calculator.py

from config import FLOW_RATES, USAGE_PATTERNS, USER_MULTIPLIERS, DRINKING_WATER

def calculate_usage(requirements):
    """
    Calculates daily water usage and survival days.
    
    IMPORTANT - How effective multipliers work (matching Excel model):
    - eff_shower/sink = SUM of (count × mult) across all user types
      → This already encodes total group usage, so NO extra × num_adults needed
    - eff_toilet      = SUM of all adult counts (toilet mult = 1 for everyone)
      → Used for display only; toilet formula uses base per-person × 1 event
    - Toilet daily    = flow × frequency × 1  (base, not scaled by eff_toilet)
    - Drinking adults = 0.7 × num_adults from CORE PARAMS (not user type total)
    """

    # ── User type counts (from User Type Distribution) ──────────────────────
    num_expert   = requirements.get("num_expert", 0)
    num_typical  = requirements.get("num_typical", 0)
    num_glamper  = requirements.get("num_glamper", 0)

    # ── Core params ──────────────────────────────────────────────────────────
    num_adults   = requirements.get("num_adults", num_expert + num_typical + num_glamper)
    num_children = requirements.get("num_children", 0)
    climate_mult = requirements.get("climate_mult", 1.0)

    # ── Effective Multipliers (SUM — already encodes all adults) ─────────────
    #    Excel: Eff Shower = 2×0.6 + 0×1.0 + 1×1.5 = 2.7  (NOT divided by adults)
    eff_shower_mult = (
        num_expert  * USER_MULTIPLIERS["expert"]["shower"] +
        num_typical * USER_MULTIPLIERS["typical"]["shower"] +
        num_glamper * USER_MULTIPLIERS["glamper"]["shower"]
    )

    eff_sink_mult = (
        num_expert  * USER_MULTIPLIERS["expert"]["sink"] +
        num_typical * USER_MULTIPLIERS["typical"]["sink"] +
        num_glamper * USER_MULTIPLIERS["glamper"]["sink"]
    )

    # Toilet mult = 1 for all types → eff_toilet = total adults (display only)
    eff_toilet_mult = num_expert + num_typical + num_glamper

    # ── Daily Fresh Water Per Activity ───────────────────────────────────────

    # Shower: flow × duration × frequency × eff_shower_mult × climate
    # (eff_shower_mult already accounts for all adults — no × num_adults)
    shower_daily = (
        FLOW_RATES["shower"] *
        USAGE_PATTERNS["shower"]["duration"] *
        USAGE_PATTERNS["shower"]["frequency"] *
        eff_shower_mult *
        climate_mult
    )

    # Kitchen Sink: same pattern
    kitchen_sink_daily = (
        FLOW_RATES["kitchen_sink"] *
        USAGE_PATTERNS["kitchen_sink"]["duration"] *
        USAGE_PATTERNS["kitchen_sink"]["frequency"] *
        eff_sink_mult *
        climate_mult
    )

    # Bathroom Sink: same pattern
    bathroom_sink_daily = (
        FLOW_RATES["bathroom_sink"] *
        USAGE_PATTERNS["bathroom_sink"]["duration"] *
        USAGE_PATTERNS["bathroom_sink"]["frequency"] *
        eff_sink_mult *
        climate_mult
    )

    # Toilet: base per-person usage only (1.8 gal × 6 flushes × 1 person base)
    # Excel shows 10.8 regardless of group size in activity table
    toilet_daily = (
        FLOW_RATES["toilet"] *
        USAGE_PATTERNS["toilet"]["frequency"] *
        1  # base single-person; eff_toilet is display only
    )

    # Drinking: uses core num_adults (e.g., 2) not user-type total
    drinking_adults_daily   = DRINKING_WATER["adult"] * num_adults
    drinking_children_daily = DRINKING_WATER["child"] * num_children
    total_drinking_daily    = drinking_adults_daily + drinking_children_daily

    # ── Totals ───────────────────────────────────────────────────────────────
    total_fresh_used_per_day = (
        shower_daily + kitchen_sink_daily + bathroom_sink_daily +
        toilet_daily + total_drinking_daily
    )
    total_grey_added_per_day  = shower_daily + kitchen_sink_daily + bathroom_sink_daily
    total_black_added_per_day = toilet_daily

    # ── Tank Levels ──────────────────────────────────────────────────────────
    fresh_cap   = requirements.get("fresh_cap", 0)
    grey_cap    = requirements.get("grey_cap", 0)
    black_cap   = requirements.get("black_cap", 0)
    fresh_level = requirements.get("fresh_level", 0)
    grey_level  = requirements.get("grey_level", 0)
    black_level = requirements.get("black_level", 0)

    # ── Survival Days ────────────────────────────────────────────────────────
    # Fresh:  runs DOWN  → days until empty
    # Grey:   fills UP   → days until full
    # Black:  fills UP   → days until full
    days_fresh = (fresh_level / total_fresh_used_per_day
                  if total_fresh_used_per_day > 0 and fresh_level > 0
                  else 0.0)

    days_grey  = ((grey_cap - grey_level) / total_grey_added_per_day
                  if total_grey_added_per_day > 0
                  else float('inf'))

    days_black = ((black_cap - black_level) / total_black_added_per_day
                  if total_black_added_per_day > 0
                  else float('inf'))

    overall_survival = min(days_fresh, days_grey, days_black)

    # Limiting factor
    tank_map = {days_fresh: "Fresh", days_grey: "Grey", days_black: "Black"}
    limiting_tank = tank_map[min(days_fresh, days_grey, days_black)]

    return {
        "daily_usage": {
            "fresh":         round(total_fresh_used_per_day, 2),
            "grey":          round(total_grey_added_per_day, 2),
            "black":         round(total_black_added_per_day, 2),
            "drinking":      round(total_drinking_daily, 2),
            "shower":        round(shower_daily, 2),
            "kitchen_sink":  round(kitchen_sink_daily, 2),
            "bathroom_sink": round(bathroom_sink_daily, 2),
            "toilet":        round(toilet_daily, 2),
        },
        "survival_days": {
            "fresh":         round(days_fresh, 4),
            "grey":          round(days_grey, 4),
            "black":         round(days_black, 4),
            "overall":       round(overall_survival, 4),
            "limiting_tank": limiting_tank,
        },
        "effective_multipliers": {
            "shower": round(eff_shower_mult, 3),
            "sink":   round(eff_sink_mult, 3),
            "toilet": eff_toilet_mult,
        },
        "tanks": {
            "fresh": {"cap": fresh_cap, "level": fresh_level},
            "grey": {"cap": grey_cap, "level": grey_level},
            "black": {"cap": black_cap, "level": black_level}
        }
    }