Gauge = {}
Gauge.__index = Gauge

local function clamp(v, lo, hi) return math.max(lo, math.min(hi, v)) end

-- Port of Gauge::draw / Gauge::draw_dan. C++ keeps the points logic and hands the
-- numbers over every frame; this only decides what gets drawn where.
function Gauge.new(is_2p, dan, string_diff)
    local self = setmetatable({}, Gauge)
    self.dan = dan

    local cells = tex.get_skin_config("gauge_cells")
    self.bar_units = (cells and cells.x and cells.x > 0) and math.floor(cells.x + 0.5) or 87

    local p = (is_2p and "2p_" or "1p_")
    local function t(name) return tex.get_texture("game/" .. name) end

    if dan then
        self.bar         = t("gauge_dan/" .. p .. "bar")
        self.bar_fade    = t("gauge_dan/" .. p .. "bar_fade")
        self.border      = t("gauge_dan/border")
        self.unfilled    = t("gauge_dan/" .. p .. "unfilled")
        self.rainbow     = t("gauge_dan/rainbow")
        self.overlay     = t("gauge_dan/overlay")
        self.fire        = t("gauge_dan/tamashii_fire")
        self.tamashii    = t("gauge_dan/tamashii")
        self.tamashii_overlay = t("gauge_dan/tamashii_overlay")
        self.tamashii_dark    = t("gauge_dan/tamashii_dark")
        self.bar_width = tex.get_texture_info("gauge_dan", p .. "bar").width
    else
        self.border      = t("gauge/border" .. string_diff)
        self.unfilled    = t("gauge/" .. p .. "unfilled" .. string_diff)
        self.bar         = t("gauge/" .. p .. "bar")
        self.clear_transition      = t("gauge/bar_clear_transition")
        self.clear_top             = t("gauge/bar_clear_top")
        self.clear_bottom          = t("gauge/bar_clear_bottom")
        self.rainbow     = t("gauge/rainbow" .. string_diff)
        self.clear_transition_fade = t("gauge/bar_clear_transition_fade")
        self.clear_fade  = t("gauge/bar_clear_fade")
        self.bar_fade    = t("gauge/" .. p .. "bar_fade")
        self.overlay     = t("gauge/overlay" .. string_diff)
        self.fire        = t("gauge/tamashii_fire")
        self.tamashii    = t("gauge/tamashii")
        self.tamashii_overlay = t("gauge/tamashii_overlay")
        self.tamashii_dark    = t("gauge/tamashii_dark")
        -- language variants (clear_ja ...) are resolved by tex.get_texture
        self.clear      = t("gauge/clear")
        self.clear_dark = t("gauge/clear_dark")
        self.bar_width = tex.get_texture_info("gauge", p .. "bar").width
        self.art_tier = (string_diff == "_easy") and 0 or (string_diff == "_normal") and 1 or 2
    end
    return self
end

-- cell bookkeeping shared by both gauges: how many cells are solid, and the alpha of the
-- sprite on the cell that was just filled (nil when there is none to show).
function Gauge:cells(points, previous_points, max_points, anim_active, anim_alpha)
    local units = self.bar_units
    local length = math.floor(points * units / max_points)
    local previous = math.floor(previous_points * units / max_points)
    local fade_in = tex.get_option("gauge_cell_fade_in")
    local pending = length <= units and length > previous and anim_active
    local solid = (fade_in and pending) and length - 1 or length
    local alpha = fade_in and 1.0 - anim_alpha or anim_alpha
    local show_up
    if fade_in then show_up = pending else show_up = length <= units and length > previous end
    return length, solid, alpha, show_up, pending, fade_in
end

function Gauge:draw(y, points, previous_points, max_points, clear_points,
                    is_clear, is_rainbow, anim_active, anim_alpha, rainbow_fade, rainbow_frac, fire_frame)
    if self.dan then
        return self:draw_dan(points, previous_points, max_points, is_rainbow,
                             anim_active, anim_alpha, rainbow_fade, rainbow_frac, fire_frame)
    end
    local mirrored = y > tex.get_screen_height() / 2
    local mirror = mirrored and "vertical" or nil
    local idx = mirrored and 1 or 0

    tex.draw_texture(self.border,   { mirror = mirror, y = y, index = idx })
    tex.draw_texture(self.unfilled, { mirror = mirror, y = y, index = idx })

    local units, bw = self.bar_units, self.bar_width
    local length, solid, alpha, show_up, pending, fade_in =
        self:cells(points, previous_points, max_points, anim_active, anim_alpha)
    local clear_point = clamp(clear_points * units // max_points, 1, units)

    if solid > 0 then
        tex.draw_texture(self.bar, { y = y, index = idx,
            x2 = math.min(solid * bw, (clear_point - 1) * bw) - bw })
    end

