use gio::MemoryInputStream;
use glib::Bytes;
use predicates::prelude::*;
use predicates::reflection::{Case, Child, PredicateReflection, Product};
use std::cmp;
use std::fmt;

use librsvg::{CairoRenderer, Length, Loader, LoadingError, SvgHandle};

/// Checks that the variable of type [u8] can be parsed as a SVG file.
#[derive(Debug)]
pub struct SvgPredicate {}

impl SvgPredicate {
    pub fn with_size(self: Self, width: Length, height: Length) -> DetailPredicate<Self> {
        DetailPredicate::<Self> {
            p: self,
            d: Detail::Size(Dimensions {
                w: width,
                h: height,
            }),
        }
    }
}

fn svg_from_bytes(data: &[u8]) -> Result<SvgHandle, LoadingError> {
    let bytes = Bytes::from(data);
    let stream = MemoryInputStream::from_bytes(&bytes);
    Loader::new().read_stream(&stream, None::<&gio::File>, None::<&gio::Cancellable>)
}

impl Predicate<[u8]> for SvgPredicate {
    fn eval(&self, data: &[u8]) -> bool {
        svg_from_bytes(data).is_ok()
    }

    fn find_case<'a>(&'a self, _expected: bool, data: &[u8]) -> Option<Case<'a>> {
        match svg_from_bytes(data) {
            Ok(_) => None,
            Err(e) => Some(Case::new(Some(self), false).add_product(Product::new("Error", e))),
        }
    }
}

impl PredicateReflection for SvgPredicate {}

impl fmt::Display for SvgPredicate {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "is an SVG")
    }
}

/// Extends a SVG Predicate by a check for its size
#[derive(Debug)]
pub struct DetailPredicate<SvgPredicate> {
    p: SvgPredicate,
    d: Detail,
}

#[derive(Debug)]
enum Detail {
    Size(Dimensions),
}

/// SVG's dimensions
#[derive(Debug)]
struct Dimensions {
    w: Length,
    h: Length,
}

impl Dimensions {
    pub fn width(self: &Self) -> f64 {
        self.w.length
    }

    pub fn height(self: &Self) -> f64 {
        self.h.length
    }
}

impl fmt::Display for Dimensions {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(
            f,
            "{}{} x {}{}",
            self.width(),
            self.w.unit,
            self.height(),
            self.h.unit
        )
    }
}

impl cmp::PartialEq for Dimensions {
    fn eq(&self, other: &Self) -> bool {
        approx_eq!(f64, self.width(), other.width(), epsilon = 0.000_001)
            && approx_eq!(f64, self.height(), other.height(), epsilon = 0.000_001)
            && (self.w.unit == self.h.unit)
            && (self.h.unit == other.h.unit)
            && (other.h.unit == other.w.unit)
    }
}

impl cmp::Eq for Dimensions {}

trait Details {
    fn get_size(&self) -> Option<Dimensions>;
}

impl DetailPredicate<SvgPredicate> {
    fn eval_doc(&self, handle: &SvgHandle) -> bool {
        match &self.d {
            Detail::Size(d) => {
                let renderer = CairoRenderer::new(handle);
                let dimensions = renderer.intrinsic_dimensions();
                (dimensions.width, dimensions.height) == (Some(d.w), Some(d.h))
            }
        }
    }

    fn find_case_for_doc<'a>(&'a self, expected: bool, handle: &SvgHandle) -> Option<Case<'a>> {
        if self.eval_doc(handle) == expected {
            let product = self.product_for_doc(handle);
            Some(Case::new(Some(self), false).add_product(product))
        } else {
            None
        }
    }

    fn product_for_doc(&self, handle: &SvgHandle) -> Product {
        match &self.d {
            Detail::Size(_) => {
                let renderer = CairoRenderer::new(handle);
                let dimensions = renderer.intrinsic_dimensions();

                Product::new(
                    "actual size",
                    format!(
                        "width={:?}, height={:?}",
                        dimensions.width, dimensions.height
                    ),
                )
            }
        }
    }
}

impl Predicate<[u8]> for DetailPredicate<SvgPredicate> {
    fn eval(&self, data: &[u8]) -> bool {
        match svg_from_bytes(data) {
            Ok(handle) => self.eval_doc(&handle),
            _ => false,
        }
    }

    fn find_case<'a>(&'a self, expected: bool, data: &[u8]) -> Option<Case<'a>> {
        match svg_from_bytes(data) {
            Ok(handle) => self.find_case_for_doc(expected, &handle),
            Err(e) => Some(Case::new(Some(self), false).add_product(Product::new("Error", e))),
        }
    }
}

impl PredicateReflection for DetailPredicate<SvgPredicate> {
    fn children<'a>(&'a self) -> Box<dyn Iterator<Item = Child<'a>> + 'a> {
        let params = vec![Child::new("predicate", &self.p)];
        Box::new(params.into_iter())
    }
}

impl fmt::Display for DetailPredicate<SvgPredicate> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match &self.d {
            Detail::Size(d) => write!(f, "is an SVG sized {}", d),
        }
    }
}
