-- Lesson 6: Lists Of Things

local STAR_COUNT  = 120
local STAR_SHADE  = 55
local BURST_COUNT = 10

local PLAYER_WIDTH  = 20
local PLAYER_HEIGHT = 6
local PLAYER_SPEED  = 3
local PLAYER_MARGIN = 6

local width  = overlayGetWidth()
local height = overlayGetHeight()

local stars       = {}
local playerX     = width // 2
local playerY     = height - PLAYER_HEIGHT - PLAYER_MARGIN
local movingLeft  = false
local movingRight = false


local function clamp(value, low, high)
    if value < low then
        return low
    end
    if value > high then
        return high
    end
    return value
end


local function newStar(y)
    local speed = math.random(1, 3)
    local star  = {
        x     = math.random(0, width - 1),
        y     = y,
        speed = speed,
        shade = math.random(60, 90) + speed * STAR_SHADE
    }
    return star
end


local function makeStars()
    for number = 1, STAR_COUNT do
        table.insert(stars, newStar(math.random(0, height - 1)))
    end
end


local function addBurst()
    for number = 1, BURST_COUNT do
        table.insert(stars, newStar(0))
    end
end


local function moveStars()
    for i = #stars, 1, -1 do
        local star = stars[i]
        star.y = star.y + star.speed
        if star.y >= height then
            table.remove(stars, i)
        end
    end
    while #stars < STAR_COUNT do
        table.insert(stars, newStar(0))
    end
end


local function drawStar(star)
    colorForeground(star.shade, star.shade, star.shade)
    overlayPlot(star.x, star.y)
end


local function drawStars()
    for _, star in ipairs(stars) do
        drawStar(star)
    end
end


local function drawPlayer()
    colorForeground(80, 255, 120)
    overlayBox(playerX, playerY, playerX + PLAYER_WIDTH, playerY + PLAYER_HEIGHT)
end


local function movePlayer()
    if movingLeft then
        playerX = playerX - PLAYER_SPEED
    end
    if movingRight then
        playerX = playerX + PLAYER_SPEED
    end
    playerX = clamp(playerX, 0, width - PLAYER_WIDTH - 1)
end


function onInputPressed(what)
    if what == SWITCH_LEFT then
        movingLeft = true
    elseif what == SWITCH_RIGHT then
        movingRight = true
    elseif what == SWITCH_BUTTON1 then
        addBurst()
    end
end


function onInputReleased(what)
    if what == SWITCH_LEFT then
        movingLeft = false
    elseif what == SWITCH_RIGHT then
        movingRight = false
    end
end


function onOverlayUpdate()
    overlayClear()
    movePlayer()
    moveStars()
    drawStars()
    drawPlayer()
    overlayPrint(0, 0, "Stars: " .. #stars)
    return OVERLAY_UPDATED
end


makeStars()