zcatgui/src/render/ttf.zig

//! TTF Font Support
//!
//! TrueType font loading and rendering support.
//! Uses zcatttf library for parsing and rasterization.
//!
//! Features:
//! - Load TTF files from memory or file
//! - Rasterize glyphs at any size with antialiasing
//! - Glyph caching for performance

const std = @import("std");
const Allocator = std.mem.Allocator;

const Style = @import("../core/style.zig");
const Layout = @import("../core/layout.zig");
const Framebuffer = @import("framebuffer.zig").Framebuffer;

// Use zcatttf library for TTF parsing and rasterization
const zcatttf = @import("zcatttf");

const Color = Style.Color;
const Rect = Layout.Rect;

// =============================================================================
// TTF Data Types (compatibility layer)
// =============================================================================

/// Glyph metrics
pub const GlyphMetrics = struct {
    /// Width of the glyph bitmap
    width: u16 = 0,
    /// Height of the glyph bitmap
    height: u16 = 0,
    /// X bearing (left side bearing)
    bearing_x: i16 = 0,
    /// Y bearing (top side bearing from baseline)
    bearing_y: i16 = 0,
    /// Advance width to next character
    advance: u16 = 0,
};

/// Cached glyph
const CachedGlyph = struct {
    /// Bitmap data (alpha values 0-255)
    bitmap: []u8,
    /// Metrics
    metrics: GlyphMetrics,
    /// Character code
    codepoint: u32,
};

/// Font metrics
pub const FontMetrics = struct {
    /// Ascent (above baseline)
    ascent: i16 = 0,
    /// Descent (below baseline, typically negative)
    descent: i16 = 0,
    /// Line gap
    line_gap: i16 = 0,
    /// Units per em
    units_per_em: u16 = 2048,
};

// =============================================================================
// TTF Font (wrapper around zcatttf)
// =============================================================================

/// TrueType font
pub const TtfFont = struct {
    allocator: Allocator,

    /// zcatttf font instance
    font: zcatttf.Font,

    /// Raw font data (kept for reference)
    data: []const u8,
    /// Whether we own the data
    owns_data: bool = false,

    /// Font metrics (cached)
    metrics: FontMetrics = .{},

    /// Number of glyphs
    num_glyphs: u16 = 0,

    /// Glyph cache (for rendered glyphs)
    glyph_cache: std.AutoHashMap(u64, CachedGlyph),

    /// Current render size
    render_size: u16 = 16,

    /// Scale factor for current size
    scale: f32 = 1.0,

    // Legacy fields for compatibility (populated from zcatttf)
    cmap_offset: u32 = 0,
    glyf_offset: u32 = 0,
    loca_offset: u32 = 0,
    index_to_loc_format: i16 = 0,

    const Self = @This();

    /// Load font from file
    pub fn loadFromFile(allocator: Allocator, path: []const u8) !Self {
        const file = try std.fs.cwd().openFile(path, .{});
        defer file.close();

        const stat = try file.stat();
        const data = try allocator.alloc(u8, stat.size);

        const bytes_read = try file.readAll(data);
        if (bytes_read != stat.size) {
            allocator.free(data);
            return error.IncompleteRead;
        }

        var ttf = try initFromMemory(allocator, data);
        ttf.owns_data = true;
        return ttf;
    }

    /// Initialize font from memory
    pub fn initFromMemory(allocator: Allocator, data: []const u8) !Self {
        // Initialize zcatttf font
        var font = try zcatttf.Font.init(allocator, data);

        // Get vertical metrics
        const vmetrics = font.getVMetrics();

        var self = Self{
            .allocator = allocator,
            .font = font,
            .data = data,
            .glyph_cache = std.AutoHashMap(u64, CachedGlyph).init(allocator),
            .num_glyphs = font.getNumGlyphs(),
            .metrics = FontMetrics{
                .ascent = vmetrics.ascender,
                .descent = vmetrics.descender,
                .line_gap = vmetrics.line_gap,
                .units_per_em = font.getUnitsPerEm(),
            },
        };

        self.setSize(16);
        return self;
    }

    /// Initialize from embedded font (DroidSans)
    pub fn initEmbedded(allocator: Allocator) !Self {
        const embedded = @import("embedded_font.zig");
        return initFromMemory(allocator, embedded.font_data);
    }

