"""Reference solution for Price-volume-mix analysis project: explain higher sales and lower contribution.
Original synthetic teaching data only. Python 3.10+, standard library.
Run python solve.py [path-to-project-inputs]. No network or credentials.
"""
from pathlib import Path
from datetime import datetime, date
import csv, json, math, statistics, sys

def read(root, name):
    with (Path(root)/name).open(newline='',encoding='utf-8') as f:
        reader=csv.DictReader(f)
        if not reader.fieldnames or len(reader.fieldnames)!=len(set(reader.fieldnames)):
            raise ValueError(f'{name}: missing or duplicate headers')
        rows=list(reader)
        if any(None in row or any(v is None for v in row.values()) for row in rows):
            raise ValueError(f'{name}: inconsistent row length')
        return rows

def rules(root): return json.loads((Path(root)/'rules.json').read_text())

def number(value):
    x=float(value)
    if not math.isfinite(x): raise ValueError('Non-finite input')
    return x

def nonnegative(value):
    x=number(value)
    if x<0:raise ValueError('Negative quantity or amount')
    return x

def flag(value):
    if value not in ('true','false'):raise ValueError('Boolean must be true or false')
    return value=='true'

def timestamp(value):
    d=datetime.fromisoformat(value.replace('Z','+00:00'))
    if d.tzinfo is None:raise ValueError('Timestamp requires an explicit time zone')
    return d

def unique(rows, keys, ignore=()):
    by={};duplicates=0
    for row in rows:
        key=tuple(row[k] for k in keys)
        if any(not k for k in key):raise ValueError('Missing record identity')
        if key in by:
            prior={k:v for k,v in by[key].items() if k not in ignore}
            new={k:v for k,v in row.items() if k not in ignore}
            if prior!=new:raise ValueError(f'Conflicting records at {key}')
            duplicates+=1
        else:by[key]=row
    return list(by.values()),duplicates

def rounded(value):
    if isinstance(value,float): return round(value,8)
    if isinstance(value,dict):return {k:rounded(v) for k,v in value.items()}
    if isinstance(value,list):return [rounded(v) for v in value]
    return value

def month_index(s):
    d=datetime.strptime(s,'%Y-%m')
    if d.strftime('%Y-%m')!=s:raise ValueError('Use YYYY-MM')
    return d.year*12+d.month

def price_volume_mix(root):
    rows,_=unique(read(root,'products.csv'),['product']);prior_rev=current_rev=prior_con=current_con=quantity=price=cost=new=exited=0.;common=[]
    for x in rows:
        q0,q1=nonnegative(x['old_units']),nonnegative(x['new_units'])
        p0,c0=(nonnegative(x['old_price']),nonnegative(x['old_unit_cost'])) if q0 else (0,0)
        p1,c1=(nonnegative(x['new_price']),nonnegative(x['new_unit_cost'])) if q1 else (0,0)
        prior_rev+=q0*p0;current_rev+=q1*p1;prior_con+=q0*(p0-c0);current_con+=q1*(p1-c1)
        if q0 and q1:
            common.append((q0,q1,p0-c0));quantity+=(q1-q0)*(p0-c0);price+=q1*(p1-p0);cost-=q1*(c1-c0)
        elif q1:new+=q1*(p1-c1)
        elif q0:exited-=q0*(p0-c0)
    if not common:raise ValueError('Common-product scale/mix split undefined')
    base_units=sum(x[0] for x in common);new_units=sum(x[1] for x in common);base_margin=sum(x[0]*x[2] for x in common)/base_units
    scale=(new_units-base_units)*base_margin;mix=quantity-scale
    if abs(prior_con+quantity+price+cost+new+exited-current_con)>1e-8:raise ValueError('Contribution bridge fails')
    return {'prior_revenue':prior_rev,'current_revenue':current_rev,'prior_contribution':prior_con,'current_contribution':current_con,'contribution_change':current_con-prior_con,'quantity_effect':quantity,'common_product_scale_effect':scale,'common_product_mix_effect':mix,'price_effect':price,'unit_cost_effect':cost,'new_product_effect':new,'exited_product_effect':exited}

def main():
    directory=Path(sys.argv[1]) if len(sys.argv)>1 else Path(__file__).resolve().parent
    try:
        result=price_volume_mix(directory)
        print(json.dumps(rounded(result),indent=2,allow_nan=False))
    except (OSError,ValueError,KeyError,TypeError,ZeroDivisionError) as exc:
        print(f"Input could not be analyzed: {exc}",file=sys.stderr);return 2
    return 0
if __name__=='__main__':raise SystemExit(main())