// SPDX-FileCopyrightText: 2020 Robin Krahl <robin.krahl@ireas.org>
// SPDX-License-Identifier: Apache-2.0 or MIT

//! User-friendly PDF generator written in pure Rust.
//!
//! `genpdf` is a high-level PDF generator built ontop of [`printpdf`][] and [`rusttype`][].  It
//! takes care of the page layout and text alignment and renders a document tree into a PDF
//! document.  All of its dependencies are written in Rust, so you don’t need any pre-installed
//! libraries or tools.
//!
//! # Quickstart
//!
//! To generate a PDF document, create an instance of the [`Document`][] struct and add
//! [`Element`][] implementations to it.  Then call the [`Document::render_to_file`][] method to
//! render the document and to write it to a file.
//!
//! <!-- Keep in sync with README.md -->
//! ```no_run
//! // Load a font from the file system
//! let font_family = genpdf::fonts::from_files("./fonts", "LiberationSans", None)
//!     .expect("Failed to load font family");
//! // Create a document and set the default font family
//! let mut doc = genpdf::Document::new(font_family);
//! // Change the default settings
//! doc.set_title("Demo document");
//! // Customize the pages
//! let mut decorator = genpdf::SimplePageDecorator::new();
//! decorator.set_margins(10);
//! doc.set_page_decorator(decorator);
//! // Add one or more elements
//! doc.push(genpdf::elements::Paragraph::new("This is a demo document."));
//! // Render the document and write it to a file
//! doc.render_to_file("output.pdf").expect("Failed to write PDF file");
//! ```
//!
//! For a complete example with all supported elements, see the [`examples/demo.rs`][] file that
//! generates [this PDF document][].
//!
//! # Overview
//!
//! A [`Document`][] consists of a [`LinearLayout`][] that renders the added elements, a
//! [`FontCache`][] instance that keeps track of the loaded fonts and a collection of default
//! values for the text style and the page layout.
//!
//! When creating a [`Document`][] instance, you always have to set the default font family that
//! will be used for the document.  You can load additional fonts with the
//! [`Document::load_font_family`][] method.
//!
//! The style of a shape or text can be set using the [`Style`][] struct.  The style is inherited
//! within the document tree.  You can set the style of an element by wrapping it in a
//! [`StyledElement`][] (see the [`Element::styled`][] method) or – for text elements – with a
//! [`StyledString`][].
//!
//! For an overview of the available elements, see the [`elements`][] module.  You can also
//! create custom elements by implementing the [`Element`][] trait.
//!
//! The actual PDF document is generated from the elements that have been added to the document
//! once you call the [`Document::render`][] or [`Document::render_to_file`][] methods.  For
//! details on the rendering process, see the next section.
//!
//! In `genpdf`, all lengths are measured in millimeters.  The only exceptions are font sizes that
//! are measured in points.  The [`Mm`][] newtype struct is used for all lengths, and the
//! [`Position`][] and [`Size`][] types are used to describe points and rectangles in the PDF
//! document.
//!
//! # Rendering Process
//!
//! The rendering process is started by calling the [`Document::render`][] or
//! [`Document::render_to_file`][] methods.  You can only render a document once.  Before the
//! rendering starts, the PDF document is created and all loaded fonts are embedded into the
//! document.
//!
//! The elements are then rendered by calling the [`Element::render`][] method of the root element,
//! a [`LinearLayout`][].  This element will then call the `render` methods of the elements stored
//! in the layout, and so on.
//!
//! The [`Element::render`][] method receives the following arguments:
//! - *context* is the context for the rendering process, see [`Context`][].  Currently, it only
//!   stores the [`FontCache`][] instance that keeps track of the loaded fonts and can be
//!   used to map a [`Style`][] instance to font data.
//! - *area* is a view on the area of the current page that can be used by the element.
//! - *style* is the [`Style`][] instance for this element.  Is is a combination of the default
