--[[
@module  proto_conv
@summary 0x7F 帧 ↔ 标准 JSON 协议转换(方案 C 核心)
@version 0.1
@date    2026.08.31
@usage
Air780 解析 vd960DBN 转发的 0x7F 帧,转换为《DLD960_IoT_MQTT协议》标准 JSON 命令:
- 0xC0 传感帧(多线圈) → loop_data JSON
- car_state / loop_state 沿检测 → event_report 事件(car_enter/car_leave/loop_cut/loop_restore)
- 4G 事件面 = 仅线圈事件(不含 DBN 内部网络事件,协议 §6.4)

0xC0 帧 payload(cmd=0xC0 之后):
  [SensType(1)][SubPkgFlag(1)][SensData: 4×12B]
每路线圈单元 12B(与《DLD960Loop_串口通信协议》§3.07 一致):
  config(1): freq_level(bit6-7) + direction(bit5) + freq_type(bit4) + sens(bit0-3)
  eval(1):   condition(bit4-7) + loop_state(bit3) + car_state(bit2) + misc_type(bit0-1)
  freq(3B LE 无符号) + variation(3B LE 有符号) + misc(4B LE)
]]

local proto_conv = {}

-- 线圈高低频档位 → level 字符串
local LEVEL_NAMES = { "high", "mid_high", "mid_low", "low" }
-- 杂项类型 → type 字符串
local MISC_NAMES  = { "time", "cut_count", "flow_count", "relay_count" }

-- 3B 小端无符号
local function u24le(s, off)
    return string.byte(s, off)
         + string.byte(s, off + 1) * 256
         + string.byte(s, off + 2) * 65536
end

-- 3B 小端有符号(补码)
local function i24le(s, off)
    local v = u24le(s, off)
    if v >= 0x800000 then
        v = v - 0x1000000
    end
    return v
end

-- 4B 小端无符号
local function u32le(s, off)
    return string.byte(s, off)
         + string.byte(s, off + 1) * 256
         + string.byte(s, off + 2) * 65536
         + string.byte(s, off + 3) * 16777216
end

-- 解析 0xC0 传感帧 payload → 4 路通道表
-- @param payload string: cmd 之后的字节(SensType + SubPkgFlag + SensData)
-- @return channels table or nil: [{ch, level, iscar, loop_ok, freq, diff, sens, cndtn, misc}]
function proto_conv.parse_sensor(payload)
    if not payload or payload:len() < 2 then
        return nil
    end
    local sens_type = string.byte(payload, 1)
    if sens_type ~= 0x0C then
        return nil                      -- 非多线圈传感类型
    end
    -- payload: [SensType(1)][SubPkgFlag(1)][SensData...]
    local data = payload:sub(3)
    local channels = {}
    local coil_count = 4                -- 960Loop 固定 4 路
    for i = 1, coil_count do
        local off = (i - 1) * 12 + 1
        if data:len() < off + 11 then
            break
        end
        local cfg = string.byte(data, off)
        local evl = string.byte(data, off + 1)
        local freq_level = (cfg >> 6) & 0x03
        local sens       = cfg & 0x0F
        local condition  = (evl >> 4) & 0x0F
        local loop_state = (evl >> 3) & 0x01
        local car_state  = (evl >> 2) & 0x01
        local misc_type  = evl & 0x03
        local freq   = u24le(data, off + 2)
        local diff   = i24le(data, off + 5)
        local misc   = u32le(data, off + 8)
        channels[i] = {
            ch      = i,
            level   = LEVEL_NAMES[freq_level + 1] or "high",
            iscar   = (car_state == 1),
            loop_ok = (loop_state == 0),
            freq    = freq,
            diff    = diff,
            sens    = sens,
            cndtn   = condition,
            misc    = { type = MISC_NAMES[misc_type + 1] or "time", value = misc },
        }
    end
    return channels
end

-- ==================== 事件沿检测 ====================
-- 保存上一帧每路 car_state / loop_state
local prev_car  = { 0, 0, 0, 0 }
local prev_loop = { 0, 0, 0, 0 }

-- 沿检测: 输入当前通道表,输出事件列表
-- @return events: [{type, ch, value}]
function proto_conv.detect_events(channels)
    local events = {}
    if not channels then
        return events
    end
    for i = 1, #channels do
        local ch = channels[i]
        local cur_car  = ch.iscar  and 1 or 0
        local cur_loop = ch.loop_ok and 0 or 1   -- loop_ok=false → 断开=1
        if i <= 4 then
            -- car 沿(线圈断开期间屏蔽,与 DBN 同策略)
            if prev_loop[i] == 0 and cur_loop == 0 then
                if prev_car[i] == 0 and cur_car == 1 then
                    events[#events + 1] = { type = "car_enter", ch = i, value = ch.misc.value }
                elseif prev_car[i] == 1 and cur_car == 0 then
                    events[#events + 1] = { type = "car_leave", ch = i, value = ch.misc.value }
                end
            end
            -- loop 沿
            if prev_loop[i] == 0 and cur_loop == 1 then
                events[#events + 1] = { type = "loop_cut", ch = i, value = 0 }
            elseif prev_loop[i] == 1 and cur_loop == 0 then
                events[#events + 1] = { type = "loop_restore", ch = i, value = 0 }
            end
            prev_car[i]  = cur_car
            prev_loop[i] = cur_loop
        end
    end
    return events
end

-- 复位沿检测状态(上电/MQTT 重连后避免误报)
function proto_conv.reset_events()
    prev_car  = { 0, 0, 0, 0 }
    prev_loop = { 0, 0, 0, 0 }
end

return proto_conv