-- =====================================================================
-- lib-core.maps — Single Tile-Grid Map Lib (P.0)
-- See: meta/docs/superpowers/specs/2026-05-09-p0-lib-maps-design.md
--
-- Forward-compat stubs (DEPRECATED-MVP) for: multi-map-graph,
-- lifecycle-states, walls, sprite-fields, generators, save-integration,
-- cross-lib tilemap resolution, override-field-merge, sub-require.
-- =====================================================================

-- Module-private state
local map_registry      = {}    -- map_id -> Map
local tilemap_registry  = {}    -- full_tilemap_id -> Tilemap
local current_map_id    = nil

-- =====================================================================
-- Packed-u32 GID encoding (Schema-v2)
-- Bit-Layout:
--   Bits 31..24 : atlas_index  (8 bits, 0..255)
--   Bits 23..4  : tile_id      (20 bits, 0..1_048_575)
--   Bits 3..2   : rotation     (2 bits, 0..3, n * 90° CW)
--   Bits 1..0   : reserved     (must be 0 in v2; future flip-h/v)
-- gid == 0 means empty cell (atlas 0 + tile 0 reserved as null).
-- =====================================================================

local GID_ATLAS_SHIFT = 24
local GID_TILE_SHIFT  = 4
local GID_ROT_SHIFT   = 2
local GID_ATLAS_MASK  = 0xFF        -- 8 bits
local GID_TILE_MASK   = 0xFFFFF     -- 20 bits
local GID_ROT_MASK    = 0x3         -- 2 bits

local function encode_gid(atlas_index, tile_id, rotation)
    rotation = rotation or 0
    return (atlas_index << GID_ATLAS_SHIFT)
         | (tile_id     << GID_TILE_SHIFT)
         | (rotation    << GID_ROT_SHIFT)
end

local function decode_gid(gid)
    local atlas_index = (gid >> GID_ATLAS_SHIFT) & GID_ATLAS_MASK
    local tile_id     = (gid >> GID_TILE_SHIFT)  & GID_TILE_MASK
    local rotation    = (gid >> GID_ROT_SHIFT)   & GID_ROT_MASK
    return atlas_index, tile_id, rotation
end

-- =====================================================================
-- Schema v1→v2 Auto-Upgrade (transparent beim Load)
-- v1: { id, tilemap, size, tiles[], tile_rotations? }
-- v2: { schema_version, id, size, atlases[], layers: { surface: { tiles[] } }, roof? }
-- =====================================================================

local function upgrade_v1_to_v2(v1)
    local atlas_id = v1.tilemap or "default_tilemap"
    local v1_tiles = v1.tiles or {}
    local v1_rots  = v1.tile_rotations or {}

    local gids = {}
    for i = 1, #v1_tiles do
        local tile_id = v1_tiles[i]
        local rot_deg = v1_rots[i] or 0
        local rot_quad = math.floor(rot_deg / 90) % 4
        if tile_id == 0 then
            gids[i] = 0
        else
            gids[i] = encode_gid(0, tile_id, rot_quad)
        end
    end

    return {
        schema_version = 2,
        id   = v1.id,
        size = v1.size,
        atlases = { atlas_id },
        layers = {
            surface = { tiles = gids }
        }
    }
end

-- =====================================================================
-- Schema-validation helper (used by both v1 and v2 validators)
-- =====================================================================

-- Schema-validation helper: reads required field with type-check.
local function require_field(t, key, expected_type, source)
    local v = t[key]
    if v == nil then
        error(string.format("maps.load: schema violation in %s: missing required field '%s'",
            source, key))
    end
    if type(v) ~= expected_type then
        error(string.format("maps.load: schema violation in %s: field '%s' must be %s, got %s",
            source, key, expected_type, type(v)))
    end
    return v
end

