ag-psd 0.1.0

/*
File: crates/ag-psd/src/helpers.rs

Purpose:
общие хелперы крейта: числовые/цветовые утилиты, таблицы соответствия blend mode
<-> 4-символьный ключ, layerColors, упаковка/распаковка данных каналов
(raw / RLE / zip-without-prediction), а также заглушки canvas-уровня.

Source compatibility:
- порт upstream-файла `test/ag-psd/src/helpers.ts` (разбиение 1:1).

Main responsibilities:
- зеркалировать соответствующий upstream-модуль при портировании;
- держать публичный контракт этого участка в одном месте.

PORT STATUS: ported except browser-canvas concerns
  (create_canvas / create_image_data / image_data_to_canvas / create_canvas_from_data /
   initialize_canvas стабированы под модель PixelData, см. пометки ниже).
*/

use std::collections::HashMap;

use flate2::{write::ZlibEncoder, Compression as FlateCompression};
use std::io::Write as _;

use crate::psd::{BlendMode, ChannelId, Compression, Layer, LayerColor, PixelData};

/// upstream: `export const MOCK_HANDLERS = false;`
pub const MOCK_HANDLERS: bool = false;
/// upstream: `export const RAW_IMAGE_DATA = false;`
pub const RAW_IMAGE_DATA: bool = false;

// ===========================================================================
// Blend mode <-> 4-char key mapping tables
// ===========================================================================

/// upstream `toBlendMode`: 4-символьный ключ -> BlendMode.
/// Сохранены ВСЕ записи и точные ключи (включая пробелы), это критично для формата.
pub fn to_blend_mode(key: &str) -> Option<BlendMode> {
    Some(match key {
        "pass" => BlendMode::PassThrough,
        "norm" => BlendMode::Normal,
        "diss" => BlendMode::Dissolve,
        "dark" => BlendMode::Darken,
        "mul " => BlendMode::Multiply,
        "idiv" => BlendMode::ColorBurn,
        "lbrn" => BlendMode::LinearBurn,
        "dkCl" => BlendMode::DarkerColor,
        "lite" => BlendMode::Lighten,
        "scrn" => BlendMode::Screen,
        "div " => BlendMode::ColorDodge,
        "lddg" => BlendMode::LinearDodge,
        "lgCl" => BlendMode::LighterColor,
        "over" => BlendMode::Overlay,
        "sLit" => BlendMode::SoftLight,
        "hLit" => BlendMode::HardLight,
        "vLit" => BlendMode::VividLight,
        "lLit" => BlendMode::LinearLight,
        "pLit" => BlendMode::PinLight,
        "hMix" => BlendMode::HardMix,
        "diff" => BlendMode::Difference,
        "smud" => BlendMode::Exclusion,
        "fsub" => BlendMode::Subtract,
        "fdiv" => BlendMode::Divide,
        "hue " => BlendMode::Hue,
        "sat " => BlendMode::Saturation,
        "colr" => BlendMode::Color,
        "lum " => BlendMode::Luminosity,
        _ => return None,
    })
}

/// upstream `fromBlendMode` (построен через
/// `Object.keys(toBlendMode).forEach(key => fromBlendMode[toBlendMode[key]] = key)`):
/// BlendMode -> 4-символьный ключ. Это обратное отображение `to_blend_mode`.
pub fn from_blend_mode(mode: BlendMode) -> &'static str {
    match mode {
        BlendMode::PassThrough => "pass",
        BlendMode::Normal => "norm",
        BlendMode::Dissolve => "diss",
        BlendMode::Darken => "dark",
        BlendMode::Multiply => "mul ",
        BlendMode::ColorBurn => "idiv",
        BlendMode::LinearBurn => "lbrn",
        BlendMode::DarkerColor => "dkCl",
        BlendMode::Lighten => "lite",
        BlendMode::Screen => "scrn",
        BlendMode::ColorDodge => "div ",
        BlendMode::LinearDodge => "lddg",
        BlendMode::LighterColor => "lgCl",
        BlendMode::Overlay => "over",
        BlendMode::SoftLight => "sLit",
        BlendMode::HardLight => "hLit",
        BlendMode::VividLight => "vLit",
        BlendMode::LinearLight => "lLit",
        BlendMode::PinLight => "pLit",
        BlendMode::HardMix => "hMix",
        BlendMode::Difference => "diff",
        BlendMode::Exclusion => "smud",
        BlendMode::Subtract => "fsub",
        BlendMode::Divide => "fdiv",
        BlendMode::Hue => "hue ",
        BlendMode::Saturation => "sat ",
        BlendMode::Color => "colr",
        BlendMode::Luminosity => "lum ",
    }
}

