import logging
from datetime import datetime, timezone, timedelta

from sqlalchemy import func

from app.extensions import db, beijing_time
from app.models.scrap_approval import ScrapApproval
from app.models.transaction import TransScrap

logger = logging.getLogger(__name__)


def _beijing():
    """
    统一时间口径：naive 北京时间。

    ★ scrap_approval 的时间列已统一为 timestamp without time zone
      （见 db_migrations/unify_approval_timezone.sql），必须返回 naive 值，
      否则 aware 值会被驱动转成 UTC 存库，比 created_at 早 8 小时。
    """
    return beijing_time()


# =============================================================================
# ★ 业务规则（单一事实来源）：报废一律需审批
#
# 与出库/借库不同，报废不过滤 is_approval_required —— 无论物料是否命中该标记，
# 所有报废申请都必须由指定审批人审批通过后才能执行。
# 前端 apply/index.vue 的「审批人」必填项与此规则保持一致。
# =============================================================================
SCRAP_ALWAYS_REQUIRES_APPROVAL = True


STOCK_MODELS = {}


def _stock_models():
    """延迟导入三张实物库存表，避免循环依赖"""
    if not STOCK_MODELS:
        from app.models.inbound.buy import StockBuy
        from app.models.inbound.semi import StockSemi
        from app.models.inbound.product import StockProduct
        STOCK_MODELS.update({
            'stock_buy': StockBuy,
            'stock_semi': StockSemi,
            'stock_product': StockProduct,
        })
    return STOCK_MODELS


class ScrapApprovalService:

    @staticmethod
    def generate_request_no():
        now = _beijing()
        prefix = f"APR-SCRAP-{now.strftime('%Y%m%d-%H%M')}-"
        n = db.session.query(func.count(func.distinct(ScrapApproval.request_no))) \
            .filter(ScrapApproval.request_no.like(f"{prefix}%")).scalar() or 0
        return f"{prefix}{(n + 1):04d}"

    # ------------------------------------------------------------------
    # 提交申请
    # ------------------------------------------------------------------
    @staticmethod
    def submit_approval(applicant_id, items, allowed_approvers=None, remark=None,
                        approver_id=None, force_approval=False):
        """
        提交报废申请（仅锁定“意向”，不扣库存；扣减在库管执行时进行）

        items 每项必须包含 source_table + stock_id（精准实物），可带 scrap_qty / 快照字段。
        """
        if not items:
            raise ValueError("报废明细不能为空")

        models = _stock_models()
        normalized = []
        for idx, it in enumerate(items):
            st = (it.get('source_table') or '').strip()
            model = models.get(st)
            sid = it.get('stock_id')
            if not model or not sid:
                raise ValueError(f"第 {idx + 1} 条报废明细必须指定 source_table 与 stock_id（精准库存行）")
            try:
                sid = int(sid)
            except (TypeError, ValueError):
                raise ValueError(f"第 {idx + 1} 条 stock_id 无效")
            row = model.query.get(sid)
            if not row:
                raise ValueError(f"第 {idx + 1} 条对应的库存记录不存在")
            try:
                qty = float(it.get('scrap_qty') or 0)
            except (TypeError, ValueError):
                raise ValueError(f"第 {idx + 1} 条报废数量无效")
            if qty <= 0:
                raise ValueError(f"第 {idx + 1} 条报废数量必须大于 0")
            avail = float(getattr(row, 'available_quantity', 0) or 0)
            if qty > avail:
                raise ValueError(f"第 {idx + 1} 条报废数量({qty})超过可用库存({avail})")

            base = getattr(row, 'base', None)
            normalized.append({
                'source_table': st,
                'stock_id': sid,
                'base_id': getattr(row, 'base_id', None),
                'sku': getattr(row, 'sku', '') or '',
                'name': (base.name if base else '') or it.get('name') or '',
                'spec_model': (base.spec_model if base else '') or it.get('spec_model') or '',
                'location': getattr(row, 'warehouse_location', '') or '',
                'batch_number': getattr(row, 'batch_number', '') or getattr(row, 'serial_number', '') or '',
                'scrap_qty': qty,
                'available_at_apply': avail,
            })

        # ★ 报废一律需审批（见 SCRAP_ALWAYS_REQUIRES_APPROVAL）。
        #   resolve_approval_control 仍调用，但仅用于生成「哪些物料命中需审批」的提示文案，
        #   不再用它决定是否需要审批。
        from app.services.approval_control import resolve_approval_control
        _, flagged_materials = resolve_approval_control(normalized)

        if not approver_id:
            if flagged_materials:
                _names = "；".join(f"{m['name']}（{m['spec_model'] or '-'}）" for m in flagged_materials)
                raise ValueError(f"以下物料需审批报废：{_names}。请选择审批人后再提交")
            raise ValueError("报废申请必须选择审批人后再提交")

        allowed_approvers = [{"type": "user", "value": int(approver_id)}]

        req = ScrapApproval(
            request_no=ScrapApprovalService.generate_request_no(),
            applicant_id=applicant_id,
            remark=remark,
        )
        req.set_items(normalized)
        req.set_allowed_approvers(allowed_approvers)