    -- first gold cell lights exactly when the gauge is cleared (not by a cell-count test:
    -- on 87 cells 8000 -> 69.6 would light it a cell early/late vs. the clear state)
    if is_clear and not (fade_in and pending and length == clear_point) then
        tex.draw_texture(self.clear_transition,
            { mirror = mirror, x = (clear_point - 1) * bw, y = y, index = idx })
    end

    -- gold zone: cells clear_point .. solid-1, one cell wide piece so stretch is (n-1)*bw
    if solid > clear_point then
        local gold_x2 = (solid - clear_point) * bw - bw
        tex.draw_texture(self.clear_top,
            { mirror = mirror, x = clear_point * bw, y = y, x2 = gold_x2, index = idx })
        tex.draw_texture(self.clear_bottom,
            { x = clear_point * bw, y = y, x2 = gold_x2, index = idx })
    end

    if is_rainbow and rainbow_fade >= 0 then
        local frame_a = math.floor(rainbow_frac) % 8
        local frame_b = (frame_a + 1) % 8
        local f = rainbow_frac - math.floor(rainbow_frac)
        tex.draw_texture(self.rainbow,
            { frame = frame_a, mirror = mirror, y = y, fade = rainbow_fade, index = idx })
        tex.draw_texture(self.rainbow,
            { frame = frame_b, mirror = mirror, y = y, fade = rainbow_fade * f, index = idx })
    end

    if show_up then
        -- sprite sits on the cell that was just filled (length-1)
        local fx = (length - 1) * bw
        if length == clear_point then
            tex.draw_texture(self.clear_transition_fade,
                { mirror = mirror, x = fx, y = y, fade = alpha, index = idx })
        elseif length > clear_point then
            tex.draw_texture(self.clear_fade, { x = fx, y = y, fade = alpha, index = idx })
        else
            tex.draw_texture(self.bar_fade, { x = fx, y = y, fade = alpha, index = idx })
        end
    end

    tex.draw_texture(self.overlay, { mirror = mirror, y = y, fade = 0.15, index = idx })

    local label = self.art_tier + (mirrored and 3 or 0)
    if is_clear then
        tex.draw_texture(self.clear, { y = y, index = label })
        if is_rainbow then
            tex.draw_texture(self.fire,
                { frame = fire_frame, scale = 0.75, center = true, y = y, index = idx })
        end
        tex.draw_texture(self.tamashii, { y = y, index = idx })
        if is_rainbow and (fire_frame == 0 or fire_frame == 1 or fire_frame == 4 or fire_frame == 5) then
            tex.draw_texture(self.tamashii_overlay, { y = y, fade = 0.5, index = idx })
        end
    else
        tex.draw_texture(self.clear_dark, { y = y, index = label })
        tex.draw_texture(self.tamashii_dark, { y = y, index = idx })
    end
end

-- dan gauge sits at absolute positions from its texture.json: no lane offset, no mirroring
function Gauge:draw_dan(points, previous_points, max_points, is_rainbow,
                        anim_active, anim_alpha, rainbow_fade, rainbow_frac, fire_frame)
    tex.draw_texture(self.border, {})
    tex.draw_texture(self.unfilled, {})

    local bw = self.bar_width
    local length, solid, alpha, show_up = self:cells(points, previous_points, max_points, anim_active, anim_alpha)

    if solid > 0 then tex.draw_texture(self.bar, { x2 = solid * bw - bw }) end

    if is_rainbow and rainbow_fade >= 0 then
        local frame_a = math.floor(rainbow_frac) % 8
        local frame_b = (frame_a + 1) % 8
        local f = rainbow_frac - math.floor(rainbow_frac)
        tex.draw_texture(self.rainbow, { frame = frame_a, fade = rainbow_fade })
        tex.draw_texture(self.rainbow, { frame = frame_b, fade = rainbow_fade * f })
    end

    if show_up and length > 0 then
        tex.draw_texture(self.bar_fade, { x = (length - 1) * bw, fade = alpha })
    end

    tex.draw_texture(self.overlay, { fade = 0.15 })

    if is_rainbow then
        tex.draw_texture(self.fire, { frame = fire_frame, scale = 0.75, center = true })
        tex.draw_texture(self.tamashii, {})
        if fire_frame == 0 or fire_frame == 1 or fire_frame == 4 or fire_frame == 5 then
            tex.draw_texture(self.tamashii_overlay, { fade = 0.5 })
        end
    else
        tex.draw_texture(self.tamashii_dark, {})
    end
end