import React from 'react';
import { useApp } from '../contexts/AppContext';
import { Card } from './ui/card';
import { Badge } from './ui/badge';
import { Progress } from './ui/progress';
import { BarChart, Bar, XAxis, YAxis, CartesianGrid, Tooltip, ResponsiveContainer, LineChart, Line } from 'recharts';
import { CheckCircle2, Clock, AlertCircle, TrendingUp } from 'lucide-react';
import { differenceInDays, format } from 'date-fns';

export const Dashboard: React.FC = () => {
  const { tasks, userStories, activeSprint } = useApp();

  if (!activeSprint) {
    return (
      <div className="p-8 text-center">
        <h2 className="mb-2">No Active Sprint</h2>
        <p className="text-muted-foreground">
          Please activate a sprint from the Sprint Management page to view the dashboard.
        </p>
      </div>
    );
  }

  const sprintTasks = tasks.filter(task => {
    const story = userStories.find(s => s.id === task.userStoryId);
    return story?.sprintId === activeSprint.id;
  });

  const todoTasks = sprintTasks.filter(t => t.status === 'todo').length;
  const inProgressTasks = sprintTasks.filter(t => t.status === 'in-progress').length;
  const blockedTasks = sprintTasks.filter(t => t.status === 'blocked').length;
  const doneTasks = sprintTasks.filter(t => t.status === 'done').length;

  const sprintStories = userStories.filter(s => s.sprintId === activeSprint.id);
  const totalPoints = sprintStories.reduce((sum, s) => sum + s.storyPoints, 0);
  const completedPoints = sprintStories
    .filter(story => {
      const storyTasks = tasks.filter(t => t.userStoryId === story.id);
      return storyTasks.length > 0 && storyTasks.every(t => t.status === 'done');
    })
    .reduce((sum, s) => sum + s.storyPoints, 0);

  const progressPercentage = totalPoints > 0 ? (completedPoints / totalPoints) * 100 : 0;

  const daysTotal = differenceInDays(new Date(activeSprint.endDate), new Date(activeSprint.startDate));
  const daysElapsed = differenceInDays(new Date(), new Date(activeSprint.startDate));
  const daysRemaining = Math.max(0, differenceInDays(new Date(activeSprint.endDate), new Date()));

  // Task distribution data
  const taskDistribution = [
    { name: 'To Do', value: todoTasks, fill: '#94a3b8' },
    { name: 'In Progress', value: inProgressTasks, fill: '#3b82f6' },
    { name: 'Blocked', value: blockedTasks, fill: '#ef4444' },
    { name: 'Done', value: doneTasks, fill: '#10b981' }
  ];

  // Mock burndown data (in a real app, this would be calculated from historical data)
  const generateBurndownData = () => {
    const data = [];
    const idealBurnRate = totalPoints / daysTotal;
    
    for (let day = 0; day <= daysTotal; day++) {
      const ideal = Math.max(0, totalPoints - (idealBurnRate * day));
      const actual = day <= daysElapsed 
        ? Math.max(0, totalPoints - (completedPoints * (day / Math.max(daysElapsed, 1))))
        : null;
      
      data.push({
        day: day,
        ideal: Math.round(ideal),
        actual: actual !== null ? Math.round(actual) : null
      });
    }
    
    return data;
  };

  const burndownData = generateBurndownData();

  // Find blocked tasks
  const blockedTasksList = sprintTasks.filter(t => t.status === 'blocked');

  return (
    <div className="p-6 space-y-6">
      <div>
        <h1>Sprint Dashboard</h1>
        <p className="text-muted-foreground">{activeSprint.name} - {activeSprint.goal}</p>
      </div>

      {/* Key Metrics */}
      <div className="grid gap-4 md:grid-cols-2 lg:grid-cols-4">
        <Card className="p-6">
          <div className="flex items-center justify-between">
            <div className="space-y-1">
              <p className="text-sm text-muted-foreground">Total Tasks</p>
              <p className="text-2xl">{sprintTasks.length}</p>
            </div>
            <CheckCircle2 className="h-8 w-8 text-muted-foreground" />
          </div>
        </Card>

        <Card className="p-6">
          <div className="flex items-center justify-between">
            <div className="space-y-1">
              <p className="text-sm text-muted-foreground">In Progress</p>
              <p className="text-2xl">{inProgressTasks}</p>
            </div>
            <Clock className="h-8 w-8 text-blue-500" />
          </div>
        </Card>

