local M = {}

local PADDING = 16
local ROW_HEIGHT = 56
local ROW_GAP = 4
local COLOR_BG          = 0x202020FF
local COLOR_ROW         = 0x303030FF
local COLOR_ROW_HOVER   = 0x404040FF
local COLOR_ROW_ACTIVE  = 0x505080FF
local COLOR_TEXT        = 0xE0E0E0FF
local COLOR_DIM         = 0xA0A0A0FF
local COLOR_TAGS        = 0x8090A0FF
local FONT              = 18
local FONT_TAGS         = 13
local SCROLLBAR_W       = 6
local COLOR_SCROLL_TRACK = 0x00000040
local COLOR_SCROLL_THUMB = 0x707070FF

-- Total scrollable content height for the current entry set (news row +
-- all module rows). Used for scroll-clamp + scrollbar sizing.
local function content_height(ctx)
    local rows = #ctx.module_entries + (ctx.news_entry and 1 or 0)
    if rows == 0 then return 0 end
    return rows * (ROW_HEIGHT + ROW_GAP) - ROW_GAP + 2 * PADDING
end

-- Draw a vertical scrollbar inset on the panel's right edge when content
-- overflows the viewport. Mirrors detail.lua's scrollbar (kept inline in
-- both panels for cognitive locality — see Lib-Cut criterion).
local function draw_scrollbar(p, scroll_y, content_h, view_h)
    if content_h <= view_h then return end
    local track_x = p.x + p.w - SCROLLBAR_W - 2
    engine.render.draw_rect(track_x, p.y, SCROLLBAR_W, view_h, COLOR_SCROLL_TRACK)
    local thumb_h = math.max(24, view_h * view_h / content_h)
    local max_scroll = content_h - view_h
    local frac = (max_scroll > 0) and (scroll_y / max_scroll) or 0
    local thumb_y = p.y + frac * (view_h - thumb_h)
    engine.render.draw_rect(track_x, thumb_y, SCROLLBAR_W, thumb_h, COLOR_SCROLL_THUMB)
end

-- Returns the rect rect-table {x,y,w,h} of the row for entry index i.
function M.row_rect(ctx, i)
    local p = ctx.list_panel_rect
    return {
        x = p.x + PADDING,
        y = p.y + PADDING + (i - 1) * (ROW_HEIGHT + ROW_GAP) - ctx.scroll_y,
        w = p.w - 2 * PADDING,
        h = ROW_HEIGHT,
    }
end

-- Row title: name only (the long `summary` moved to the detail panel).
local function label_for(entry)
    return entry.name or entry.id
end

-- Compact genre-tag subline ("Mittelalter · Hightech"), or nil if the
-- module's manifest.launcher.md carries no tags.
local function tags_line(entry)
    if not entry.tags or #entry.tags == 0 then return nil end
    return table.concat(entry.tags, " · ")
end

function M.render(ctx)
    local p = ctx.list_panel_rect
    -- Apply whole-list bg tint per L-Q6 if conflicts exist.
    local bg = COLOR_BG
    if ctx.list_tint == "warn"  then bg = 0x4A3A1AFF end
    if ctx.list_tint == "error" then bg = 0x4A1A1AFF end
    engine.render.draw_rect(p.x, p.y, p.w, p.h, bg)

    -- News row pinned on top.
    if ctx.news_entry then
        local rect = {
            x = p.x + PADDING, y = p.y + PADDING - ctx.scroll_y,
            w = p.w - 2 * PADDING, h = ROW_HEIGHT,
        }
        local col = (ctx.selected_entry == "news") and COLOR_ROW_ACTIVE or COLOR_ROW
        engine.render.draw_rect(rect.x, rect.y, rect.w, rect.h, col)
        engine.render.draw_text(
            ctx.news_entry.title or ctx.t("news_default_title"),
            rect.x + PADDING, rect.y + PADDING, FONT, COLOR_TEXT)
        ctx.news_entry.rect = rect
    end

    for i, entry in ipairs(ctx.module_entries) do
        local rect = M.row_rect(ctx, i + (ctx.news_entry and 1 or 0))
        if rect.y + rect.h >= p.y and rect.y <= p.y + p.h then
            local col = COLOR_ROW
            if ctx.selected_entry == entry.id then col = COLOR_ROW_ACTIVE end
            engine.render.draw_rect(rect.x, rect.y, rect.w, rect.h, col)
            -- Module name on top, genre tags small below.
            engine.render.draw_text(label_for(entry),
                rect.x + PADDING, rect.y + 8, FONT, COLOR_TEXT)
            local tags = tags_line(entry)
            if tags then
                engine.render.draw_text(tags,
                    rect.x + PADDING, rect.y + 8 + FONT + 6, FONT_TAGS, COLOR_TAGS)
            end
        end
        entry.rect = rect
    end

    draw_scrollbar(p, ctx.scroll_y, content_height(ctx), p.h)
end

-- Selecting a different entry resets the detail panel's scroll so the new
-- module's content starts from the top.
local function select(ctx, id)
    if ctx.selected_entry ~= id then ctx.detail_scroll_y = 0 end
    ctx.selected_entry = id
end

function M.handle_click(ctx, mx, my)
    if ctx.news_entry and engine.spatial.aabb_contains_point(ctx.news_entry.rect, mx, my) then
        select(ctx, "news")
        return true
    end
    for _, entry in ipairs(ctx.module_entries) do
        if entry.rect and engine.spatial.aabb_contains_point(entry.rect, mx, my) then
            select(ctx, entry.id)
            return true
        end
    end
    return false
end

function M.handle_scroll(ctx, dy)
    local p = ctx.list_panel_rect
    local max_scroll = math.max(0, content_height(ctx) - p.h)
    ctx.scroll_y = math.max(0, math.min(max_scroll, ctx.scroll_y - dy * 24))
end

return M