/// upstream `layerColors`.
pub const LAYER_COLORS: [LayerColor; 8] = [
    LayerColor::None,
    LayerColor::Red,
    LayerColor::Orange,
    LayerColor::Yellow,
    LayerColor::Green,
    LayerColor::Blue,
    LayerColor::Violet,
    LayerColor::Gray,
];

/// upstream `largeAdditionalInfoKeys`.
pub const LARGE_ADDITIONAL_INFO_KEYS: [&str; 14] = [
    // from documentation
    "LMsk", "Lr16", "Lr32", "Layr", "Mt16", "Mt32", "Mtrn", "Alph", "FMsk", "lnk2", "FEid",
    "FXid", "PxSD", // from guessing
    "cinf",
];

// ===========================================================================
// Dict / enum descriptor helpers
// ===========================================================================

/// upstream `Dict` = `{ [key: string]: string }`.
pub type Dict = HashMap<String, String>;

/// upstream `revMap`: меняет местами ключи и значения словаря.
pub fn rev_map(map: &Dict) -> Dict {
    let mut result = Dict::new();
    for (key, value) in map {
        result.insert(value.clone(), key.clone());
    }
    result
}

/// upstream `createEnum<T>`: возвращает пару (decode, encode) для дескрипторного
/// enum вида `prefix.value`. Так как в Rust замыкания неудобно возвращать парой,
/// предоставляем структуру с теми же decode/encode.
pub struct EnumCodec {
    prefix: String,
    def: String,
    map: Dict,
    rev: Dict,
}

impl EnumCodec {
    /// upstream `createEnum(prefix, def, map)`.
    pub fn new(prefix: &str, def: &str, map: Dict) -> Self {
        let rev = rev_map(&map);
        EnumCodec {
            prefix: prefix.to_string(),
            def: def.to_string(),
            map,
            rev,
        }
    }

    /// upstream `decode(val)`: `val.split('.')[1]` -> reverse-lookup -> def.
    /// Бросает (Err) при нераспознанном непустом значении.
    pub fn decode(&self, val: &str) -> Result<String, String> {
        // val.split('.')[1] — второй сегмент (может отсутствовать => "").
        let value = val.split('.').nth(1).unwrap_or("");
        if !value.is_empty() && !self.rev.contains_key(value) {
            return Err(format!("Unrecognized value for enum: '{val}'"));
        }
        Ok(self
            .rev
            .get(value)
            .cloned()
            .unwrap_or_else(|| self.def.clone()))
    }

    /// upstream `encode(val)`: `${prefix}.${map[val] || map[def]}`.
    /// `val == None` зеркалирует `undefined` в TS.
    /// Бросает (Err) при невалидном непустом значении.
    pub fn encode(&self, val: Option<&str>) -> Result<String, String> {
        if let Some(v) = val {
            if !self.map.contains_key(v) {
                return Err(format!("Invalid value for enum: '{v}'"));
            }
        }
        let mapped = val
            .and_then(|v| self.map.get(v))
            .or_else(|| self.map.get(&self.def))
            .cloned()
            .unwrap_or_default();
        Ok(format!("{}.{}", self.prefix, mapped))
    }
}

// ===========================================================================
// Numeric const enums (port of TS `const enum`)
// ===========================================================================

