-- Agent-authored server policy. Geometry is calculated here, not baked into
-- one building prefab. Only immutable frames and typed build commands cross.
local PACKAGE = "studio.generated.meshy-hero"
local FLOORS, BAYS_X, BAYS_Z = 3, 5, 4
local BAY, STOREY, FRONT = 4, 4.2, 8
local BATCH, CADENCE = 10, 5

local plan = {}
local function put(part, x, y, z, yaw)
    table.insert(plan, {kind="build_prefab", prefab="package:"..PACKAGE..":"..part,
        x=x, y=y, z=z, yaw=yaw or 0, scale=1})
end
local width, depth = BAYS_X*BAY, BAYS_Z*BAY
local half = width/2

-- Courtyard slabs; the two middle bays remain an open atrium above ground.
for floor=0,FLOORS do
    for ix=0,BAYS_X-1 do
        for iz=0,BAYS_Z-1 do
            local atrium = floor>0 and ix==2 and (iz==1 or iz==2)
            if not atrium then
                put(floor==FLOORS and "roof" or "floor", -half+2+ix*BAY,
                    0.18+floor*STOREY, FRONT+2+iz*BAY)
            end
        end
    end
    if floor<FLOORS then
        for ix=0,BAYS_X do
            for iz=0,BAYS_Z do
                if ix==0 or ix==BAYS_X or iz==0 or iz==BAYS_Z or ix==2 then
                    put("column", -half+ix*BAY, 2.1+floor*STOREY, FRONT+iz*BAY)
                end
            end
        end
        -- Repeated window bays, an open front entrance, and side stair doors.
        for side=0,1 do
            local z=FRONT+side*depth
            for bay=0,BAYS_X-1 do
                local x=-half+2+bay*BAY
                local door = floor==0 and side==0 and bay==2
                if not door then
                    put("wall",x,0.9+floor*STOREY,z)
                    put("sill",x,1.62+floor*STOREY,z)
                end
                put("lintel",x,3.85+floor*STOREY,z)
            end
        end
        for side=0,1 do
            local x=-half+side*width
            for bay=0,BAYS_Z-1 do
                local z=FRONT+2+bay*BAY
                local stairDoor=side==0 and (bay==0 or bay==2)
                if not stairDoor then
                    put("wall",x,0.9+floor*STOREY,z,math.pi/2)
                    put("sill",x,1.62+floor*STOREY,z,math.pi/2)
                end
                put("lintel",x,3.85+floor*STOREY,z,math.pi/2)
            end
        end
    end
end

-- Switchback stairs and landings make the upper floors reachable.
for floor=0,FLOORS-2 do
    for step=1,12 do
        local z = floor%2==0 and (FRONT-1+step*0.8) or (FRONT+9.4-step*0.8)
        put("step",-half-1.5,0.18+floor*STOREY+step*STOREY/12,z)
    end
    put("landing",-half-1.5,0.18+(floor+1)*STOREY,
        floor%2==0 and FRONT+9.4 or FRONT-1)
end

-- Rooftop safety rails, a gantry, service vents and the entrance canopy.
for bay=0,BAYS_X-1 do
    for side=0,1 do
        put("rail",-half+2+bay*BAY,1+FLOORS*STOREY,FRONT+side*depth)
    end
end
for bay=0,BAYS_Z-1 do
    for side=0,1 do
        put("rail",-half+side*width,1+FLOORS*STOREY,FRONT+2+bay*BAY,math.pi/2)
    end
end
for i=0,2 do put("vent",-6+i*4,13.6,FRONT+depth-3) end
for i=-1,1 do
    put("canopy",i*4,3.45,FRONT-2)
    put("bollard",i*4,0.55,FRONT-4)
end
for i=0,3 do put("beam",-6+i*4,15,FRONT+2) end
put("gantry-post",-8,13.8,FRONT+2)
put("gantry-post",8,13.8,FRONT+2)

-- Attached four-storey observation tower and a bridge to the upper gallery.
local tx,tz=half+5,FRONT+depth-3
for floor=0,4 do
    put("tower-floor",tx,0.18+floor*STOREY,tz)
    for ix=-1,1,2 do
        for iz=-1,1,2 do
            if floor<4 then put("column",tx+ix*2,2.1+floor*STOREY,tz+iz*2) end
        end
    end
    if floor<4 then
        for side=-1,1,2 do
            put("wall",tx,0.9+floor*STOREY,tz+side*2)
            put("lintel",tx,3.85+floor*STOREY,tz+side*2)
            put("wall",tx+side*2,0.9+floor*STOREY,tz,math.pi/2)
            put("lintel",tx+side*2,3.85+floor*STOREY,tz,math.pi/2)
        end
    end
end
put("bridge",half+1.5,0.18+2*STOREY,tz)
put("beacon",tx,18,tz)

return {
    state_schema_version=1,
    initialize=function() return {type="integer",value=0} end,
    migrate=function(_,state) return state end,
    tick=function(frame,state)
        if state.value>=#plan or frame.tick%CADENCE~=0 then return {},state end
        local last=math.min(state.value+BATCH,#plan)
        local commands={}
        for index=state.value+1,last do table.insert(commands,plan[index]) end
        -- Cursor advances in the SAME authoritative transaction as the pieces.
        -- Checkpoint recovery continues exactly once; it never rebuilds a hole.
        return commands,{type="integer",value=last}
    end,
}