/**
 * Investigation State Assessment — Experiment 18 First Executable Slice
 *
 * Pure deterministic function that evaluates investigation state across
 * three dimensions: phase, progress, and conversation health.
 *
 * Conservative by design: prefers cannot_determine over invented precision.
 * Safe with missing fields — returns cannot_determine for any dimension
 * whose data is insufficient rather than guessing.
 *
 * Contract reference: docs/investigation-state-assessment-contract.md
 */

/* ── Helpers ─────────────────────────────────────────────── */

/**
 * Normalise resolvedNodeIds from the fixture format ({ resolved: [...] })
 * or from orchestrator format (resolvedNodeIds directly).
 */
function getResolvedIds(input) {
  const fromGraph = input.situationGraph?.resolvedNodeIds;
  if (Array.isArray(fromGraph)) return fromGraph;

  // Legacy scenario fixture shape
  const fromResolved = input.resolved;
  if (Array.isArray(fromResolved)) return fromResolved;

  return [];
}

/**
 * Normalise the activeUnknownNodeId across formats.
 */
function getActiveUnknownId(input) {
  const fromGraph = input.situationGraph?.activeUnknownNodeId;
  if (fromGraph !== undefined && fromGraph !== null) return fromGraph;

  const fromScenario = input.active;
  if (fromScenario !== undefined && fromScenario !== null) return fromScenario;

  return null;
}

/**
 * Count resolved nodes — either via the explicit array or by checking
 * per-node status === "resolved".
 */
function countResolved(input, nodes) {
  const resolvedIds = getResolvedIds(input);
  if (resolvedIds.length > 0) {
    return nodes.filter(n => n && resolvedIds.includes(n.id)).length;
  }
  // Fallback: count nodes with status === "resolved"
  return nodes.filter(n => n && n.status === "resolved").length;
}

/**
 * Classify node confidence as a normalised score for comparison.
 */
function confidenceScore(confidence) {
  if (!confidence) return 0;
  const map = { low: 1, medium: 2, high: 3 };
  return map[confidence] ?? 0;
}

/**
 * Normalise confidence label from score.
 */
function scoreToConfidence(score) {
  if (score >= 7) return "high";
  if (score >= 3) return "medium";
  return "low";
}

/**
 * Count observations: explicit observation kind with known/resolved status,
 * or high-confidence evidence nodes. Deliberately excludes scaffolding state
 * nodes and already-resolved unknowns (they have their own assessment).
 */
function countObservations(nodes, resolvedIds) {
  if (!Array.isArray(nodes)) return 0;

  const resolvedSet = new Set(resolvedIds);

  let count = 0;
  for (const node of nodes) {
    if (!node || typeof node.kind !== "string") continue;

    // Skip already-resolved unknowns — their resolution is tracked separately
    if (resolvedSet.has(node.id)) continue;

    // Include explicit observation kind with known/resolved status
    if (node.kind === "observation" && (node.status === "known" || node.status === "resolved")) {
      count++;
      continue;
    }

    // Include non-unknown nodes with high confidence that aren't scaffolding states
    if (confidenceScore(node.confidence) >= 3 && node.kind !== "state") {
      count++;
      continue;
    }
  }
  return count;
}

/**
 * Count total active (non-resolved) unknowns.
 */
function countActiveUnknowns(input, nodes, resolvedIds) {
  const activeId = getActiveUnknownId(input);

  if (!Array.isArray(nodes)) return activeId ? 1 : 0;

  // Nodes explicitly marked as "unknown" kind that are not resolved
  let count = 0;
  for (const node of nodes) {
    if (!node || node.kind !== "unknown") continue;
    const isResolved = resolvedIds.includes(node.id) || node.status === "resolved";
    if (!isResolved) count++;
  }

