-- =====================================================================
-- 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

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

-- Splits "lib-x.foo" -> "lib-x", "foo" (split at FIRST dot only).
-- Returns (nil, full_id) if no dot present.
local function split_namespaced_id(full_id)
    local dot = string.find(full_id, ".", 1, true)
    if not dot then return nil, full_id end
    return string.sub(full_id, 1, dot-1), string.sub(full_id, dot+1)
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

-- 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

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 lib_id, local_name = split_namespaced_id(full_id)
    local current_lib = engine.module.id()
    if lib_id ~= current_lib 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, current_lib))
    end
    local path = "assets/tiles/" .. local_name .. ".tilemap.json"
    local raw = engine.asset.load_json(path)
    validate_tilemap_table(raw, path, local_name)
    local tilemap = {
        id        = full_id,
        tile_size = raw.tile_size,
        tiles     = raw.tiles,
    }
    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
        tilemap   = tilemap,             -- shallow-ref
        -- DEPRECATED-MVP: forward-compat stubs (multi-map slice fills)
        walls     = {},
        regions   = {},
        edges     = {},
        state     = "Active",
        pinned    = false,
    }
end

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

local M = {}

function M.load(path)
    local raw = engine.asset.load_json(path)
    validate_map_table(raw, path)
    local full_id = resolve_tilemap_id(raw.tilemap)
    local tilemap = load_tilemap(full_id)
    local map = build_map(raw, tilemap)
    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
    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
    return map_registry[id].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

-- 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

return M