terrio 0.1.1

//! Raster tiles as rasters: reading a zoom level (and the lower ones as overviews) by window, and
//! writing rasters as tile pyramids, as GDAL's MBTiles and PMTiles drivers do.

use super::{MAX_GM, TileArchive, TileFormat, TileWriteOptions, lonlat_to_mercator, mercator_to_lonlat};
use crate::crs::SpatialRef;
use crate::{Error, RasterDataset, Result};
use std::collections::HashMap;
use wbraster::DataType;
use wbraster::raster::RasterData;

/// The resolution of zoom level `z` with tiles of `ts` pixels.
fn resolution(z: u8, ts: usize) -> f64 {
    2.0 * MAX_GM / ts as f64 / (1u64 << z) as f64
}

// ─── Tile images ────────────────────────────────────────────────────────────────────────────────

/// A decoded tile: width, height, channels (1 gray, 2 gray and alpha, 3 RGB, 4 RGBA), samples.
pub(crate) struct Image {
    pub w: usize,
    pub h: usize,
    pub channels: usize,
    pub data: Vec<u8>,
    /// Whether it had a palette (GDAL reads those as RGB).
    pub palette: bool,
}

/// Decodes a PNG, JPEG or WebP tile to 8-bit samples.
pub(crate) fn decode_image(b: &[u8]) -> Result<Image> {
    let err = |e: &dyn std::fmt::Display| Error::InvalidData(format!("tile image: {e}"));
    if b.starts_with(b"\x89PNG") {
        let mut d = png::Decoder::new(std::io::Cursor::new(b));
        d.set_transformations(png::Transformations::normalize_to_color8());
        let mut reader = d.read_info().map_err(|e| err(&e))?;
        let palette = reader.info().color_type == png::ColorType::Indexed;
        let mut buf = vec![0u8; reader.output_buffer_size().ok_or_else(|| err(&"too large"))?];
        let info = reader.next_frame(&mut buf).map_err(|e| err(&e))?;
        let channels = info.color_type.samples();
        let (w, h) = (info.width as usize, info.height as usize);
        buf.truncate(w * h * channels);
        return Ok(Image { w, h, channels, data: buf, palette });
    }
    if b.starts_with(&[0xff, 0xd8]) {
        let mut d = jpeg_decoder::Decoder::new(std::io::Cursor::new(b));
        let data = d.decode().map_err(|e| err(&e))?;
        let info = d.info().ok_or_else(|| err(&"no JPEG header"))?;
        let (w, h) = (info.width as usize, info.height as usize);
        let channels = (data.len() / (w * h).max(1)).clamp(1, 4);
        return Ok(Image { w, h, channels, data, palette: false });
    }
    if b.len() > 12 && &b[0..4] == b"RIFF" && &b[8..12] == b"WEBP" {
        let mut d = image_webp::WebPDecoder::new(std::io::Cursor::new(b)).map_err(|e| err(&e))?;
        let (w, h) = d.dimensions();
        let channels = if d.has_alpha() { 4 } else { 3 };
        let mut data = vec![0u8; d.output_buffer_size().ok_or_else(|| err(&"too large"))?];
        d.read_image(&mut data).map_err(|e| err(&e))?;
        return Ok(Image { w: w as usize, h: h as usize, channels, data, palette: false });
    }
    Err(err(&"unsupported tile format (PNG, JPEG and WebP are supported)"))
}

/// One pixel of a tile as `bands` values: gray and RGB values for the first bands, alpha (opaque
/// when the tile has none) for the last of 2 or 4, as GDAL expands tiles.
fn pixel(img: &Image, i: usize, bands: usize, out: &mut [u8]) {
    let px = &img.data[i * img.channels..(i + 1) * img.channels];
    let rgba = match px.len() {
        1 => [px[0], px[0], px[0], 255],
        2 => [px[0], px[0], px[0], px[1]],
        3 => [px[0], px[1], px[2], 255],
        _ => [px[0], px[1], px[2], px[3]],
    };
    match bands {
        1 => out[0] = rgba[0],
        2 => {
            out[0] = rgba[0];
            out[1] = rgba[3];
        }
        3 => out[..3].copy_from_slice(&rgba[..3]),
        _ => out[..4].copy_from_slice(&rgba),
    }
}

fn encode_png(w: usize, h: usize, channels: usize, data: &[u8]) -> Result<Vec<u8>> {
    let err = |e: png::EncodingError| Error::InvalidData(format!("PNG tile: {e}"));
    let mut out = Vec::new();
    {
        let mut enc = png::Encoder::new(&mut out, w as u32, h as u32);
        enc.set_color(match channels {
            1 => png::ColorType::Grayscale,
            2 => png::ColorType::GrayscaleAlpha,
            3 => png::ColorType::Rgb,
            _ => png::ColorType::Rgba,
        });
        enc.set_depth(png::BitDepth::Eight);
        let mut wr = enc.write_header().map_err(err)?;
        wr.write_image_data(data).map_err(err)?;
        wr.finish().map_err(err)?;
    }
    Ok(out)
}