  // Fallback: if no unknown-kinded nodes and we have an active ID,
  // the active node itself counts as an active unknown
  if (count === 0 && activeId) {
    const isActiveNode = nodes.find(n => n && n.id === activeId);
    if (!isActiveNode || isActiveNode.status !== "resolved") count = 1;
  }

  return count;
}

/**
 * Compute resolution ratio: resolved / total non-empty nodes.
 */
function computeResolutionRatio(resolvedCount, totalNodes) {
  if (totalNodes <= 0 || resolvedCount === 0) return null;
  return resolvedCount / totalNodes;
}

/**
 * Count distinct reasoning patterns from selected question or diagnostics.
 */
function getReasoningPatterns(input) {
  const patterns = [];

  // From selectedQuestion.reason (may contain reasoning pattern keyword)
  if (input.selectedQuestion?.reasoningPattern) {
    patterns.push(input.selectedQuestion.reasoningPattern);
  }

  // From diagnostics
  const diag = input.diagnostics || {};
  if (diag.reasoningPattern && !patterns.includes(diag.reasoningPattern)) {
    patterns.push(diag.reasoningPattern);
  }
  if (diag.investigationStrategy?.key && !patterns.includes(diag.investigationStrategy.key)) {
    patterns.push(diag.investigationStrategy.key);
  }

  return patterns;
}

/**
 * Count edges connected to each node for structural analysis.
 */
function countEdgeConnections(nodes, edges) {
  if (!Array.isArray(edges)) return {};

  const counts = {};
  for (const edge of edges) {
    if (!edge || !edge.fromNodeId || !edge.toNodeId) continue;
    counts[edge.fromNodeId] = (counts[edge.fromNodeId] ?? 0) + 1;
    counts[edge.toNodeId] = (counts[edge.toNodeId] ?? 0) + 1;
  }
  return counts;
}

/**
 * Determine the minimum confidence across all dimensions.
 */
function minConfidence(...confidences) {
  const priority = { high: 3, medium: 2, low: 1, cannot_determine: 0 };
  let minScore = 4;
  let result = "high";

  for (const c of confidences) {
    const s = priority[c] ?? 4;
    if (s < minScore) {
      minScore = s;
      result = c;
    }
  }
  return result;
}

/* ── Phase Classification ────────────────────────────────── */

function assessPhase(input) {
  const resolvedIds = getResolvedIds(input);
  const nodes = input.situationGraph?.nodes || [];
  const totalNodes = Array.isArray(nodes) ? nodes.length : 0;
  const resolvedCount = countResolved(input, nodes);
  const activeUnknownCount = countActiveUnknowns(input, nodes, resolvedIds);
  const observations = countObservations(nodes, resolvedIds);
  const ratio = computeResolutionRatio(resolvedCount, totalNodes);
  const hasQuestion = Boolean(input.selectedQuestion && input.selectedQuestion.nodeId);
  const activeUnknownId = getActiveUnknownId(input);

  // Terminal: no active unknowns + sufficient history + no current question
  if (activeUnknownCount === 0 && resolvedCount >= 2 && !hasQuestion) {
    return {
      value: "concluding",
      confidence: scoreToConfidence(observations * 2 + resolvedCount),
      signals: [
        `All investigation areas resolved (${resolvedCount} items)`,
        `No active question — investigation complete`
      ],
      evidence: {
        resolvedNodeCount: resolvedCount,
        activeUnknownCount: 0,
        unknownResolutionRatio: ratio,
        observationDensity: observations,
        evidenceDepth: observations >= 4 ? "deep" : observations >= 2 ? "moderate" : "shallow"
      }
    };
  }

  // Synthesising: near-completion with majority resolved
  if (activeUnknownCount <= 1 && ratio !== null && ratio > 0.5) {
    return {
      value: "synthesising",
      confidence: scoreToConfidence(observations * 2 + resolvedCount),
      signals: [
        `Near completion: ${resolvedCount} of ${totalNodes} resolved`,
        `Resolution ratio: ${(ratio * 100).toFixed(0)}%`
      ],
      evidence: {
        resolvedNodeCount: resolvedCount,
        activeUnknownCount,
        unknownResolutionRatio: ratio,
        observationDensity: observations,
        evidenceDepth: observations >= 4 ? "deep" : observations >= 2 ? "moderate" : "shallow"
      }
    };
  }