/// upstream `const enum ColorSpace`.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ColorSpace {
    Rgb = 0,
    Hsb = 1,
    Cmyk = 2,
    Lab = 7,
    Grayscale = 8,
}

/// upstream `const enum LayerMaskFlags`.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum LayerMaskFlags {
    PositionRelativeToLayer = 1,
    LayerMaskDisabled = 2,
    /// obsolete
    InvertLayerMaskWhenBlending = 4,
    LayerMaskFromRenderingOtherData = 8,
    MaskHasParametersAppliedToIt = 16,
}

/// upstream `const enum MaskParams`.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum MaskParams {
    UserMaskDensity = 1,
    UserMaskFeather = 2,
    VectorMaskDensity = 4,
    VectorMaskFeather = 8,
}

// ===========================================================================
// Channel / bounds data shapes
// ===========================================================================

/// upstream `ChannelData`.
#[derive(Debug, Clone)]
pub struct ChannelData {
    pub channel_id: ChannelId,
    pub compression: Compression,
    pub buffer: Option<Vec<u8>>,
    pub length: usize,
}

/// upstream `Bounds`.
#[derive(Debug, Clone, Copy, Default)]
pub struct Bounds {
    pub top: i32,
    pub left: i32,
    pub right: i32,
    pub bottom: i32,
}

/// upstream `LayerChannelData`.
pub struct LayerChannelData {
    pub layer: Layer,
    pub channels: Vec<ChannelData>,
    pub top: i32,
    pub left: i32,
    pub right: i32,
    pub bottom: i32,
    pub mask: Option<Bounds>,
    pub real_mask: Option<Bounds>,
}

// ===========================================================================
// Pure numeric helpers
// ===========================================================================

/// upstream `offsetForChannel(channelId, cmyk)`.
/// В TS работает с числовыми значениями enum; здесь повторяем арифметику через i32.
pub fn offset_for_channel(channel_id: ChannelId, cmyk: bool) -> i32 {
    let id = channel_id as i32;
    match channel_id {
        ChannelId::Color0 => 0,
        ChannelId::Color1 => 1,
        ChannelId::Color2 => 2,
        ChannelId::Color3 => {
            if cmyk {
                3
            } else {
                id + 1
            }
        }
        ChannelId::Transparency => {
            if cmyk {
                4
            } else {
                3
            }
        }
        _ => id + 1,
    }
}

/// upstream `clamp(value, min, max)`.
pub fn clamp(value: f64, min: f64, max: f64) -> f64 {
    if value < min {
        min
    } else if value > max {
        max
    } else {
        value
    }
}

/// upstream `hasAlpha(data)`: true, если есть пиксель с alpha != 255.
pub fn has_alpha(data: &PixelData) -> bool {
    let size = (data.width as usize) * (data.height as usize) * 4;
    let mut i = 3usize;
    while i < size {
        if data.data[i] != 255 {
            return true;
        }
        i += 4;
    }
    false
}

/// upstream `resetImageData({ data })`.
/// В оригинале alpha зависит от типа массива (Float32/Uint16/Uint8); наша модель
/// PixelData хранит байты RGBA8, поэтому alpha = 0xff.
pub fn reset_image_data(data: &mut PixelData) {
    let buf = &mut data.data;
    let alpha = 0xffu8;
    let size = buf.len();
    let mut p = 0usize;
    while p < size {
        buf[p] = 0;
        buf[p + 1] = 0;
        buf[p + 2] = 0;
        buf[p + 3] = alpha;
        p += 4;
    }
}

/// upstream `decodeBitmap(input, output, width, height)`.
/// Распаковывает 1-битное изображение в RGBA8: бит=1 -> чёрный (0), бит=0 -> белый (255).
pub fn decode_bitmap(input: &[u8], output: &mut [u8], width: usize, height: usize) {
    let mut p = 0usize;
    let mut o = 0usize;
    for _y in 0..height {
        let mut x = 0usize;
        while x < width {
            let mut b = input[o];
            o += 1;
            let mut i = 0;
            while i < 8 && x < width {
                let v: u8 = if b & 0x80 != 0 { 0 } else { 255 };
                b <<= 1;
                output[p] = v;
                output[p + 1] = v;
                output[p + 2] = v;
                output[p + 3] = 255;
                i += 1;
                x += 1;
                p += 4;
            }
        }
    }
}

