use winapi;
use user32;

use std::collections::VecDeque;
use std::mem;

use super::EventsLoop;

/// Win32 implementation of the main `MonitorId` object.
#[derive(Clone)]
pub struct MonitorId {
    /// The system name of the adapter.
    adapter_name: [winapi::WCHAR; 32],

    /// The system name of the monitor.
    monitor_name: String,

    /// Name to give to the user.
    readable_name: String,

    /// See the `StateFlags` element here:
    /// http://msdn.microsoft.com/en-us/library/dd183569(v=vs.85).aspx
    flags: winapi::DWORD,

    /// True if this is the primary monitor.
    primary: bool,

    /// The position of the monitor in pixels on the desktop.
    ///
    /// A window that is positioned at these coordinates will overlap the monitor.
    position: (i32, i32),

    /// The current resolution in pixels on the monitor.
    dimensions: (u32, u32),
}

struct DeviceEnumerator {
    parent_device: *const winapi::WCHAR,
    current_index: u32,
}

impl DeviceEnumerator {
    fn adapters() -> DeviceEnumerator {
        use std::ptr;
        DeviceEnumerator {
            parent_device: ptr::null(),
            current_index: 0
        }
    }

    fn monitors(adapter_name: *const winapi::WCHAR) -> DeviceEnumerator {
        DeviceEnumerator {
            parent_device: adapter_name,
            current_index: 0
        }
    }
}

impl Iterator for DeviceEnumerator {
    type Item = winapi::DISPLAY_DEVICEW;
    fn next(&mut self) -> Option<winapi::DISPLAY_DEVICEW> {
        use std::mem;
        loop {
            let mut output: winapi::DISPLAY_DEVICEW = unsafe { mem::zeroed() };
            output.cb = mem::size_of::<winapi::DISPLAY_DEVICEW>() as winapi::DWORD;

            if unsafe { user32::EnumDisplayDevicesW(self.parent_device,
                self.current_index as winapi::DWORD, &mut output, 0) } == 0
            {
                // the device doesn't exist, which means we have finished enumerating
                break;
            }
            self.current_index += 1;

            if  (output.StateFlags & winapi::DISPLAY_DEVICE_ACTIVE) == 0 ||
                (output.StateFlags & winapi::DISPLAY_DEVICE_MIRRORING_DRIVER) != 0
            {
                // the device is not active
                // the Win32 api usually returns a lot of inactive devices
                continue;
            }

            return Some(output);
        }
        None
    }
}

fn wchar_as_string(wchar: &[winapi::WCHAR]) -> String {
    String::from_utf16_lossy(wchar)
        .trim_right_matches(0 as char)
        .to_string()
}

impl EventsLoop {
    pub fn get_available_monitors(&self) -> VecDeque<MonitorId> {
        // return value
        let mut result = VecDeque::new();

        for adapter in DeviceEnumerator::adapters() {
            // getting the position
            let (position, dimensions) = unsafe {
                let mut dev: winapi::DEVMODEW = mem::zeroed();
                dev.dmSize = mem::size_of::<winapi::DEVMODEW>() as winapi::WORD;

                if user32::EnumDisplaySettingsExW(adapter.DeviceName.as_ptr(), 
                    winapi::ENUM_CURRENT_SETTINGS,
                    &mut dev, 0) == 0
                {
                    continue;
                }

                let point: &winapi::POINTL = mem::transmute(&dev.union1);
                let position = (point.x as i32, point.y as i32);

                let dimensions = (dev.dmPelsWidth as u32, dev.dmPelsHeight as u32);

                (position, dimensions)
            };

            for (num, monitor) in DeviceEnumerator::monitors(adapter.DeviceName.as_ptr()).enumerate() {
                // adding to the resulting list
                result.push_back(MonitorId {
                    adapter_name: adapter.DeviceName,
                    monitor_name: wchar_as_string(&monitor.DeviceName),
                    readable_name: wchar_as_string(&monitor.DeviceString),
                    flags: monitor.StateFlags,
                    primary: (adapter.StateFlags & winapi::DISPLAY_DEVICE_PRIMARY_DEVICE) != 0 &&
                            num == 0,
                    position: position,
                    dimensions: dimensions,
                });
            }
        }
        result
    }

    pub fn get_primary_monitor(&self) -> MonitorId {
        // we simply get all available monitors and return the one with the `PRIMARY_DEVICE` flag
        // TODO: it is possible to query the win32 API for the primary monitor, this should be done
        //  instead
        for monitor in self.get_available_monitors().into_iter() {
            if monitor.primary {
                return monitor;
            }
        }

        panic!("Failed to find the primary monitor")
    }
}

impl MonitorId {
    /// See the docs if the crate root file.
    #[inline]
    pub fn get_name(&self) -> Option<String> {
        Some(self.readable_name.clone())
    }

    /// See the docs of the crate root file.
    #[inline]
    pub fn get_native_identifier(&self) -> String {
        self.monitor_name.clone()
    }

    /// See the docs if the crate root file.
    #[inline]
    pub fn get_dimensions(&self) -> (u32, u32) {
        // TODO: retreive the dimensions every time this is called
        self.dimensions
    }

    /// This is a Win32-only function for `MonitorId` that returns the system name of the adapter
    /// device.
    #[inline]
    pub fn get_adapter_name(&self) -> &[winapi::WCHAR] {
        &self.adapter_name
    }

    /// A window that is positioned at these coordinates will overlap the monitor.
    #[inline]
    pub fn get_position(&self) -> (i32, i32) {
        self.position
    }

    #[inline]
    pub fn get_hidpi_factor(&self) -> f32 {
        1.0
    }
}