  // Focusing: single remaining unknown with sufficient context
  if (activeUnknownCount === 1 && observations >= 3) {
    return {
      value: "focusing",
      confidence: scoreToConfidence(observations * 2 + resolvedCount),
      signals: [
        `Single active unknown: ${activeUnknownId ?? "unspecified"}`,
        `${observations} established observations provide sufficient context`
      ],
      evidence: {
        resolvedNodeCount: resolvedCount,
        activeUnknownCount,
        unknownResolutionRatio: ratio,
        observationDensity: observations,
        evidenceDepth: observations >= 4 ? "deep" : "moderate"
      }
    };
  }

  // Exploring: gathering initial evidence — multiple observations but low resolution
  if (observations >= 2 && (ratio === null || ratio < 0.4)) {
    return {
      value: "exploring",
      confidence: scoreToConfidence(observations + resolvedCount),
      signals: [
        `${observations} initial observations gathered`,
        `Resolution progress low (${resolvedCount}/${totalNodes} or unknown)`
      ],
      evidence: {
        resolvedNodeCount: resolvedCount,
        activeUnknownCount,
        unknownResolutionRatio: ratio,
        observationDensity: observations,
        evidenceDepth: "shallow"
      }
    };
  }

  // Deepening: structured investigation with remaining unknowns
  if (activeUnknownCount > 1 && resolvedCount >= 3) {
    return {
      value: "deepening",
      confidence: scoreToConfidence(resolvedCount + observations),
      signals: [
        `Structured investigation in progress`,
        `${resolvedCount} resolved, ${activeUnknownCount} active unknowns remaining`
      ],
      evidence: {
        resolvedNodeCount: resolvedCount,
        activeUnknownCount,
        unknownResolutionRatio: ratio,
        observationDensity: observations,
        evidenceDepth: observations >= 4 ? "deep" : "moderate"
      }
    };
  }

  // Cannot determine — insufficient data
  return {
    value: "cannot_determine",
    confidence: "low",
    signals: [
      `Insufficient data for phase classification`,
      `Total nodes: ${totalNodes}, resolved: ${resolvedCount}, active: ${activeUnknownCount}`
    ],
    evidence: {
      resolvedNodeCount: resolvedCount,
      activeUnknownCount,
      unknownResolutionRatio: ratio,
      observationDensity: observations ?? 0,
      evidenceDepth: totalNodes < 3 ? "insufficient" : "shallow"
    }
  };
}

/* ── Progress Classification ─────────────────────────────── */

function assessProgress(input) {
  const resolvedIds = getResolvedIds(input);
  const nodes = input.situationGraph?.nodes || [];
  const totalNodes = Array.isArray(nodes) ? nodes.length : 0;
  const resolvedCount = countResolved(input, nodes);
  const ratio = computeResolutionRatio(resolvedCount, totalNodes);

  // No data at all — cannot determine
  if (totalNodes <= 2 || resolvedCount === 0) {
    return {
      value: "cannot_determine",
      confidence: "low",
      signals: [
        `Insufficient data for progress assessment`,
        `Total nodes: ${totalNodes}, resolved: ${resolvedCount}`
      ],
      evidence: {
        turnCount: 0,
        recentResolutionsLastTurn: 0,
        newUnknownsPerTurn: null,
        repeatedNodeIds: []
      }
    };
  }