//!   style of the [`Document`][] and the style set by [`StyledElement`][] instances that are
//!   parents of the current element.
//!
//! The `render` method tries to render the entire element in the provided area.  The returned
//! [`RenderResult`][] stores the size of the area that has actually been used to render the
//! element.  If the element did not fit into the provided area, the `has_more` field of the
//! [`RenderResult`][] is set to `true`.  This causes the `Document` to add a new page to the PDF
//! document and then call the `render` method again with an area of the new page.  This is
//! repeated until all elements have been rendered completely, that means until all elements return
//! a [`RenderResult`][] with `has_more == false`.
//!
//! Elements may print to the provided area using the methods of the [`Area`][] struct, or by
//! calling the `render` method of other elements, or both.
//!
//! Every new page is prepared by calling the document’s [`PageDecorator`][] (if set).  This
//! decorator can add a margin to the page, print a header, a footer, or perform other tasks.
//!
//! The render process is cancelled if an `Element` returns an error, or if no content has been
//! rendered to a newly created page.  This indicates that an element does not fit on a clear page
//! and can’t even be rendered partially, so the rendering process is cancelled.
//!
//! As the [`Element::render`][] method is called repeatedly until the complete element has been
//! rendered, the element has to keep track of the content that has already been rendered.  As
//! there is only one rendering process per document, elements may discard data that has been
//! rendered and that is no longer needed.
//!
//! # Low-Level Interface
//!
//! The [`render`][] module contains a low-level interface for creating PDF files.  It keeps track
//! of page sizes and layers and has utility methods for easier text and shape rendering.  But it
//! does not provide support for measuring the size of rendered text or for laying out elements.
//! If possible, you should always try to use `genpdf`’s high-level interface and implement the
//! [`Element`][] trait if you want to customize a document instead of using the low-level
//! interface directly.
//!
//! # Known Issues
//!
//! - Currently, `genpdf` adds all loaded fonts to the PDF document, even if they are not used.
//!   `printpdf` then adds all available glyphs for these fonts to the document, even if they are
//!   not used in the document.  This increases the file size by 100–200 KiB per font (500–1000 KiB
//!   per font family).  Until this is fixed, you can pass the generated file through `ps2pdf` to
//!   significantly reduce its size.  Alternatively, you can use a built-in font if you don’t need
//!   any characters that are not supported by the [Windows-1252][] encoding.
//!
//! [`printpdf`]: https://docs.rs/printpdf
//! [`rusttype`]: https://docs.rs/rusttype
//! [`render`]: ./render/
//! [`elements`]: ./elements/
//! [`Context`]: struct.Context.html
//! [`Document`]: struct.Document.html
//! [`Document::render`]: struct.Document.html#method.render
//! [`Document::render_to_file`]: struct.Document.html#method.render_to_file
//! [`Document::load_font_family`]: struct.Document.html#method.load_font_family
//! [`Element`]: trait.Element.html
//! [`Element::render`]: trait.Element.html#tymethod.render
//! [`Element::styled`]: trait.Element.html#tymethod.styled
//! [`PageDecorator`]: trait.PageDecorator.html
//! [`RenderResult`]: struct.RenderResult.html
//! [`LinearLayout`]: elements/struct.LinearLayout.html
//! [`StyledElement`]: elements/StyledElement.html
//! [`FontCache`]: fonts/struct.FontCache.html
//! [`Area`]: render/struct.Area.html
//! [`Mm`]: struct.Mm.html
//! [`Size`]: struct.Size.html
//! [`Position`]: struct.Position.html
//! [`Style`]: style/struct.Style.html
//! [`StyledString`]: style/struct.StyledString.html
//! [`examples/demo.rs`]: https://git.sr.ht/~ireas/genpdf-rs/tree/master/examples/demo.rs
//! [this PDF document]: https://genpdf-rs.ireas.org/examples/demo.pdf
//! [Windows-1252]: https://en.wikipedia.org/wiki/Windows-1252

