-- Voxel world mode: free movement for the free-roam rungs.
--
-- The engine walks a grid: sixteen frames per cell, four directions,
-- input locked mid-step. Inside a camera that stands with the player that
-- gait reads as riding a rail, so while 1ST or 3RD drives, this module
-- replaces the WALK and nothing else: the player's position becomes
-- continuous, steered by the camera's own yaw -- push forward and you go
-- where you look, at any angle, sliding along whatever you graze.
--
-- Both rungs walk identically: the boom behind the shoulder (3RD) changes
-- where the eye stands, not which way it points, and the walk was always
-- rotated by the YAW. The one thing it does change is which way the body
-- POINTS while it moves -- see bodyFacing in the tick.
--
-- THE GRID IS STILL THE GAME. Every fact the world cares about is a fact
-- about cells -- what blocks, what warps, what rustles, what bites -- and
-- this module keeps the player's logical cell synced to wherever the free
-- walk stands, then reuses the engine's own machinery for every one of
-- those questions:
--
--   passability      the same isWalkableCell / water-while-surfing /
--                    tile-pair / entity-occupancy verdicts Collision
--                    hands the grid walker, asked per cell the player's
--                    body overlaps.
--
--   cell arrival     OverworldState:onStepComplete, the same landing
--                    pipeline a grid step runs -- warps, spinners, gates,
--                    forced currents, poison, repel, encounters, the
--                    step counters -- fired once per cell crossed, which
--                    is exactly the rate a grid walk fires it.
--
--   the special pushes   walking off the map edge, into a ledge, or into
--                    a boulder hands the quantised direction straight to
--                    checkEdgeExit / checkLedgeHop / checkBoulderPush,
--                    the engine's own handlers, which validate and stage
--                    everything themselves (connections, the hop arc,
--                    the two-push arm). While any of those animates a
--                    scripted grid move, this module stands aside and
--                    adopts the result.
--
-- Nothing here writes save state, rolls encounters, or decides what a
-- warp does -- it moves a point, keeps the cell honest, and lets the
-- engine be the engine. Stepping off the rung snaps the point to its
-- cell and hands the walk back to the grid, and with the rung off this
-- module costs one gate check per frame.

-- the mod namespace (see main.lua): V.require loads a sibling module
local V = ...

local FirstPerson = V.require("FirstPerson")

local FreeMove = {}

-- The body: a circle in the ground plane. Small enough to walk every
-- one-cell corridor the grid game has (half a cell is 8), big enough to
-- keep the eye's near plane out of wall faces when sliding along them.
FreeMove.RADIUS = 5.5

-- World pixels per fixed 60Hz frame -- the grid walker's own speeds (16
-- frames per 16px cell on foot, 8 on the bike), so distance covered per
-- second is unchanged and the encounter rate per tile crossed stays the
-- game's own.
FreeMove.WALK = 1.0
FreeMove.BIKE = 2.0

local EPS = 0.01

-- the free position (player centre, world px) and the px/py we last wrote
-- -- if they differ from the player's, something else (a warp, a script)
-- moved them, and the free walk adopts rather than fights
local pos = nil
local lastPx, lastPy = nil, nil

local function adopt(p)
  pos = { x = p.px + 8, z = p.py + 8 }
  lastPx, lastPy = p.px, p.py
end

function FreeMove.drop()
  pos = nil
  -- and the body with it: while something else is walking the player --
  -- a scripted move, a ledge hop, the grid walk off the rung -- the
  -- engine's own four-direction facing is the whole truth about which way
  -- they point, so the card must stop reading our finer one
  FirstPerson.releaseBody()
end

-- named for the suite: the module's live position, nil while dropped
function FreeMove._pos()
  return pos
end

-- ------- the per-cell verdict
--
-- The same questions Collision.canMove asks for a grid step, asked of one
-- cell from the player's current standing. The player's OWN cell never
-- blocks -- the body must always be free to leave wherever it stands
-- (a warp mat, the water it is surfing, a cell an NPC just stepped
-- against).

local function pairBlocked(map, surfing, sx, sy, tx, ty)
  local Game = require("src.core.Game")
  local tp = Game.data and Game.data.field and Game.data.field.tilePairs
  if not tp then return false end
  local list = surfing and tp.water or tp.land
  if not list or #list == 0 then return false end
  local tileset = map.def.tileset
  local a = map:cellTile(sx, sy)
  local b = map:cellTile(tx, ty)
  for _, p in ipairs(list) do
    if p.tileset == tileset
       and ((p.a == a and p.b == b) or (p.a == b and p.b == a)) then
      return true
    end
  end
  return false
end

