var CalendarViewType = {
  CALENDAR: 1,
  MONTH: 2,
  YEAR: 3
};

var DAYS_IN_WEEK = 7;

var MONTHS_IN_YEAR = 12;

var MONTHS = [
  'January', 'February', 'March', 'April', 'May',
  'June', 'July', 'August', 'September', 'October',
  'November', 'December'
];

var MONTHS_ABBREVIATED = [
  'Jan', 'Feb', 'Mar', 'Apr', 'May',
  'Jun', 'Jul', 'Aug', 'Sep', 'Oct',
  'Nov', 'Dec'
];

var DAYS_OF_WEEK = ['Su', 'Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa'];

var getFirstOfMonthDate = function(dt) {
  var dtStart = new Date(dt.getTime());
  dtStart.setDate(1);
  return dtStart;
};

var getLastOfMonthDate = function(dt) {
  var dtEnd = new Date(dt.getTime());
  dtEnd.setDate(1);
  dtEnd.setMonth(dtEnd.getMonth() + 1);
  dtEnd.setDate(dtEnd.getDate() - 1);
  return dtEnd;
};

var getEndOfLastMonthDate = function(dt) {
  var dtLast = getFirstOfMonthDate(dt);
  dtLast.setDate(dtLast.getDate() - 1);
  return dtLast;
}

var generateCalendar = function(dt) {
  var dtStart = getFirstOfMonthDate(dt);
  var dtEnd = getLastOfMonthDate(dt);
  var dtEndLastMonth = getEndOfLastMonthDate(dt);

  var calendar = [
    _.range(
      dtEndLastMonth.getDate() + 1 - dtStart.getDay(),
      dtEndLastMonth.getDate() + 1
    ).concat(
      _.range(1, DAYS_IN_WEEK - dtStart.getDay() + 1)
    )
  ];

  var dayCount = calendar[0][DAYS_IN_WEEK - 1] + 1;
  while (dayCount <= dtEnd.getDate() - DAYS_IN_WEEK) {
    var endDay = dayCount + DAYS_IN_WEEK;
    calendar.push(_.range(dayCount, endDay));
    dayCount = endDay;
  }

  calendar.push(
    _.range(
      dayCount, dtEnd.getDate() + 1
    ).concat(
      _.range(1, DAYS_IN_WEEK - dtEnd.getDay())
    )
  );

  return calendar;
};


var CalendarHeader = React.createClass({
  render: function() {
    return (
      <div>
        <button onClick={this.handleClickPrev}>Prev</button>
        <span onClick={this.handleClickHeader}>{this.props.title}</span>
        <button onClick={this.handleClickNext}>Next</button>
      </div>
    );
  },
  handleClickPrev: function() {
    if (this.props.onClickPrev) {
      this.props.onClickPrev();
    }
  },
  handleClickNext: function() {
    if (this.props.onClickNext) {
      this.props.onClickNext();
    }
  },
  handleClickHeader: function() {
    if (this.props.onClickHeader) {
      this.props.onClickHeader();
    }
  }
});

var YearGrid = React.createClass({
  COLS_PER_ROW: 5,
  render: function() {
    var yearGrid = _.range(
      this.props.startYear, this.props.startYear + this.props.range, this.COLS_PER_ROW
    ).map(function(startYear) {
      return <tr key={"year-row-" + startYear}>{this.renderRow(startYear, startYear + this.COLS_PER_ROW)}</tr>;
    }.bind(this));
  },
  renderRow: function(startYear, endYear) {
    return _.range(startYear, endYear).map(function(year) {
      return (
        <td
          onClick={this.handleClickYearWrapper(year)}
          key={"year-" + year}>{year}</td>
      )
    }.bind(this));
  },
  handleClickYearWrapper: function(year) {
    return function() {
      this.handleClickYear(year)
    }.bind(this);
  },
  handleClickYear: function(year) {
    if (this.props.onClickYear) {
      this.props.onClickYear(year);
    }
  }
});