        <Card className="p-6">
          <div className="flex items-center justify-between">
            <div className="space-y-1">
              <p className="text-sm text-muted-foreground">Blocked</p>
              <p className="text-2xl">{blockedTasks}</p>
            </div>
            <AlertCircle className="h-8 w-8 text-red-500" />
          </div>
        </Card>

        <Card className="p-6">
          <div className="flex items-center justify-between">
            <div className="space-y-1">
              <p className="text-sm text-muted-foreground">Days Remaining</p>
              <p className="text-2xl">{daysRemaining}</p>
            </div>
            <TrendingUp className="h-8 w-8 text-green-500" />
          </div>
        </Card>
      </div>

      {/* Sprint Progress */}
      <Card className="p-6">
        <div className="space-y-4">
          <div className="flex items-center justify-between">
            <h3>Sprint Progress</h3>
            <Badge>{completedPoints} / {totalPoints} points</Badge>
          </div>
          <Progress value={progressPercentage} className="h-3" />
          <div className="flex items-center justify-between text-sm text-muted-foreground">
            <span>{Math.round(progressPercentage)}% complete</span>
            <span>
              {format(new Date(activeSprint.startDate), 'MMM dd')} - {format(new Date(activeSprint.endDate), 'MMM dd')}
            </span>
          </div>
        </div>
      </Card>

      {/* Charts */}
      <div className="grid gap-6 md:grid-cols-2">
        {/* Task Distribution */}
        <Card className="p-6">
          <h3 className="mb-4">Task Distribution</h3>
          <ResponsiveContainer width="100%" height={250}>
            <BarChart data={taskDistribution}>
              <CartesianGrid strokeDasharray="3 3" />
              <XAxis dataKey="name" />
              <YAxis />
              <Tooltip />
              <Bar dataKey="value" fill="#3b82f6" />
            </BarChart>
          </ResponsiveContainer>
        </Card>

        {/* Sprint Burndown */}
        <Card className="p-6">
          <h3 className="mb-4">Sprint Burndown</h3>
          <ResponsiveContainer width="100%" height={250}>
            <LineChart data={burndownData}>
              <CartesianGrid strokeDasharray="3 3" />
              <XAxis dataKey="day" label={{ value: 'Days', position: 'insideBottom', offset: -5 }} />
              <YAxis label={{ value: 'Points', angle: -90, position: 'insideLeft' }} />
              <Tooltip />
              <Line type="monotone" dataKey="ideal" stroke="#94a3b8" strokeDasharray="5 5" name="Ideal" />
              <Line type="monotone" dataKey="actual" stroke="#3b82f6" strokeWidth={2} name="Actual" />
            </LineChart>
          </ResponsiveContainer>
        </Card>
      </div>

      {/* Blocked Items Alert */}
      {blockedTasks > 0 && (
        <Card className="p-6 border-red-200 bg-red-50">
          <div className="flex items-start gap-4">
            <AlertCircle className="h-6 w-6 text-red-500 mt-1" />
            <div className="flex-1 space-y-2">
              <h3 className="text-red-900">Blocked Tasks Require Attention</h3>
              <p className="text-sm text-red-700">
                {blockedTasks} task{blockedTasks !== 1 ? 's are' : ' is'} currently blocked and may impact sprint progress.
              </p>
              <div className="space-y-1 mt-3">
                {blockedTasksList.map(task => (
                  <div key={task.id} className="text-sm text-red-800">
                    • {task.title}
                  </div>
                ))}
              </div>
            </div>
          </div>
        </Card>
      )}

      {/* Team Velocity Insights */}
      <Card className="p-6">
        <h3 className="mb-4">Team Insights</h3>
        <div className="space-y-3">
          <div className="flex items-center justify-between p-3 bg-muted rounded-lg">
            <span className="text-sm">Sprint Capacity</span>
            <span className="font-medium">{activeSprint.capacity} points</span>
          </div>
          <div className="flex items-center justify-between p-3 bg-muted rounded-lg">
            <span className="text-sm">Committed Points</span>
            <span className="font-medium">{totalPoints} points</span>
          </div>
          <div className="flex items-center justify-between p-3 bg-muted rounded-lg">
            <span className="text-sm">Completed Points</span>
            <span className="font-medium">{completedPoints} points</span>
          </div>
          <div className="flex items-center justify-between p-3 bg-muted rounded-lg">
            <span className="text-sm">Capacity Utilization</span>
            <span className="font-medium">
              {activeSprint.capacity > 0 ? Math.round((totalPoints / activeSprint.capacity) * 100) : 0}%
            </span>
          </div>
        </div>
      </Card>
    </div>
  );
};