// ===========================================================================
// Channel data writers (raw / RLE / zip)
// ===========================================================================

/// upstream `writeDataRaw(data, offset, width, height)`.
/// Извлекает один канал (по offset) в плотный массив длиной width*height.
pub fn write_data_raw(data: &PixelData, offset: usize, width: usize, height: usize) -> Option<Vec<u8>> {
    if width == 0 || height == 0 {
        return None;
    }
    let mut array = vec![0u8; width * height];
    for (i, slot) in array.iter_mut().enumerate() {
        *slot = data.data[i * 4 + offset];
    }
    Some(array)
}

/// upstream `writeDataRLE(buffer, { data, width, height }, offsets, large)`.
/// Сжимает каналы по PackBits, как в оригинале (включая раскладку length-таблицы
/// в начале буфера). Возвращает срез использованной части буфера.
pub fn write_data_rle(
    buffer: &mut [u8],
    data_pixels: &PixelData,
    offsets: &[usize],
    large: bool,
) -> Option<Vec<u8>> {
    let width = data_pixels.width as i64;
    let height = data_pixels.height as i64;
    if width == 0 || height == 0 {
        return None;
    }
    let data = &data_pixels.data;
    let stride = 4 * width;

    let mut ol: i64 = 0;
    let mut o: i64 = (offsets.len() as i64) * (if large { 4 } else { 2 }) * height;

    let get = |idx: i64| -> i64 { data[idx as usize] as i64 };

    // upstream writes into a `Uint8Array`; writing past its end is a silent
    // no-op in JS (the value is simply dropped), and `buffer.slice(0, o)` later
    // returns only the bytes that fit. The buffer is sized by an estimate that
    // can be too small for tiny images (e.g. 1x1 with alpha), so faithfully
    // mirror the TypedArray semantics by ignoring out-of-bounds writes instead
    // of panicking. `o`/`ol` still advance so the returned length matches TS.
    macro_rules! set {
        ($buf:expr, $idx:expr, $val:expr) => {{
            let idx = $idx as usize;
            if idx < $buf.len() {
                $buf[idx] = $val;
            }
        }};
    }

    for &offset in offsets {
        let offset = offset as i64;
        for y in 0..height {
            let stride_start = y * stride;
            let stride_end = stride_start + stride;
            let last_index = stride_end + offset - 4;
            let last_index2 = last_index - 4;
            let start_offset = o;

            let mut p = stride_start + offset;
            while p < stride_end {
                if p < last_index2 {
                    let mut value1 = get(p);
                    p += 4;
                    let mut value2 = get(p);
                    p += 4;
                    let mut value3 = get(p);

                    if value1 == value2 && value1 == value3 {
                        let mut count: i64 = 3;
                        while count < 128 && p < last_index && get(p + 4) == value1 {
                            count += 1;
                            p += 4;
                        }
                        set!(buffer, o, (1 - count) as u8);
                        o += 1;
                        set!(buffer, o, value1 as u8);
                        o += 1;
                    } else {
                        let count_index = o;
                        let mut write_last = true;
                        let mut count: i64 = 1;
                        set!(buffer, o, 0);
                        o += 1;
                        set!(buffer, o, value1 as u8);
                        o += 1;

                        while p < last_index && count < 128 {
                            p += 4;
                            value1 = value2;
                            value2 = value3;
                            value3 = get(p);

                            if value1 == value2 && value1 == value3 {
                                p -= 12;
                                write_last = false;
                                break;
                            } else {
                                count += 1;
                                set!(buffer, o, value1 as u8);
                                o += 1;
                            }
                        }