#![warn(missing_docs, rust_2018_idioms)]

mod wrap;

pub mod elements;
pub mod error;
pub mod fonts;
pub mod render;
pub mod style;

use std::fs;
use std::io;
use std::path;

use derive_more::{
    Add, AddAssign, Div, DivAssign, From, Into, Mul, MulAssign, Sub, SubAssign, Sum,
};

use error::Context as _;

/// A length measured in millimeters.
///
/// `genpdf` always uses millimeters as its length unit, except for the font size that is measured
/// in points.
///
/// If you want to convert pixels or points into millimeters, you can use the [`printpdf::Pt`][]
/// and [`printpdf::Px`][] types.
///
/// [`printpdf::Pt`]: https://docs.rs/printpdf/0.3.2/printpdf/scale/struct.Pt.html
/// [`printpdf::Px`]: https://docs.rs/printpdf/0.3.2/printpdf/scale/struct.Px.html
#[derive(
    Clone,
    Copy,
    Debug,
    Default,
    PartialEq,
    PartialOrd,
    Add,
    AddAssign,
    Div,
    DivAssign,
    From,
    Into,
    Mul,
    MulAssign,
    Sub,
    SubAssign,
    Sum,
)]
pub struct Mm(f64);

impl Mm {
    /// Returns the maximum of this value and the given value.
    pub fn max(self, other: Mm) -> Mm {
        Mm(self.0.max(other.0))
    }
}

impl From<i8> for Mm {
    fn from(mm: i8) -> Mm {
        Mm(mm.into())
    }
}

impl From<i16> for Mm {
    fn from(mm: i16) -> Mm {
        Mm(mm.into())
    }
}

impl From<i32> for Mm {
    fn from(mm: i32) -> Mm {
        Mm(mm.into())
    }
}

impl From<u8> for Mm {
    fn from(mm: u8) -> Mm {
        Mm(mm.into())
    }
}

impl From<u16> for Mm {
    fn from(mm: u16) -> Mm {
        Mm(mm.into())
    }
}

impl From<u32> for Mm {
    fn from(mm: u32) -> Mm {
        Mm(mm.into())
    }
}

impl From<f32> for Mm {
    fn from(mm: f32) -> Mm {
        Mm(mm.into())
    }
}

impl From<printpdf::Mm> for Mm {
    fn from(mm: printpdf::Mm) -> Mm {
        Mm(mm.0)
    }
}

impl From<printpdf::Pt> for Mm {
    fn from(pt: printpdf::Pt) -> Mm {
        let mm: printpdf::Mm = pt.into();
        mm.into()
    }
}

impl From<Mm> for printpdf::Mm {
    fn from(mm: Mm) -> printpdf::Mm {
        printpdf::Mm(mm.0)
    }
}

impl From<Mm> for printpdf::Pt {
    fn from(mm: Mm) -> printpdf::Pt {
        printpdf::Mm(mm.0).into()
    }
}

/// The alignment of a [`Paragraph`][] or ['Image'][].
///
/// The default alignment is left-flushed.
///
/// [`Paragraph`]: elements/struct.Paragraph.html
/// [`Image`]: elements/struct.Image.html
#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub enum Alignment {
    /// Left-flushed.
    Left,
    /// Right-flushed.
    Right,
    /// Centered.
    Center,
}

impl Default for Alignment {
    fn default() -> Alignment {
        Alignment::Left
    }
}

/// A position on a PDF layer, measured in millimeters.
///
/// All positions used by `genpdf` are measured from the top left corner of the reference area.
#[derive(Clone, Copy, Debug, Default, PartialEq, PartialOrd, Add, AddAssign, Sub, SubAssign)]
pub struct Position {
    /// The x coordinate of the position, measured from the left border of the reference area.
    pub x: Mm,
    /// The y coordinate of the position, measured from the top border of the reference area.
    pub y: Mm,
}

impl Position {
    /// Creates a new position from the given coordinates.
    pub fn new(x: impl Into<Mm>, y: impl Into<Mm>) -> Position {
        Position {
            x: x.into(),
            y: y.into(),
        }
    }
}

impl From<Position> for printpdf::Point {
    fn from(pos: Position) -> printpdf::Point {
        printpdf::Point::new(pos.x.into(), pos.y.into())
    }
}

impl<X: Into<Mm>, Y: Into<Mm>> From<(X, Y)> for Position {
    fn from(values: (X, Y)) -> Position {
        Position::new(values.0, values.1)
    }
}

/// A rotation in degrees clock-wise in range [-180.0, 180.0] inclusive.
#[derive(Clone, Copy, Default, Debug, PartialEq, PartialOrd, Add, AddAssign, Sub, SubAssign)]
pub struct Rotation {
    degrees: f64,
}

impl Rotation {
    /// Creates a new rotation with the given number of degrees.
    pub fn from_degrees(degrees: f64) -> Self {
        let degrees = degrees % 360.0;
        let degrees = if degrees > 180.0 {
            degrees - 360.0
        } else if degrees < -180.0 {
            360.0 + degrees
        } else {
            degrees
        };
        Rotation { degrees }
    }

    /// Returns the rotation in degrees clock-wise in the range [-180.0, 180.0] inclusive or `None`
    /// if there is no rotation.
    pub fn degrees(&self) -> Option<f64> {
        if self.degrees != 0.0 {
            Some(self.degrees)
        } else {
            None
        }
    }
}

impl From<f64> for Rotation {
    fn from(degrees: f64) -> Rotation {
        // Perhaps a poor assumption that we'll always work with degrees?
        Rotation::from_degrees(degrees)
    }
}

impl From<Rotation> for Option<f64> {
    fn from(rotation: Rotation) -> Option<f64> {
        rotation.degrees()
    }
}

