#!/usr/bin/env -S bun --no-env-file --config=/dev/null
/**
 * gstack-decision-trail — append one row to a run's decision trail: a TSV with
 * one line per decision (ts, phase, decision, why, evidence, result) that a
 * reviewer reads top to bottom after the run. Append-only: a wrong call gets a
 * new row that supersedes it, never an edit.
 *
 * Usage:
 *   gstack-decision-trail [--run <id>] <file> <phase> <decision> <why> <evidence> <result>
 *   gstack-decision-trail start <file> <run-id>
 *   gstack-decision-trail --help
 *
 * The write rules are a port of pstack's show-me-your-work/scripts/log.sh
 * (Copyright Lauren Tan, MIT; https://github.com/cursor/plugins,
 * pstack/skills/show-me-your-work at 99b609a7), in TypeScript: the header is
 * written once and only ever appended, cells lose their tabs and line breaks,
 * and a cell whose first byte a spreadsheet would run as a formula (=, +, -, @)
 * gets a leading apostrophe, so evidence taken from PR titles, filenames or
 * generated text cannot execute when a reviewer opens the file. License text:
 * licenses/MIT-pstack.txt; NOTICE.md carries the entry.
 *
 * The start-row rule is gstack's mechanisation of the same skill's prose: a run
 * (one agent conversation, with its later turns) that writes to a trail already
 * holding rows opens with a `start` row naming the rows it did not write, and
 * its evidence names the run (`run:<id>`). `start` is idempotent for the same
 * id, and an append with `--run <id>` refuses until that run's start row is the
 * newest start row in the file (DECISION_TRAIL_START_REQUIRED, exit 3).
 */
import * as fs from "node:fs";
import * as path from "node:path";

const COLUMNS = ["ts", "phase", "decision", "why", "evidence", "result"] as const;
const HEADER = COLUMNS.join("\t") + "\n";
const USAGE = `Usage:
  gstack-decision-trail [--run <id>] <file> <phase> <decision> <why> <evidence> <result>
  gstack-decision-trail start <file> <run-id>
  gstack-decision-trail --help

Appends one tab-separated row (ts is stamped in UTC) to <file>, writing the
header line first when the file is missing or empty. Cells are flattened to
one line, and a cell starting with =, +, - or @ is prefixed with a quote so a
spreadsheet cannot run it as a formula. Nothing is ever rewritten or removed.

  phase     the phase or workstream the decision belongs to; 'start' is reserved
  decision  what was chosen or done, one line, in plain words
  why       the reason, as you would tell a teammate
  evidence  a pointer that resolves: commit, PR, file:line, artifact path
  result    the outcome: tests green, reverted, INCONCLUSIVE, open, ...

start <file> <run-id> appends this run's start row (phase 'start', evidence
'run:<run-id>') naming the rows earlier runs wrote. Running it again for the
same run is a no-op while that start row is still the newest one. A run id is
letters, digits and . _ : @ / - (a Capy jam_ id, a session id, a PR number).

--run <id> on an append refuses with DECISION_TRAIL_START_REQUIRED (exit 3)
when the trail has rows and the newest start row is another run's.
`;

type Row = { line: number; cells: string[] };

function clean(cell: string): string {
  const flat = cell.replace(/[\t\n\r]/g, " ");
  return /^[=+\-@]/.test(flat) ? `'${flat}` : flat;
}

function readRows(file: string): Row[] {
  if (!fs.existsSync(file)) return [];
  const lines = fs.readFileSync(file, "utf8").split("\n");
  const rows: Row[] = [];
  lines.forEach((raw, i) => {
    let text = raw.endsWith("\r") ? raw.slice(0, -1) : raw;
    if (i === 0 && text.startsWith("\uFEFF")) text = text.slice(1);
    // A repeated header (the append-on-flaky-mount case) is never a row.
    if (text === "" || text === HEADER.trimEnd()) return;
    rows.push({ line: i + 1, cells: text.split("\t") });
  });
  return rows;
}

