Sessions 5-7a: 955 tests, deployment ready

src/services/altLineScanner.js

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+/**
+ * Normal CDF using rational approximation (Abramowitz & Stegun).
+ */
+function normalCDF(x, mean = 0, stddev = 1) {
+  if (stddev <= 0) return x >= mean ? 1 : 0;
+  const z = (x - mean) / stddev;
+  const t = 1 / (1 + 0.2316419 * Math.abs(z));
+  const d = 0.3989422804014327; // 1/sqrt(2*pi)
+  const p = d * Math.exp(-z * z / 2) *
+    (t * (0.3193815 + t * (-0.3565638 + t * (1.781478 + t * (-1.8212560 + t * 1.3302744)))));
+  return z > 0 ? 1 - p : p;
+}
+
+/**
+ * Calculate model probability for a prop line using normal distribution.
+ * @param {number} mean - Projected mean
+ * @param {number} stddev - Standard deviation
+ * @param {number} line - The prop line
+ * @param {string} direction - 'over' or 'under'
+ * @returns {number} Probability 0-1
+ */
+function calculateModelProbability(mean, stddev, line, direction) {
+  if (stddev <= 0) {
+    if (direction === 'over') return mean > line ? 1 : 0;
+    return mean < line ? 1 : 0;
+  }
+
+  const cdf = normalCDF(line, mean, stddev);
+  return direction === 'over' ? 1 - cdf : cdf;
+}
+
+/**
+ * Convert American odds to implied probability.
+ * @param {number} odds - American odds (e.g. -110, +150)
+ * @returns {number} Implied probability 0-1
+ */
+function americanToImplied(odds) {
+  if (odds < 0) return Math.abs(odds) / (Math.abs(odds) + 100);
+  return 100 / (odds + 100);
+}
+
+/**
+ * Compare model probability to book implied probability.
+ * @param {number} modelProb - Model-calculated probability
+ * @param {number} bookOdds - American odds from the book
+ * @returns {object} { model_prob, book_implied, edge, value_detected }
+ */
+function compareToBookImplied(modelProb, bookOdds) {
+  const bookImplied = americanToImplied(bookOdds);
+  const edge = modelProb - bookImplied;
+
+  return {
+    model_prob: Math.round(modelProb * 1000) / 1000,
+    book_implied: Math.round(bookImplied * 1000) / 1000,
+    edge: Math.round(edge * 1000) / 1000,
+    value_detected: edge > 0,
+  };
+}
+
+/**
+ * Scan alternate lines for A-grade props to find optimal value.
+ * @param {object} prop - { player, stat, projected_mean, projected_stddev, grade }
+ * @param {Array} oddsData - Array of { line, odds, book } from alt markets
+ * @returns {object|null} Best alt line with edge, or null
+ */
+function scanAltLines(prop, oddsData) {
+  if (!prop || !oddsData || oddsData.length === 0) return null;
+
+  const { projected_mean, projected_stddev } = prop;
+  const direction = prop.direction || 'over';
+
+  const evaluated = oddsData.map(alt => {
+    const modelProb = calculateModelProbability(projected_mean, projected_stddev, alt.line, direction);
+    const comparison = compareToBookImplied(modelProb, alt.odds);
+
+    return {
+      line: alt.line,
+      odds: alt.odds,
+      book: alt.book,
+      model_probability: comparison.model_prob,
+      book_implied: comparison.book_implied,
+      edge: comparison.edge,
+      value_detected: comparison.value_detected,
+    };
+  });
+
+  const withValue = evaluated.filter(e => e.value_detected);
+  if (withValue.length === 0) return null;
+
+  withValue.sort((a, b) => b.edge - a.edge);
+  const optimal = withValue[0];
+
+  return {
+    optimal_line: optimal.line,
+    odds: optimal.odds,
+    book: optimal.book,
+    model_probability: optimal.model_probability,
+    book_implied: optimal.book_implied,
+    edge: optimal.edge,
+    all_value_lines: withValue,
+  };
+}
+
+module.exports = {
+  scanAltLines,
+  calculateModelProbability,
+  compareToBookImplied,
+  normalCDF,
+  americanToImplied,
+};