from flask import Flask, render_template, request, jsonify, send_from_directory
import numpy as np
from scipy import stats
import os
import json
from werkzeug.exceptions import RequestEntityTooLarge

app = Flask(__name__)
app.config['MAX_CONTENT_LENGTH'] = 6 * 1024 * 1024

@app.route('/')
def index():
    return render_template('index.html')

@app.route('/health')
def health():
    return "OK", 200

@app.route('/api/optimize', methods=['POST'])
def optimize():
    """
    基于历史价格-销量数据估计线性需求曲线并推荐最优价格。
    输入: JSON { "history": [ {"price": 10, "sales": 50}, ... ], "mc": 5 }
    输出: JSON { "elasticity": -1.5, "optimal_price": 12.5 }
    """
    data = request.json
    history = data.get('history', [])
    marginal_cost = data.get('mc', 0)
    
    if len(history) < 3:
        return jsonify({"error": "至少需要 3 条数据点"}), 400

    prices = np.array([h['price'] for h in history])
    sales = np.array([h['sales'] for h in history])

    # Simple Linear Regression: Q = a + bP
    # b should be negative (Law of Demand)
    slope, intercept, r_value, p_value, std_err = stats.linregress(prices, sales)

    if slope >= 0:
        return jsonify({
            "status": "warning",
            "message": "需求曲线异常或过于平坦（斜率≥0），无法优化，建议保持当前价格。",
            "slope": slope,
            "optimal_price": prices[-1]
        })

    # Profit = (P - MC) * Q = (P - MC) * (a + bP)
    # Profit = aP + bP^2 - aMC - bP(MC)
    # Profit = bP^2 + (a - bMC)P - aMC
    # dProfit/dP = 2bP + (a - bMC) = 0
    # P_opt = -(a - bMC) / (2b) = (bMC - a) / 2b = MC/2 - a/2b
    
    optimal_price = (slope * marginal_cost - intercept) / (2 * slope)
    
    # Ensure optimal price is within reasonable bounds (not negative)
    optimal_price = max(0, optimal_price)
    
    # Calculate Price Elasticity at average price point
    avg_p = np.mean(prices)
    avg_q = slope * avg_p + intercept
    elasticity = (slope * avg_p) / avg_q if avg_q != 0 else 0

    return jsonify({
        "status": "success",
        "slope": slope,
        "intercept": intercept,
        "r_squared": r_value**2,
        "optimal_price": round(optimal_price, 2),
        "elasticity": round(elasticity, 2),
        "message": "线性需求模型优化成功，已生成建议价格。"
    })

@app.route('/api/upload', methods=['POST'])
def upload():
    """
    上传并解析历史数据 JSON 文件，返回标准化的 history。
    支持两种格式：
      1) { "history": [ {price, sales, ...}, ... ] }
      2) [ {price, sales, ...}, ... ]
    约束：文件大小 ≤ 5MB，必须为 UTF-8 文本 JSON。
    """
    if 'file' not in request.files:
        return jsonify({"error": "未找到文件字段"}), 400
    file = request.files['file']
    filename = (file.filename or '').lower()
    if not filename.endswith('.json'):
        return jsonify({"error": "只支持 JSON 文件"}), 400

    # 读取并校验大小
    file.seek(0, os.SEEK_END)
    size = file.tell()
    file.seek(0)
    if size > 5 * 1024 * 1024:
        return jsonify({"error": "文件大小不能超过 5MB"}), 400

    try:
        raw = file.read()
        try:
            text = raw.decode('utf-8')
        except UnicodeDecodeError:
            return jsonify({"error": "文件内容不是有效的 UTF-8 文本"}), 400

        payload = json.loads(text)
        if isinstance(payload, dict) and 'history' in payload:
            incoming = payload['history']
        elif isinstance(payload, list):
            incoming = payload
        else:
            return jsonify({"error": "JSON 格式不正确，应为 {history: [...]} 或数组"}), 400

        cleaned = []
        day_counter = 0
        for item in incoming:
            try:
                price = float(item.get('price'))
                sales = int(item.get('sales'))
            except Exception:
                # 跳过不可解析的数据行
                continue
            if price <= 0 or sales < 0:
                continue
            day_counter += 1
            revenue = item.get('revenue')
            if revenue is None:
                revenue = price * sales
            competitor_price = item.get('competitorPrice', 50)
            cleaned.append({
                "day": item.get('day', day_counter),
                "price": price,
                "sales": sales,
                "revenue": revenue,
                "competitorPrice": competitor_price
            })

        if not cleaned:
            return jsonify({"error": "数据为空或格式不正确"}), 400

        return jsonify({"history": cleaned})
    except json.JSONDecodeError:
        return jsonify({"error": "JSON 解析失败，请检查文件内容"}), 400
    except Exception as e:
        return jsonify({"error": f"服务器解析失败: {str(e)}"}), 500

@app.errorhandler(404)
def handle_404(e):
    if request.path.startswith('/api/'):
        return jsonify({"error": "未找到接口", "path": request.path}), 404
    return render_template('index.html'), 404

@app.errorhandler(500)
def handle_500(e):
    if request.path.startswith('/api/'):
        return jsonify({"error": "服务器内部错误"}), 500
    return render_template('index.html'), 500

@app.errorhandler(RequestEntityTooLarge)
def handle_file_too_large(e):
    return jsonify({"error": "文件过大，服务端限制为 6MB"}), 413

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=7860, debug=True)