fn encode_jpeg(w: usize, h: usize, channels: usize, data: &[u8], quality: u8) -> Result<Vec<u8>> {
    let mut out = Vec::new();
    let enc = jpeg_encoder::Encoder::new(&mut out, quality);
    let color = if channels == 1 { jpeg_encoder::ColorType::Luma } else { jpeg_encoder::ColorType::Rgb };
    enc.encode(data, w as u16, h as u16, color).map_err(|e| Error::InvalidData(format!("JPEG tile: {e}")))?;
    Ok(out)
}

fn encode_webp(w: usize, h: usize, channels: usize, data: &[u8]) -> Result<Vec<u8>> {
    // The lossless encoder takes RGB(A): gray tiles are expanded.
    let (rgb, color): (std::borrow::Cow<[u8]>, _) = match channels {
        1 => (data.iter().flat_map(|v| [*v, *v, *v]).collect::<Vec<u8>>().into(), image_webp::ColorType::Rgb8),
        2 => (data.chunks(2).flat_map(|p| [p[0], p[0], p[0], p[1]]).collect::<Vec<u8>>().into(), image_webp::ColorType::Rgba8),
        3 => (data.into(), image_webp::ColorType::Rgb8),
        _ => (data.into(), image_webp::ColorType::Rgba8),
    };
    let mut out = Vec::new();
    image_webp::WebPEncoder::new(&mut out)
        .encode(&rgb, w as u32, h as u32, color)
        .map_err(|e| Error::InvalidData(format!("WebP tile: {e}")))?;
    Ok(out)
}

// ─── Reading ────────────────────────────────────────────────────────────────────────────────────

/// A zoom level read as a raster: its size and the global pixel position of its first pixel.
#[derive(Debug, Clone, Copy)]
struct Level {
    zoom: u8,
    width: usize,
    height: usize,
    shift_x: i64,
    shift_y: i64,
}

/// A tile archive's image tiles read as a raster in EPSG:3857: a zoom level as full resolution
/// and the lower ones as overviews, read by window.
pub(crate) struct TileRaster {
    archive: TileArchive,
    levels: Vec<Level>,
    pub bands: usize,
    tile_size: usize,
    /// `[min_x, min_y, max_x, max_y]` in EPSG:3857.
    extent: [f64; 4],
    cache: HashMap<(u8, u32, u32), Option<std::sync::Arc<Image>>>,
}

impl std::fmt::Debug for TileRaster {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("TileRaster").field("levels", &self.levels).field("bands", &self.bands).finish_non_exhaustive()
    }
}

impl TileRaster {
    /// Reads an archive's layout: the full resolution zoom level (the highest by default), its
    /// extent and band count. MBTiles extents come from the `bounds` metadata (or the tiles), as
    /// in GDAL's MBTiles driver; PMTiles extents from the header's bounds aligned on the pixel
    /// grid, as in GDAL's PMTiles driver. MBTiles are read as 4 bands (RGBA), PMTiles with the
    /// bands of their tiles.
    pub(crate) fn new(mut archive: TileArchive, zoom_level: Option<u8>) -> Result<Self> {
        if archive.is_vector() {
            return Err(Error::Unsupported("the archive holds vector tiles, not a raster".into()));
        }
        if archive.format() == TileFormat::Avif {
            return Err(Error::Unsupported("AVIF tiles are not supported".into()));
        }
        let (min_z, max_z) = archive.zoom_range();
        let zoom = zoom_level.unwrap_or(max_z);
        if zoom < min_z || zoom > max_z {
            return Err(Error::InvalidArgument(format!("invalid zoom level {zoom}: the archive has zoom levels {min_z} to {max_z}")));
        }
        let present = archive.tiles_at_zoom(zoom)?;
        let &(fx, fy) = present.first().ok_or_else(|| Error::InvalidData(format!("the archive has no tiles at zoom level {zoom}")))?;
        let first = archive.tile(zoom, fx, fy)?.ok_or_else(|| Error::InvalidData("missing tile".into()))?;
        let img = decode_image(&first)?;
        let tile_size = img.w.max(1);
        let res = resolution(zoom, tile_size);
        let kind = archive.kind();
        let tile_extent = || {
            let (x0, x1) = (present.iter().map(|t| t.0).min().unwrap_or(0), present.iter().map(|t| t.0).max().unwrap_or(0));
            let (y0, y1) = (present.iter().map(|t| t.1).min().unwrap_or(0), present.iter().map(|t| t.1).max().unwrap_or(0));
            let dim = 2.0 * MAX_GM / (1u64 << zoom) as f64;
            [-MAX_GM + x0 as f64 * dim, MAX_GM - (y1 + 1) as f64 * dim, -MAX_GM + (x1 + 1) as f64 * dim, MAX_GM - y0 as f64 * dim]
        };
        let to_merc = |b: [f64; 4]| {
            let (x0, y0) = lonlat_to_mercator(b[0], b[1]);
            let (x1, y1) = lonlat_to_mercator(b[2], b[3]);
            [x0, y0.max(-MAX_GM), x1, y1.min(MAX_GM)]
        };
        let (extent, width, height, bands) = match kind {
            super::ArchiveKind::MBTiles => {
                let e = archive.bounds().map(to_merc).unwrap_or_else(tile_extent);
                let w = (0.5 + (e[2] - e[0]) / res) as usize;
                let h = (0.5 + (e[3] - e[1]) / res) as usize;
                (e, w, h, 4)
            }
            super::ArchiveKind::PMTiles => {
                let b = archive.bounds().filter(|b| b[0] < b[2] && b[1] < b[3]);
                let e = b.map(to_merc).unwrap_or_else(tile_extent);
                const EPS: f64 = 1e-2;
                let e = [
                    (e[0] / res + EPS).floor() * res,
                    (e[1] / res + EPS).floor() * res,
                    (e[2] / res - EPS).ceil() * res,
                    (e[3] / res - EPS).ceil() * res,
                ];
                let w = (((e[2] - e[0]) / res + EPS) as usize).max(1);
                let h = (((e[3] - e[1]) / res + EPS) as usize).max(1);
                let bands = if img.palette { 3 } else { img.channels };
                (e, w, h, bands)
            }
        };
        if width == 0 || height == 0 {
            return Err(Error::InvalidData("the archive's extent is empty".into()));
        }
        let mut levels = Vec::new();
        for z in (min_z..=zoom).rev() {
            let r = resolution(z, tile_size);
            let (w, h) = if z == zoom {
                (width, height)
            } else {
                (((extent[2] - extent[0]) / r + 0.5).max(1.0) as usize, ((extent[3] - extent[1]) / r + 0.5).max(1.0) as usize)
            };
            let shift_x = ((extent[0] + MAX_GM) / r + 0.5).floor() as i64;
            let shift_y = ((MAX_GM - extent[3]) / r + 0.5).floor() as i64;
            levels.push(Level { zoom: z, width: w, height: h, shift_x, shift_y });
        }
        Ok(Self { archive, levels, bands, tile_size, extent, cache: HashMap::new() })
    }