/// A size to stretch an image on a PDF layer; measured in percentage.
#[derive(Clone, Copy, Debug, PartialEq, PartialOrd, Add, AddAssign, Sub, SubAssign)]
pub struct Scale {
    /// The percentage to scale on the x-axis.
    pub x: f64,
    /// The percentage to scale on the y-axis.
    pub y: f64,
}

// Overriding default of (0,0) as that would scale it to 0.
impl Default for Scale {
    fn default() -> Scale {
        Scale::new(1, 1)
    }
}

impl Scale {
    /// Creates a new scale for the given x/y values.
    pub fn new(x: impl Into<f64>, y: impl Into<f64>) -> Scale {
        Scale {
            x: x.into(),
            y: y.into(),
        }
    }
}

impl<X: Into<f64>, Y: Into<f64>> From<(X, Y)> for Scale {
    fn from(values: (X, Y)) -> Scale {
        Scale::new(values.0, values.1)
    }
}

/// A size of an area on a PDF layer, measured in millimeters.
#[derive(Clone, Copy, Debug, Default, PartialEq, PartialOrd, Add, AddAssign, Sub, SubAssign)]
pub struct Size {
    /// The width of the area.
    pub width: Mm,
    /// The height of the area.
    pub height: Mm,
}

impl Size {
    /// Creates a new size from the given width and height.
    pub fn new(width: impl Into<Mm>, height: impl Into<Mm>) -> Size {
        Size {
            width: width.into(),
            height: height.into(),
        }
    }

    /// Stacks the given size vertically on this size and returns the result.
    ///
    /// This means that the width is set to the maximum of the widths and the height is set to the
    /// sum of the heights.
    #[must_use]
    pub fn stack_vertical(mut self, other: Size) -> Size {
        self.width = self.width.max(other.width);
        self.height += other.height;
        self
    }
}

impl<W: Into<Mm>, H: Into<Mm>> From<(W, H)> for Size {
    fn from(values: (W, H)) -> Size {
        Size::new(values.0, values.1)
    }
}

/// A paper size like A4, legal or letter.
///
/// This enum provides variants for typical paper sizes that can be converted into [`Size`][]
/// instances.
///
/// [`Size`]: struct.Size.html
#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
pub enum PaperSize {
    /// The A4 paper size (210x297mm).
    A4,
    /// The legal paper size (216x356mm).
    Legal,
    /// The letter paper size (216x279mm).
    Letter,
}

impl From<PaperSize> for Size {
    fn from(size: PaperSize) -> Size {
        match size {
            PaperSize::A4 => Size::new(210, 297),
            PaperSize::Legal => Size::new(216, 356),
            PaperSize::Letter => Size::new(216, 279),
        }
    }
}

/// The margins of an area, measured in millimeters.
#[derive(Clone, Copy, Debug, Default, PartialEq, PartialOrd)]
pub struct Margins {
    /// The top margin of the area.
    top: Mm,
    /// The right margin of the area.
    right: Mm,
    /// The bottom margin of the area.
    bottom: Mm,
    /// The left margin of the area.
    left: Mm,
}

impl Margins {
    /// Creates a new `Margins` instance from the given top, right, bottom and left margins.
    pub fn trbl(
        top: impl Into<Mm>,
        right: impl Into<Mm>,
        bottom: impl Into<Mm>,
        left: impl Into<Mm>,
    ) -> Margins {
        Margins {
            top: top.into(),
            right: right.into(),
            bottom: bottom.into(),
            left: left.into(),
        }
    }

    /// Creates a new `Margins` instance from the given vertical (top and bottom) and horizontal
    /// (left and right) margins.
    pub fn vh(vertical: impl Into<Mm>, horizontal: impl Into<Mm>) -> Margins {
        let (vertical, horizontal) = (vertical.into(), horizontal.into());
        Margins::trbl(vertical, horizontal, vertical, horizontal)
    }

    /// Creates a new `Margins` instance with all four margins set to the given value.
    pub fn all(all: impl Into<Mm>) -> Margins {
        let all = all.into();
        Margins::trbl(all, all, all, all)
    }
}

impl<T: Into<Mm>, R: Into<Mm>, B: Into<Mm>, L: Into<Mm>> From<(T, R, B, L)> for Margins {
    fn from(values: (T, R, B, L)) -> Margins {
        Margins::trbl(values.0, values.1, values.2, values.3)
    }
}

impl<V: Into<Mm>, H: Into<Mm>> From<(V, H)> for Margins {
    fn from(values: (V, H)) -> Margins {
        Margins::vh(values.0, values.1)
    }
}

impl<T: Into<Mm>> From<T> for Margins {
    fn from(value: T) -> Margins {
        Margins::all(value)
    }
}