-- =====================================================================
-- Schema-v2 Layer-Whitelist + Validation
-- =====================================================================

local VALID_LAYER_NAMES = {
    foundation  = true,
    subsurface  = true,
    surface     = true,
    topsurface  = true,
    lower_wall  = true,
    wall        = true,
    upper_wall  = true,
    canopy      = true,
}

local function validate_map_table_v2(t, source)
    require_field(t, "schema_version", "number", source)
    if t.schema_version ~= 2 then
        error(string.format("maps.load: schema_version %d not supported (expected 2)",
            t.schema_version))
    end
    require_field(t, "id", "string", source)
    local size = require_field(t, "size", "table", source)
    require_field(size, "w", "number", source .. ".size")
    require_field(size, "h", "number", source .. ".size")
    local expected = size.w * size.h

    local atlases = require_field(t, "atlases", "table", source)
    if #atlases == 0 then
        error(string.format("maps.load: schema violation in %s: atlases[] must be non-empty", source))
    end
    if #atlases > 256 then
        error(string.format("maps.load: schema violation in %s: atlases[] has %d entries, max 256", source, #atlases))
    end

    local layers = t.layers or {}
    for layer_name, layer_data in pairs(layers) do
        if not VALID_LAYER_NAMES[layer_name] then
            engine.print(string.format("maps.load: %s: ignoring unknown layer '%s'", source, layer_name))
        else
            local tiles = require_field(layer_data, "tiles", "table",
                source .. ".layers." .. layer_name)
            if #tiles ~= expected then
                error(string.format("maps.load: schema violation in %s.layers.%s: tiles length %d != %d",
                    source, layer_name, #tiles, expected))
            end
        end
    end

    if t.roof ~= nil then
        if type(t.roof) ~= "table" then
            error(string.format("maps.load: %s: roof must be array", source))
        end
        if #t.roof ~= expected then
            error(string.format("maps.load: %s: roof length %d != %d", source, #t.roof, expected))
        end
    end
end

-- =====================================================================
-- Internal helpers
-- =====================================================================

-- Checks whether `full_id` is a tilemap belonging to the current module.
-- Module-IDs can themselves contain dots (e.g. `lib-core.maps-test`), so a
-- naive first-dot-split is wrong. Match by prefix `<current-module-id>.`.
-- Returns (is_local, local_name) — local_name is nil if not local.
local function split_local_tilemap(full_id)
    local mod = engine.module.id()
    local prefix = mod .. "."
    if string.sub(full_id, 1, #prefix) == prefix then
        return true, string.sub(full_id, #prefix + 1)
    end
    return false, nil
end

-- "demo_tilemap"           -> "<current-module-id>.demo_tilemap"
-- "lib-x.foo"              -> "lib-x.foo" (cross-lib path; checked at load)
local function resolve_tilemap_id(ref)
    if string.find(ref, ".", 1, true) then
        return ref
    end
    return engine.module.id() .. "." .. ref
end

local function validate_map_table(t, source)
    require_field(t, "id", "string", source)
    require_field(t, "tilemap", "string", source)
    local size = require_field(t, "size", "table", source)
    require_field(size, "w", "number", source .. ".size")
    require_field(size, "h", "number", source .. ".size")
    local tiles = require_field(t, "tiles", "table", source)
    local expected = size.w * size.h
    if #tiles ~= expected then
        error(string.format("maps.load: schema violation in %s: tiles array length %d != size.w * size.h (%d)",
            source, #tiles, expected))
    end
end

local function validate_tilemap_table(t, source, expected_local_name)
    require_field(t, "id", "string", source)
    if t.id ~= expected_local_name then
        error(string.format("maps.load: tilemap manifest id '%s' mismatches filename-stem '%s' in %s",
            t.id, expected_local_name, source))
    end
    require_field(t, "tile_size", "number", source)
    local tiles = require_field(t, "tiles", "table", source)
    for i, entry in ipairs(tiles) do
        if type(entry) ~= "table" then
            error(string.format("maps.load: tilemap %s tiles[%d] must be table", source, i))
        end
        require_field(entry, "id", "string", source .. ".tiles[" .. i .. "]")
        require_field(entry, "walkable", "boolean", source .. ".tiles[" .. i .. "]")
    end
end