    /// Deinitialize font
    pub fn deinit(self: *Self) void {
        // Free cached glyphs
        var it = self.glyph_cache.iterator();
        while (it.next()) |entry| {
            self.allocator.free(entry.value_ptr.bitmap);
        }
        self.glyph_cache.deinit();

        // Deinit zcatttf font
        self.font.deinit();

        // Free data if we own it
        if (self.owns_data) {
            self.allocator.free(@constCast(self.data));
        }
    }

    /// Set render size
    pub fn setSize(self: *Self, size: u16) void {
        self.render_size = size;
        self.scale = @as(f32, @floatFromInt(size)) / @as(f32, @floatFromInt(self.metrics.units_per_em));
        self.font.setPixelHeight(@floatFromInt(size));
    }

    /// Get glyph index for codepoint
    pub fn getGlyphIndex(self: Self, codepoint: u32) u16 {
        return self.font.getGlyphIndex(@intCast(codepoint));
    }

    /// Get horizontal metrics for glyph
    pub fn getHMetrics(self: Self, glyph_index: u16) struct { advance: u16, lsb: i16 } {
        const hm = self.font.getScaledHMetrics(glyph_index);
        return .{
            .advance = @intFromFloat(hm.advance_width),
            .lsb = @intFromFloat(hm.left_side_bearing),
        };
    }

    /// Get glyph metrics (scaled)
    pub fn getGlyphMetrics(self: Self, codepoint: u32) GlyphMetrics {
        const glyph_index = self.getGlyphIndex(codepoint);
        const h_metrics = self.getHMetrics(glyph_index);

        return GlyphMetrics{
            .advance = h_metrics.advance,
            .bearing_x = h_metrics.lsb,
        };
    }

    /// Get text width
    pub fn textWidth(self: Self, text: []const u8) u32 {
        var width: u32 = 0;
        var i: usize = 0;
        while (i < text.len) {
            const codepoint = decodeUtf8(text[i..]) orelse {
                i += 1;
                continue;
            };
            const metrics = self.getGlyphMetrics(codepoint.char);
            width += metrics.advance;
            i += codepoint.len;
        }
        return width;
    }

    /// Get line height
    pub fn lineHeight(self: Self) u32 {
        const vm = self.font.getScaledVMetrics();
        return @intFromFloat(vm.ascender - vm.descender + vm.line_gap);
    }

    /// Get ascent (scaled)
    pub fn ascent(self: Self) i32 {
        const vm = self.font.getScaledVMetrics();
        return @intFromFloat(vm.ascender);
    }

    /// Get descent (scaled)
    pub fn descent(self: Self) i32 {
        const vm = self.font.getScaledVMetrics();
        return @intFromFloat(vm.descender);
    }

    /// Draw text using TTF font with real glyph rasterization
    pub fn drawText(
        self: *Self,
        fb: *Framebuffer,
        x: i32,
        y: i32,
        text: []const u8,
        color: Color,
        clip: Rect,
    ) void {
        var cx = x;
        const baseline_y = y + self.ascent();

        var i: usize = 0;
        while (i < text.len) {
            // Decode UTF-8
            const decoded = decodeUtf8(text[i..]) orelse {
                i += 1;
                continue;
            };
            const codepoint = decoded.char;
            i += decoded.len;

            if (codepoint == '\n') continue;
            if (codepoint == ' ') {
                const metrics = self.getGlyphMetrics(codepoint);
                cx += @intCast(metrics.advance);
                continue;
            }

            // Try to get cached glyph or rasterize
            const cache_key = makeCacheKey(codepoint, self.render_size);

            if (self.glyph_cache.get(cache_key)) |cached| {
                // Draw cached glyph
                self.drawGlyphBitmap(fb, cx, baseline_y, cached, color, clip);
                cx += @intCast(cached.metrics.advance);
            } else {
                // Rasterize using zcatttf
                const glyph_index = self.getGlyphIndex(codepoint);
                if (glyph_index == 0) continue;

                if (self.font.rasterizeGlyph(glyph_index)) |bitmap| {
                    var bitmap_mut = bitmap;
                    defer bitmap_mut.deinit();

