//! Calculate glyph positions.

//!

//! [GlyphLayout] is used to obtain the positions for a collection of shaped glyphs. The position

//! for each glyph includes its horizontal and vertical advance as well as any `(x, y)` offset from

//! the origin. Horizontal layout in left-to-right and right-to-left directions is supported. Basic

//! (but incomplete) support for vertical text is present too.

//!

//! The position of a series of glyphs is determined from an initial pen position, which is

//! incremented by the advance of each glyph as they are processed. The position of a particular

//! glyph is the current pen position plus `x_offset` and `y_offset`.

use crate::context::Glyph;

use crate::error::ParseError;

use crate::gpos::{Info, Placement};

use crate::tables::FontTableProvider;

use crate::unicode::codepoint::is_upright_char;

use crate::Font;

/// Used to calculate the position of shaped glyphs.

pub struct GlyphLayout<'f, 'i, T>

where

    T: FontTableProvider,

{

    font: &'f mut Font<T>,

    infos: &'i [Info],

    direction: TextDirection,

    vertical: bool,

}

/// The position and advance of a glyph.

#[derive(Copy, Clone, Eq, Debug, Default)]

pub struct GlyphPosition {

    /// Horizontal advance

    pub hori_advance: i32,

    /// Vertical advance

    pub vert_advance: i32,

    /// Offset in the X (horizontal) direction of this glyph

    pub x_offset: i32,

    /// Offset in the Y (vertical) direction of this glyph

    pub y_offset: i32,

    cursive_attachment: Option<u16>,

}

/// The horizontal text layout direction.

#[derive(Copy, Clone, Eq, PartialEq, Debug)]

pub enum TextDirection {

    LeftToRight,

    RightToLeft,

}

impl<'f, 'i, T: FontTableProvider> GlyphLayout<'f, 'i, T> {

    /// Construct a new `GlyphLayout` instance.

    ///

    /// **Arguments**

    ///

    /// * `font` — the font that the glyphs belong to.

    /// * `infos` — the shaped glyphs to lay out.

    /// * `direction` — the horizontal text layout direction.

    /// * `vertical` — `true` if the text is being laid out top to bottom.

    /// Retrieve the glyphs positions.

                }

                            };

                        }

                        None => {

                        }

                    }

                }

                }

                    // Validate index

                    // Link to exit glyph

                }

            };

        }

                Placement::None

                | Placement::Distance(_, _)

                | Placement::MarkAnchor(_, _, _)

                Placement::CursiveAnchor(

                ) => {

                    // Anchor alignment can result in horizontal or vertical positioning adjustments,

                    // or both. Note that the positioning effects in the text-layout direction

                    // (horizontal, for horizontal layout) work differently than for the cross-stream

                    // direction (vertical, in horizontal layout):

                    //

                    // * For adjustments in the line-layout direction, the layout engine adjusts the

                    //   advance of the first glyph (in logical order). This effectively moves the

                    //   second glyph relative to the first so that the anchors are aligned in that

                    //   direction.

                    // * For the cross-stream direction, placement of one glyph is adjusted to make

                    //   the anchors align. Which glyph is adjusted is determined by the RIGHT_TO_LEFT

                    //   flag in the parent lookup table: if the RIGHT_TO_LEFT flag is clear, the

                    //   second glyph is adjusted to align anchors with the first glyph; if the

                    //   RIGHT_TO_LEFT flag is set, the first glyph is adjusted to align anchors with

                    //   the second glyph.