var YearView = React.createClass({
  YEAR_RANGE: 20,
  getInitialState: function() {
    return {
      selectedDate: this.props.selectedDate,
      viewingMonth: this.props.viewingMonth,
      startYear: this.props.viewingYear - (this.props.viewingYear % this.YEAR_RANGE)
    };
  },
  render: function() {
    return (
      <div className="month-view">
        <CalendarHeader
          title={this.state.viewingYear}
          onClickPrev={this.handleClickPrev}
          onClickNext={this.handleClickNext}
        />
        <YearGrid
          onClickYear={this.handleClickYear}
          startYear={this.state.startYear}
          yearRange={this.YEAR_RANGE} />
      </div>
    );
  },
  handleClickPrev: function() {
    this.setState({ viewingYear: this.state.viewingYear - this.YEAR_RANGE });
  },
  handleClickNext: function() {
    this.setState({ viewingYear: this.state.viewingYear + this.YEAR_RANGE });
  },
  handleClickYear: function(year) {
    if (this.props.onClickYear) {
      this.props.onClickYear(month, year);
    }
  }
});

var MonthGrid = React.createClass({
  COLS_PER_ROW: 3,
  render: function() {
    var monthGrid = _.range(0, MONTHS.length, this.COLS_PER_ROW).map(function(startCol) {
      return <tr key={"month-row-" + startCol}>{this.renderRow(startCol, startCol + this.COLS_PER_ROW)}</tr>;
    }.bind(this));
    return <table><tbody>{monthGrid}</tbody></table>;
  },
  renderRow: function(startCol, endCol) {
    return _.range(startCol, endCol).map(function(monthIndex) {
      return (
        <td
          onClick={this.handleClickMonthWrapper(monthIndex)}
          key={"month-" + monthIndex}>{MONTHS_ABBREVIATED[monthIndex]}</td>
      )
    }.bind(this));
  },
  handleClickMonthWrapper: function(monthIndex) {
    return function() {
      this.handleClickMonth(monthIndex)
    }.bind(this);
  },
  handleClickMonth: function(monthIndex) {
    if (this.props.onClickMonth) {
      this.props.onClickMonth(monthIndex);
    }
  }
});

var MonthView = React.createClass({
  getInitialState: function() {
    return {
      selectedDate: this.props.selectedDate,
      viewingMonth: this.props.viewingMonth,
      viewingYear: this.props.viewingYear
    };
  },
  render: function() {
    return (
      <div className="month-view">
        <CalendarHeader
          title={this.state.viewingYear}
          onClickPrev={this.handleClickPrev}
          onClickNext={this.handleClickNext}
          onClickHeader={this.handleClickHeader}
        />
        <MonthGrid
          onClickMonth={this.handleClickMonth}
          month={this.state.viewingMonth}
          year={this.state.viewingYear} />
      </div>
    );
  },
  handleClickPrev: function() {
    this.setState({viewingYear: this.state.viewingYear - 1});
  },
  handleClickNext: function() {
    this.setState({viewingYear: this.state.viewingYear + 1});
  },
  handleClickHeader: function() {
    if (this.props.onClickHeader) {
      this.props.onClickHeader(this.state.viewingMonth, this.state.viewingYear);
    }
  },
  handleClickMonth: function(month) {
    if (this.props.onClickMonth) {
      this.props.onClickMonth(month, this.state.viewingYear);
    }
  }
});

var DayOfWeekRow = React.createClass({
  render: function() {
    var daysRow = DAYS_OF_WEEK.map(function(day) {
      return <th key={day}>{day}</th>;
    });
    return <tr>{daysRow}</tr>;
  }
});