    pub(crate) fn width(&self) -> usize {
        self.levels[0].width
    }

    pub(crate) fn height(&self) -> usize {
        self.levels[0].height
    }

    /// The overview sizes, largest first.
    pub(crate) fn overviews(&self) -> Vec<(usize, usize)> {
        self.levels[1..].iter().map(|l| (l.width, l.height)).collect()
    }

    /// The geotransform of the full resolution.
    pub(crate) fn geo_transform(&self) -> [f64; 6] {
        let res = resolution(self.levels[0].zoom, self.tile_size);
        [self.extent[0], res, 0.0, self.extent[3], 0.0, -res]
    }

    /// The archive's metadata, with the zoom level read, as GDAL lists it.
    pub(crate) fn metadata(&self) -> Vec<(String, String)> {
        let mut md = vec![("ZOOM_LEVEL".to_string(), self.levels[0].zoom.to_string())];
        md.extend(self.archive.metadata().into_iter().filter(|(k, _)| k != "json"));
        md
    }

    pub(crate) fn driver(&self) -> crate::formats::RasterDriver {
        match self.archive.kind() {
            super::ArchiveKind::PMTiles => crate::formats::RasterDriver::PMTiles,
            super::ArchiveKind::MBTiles => crate::formats::RasterDriver::MBTiles,
        }
    }

    /// Reads a window of a level (0 is the full resolution) for some bands (from 1), as Byte
    /// band-major samples. Pixels without tiles are 0.
    pub(crate) fn read(&mut self, level: usize, win: crate::Window, bands: &[usize]) -> Result<RasterData> {
        let l = *self.levels.get(level).ok_or_else(|| Error::InvalidArgument(format!("no level {level}")))?;
        let ts = self.tile_size as i64;
        let n = (1i64 << l.zoom) - 1;
        let gx0 = l.shift_x + win.x as i64;
        let gy0 = l.shift_y + win.y as i64;
        let (gx1, gy1) = (gx0 + win.width as i64, gy0 + win.height as i64);
        let (tx0, tx1) = (gx0.div_euclid(ts).max(0), (gx1 - 1).div_euclid(ts).min(n));
        let (ty0, ty1) = (gy0.div_euclid(ts).max(0), (gy1 - 1).div_euclid(ts).min(n));
        let mut wanted = Vec::new();
        for ty in ty0..=ty1 {
            for tx in tx0..=tx1 {
                let key = (l.zoom, tx as u32, ty as u32);
                if !self.cache.contains_key(&key) {
                    wanted.push(key);
                }
            }
        }
        if !wanted.is_empty() {
            if self.cache.len() > 4096 {
                self.cache.clear();
            }
            for chunk in wanted.chunks(512) {
                let data = self.archive.tiles(chunk)?;
                for (key, bytes) in chunk.iter().zip(data) {
                    let img = match bytes {
                        Some(b) => Some(std::sync::Arc::new(decode_image(&b)?)),
                        None => None,
                    };
                    self.cache.insert(*key, img);
                }
            }
        }
        let nb = self.bands;
        let (w, h) = (win.width, win.height);
        let mut out = vec![0u8; bands.len() * w * h];
        let mut px = [0u8; 4];
        for ty in ty0..=ty1 {
            for tx in tx0..=tx1 {
                let Some(Some(img)) = self.cache.get(&(l.zoom, tx as u32, ty as u32)) else { continue };
                let img = img.clone();
                for y in 0..ts.min(img.h as i64) {
                    let gy = ty * ts + y;
                    if gy < gy0 || gy >= gy1 {
                        continue;
                    }
                    let oy = (gy - gy0) as usize;
                    for x in 0..ts.min(img.w as i64) {
                        let gx = tx * ts + x;
                        if gx < gx0 || gx >= gx1 {
                            continue;
                        }
                        let ox = (gx - gx0) as usize;
                        pixel(&img, y as usize * img.w + x as usize, nb, &mut px);
                        for (i, b) in bands.iter().enumerate() {
                            out[(i * h + oy) * w + ox] = px[b - 1];
                        }
                    }
                }
            }
        }
        Ok(RasterData::U8(out))
    }

