"""User settings, persisted to ~/.config/screencast/config.json."""
from __future__ import annotations

from .util import config_dir, read_json, write_json

DEFAULTS = {
    "fps": 30,
    "maxHeight": 1080,          # the capture is scaled down to this before encoding
    "bitrate": 8000,            # kbit/s
    "encoder": "auto",          # auto | nvenc | vaapi | x264 | vp8 | vp9
    "audio": True,              # mix desktop audio into the stream
    "cursor": True,             # draw the pointer into the capture
    "port": 8011,               # local HTTP server the receiver pulls the stream from
    "lastDevice": "",           # id of the device cast to last, for the "cast again" default
    "autoReconnect": True,      # restart the pipeline if the receiver drops the stream
    "portVerified": False,      # set once a receiver has actually fetched the stream
}

# Settings that only take effect on the next session (changing them mid-cast
# restarts the pipeline instead of being ignored).
PIPELINE_KEYS = {"fps", "maxHeight", "bitrate", "encoder", "audio", "cursor"}


class Config:
    def __init__(self) -> None:
        self.path = config_dir() / "config.json"
        self.values = dict(DEFAULTS)
        self.values.update(read_json(self.path, {}) or {})

    def __getitem__(self, key):
        return self.values.get(key, DEFAULTS.get(key))

    def get(self, key, default=None):
        return self.values.get(key, DEFAULTS.get(key, default))

    def update(self, patch: dict) -> set[str]:
        """Apply a patch, returning the keys that actually changed."""
        changed = set()
        for key, value in (patch or {}).items():
            if key not in DEFAULTS:
                continue
            want = _coerce(key, value)
            if want is None or self.values.get(key) == want:
                continue
            self.values[key] = want
            changed.add(key)
        if changed:
            self.save()
        return changed

    def save(self) -> None:
        write_json(self.path, self.values)


def _coerce(key, value):
    ref = DEFAULTS[key]
    try:
        if isinstance(ref, bool):
            return bool(value)
        if isinstance(ref, int):
            v = int(value)
            if key == "fps":
                return max(5, min(60, v))
            if key == "maxHeight":
                return max(360, min(2160, v))
            if key == "bitrate":
                return max(500, min(50000, v))
            if key == "port":
                return max(1024, min(65535, v))
            return v
        return str(value)
    except (TypeError, ValueError):
        return None