                    // Copy bitmap data for cache
                    const bitmap_data = self.allocator.alloc(u8, bitmap.data.len) catch continue;
                    @memcpy(bitmap_data, bitmap.data);

                    const cached_glyph = CachedGlyph{
                        .bitmap = bitmap_data,
                        .metrics = GlyphMetrics{
                            .width = @intCast(bitmap.width),
                            .height = @intCast(bitmap.height),
                            .bearing_x = @intCast(bitmap.x_offset),
                            .bearing_y = @intCast(bitmap.y_offset),
                            .advance = @intFromFloat(bitmap.advance_width),
                        },
                        .codepoint = codepoint,
                    };

                    self.glyph_cache.put(cache_key, cached_glyph) catch {};
                    self.drawGlyphBitmap(fb, cx, baseline_y, cached_glyph, color, clip);
                    cx += @intCast(cached_glyph.metrics.advance);
                } else |_| {
                    // Rasterization failed, skip character
                    const metrics = self.getGlyphMetrics(codepoint);
                    cx += @intCast(metrics.advance);
                }
            }
        }
    }

    /// Draw a cached glyph bitmap with alpha blending
    /// Optimized: pre-calculate visible region, direct pixel access
    fn drawGlyphBitmap(
        self: Self,
        fb: *Framebuffer,
        x: i32,
        baseline_y: i32,
        glyph: CachedGlyph,
        color: Color,
        clip: Rect,
    ) void {
        @setRuntimeSafety(false); // Hot path: bounds validated in visible region calculation
        _ = self;

        const width: u32 = glyph.metrics.width;
        const height: u32 = glyph.metrics.height;
        if (width == 0 or height == 0) return;

        // Calculate glyph position
        const glyph_x = x + glyph.metrics.bearing_x;
        const glyph_y = baseline_y - glyph.metrics.bearing_y;

        // Early exit: entire glyph outside clip or framebuffer
        const glyph_right = glyph_x + @as(i32, @intCast(width));
        const glyph_bottom = glyph_y + @as(i32, @intCast(height));
        const clip_right = clip.x + @as(i32, @intCast(clip.w));
        const clip_bottom = clip.y + @as(i32, @intCast(clip.h));

        if (glyph_right <= clip.x or glyph_x >= clip_right) return;
        if (glyph_bottom <= clip.y or glyph_y >= clip_bottom) return;
        if (glyph_right <= 0 or glyph_x >= @as(i32, @intCast(fb.width))) return;
        if (glyph_bottom <= 0 or glyph_y >= @as(i32, @intCast(fb.height))) return;

        // Calculate visible region (intersection of glyph, clip, and framebuffer)
        const vis_x0 = @max(0, @max(glyph_x, clip.x));
        const vis_y0 = @max(0, @max(glyph_y, clip.y));
        const vis_x1 = @min(@as(i32, @intCast(fb.width)), @min(glyph_right, clip_right));
        const vis_y1 = @min(@as(i32, @intCast(fb.height)), @min(glyph_bottom, clip_bottom));

        if (vis_x0 >= vis_x1 or vis_y0 >= vis_y1) return;

        // Precompute color for blending (u32 to avoid per-pixel struct creation)
        const color_r: u32 = color.r;
        const color_g: u32 = color.g;
        const color_b: u32 = color.b;
        const color_packed = color.toABGR();

