-- Freefalling debris: 6 shrapnel pieces spawned when a tank is destroyed.
-- Random linear + angular velocity with gravity; auto-despawn when they fall below ground.
local Palette = require("rendering.palette")
local Projection = require("rendering.projection")
local Models = require("data.models")

local Debris = {}

local pieces = {}

local PIECES_PER_EXPLOSION = 6
local MAX_VELOCITY = 120          -- spread of initial shrapnel velocities
local MAX_ANG_VELOCITY = 10       -- rad/s on each axis
local GRAVITY = 90                -- world units/sec² downward

local function randomModel()
    local pool = Models.debrisPool
    return pool[math.random(1, #pool)]
end

function Debris.explode(x, y, z)
    y = y or 0
    for _ = 1, PIECES_PER_EXPLOSION do
        table.insert(pieces, {
            x = x, y = y, z = z,
            vx = (math.random() * 2 - 1) * MAX_VELOCITY,
            vy = math.random() * MAX_VELOCITY,               -- up (positive in our world)
            vz = (math.random() * 2 - 1) * MAX_VELOCITY,
            rx = math.random() * math.pi * 2,
            ry = math.random() * math.pi * 2,
            rz = math.random() * math.pi * 2,
            drx = (math.random() * 2 - 1) * MAX_ANG_VELOCITY,
            dry = (math.random() * 2 - 1) * MAX_ANG_VELOCITY,
            drz = (math.random() * 2 - 1) * MAX_ANG_VELOCITY,
            model = randomModel(),
        })
    end
end

function Debris.update(dt)
    for i = #pieces, 1, -1 do
        local d = pieces[i]
        d.x = d.x + d.vx * dt
        d.y = d.y + d.vy * dt
        d.z = d.z + d.vz * dt
        d.rx = d.rx + d.drx * dt
        d.ry = d.ry + d.dry * dt
        d.rz = d.rz + d.drz * dt
        d.vy = d.vy - GRAVITY * dt
        if d.y < 0 then
            table.remove(pieces, i)
        end
    end
end

function Debris.draw()
    local p = Palette.get()
    love.graphics.setColor(p.bright)
    love.graphics.setLineWidth(1.5)
    for _, d in ipairs(pieces) do
        Projection.drawModelXYZ(d.model, d.x, d.y, d.z, d.rx, d.ry, d.rz)
    end
end

function Debris.clear()
    pieces = {}
end

return Debris