// export_preference.ts — Phase 4c preference dataset export.
//
// Pairs scored runs that attempted comparable tasks but landed in
// different categories (one accepted, one rejected). The "chosen" is
// the better outcome's text, the "rejected" is the worse outcome's
// text, and "reason" cites the explicit category transition.
//
// Pairing signal v1: SAME task_id with categories accepted/rejected
// (or accepted/partially_accepted as a softer pair).
//
// Hard rules from spec:
//   - chosen != rejected at content level
//   - chosen_run_id != rejected_run_id
//   - reason non-empty
//   - never fabricate pairs from unrelated records
//
// If insufficient valid pairs exist for a task_id, we don't pad — we
// just emit fewer pairs and note the gap.

import { existsSync, readFileSync, readdirSync, mkdirSync, appendFileSync, statSync } from "node:fs";
import { resolve, dirname } from "node:path";
import {
  PREFERENCE_SAMPLE_SCHEMA_VERSION, validatePreferenceSample, type PreferenceSample,
} from "../../auditor/schemas/distillation/preference_sample";
import type { ScoredRun } from "../../auditor/schemas/distillation/scored_run";
import type { EvidenceRecord } from "../../auditor/schemas/distillation/evidence_record";
import { QuarantineWriter } from "./quarantine";

export interface ExportPreferenceOptions {
  root: string;
  recorded_at: string;
  dry_run?: boolean;
}

export interface ExportPreferenceResult {
  scored_files_read: number;
  records_read: number;
  task_ids_with_pairs: number;
  pairs_exported: number;
  records_quarantined: number;
  output_path: string;
  quarantine_summary: string;
  insufficient_pair_task_ids: number;  // tasks where we had only 1 record OR all same category
}

const DEFAULT_ROOT = process.env.LH_DISTILL_ROOT ?? "/home/profit/lakehouse";

interface IndexedRecord {
  scored: ScoredRun;
  ev: EvidenceRecord;
  scored_path: string;
  line: number;
}

function listScoredRunFiles(root: string): string[] {
  const out: string[] = [];
  const dir = resolve(root, "data/scored-runs");
  if (!existsSync(dir)) return out;
  for (const yyyy of readdirSync(dir).sort()) {
    const yp = resolve(dir, yyyy);
    if (!statSync(yp).isDirectory()) continue;
    for (const mm of readdirSync(yp).sort()) {
      const mp = resolve(yp, mm);
      if (!statSync(mp).isDirectory()) continue;
      for (const dd of readdirSync(mp).sort()) {
        const dp = resolve(mp, dd);
        if (!statSync(dp).isDirectory()) continue;
        for (const f of readdirSync(dp)) {
          if (f.endsWith(".jsonl")) out.push(resolve(dp, f));
        }
      }
    }
  }
  return out;
}

function loadEvidenceByRunId(
  scored_path: string,
  cache: Map<string, Map<string, EvidenceRecord>>,
): Map<string, EvidenceRecord> {
  const evidence_path = scored_path.replace("/scored-runs/", "/evidence/");
  if (cache.has(evidence_path)) return cache.get(evidence_path)!;
  const m = new Map<string, EvidenceRecord>();
  if (!existsSync(evidence_path)) { cache.set(evidence_path, m); return m; }
  for (const line of readFileSync(evidence_path, "utf8").split("\n")) {
    if (!line) continue;
    try { const ev = JSON.parse(line) as EvidenceRecord; m.set(ev.run_id, ev); } catch {}
  }
  cache.set(evidence_path, m);
  return m;
}

// Build a pair from accepted + rejected (or accepted + partially) within
// the same task_id. Never invents pairs.
function buildPair(
  chosen: IndexedRecord,
  rejected: IndexedRecord,
  recorded_at: string,
): PreferenceSample | { error: string } {
  if (chosen.scored.evidence_task_id !== rejected.scored.evidence_task_id) {
    return { error: "task_id mismatch — comparable signal violation" };
  }
  if (chosen.scored.evidence_run_id === rejected.scored.evidence_run_id) {
    return { error: "same run_id — self-pairing" };
  }
  const chosenText = (chosen.ev.text ?? "").trim();
  const rejectedText = (rejected.ev.text ?? "").trim();
  if (chosenText.length === 0 || rejectedText.length === 0) {
    return { error: "empty text in chosen or rejected" };
  }
  if (chosenText === rejectedText) {
    return { error: "chosen and rejected texts identical" };
  }

