use std::io::{Read, Write};

use chrono::{self, Utc, TimeZone, Datelike, Timelike};

use encoding::*;
use basic_types::*;

const NANOS_PER_SECOND: i64 = 1_000_000_000;
const NANOS_PER_TICK: i64 = 100;
const TICKS_PER_SECOND: i64 = NANOS_PER_SECOND / NANOS_PER_TICK;

const MIN_YEAR: UInt16 = 1601;
const MAX_YEAR: UInt16 = 9999;

/// Data type ID 13
//
/// Holds a date/time. This is a wrapper around the chrono type with extra functionality
/// for obtaining ticks in OPC UA measurements, endtimes, epoch etc.
#[derive(PartialEq, Debug, Clone)]
pub struct DateTime {
    pub date_time: chrono::DateTime<Utc>,
}

/// DateTime encoded as 64-bit signed int
impl BinaryEncoder<DateTime> for DateTime {
    fn byte_len(&self) -> usize {
        8
    }

    fn encode<S: Write>(&self, stream: &mut S) -> EncodingResult<usize> {
        let ticks = self.checked_ticks();
        write_i64(stream, ticks)
    }

    fn decode<S: Read>(stream: &mut S) -> EncodingResult<Self> {
        let ticks = read_i64(stream)?;
        Ok(DateTime::from(ticks))
    }
}

impl Default for DateTime {
    fn default() -> Self {
        DateTime::epoch()
    }
}

// From ymd_hms
impl From<(UInt16, UInt16, UInt16, UInt16, UInt16, UInt16)> for DateTime {
    fn from(dt: (UInt16, UInt16, UInt16, UInt16, UInt16, UInt16)) -> Self {
        let (year, month, day, hour, minute, second) = dt;
        DateTime::from((year, month, day, hour, minute, second, 0))
    }
}

// From ymd_hms
impl From<(UInt16, UInt16, UInt16, UInt16, UInt16, UInt16, UInt32)> for DateTime {
    fn from(dt: (UInt16, UInt16, UInt16, UInt16, UInt16, UInt16, UInt32)) -> Self {
        let (year, month, day, hour, minute, second, nanos) = dt;
        if month < 1 || month > 12 {
            panic!("Invalid month");
        }
        if day < 1 || day > 31 {
            panic!("Invalid day");
        }
        if hour > 23 {
            panic!("Invalid hour");
        }
        if minute > 59 {
            panic!("Invalid minute");
        }
        if second > 59 {
            panic!("Invalid second");
        }
        if nanos as i64 >= NANOS_PER_SECOND {
            panic!("Invalid nanosecond");
        }
        let dt = Utc.ymd(year as i32, month as u32, day as u32)
            .and_hms_nano(hour as u32, minute as u32, second as u32, nanos);
        DateTime::from(dt)
    }
}

impl From<chrono::DateTime<Utc>> for DateTime {
    fn from(date_time: chrono::DateTime<Utc>) -> Self {
        // OPC UA date time is more granular with nanos, so the value supplied is made granular too
        let year = date_time.year();
        let month = date_time.month();
        let day = date_time.day();
        let hour = date_time.hour();
        let minute = date_time.minute();
        let second = date_time.second();
        let nanos = (date_time.nanosecond() / NANOS_PER_TICK as u32) * NANOS_PER_TICK as u32;
        let date_time = Utc.ymd(year, month, day)
            .and_hms_nano(hour, minute, second, nanos);
        DateTime { date_time }
    }
}

impl From<Int64> for DateTime {
    fn from(value: Int64) -> Self {
        if value == i64::max_value() {
            // Max signifies end times
            Self::endtimes()
        } else {
            let secs = value / TICKS_PER_SECOND;
            let nanos = (value - secs * TICKS_PER_SECOND) * NANOS_PER_TICK;
            let duration = chrono::Duration::seconds(secs) + chrono::Duration::nanoseconds(nanos);
            Self::from(Self::epoch_chrono() + duration)
        }
    }
}

impl Into<Int64> for DateTime {
    fn into(self) -> Int64 {
        self.checked_ticks()
    }
}

impl Into<chrono::DateTime<Utc>> for DateTime {
    fn into(self) -> chrono::DateTime<Utc> {
        self.as_chrono()
    }
}

impl DateTime {
    /// Constructs from the current time
    pub fn now() -> DateTime {
        DateTime::from(Utc::now())
    }

