//! Minimal Tiled-CSV map loader.
//!
//! Reads a bare comma-separated tile grid (Tiled's "CSV" layer export, stripped of the
//! surrounding TMX/XML). Dimensions are derived from the content: columns from the first
//! row, height from the row count. Tiled encodes per-tile flip/rotation in the top bits of
//! each 32-bit GID, which makes flipped tiles show up as large negative decimals — those
//! bits are masked off here, leaving the bare tile_id. Flip orientation is discarded for now.

use crate::chunk::TileFlags;

/// Top three bits hold horizontal / vertical / diagonal flip flags; the rest is the tile id.
const GID_FLIP_MASK: u32 = 0x1FFF_FFFF;

pub struct TileMap {
    pub width:  u16,
    pub height: u16,
    pub tiles:  Vec<u16>, // row-major, len == width * height
}

impl TileMap {
    pub fn from_csv(path: &str) -> Self {
        let text = std::fs::read_to_string(path)
            .unwrap_or_else(|e| panic!("failed to read map {path}: {e}"));

        let mut tiles = Vec::new();
        let mut width = 0usize;
        let mut height = 0usize;

        for line in text.lines() {
            if line.trim().is_empty() {
                continue;
            }
            let mut cols = 0usize;
            for field in line.split(',') {
                let field = field.trim();
                if field.is_empty() {
                    continue; // tolerate a trailing comma
                }
                // Parse as i64 so the "negative" flipped GIDs fit, then reinterpret the low
                // 32 bits as u32 and strip the flip flags.
                let raw = field.parse::<i64>()
                    .unwrap_or_else(|_| panic!("invalid tile value {field:?} in {path}"));
                let gid = (raw as u32) & GID_FLIP_MASK;
                tiles.push(gid as u16);
                cols += 1;
            }
            if width == 0 {
                width = cols;
            } else if cols != width {
                panic!("ragged map row in {path}: expected {width} cols, got {cols}");
            }
            height += 1;
        }

        TileMap { width: width as u16, height: height as u16, tiles }
    }

    /// Tile id at map coordinates, or 0 (empty) when outside the map bounds.
    pub fn tile(&self, x: i16, y: i16) -> u16 {
        if x < 0 || y < 0 || x >= self.width as i16 || y >= self.height as i16 {
            return 0;
        }
        self.tiles[y as usize * self.width as usize + x as usize]
    }
}

/// Gameplay flags for a global tile id. Collision comes from the shared movement
/// vocabulary (`shared::tile_collidable`) so the client can predict it identically;
/// other flags (opaque, …) stay server-side. Tile ids index into `overworld.tga`.
pub fn tile_flags(tile_id: u16) -> TileFlags {
    let mut bits = 0u8;
    if shared::tile_collidable(tile_id) {
        bits |= TileFlags::COLLIDABLE;
    }
    TileFlags(bits)
}