                        if write_last {
                            if count < 127 {
                                set!(buffer, o, value2 as u8);
                                o += 1;
                                set!(buffer, o, value3 as u8);
                                o += 1;
                                count += 2;
                            } else if count < 128 {
                                set!(buffer, o, value2 as u8);
                                o += 1;
                                count += 1;
                                p -= 4;
                            } else {
                                p -= 8;
                            }
                        }

                        set!(buffer, count_index, (count - 1) as u8);
                    }
                } else if p == last_index {
                    set!(buffer, o, 0);
                    o += 1;
                    set!(buffer, o, get(p) as u8);
                    o += 1;
                } else {
                    // p === lastIndex2
                    set!(buffer, o, 1);
                    o += 1;
                    set!(buffer, o, get(p) as u8);
                    o += 1;
                    p += 4;
                    set!(buffer, o, get(p) as u8);
                    o += 1;
                }

                p += 4;
            }

            let length = o - start_offset;

            if large {
                set!(buffer, ol, ((length >> 24) & 0xff) as u8);
                ol += 1;
                set!(buffer, ol, ((length >> 16) & 0xff) as u8);
                ol += 1;
            }

            set!(buffer, ol, ((length >> 8) & 0xff) as u8);
            ol += 1;
            set!(buffer, ol, (length & 0xff) as u8);
            ol += 1;
        }
    }

    // mirror `buffer.slice(0, o)`: clamp to the buffer length so we never read
    // past the end when the size estimate fell short (out-of-bounds writes above
    // were dropped, so those positions hold zero/stale bytes which TS omits too).
    let end = (o as usize).min(buffer.len());
    Some(buffer[..end].to_vec())
}

/// upstream `writeDataZipWithoutPrediction({ data, width, height }, offsets)`.
/// Извлекает каждый канал и сжимает zlib/deflate, конкатенируя результаты.
pub fn write_data_zip_without_prediction(data_pixels: &PixelData, offsets: &[usize]) -> Option<Vec<u8>> {
    let size = (data_pixels.width as usize) * (data_pixels.height as usize);
    let data = &data_pixels.data;
    let mut channel = vec![0u8; size];
    let mut buffers: Vec<Vec<u8>> = Vec::new();
    let mut total_length = 0usize;

    for &offset in offsets {
        let mut o = offset;
        for slot in channel.iter_mut().take(size) {
            *slot = data[o];
            o += 4;
        }

        let buffer = deflate_sync(&channel);
        total_length += buffer.len();
        buffers.push(buffer);
    }

    if !buffers.is_empty() {
        let mut buffer = Vec::with_capacity(total_length);
        for b in &buffers {
            buffer.extend_from_slice(b);
        }
        Some(buffer)
    } else {
        // upstream возвращает buffers[0] (undefined при пустом списке).
        None
    }
}

/// Эквивалент `deflate` из `pako` (zlib-обёрнутый deflate).
fn deflate_sync(input: &[u8]) -> Vec<u8> {
    let mut encoder = ZlibEncoder::new(Vec::new(), FlateCompression::default());
    encoder.write_all(input).expect("zlib write");
    encoder.finish().expect("zlib finish")
}

// ===========================================================================
// Canvas-уровень — заглушки под модель PixelData
// ===========================================================================

/// upstream `imageDataToCanvas(pixelData)`.
/// TODO: browser-canvas concern. Наша модель уже хранит RGBA8 в PixelData, так что
/// "канвас" — это и есть копия PixelData. Гамма/битность-конверсии оригинала
/// (Float32 pow(1/2.2), Uint16 >>8) не нужны для байтовой модели.
pub fn image_data_to_canvas(pixel_data: &PixelData) -> PixelData {
    pixel_data.clone()
}

/// upstream `createCanvasFromData(data)` — декодирование JPEG в канвас.
/// TODO: browser-canvas concern; зависит от не-портированного `decode_jpeg`.
/// Стаб: возвращает пустой PixelData 100x100, как и стартовый канвас в оригинале.
pub fn create_canvas_from_data(_data: &[u8]) -> PixelData {
    create_canvas(100, 100)
}