    /// The raster's metadata (size, bands, georeferencing, CRS, metadata items) without pixels.
    pub(crate) fn header(&self) -> RasterDataset {
        let gt = self.geo_transform();
        let (w, h) = (self.width(), self.height());
        let crs = SpatialRef::from_epsg(3857).map(|s| s.to_crs_info()).unwrap_or_default();
        let raster = wbraster::Raster {
            cols: w,
            rows: h,
            bands: self.bands,
            x_min: gt[0],
            y_min: gt[3] + gt[5] * h as f64,
            cell_size_x: gt[1],
            cell_size_y: -gt[5],
            nodata: -9999.0,
            data_type: DataType::U8,
            crs,
            metadata: self.metadata(),
            data: RasterData::new_filled(DataType::U8, 0, 0.0),
        };
        RasterDataset { raster, driver: self.driver(), has_nodata: false }
    }

    /// Reads the whole full resolution level.
    pub(crate) fn read_all(&mut self) -> Result<RasterDataset> {
        let (w, h) = (self.width(), self.height());
        if (w as u64) * (h as u64) * (self.bands as u64) > 1 << 32 {
            return Err(Error::Unsupported(format!(
                "the zoom level {} raster is {w} x {h} pixels: read it by window (LazyRaster) or open a lower zoom level",
                self.levels[0].zoom
            )));
        }
        let bands: Vec<usize> = (1..=self.bands).collect();
        let data = self.read(0, crate::Window::full(w, h), &bands)?;
        let crs = SpatialRef::from_epsg(3857)?.to_crs_info();
        let mut raster = crate::drivers::common::make_raster(w, h, self.bands, data, self.geo_transform(), crs, None)?;
        raster.metadata = self.metadata();
        Ok(RasterDataset { raster, driver: self.driver(), has_nodata: false })
    }
}

impl crate::cog::WindowSource for TileRaster {
    fn overviews(&self) -> Vec<(usize, usize)> {
        TileRaster::overviews(self)
    }

    fn read(&mut self, level: usize, window: crate::Window, bands: &[usize]) -> Result<RasterData> {
        TileRaster::read(self, level, window, bands)
    }
}

/// Opens a PMTiles or MBTiles archive of image tiles for reading by window. `None` when the path
/// does not name a tile archive.
pub(crate) fn open_lazy(path: &str) -> Result<Option<TileRaster>> {
    let loc = crate::vfs::Location::parse(path);
    if matches!(loc, crate::vfs::Location::Zip { .. }) || super::archive_kind(&loc.file_name()).is_none() {
        return Ok(None);
    }
    let archive = TileArchive::open(path)?;
    if archive.is_vector() {
        return Err(Error::Unsupported(format!("'{path}' holds vector tiles, not a raster")));
    }
    TileRaster::new(archive, None).map(Some)
}

/// Opens an archive of image tiles held in memory for reading by window.
pub(crate) fn open_lazy_bytes(bytes: Vec<u8>) -> Result<TileRaster> {
    TileRaster::new(TileArchive::from_bytes(bytes)?, None)
}

// ─── Writing ────────────────────────────────────────────────────────────────────────────────────

/// A level of the pyramid being written: data bands (1 or 3) and an alpha band, band-major.
struct Pixels {
    w: usize,
    h: usize,
    bands: usize,
    data: Vec<u8>,
    alpha: Vec<u8>,
}

/// A resampling kernel: its weight at a distance (in source pixels).
type Kernel = fn(f64) -> f64;

/// Tiles `(z, x, y, bytes)`.
type Tiles = Vec<(u8, u32, u32, Vec<u8>)>;