                    //

                    // https://docs.microsoft.com/en-us/typography/opentype/spec/gpos#lookup-type-3-cursive-attachment-positioning-subtable

                    // First glyph in logical order is the one with the lower index

                    } else {

                    };

                    // Line-layout direction

                    // TODO: Handle vertical text

                        TextDirection::LeftToRight => {

                        }

                        TextDirection::RightToLeft => {

                        }

                    }

                    // Cross-stream direction

                    } else {

                    }

                }

            }

        }

                Placement::None

                | Placement::Distance(_, _)

                    };

                    // Add the x & y offset of the base glyph to the mark

                    // Shift the mark back the advance of the base glyph and glyphs leading to it

                    // so that it is positioned above it

                    }

                }

            }

        }

}

impl GlyphPosition {

}

impl PartialEq for GlyphPosition {

}

        // TODO: prevent cycles

    } else {

    };

#[cfg(test)]

mod tests {

    use std::error::Error;

    use std::path::Path;

    use super::*;

    use crate::binary::read::ReadScope;

    use crate::font::MatchingPresentation;

    use crate::font_data::FontData;

    use crate::gsub::{Feature, FeatureMask, FeatureMaskExt};

    use crate::tag;

    use crate::tests::read_fixture;

    fn get_positions(

        text: &str,

        font: &str,

        script: u32,

        lang: u32,

        direction: TextDirection,

    ) -> Result<Vec<GlyphPosition>, Box<dyn Error>> {

        get_positions_with_gpos_features(

            text,

            font,

            script,

            lang,

            FeatureMask::default_mask(),

            direction,

            false,

        )

    }

    fn get_positions_with_gpos_features(

        text: &str,

        font: &str,

        script: u32,

        lang: u32,

        feature_mask: FeatureMask,

        direction: TextDirection,

        vertical: bool,

    ) -> Result<Vec<GlyphPosition>, Box<dyn Error>> {

        let path = Path::new("tests/fonts").join(font);

        let data = read_fixture(&path);

        let scope = ReadScope::new(&data);

        let font_file = scope.read::<FontData<'_>>()?;

        let provider = font_file.table_provider(0)?;

        let mut font = Font::new(provider)?;

        // Map text to glyphs and then apply font shaping

        let glyphs = font.map_glyphs(text, script, MatchingPresentation::NotRequired);

        let infos = font

            .shape(glyphs, script, Some(lang), feature_mask, &[], None, true)

            .map_err(|(err, _info)| err)?;

        let mut layout = GlyphLayout::new(&mut font, &infos, direction, vertical);

        layout.glyph_positions().map_err(|err| err.into())

    }

    #[test]

    fn ltr_kerning() -> Result<(), Box<dyn Error>> {

        let script = tag::LATN;

        let lang = tag!(b"ENG ");

        // V gets kerned closer to A in AV

        let positions = get_positions(

            "AV AA",

            "opentype/Klei.otf",

            script,

            lang,

            TextDirection::LeftToRight,

        )?;

        let expected = &[

            GlyphPosition {

                hori_advance: 597,

                ..Default::default()

            },

            GlyphPosition {

                hori_advance: 758,

                ..Default::default()

            },

            GlyphPosition {

                hori_advance: 280,

                ..Default::default()

            },

            GlyphPosition {

                hori_advance: 777,

                ..Default::default()

            },

            GlyphPosition {

                hori_advance: 777,

                ..Default::default()

            },

        ];

        assert_eq!(positions, expected);

        Ok(())

    }

    #[test]

    fn ltr_mark_attach() -> Result<(), Box<dyn Error>> {

        let script = tag::KNDA;

        let lang = tag!(b"KAN ");

        // U+0CBC is a mark on U+0C9F

        let positions = get_positions(

            "\u{0C9F}\u{0CBC}",

            "noto/NotoSansKannada-Regular.ttf",

            script,

            lang,

            TextDirection::LeftToRight,

        )?;

        let expected = &[

            GlyphPosition {

                hori_advance: 1669,

                ..Default::default()

            },

            GlyphPosition {

                x_offset: -260,

                ..Default::default()

            },

        ];

        assert_eq!(positions, expected);

        Ok(())