/// A PDF document.
///
/// This struct is the entry point for the high-level `genpdf` API.  It stores a set of elements
/// and default style and layout settings.  Add elements to the document by calling the [`push`][]
/// method and then render them to a PDF file using the [`render`][] and [`render_to_file`][]
/// methods.
///
/// The root element of the document is a [`LinearLayout`][] that vertically arranges all elements.
/// For details on the rendering process, see the [Rendering Process section of the crate
/// documentation](index.html#rendering-process).
///
/// You can add a [`PageDecorator`][] to this document by calling [`set_page_decorator`][].  This
/// page decorator will be called for every new page and can add a margin, a header or other
/// elements to the page before it is filled with the actual document content.  See the
/// [`SimplePageDecorator`][] for a basic implementation.
///
/// If the `hyphenation` feature is enabled, users can activate hyphenation with the
/// [`set_hyphenator`][] method.
///
/// # Example
///
/// ```no_run
/// // Load a font from the file system
/// let font_family = genpdf::fonts::from_files("./fonts", "LiberationSans", None)
///     .expect("Failed to load font family");
/// // Create a document and set the default font family
/// let mut doc = genpdf::Document::new(font_family);
/// doc.push(genpdf::elements::Paragraph::new("Document content"));
/// doc.render_to_file("output.pdf").expect("Failed to render document");
/// ```
///
/// [`push`]: #method.push
/// [`render`]: #method.render
/// [`render_to_file`]: #method.render_to_file
/// [`set_hyphenation`]: #method.set_hyphenation
/// [`set_page_decorator`]: #method.set_page_decorator
/// [`PageDecorator`]: trait.PageDecorator.html
/// [`SimplePageDecorator`]: struct.SimplePageDecorator.html
/// [`LinearLayout`]: elements/struct.LinearLayout.html
pub struct Document {
    root: elements::LinearLayout,
    title: String,
    context: Context,
    style: style::Style,
    paper_size: Size,
    decorator: Option<Box<dyn PageDecorator>>,
    conformance: Option<printpdf::PdfConformance>,
}

impl Document {
    /// Creates a new document with the given default font family.
    pub fn new(default_font_family: fonts::FontFamily<fonts::FontData>) -> Document {
        let font_cache = fonts::FontCache::new(default_font_family);
        Document {
            root: elements::LinearLayout::vertical(),
            title: String::new(),
            context: Context::new(font_cache),
            style: style::Style::new(),
            paper_size: PaperSize::A4.into(),
            decorator: None,
            conformance: None,
        }
    }

    /// Adds the given font family to the font cache for this document and returns a reference to
    /// it.
    ///
    /// Note that the returned font reference may only be used for this document.  It cannot be
    /// shared with other `Document` or [`FontCache`][] instances.
    ///
    /// [`FontCache`]: fonts/struct.FontCache.html
    pub fn add_font_family(
        &mut self,
        font_family: fonts::FontFamily<fonts::FontData>,
    ) -> fonts::FontFamily<fonts::Font> {
        self.context.font_cache.add_font_family(font_family)
    }

    /// Returns the font cache used by this document.
    ///
    /// You can use the font cache to get the default font and to query glyph metrics for a font.
    /// Use the [`load_font_family`][] method instead if you want to add fonts to this document.
    ///
    /// [`load_font_family`]: #method.load_font_family
    pub fn font_cache(&self) -> &fonts::FontCache {
        &self.context.font_cache
    }

    /// Activates hyphenation and sets the hyphentor to use.
    ///
    /// *Only available if the `hyphenation` feature is enabled.*
    #[cfg(feature = "hyphenation")]
    pub fn set_hyphenator(&mut self, hyphenator: hyphenation::Standard) {
        self.context.hyphenator = Some(hyphenator);
    }

    /// Sets the title of the PDF document.
    ///
    /// If this method is not called, the PDF title will be empty.
    pub fn set_title(&mut self, title: impl Into<String>) {
        self.title = title.into();
    }

    /// Sets the default font size in points for this document.
    ///
    /// If this method is not called, the default value of 12 points is used.
    pub fn set_font_size(&mut self, font_size: u8) {
        self.style.set_font_size(font_size);
    }

    /// Sets the default line spacing factor for this document.
    ///
    /// If this method is not called, the default value of 1 is used.
    pub fn set_line_spacing(&mut self, line_spacing: f64) {
        self.style.set_line_spacing(line_spacing);
    }