        // Draw only visible region with direct pixel access
        var screen_y = vis_y0;
        while (screen_y < vis_y1) : (screen_y += 1) {
            const glyph_py: u32 = @intCast(screen_y - glyph_y);
            const dst_row: u32 = @intCast(screen_y);
            const dst_row_start = dst_row * fb.width;
            const src_row_start = glyph_py * width;

            var screen_x = vis_x0;
            while (screen_x < vis_x1) : (screen_x += 1) {
                const glyph_px: u32 = @intCast(screen_x - glyph_x);
                const alpha = glyph.bitmap[src_row_start + glyph_px];
                if (alpha == 0) continue;

                const dst_idx = dst_row_start + @as(u32, @intCast(screen_x));

                if (alpha == 255) {
                    // Fully opaque: direct write
                    fb.pixels[dst_idx] = color_packed;
                } else {
                    // Alpha blend with direct u32 math
                    const bg = fb.pixels[dst_idx];
                    const bg_r: u32 = bg & 0xFF;
                    const bg_g: u32 = (bg >> 8) & 0xFF;
                    const bg_b: u32 = (bg >> 16) & 0xFF;

                    const a: u32 = alpha;
                    const inv_a: u32 = 255 - a;

                    const out_r: u8 = @intCast((color_r * a + bg_r * inv_a) / 255);
                    const out_g: u8 = @intCast((color_g * a + bg_g * inv_a) / 255);
                    const out_b: u8 = @intCast((color_b * a + bg_b * inv_a) / 255);

                    fb.pixels[dst_idx] = @as(u32, out_r) | (@as(u32, out_g) << 8) | (@as(u32, out_b) << 16) | (0xFF << 24);
                }
            }
        }
    }
};

/// Create cache key from codepoint and size
fn makeCacheKey(codepoint: u32, size: u16) u64 {
    return (@as(u64, codepoint) << 16) | @as(u64, size);
}

/// Blend foreground color with background using alpha
fn blendColors(fg: Color, bg: Color, alpha: u8) Color {
    const a = @as(u16, alpha);
    const inv_a = 255 - a;

    return Color{
        .r = @intCast((@as(u16, fg.r) * a + @as(u16, bg.r) * inv_a) / 255),
        .g = @intCast((@as(u16, fg.g) * a + @as(u16, bg.g) * inv_a) / 255),
        .b = @intCast((@as(u16, fg.b) * a + @as(u16, bg.b) * inv_a) / 255),
        .a = 255,
    };
}

/// Decode UTF-8 codepoint from byte slice
fn decodeUtf8(bytes: []const u8) ?struct { char: u32, len: usize } {
    if (bytes.len == 0) return null;

    const b0 = bytes[0];

    // ASCII (0xxxxxxx)
    if (b0 < 0x80) {
        return .{ .char = b0, .len = 1 };
    }

    // 2-byte sequence (110xxxxx 10xxxxxx)
    if (b0 >= 0xC0 and b0 < 0xE0) {
        if (bytes.len < 2) return null;
        const b1 = bytes[1];
        if ((b1 & 0xC0) != 0x80) return null;
        const char = (@as(u32, b0 & 0x1F) << 6) | @as(u32, b1 & 0x3F);
        return .{ .char = char, .len = 2 };
    }

    // 3-byte sequence (1110xxxx 10xxxxxx 10xxxxxx)
    if (b0 >= 0xE0 and b0 < 0xF0) {
        if (bytes.len < 3) return null;
        const b1 = bytes[1];
        const b2 = bytes[2];
        if ((b1 & 0xC0) != 0x80 or (b2 & 0xC0) != 0x80) return null;
        const char = (@as(u32, b0 & 0x0F) << 12) | (@as(u32, b1 & 0x3F) << 6) | @as(u32, b2 & 0x3F);
        return .{ .char = char, .len = 3 };
    }

    // 4-byte sequence (11110xxx 10xxxxxx 10xxxxxx 10xxxxxx)
    if (b0 >= 0xF0 and b0 < 0xF8) {
        if (bytes.len < 4) return null;
        const b1 = bytes[1];
        const b2 = bytes[2];
        const b3 = bytes[3];
        if ((b1 & 0xC0) != 0x80 or (b2 & 0xC0) != 0x80 or (b3 & 0xC0) != 0x80) return null;
        const char = (@as(u32, b0 & 0x07) << 18) | (@as(u32, b1 & 0x3F) << 12) | (@as(u32, b2 & 0x3F) << 6) | @as(u32, b3 & 0x3F);
        return .{ .char = char, .len = 4 };
    }

    return null;
}

// =============================================================================
// Font Interface - Unified API for both bitmap and TTF fonts
// =============================================================================

