//! Glyph configuration for scrollbar rendering.

/// Glyphs used to render the track, arrows, and thumb.
///
/// Arrays use indices 0..=7 to represent 1/8th through full coverage.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct GlyphSet {
    /// Track glyph for vertical scrollbars.
    pub track_vertical: char,
    /// Track glyph for horizontal scrollbars.
    pub track_horizontal: char,
    /// Arrow glyph for the start of a vertical scrollbar (top).
    pub arrow_vertical_start: char,
    /// Arrow glyph for the end of a vertical scrollbar (bottom).
    pub arrow_vertical_end: char,
    /// Arrow glyph for the start of a horizontal scrollbar (left).
    pub arrow_horizontal_start: char,
    /// Arrow glyph for the end of a horizontal scrollbar (right).
    pub arrow_horizontal_end: char,
    /// Thumb glyphs for vertical lower fills (1/8th through full).
    pub thumb_vertical_lower: [char; 8],
    /// Thumb glyphs for vertical upper fills (1/8th through full).
    pub thumb_vertical_upper: [char; 8],
    /// Thumb glyphs for horizontal left fills (1/8th through full).
    pub thumb_horizontal_left: [char; 8],
    /// Thumb glyphs for horizontal right fills (1/8th through full).
    pub thumb_horizontal_right: [char; 8],
}

impl GlyphSet {
    /// Minimal glyphs: no visible track by default.
    ///
    /// Choose this when the thumb should stand out by color against a filled background instead of
    /// a visible line.
    ///
    /// This uses a space character for the track so the scrollbar is "all thumb", with the
    /// background color coming from `track_style`.
    ///
    /// ```plain
    /// [██      ]
    /// [🮋█▏     ]
    /// [🮊█▎     ]
    /// [🮉█▍     ]
    /// [▐█▌     ]
    /// [🮈█▋     ]
    /// [🮇█▊     ]
    /// [▕█▉     ]
    /// [ ██     ]
    /// ```
    pub const fn minimal() -> Self {
        let mut glyphs = Self::symbols_for_legacy_computing();
        glyphs.track_vertical = ' ';
        glyphs.track_horizontal = ' ';
        glyphs
    }

    /// Glyphs that include box-drawing line symbols for the track.
    ///
    /// Choose this when callers should see a visible track line behind the thumb.
    ///
    /// ```plain
    /// [██──────]
    /// [🮋█▏─────]
    /// [🮊█▎─────]
    /// [🮉█▍─────]
    /// [▐█▌─────]
    /// [🮈█▋─────]
    /// [🮇█▊─────]
    /// [▕█▉─────]
    /// [─██─────]
    /// ```
    pub const fn box_drawing() -> Self {
        Self::symbols_for_legacy_computing()
    }

    /// Glyphs that mix standard block elements with legacy supplement glyphs.
    ///
    /// Choose this when the terminal font supports [Symbols for Legacy Computing] and you want
    /// precise 1/8th-cell rendering on every thumb edge.
    ///
    /// Use this to get full 1/8th coverage for upper and right edges that the standard block set
    /// lacks; these glyphs come from [Symbols for Legacy Computing].
    ///
    /// ```plain
    /// [██──────]
    /// [🮋█▏─────]
    /// [🮊█▎─────]
    /// [🮉█▍─────]
    /// [▐█▌─────]
    /// [🮈█▋─────]
    /// [🮇█▊─────]
    /// [▕█▉─────]
    /// [─██─────]
    /// ```
    ///
    /// [Symbols for Legacy Computing]: https://en.wikipedia.org/wiki/Symbols_for_Legacy_Computing
    pub const fn symbols_for_legacy_computing() -> Self {
        let vertical_lower = ['▁', '▂', '▃', '▄', '▅', '▆', '▇', '█'];
        let vertical_upper = ['▔', '🮂', '🮃', '▀', '🮄', '🮅', '🮆', '█'];
        let horizontal_left = ['▏', '▎', '▍', '▌', '▋', '▊', '▉', '█'];
        let horizontal_right = ['▕', '🮇', '🮈', '▐', '🮉', '🮊', '🮋', '█'];
        Self {
            track_vertical: '│',
            track_horizontal: '─',
            arrow_vertical_start: '▲',
            arrow_vertical_end: '▼',
            arrow_horizontal_start: '◀',
            arrow_horizontal_end: '▶',
            thumb_vertical_lower: vertical_lower,
            thumb_vertical_upper: vertical_upper,
            thumb_horizontal_left: horizontal_left,
            thumb_horizontal_right: horizontal_right,
        }
    }

    /// Glyphs using only standard Unicode block elements.
    ///
    /// Choose this if your font lacks the legacy glyphs.
    ///
    /// The standard block set does not include 1/8th upper or right fills (those come from
    /// [Symbols for Legacy Computing]), so this set approximates upper and right partials by
    /// rounding to coarse blocks:
    ///
    /// - ~1/4: `▔` / `▕`
    /// - ~1/2 and ~3/4: `▀` / `▐`
    /// - ~7/8 and full: `█`
    ///
    /// ```plain
    /// [██──────]
    /// [██▏─────]
    /// [▐█▎─────]
    /// [▐█▍─────]
    /// [▐█▌─────]
    /// [▐█▋─────]
    /// [▕█▊─────]
    /// [▕█▉─────]
    /// [─██─────]
    /// ```
    ///
    /// [Symbols for Legacy Computing]: https://en.wikipedia.org/wiki/Symbols_for_Legacy_Computing
    pub const fn unicode() -> Self {
        let vertical_lower = ['▁', '▂', '▃', '▄', '▅', '▆', '▇', '█'];
        let vertical_upper = ['▔', '▔', '▀', '▀', '▀', '▀', '█', '█'];
        let horizontal_left = ['▏', '▎', '▍', '▌', '▋', '▊', '▉', '█'];
        let horizontal_right = ['▕', '▕', '▐', '▐', '▐', '▐', '█', '█'];
        Self {
            track_vertical: '│',
            track_horizontal: '─',
            arrow_vertical_start: '▲',
            arrow_vertical_end: '▼',
            arrow_horizontal_start: '◀',
            arrow_horizontal_end: '▶',
            thumb_vertical_lower: vertical_lower,
            thumb_vertical_upper: vertical_upper,
            thumb_horizontal_left: horizontal_left,
            thumb_horizontal_right: horizontal_right,
        }
    }
}

impl Default for GlyphSet {
    fn default() -> Self {
        Self::minimal()
    }
}