local function load_tilemap(full_id)
    if tilemap_registry[full_id] then
        return tilemap_registry[full_id]
    end
    local is_local, local_name = split_local_tilemap(full_id)
    if not is_local then
        -- DEPRECATED-MVP: cross-lib tilemap resolution deferred to render-slice
        error(string.format("maps.load: cross-lib tilemap resolution deferred [DEPRECATED-MVP]; tilemap '%s' not from current module '%s'",
            full_id, engine.module.id()))
    end
    local path = "assets/tiles/" .. local_name .. ".tilemap.json"
    local raw = engine.asset.load_json(path)
    validate_tilemap_table(raw, path, local_name)
    -- Cook tiles: copy raw fields and add texture + texture_handle slots.
    local cooked = {}
    for i, t in ipairs(raw.tiles) do
        cooked[i] = {
            id             = t.id,
            walkable       = (t.walkable == true),
            color          = t.color,        -- color-mode fallback
            texture        = t.texture,      -- optional atlas-id
            texture_handle = nil,            -- populated by load_textures
        }
    end
    local tilemap = {
        id         = full_id,
        tile_size  = raw.tile_size,
        asset_pack = raw.asset_pack,         -- optional alias-key
        tiles      = cooked,
    }
    tilemap_registry[full_id] = tilemap
    return tilemap
end

local function build_map(t_map, tilemap)
    -- Verify each tile-id is in palette range
    for i, tid in ipairs(t_map.tiles) do
        if type(tid) ~= "number" or tid < 1 or tid > #tilemap.tiles then
            error(string.format("maps.load: tile-id %s at index %d exceeds palette size %d (in map '%s')",
                tostring(tid), i, #tilemap.tiles, t_map.id))
        end
    end
    return {
        id             = t_map.id,
        size           = t_map.size,
        tile_size      = t_map.tile_size or tilemap.tile_size,
        tiles          = t_map.tiles,           -- shallow-ref
        tile_rotations = t_map.tile_rotations,  -- optional parallel array (NEW)
        tilemap        = tilemap,               -- shallow-ref
        -- DEPRECATED-MVP: forward-compat stubs (multi-map slice fills)
        walls          = {},
        regions        = {},
        edges          = {},
        state          = "Active",
        pinned         = false,
    }
end

local function build_map_v2(t_map, resolved_atlases)
    local size = t_map.size
    return {
        id              = t_map.id,
        schema_version  = 2,
        size            = size,
        tile_size       = resolved_atlases[1].tile_size,  -- assume uniform; first atlas wins
        atlases         = resolved_atlases,
        atlas_aliases   = t_map.atlases,  -- alias strings, parallel to atlases
        layers          = t_map.layers or {},
        roof            = t_map.roof,
        -- DEPRECATED-MVP stubs
        walls   = {},
        regions = {},
        edges   = {},
        state   = "Active",
        pinned  = false,
    }
end

-- =====================================================================
-- Public API
-- =====================================================================

local M = {}

function M.load(path)
    local raw = engine.asset.load_json(path)
    if raw.schema_version == nil or raw.schema_version == 1 then
        raw = upgrade_v1_to_v2(raw)
        engine.print(string.format("maps.load: auto-upgraded v1 map '%s' to v2", raw.id or "<unnamed>"))
    end
    validate_map_table_v2(raw, path)

    -- Resolve atlas-aliases (each entry is a tilemap-id, possibly local or fully-qualified)
    local resolved_atlases = {}
    for i, alias in ipairs(raw.atlases) do
        local full_id = resolve_tilemap_id(alias)
        resolved_atlases[i] = load_tilemap(full_id)
    end

    local map = build_map_v2(raw, resolved_atlases)
    if map_registry[map.id] then
        error(string.format("maps.load: map-id '%s' already registered", map.id))
    end
    map_registry[map.id] = map
    return map.id
end