/// upstream `createCanvas(width, height)`.
/// TODO: browser-canvas concern, not needed for byte IO. Возвращаем нулевой
/// RGBA8-буфер нужного размера вместо HTMLCanvasElement.
pub fn create_canvas(width: u32, height: u32) -> PixelData {
    PixelData {
        width,
        height,
        data: vec![0u8; (width as usize) * (height as usize) * 4],
    }
}

/// upstream `createImageData(width, height)`.
/// TODO: browser-canvas concern, not needed for byte IO.
pub fn create_image_data(width: u32, height: u32) -> PixelData {
    create_canvas(width, height)
}

/// upstream `initializeCanvas(createCanvasMethod, createImageDataMethod?)`.
/// TODO: browser-canvas concern — установка глобальной фабрики канваса.
/// В байтовой модели не требуется; намеренный no-op.
pub fn initialize_canvas() {
    // no-op
}

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

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn blend_mode_round_trip_all_entries() {
        let all = [
            BlendMode::PassThrough,
            BlendMode::Normal,
            BlendMode::Dissolve,
            BlendMode::Darken,
            BlendMode::Multiply,
            BlendMode::ColorBurn,
            BlendMode::LinearBurn,
            BlendMode::DarkerColor,
            BlendMode::Lighten,
            BlendMode::Screen,
            BlendMode::ColorDodge,
            BlendMode::LinearDodge,
            BlendMode::LighterColor,
            BlendMode::Overlay,
            BlendMode::SoftLight,
            BlendMode::HardLight,
            BlendMode::VividLight,
            BlendMode::LinearLight,
            BlendMode::PinLight,
            BlendMode::HardMix,
            BlendMode::Difference,
            BlendMode::Exclusion,
            BlendMode::Subtract,
            BlendMode::Divide,
            BlendMode::Hue,
            BlendMode::Saturation,
            BlendMode::Color,
            BlendMode::Luminosity,
        ];
        for mode in all {
            let key = from_blend_mode(mode);
            assert_eq!(key.len(), 4, "key must be 4 chars: {key:?}");
            assert_eq!(to_blend_mode(key), Some(mode), "round trip failed for {key:?}");
        }
    }

    #[test]
    fn blend_mode_spacey_keys() {
        assert_eq!(to_blend_mode("mul "), Some(BlendMode::Multiply));
        assert_eq!(to_blend_mode("div "), Some(BlendMode::ColorDodge));
        assert_eq!(from_blend_mode(BlendMode::Luminosity), "lum ");
        assert_eq!(to_blend_mode("nope"), None);
    }

    #[test]
    fn clamp_edges() {
        assert_eq!(clamp(-1.0, 0.0, 10.0), 0.0);
        assert_eq!(clamp(11.0, 0.0, 10.0), 10.0);
        assert_eq!(clamp(5.0, 0.0, 10.0), 5.0);
        assert_eq!(clamp(0.0, 0.0, 10.0), 0.0);
        assert_eq!(clamp(10.0, 0.0, 10.0), 10.0);
    }

    #[test]
    fn offset_for_channel_rgb_and_cmyk() {
        assert_eq!(offset_for_channel(ChannelId::Color0, false), 0);
        assert_eq!(offset_for_channel(ChannelId::Color1, false), 1);
        assert_eq!(offset_for_channel(ChannelId::Color2, false), 2);
        // Color3 == 3: rgb branch -> id+1 == 4; cmyk -> 3.
        assert_eq!(offset_for_channel(ChannelId::Color3, false), 4);
        assert_eq!(offset_for_channel(ChannelId::Color3, true), 3);
        // Transparency == -1.
        assert_eq!(offset_for_channel(ChannelId::Transparency, false), 3);
        assert_eq!(offset_for_channel(ChannelId::Transparency, true), 4);
        // default: UserMask == -2 -> id+1 == -1.
        assert_eq!(offset_for_channel(ChannelId::UserMask, false), -1);
        assert_eq!(offset_for_channel(ChannelId::RealUserMask, true), -2);
    }