    /// Sets the paper size for all pages of this document.
    ///
    /// If this method is not called, the default size [`A4`][] is used.
    ///
    /// [`A4`]: enum.PaperSize.html#variant.A4
    pub fn set_paper_size(&mut self, paper_size: impl Into<Size>) {
        self.paper_size = paper_size.into();
    }

    /// Sets the page decorator for this document.
    ///
    /// The page decorator is called for every page before it is filled with the document content.
    /// It can add margins, headers or other elements.
    ///
    /// See the [`SimplePageDecorator`][] for an example implementation.
    ///
    /// [`SimplePageDecorator`]: struct.SimplePageDecorator.html
    pub fn set_page_decorator<D: PageDecorator + 'static>(&mut self, decorator: D) {
        self.decorator = Some(Box::new(decorator));
    }

    /// Sets the PDF conformance settings for this document.
    pub fn set_conformance(&mut self, conformance: printpdf::PdfConformance) {
        self.conformance = Some(conformance);
    }

    /// Sets the minimal PDF conformance settings for this document.
    ///
    /// If this method is called, the generation of ICC profiles and XMP metadata is deactivated,
    /// leading to a smaller file size.
    pub fn set_minimal_conformance(&mut self) {
        self.set_conformance(printpdf::PdfConformance::Custom(
            printpdf::CustomPdfConformance {
                requires_icc_profile: false,
                requires_xmp_metadata: false,
                ..Default::default()
            },
        ));
    }

    /// Adds the given element to the document.
    ///
    /// The given element is appended to the list of elements that is rendered by the root
    /// [`LinearLayout`][] once [`render`][] or [`render_to_file`][] is called.
    ///
    /// [`LinearLayout`]: elements/struct.LinearLayout.html
    /// [`render`]: #method.render
    /// [`render_to_file`]: #method.render_to_file
    pub fn push<E: Element + 'static>(&mut self, element: E) {
        self.root.push(element);
    }

    /// Renders this document into a PDF file and writes it to the given writer.
    ///
    /// The given writer is always wrapped in a buffered writer.  For details on the rendering
    /// process, see the [Rendering Process section of the crate
    /// documentation](index.html#rendering-process).
    pub fn render(mut self, w: impl io::Write) -> Result<(), error::Error> {
        let mut renderer = render::Renderer::new(self.paper_size, &self.title)?;
        if let Some(conformance) = self.conformance {
            renderer = renderer.with_conformance(conformance);
        }
        self.context.font_cache.load_pdf_fonts(&renderer)?;
        loop {
            let mut area = renderer.last_page().last_layer().area();
            if let Some(decorator) = &mut self.decorator {
                area = decorator.decorate_page(&self.context, area, self.style)?;
            }
            let result = self.root.render(&self.context, area, self.style)?;
            if result.has_more {
                if result.size == Size::new(0, 0) {
                    return Err(error::Error::new(
                        "Could not fit an element on a new page",
                        error::ErrorKind::PageSizeExceeded,
                    ));
                }
                renderer.add_page(self.paper_size);
            } else {
                break;
            }
        }
        renderer.write(w)
    }

    /// Renders this document into a PDF file at the given path.
    ///
    /// If the given file does not exist, it is created.  If it exists, it is overwritten.
    ///
    /// For details on the rendering process, see the [Rendering Process section of the crate
    /// documentation](index.html#rendering-process).
    pub fn render_to_file(self, path: impl AsRef<path::Path>) -> Result<(), error::Error> {
        let path = path.as_ref();
        let file = fs::File::create(path)
            .with_context(|| format!("Could not create file {}", path.display()))?;
        self.render(file)
    }
}

/// The result of the rendering process.
///
/// This struct is returned by implementations of the [`Element::render`][] method.  It contains
/// the size of the area that has been written to (measured from the origin of the area that was
/// provided to the render method) and information about additional content that did not fit in the
/// provided area.
///
/// See the [Rendering Process section of the crate documentation](index.html#rendering-process)
/// for more information on the rendering process.
///
/// [`Element::render`]: trait.Element.html#tymethod.render
#[derive(Clone, Copy, Debug, Default, PartialEq, PartialOrd)]
pub struct RenderResult {
    /// The size of the area that has been written to, starting from the origin of the provided
    /// area.
    pub size: Size,
    /// Indicates whether the element contains more content that did not fit in the provided area.
    pub has_more: bool,
}