/// Downsamples a level to `w` x `h` pixels, as GDAL computes overviews (`gdaladdo`): nearest,
/// average, or a separable convolution (bilinear, cubic) whose kernel is stretched by the
/// reduction factor, with the alpha band as the weights of every band (horizontal pass, then
/// vertical pass over the horizontally filtered alpha), as GDAL weights by a dataset's mask.
fn downsample(src: &Pixels, w: usize, h: usize, method: &str) -> Pixels {
    let (sw, sh) = (src.w, src.h);
    let (rx, ry) = (sw as f64 / w as f64, sh as f64 / h as f64);
    let nb = src.bands + 1;
    let n = sw * sh;
    // Band `b` of the source (the alpha band last).
    let band = |b: usize, i: usize| if b < src.bands { src.data[b * n + i] } else { src.alpha[i] } as f64;
    let mut out = vec![0u8; nb * w * h];
    let kernel: Option<(f64, Kernel)> = match method {
        "bilinear" => Some((1.0, |x: f64| (1.0 - x.abs()).max(0.0))),
        "cubic" => Some((2.0, |x: f64| {
            let x = x.abs();
            let a = -0.5;
            if x <= 1.0 {
                ((a + 2.0) * x - (a + 3.0)) * x * x + 1.0
            } else if x < 2.0 {
                a * (((x - 5.0) * x + 8.0) * x - 4.0)
            } else {
                0.0
            }
        })),
        _ => None,
    };
    if let Some((radius, k)) = kernel {
        // Per-axis taps, as GDAL computes them: for each output index, the first source index and
        // the weights.
        let taps = |dst: usize, src_n: usize, ratio: f64| -> Vec<(usize, Vec<f64>)> {
            let scale = (1.0 / ratio).min(1.0);
            let r = radius / scale;
            (0..dst)
                .map(|i| {
                    let c = (i as f64 + 0.5) * ratio;
                    let lo = ((c - r + 0.5).floor() as i64).max(0) as usize;
                    let hi = ((c + r + 0.5) as i64).min(src_n as i64).max(lo as i64) as usize;
                    (lo, (lo..hi).map(|j| k(scale * (j as f64 - c + 0.5))).collect())
                })
                .collect()
        };
        let (tx, ty) = (taps(w, sw, rx), taps(h, sh, ry));
        // Horizontal pass: values and the filtered mask, per source row.
        let mut hv = vec![0.0f64; nb * sh * w];
        let mut hm = vec![0.0f64; sh * w];
        for y in 0..sh {
            for (x, (lo, wt)) in tx.iter().enumerate() {
                let (mut sa, mut sw_) = (0.0, 0.0);
                let mut sv = [0.0f64; 4];
                for (t, &wj) in wt.iter().enumerate() {
                    let i = y * sw + lo + t;
                    let m = wj * src.alpha[i] as f64;
                    sa += m;
                    sw_ += wj;
                    for (b, v) in sv.iter_mut().enumerate().take(nb) {
                        *v += m * band(b, i);
                    }
                }
                let o = y * w + x;
                if sa > 0.0 {
                    for (b, v) in sv.iter().enumerate().take(nb) {
                        hv[(b * sh + y) * w + x] = (v / sa).clamp(0.0, 255.0);
                    }
                    hm[o] = (sa / sw_ + 0.5).min(255.0).floor();
                }
            }
        }
        // Vertical pass.
        for (y, (lo, wt)) in ty.iter().enumerate() {
            for x in 0..w {
                let mut sa = 0.0;
                let mut sv = [0.0f64; 4];
                for (t, &wj) in wt.iter().enumerate() {
                    let r = lo + t;
                    let m = wj * hm[r * w + x];
                    sa += m;
                    for (b, v) in sv.iter_mut().enumerate().take(nb) {
                        *v += m * hv[(b * sh + r) * w + x];
                    }
                }
                if sa > 0.0 {
                    for (b, v) in sv.iter().enumerate().take(nb) {
                        out[(b * h + y) * w + x] = (v / sa + 0.5).clamp(0.0, 255.0) as u8;
                    }
                }
            }
        }
    } else if method == "average" {
        for y in 0..h {
            let y0 = (y as f64 * ry + 1e-8) as usize;
            let y1 = (((y + 1) as f64 * ry - 1e-8).ceil() as usize).clamp(y0 + 1, sh);
            for x in 0..w {
                let x0 = (x as f64 * rx + 1e-8) as usize;
                let x1 = (((x + 1) as f64 * rx - 1e-8).ceil() as usize).clamp(x0 + 1, sw);
                let mut sa = 0.0;
                let mut sv = [0.0f64; 4];
                for sy in y0..y1 {
                    for sx in x0..x1 {
                        let i = sy * sw + sx;
                        let m = src.alpha[i] as f64;
                        sa += m;
                        for (b, v) in sv.iter_mut().enumerate().take(nb) {
                            *v += m * band(b, i);
                        }
                    }
                }
                if sa > 0.0 {
                    for (b, v) in sv.iter().enumerate().take(nb) {
                        out[(b * h + y) * w + x] = (v / sa + 0.5).clamp(0.0, 255.0) as u8;
                    }
                }
            }
        }
    } else {
        for y in 0..h {
            let sy = (((y as f64 + 0.5) * ry) as usize).min(sh - 1);
            for x in 0..w {
                let sx = (((x as f64 + 0.5) * rx) as usize).min(sw - 1);
                for b in 0..nb {
                    out[(b * h + y) * w + x] = band(b, sy * sw + sx) as u8;
                }
            }
        }
    }
    let alpha = out.split_off(src.bands * w * h);
    Pixels { w, h, bands: src.bands, data: out, alpha }
}