  // Prompt synthesis: best-effort. For task_ids that encode a file
  // (e.g. scrum_review:<file>), include the file. Generic otherwise.
  const taskId = chosen.scored.evidence_task_id;
  let prompt = `Task: ${taskId}`;
  const file = chosen.ev.source_files?.[0];
  if (file) prompt += ` · file=${file}`;

  // Reason cites the explicit category gap.
  const reasonParts = [
    `chosen scored '${chosen.scored.category}'`,
    `rejected scored '${rejected.scored.category}'`,
  ];
  if (chosen.scored.reasons.length > 0) reasonParts.push(`chosen-rationale: ${chosen.scored.reasons[0].slice(0, 80)}`);
  if (rejected.scored.reasons.length > 0) reasonParts.push(`rejected-rationale: ${rejected.scored.reasons[0].slice(0, 80)}`);
  const reason = reasonParts.join(" | ");

  const id_seed = `${chosen.scored.evidence_run_id}|${rejected.scored.evidence_run_id}|${taskId}`;
  const hasher = new Bun.CryptoHasher("sha256");
  hasher.update(id_seed);
  const pref_id = "pref-" + hasher.digest("hex").slice(0, 16);

  return {
    schema_version: PREFERENCE_SAMPLE_SCHEMA_VERSION,
    id: pref_id,
    prompt,
    chosen: chosenText,
    rejected: rejectedText,
    reason,
    chosen_run_id: chosen.scored.evidence_run_id,
    rejected_run_id: rejected.scored.evidence_run_id,
    created_at: recorded_at,
    provenance: {
      source_file: chosen.scored.provenance.source_file,
      line_offset: chosen.scored.provenance.line_offset,
      // sig_hash for the pair = canonical sha of {chosen_run_id, rejected_run_id}
      // sorted so re-running produces the same provenance.
      sig_hash: pref_id_to_sig(chosen.scored.evidence_run_id, rejected.scored.evidence_run_id),
      recorded_at,
    },
  };
}

function pref_id_to_sig(a: string, b: string): string {
  const seed = [a, b].sort().join("|");
  const h = new Bun.CryptoHasher("sha256");
  h.update(seed);
  return h.digest("hex");
}

export async function exportPreference(opts: ExportPreferenceOptions): Promise<ExportPreferenceResult> {
  const { root, recorded_at, dry_run = false } = opts;
  const out_path = resolve(root, "exports/preference/chosen_rejected.jsonl");
  const q = new QuarantineWriter(root, "preference", dry_run);

  let records_read = 0;
  const seenIds = new Set<string>();
  if (!dry_run && existsSync(out_path)) {
    for (const line of readFileSync(out_path, "utf8").split("\n")) {
      if (!line) continue;
      try { const r = JSON.parse(line); if (r.id) seenIds.add(r.id); } catch {}
    }
  }

  // Index by task_id.
  const evidenceCache = new Map<string, Map<string, EvidenceRecord>>();
  const byTask = new Map<string, IndexedRecord[]>();
  const scored_files = listScoredRunFiles(root);
  for (const sp of scored_files) {
    const evMap = loadEvidenceByRunId(sp, evidenceCache);
    const lines = readFileSync(sp, "utf8").split("\n").filter(Boolean);
    for (let i = 0; i < lines.length; i++) {
      records_read++;
      let scored: ScoredRun;
      try { scored = JSON.parse(lines[i]) as ScoredRun; } catch { continue; }
      const ev = evMap.get(scored.evidence_run_id);
      if (!ev) continue;
      if (!scored.evidence_task_id) continue;
      const list = byTask.get(scored.evidence_task_id) ?? [];
      list.push({ scored, ev, scored_path: sp, line: i });
      byTask.set(scored.evidence_task_id, list);
    }
  }