/// Prepares a page of a document.
///
/// If you set an implementation of this trait for a [`Document`][] using the
/// [`set_page_decorator`][] method, its [`decorate_page`][] method is called every time a new page
/// is added to the document.  The decorator can prepare the page before it is filled with the
/// actual content.  See [`SimplePageDecorator`][] for a basic implementation.
///
/// [`Document`]: struct.Document.html
/// [`set_page_decorator`]: struct.Document.html#method.set_page_decorator
/// [`SimplePageDecorator`]: struct.SimplePageDecorator.html
/// [`decorate_page`]: #tymethod.decorate_page
pub trait PageDecorator {
    /// Prepares the page with the given area before it is filled with the document content and
    /// returns the writable area of the page.
    ///
    /// The returned area will be passed to the document content.
    fn decorate_page<'a>(
        &mut self,
        context: &Context,
        area: render::Area<'a>,
        style: style::Style,
    ) -> Result<render::Area<'a>, error::Error>;
}

type HeaderCallback = Box<dyn Fn(usize) -> Box<dyn Element>>;

/// Prepares a page of a document with margins and a header.
///
/// Per default, this decorator does not modify the page.  If margins have been set with the
/// [`set_margins`][] method, they are applied to every page.  If a header callback is configured
/// with the [`set_header`][] method, it will be called for every page and its return value will be
/// rendered at the beginning of the page (after the margins have been applied).
///
/// [`set_margins`]: #method.set_margins
/// [`set_header`]: #method.set_header
#[derive(Default)]
pub struct SimplePageDecorator {
    page: usize,
    margins: Option<Margins>,
    header_cb: Option<HeaderCallback>,
}

impl SimplePageDecorator {
    /// Creates a new page decorator that does not modify the page.
    pub fn new() -> SimplePageDecorator {
        SimplePageDecorator::default()
    }

    /// Sets the margins for all pages of this document.
    ///
    /// If this method is not called, the full page is used.
    pub fn set_margins(&mut self, margins: impl Into<Margins>) {
        self.margins = Some(margins.into());
    }

    /// Sets the header generator for this document.
    ///
    /// The given closure will be called once per page.  Its argument is the page number (starting
    /// with 1), and its return value will be rendered at the top of the page.  The document
    /// content will start directly after the element.
    pub fn set_header<F, E>(&mut self, cb: F)
    where
        F: Fn(usize) -> E + 'static,
        E: Element + 'static,
    {
        // We manually box the return type of the callback so that it is easier to write closures.
        self.header_cb = Some(Box::new(move |page| Box::new(cb(page))));
    }
}

impl PageDecorator for SimplePageDecorator {
    fn decorate_page<'a>(
        &mut self,
        context: &Context,
        mut area: render::Area<'a>,
        style: style::Style,
    ) -> Result<render::Area<'a>, error::Error> {
        self.page += 1;
        if let Some(margins) = self.margins {
            area.add_margins(margins);
        }
        if let Some(cb) = &self.header_cb {
            let mut element = cb(self.page);
            let result = element.render(context, area.clone(), style)?;
            area.add_offset(Position::new(0, result.size.height));
        }
        Ok(area)
    }
}

/// An element of a PDF document.
///
/// This trait is implemented by all elements that can be added to a [`Document`][].  Implementors
/// have to define the [`render`][] method that writes the content of this element to the generated
/// PDF document.
///
/// See the [Rendering Process section of the crate documentation](index.html#rendering-process)
/// for more information on the rendering process.
///
/// [`Document`]: struct.Document.html
/// [`render`]: #tymethod.render
pub trait Element {
    /// Renders this element to the given area using the given style and font cache.
    ///
    /// For an overview over the rendering process, see the [Rendering Process section of the crate
    /// documentation](index.html#rendering-process).
    ///
    /// This method is called once for every element that has been added to a [`Document`][] once
    /// the [`render`][] or [`render_to_file`][] methods have been called.  If this method is
    /// called, it should print the element’s content to the given area.  If the content does not
    /// fit in the given area, it should set the `has_more` flag of the returned
    /// [`RenderResult`][].  It will then be called again with a new area on a new page until it
    /// returns a [`RenderResult`][] with `has_more == false`.  Regardless of whether the content
    /// fitted in the area or not, the `size` field of the [`RenderResult`][] must always be set to
    /// the size of the area that has been used, starting at the origin of the provided area.
    ///
    /// The following guarantuees are made by `genpdf`’s elements and must be followed by
    /// implementations of this trait:
    ///
    /// - There is only one rendering process per element instance.  This means that the first call
    ///   to this method is always the start of the rendering process, and subsequent calls are
    ///   always continuations of the same rendering process.  This means that the element does not
    ///   have to reset its state after it has processed all content, and it is allowed to drop
    ///   content that has already been rendered.
    /// - If a call to this method returns an `Err` value, it will not be called again.
    /// - After the first call, the method will only be called again if the `has_more` of the last
    ///   [`RenderResult`][] was set to true.
    /// - If none of the element’s content could be fitted in the provided area, the size of the
    ///   [`RenderResult`][] must be `(0, 0)`.  If the size is non-zero, this method must return a
    ///   [`RenderResult`] with `has_more == false` after a finite number of calls.
    ///
    /// [`Document`]: struct.Document.html
    /// [`render`]: struct.Document.html#method.render
    /// [`render_to_file`]: struct.Document.html#method.render_to_file
    /// [`RenderResult`]: struct.RenderResult.html
    fn render(
        &mut self,
        context: &Context,
        area: render::Area<'_>,
        style: style::Style,
    ) -> Result<RenderResult, error::Error>;

