lakehouse/bot/propose.ts

// Gap detection + cloud proposal.
//
// Gap detection: scan docs/PRD.md for lines tagged [bot-eligible].
// Each match becomes a Gap with surrounding context.
//
// Proposal: one-shot call to the T3 cloud model via the Python sidecar's
// /generate endpoint. Asks for a structured JSON response with file
// contents. Truncation-resistant via Phase 21's generate_continuable —
// for now we pass max_tokens high and rely on the model completing in
// one pass; swap to the Rust continuation wrapper if we see truncation.

import { readFile } from "node:fs/promises";
import { createHash } from "node:crypto";
import type { Gap, Proposal } from "./types.ts";

const SIDECAR_URL = process.env.LH_SIDECAR_URL ?? "http://localhost:3200";
const REPO_ROOT = "/home/profit/lakehouse";
const PRD_PATH = `${REPO_ROOT}/docs/PRD.md`;
const CLOUD_MODEL = process.env.LH_BOT_MODEL ?? "gpt-oss:120b";
const MAX_TOKENS = 6000;

export async function findGaps(): Promise<Gap[]> {
  const prd = await readFile(PRD_PATH, "utf8");
  const lines = prd.split("\n");
  const gaps: Gap[] = [];
  for (let i = 0; i < lines.length; i++) {
    if (!lines[i].includes("[bot-eligible]")) continue;
    const contextLines = lines.slice(i, Math.min(i + 6, lines.length)).join("\n");
    const id = createHash("sha256").update(lines[i]).digest("hex").slice(0, 12);
    gaps.push({
      id,
      prd_line: lines[i].trim(),
      context: contextLines,
      source_file: "docs/PRD.md",
      line_number: i + 1,
    });
  }
  return gaps;
}

const SYSTEM_PROMPT = `You are an assistant that proposes small, testable code changes to the Lakehouse repo.
The Lakehouse is a Rust-first data platform with 13 crates + Bun/TypeScript test harness.
You will be given one PRD gap tagged [bot-eligible] and must respond with a STRICT JSON object — no prose.

Rules:
- Response MUST be a single JSON object, no markdown fences, no commentary.
- Change MUST be small: <200 lines total, ≤5 files.
- Include at least one test file (new or modified) that proves the change.
- NEVER touch .git/, secrets, lakehouse.toml, docs/ADR-*, docs/DECISIONS.md, docs/PRD.md, /etc/, /root/, Cargo.lock.
- Paths MUST be repo-relative (no leading /).
- Whole-file contents only — no patches, no diffs.

Response shape:
{
  "summary": "one line",
  "rationale": "why this addresses the gap",
  "files": [ { "path": "crates/foo/src/bar.rs", "content": "<full file>", "is_new": false } ],
  "estimated_loc": 42
}`;

export async function generateProposal(gap: Gap, historySummary: string = ""): Promise<Proposal> {
  const sections = [
    `PRD gap (line ${gap.line_number}):`,
    "```",
    gap.context,
    "```",
    "",
  ];
  if (historySummary) {
    sections.push(historySummary, "");
  }
  sections.push("Propose a small change that addresses this gap. Respond with the JSON object only.");
  const userPrompt = sections.join("\n");

  const r = await fetch(`${SIDECAR_URL}/generate`, {
    method: "POST",
    headers: { "content-type": "application/json" },
    body: JSON.stringify({
      model: CLOUD_MODEL,
      system: SYSTEM_PROMPT,
      prompt: userPrompt,
      temperature: 0.2,
      max_tokens: MAX_TOKENS,
      think: false,
    }),
    signal: AbortSignal.timeout(180000), // cloud T3 can be slow — 3 min
  });
  if (!r.ok) {
    throw new Error(`sidecar ${r.status}: ${await r.text()}`);
  }
  const j = await r.json() as any;
  const raw: string = j.text ?? j.response ?? "";
  const usage = j.usage ?? {};
  const tokens = (usage.prompt_tokens ?? 0) + (usage.completion_tokens ?? 0);

  const parsed = extractJson(raw);
  if (!parsed || typeof parsed !== "object") {
    throw new Error(`model returned no JSON object. Raw head: ${raw.slice(0, 300)}`);
  }
  if (!Array.isArray(parsed.files)) {
    throw new Error(`proposal.files not an array: ${JSON.stringify(parsed).slice(0, 200)}`);
  }

  return {
    summary: String(parsed.summary ?? "").trim(),
    rationale: String(parsed.rationale ?? "").trim(),
    files: parsed.files.map((f: any) => ({
      path: String(f.path ?? ""),
      content: String(f.content ?? ""),
      is_new: Boolean(f.is_new),
    })).filter((f: any) => f.path && f.content !== undefined),
    estimated_loc: Number(parsed.estimated_loc ?? 0),
    model_used: CLOUD_MODEL,
    tokens_used: tokens,
  };
}

// Find the first balanced JSON object in the string. Tolerates leading
// "```json" fences even though we asked the model not to emit them.
function extractJson(text: string): any | null {
  const cleaned = text.replace(/^```(?:json)?\s*/i, "").replace(/```\s*$/i, "").trim();
  let depth = 0;
  let start = -1;
  for (let i = 0; i < cleaned.length; i++) {
    const c = cleaned[i];
    if (c === "{") {
      if (depth === 0) start = i;
      depth++;
    } else if (c === "}") {
      depth--;
      if (depth === 0 && start >= 0) {
        try {
          return JSON.parse(cleaned.slice(start, i + 1));
        } catch {
          start = -1;
        }
      }
    }
  }
  return null;
}