  // Accelerating: resolving faster than accumulating — high ratio
  if (ratio !== null && ratio > 0.6) {
    return {
      value: "accelerating",
      confidence: scoreToConfidence(resolvedCount * 2 + totalNodes),
      signals: [
        `High resolution progress: ${(ratio * 100).toFixed(0)}% of nodes resolved`,
        `${resolvedCount} of ${totalNodes} nodes resolved`
      ],
      evidence: {
        turnCount: Math.floor(totalNodes / 3), // approximation per scenario pattern
        recentResolutionsLastTurn: resolvedCount,
        newUnknownsPerTurn: null,
        repeatedNodeIds: []
      }
    };
  }

  // Steady: moderate progress — ratio between 0.2 and 0.6
  if (ratio !== null && ratio >= 0.2) {
    return {
      value: "steady",
      confidence: scoreToConfidence(resolvedCount + totalNodes),
      signals: [
        `Moderate resolution progress: ${(ratio * 100).toFixed(0)}% of nodes resolved`,
        `${resolvedCount} of ${totalNodes} nodes resolved`
      ],
      evidence: {
        turnCount: Math.floor(totalNodes / 3),
        recentResolutionsLastTurn: resolvedCount,
        newUnknownsPerTurn: null,
        repeatedNodeIds: []
      }
    };
  }

  // Stalled: some work done but insufficient momentum
  if (resolvedCount >= 1) {
    return {
      value: "stalled",
      confidence: scoreToConfidence(resolvedCount + totalNodes),
      signals: [
        `Low resolution progress: ${(ratio !== null ? (ratio * 100).toFixed(0) : "<10")}% of nodes resolved`,
        `${resolvedCount} of ${totalNodes} nodes resolved — insufficient momentum`
      ],
      evidence: {
        turnCount: Math.floor(totalNodes / 3),
        recentResolutionsLastTurn: resolvedCount,
        newUnknownsPerTurn: null,
        repeatedNodeIds: []
      }
    };
  }

  // Cannot determine (safety net)
  return {
    value: "cannot_determine",
    confidence: "low",
    signals: [
      `Cannot classify progress with available data`,
      `Total nodes: ${totalNodes}, resolved: ${resolvedCount}`
    ],
    evidence: {
      turnCount: 0,
      recentResolutionsLastTurn: 0,
      newUnknownsPerTurn: null,
      repeatedNodeIds: []
    }
  };
}

/* ── Conversation Health Classification ──────────────────── */

function assessConversationHealth(input) {
  const resolvedIds = getResolvedIds(input);
  const nodes = input.situationGraph?.nodes || [];
  const totalNodes = Array.isArray(nodes) ? nodes.length : 0;
  const observations = countObservations(nodes, resolvedIds);
  const activeUnknownCount = countActiveUnknowns(input, nodes, resolvedIds);
  const hasQuestion = Boolean(input.selectedQuestion && input.selectedQuestion.nodeId);
  const hasActiveUnknown = activeUnknownCount > 0;
  const ratio = computeResolutionRatio(countResolved(input, nodes), totalNodes);

  // Terminal state with all resolved — healthy (closed loop)
  if (!hasActiveUnknown && !hasQuestion) {
    return {
      value: "healthy",
      confidence: scoreToConfidence(observations + countResolved(input, nodes)),
      signals: ["Investigation closed — no active question or unknowns"],
      evidence: {
        questionTypeDistribution: null,
        activeUnknownCount: 0,
        resolvedNodeRatio: ratio,
        hasActiveQuestion: false,
        summaryLength: (input.situationGraph?.currentSummary || "").length
      }
    };
  }

  // Too broad: multiple unresolved unknowns without sufficient resolved context
  if (activeUnknownCount > 3 && countResolved(input, nodes) < 2) {
    return {
      value: "too_broad",
      confidence: scoreToConfidence(totalNodes),
      signals: [
        `${activeUnknownCount} active unknowns with fewer than 2 resolved items`,
        `Investigation may be spreading too thin`
      ],
      evidence: {
        questionTypeDistribution: null,
        activeUnknownCount,
        resolvedNodeRatio: ratio,
        hasActiveQuestion: hasQuestion,
        summaryLength: (input.situationGraph?.currentSummary || "").length
      }
    };
  }