    /// Constructs a date time for the epoch
    pub fn epoch() -> DateTime {
        DateTime::from(Self::epoch_chrono())
    }

    /// Constructs a date time for the endtimes
    pub fn endtimes() -> DateTime {
        DateTime::from(Self::endtimes_chrono())
    }

    /// Returns the maximum tick value, corresponding to the end of time
    pub fn endtimes_ticks() -> i64 {
        Self::duration_to_ticks(Self::endtimes_chrono().signed_duration_since(Self::epoch_chrono()))
    }

    /// Constructs from a year, month, day
    pub fn ymd(year: UInt16, month: UInt16, day: UInt16) -> DateTime {
        DateTime::ymd_hms(year, month, day, 0, 0, 0)
    }

    /// Constructs from a year, month, day, hour, minute, second
    pub fn ymd_hms(year: UInt16,
                   month: UInt16,
                   day: UInt16,
                   hour: UInt16,
                   minute: UInt16,
                   second: UInt16)
                   -> DateTime {
        DateTime::from((year, month, day, hour, minute, second))
    }

    /// Constructs from a year, month, day, hour, minute, second, nanosecond
    pub fn ymd_hms_nano(year: UInt16,
                        month: UInt16,
                        day: UInt16,
                        hour: UInt16,
                        minute: UInt16,
                        second: UInt16,
                        nanos: UInt32) -> DateTime {
        DateTime::from((year, month, day, hour, minute, second, nanos))
    }

    /// Returns the time in ticks, of 100 nanosecond intervals
    pub fn ticks(&self) -> i64 {
        Self::duration_to_ticks(self.date_time.signed_duration_since(Self::epoch_chrono()))
    }

    /// To checked ticks. Function returns 0 or MAX_INT64
    /// if date exceeds valid OPC UA range
    pub fn checked_ticks(&self) -> i64 {
        let nanos = self.ticks();
        if nanos < 0 {
            return 0;
        }
        if nanos > Self::endtimes_ticks() {
            return i64::max_value();
        }
        nanos
    }

    /// Time as chrono
    pub fn as_chrono(&self) -> chrono::DateTime<Utc> {
        self.date_time.clone()
    }

    /// The OPC UA epoch - Jan 1 1601 00:00:00
    fn epoch_chrono() -> chrono::DateTime<Utc> {
        Utc.ymd(MIN_YEAR as i32, 1, 1).and_hms(0, 0, 0)
    }

    /// The OPC UA endtimes - Dec 31 9999 23:59:59 i.e. the date after which dates are returned as MAX_INT64 ticks
    /// Spec doesn't say what happens in the last second before midnight...
    fn endtimes_chrono() -> chrono::DateTime<Utc> {
        Utc.ymd(MAX_YEAR as i32, 12, 31).and_hms(23, 59, 59)
    }

    /// Turns a duration to ticks
    fn duration_to_ticks(duration: chrono::Duration) -> i64 {
        // We can't directly ask for nanos because it will exceed i64,
        // so we have to subtract the total seconds before asking for the nano portion
        let seconds_part = chrono::Duration::seconds(duration.num_seconds());
        let seconds = seconds_part.num_seconds();
        let nanos = (duration - seconds_part).num_nanoseconds().unwrap();
        // Put it back together in ticks
        seconds * TICKS_PER_SECOND + nanos / NANOS_PER_TICK
    }
}