/// Font type tag
pub const FontType = enum {
    bitmap,
    ttf,
};

/// Unified font reference
pub const FontRef = union(FontType) {
    bitmap: *const @import("font.zig").Font,
    ttf: *TtfFont,

    pub fn textWidth(self: FontRef, text: []const u8) u32 {
        return switch (self) {
            .bitmap => |f| f.textWidth(text),
            .ttf => |f| f.textWidth(text),
        };
    }

    pub fn charHeight(self: FontRef) u32 {
        return switch (self) {
            .bitmap => |f| f.charHeight(),
            .ttf => |f| f.lineHeight(),
        };
    }

    pub fn drawText(
        self: FontRef,
        fb: *Framebuffer,
        x: i32,
        y: i32,
        text: []const u8,
        color: Color,
        clip: Rect,
    ) void {
        switch (self) {
            .bitmap => |f| f.drawText(fb, x, y, text, color, clip),
            .ttf => |f| @constCast(f).drawText(fb, x, y, text, color, clip),
        }
    }
};

// =============================================================================
// Legacy exports for compatibility
// =============================================================================

/// Rasterized glyph bitmap (legacy, for code that uses this directly)
pub const GlyphBitmap = struct {
    data: []u8,
    width: u32,
    height: u32,
    bearing_x: i32,
    bearing_y: i32,
    allocator: Allocator,

    pub fn deinit(self: *GlyphBitmap) void {
        self.allocator.free(self.data);
    }
};

// =============================================================================
// Tests
// =============================================================================

test "TTF types" {
    const metrics = GlyphMetrics{
        .width = 10,
        .height = 12,
        .bearing_x = 1,
        .bearing_y = 10,
        .advance = 8,
    };

    try std.testing.expectEqual(@as(u16, 10), metrics.width);
    try std.testing.expectEqual(@as(u16, 8), metrics.advance);
}

test "FontRef bitmap" {
    const bitmap_font = @import("font.zig");
    const font_ref = FontRef{ .bitmap = &bitmap_font.default_font };

    try std.testing.expectEqual(@as(u32, 40), font_ref.textWidth("Hello"));
    try std.testing.expectEqual(@as(u32, 8), font_ref.charHeight());
}

test "decodeUtf8" {
    // ASCII
    const ascii = decodeUtf8("A").?;
    try std.testing.expectEqual(@as(u32, 'A'), ascii.char);
    try std.testing.expectEqual(@as(usize, 1), ascii.len);

    // 2-byte (é = 0xC3 0xA9)
    const e_acute = decodeUtf8("\xC3\xA9").?;
    try std.testing.expectEqual(@as(u32, 0xE9), e_acute.char);
    try std.testing.expectEqual(@as(usize, 2), e_acute.len);

    // 3-byte (€ = 0xE2 0x82 0xAC)
    const euro = decodeUtf8("\xE2\x82\xAC").?;
    try std.testing.expectEqual(@as(u32, 0x20AC), euro.char);
    try std.testing.expectEqual(@as(usize, 3), euro.len);
}

test "TtfFont with zcatttf" {
    const allocator = std.testing.allocator;

    // Try to load DroidSans from system
    var font = TtfFont.loadFromFile(allocator, "/usr/share/fonts/google-droid-sans-fonts/DroidSans.ttf") catch {
        // Font not available on this system, skip test
        return;
    };
    defer font.deinit();

    // Verify font was loaded
    try std.testing.expect(font.num_glyphs > 0);
    try std.testing.expect(font.metrics.units_per_em > 0);

    // Get glyph index for 'A'
    const glyph_index = font.getGlyphIndex('A');
    try std.testing.expect(glyph_index > 0);

    // Get metrics
    const metrics = font.getGlyphMetrics('A');
    try std.testing.expect(metrics.advance > 0);

    // Test text width
    const width = font.textWidth("Hello");
    try std.testing.expect(width > 0);
}