  // Too narrow: asking a question without sufficient context
  if (observations <= 1 && hasQuestion) {
    return {
      value: "too_narrow",
      confidence: "low",
      signals: [
        `Only ${observations} observation(s) available before active question`,
        `Asking requires more contextual evidence`
      ],
      evidence: {
        questionTypeDistribution: null,
        activeUnknownCount,
        resolvedNodeRatio: ratio,
        hasActiveQuestion: true,
        summaryLength: (input.situationGraph?.currentSummary || "").length
      }
    };
  }

  // Healthy: active investigation with open questions and balanced state
  if (hasActiveUnknown && hasQuestion) {
    return {
      value: "healthy",
      confidence: scoreToConfidence(observations + countResolved(input, nodes)),
      signals: [
        `Active investigation in progress: ${activeUnknownCount} unresolved unknown(s)`,
        `Question actively driving the investigation forward`
      ],
      evidence: {
        questionTypeDistribution: null,
        activeUnknownCount,
        resolvedNodeRatio: ratio,
        hasActiveQuestion: true,
        summaryLength: (input.situationGraph?.currentSummary || "").length
      }
    };
  }

  // Cannot determine — safety net
  return {
    value: "cannot_determine",
    confidence: "low",
    signals: [
      `Insufficient conversation signals to evaluate health`,
      `activeUnknowns: ${activeUnknownCount}, hasQuestion: ${hasQuestion}, observations: ${observations}`
    ],
    evidence: {
      questionTypeDistribution: null,
      activeUnknownCount,
      resolvedNodeRatio: ratio,
      hasActiveQuestion: hasQuestion,
      summaryLength: (input.situationGraph?.currentSummary || "").length
    }
  };
}

/* ── Main Assessor Function ──────────────────────────────── */

/**
 * Assess investigation state across three deterministic dimensions.
 *
 * This is a pure function with no side effects, no network calls, and no
 * mutation of input state. It handles missing or partial data gracefully
 * by returning cannot_determine for any dimension whose evidence is
 * insufficient rather than guessing.
 *
 * @param {Object} input — Investigation state from orchestrator or scenario fixture
 * @param {Object} [input.situationGraph] — Graph with nodes, edges, activeUnknownNodeId, resolvedNodeIds
 * @param {Object[]} [input.situationGraph.nodes] — Node array
 * @param {string[]} [input.situationGraph.resolvedNodeIds] — Resolved node ID strings
 * @param {string|null} [input.situationGraph.activeUnknownNodeId] — Currently targeted unknown
 * @param {Object|null} [input.selectedQuestion] — Current question { nodeId, question, reason }
 * @param {Object}   [input.diagnostics] — Turn diagnostics with reasoningPattern, nodeCount, etc.
 * @param {string|null} [input.noQuestionReason] — Why no question was selected
 * @returns {{version: string, assessedAt: string, confidence: string, phase: Object, progress: Object, conversationHealth: Object}}
 */
export function assessInvestigationState(input) {
  if (!input) {
    return {
      version: "v0.1",
      assessedAt: new Date().toISOString(),
      confidence: "low",
      phase: { value: "cannot_determine", confidence: "low", signals: ["No input provided"], evidence: {} },
      progress: { value: "cannot_determine", confidence: "low", signals: ["No input provided"], evidence: {} },
      conversationHealth: { value: "cannot_determine", confidence: "low", signals: ["No input provided"], evidence: {} }
    };
  }

  const phase = assessPhase(input);
  const progress = assessProgress(input);
  const health = assessConversationHealth(input);
  const overallConfidence = minConfidence(phase.confidence, progress.confidence, health.confidence);

  return {
    version: "v0.1",
    assessedAt: new Date().toISOString(),
    confidence: overallConfidence,
    phase,
    progress,
    conversationHealth: health
  };
}

export default assessInvestigationState;