        # ★ 恒为「待审批」，不再走免审批自动通过分支
        req.status = 0

        db.session.add(req)
        db.session.commit()
        logger.info(f"[ScrapApproval] 提交成功 {req.request_no} approver={approver_id}")
        return req

    # ------------------------------------------------------------------
    # 列表
    # ------------------------------------------------------------------
    @staticmethod
    def get_list(page=1, limit=10, status=None, applicant_id=None, approver_id=None):
        query = ScrapApproval.query
        if status is not None:
            query = query.filter(ScrapApproval.status == status)
        if applicant_id is not None:
            query = query.filter(ScrapApproval.applicant_id == applicant_id)
        if approver_id is not None:
            query = query.filter(ScrapApproval.allowed_approvers.like(f'%"value": {approver_id}%'))
        query = query.order_by(ScrapApproval.created_at.desc())
        pg = query.paginate(page=page, per_page=limit, error_out=False)
        return {
            'items': [r.to_dict() for r in pg.items],
            'total': pg.total,
            'pages': pg.pages,
            'current_page': page,
        }

    # ------------------------------------------------------------------
    # 审批
    # ------------------------------------------------------------------
    @staticmethod
    def approve(request_id, operator_id, action, reject_reason=None):
        req = db.session.get(ScrapApproval, request_id)
        if not req:
            raise ValueError("报废申请不存在")
        if req.status != 0:
            raise ValueError("当前状态不允许审批（仅待审批可操作）")

        # 仅被指定的审批人可操作
        allowed = req.get_allowed_approvers() or []
        user_entries = [str(a.get('value')) for a in allowed if a.get('type') == 'user']
        if user_entries and str(operator_id) not in user_entries:
            raise ValueError("只有被指定的审批人可以审批该申请")

        if action == 'approve':
            req.status = 1
            req.actual_approver_id = operator_id
            req.approved_at = _beijing()
            req.reject_reason = None
        elif action == 'reject':
            req.status = 2
            req.actual_approver_id = operator_id
            req.reject_reason = reject_reason or '未说明原因'
        else:
            raise ValueError("无效的审批动作")
        db.session.commit()
        logger.info(f"[ScrapApproval] {req.request_no} 审批 {action} by {operator_id}")
        return req

    # ------------------------------------------------------------------
    # 执行（按单报废：扣减实物库存 + 写报废流水）
    # ------------------------------------------------------------------
    @staticmethod
    def _to_int(v):
        try:
            return int(v)
        except (TypeError, ValueError):
            return None

    @staticmethod
    def _norm_sku(sku):
        """SKU 归一化：去首尾空白。空 SKU 返回 ''，由调用方回退到行级匹配键。"""
        return str(sku or '').strip()

    @staticmethod
    def _match_key(source_table, stock_id, sku):
        """
        ★ 扫码匹配键 —— SKU 优先。

        已核验：SKU 在同一库存表内唯一，且不存在跨表重名（stock_buy /
        stock_semi / stock_product 三表交叉无冲突），故 SKU 可安全作为
        跨来源的稳定标识。

        例外：个别历史库存行的 SKU 为空，这类行无法用 SKU 标识，回退为
        source_table + stock_id 复合键。前缀区分（'sku:' / 'row:'）保证
        空 SKU 行绝不会与任何正常 SKU 串键。
        """
        s = ScrapApprovalService._norm_sku(sku)
        if s:
            return ('sku', s)
        return ('row', f"{source_table}#{stock_id}")

    @staticmethod
    def _build_approved_index(items):
        """
        申请单明细 → {匹配键: 批准信息}

        每项保留其 source_table + stock_id 清单（rows），执行时据此定位到
        批准时指定的那条库存记录做加锁扣减。同一 SKU 若在批准单中出现多行，
        数量累加、rows 按批准顺序保留。
        """
        index = {}
        for it in items:
            sid = ScrapApprovalService._to_int(it.get('stock_id'))
            st = str(it.get('source_table') or '').strip()
            if not st or sid is None:
                continue
            key = ScrapApprovalService._match_key(st, sid, it.get('sku'))
            entry = index.setdefault(key, {
                'qty': 0.0,
                'label': ScrapApprovalService._norm_sku(it.get('sku'))
                         or it.get('name') or f"{st}#{sid}",
                'rows': [],
            })
            qty = float(it.get('scrap_qty') or 0)
            entry['qty'] += qty
            entry['rows'].append({'source_table': st, 'stock_id': sid, 'qty': qty})
        return index

