//! SCI's core rendering model: every room is FOUR aligned screens.
//!
//! AGI squeezed depth and walls into one buffer (values 0-3 were walls, 4-15
//! were depth) — which is why AGI rooms can't have a wall you also walk
//! behind. SCI split them, and so do we:
//!
//! * **visual** — palette indices (0..=255), what the player sees
//! * **priority** — depth bands 0..=15 (higher = nearer the camera)
//! * **control** — walkability bitflags (block / water), independent of depth
//! * **hotspot** — a click/step map: each pixel names the hotspot it belongs to
//!
//! The ego is drawn a pixel at a time, only where its priority >= the
//! scenery's — the whole "walk behind the column" trick with zero per-object
//! Z bookkeeping — while walls live on a *different* screen, so a barrier can
//! sit at any depth.

pub const PIC_W: usize = 320;
pub const PIC_H: usize = 190;

/// The "open" color the visual buffer clears to.
pub const BG_VISUAL: u8 = 0;

// --- control bitflags -------------------------------------------------------
/// Nothing may step here.
pub const CTL_BLOCK: u8 = 1;
/// Water: actors flagged `on_land_only` refuse it; scripts can ask `on_water()`.
pub const CTL_WATER: u8 = 2;

/// Number of depth bands.
pub const BANDS: u8 = 16;

/// Map a screen row to its default depth band: 0 at the top of the play area
/// down to 15 at the very bottom. This is what makes a flat floor sort
/// correctly with no extra work from the room author.
#[inline]
pub fn band(y: usize) -> u8 {
    ((y * BANDS as usize) / PIC_H).min(15) as u8
}

pub struct Screens {
    pub visual: Vec<u8>,
    pub priority: Vec<u8>,
    pub control: Vec<u8>,
    pub hotspot: Vec<u8>,
}

impl Screens {
    pub fn new() -> Self {
        let mut s = Screens {
            visual: vec![BG_VISUAL; PIC_W * PIC_H],
            priority: vec![0; PIC_W * PIC_H],
            control: vec![0; PIC_W * PIC_H],
            hotspot: vec![0; PIC_W * PIC_H],
        };
        s.clear();
        s
    }

    /// Reset to a blank room: black visual, default depth bands, all-open
    /// control, no hotspots.
    pub fn clear(&mut self) {
        for y in 0..PIC_H {
            let p = band(y);
            let row = y * PIC_W;
            for x in 0..PIC_W {
                self.visual[row + x] = BG_VISUAL;
                self.priority[row + x] = p;
                self.control[row + x] = 0;
                self.hotspot[row + x] = 0;
            }
        }
    }

    #[inline]
    pub fn in_bounds(x: i32, y: i32) -> bool {
        x >= 0 && y >= 0 && (x as usize) < PIC_W && (y as usize) < PIC_H
    }

    #[inline]
    pub fn idx(x: i32, y: i32) -> usize {
        y as usize * PIC_W + x as usize
    }

    /// Control flags at a point; off-screen reads as a solid wall.
    #[inline]
    pub fn control_at(&self, x: i32, y: i32) -> u8 {
        if Self::in_bounds(x, y) {
            self.control[Self::idx(x, y)]
        } else {
            CTL_BLOCK
        }
    }

    /// Is this point free to stand on?
    #[inline]
    pub fn walkable(&self, x: i32, y: i32) -> bool {
        self.control_at(x, y) & CTL_BLOCK == 0
    }

    #[inline]
    pub fn priority_at(&self, x: i32, y: i32) -> u8 {
        if Self::in_bounds(x, y) {
            self.priority[Self::idx(x, y)]
        } else {
            15
        }
    }

    /// Which hotspot (0 = none) owns this pixel?
    #[inline]
    pub fn hotspot_at(&self, x: i32, y: i32) -> u8 {
        if Self::in_bounds(x, y) {
            self.hotspot[Self::idx(x, y)]
        } else {
            0
        }
    }
}

impl Default for Screens {
    fn default() -> Self {
        Self::new()
    }
}