parse

pub fn parse(comptime bytes: []const u8) Placeholder {
    var parser: Parser = .{ .bytes = bytes, .i = 0 };
    const arg = parser.specifier() catch |err| @compileError(@errorName(err));
    const specifier_arg = parser.until(':');
    if (parser.char()) |b| {
        if (b != ':') @compileError("expected : or }, found '" ++ &[1]u8{b} ++ "'");
    }

    // Parse the fill byte, if present.
    //
    // When the width field is also specified, the fill byte must
    // be followed by an alignment specifier, unless it's '0' (zero)
    // (in which case it's handled as part of the width specifier).
    var fill: ?u8 = if (parser.peek(1)) |b|
        switch (b) {
            '<', '^', '>' => parser.char(),
            else => null,
        }
    else
        null;

    // Parse the alignment parameter
    const alignment: ?Alignment = if (parser.peek(0)) |b| init: {
        switch (b) {
            '<', '^', '>' => {
                // consume the character
                break :init switch (parser.char().?) {
                    '<' => .left,
                    '^' => .center,
                    else => .right,
                };
            },
            else => break :init null,
        }
    } else null;

    // When none of the fill character and the alignment specifier have
    // been provided, check whether the width starts with a zero.
    if (fill == null and alignment == null) {
        fill = if (parser.peek(0) == '0') '0' else null;
    }

    // Parse the width parameter
    const width = parser.specifier() catch |err| @compileError(@errorName(err));

    // Skip the dot, if present
    if (parser.char()) |b| {
        if (b != '.') @compileError("expected . or }, found '" ++ &[1]u8{b} ++ "'");
    }

    // Parse the precision parameter
    const precision = parser.specifier() catch |err| @compileError(@errorName(err));

    if (parser.char()) |b| @compileError("extraneous trailing character '" ++ &[1]u8{b} ++ "'");

    const specifier_array = specifier_arg[0..specifier_arg.len].*;

    return .{
        .specifier_arg = &specifier_array,
        .fill = fill orelse default_fill_char,
        .alignment = alignment orelse default_alignment,
        .arg = arg,
        .width = width,
        .precision = precision,
    };
}