"""Customer tracking derived from explicit order-linked facts, without inference."""

import json
from datetime import datetime, timezone


# Maritime codes follow the firstleg standard; warehouse facts remain distinct.
NODE_LABELS = {
    'DOMESTIC_RECEIVED': (0, '已入国内仓', '预计入国内仓'),
    'LOADING_COMPLETED': (5, '已完成装柜', '预计完成装柜'),
    'DEPARTED_WAREHOUSE': (10, '已离开国内仓库', '预计离开国内仓库'),
    'AT_ORIGIN_PORT': (20, '重箱已进入起运港或码头', '预计进入起运港或码头'),
    'LOADED_ON_VESSEL': (30, '已装船', '预计装船'),
    'DEPARTED_ORIGIN_PORT': (40, '船舶已离开起运港', '预计离开起运港'),
    'IN_TRANSIT': (50, '海运途中', '预计进入海运阶段'),
    'ARRIVED_DESTINATION_PORT': (60, '船舶已到目的港', '预计到达目的港'),
    'DISCHARGED_FROM_VESSEL': (70, '已卸船、未清关', '预计卸船'),
    'PICKUP_READY': (80, '已清关、可提柜', '预计可提柜'),
    'PICKED_UP': (90, '已提柜', '预计提柜'),
    'EMPTY_RETURNED': (100, '已还柜', '预计还柜'),
}


def parse_time(value):
    if not isinstance(value, str) or not value.strip():
        return None
    try:
        result = datetime.fromisoformat(value.strip().replace('Z', '+00:00'))
        if result.tzinfo:
            result = result.astimezone(timezone.utc).replace(tzinfo=None)
        return result
    except (ValueError, OverflowError):
        return None


def build_tracking(raw):
    """Latest observation corrects a milestone; forecasts never advance progress."""
    try:
        facts = json.loads(raw) if isinstance(raw, str) else raw
    except (ValueError, TypeError):
        return None
    if not isinstance(facts, list):
        return None
    actual, estimated = {}, {}
    for index, fact in enumerate(facts):
        if not isinstance(fact, dict) or not isinstance(fact.get('code'), str) or fact['code'] not in NODE_LABELS:
            continue
        shipment = str(fact.get('shipment_key') or '')
        key = (shipment, fact['code'])
        observation = parse_time(fact.get('observed_at')) or parse_time(fact.get('created_at')) or datetime.min
        for field, target in (('actual_at', actual), ('estimated_at', estimated)):
            when = parse_time(fact.get(field))
            if when is None:
                continue
            candidate = (observation, index, when, fact)
            if key not in target or candidate[:2] > target[key][:2]:
                target[key] = candidate
    if not actual and not estimated:
        return None

    shipments = sorted({key[0] for key in actual.keys() | estimated.keys()} - {''})
    multiple = len(shipments) > 1
    progress = {}
    for (shipment, code), (_, _, when, fact) in actual.items():
        sequence = NODE_LABELS[code][0]
        if shipment not in progress or sequence > progress[shipment][0]:
            progress[shipment] = (sequence, code, fact)

    def label_shipment(shipment, fact):
        if not multiple or not shipment:
            return ''
        return '货柜 ' + str(fact.get('shipment_no') or (shipments.index(shipment) + 1))

    def node(shipment, code, value, forecast=False):
        _, _, when, fact = value
        place = str(fact.get('place') or '')
        scope = label_shipment(shipment, fact)
        return {'time': str(fact['estimated_at' if forecast else 'actual_at']),
                'text': NODE_LABELS[code][2 if forecast else 1],
                'place': ' · '.join(part for part in (scope, place) if part)}

    nodes = [node(shipment, code, value) for (shipment, code), value in
             sorted(actual.items(), key=lambda item: (item[1][2], NODE_LABELS[item[0][1]][0]), reverse=True)]
    forecasts = [node(shipment, code, value, True) for (shipment, code), value in
                 sorted(estimated.items(), key=lambda item: item[1][2])
                 if (shipment, code) not in actual and NODE_LABELS[code][0] > progress.get(shipment, (-1,))[0]]
    # Multiple containers keep independent progress rather than claiming the whole order advanced.
    current = [(shipment, value) for shipment, value in sorted(progress.items()) if shipment or not shipments]
    if not current and '' in progress:
        current = [('', progress[''])]
    statuses = ['：'.join(part for part in (label_shipment(shipment, value[2]), NODE_LABELS[value[1]][1]) if part)
                for shipment, value in current]
    return {'nodes': nodes[:50], 'estimated_nodes': forecasts[:20], 'status': '；'.join(statuses)}