use serde::Deserialize;
use std::{collections::HashMap, error::Error, fs::File, io::BufReader, path::Path};

fn load_img(path: &Path) -> Result<(Vec<u8>, u32, u32), Box<dyn Error>> {
    let mut decoder = png::Decoder::new(BufReader::new(File::open(path)?));
    decoder.set_transformations(png::Transformations::IDENTITY);

    let mut reader = decoder.read_info()?;
    // only None if it's too big for memory
    let mut buf = vec![0; reader.output_buffer_size().unwrap()];
    let info = reader.next_frame(&mut buf)?;

    if info.color_type != png::ColorType::Indexed {
        return Err(format!("{:#?}: not indexed", path.to_str()).into());
    }
    if info.bit_depth != png::BitDepth::Eight {
        return Err(format!(
            "{:#?}: expected 8-bit, got {:?}",
            path.to_str(),
            info.bit_depth
        )
        .into());
    }

    buf.truncate(info.buffer_size());
    Ok((buf, info.width, info.height))
}

#[derive(Deserialize, Clone, Copy, Debug)]
pub struct TileDimensions {
    pub short: u32,
    pub long: u32,
}

#[derive(Deserialize, Clone, Copy, Debug)]
pub enum TilesetPixelType {
    Void = 0,
    Terrain,
}

#[derive(Deserialize, Debug)]
struct TilesetManifest {
    dimensions: TileDimensions,
    palette: HashMap<u8, TilesetPixelType>,
}

fn load_manifest(path: &Path) -> Result<TilesetManifest, Box<dyn Error>> {
    Ok(toml::from_str(&std::fs::read_to_string(path)?)?)
}

#[derive(Debug)]
pub struct Tile {
    pub orientation: TileOrientation,
    pub dimensions: TileDimensions,
    pub pixels: Vec<TilesetPixelType>,
}

#[derive(Debug)]
pub struct Tileset {
    pub dimensions: TileDimensions,
    pub vertical_tiles: Vec<Tile>,
    pub horizontal_tiles: Vec<Tile>,
}

#[derive(Debug, Clone, Copy)]
pub enum TileOrientation {
    Horizontal,
    Vertical,
}

fn parse_row(
    y: u32,
    img: &(Vec<u8>, u32, u32),
    manifest: &TilesetManifest,
    orientation: TileOrientation,
) -> Result<Vec<Tile>, String> {
    let ey = match orientation {
        TileOrientation::Horizontal => y + manifest.dimensions.short,
        TileOrientation::Vertical => y + manifest.dimensions.long,
    };
    let mut tiles = Vec::new();
    let mut x = 1;
    loop {
        if x >= img.1 {
            break;
        }
        let left_border = img.0[(x - 1 + y * img.1) as usize];
        // 2 = border color
        if left_border != 2 {
            break;
        }

        let mut tile_pixels = Vec::new();
        let ex = match orientation {
            TileOrientation::Horizontal => x + manifest.dimensions.long,
            TileOrientation::Vertical => x + manifest.dimensions.short,
        };

        for py in y..ey {
            for px in x..ex {
                let idx = img.0[(px + py * img.1) as usize];
                let palette = manifest.palette.get(&idx);

                match palette {
                    Some(pixel_type) => tile_pixels.push(*pixel_type),
                    None => {
                        return Err(format!(
                            "Pixel ({px},{py}) resolved to idx {idx} which isn't in the palette"
                        ));
                    }
                }
            }
        }

        debug_assert!(
            tile_pixels.len() == (manifest.dimensions.long * manifest.dimensions.short) as usize
        );

        tiles.push(Tile {
            orientation,
            dimensions: manifest.dimensions,
            pixels: tile_pixels,
        });

        x = ex + 3;
    }
    Ok(tiles)
}

fn parse_tiles(
    img: &(Vec<u8>, u32, u32),
    manifest: &TilesetManifest,
) -> Result<(Vec<Tile>, Vec<Tile>), String> {
    let mut horizontal_tiles = Vec::new();
    let mut vertical_tiles = Vec::new();
    let mut y = 0;
    loop {
        if y >= img.2 {
            break;
        }

        let edge = img.0[((y) * img.1) as usize] == 2;
        if !edge {
            y += 1;
            continue;
        }

        let orientation = if img.0[((y + manifest.dimensions.short + 2) * img.1) as usize] == 0 {
            TileOrientation::Horizontal
        } else {
            TileOrientation::Vertical
        };

        let parse_result = parse_row(y + 1, img, manifest, orientation);
        match parse_result {
            Ok(mut tiles) => match orientation {
                TileOrientation::Horizontal => {
                    println!("Parsed horizontal row {y}. {n} entries", n = tiles.len());
                    horizontal_tiles.append(&mut tiles);
                    y += manifest.dimensions.short + 3;
                }
                TileOrientation::Vertical => {
                    println!("Parsed vertical row {y}. {n} entries", n = tiles.len());
                    vertical_tiles.append(&mut tiles);
                    y += manifest.dimensions.long + 3;
                }
            },
            Err(e) => {
                return Err(format!(
                    "Failed to parse row {} ({:#?}): {e}",
                    y + 1,
                    orientation
                ));
            }
        }
    }

    Ok((horizontal_tiles, vertical_tiles))
}

pub fn load_tileset(path: &str) -> Tileset {
    let img_result = load_img(&Path::join(Path::new(path), Path::new("img.png")));
    match img_result {
        Ok(img_result) => {
            let manifest_result =
                load_manifest(&Path::join(Path::new(path), Path::new("manifest.toml")));
            match manifest_result {
                Ok(manifest) => {
                    debug_assert!(manifest.dimensions.long == manifest.dimensions.short * 2);
                    let (horizontal_tiles, vertical_tiles) =
                        parse_tiles(&img_result, &manifest).unwrap();

                    Tileset {
                        dimensions: manifest.dimensions,
                        vertical_tiles,
                        horizontal_tiles,
                    }
                }
                Err(e) => {
                    panic!("Couldn't load sprite: {}", e)
                }
            }
        }
        Err(e) => {
            panic!("Couldn't load sprite: {}", e)
        }
    }
}