# Runtime configuration. Built once at startup, then treated as immutable.
# Every knob has a default so the service runs with zero configuration, and
# every knob can be overridden by an environment variable (see `config_from_env`).

Base.@kwdef struct Config
    host::String        = "127.0.0.1"
    port::Int           = 8080
    worker_count::Int   = Threads.nthreads()
    queue_capacity::Int = 1000
    spool_dir::String   = "data/spool"   # files land here on intake (pending)
    done_dir::String    = "data/done"    # files move here after successful processing
    failed_dir::String  = "data/failed"  # files move here if a worker throws
end

"""
    config_from_env(; overrides...)

Build a `Config` from environment variables, falling back to the struct
defaults. Any keyword `overrides` win over the environment (useful for tests
and for `FileServer.run(; port=...)`).

Recognised variables:
  FS_HOST, FS_PORT, FS_WORKERS, FS_QUEUE_CAPACITY,
  FS_SPOOL_DIR, FS_DONE_DIR, FS_FAILED_DIR
"""
function config_from_env(; host=nothing, port=nothing, worker_count=nothing,
                          queue_capacity=nothing, spool_dir=nothing,
                          done_dir=nothing, failed_dir=nothing)
    Config(
        host           = something(host,           get(ENV, "FS_HOST", "127.0.0.1")),
        port           = something(port,           parse(Int, get(ENV, "FS_PORT", "8080"))),
        worker_count   = something(worker_count,   parse(Int, get(ENV, "FS_WORKERS", string(Threads.nthreads())))),
        queue_capacity = something(queue_capacity, parse(Int, get(ENV, "FS_QUEUE_CAPACITY", "1000"))),
        spool_dir      = something(spool_dir,      get(ENV, "FS_SPOOL_DIR", "data/spool")),
        done_dir       = something(done_dir,       get(ENV, "FS_DONE_DIR", "data/done")),
        failed_dir     = something(failed_dir,     get(ENV, "FS_FAILED_DIR", "data/failed")),
    )
end

"Create the spool/done/failed directories if they don't already exist."
function ensure_dirs(cfg::Config)
    for d in (cfg.spool_dir, cfg.done_dir, cfg.failed_dir)
        mkpath(d)
    end
    return nothing
end