () => ""), ...rows.map((row) => left + row)];

  };

  /** A framed row holding centered content, given the content's visible width. */

  const padded = (innerWidth: number, visible: number, styled: string): string => {

    const leftPad = Math.max(0, Math.floor((innerWidth - visible) / 2));

    const rightPad = Math.max(0, innerWidth - visible - leftPad);

    return `${DIM}│${RESET}${" ".repeat(leftPad)}${styled}${" ".repeat(rightPad)}${DIM}│${RESET}`;

  };

  /** A framed row of the binary field, edge to edge. */

  const texture = (row: number, innerWidth: number): string =>

    `${DIM}│${splashTexture(row, innerWidth)}│${RESET}`;

  // Four columns of air either side of the wordmark, so the letters do not

  // touch the field above them. Height needs the six rows of the word plus the

  // frame, the texture, the air, and the hint.

  const fullInner = wordWidth + 8;

  if (width >= fullInner + 2 && height >= SPLASH_WORD.length + 7) {

    const inner: string[] = [texture(0, fullInner), padded(fullInner, 0, "")];

    for (const line of SPLASH_WORD) {

      inner.push(padded(fullInner, wordWidth, `${CYAN}${line}${RESET}`));

    }

    inner.push(padded(fullInner, 0, ""));

    inner.push(padded(fullInner, SPLASH_HINT.length, `${DIM}${SPLASH_HINT}${RESET}`));

    inner.push(texture(1, fullInner));

    return framed(inner, fullInner);

  }

  // Too narrow or too short for the wordmark: the word spelled out in the same

  // frame, three rows tall, which fits down to a seventeen-column terminal.

  const compactInner = 15;

  if (width >= compactInner + 2 && height >= 5) {

    const word = "C O D E R";

    return framed(

      [

        texture(0, compactInner),

        padded(compactInner, [...word].length, `${CYAN}${BOLD}${word}${RESET}`),

        texture(1, compactInner),

      ],

      compactInner,

    );

  }

  // A viewport with no room for a frame at all still says whose screen it is.

  return [truncate("CODER", Math.max(1, width))];

}

/**

 * Match a complete escape sequence at `index`, or return undefined when the

 * bytes so far could still be the start of one. Covers CSI (`\x1b[…final`),

      const sidebar = snapshot.tasks.length > 0 && width >= SIDEBAR_MINIMUM_TERMINAL;

      const transcriptWidth = sidebar ? width - SIDEBAR_WIDTH - 1 : width;

      const lines = transcriptLines(snapshot, transcriptWidth, sidebar);

      // Before the first entry exists there is no conversation to draw, so

      // the viewport shows the splash instead of nothing. Gated on the entries

      // rather than on what they render to: a transcript whose entries all

      // settled empty is a conversation that happened, and greeting it again

      // would say that it had not.

      const lines =

        snapshot.entries.length === 0

          ? splashLines(transcriptWidth, transcriptHeight)

          : transcriptLines(snapshot, transcriptWidth, sidebar);

      lineCount = lines.length;

      viewport = transcriptHeight;

  });

});

describe("the splash before the first message", () => {

  /** Open a fresh session, send nothing, and read what it painted. */

  const openFresh = async (columns = 100, rows = 24) => {

    const stdin = new FakeIn();

    const stdout = new FakeOut();

    stdout.columns = columns;

    stdout.rows = rows;

    const session = new CoderSession(source([]), "repo", "main");

    const running = runCoderUi(session, {

      stdin: stdin as unknown as NodeJS.ReadStream,

      stdout: stdout as unknown as NodeJS.WriteStream,

    });

    const painted = screen(stdout.written);

    stdin.emit("data", "\x04");

    await running;

    return painted;

  };

  it("greets an empty session with the wordmark, a frame, and the binary field", async () => {

    const rows = await openFresh();

    const joined = rows.join("\n");

    // The wordmark, its frame, and the field of digits around it. The hint

    // says what to do next without repeating what the status line says.

    expect(joined).toContain("██████╗");

    expect(joined).toContain("┌");

    expect(joined).toContain("└");

    expect(joined).toMatch(/[01]{20}/);

    expect(joined).toContain("type a prompt below to begin");

  });

  it("is gone the moment the first entry exists, and stays gone", async () => {

    const { rows } = await drive([{ type: "text", value: "hello" }]);

    const joined = rows.join("\n");

    // The splash is only what an empty transcript looks like, so a transcript

    // with anything in it must show no row of it.

    expect(joined).toContain("hello");

    expect(joined).not.toContain("██");

    expect(joined).not.toContain("type a prompt below to begin");

    expect(joined).not.toMatch(/[01]{20}/);

  });

  it("paints the same frame every time the same empty state renders", async () => {

    // Same snapshot and same size mean the same rows: the texture is seeded

    // from cell positions, so nothing in the frame depends on time or chance.

    const first = await openFresh();

    const second = await openFresh();

    expect(second).toEqual(first);

  });

  it("falls back on a narrow terminal and never emits a row past the edge", async () => {

    const rows = await openFresh(40);

    const joined = rows.join("\n");

    // Too narrow for the wordmark, so the word is spelled out in the same

    // frame — and no row may be wider than the terminal, which would wrap it.

    expect(joined).not.toContain("██████╗");

    expect(joined).toContain("C O D E R");

    for (const row of rows) {

      expect([...row].length).toBeLessThanOrEqual(40);

    }

  });

});

describe("where a running child is shown", () => {

  /** A session with a running delegate tool call, at a given terminal width. */

  const driveDelegated = async (