docs: introduce Mercury Notebook Deliverable Pattern

template/MercuryNotebook/studylib/model.py

@@ -0,0 +1,166 @@
+"""
+Study engine — the single source of truth for every number in the notebooks.
+
+Replace the toy domain below with the study's real model; the *structure*
+is the pattern:
+
+- ``ANCHOR_VERBATIM`` — the client/vendor source record, never edited.
+- ``ANCHOR_CONTRACTED`` — signed values layered over it; ``anchor()`` reads
+  through, so the source anchor survives for as-pitched comparisons.
+- ``*_by_year`` schedules keyed by calendar year.
+- A baseline-relative case frame (``case_flows`` / ``case_kpis``).
+
+The notebooks hold no math — they call this module and render.
+"""
+
+from __future__ import annotations
+
+import math
+
+# ── Timeline ─────────────────────────────────────────────────────────
+
+YEARS = [2026, 2027, 2028]             # model window; contract starts Jan of YEARS[0]
+_MONTHS = ["Jan", "Feb", "Mar", "Apr", "May", "Jun",
+           "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"]
+
+
+def month_label(m: int) -> str:
+    """Calendar label for a 1-indexed month from Jan of YEARS[0]."""
+    return f"{_MONTHS[(m - 1) % 12]} {YEARS[0] + (m - 1) // 12}"
+
+
+# ── Anchors: verbatim source record + contracted overlay ─────────────
+
+#: The vendor's pitch / the client's source deck — VERBATIM, do not edit.
+ANCHOR_VERBATIM: dict[str, float] = {
+    "baseline_annual": 1_000_000,   # do-nothing run-rate
+    "platform_annual": 600_000,     # pitched platform run-rate
+    "services_y1": 250_000,         # pitched one-off services, year 1
+    "benefit_3yr": 900_000,         # claimed 3-yr benefit
+    "npv_discount_rate": 0.10,
+}
+
+#: Signed values where they differ from the pitch — 🟢 contractual.
+ANCHOR_CONTRACTED: dict[str, float] = {
+    "platform_annual": 500_000,     # signed run-rate (pitch said $600K)
+}
+
+
+def anchor(key: str) -> float:
+    """Contracted value where one exists, else the verbatim anchor."""
+    return ANCHOR_CONTRACTED.get(key, ANCHOR_VERBATIM[key])
+
+
+DEFAULT_RAMP_MONTHS = 6                # platform billing starts month 7
+DEFAULT_TERMINATION_YEAR = 2027        # existing platform bills through this year
+REALIZE_MONTH = 18                     # benefits realize from month 19
+
+
+# ── Cost & benefit schedules (calendar-year keyed) ───────────────────
+
+
+def platform_costs_by_year(
+    ramp_months: int = DEFAULT_RAMP_MONTHS, annual: float | None = None
+) -> dict[int, float]:
+    """Ramp programme: billing starts in calendar month ramp_months + 1."""
+    rate = ANCHOR_VERBATIM["platform_annual"] if annual is None else annual
+    out = {}
+    for yi, y in enumerate(YEARS, start=1):
+        start, end = 12 * (yi - 1) + 1, 12 * yi
+        months = max(0, end - max(start, ramp_months + 1) + 1)
+        out[y] = rate * months / 12
+    return out
+
+
+def current_costs_by_year(
+    termination_year: int = DEFAULT_TERMINATION_YEAR, annual: float | None = None
+) -> dict[int, float]:
+    """Existing-platform run-off (the double-billing line)."""
+    rate = ANCHOR_VERBATIM["baseline_annual"] if annual is None else annual
+    return {y: (rate if y <= termination_year else 0.0) for y in YEARS}
+
+
+def services_by_year() -> dict[int, float]:
+    """One-off services — verbatim, year 1 only."""
+    return {y: (ANCHOR_VERBATIM["services_y1"] if y == YEARS[0] else 0.0)
+            for y in YEARS}
+
+
+def benefits_by_year(realize_month: int = REALIZE_MONTH) -> dict[int, float]:
+    """Phase the claimed 3-yr benefit across its live months."""
+    live = {y: max(0, 12 * yi - max(12 * (yi - 1), realize_month))
+            for yi, y in enumerate(YEARS, start=1)}
+    total = sum(live.values())
+    return {y: anchor("benefit_3yr") * m / total if total else 0.0
+            for y, m in live.items()}
+
+
+# ── Business case (baseline-relative frame) ──────────────────────────
+
+
+def case_flows(
+    total_cost_by_year: dict[int, float],
+    benefit_by_year: dict[int, float],
+    baseline_annual: float | None = None,
+) -> tuple[dict[int, float], dict[int, float]]:
+    """(incremental cost, net) vs the do-nothing baseline."""
+    base = ANCHOR_VERBATIM["baseline_annual"] if baseline_annual is None \
+        else baseline_annual
+    inc = {y: total_cost_by_year[y] - base for y in YEARS}
+    net = {y: benefit_by_year[y] - inc[y] for y in YEARS}
+    return inc, net
+
+
+def npv(flows: list[float], rate: float) -> float:
+    """NPV with the first flow discounted one full year."""
+    return sum(v / (1 + rate) ** i for i, v in enumerate(flows, start=1))
+
+
+def payback_label(net_by_year: dict[int, float]) -> str:
+    cum = 0.0
+    for i, y in enumerate(YEARS):
+        step = net_by_year[y]
+        if cum + step >= 0:
+            if i == 0 and step >= 0:
+                return "immediate"
+            frac = (-cum / step) if step > 0 else 0.0
+            m = math.ceil((i + frac) * 12)
+            return f"{m} months (~{month_label(m)})"
+        cum += step
+    return f"beyond {YEARS[-1]}"
+
+
+def case_kpis(
+    inc: dict[int, float],
+    net: dict[int, float],
+    discount_rate: float | None = None,
+) -> dict:
+    """KPIs for one cost frame. Benefits are recoverable as net + inc."""
+    rate = ANCHOR_VERBATIM["npv_discount_rate"] if discount_rate is None \
+        else discount_rate
+    net_list = [net[y] for y in YEARS]
+    inc_total = sum(inc.values())
+    net_total = sum(net_list)
+    return {
+        "benefits_3yr": net_total + inc_total,
+        "incremental_cost_3yr": inc_total,
+        "net_3yr": net_total,
+        "roi": (net_total / inc_total) if inc_total > 0 else None,
+        "npv": npv(net_list, rate),
+        "discount_rate": rate,
+        "payback": payback_label(net),
+    }
+
+
+# ── Display helpers ──────────────────────────────────────────────────
+
+
+def money(v: float) -> str:
+    sign, a = ("-" if v < 0 else ""), abs(v)
+    return f"{sign}${a/1e6:,.1f}M" if a >= 1e6 else f"{sign}${a/1e3:,.0f}K"
+
+
+def html_money(v: float) -> str:
+    """Plotly text with two or more bare ``$`` triggers MathJax math mode —
+    annotations holding several amounts must use the HTML entity instead."""
+    return money(v).replace("$", "&#36;")