-- Programmatic creation (tests, future procedural-map generators).
-- Caller must provide a fully-built tilemap-table (not a path/id ref).
function M.create(t)
    if type(t.tilemap_table) ~= "table" then
        error("maps.create: tilemap_table required (use maps.load for JSON path)")
    end
    local map = build_map(t, t.tilemap_table)
    if map_registry[map.id] then
        error(string.format("maps.create: map-id '%s' already registered", map.id))
    end
    map_registry[map.id] = map
    return map.id
end

function M.size(map_id)
    local id = map_id or current_map_id
    if not id then error("maps.size: no current map") end
    return map_registry[id].size
end

function M.tile_size(map_id)
    local id = map_id or current_map_id
    if not id then error("maps.tile_size: no current map") end
    return map_registry[id].tile_size
end

-- Arity-flex sugar: tile_at(tx, ty) uses current_map_id; tile_at(map_id, tx, ty)
-- is explicit. Both forms accept nil map_id and fall back to current_map_id.
function M.tile_at(a, b, c)
    local map_id, tx, ty
    if c == nil then
        map_id, tx, ty = current_map_id, a, b
    else
        map_id, tx, ty = a, b, c
        if map_id == nil then map_id = current_map_id end
    end
    if not map_id then
        error("maps.tile_at: no current map; call set_current() first or pass map_id")
    end
    local m = map_registry[map_id]
    if not m then
        error(string.format("maps.tile_at: unknown map-id '%s'", tostring(map_id)))
    end
    if tx < 0 or tx >= m.size.w or ty < 0 or ty >= m.size.h then
        return nil
    end
    -- v2 path: read from surface layer using GID encoding
    if m.schema_version == 2 then
        local surface = m.layers and m.layers.surface
        if not surface then return nil end
        local gid = surface.tiles[ty * m.size.w + tx + 1]
        if not gid or gid == 0 then return nil end
        local atlas_index, tile_id, _ = decode_gid(gid)
        local atlas = m.atlases[atlas_index + 1]
        if not atlas then return nil end
        return atlas.tiles[tile_id]
    end
    -- v1 legacy path (should not be reached after M.load auto-upgrades, kept for M.create)
    local palette_id = m.tiles[ty * m.size.w + tx + 1]
    return m.tilemap.tiles[palette_id]
end

function M.is_walkable(a, b, c)
    local t = M.tile_at(a, b, c)
    if t == nil then return false end
    return t.walkable == true
end

function M.tilemap_id(map_id)
    local id = map_id or current_map_id
    local m = map_registry[id]
    -- v2: return first atlas alias (backwards-compat for single-atlas maps)
    if m.schema_version == 2 then
        return m.atlas_aliases and m.atlas_aliases[1] or (m.atlases[1] and m.atlases[1].id)
    end
    return m.tilemap.id
end

function M.current()
    return current_map_id
end

function M.set_current(map_id)
    if not map_registry[map_id] then
        error(string.format("maps.set_current: unknown map-id '%s'", tostring(map_id)))
    end
    current_map_id = map_id
end

function M.list()
    local out = {}
    for id, _ in pairs(map_registry) do
        out[#out+1] = id
    end
    return out
end

function M.atlas_count(map_id)
    local id = map_id or current_map_id
    if not id then error("maps.atlas_count: no current map") end
    local m = map_registry[id]
    if m.schema_version ~= 2 then return 1 end  -- v1 (pre-upgrade) always 1
    return #m.atlases
end

function M.atlas_id_at(idx, map_id)
    local id = map_id or current_map_id
    if not id then error("maps.atlas_id_at: no current map") end
    local m = map_registry[id]
    return m.atlas_aliases and m.atlas_aliases[idx + 1]
        or m.atlases[idx + 1] and m.atlases[idx + 1].id
end

function M.has_layer(layer_name, map_id)
    local id = map_id or current_map_id
    if not id then error("maps.has_layer: no current map") end
    local m = map_registry[id]
    return m.layers and m.layers[layer_name] ~= nil
end

function M.is_indoor(x, y, map_id)
    local id = map_id or current_map_id
    if not id then error("maps.is_indoor: no current map") end
    local m = map_registry[id]
    if not m.roof then return false end
    if x < 0 or x >= m.size.w or y < 0 or y >= m.size.h then return false end
    return m.roof[y * m.size.w + x + 1] == 1
end

