/**
 * Finding helpers — v1 minimum handoff from focused contributions.
 *
 * Deterministic (no LLM). Each observation in a focused contribution
 * yields exactly one provisional Finding.  Findings may influence
 * Current Understanding only and must never touch SituationGraph,
 * activeUnknownNodeId, selectedQuestion, or frontier selection.
 */

// ── Fixed disposition values ──────────────────────────────

export const FINDING_DISPOSITION_VALUES = ["agree", "not_quite", "not_relevant"];

// ── Deterministic id derivation ───────────────────────────

/**
 * Derive a stable, collision-resistant Finding id from the source observation
 * and its originating contribution reference.
 */
function hashString(str) {
  let h = 0;
  for (let i = 0; i < str.length; i++) {
    h = (Math.imul(31, h) + str.charCodeAt(i)) | 0;
  }
  return h;
}

export function deriveFindingId(sourceObservation, contributionId) {
  const seed = `${contributionId}|${sourceObservation}`;
  const hash = hashString(seed);
  return "finding-" + Math.abs(hash).toString(36).slice(0, 7);
}

// ── Finding derivation (contribution → findings) ──────────

/**
 * Given an array of contributions that each carry observations[],
 * produce one provisional Finding per observation.
 *
 * Returns: { findings, evaluation } — pure result, no side effects.
 */
export function deriveFindingsFromContributions(contributions) {
  const findings = [];
  let contribIdx = 0;

  for (const contrib of contributions) {
    if (!contrib?.observations || !Array.isArray(contrib.observations)) continue;
    const targetId = contrib.targetNodeId ?? "";
    const contribSeq = contrib.sequence != null ? String(contrib.sequence) : String(++contribIdx);
    const contribId = contrib.id ?? `contrib-${String(contribIdx).padStart(4, "0")}`;

    for (const obs of contrib.observations) {
      if (typeof obs !== "string" || !obs.trim()) continue;
      findings.push({
        id: deriveFindingId(obs, contribId),
        proposition: obs,            // Finding proposition = exact observation text
        status: "provisional",
        userDisposition: null,       // default: silence ≠ agreement
        originatingTargetNodeId: targetId,
        contributionId: contribId,
        sourceObservation: obs,      // immutable provenance anchor
        createdAt: new Date().toISOString(),
      });
    }
  }

  return { findings };
}

// ── Server-side validation ────────────────────────────────

/** Validate a single incoming finding. Returns null when valid or an error string. */
export function validateSingleFinding(finding) {
  if (!finding || typeof finding !== "object") return "Finding is not an object";
  if (typeof finding.proposition !== "string" || !finding.proposition.trim())
    return "Malformed: empty or missing proposition";
  if (typeof finding.contributionId !== "string" || !finding.contributionId)
    return "Malformed: contributionId required";
  if (!finding.sourceObservation || typeof finding.sourceObservation !== "string")
    return "Malformed: sourceObservation required and must be string";
  if (finding.userDisposition !== null && FINDING_DISPOSITION_VALUES.indexOf(finding.userDisposition) === -1)
    return "Malformed: invalid userDisposition";
  // No graph mutation fields allowed in findings
  const forbidden = ["situationGraph", "nodes", "edges", "activeUnknownNodeId", "selectedQuestion"];
  for (const key of forbidden) {
    if (key in finding) return `Malformed: unexpected graph field "${key}"`;
  }
  // Must have a traceable contribution reference format
  if (!finding.contributionId.startsWith("contrib-"))
    return "Untraceable: contributionId must start with contrib-";
  return null;
}

/** Validate an array of findings; return { valid, rejectedErrors }. */
export function validateFindings(findings) {
  const results = [];
  const idSet = new Set();

  for (const f of findings) {
    const err = validateSingleFinding(f);
    if (err) {
      results.push({ ...f, evaluation: "rejected", reason: err });
      continue;
    }
    if (idSet.has(f.id)) {
      results.push({ ...f, evaluation: "rejected", reason: "Duplicate finding id" });
      continue;
    }
    idSet.add(f.id);
    // Normalize disposition to canonical value
    const disposition = f.userDisposition === null ? null : FINDING_DISPOSITION_VALUES.indexOf(f.userDisposition) !== -1 ? f.userDisposition : null;
    results.push({ ...f, evaluation: "considered", userDisposition: disposition });
  }
  return { findings: results };
}

// ── Deduplicate + map dispositions (client helper) ─────────

/** Deduplicate by id and map userDisposition to canonical value. */
export function normalizeFindings(findings) {
  const seen = new Set();
  return findings.filter((f) => {
    if (seen.has(f.id)) return false;
    seen.add(f.id);
    return true;
  }).map((f) => ({
    ...f,
    userDisposition: f.userDisposition === null ? null : FINDING_DISPOSITION_VALUES.indexOf(f.userDisposition) !== -1 ? f.userDisposition : null,
  }));
}

// ── Apply validated findings to Current Understanding ─────

/** Return new summary string that appends valid finding propositions. */
export function applyFindingsToSummary(summary, validatedFindings) {
  let text = summary;
  const agreeTexts = [];
  const notQuiteTexts = [];
  const notRelevantTexts = [];

  for (const f of validatedFindings) {
    if (f.evaluation === "rejected") continue;
    // Map disposition to evaluation state
    switch (f.userDisposition) {
      case "agree":     f.evaluation = "used";      agreeTexts.push(f.proposition); break;
      case "not_quite": f.evaluation = "not_used";  notQuiteTexts.push(f.proposition); break;
      case "not_relevant": f.evaluation = "not_used"; notRelevantTexts.push(f.proposition); break;
      default:          /* null disposition → considered only */ break;
    }
  }

  if (agreeTexts.length === 0 && notQuiteTexts.length === 0 && notRelevantTexts.length === 0) {
    return summary; // no textual change
  }

  const parts = [];
  if (agreeTexts.length > 0) {
    parts.push(`Confirmed observation${agreeTexts.length > 1 ? "s" : ""}: ${agreeTexts.join("; ")}`);
  }
  if (notQuiteTexts.length > 0) {
    parts.push(`Partial match${notQuiteTexts.length > 1 ? "es" : ""}: ${notQuiteTexts.join("; ")}`);
  }
  if (notRelevantTexts.length > 0) {
    parts.push(`Noted as not directly relevant: ${notRelevantTexts.join("; ")}`);
  }

  return text + " [" + parts.join(" | ") + "]";
}

// ── Post-authoritative experimental understanding producer ──

/**
 * Deterministic proof-seam: produce Current Understanding from validated findings
 * AFTER authoritative graph update is settled.
 *
 * Eligibility contract (closed):
 *   null           → eligible provisional working interpretation
 *   "agree"        → eligible confirmed evidence
 *   other/falsy    → excluded (not_relevant, rejected, etc.)
 *
 * Output affects ONLY the summary/current understanding string.
 */
export function produceFindingInformedSummary(originalSummary, appendedFindings) {
  if (!appendedFindings || appendedFindings.length === 0) {
    return originalSummary;
  }

  const parts = [];

  for (const f of appendedFindings) {
    if (f.evaluation === "rejected") continue;
    // null disposition → eligible (provisional working interpretation)
    // "agree" disposition → eligible (confirmed evidence)
    if (f.userDisposition === null || f.userDisposition === "agree") {
      parts.push(f.proposition);
    }
    // not_relevant and not_quite → excluded
  }

  if (parts.length === 0) {
    return originalSummary; // no eligible findings
  }

  const evidenceText = `Evidence: [${parts.join("; ")}]`;
  return originalSummary + " " + evidenceText;
}