var CalendarGrid = React.createClass({
  render: function() {
    var dt = new Date(this.props.year, this.props.month, 1);
    var calendar = generateCalendar(dt);
    var calendarRows = calendar.map(function(row, index) {
      return <tr key={"c-row-" + index}>{this.renderRow(row, index)}</tr>;
    }.bind(this));
    return <table><thead><DayOfWeekRow /></thead><tbody>{calendarRows}</tbody></table>;
  },
  renderRow: function(row, rowIndex) {
    return row.map(function(day) {
      return <td key={"c-row-" + rowIndex + "-day-" + day}>{day}</td>;
    });
  }
});

var CalendarView = React.createClass({
  getInitialState: function() {
    return {
      selectedDate: this.props.selectedDate,
      viewingMonth: this.props.viewingMonth,
      viewingYear: this.props.viewingYear
    };
  },
  render: function() {
    return (
      <div className="calendar-view">
        <CalendarHeader
          title={MONTHS[this.state.viewingMonth] + " " + this.state.viewingYear}
          onClickPrev={this.handleClickPrev}
          onClickNext={this.handleClickNext}
          onClickHeader={this.handleClickHeader}
        />
        <CalendarGrid month={this.state.viewingMonth} year={this.state.viewingYear} />
      </div>
    );
  },
  handleClickPrev: function() {
    var updatedMonth = this.state.viewingMonth - 1;
    var updatedYear = this.state.viewingYear;
    if (updatedMonth === -1) {
      updatedMonth = MONTHS_IN_YEAR - 1;
      updatedYear -= 1;
    }
    this.setState({viewingMonth: updatedMonth, viewingYear: updatedYear});
  },
  handleClickNext: function() {
    var updatedMonth = this.state.viewingMonth + 1;
    var updatedYear = this.state.viewingYear;
    if (updatedMonth === MONTHS_IN_YEAR) {
      updatedMonth %= MONTHS_IN_YEAR;
      updatedYear += 1;
    }
    this.setState({viewingMonth: updatedMonth, viewingYear: updatedYear});
  },
  handleClickHeader: function() {
    if (this.props.onClickHeader) {
      this.props.onClickHeader(this.state.viewingMonth, this.state.viewingYear);
    }
  }
});

var CalendarWidget = React.createClass({
  getInitialState: function() {
    var today = new Date();
    return {
      selectedDate: today,
      viewingMonth: today.getMonth(),
      viewingYear: today.getFullYear(),
      view: CalendarViewType.CALENDAR
    };
  },
  render: function() {
    var calendarView = null;
    if (this.state.view === CalendarViewType.CALENDAR) {
      calendarView = (
        <CalendarView
          selectedDate={this.state.selectedDate}
          viewingMonth={this.state.viewingMonth}
          viewingYear={this.state.viewingYear}
          onClickHeader={this.showMonthView} />
      );
    } else if (this.state.view === CalendarViewType.MONTH) {
      calendarView = (
        <MonthView
          selectedDate={this.state.selectedDate}
          viewingMonth={this.state.viewingMonth}
          viewingYear={this.state.viewingYear}
          onClickHeader={this.showYearView}
          onClickMonth={this.showCalendarView} />
      );
    } else if (this.state.view === CalendarViewType.YEAR) {
      calendarView = (
        <YearView
          selectedDate={this.state.selectedDate}
          viewingMonth={this.state.viewingMonth}
          viewingYear={this.state.viewingYear}
          onClickYear={this.showMonthView} />
      );
    }
    return <div className="calendar-widget">{calendarView}</div>
  },
  updateDate: function(day, month, year) {

  },
  showCalendarView: function(month, year) {
    this.setState({view: CalendarViewType.CALENDAR, viewingMonth: month, viewingYear: year});
  },
  showMonthView: function(month, year) {
    this.setState({view: CalendarViewType.MONTH, viewingMonth: month, viewingYear: year});
  },
  showYearView: function(month, year) {
    this.setState({view: CalendarViewType.YEAR, viewingMonth: month, viewingYear: year});
  }
});

React.render(
    <CalendarWidget />,
    document.getElementById('calendar')
);