local cjson = require "cjson"
local redirect_follow = require "sm.service.redirect_follow"

local _M = {}

local function parse_upstream_status(status)
    local parsed = tostring(status or ""):match("(%d%d%d)")
    return tonumber(parsed) or ngx.HTTP_MOVED_TEMPORARILY
end

local function decode_site_config()
    local site_json = ngx.var.site
    if not site_json or site_json == "" then
        return nil, "site config missing"
    end

    local ok, hostname = pcall(cjson.decode, site_json)
    if not ok or type(hostname) ~= "table" then
        return nil, hostname
    end

    return hostname, nil
end

local function apply_response_headers(headers)
    for header_name, header_value in pairs(headers or {}) do
        local lower_name = tostring(header_name):lower()
        if lower_name ~= "connection"
            and lower_name ~= "keep-alive"
            and lower_name ~= "transfer-encoding"
            and lower_name ~= "age"
            and lower_name ~= "agc-cache-status"
            and lower_name ~= "agc-cache-policy"
            and lower_name ~= "agc-swift-cachetime"
            and lower_name ~= "agc-swift-savetime" then
            ngx.header[header_name] = header_value
        end
    end
end

function _M.exit_redirect(status, location)
    if location and location ~= "" then
        ngx.header["Location"] = location
    end

    return ngx.exit(status)
end

function _M.resolve_follow_mode(hostname)
    local route_lane = ngx.var.route_lane or ""
    if route_lane:match("follow$") and hostname["redirect_follow"] == "true" then
        return "follow"
    end

    return "passthrough"
end

function _M.apply_follow_result(result)
    ngx.header["AGC-Redirect-Follow"] = tostring(result.followed or 0)

    if result.kind == "redirect" then
        return _M.exit_redirect(result.status or ngx.HTTP_MOVED_TEMPORARILY, result.location)
    end

    ngx.status = result.status or ngx.HTTP_OK
    apply_response_headers(result.headers)

    ngx.ctx.follow_cache_meta = result.cache_meta

    if result.body and result.body ~= "" then
        ngx.print(result.body)
    end
end

function _M.redirect_dispatch()
    local redirect_location = ngx.var.upstream_http_location
    local redirect_status = parse_upstream_status(ngx.var.upstream_status)
    local hostname, err = decode_site_config()

    if not hostname then
        ngx.log(ngx.ERR, "[Content] Failed to decode site config: " .. tostring(err))
        return ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR)
    end

    if not redirect_location or redirect_location == "" then
        ngx.log(ngx.ERR, "[Content] No redirect location found")
        return ngx.exit(ngx.HTTP_BAD_GATEWAY)
    end

    local follow_mode = _M.resolve_follow_mode(hostname)
    ngx.log(ngx.INFO, "[Content] redirect dispatch lane=" .. tostring(ngx.var.route_lane)
        .. " mode=" .. follow_mode
        .. " status=" .. redirect_status
        .. " location=" .. redirect_location)

    if follow_mode ~= "follow" then
        return _M.exit_redirect(redirect_status, redirect_location)
    end

    local backend_protocol = ngx.var.backend_protocol
    local orig_scheme = ngx.var.scheme or "http"
    if backend_protocol and backend_protocol ~= "" then
        orig_scheme = backend_protocol:gsub("://", "")
    end

    local result, follow_err = redirect_follow.follow({
        route_lane = ngx.var.route_lane,
        status = redirect_status,
        location = redirect_location,
        orig_scheme = orig_scheme,
        orig_host = ngx.var.host,
        orig_args = ngx.var.args,
        orig_headers = ngx.req.get_headers(),
        method = ngx.req.get_method(),
        max_redirects = hostname["redirect_follow_max"],
        keep_args = hostname["redirect_follow_keep_args"],
        keep_headers = hostname["redirect_follow_keep_headers"],
        redirect_follow_host = hostname["redirect_follow_host"],
        cache_config = ngx.var.cache_config,
        cache_key = ngx.var.cache_key,
    })

    if not result then
        ngx.log(ngx.ERR, "[Content] Redirect follow failed: " .. tostring(follow_err))
        return ngx.exit(ngx.HTTP_BAD_GATEWAY)
    end

    return _M.apply_follow_result(result)
end

return _M