/// A raster as a tile pyramid: its tiles `(z, x, y, bytes)`, the bounds (lon/lat), the zoom
/// levels and the tile format name.
pub(crate) struct RasterTiles {
    pub tiles: Vec<(u8, u32, u32, Vec<u8>)>,
    pub bounds: [f64; 4],
    pub min_zoom: u8,
    pub max_zoom: u8,
    pub format: TileFormat,
}

/// Cuts a raster into a tile pyramid as GDAL's MBTiles driver does: reprojected to EPSG:3857
/// (bilinear by default) at the zoom level whose resolution is closest to the source's, with an
/// alpha band when the source is not already in EPSG:3857 (or has one), placed on the tile grid
/// by whole pixels; and the lower zoom levels as overviews computed from it (as `gdaladdo`
/// would), down to `min_zoom` or the level whose single tile covers the raster.
pub(crate) fn make_tiles(ds: &RasterDataset, o: &TileWriteOptions) -> Result<RasterTiles> {
    let r = &ds.raster;
    if r.data_type != DataType::U8 || !(1..=4).contains(&r.bands) {
        return Err(Error::Unsupported(format!(
            "tile archives hold 1 to 4 Byte bands (gray, gray and alpha, RGB or RGBA), not {} band(s) of {}: convert the data type first (for example with `terrio translate --ot Byte --scale`)",
            r.bands,
            crate::info::gdal_type_name(r.data_type)
        )));
    }
    let format = match o.tile_format.as_deref().map(str::to_ascii_uppercase).as_deref() {
        None | Some("PNG") | Some("PNG8") => TileFormat::Png,
        Some("JPEG") | Some("JPG") => TileFormat::Jpeg,
        Some("WEBP") => TileFormat::Webp,
        Some(f) => return Err(Error::InvalidArgument(format!("unknown tile format '{f}' (PNG, JPEG, WEBP)"))),
    };
    let src_srs = ds.crs();
    if src_srs.is_unknown() {
        return Err(Error::InvalidArgument("the raster has no CRS: tiles need one to be reprojected to EPSG:3857".into()));
    }
    let web = SpatialRef::from_epsg(3857)?;
    let resampling = crate::ops::Resampling::parse(o.resampling.as_deref().unwrap_or("bilinear"))?;

    // Latitudes beyond Web Mercator's are cut off first, as GDAL does.
    const MAX_LAT: f64 = 85.0511287798066;
    let gt = ds.geo_transform();
    let mut src = std::borrow::Cow::Borrowed(ds);
    let (mut clamp_max, mut clamp_min) = (false, false);
    if src_srs.is_geographic() && gt[2] == 0.0 && gt[4] == 0.0 && gt[5] < 0.0 {
        let max_lat = gt[3];
        let min_lat = gt[3] + r.rows as f64 * gt[5];
        clamp_max = max_lat > MAX_LAT;
        clamp_min = min_lat < -MAX_LAT;
        if clamp_max || clamp_min {
            let to = crate::ops::translate::TranslateOptions {
                proj_win: Some((gt[0], max_lat.min(MAX_LAT), gt[0] + r.cols as f64 * gt[1], min_lat.max(-MAX_LAT))),
                ..Default::default()
            };
            src = std::borrow::Cow::Owned(crate::ops::translate::translate(ds, &to)?);
        }
    }
    let (sgt, _, _, mut ext) = crate::ops::warp::suggested_output(&src, &web)?;
    let mut sgt = sgt;
    if clamp_max {
        sgt[3] = MAX_GM;
        ext[3] = MAX_GM;
    }
    if clamp_min {
        ext[1] = -MAX_GM;
    }
    if (clamp_max || clamp_min) && gt[0] + r.cols as f64 * gt[1] == 180.0 {
        ext[2] = MAX_GM;
    }

    // The zoom level, as GDAL picks it.
    let computed = sgt[1];
    let res0 = 2.0 * MAX_GM / 256.0;
    let (mut zoom, mut prev, mut res) = (0u8, 0.0, 0.0);
    while zoom < 25 {
        res = res0 / (1u64 << zoom) as f64;
        if computed > res {
            break;
        }
        prev = res;
        zoom += 1;
    }
    if zoom == 25 {
        return Err(Error::InvalidArgument("could not find an appropriate zoom level".into()));
    }
    if ((computed - res) / res).abs() > 1e-8 {
        match o.zoom_level_strategy.as_str() {
            "LOWER" => zoom = zoom.saturating_sub(1),
            "UPPER" => {}
            _ => {
                if zoom > 0 && prev / computed < computed / res {
                    zoom -= 1;
                }
            }
        }
    }
    if let Some(z) = o.max_zoom {
        zoom = z;
    }
    let res = res0 / (1u64 << zoom) as f64;
    let width = (0.5 + (ext[2] - ext[0]) / res) as usize;
    let height = (0.5 + (ext[3] - ext[1]) / res) as usize;
    if width == 0 || height == 0 {
        return Err(Error::InvalidArgument("the raster is empty at that zoom level".into()));
    }
    if (width as u64) * (height as u64) > 1 << 31 {
        return Err(Error::Unsupported(format!(
            "the raster would be {width} x {height} pixels at zoom level {zoom}: choose a lower MAXZOOM"
        )));
    }