    #[test]
    fn has_alpha_detects_non_opaque() {
        let opaque = PixelData {
            width: 2,
            height: 1,
            data: vec![1, 2, 3, 255, 4, 5, 6, 255],
        };
        assert!(!has_alpha(&opaque));

        let translucent = PixelData {
            width: 2,
            height: 1,
            data: vec![1, 2, 3, 255, 4, 5, 6, 128],
        };
        assert!(has_alpha(&translucent));
    }

    #[test]
    fn reset_image_data_sets_black_opaque() {
        let mut pd = PixelData {
            width: 2,
            height: 1,
            data: vec![9, 9, 9, 9, 9, 9, 9, 9],
        };
        reset_image_data(&mut pd);
        assert_eq!(pd.data, vec![0, 0, 0, 255, 0, 0, 0, 255]);
    }

    #[test]
    fn decode_bitmap_packs_bits() {
        // One byte 0b10100000 over width 8: bits -> black,white,black,white,...
        let input = [0b1010_0000u8];
        let mut output = vec![0u8; 8 * 4];
        decode_bitmap(&input, &mut output, 8, 1);
        // pixel0 bit set -> 0; pixel1 bit clear -> 255; pixel2 -> 0; pixel3 -> 255 ...
        assert_eq!(output[0], 0);
        assert_eq!(output[4], 255);
        assert_eq!(output[8], 0);
        assert_eq!(output[12], 255);
        // alpha always 255
        assert_eq!(output[3], 255);
    }

    #[test]
    fn write_data_raw_extracts_channel() {
        // 2x1 RGBA: [r0 g0 b0 a0, r1 g1 b1 a1]
        let pd = PixelData {
            width: 2,
            height: 1,
            data: vec![10, 20, 30, 40, 50, 60, 70, 80],
        };
        assert_eq!(write_data_raw(&pd, 0, 2, 1), Some(vec![10, 50])); // red
        assert_eq!(write_data_raw(&pd, 3, 2, 1), Some(vec![40, 80])); // alpha
        assert_eq!(write_data_raw(&pd, 0, 0, 1), None);
    }

    #[test]
    fn zip_without_prediction_round_trips() {
        use flate2::read::ZlibDecoder;
        use std::io::Read;

        let pd = PixelData {
            width: 4,
            height: 1,
            data: vec![
                1, 0, 0, 0, 2, 0, 0, 0, 3, 0, 0, 0, 4, 0, 0, 0,
            ],
        };
        let out = write_data_zip_without_prediction(&pd, &[0]).unwrap();
        let mut decoder = ZlibDecoder::new(&out[..]);
        let mut decoded = Vec::new();
        decoder.read_to_end(&mut decoded).unwrap();
        assert_eq!(decoded, vec![1, 2, 3, 4]);
    }

    #[test]
    fn rev_map_swaps() {
        let mut m = Dict::new();
        m.insert("a".into(), "1".into());
        m.insert("b".into(), "2".into());
        let r = rev_map(&m);
        assert_eq!(r.get("1"), Some(&"a".to_string()));
        assert_eq!(r.get("2"), Some(&"b".to_string()));
    }

    #[test]
    fn enum_codec_encode_decode() {
        let mut map = Dict::new();
        map.insert("alpha".into(), "Alph".into());
        map.insert("beta".into(), "Beta".into());
        let codec = EnumCodec::new("Enum", "alpha", map);

        assert_eq!(codec.encode(Some("beta")).unwrap(), "Enum.Beta");
        assert_eq!(codec.encode(None).unwrap(), "Enum.Alph"); // falls back to def
        assert!(codec.encode(Some("gamma")).is_err());

        assert_eq!(codec.decode("Enum.Beta").unwrap(), "beta");
        assert_eq!(codec.decode("Enum.Alph").unwrap(), "alpha");
        // empty second segment -> default
        assert_eq!(codec.decode("Enum").unwrap(), "alpha");
        assert!(codec.decode("Enum.Zzzz").is_err());
    }
}