-- ====================================================================
-- Resolve tilemap-tile atlas-ids to texture-handles via asset-lib.
-- Operates on the current map's tilemap; call after maps.set_current.
-- asset_aliases: { [alias-key] = asset-lib-id } from module's manifest.
-- ====================================================================
function M.load_textures(asset_aliases)
    local map_id = M.current()
    if map_id == nil then
        error("maps.load_textures: no current map; call maps.set_current first")
    end
    local m = map_registry[map_id]
    local tm = m.tilemap
    if tm.asset_pack == nil then return end  -- color-only tilemap, no textures
    local lib_id = asset_aliases[tm.asset_pack]
    if lib_id == nil then
        error("maps.load_textures: asset-pack alias '" .. tm.asset_pack
              .. "' not in asset_aliases")
    end
    local atlas_path = lib_id .. "/assets/atlas.json"
    local atlas = engine.asset.load_json(atlas_path)
    local pack = atlas[tm.asset_pack]
    if pack == nil then
        error("maps.load_textures: asset_pack '" .. tm.asset_pack
              .. "' not declared in atlas of '" .. lib_id .. "'")
    end
    for _, tile in ipairs(tm.tiles) do
        if tile.texture then
            local entry = pack[tile.texture]
            if entry == nil then
                error("maps.load_textures: atlas-id '" .. tile.texture
                      .. "' not in asset_pack '" .. tm.asset_pack .. "'")
            end
            tile.texture_handle = engine.asset.load_texture(lib_id .. "/assets/" .. entry.file)
        end
    end
end

function M.draw_map()
    local map_id = M.current()
    if map_id == nil then return end
    local m = map_registry[map_id]
    local tm = m.tilemap
    local ts = tm.tile_size
    for y = 0, m.size.h - 1 do
        for x = 0, m.size.w - 1 do
            local idx = y * m.size.w + x + 1
            local tile_id = m.tiles[idx]
            local tile = tm.tiles[tile_id]
            local rot_deg = (m.tile_rotations and m.tile_rotations[idx]) or 0
            local px = x * ts
            local py = y * ts
            if tile.texture_handle then
                -- Sprite mode: draw_sprite_transform with rotation about tile center.
                engine.render.draw_sprite_transform(
                    tile.texture_handle,
                    px + ts / 2, py + ts / 2,
                    math.rad(rot_deg),
                    1.0, 1.0,
                    ts / 2, ts / 2,
                    0xFFFFFFFF
                )
            else
                -- Color fallback (Phase 1 mode).
                local c = tile.color or { 100, 100, 100 }
                engine.render.draw_rect(px, py, ts, ts, engine.render.rgb(c[1], c[2], c[3]))
            end
        end
    end
end

-- Forward-compat stubs (DEPRECATED-MVP — implemented in later slices)
function M.state(map_id)
    -- DEPRECATED-MVP: lifecycle states (Virgin/Inert/Passive/Active/Pinned) — multi-map slice
    return "Active"
end

function M.pin(map_id, reason)
    -- DEPRECATED-MVP: world.pin_map mechanic — multi-map slice
    engine.warn("maps.pin: deferred to map-topology lifecycle slice")
end

M.encode_gid = encode_gid
M.decode_gid = decode_gid
M.upgrade_v1_to_v2 = upgrade_v1_to_v2
M.validate_map_table_v2 = validate_map_table_v2

return M