    // Warp, with an alpha band: the source's, or one added when reprojecting gray or RGB.
    let src_alpha = matches!(src.raster.bands, 2 | 4);
    let data_bands = if src_alpha { src.raster.bands - 1 } else { src.raster.bands };
    let add_alpha = !src_alpha && src_srs.epsg != Some(3857);
    let sn = src.raster.cols * src.raster.rows;
    let values = src.raster.data.to_f64_vec();
    let with_bands = |v: Vec<f64>, bands: usize, t: DataType| {
        let mut d = (*src).clone();
        d.raster.data = RasterData::from_f64_vec(t, v);
        d.raster.data_type = t;
        d.raster.bands = bands;
        d.has_nodata = false;
        d
    };
    let mut wo = crate::ops::warp::WarpOptions {
        dst_srs: Some(web.clone()),
        extent: Some((sgt[0], sgt[3] - height as f64 * res, sgt[0] + width as f64 * res, sgt[3])),
        size: Some((width, height)),
        resampling,
        src_nodata: crate::ops::warp::Nodata::None,
        dst_nodata: crate::ops::warp::Nodata::None,
        output_type: Some(DataType::U8),
        ..Default::default()
    };
    let bytes = |ds: RasterDataset| match ds.raster.data {
        RasterData::U8(v) => v,
        d => d.to_f64_vec().into_iter().map(|v| v.clamp(0.0, 255.0) as u8).collect(),
    };
    // Fully transparent source pixels do not count, as with GDAL's source alpha.
    let color = if src_alpha {
        let a = &values[data_bands * sn..];
        let mut v = values[..data_bands * sn].to_vec();
        for (i, x) in v.iter_mut().enumerate() {
            if a[i % sn] == 0.0 {
                *x = f64::NAN;
            }
        }
        wo.src_nodata = crate::ops::warp::Nodata::Values(vec![f64::NAN]);
        with_bands(v, data_bands, DataType::F32)
    } else {
        with_bands(values[..data_bands * sn].to_vec(), data_bands, DataType::U8)
    };
    let data = bytes(crate::ops::warp::warp(&[&color], &wo)?);
    wo.src_nodata = crate::ops::warp::Nodata::None;
    // The alpha band: the source's, or opaque where the source is; GDAL's warper takes it from
    // the nearest source pixel.
    let alpha = if src_alpha || add_alpha {
        wo.resampling = crate::ops::Resampling::Nearest;
        let a = if src_alpha { values[data_bands * sn..].to_vec() } else { vec![255.0; sn] };
        bytes(crate::ops::warp::warp(&[&with_bands(a, 1, DataType::U8)], &wo)?)
    } else {
        vec![255u8; width * height]
    };
    // Pixels left transparent are not written by the warper.
    let mut data = data;
    if src_alpha {
        let n = width * height;
        for (i, x) in data.iter_mut().enumerate() {
            if alpha[i % n] == 0 {
                *x = 0;
            }
        }
    }
    let mut level = Pixels { w: width, h: height, bands: data_bands, data, alpha };

    // Overviews: down to the level whose single tile covers the raster (GDAL's PMTiles driver).
    let min_zoom = match o.min_zoom {
        Some(z) => z.min(zoom),
        None => {
            let count = ((width.max(height) as f64 / 256.0).log2().ceil()).max(0.0) as u8;
            zoom.saturating_sub(count)
        }
    };
    let method = o.resampling.as_deref().unwrap_or("bilinear").to_ascii_lowercase();
    let method = match method.as_str() {
        "near" | "nearest" => "nearest",
        "average" => "average",
        "cubic" | "cubicspline" | "lanczos" => "cubic",
        _ => "bilinear",
    };
    let (minx, maxy) = (sgt[0], sgt[3]);
    let (maxx, miny) = (minx + width as f64 * res, maxy - height as f64 * res);

    // The bounds, as GDAL records them.
    let (mut lon0, mut lat0) = mercator_to_lonlat(minx, miny);
    let (mut lon1, mut lat1) = mercator_to_lonlat(maxx, maxy);
    if (lon0 + 180.0).abs() < 1e-7 {
        lon0 = -180.0;
    }
    if (lon1 - 180.0).abs() < 1e-7 {
        lon1 = 180.0;
    }
    let ok_max = mercator_to_lonlat(0.0, MAX_GM).1;
    lat1 = lat1.min(ok_max);
    lat0 = lat0.max(-ok_max);