  let pairs_exported = 0;
  let task_ids_with_pairs = 0;
  let insufficient_pair_task_ids = 0;
  const rowsToWrite: string[] = [];

  for (const [taskId, recs] of byTask) {
    if (recs.length < 2) {
      insufficient_pair_task_ids++;
      continue;
    }
    const accepted = recs.filter(r => r.scored.category === "accepted");
    const rejected = recs.filter(r => r.scored.category === "rejected");
    const partial = recs.filter(r => r.scored.category === "partially_accepted");

    // Strongest signal: accepted vs rejected.
    let pairs = pairUp(accepted, rejected);
    // Weaker but still valid: accepted vs partial.
    if (pairs.length === 0) pairs = pairUp(accepted, partial);

    if (pairs.length === 0) {
      insufficient_pair_task_ids++;
      continue;
    }

    let exportedThisTask = 0;
    for (const [chosen, rej] of pairs) {
      const built = buildPair(chosen, rej, recorded_at);
      if ("error" in built) {
        q.add({
          reason: "invalid_preference_pairing",
          source_record: { task_id: taskId, chosen_run_id: chosen.scored.evidence_run_id, rejected_run_id: rej.scored.evidence_run_id },
          errors: [built.error],
          recorded_at,
          source_provenance: chosen.scored.provenance,
        });
        continue;
      }

      if (seenIds.has(built.id)) continue;
      const v = validatePreferenceSample(built);
      if (!v.valid) {
        q.add({
          reason: "schema_violation",
          source_record: built as unknown as Record<string, unknown>,
          errors: v.errors,
          recorded_at,
          source_provenance: chosen.scored.provenance,
        });
        continue;
      }
      seenIds.add(built.id);
      rowsToWrite.push(JSON.stringify(v.value));
      pairs_exported++;
      exportedThisTask++;
    }
    if (exportedThisTask > 0) task_ids_with_pairs++;
  }

  if (!dry_run && rowsToWrite.length > 0) {
    mkdirSync(dirname(out_path), { recursive: true });
    appendFileSync(out_path, rowsToWrite.join("\n") + "\n");
  }

  return {
    scored_files_read: scored_files.length,
    records_read,
    task_ids_with_pairs,
    pairs_exported,
    records_quarantined: q.total,
    output_path: out_path.replace(root + "/", ""),
    quarantine_summary: q.summary(),
    insufficient_pair_task_ids,
  };
}

// Cross-product pairing: every accepted × every rejected. For any
// task_id with k accepted and m rejected, we get k*m pairs. Capped
// per task to keep the dataset balanced.
const MAX_PAIRS_PER_TASK = 5;
function pairUp(a: IndexedRecord[], b: IndexedRecord[]): Array<[IndexedRecord, IndexedRecord]> {
  const pairs: Array<[IndexedRecord, IndexedRecord]> = [];
  for (const x of a) {
    for (const y of b) {
      if (pairs.length >= MAX_PAIRS_PER_TASK) return pairs;
      pairs.push([x, y]);
    }
  }
  return pairs;
}

async function cli() {
  const dry_run = process.argv.includes("--dry-run");
  const recorded_at = new Date().toISOString();
  const r = await exportPreference({ root: DEFAULT_ROOT, recorded_at, dry_run });

  console.log(`[export_preference] read=${r.records_read} pairs=${r.pairs_exported} task_ids_paired=${r.task_ids_with_pairs} ${r.quarantine_summary}${dry_run ? " (DRY RUN)" : ""}`);
  console.log(`[export_preference] insufficient_pair_task_ids=${r.insufficient_pair_task_ids} (only one record OR all-same-category)`);
  console.log(`[export_preference] output: ${r.output_path}`);
}

if (import.meta.main) cli().catch(e => { console.error(e); process.exit(1); });