function appendRow(file: string, cells: readonly string[]): number {
  const dir = path.dirname(file);
  if (dir && dir !== "." && !fs.existsSync(dir)) fs.mkdirSync(dir, { recursive: true });
  // Append the header too, never truncate: on a flaky mount the worst case is
  // one stray header line, not lost rows.
  // A file with no header line anywhere (empty, blank, or rows written by hand)
  // gets one appended once; readRows skips a header line wherever it sits.
  const size = fs.existsSync(file) ? fs.statSync(file).size : 0;
  if (size > 0 && !endsWithNewline(file, size)) fs.appendFileSync(file, "\n");
  if (size === 0 || !hasHeader(file)) fs.appendFileSync(file, HEADER);
  const ts = new Date().toISOString().replace(/\.\d{3}Z$/, "Z");
  fs.appendFileSync(file, [ts, ...cells.map(clean)].join("\t") + "\n");
  return readRows(file).length;
}

function hasHeader(file: string): boolean {
  return fs.readFileSync(file, "utf8").replace(/^\uFEFF/, "").split("\n")
    .some(line => line.replace(/\r$/, "") === HEADER.trimEnd());
}

function endsWithNewline(file: string, size: number): boolean {
  const fd = fs.openSync(file, "r");
  try {
    const last = Buffer.alloc(1);
    fs.readSync(fd, last, 0, 1, size - 1);
    return last[0] === 0x0a;
  } finally {
    fs.closeSync(fd);
  }
}

const RUN_ID = /^[A-Za-z0-9._:@/-]+$/;
function checkRunId(runId: string): void {
  if (!RUN_ID.test(runId)) fail(`run id must match ${RUN_ID} (letters, digits, . _ : @ / -), got ${JSON.stringify(runId)}`, 2);
}

function newestStart(rows: Row[]): Row | undefined {
  for (let i = rows.length - 1; i >= 0; i--) if (rows[i]!.cells[1] === "start") return rows[i];
  return undefined;
}

function fail(message: string, code: number): never {
  process.stderr.write(`gstack-decision-trail: ${message}\n`);
  process.exit(code);
}

const argv = process.argv.slice(2);
// Only a leading --help asks for help: a cell whose text is "-h" is data and gets appended (quoted).
if (argv.length === 0 || argv[0] === "--help" || argv[0] === "-h") {
  process.stdout.write(USAGE);
  process.exit(argv.length === 0 ? 2 : 0);
}

if (argv[0] === "start") {
  const [, file, runId, ...extra] = argv;
  if (!file || !runId || extra.length > 0) fail(`start takes <file> <run-id>\n${USAGE}`, 2);
  checkRunId(runId);
  const rows = readRows(file);
  const newest = newestStart(rows);
  if (newest && newest.cells[4] === `run:${runId}`) {
    process.stdout.write(`start row for run ${runId} already present at ${file}:${newest.line}\n`);
    process.exit(0);
  }
  const earlier = rows.length === 0
    ? "no earlier rows"
    : `${rows.length} earlier row${rows.length === 1 ? "" : "s"} (${rows[0]!.cells[0]}..${rows[rows.length - 1]!.cells[0]}) written by other runs`;
  const line = appendRow(file, ["start", rows.length === 0 ? `run ${runId} opens this trail` : `run ${runId} joins this trail`, earlier, `run:${runId}`, "open"]);
  process.stdout.write(`appended start row ${line} for run ${runId} to ${file}\n`);
  process.exit(0);
}

let runId: string | undefined;
const positional = [...argv];
while (positional[0]?.startsWith("--")) {
  const flag = positional.shift()!;
  if (flag === "--run") {
    runId = positional.shift();
    if (!runId) fail("--run needs an id", 2);
    checkRunId(runId);
  } else fail(`unknown option ${flag}\n${USAGE}`, 2);
}
if (positional.length !== 6) fail(`expected <file> and five cells, got ${positional.length} argument${positional.length === 1 ? "" : "s"}\n${USAGE}`, 2);
const [file, ...cells] = positional as [string, string, string, string, string, string];
if (cells[0] === "start") fail("phase 'start' is reserved; use: gstack-decision-trail start <file> <run-id>", 2);

if (runId) {
  const rows = readRows(file);
  if (rows.length > 0 && newestStart(rows)?.cells[4] !== `run:${runId}`) {
    fail(`DECISION_TRAIL_START_REQUIRED: ${file} has ${rows.length} rows and run ${runId} has no start row after the newest one; run: gstack-decision-trail start ${file} ${runId}`, 3);
  }
}
const line = appendRow(file, cells);
process.stdout.write(`appended row ${line} to ${file}\n`);