-- Why (cx, cy) refuses the player's body, or nil when it may enter:
-- "bounds" | "tile" | "entity", the grid verdict's own names.
local function blockedCell(state, p, cx, cy)
  if cx == p.cellX and cy == p.cellY then return nil end
  local map = state.map
  if not map:inBounds(cx, cy) then return "bounds" end
  if not map:isWalkableCell(cx, cy) then
    if not (p.surfing and map:isWaterCell(cx, cy)) then return "tile" end
  end
  if pairBlocked(map, p.surfing, p.cellX, p.cellY, cx, cy) then
    return "tile"
  end
  local Collision = require("src.world.Collision")
  if Collision.occupied(state.entities, cx, cy, p) then return "entity" end
  return nil
end

FreeMove._blockedCell = blockedCell   -- named for the suite

-- ------- the slide
--
-- One axis at a time, clamped at the first refusing cell's face: the
-- classic axis-separated walk, which is where wall-sliding comes from --
-- the blocked axis stops and the free one keeps going. Returns the
-- refusal ("bounds"/"tile"/"entity") when this axis was clamped.

local function slideX(state, p, dx)
  if dx == 0 then return nil end
  local r = FreeMove.RADIUS
  local nx = pos.x + dx
  local z0 = math.floor((pos.z - r + EPS) / 16)
  local z1 = math.floor((pos.z + r - EPS) / 16)
  local hit = nil
  local edge = dx > 0 and math.floor((nx + r) / 16)
               or math.floor((nx - r) / 16)
  for zc = z0, z1 do
    hit = blockedCell(state, p, edge, zc)
    if hit then break end
  end
  if hit then
    if dx > 0 then nx = math.min(nx, edge * 16 - r - EPS)
    else nx = math.max(nx, (edge + 1) * 16 + r + EPS) end
  end
  pos.x = nx
  return hit
end

local function slideZ(state, p, dz)
  if dz == 0 then return nil end
  local r = FreeMove.RADIUS
  local nz = pos.z + dz
  local x0 = math.floor((pos.x - r + EPS) / 16)
  local x1 = math.floor((pos.x + r - EPS) / 16)
  local hit = nil
  local edge = dz > 0 and math.floor((nz + r) / 16)
               or math.floor((nz - r) / 16)
  for xc = x0, x1 do
    hit = blockedCell(state, p, xc, edge)
    if hit then break end
  end
  if hit then
    if dz > 0 then nz = math.min(nz, edge * 16 - r - EPS)
    else nz = math.max(nz, (edge + 1) * 16 + r + EPS) end
  end
  pos.z = nz
  return hit
end

-- ------- the blocked push
--
-- The grid game's blocked step is where half its verbs live: the map-edge
-- crossing, the ledge hop, the boulder shove, the route-gate warp fired
-- by collision, and the honest bonk. Hand the engine the quantised
-- direction and let its own handlers decide -- each one validates itself
-- (checkLedgeHop matches the tile pair, checkEdgeExit checks the bounds),
-- so calling them on every firm push is safe. Returns true when one of
-- them took the frame over.
local function pushSpecials(state, dir, why)
  local p = state.player
  p.facing = dir      -- the handlers read the push off the facing
  if why == "bounds" and state:checkEdgeExit(dir) then return true end
  if state:checkLedgeHop(dir) then return true end
  if state:checkBoulderPush(dir) then return true end
  if why ~= "entity" and state:canCollisionWarp() then
    local Game = require("src.core.Game")
    local Warp = require("src.world.Warp")
    local w = Warp.onCollision(state.map, Game.data.field.warpCarpets,
                               p.cellX, p.cellY, dir)
    if w then
      state:takeWarp(w.def)
      return true
    end
  end
  -- and NO bonk. The grid walk's collision sound marks a discrete event:
  -- you pressed a direction, the step was refused, nothing happened. A
  -- free walk has no such moment -- the body slides along every wall it
  -- grazes, continuously, and a corridor taken at a slight angle is a
  -- steady graze from end to end. Rate-limited or not, that came out as a
  -- machine-gun of bonks for walking normally down a hallway. The wall
  -- stopping you is the feedback; the sound only ever said so twice a
  -- second whether or not anything had changed.
  return false
end

-- ------- the tick
--
-- Runs in place of OverworldState:handleInput while first person drives
-- (see install below), which means it inherits every gate the grid walk
-- has: never during scripted moves, transitions, or with anything above
-- the overworld on the stack.