    // Overviews are laid out over the extent read back from the bounds, as GDAL builds them on
    // the file it wrote.
    let (bx0, by0) = lonlat_to_mercator(lon0, lat0);
    let (bx1, by1) = lonlat_to_mercator(lon1, lat1);
    let (bx0, by0, bx1, by1) = (bx0, by0.max(-MAX_GM), bx1, by1.min(MAX_GM));
    let mut tiles = Vec::new();
    for z in (min_zoom..=zoom).rev() {
        let r = res0 / (1u64 << z) as f64;
        let (ox, oy) = if z == zoom { (minx, maxy) } else { (bx0, by1) };
        if z != zoom {
            let w = ((bx1 - bx0) / r + 0.5).max(1.0) as usize;
            let h = ((by1 - by0) / r + 0.5).max(1.0) as usize;
            level = downsample(&level, w, h, method);
        }
        let sx = ((ox + MAX_GM) / r + 0.5).floor() as i64;
        let sy = ((MAX_GM - oy) / r + 0.5).floor() as i64;
        tiles.extend(cut_tiles(&level, z, sx, sy, format, o.quality)?);
    }
    Ok(RasterTiles { tiles, bounds: [lon0, lat0, lon1, lat1], min_zoom, max_zoom: zoom, format })
}

/// Cuts a level into 256-pixel tiles of zoom `z`, its first pixel at global pixel `(sx, sy)`.
/// Fully transparent tiles are left out. Every tile has an alpha band (but JPEG ones), so that
/// readers that take the band count of a tile (GDAL's PMTiles driver) see the same bands.
fn cut_tiles(l: &Pixels, z: u8, sx: i64, sy: i64, format: TileFormat, quality: u8) -> Result<Tiles> {
    const TS: i64 = 256;
    let nmax = (1i64 << z) - 1;
    let (tx0, tx1) = (sx.div_euclid(TS).max(0), (sx + l.w as i64 - 1).div_euclid(TS).min(nmax));
    let (ty0, ty1) = (sy.div_euclid(TS).max(0), (sy + l.h as i64 - 1).div_euclid(TS).min(nmax));
    let n = l.w * l.h;
    let mut out = Vec::new();
    for ty in ty0..=ty1 {
        for tx in tx0..=tx1 {
            let ch = l.bands + 1;
            let mut px = vec![0u8; (TS * TS) as usize * ch];
            let mut any = false;
            for y in 0..TS {
                let gy = ty * TS + y - sy;
                for x in 0..TS {
                    let gx = tx * TS + x - sx;
                    let o = (y * TS + x) as usize * ch;
                    if gy < 0 || gy >= l.h as i64 || gx < 0 || gx >= l.w as i64 {
                        continue;
                    }
                    let i = gy as usize * l.w + gx as usize;
                    let a = l.alpha[i];
                    any |= a != 0;
                    for b in 0..l.bands {
                        px[o + b] = l.data[b * n + i];
                    }
                    px[o + l.bands] = a;
                }
            }
            if !any {
                continue;
            }
            let drop_alpha = format == TileFormat::Jpeg;
            let (channels, samples) =
                if drop_alpha { (l.bands, px.chunks(ch).flat_map(|p| p[..ch - 1].to_vec()).collect::<Vec<u8>>()) } else { (ch, px) };
            let t = TS as usize;
            let bytes = match format {
                TileFormat::Jpeg => encode_jpeg(t, t, channels, &samples, quality)?,
                TileFormat::Webp => encode_webp(t, t, channels, &samples)?,
                _ => encode_png(t, t, channels, &samples)?,
            };
            out.push((z, tx as u32, ty as u32, bytes));
        }
    }
    Ok(out)
}

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

    #[test]
    fn rasters_round_trip_through_tiles() {
        // A 512 x 256 RGB raster in EPSG:3857 at zoom 10's resolution, on the tile grid.
        let res = resolution(10, 256);
        let (w, h) = (512, 256);
        let mut v = Vec::new();
        for b in 0..3 {
            for y in 0..h {
                for x in 0..w {
                    v.push(((x + y * 2 + b * 50) % 256) as f64);
                }
            }
        }
        let crs = SpatialRef::from_epsg(3857).unwrap().to_crs_info();
        let gt = [-MAX_GM + 300.0 * 256.0 * res, res, 0.0, MAX_GM - 400.0 * 256.0 * res, 0.0, -res];
        let raster =
            crate::drivers::common::make_raster(w, h, 3, RasterData::from_f64_vec(DataType::U8, v.clone()), gt, crs, None).unwrap();
        let ds = RasterDataset { raster, driver: crate::formats::RasterDriver::GTiff, has_nodata: false };
        let o = TileWriteOptions { resampling: Some("near".into()), ..Default::default() };
        let rt = make_tiles(&ds, &o).unwrap();
        assert_eq!(rt.max_zoom, 10);
        assert_eq!(rt.min_zoom, 9);
        let bytes = super::super::write_raster_archive(&rt, &o, "t", super::super::ArchiveKind::PMTiles).unwrap();
        let mut tr = TileRaster::new(TileArchive::from_bytes(bytes).unwrap(), None).unwrap();
        assert_eq!((tr.width(), tr.height(), tr.bands), (512, 256, 4));
        assert_eq!(tr.overviews(), vec![(256, 128)]);
        let back = tr.read_all().unwrap();
        assert_eq!(back.raster.data.to_f64_vec()[..v.len()], v[..]);
        let gtb = back.geo_transform();
        assert!((gtb[0] - gt[0]).abs() < 1e-6 && (gtb[3] - gt[3]).abs() < 1e-6);
    }
}