    }

    #[test]

    fn ltr_attach_distance() -> Result<(), Box<dyn Error>> {

        let script = tag!(b"latn");

        let lang = tag!(b"ENG ");

        let feature_mask = FeatureMask::default_mask() | Feature::FRAC;

        // '⁄' is U+2044 FRACTION SLASH, which when the `frac` GPOS feature is enabled is

        // positioned to be under the previous character and above the next.

        let positions = get_positions_with_gpos_features(

            "1⁄99",

            "opentype/SourceCodePro-Regular.otf",

            script,

            lang,

            feature_mask,

            TextDirection::LeftToRight,

            false,

        )?;

        let expected = &[

            GlyphPosition {

                hori_advance: 600,

                ..Default::default()

            },

            GlyphPosition {

                hori_advance: 0,

                x_offset: -300,

                ..Default::default()

            },

            GlyphPosition {

                hori_advance: 600,

                ..Default::default()

            },

            GlyphPosition {

                hori_advance: 600,

                ..Default::default()

            },

        ];

        assert_eq!(positions, expected);

        Ok(())

    }

    #[test]

    fn ltr_mark_overprint() -> Result<(), Box<dyn Error>> {

        let script = tag::LATN;

        let lang = tag!(b"ENG ");

        // TerminusTTF does not have GPOS or GSUB tables. As a result it hits the fallback mark

        // handling code that results in characters belonging to the Nonspacing Mark General

        // Category to be Mark::Overprint. Combining characters are examples of such characters.

        // This test is 'a' followed by COMBINING TILDE.

        let positions = get_positions(

            "a\u{0303}",

            "opentype/TerminusTTF-4.47.0.ttf",

            script,

            lang,

            TextDirection::LeftToRight,

        )?;

        let expected = &[

            GlyphPosition {

                hori_advance: 500,

                ..Default::default()

            },

            GlyphPosition::default(),

        ];

        assert_eq!(positions, expected);

        Ok(())

    }

    #[test]

    fn ltr_cursive() -> Result<(), Box<dyn Error>> {

        let script = tag::KNDA;

        let lang = tag!(b"KAN ");

        // Text is RTL Arabic with cursive connections

        let positions = get_positions(

            "ಇನ್ಫ್ಲೆಕ್ಷನ್",

            "noto/NotoSansKannada-Regular.ttf",

            script,

            lang,

            TextDirection::LeftToRight,

        )?;

        // [8=0+1457|256=1+1456|118=1+346|335=1+791|282=7+1176|186=10+2096]

        let expected = &[

            GlyphPosition {

                hori_advance: 1457,

                ..Default::default()

            },

            GlyphPosition {

                hori_advance: 1456,

                ..Default::default()

            },

            GlyphPosition {

                hori_advance: 346, // This glyph's advance gets adjusted to align with the next one

                ..Default::default()

            },

            GlyphPosition {

                hori_advance: 791,

                ..Default::default()

            },

            GlyphPosition {

                hori_advance: 1176,

                ..Default::default()

            },

            GlyphPosition {

                hori_advance: 2096,

                ..Default::default()

            },

        ];

        assert_eq!(positions, expected);

        Ok(())

    }

    #[test]

    fn rtl_cursive() -> Result<(), Box<dyn Error>> {

        let script = tag::ARAB;

        let lang = tag!(b"URD ");

        // Text is RTL Arabic with cursive connections

        let positions = get_positions(

            "لسان",

            "arabic/NafeesNastaleeq.ttf",

            script,

            lang,

            TextDirection::RightToLeft,

        )?;

        let expected = &[

            GlyphPosition {

                hori_advance: 391,

                y_offset: -409,

                ..Default::default()

            },

            GlyphPosition {

                hori_advance: 989,

                ..Default::default()

            },

            GlyphPosition {

                hori_advance: 213,

                ..Default::default()

            },

            GlyphPosition {

                hori_advance: 1561,

                ..Default::default()

            },

        ];

        assert_eq!(positions, expected);

        Ok(())

    }

}