function FreeMove.tick(state)
  local p = state.player

  -- a grid move is animating -- a ledge hop, a spinner slide, a scripted
  -- walk -- or a cutscene owns the player: stand aside, adopt the result
  if p.moving or p.inputLocked then
    FreeMove.drop()
    return
  end
  if not pos or p.px ~= lastPx or p.py ~= lastPy then adopt(p) end

  local Game = require("src.core.Game")
  local input = Game.input

  -- the head is the facing: what A talks to, what the sun's card shows,
  -- which way a bonk points. (A body that is WALKING may turn along its
  -- travel instead -- see below, once there is a travel to turn along; a
  -- standing one always faces where the camera looks, which is what makes
  -- A predictable.) pointBody rather than compassFacing, so the card also
  -- gets the CONTINUOUS bearing behind that compass point.
  p.facing = FirstPerson.pointBody(0, 0)

  if input:wasPressed("a") then
    state:interact()
    return
  end
  if input:wasPressed("start") then
    require("src.core.Sound").play(Game.data, "Start_Menu")
    require("src.ui.Screens").push(Game, "StartMenu")
    return
  end

  local mx, mz = FirstPerson.moveVector()
  local wx, wz = FirstPerson.moveWorld(mx, mz)

  -- Cycling Road's downhill pull, the free-walk restatement of the grid
  -- path's simulated PAD_DOWN: south drift with nothing held, braked by
  -- holding A or B exactly as the Route 17 sign promises
  local moving = (mx ~= 0 or mz ~= 0)
  if not moving and Game.save and Game.save.onBike then
    local fm = Game.data.field.forcedMovement
    local braking = input:isDown("a") or input:isDown("b")
    if fm and not braking then
      for _, m in ipairs(fm.slopeMaps or {}) do
        if m == state.map.id then
          wx, wz, moving = 0, 1, true
          break
        end
      end
    end
  end

  if not moving then return end

  -- and once there IS a direction of travel, the body may point along it
  -- rather than along the head: on the boom (3RD) you can see yourself, so
  -- a strafe has to look like walking sideways. In the head it is the head
  -- either way -- bodyBearing says so.
  p.facing = FirstPerson.pointBody(wx, wz)

  -- the engine's own bonk clock, kept draining while the free walk has the
  -- wheel: nothing here rings it (see pushSpecials), but stepping back onto
  -- the grid must not inherit a cooldown frozen at whatever it held when
  -- the rung was picked
  state.bumpCooldown = math.max(0, (state.bumpCooldown or 0) - 1)

  local speed = (Game.save and Game.save.onBike) and FreeMove.BIKE
                or FreeMove.WALK
  local dx, dz = wx * speed, wz * speed

  local hitX = slideX(state, p, dx)
  local hitZ = slideZ(state, p, dz)

  -- the walk cycle: the wall-bonk clock animates the legs of a player the
  -- grid thinks is standing still, refreshed while the free walk covers
  -- ground (Player:update ticks animClock off it; walkPhase reads it)
  p.bumpFrames = 2

  p.px, p.py = pos.x - 8, pos.z - 8
  lastPx, lastPy = p.px, p.py

  -- the cell the body stands in; crossing into a new one IS a step
  local ncx = math.floor(pos.x / 16)
  local ncy = math.floor(pos.z / 16)
  if ncx ~= p.cellX or ncy ~= p.cellY then
    p.cellX, p.cellY = ncx, ncy
    state:onStepComplete()
    -- a warp or a battle may have moved the world out from under the
    -- walk; the adopt check on the next tick picks the pieces up
    return
  end

  -- a firm push into something that refused: the engine's own blocked-step
  -- verbs, aimed the way the push leans
  local hit, dir
  if hitX and (not hitZ or math.abs(dx) >= math.abs(dz)) then
    hit, dir = hitX, (dx > 0 and "right" or "left")
  elseif hitZ then
    hit, dir = hitZ, (dz > 0 and "down" or "up")
  end
  if hit and math.max(math.abs(dx), math.abs(dz)) > 0.4 * speed then
    if pushSpecials(state, dir, hit) then
      FreeMove.drop()
      return
    end
    -- the push handlers may have turned the facing; the walk still rules
    p.facing = FirstPerson.pointBody(wx, wz)
  end
end

-- ------- the seam
--
-- OverworldState:handleInput is the one choke point where the grid walk
-- reads the pad -- the same seam the engine's own Cycling Road pull and
-- collision warps live behind -- so replacing the walk means wrapping it
-- and nothing else. Every gate ABOVE the call (scripted moves, trainer
-- engagement, transitions, anything on the stack) still applies to the
-- free walk, because the wrap sits below them all.
function FreeMove.install()
  local OverworldState = require("src.world.OverworldController")
  if OverworldState.dramaticShapeFreeMoveHook then return end
  local inner = OverworldState.handleInput

  function OverworldState:handleInput()
    if not FirstPerson.driving() then
      if pos then
        -- stepping off the rung: back onto the grid, on the cell the
        -- free walk stood in
        local p = self.player
        p.px, p.py = p.cellX * 16, p.cellY * 16
        FreeMove.drop()
      end
      return inner(self)
    end
    return FreeMove.tick(self)
  end

  OverworldState.dramaticShapeFreeMoveHook = true
end

return FreeMove