    /// Draws a frame around this element.
    fn framed(self) -> elements::FramedElement<Self>
    where
        Self: Sized,
    {
        elements::FramedElement::new(self)
    }

    /// Adds a padding to this element.
    fn padded(self, padding: impl Into<Margins>) -> elements::PaddedElement<Self>
    where
        Self: Sized,
    {
        elements::PaddedElement::new(self, padding)
    }

    /// Sets the default style for this element and its children.
    fn styled(self, style: impl Into<style::Style>) -> elements::StyledElement<Self>
    where
        Self: Sized,
    {
        elements::StyledElement::new(self, style.into())
    }
}

/// The context for a rendering process.
///
/// This struct stores data that is shared between all elements during the rendering process.
#[derive(Debug)]
#[non_exhaustive]
pub struct Context {
    /// The font cache for this rendering process.
    pub font_cache: fonts::FontCache,
    /// The hyphenator to use for hyphenation.
    ///
    /// *Only available if the `hyphenation` feature is enabled.*
    ///
    /// If this field is `None`, hyphenation is disabled.
    #[cfg(feature = "hyphenation")]
    pub hyphenator: Option<hyphenation::Standard>,
}

impl Context {
    #[cfg(not(feature = "hyphenation"))]
    fn new(font_cache: fonts::FontCache) -> Context {
        Context { font_cache }
    }

    #[cfg(feature = "hyphenation")]
    fn new(font_cache: fonts::FontCache) -> Context {
        Context {
            font_cache,
            hyphenator: None,
        }
    }
}

#[cfg(test)]
mod tests {
    impl float_cmp::ApproxEq for super::Mm {
        type Margin = float_cmp::F64Margin;

        fn approx_eq<M: Into<Self::Margin>>(self, other: Self, margin: M) -> bool {
            self.0.approx_eq(other.0, margin)
        }
    }

    impl float_cmp::ApproxEq for super::Size {
        type Margin = float_cmp::F64Margin;

        fn approx_eq<M: Into<Self::Margin>>(self, other: Self, margin: M) -> bool {
            let margin = margin.into();
            self.width.approx_eq(other.width, margin) && self.height.approx_eq(other.height, margin)
        }
    }

    impl float_cmp::ApproxEq for super::Position {
        type Margin = float_cmp::F64Margin;

        fn approx_eq<M: Into<Self::Margin>>(self, other: Self, margin: M) -> bool {
            let margin = margin.into();
            self.x.approx_eq(other.x, margin) && self.y.approx_eq(other.y, margin)
        }
    }

    #[test]
    fn test_rotation() {
        use super::Rotation;

        assert_eq!(None, Rotation::from(0.0).degrees());

        assert_eq!(Some(90.0), Rotation::from(90.0).degrees());
        assert_eq!(Some(180.0), Rotation::from(180.0).degrees());
        assert_eq!(Some(-90.0), Rotation::from(270.0).degrees());
        assert_eq!(None, Rotation::from(360.0).degrees());
        assert_eq!(Some(90.0), Rotation::from(450.0).degrees());
        assert_eq!(Some(180.0), Rotation::from(540.0).degrees());

        assert_eq!(Some(-90.0), Rotation::from(-90.0).degrees());
        assert_eq!(Some(-180.0), Rotation::from(-180.0).degrees());
        assert_eq!(Some(90.0), Rotation::from(-270.0).degrees());
        assert_eq!(None, Rotation::from(-360.0).degrees());
        assert_eq!(Some(-90.0), Rotation::from(-450.0).degrees());
        assert_eq!(Some(-180.0), Rotation::from(-540.0).degrees());
    }
}