    @staticmethod
    def _build_scanned_index(scanned_items, models):
        """前端实扫明细 → {匹配键: 累计扫码数量}"""
        index = {}
        for idx, s in enumerate(scanned_items):
            sku = ScrapApprovalService._norm_sku(s.get('sku'))
            st = str(s.get('source_table') or '').strip()
            sid = ScrapApprovalService._to_int(s.get('stock_id'))
            if not sku and (not st or sid is None):
                raise ValueError(f"第 {idx + 1} 条扫码明细缺少 SKU，且无有效的 source_table / stock_id")
            if st and st not in models:
                raise ValueError(f"第 {idx + 1} 条扫码来源不支持：{st}")
            qty = float(s.get('quantity') or 0)
            if qty <= 0:
                raise ValueError(f"第 {idx + 1} 条扫码数量必须大于 0")
            key = ScrapApprovalService._match_key(st, sid, sku)
            entry = index.setdefault(key, {
                'qty': 0.0,
                'label': sku or s.get('name') or f"{st}#{sid}",
            })
            entry['qty'] += qty
        return index

    @staticmethod
    def execute(request_id, operator_name='System', scanned_items=None):
        """
        按单执行报废：以「实际扫码明细」为准，按 SKU 匹配批准明细后扣减库存。

        scanned_items: [{'sku', 'quantity', 'source_table', 'stock_id'(可选，空 SKU 时必填)}]
          · 以 SKU 为主校验键：扫码 SKU 必须在申请单 items_json 中存在；
          · 同一 SKU 多次扫码累加，累计不得超过该 SKU 的批准总量；
          · 允许合法子集（少扫 = 本次不报废该行）；
          · 扣减时以批准单配对的 source_table + stock_id 定位库存行加锁。
        """
        models = _stock_models()
        req = db.session.get(ScrapApproval, request_id)
        if not req:
            raise ValueError("报废申请不存在")
        if req.status != 1:
            raise ValueError("仅“已通过(待执行)”的报废单可执行")

        approved_items = req.get_items()
        if not approved_items:
            raise ValueError("报废明细为空，无法执行")

        # ★ 强制按单扫码：未提交实扫明细不允许执行
        if not scanned_items:
            raise ValueError("请先扫码并提交实际报废物料，再执行报废")

        approved = ScrapApprovalService._build_approved_index(approved_items)
        scanned = ScrapApprovalService._build_scanned_index(scanned_items, models)

        # ★ 校验一：扫码 SKU 必须在批准明细内
        for key, acc in scanned.items():
            if key not in approved:
                raise ValueError(
                    f"SKU【{acc['label']}】不在该报废申请单的批准明细中（SKU 不匹配），禁止报废"
                )

        # ★ 校验二：同一 SKU 的累计扫码量不得超过批准总量
        for key, acc in scanned.items():
            appr = approved[key]
            if acc['qty'] > appr['qty']:
                raise ValueError(
                    f"SKU【{acc['label']}】扫码数量({acc['qty']})超出批准数量({appr['qty']})，禁止报废"
                )

        # ★ 扣减：按批准单配对的 source_table + stock_id 定位库存行，逐行加锁扣减
        for key, acc in scanned.items():
            appr = approved[key]
            remaining = acc['qty']

            for ref in appr['rows']:
                if remaining <= 0:
                    break
                take = min(remaining, ref['qty'])
                if take <= 0:
                    continue

                st, sid = ref['source_table'], ref['stock_id']
                row = models[st].query.with_for_update().get(sid)
                if not row:
                    raise ValueError(f"库存记录已不存在（{acc['label']}）")

                avail = float(getattr(row, 'available_quantity', 0) or 0)
                stock = float(getattr(row, 'stock_quantity', 0) or 0)
                if take > avail:
                    raise ValueError(f"库存 SKU【{acc['label']}】可用不足（剩 {avail}），无法报废 {take}")
                if take > stock:
                    raise ValueError(f"库存 SKU【{acc['label']}】实物不足（剩 {stock}），无法报废 {take}")

                # ★ 真正扣减：报废 = 实物销毁，实物库存与可用库存需同时扣减
                row.available_quantity = avail - take
                row.stock_quantity = stock - take
                db.session.flush()

                # 写报废流水（台账）
                db.session.add(TransScrap(
                    sku=getattr(row, 'sku', '') or acc['label'],
                    source_table=st,
                    stock_id=sid,
                    quantity=take,
                    reason=req.remark or '',
                    operator_name=operator_name,
                    approver_name=ScrapApproval._user_name(req.actual_approver_id),
                    approval_status='executed',
                    scrap_request_no=req.request_no,
                ))

                remaining -= take

        req.status = 3
        req.executed_at = _beijing()
        req.executor_name = operator_name
        db.session.commit()
        logger.info(
            f"[ScrapApproval] {req.request_no} 执行报废完成 by {operator_name} "
            f"(批准 {len(approved)} 项 / 实扫 {len(scanned)} 项)"
        )
        return req