"""Gateway runtime-metadata footer (model · context % · cwd), off by default
to keep replies minimal.

Config (``display.runtime_footer``, per-platform override under
``display.platforms.<platform>.runtime_footer``; toggled by ``/footer on|off``)::

    display:
      runtime_footer:
        enabled: true
        fields: [model, context_pct, cwd]   # order shown; drop any to hide

Fields: ``model`` (vendor prefix dropped), ``context_pct`` (last-call
occupancy), ``latency`` (turn wall-clock, opt-in — NOT in the default set so an
unset ``fields`` renders exactly as before), ``cwd`` (home-relative).

``gateway/run.py`` appends the footer to the final response only (never to
tool-progress or streaming partials); when streaming already delivered the text,
it goes out as a trailing message via ``send_trailing_footer()``.
"""

from __future__ import annotations

import os
from typing import Any, Iterable, Optional

_DEFAULT_FIELDS: tuple[str, ...] = ("model", "context_pct", "cwd")
_SEP = " · "


def _home_relative_cwd(cwd: str) -> str:
    """Return *cwd* with ``$HOME`` collapsed to ``~``.  Empty string if unset."""
    if not cwd:
        return ""
    try:
        home = os.path.expanduser("~")
        p = os.path.abspath(cwd)
        if home and (p == home or p.startswith(home + os.sep)):
            return "~" + p[len(home):]
        return p
    except Exception:
        return cwd


def _model_short(model: Optional[str]) -> str:
    """Drop ``vendor/`` prefix (``openai/gpt-5.4`` → ``gpt-5.4``)."""
    return model.rsplit("/", 1)[-1] if model else ""


def _env_cwd() -> str:
    try:
        from tools.terminal_scope import terminal_env
    except ImportError:
        return os.environ.get("TERMINAL_CWD", "")
    return terminal_env("TERMINAL_CWD", "")


def _apply_footer_section(resolved: dict[str, Any], section: Any) -> None:
    if not isinstance(section, dict):
        return
    if "enabled" in section:
        resolved["enabled"] = bool(section.get("enabled"))
    if isinstance(section.get("fields"), list) and section["fields"]:
        resolved["fields"] = [str(f) for f in section["fields"]]


def resolve_footer_config(
    user_config: dict[str, Any] | None,
    platform_key: str | None = None,
) -> dict[str, Any]:
    """Resolve effective footer config: defaults (enabled=False) <
    ``display.runtime_footer`` < ``display.platforms.<platform_key>.runtime_footer``."""
    resolved = {"enabled": False, "fields": list(_DEFAULT_FIELDS)}
    cfg = (user_config or {}).get("display") or {}
    _apply_footer_section(resolved, cfg.get("runtime_footer"))
    if platform_key:
        plat_cfg = (cfg.get("platforms") or {}).get(platform_key)
        if isinstance(plat_cfg, dict):
            _apply_footer_section(resolved, plat_cfg.get("runtime_footer"))
    return resolved


def _format_latency(seconds: float) -> str:
    """Humanize a turn duration: ``<1s``, ``22s``, ``1m05s``."""
    if seconds < 1:
        return "<1s"
    total = int(round(seconds))
    if total < 60:
        return f"{total}s"
    m, sec = divmod(total, 60)
    return f"{m}m{sec:02d}s"


def _context_pct(context_tokens: int, context_length: Optional[int]) -> str:
    if context_length and context_length > 0 and context_tokens >= 0:
        return f"{max(0, min(100, round((context_tokens / context_length) * 100)))}%"
    return ""


def format_runtime_footer(
    *,
    model: Optional[str],
    context_tokens: int,
    context_length: Optional[int],
    cwd: Optional[str] = None,
    turn_seconds: Optional[float] = None,
    fields: Iterable[str] = _DEFAULT_FIELDS,
) -> str:
    """Render the footer line, or "" if no fields have data.

    Fields whose data is missing (and unknown field names) are skipped silently —
    a partial footer beats ``?%`` or empty slots.
    """
    renderers = {
        "model": lambda: _model_short(model),
        "context_pct": lambda: _context_pct(context_tokens, context_length),
        # Skipped when the caller did not measure (None) or the value is negative.
        "latency": lambda: _format_latency(turn_seconds) if turn_seconds is not None and turn_seconds >= 0 else "",
        "cwd": lambda: _home_relative_cwd(cwd or _env_cwd()),
    }
    parts = [value for field in fields if (render := renderers.get(field)) and (value := render())]
    return _SEP.join(parts)


def build_footer_line(
    *,
    user_config: dict[str, Any] | None,
    platform_key: str | None,
    model: Optional[str],
    context_tokens: int,
    context_length: Optional[int],
    cwd: Optional[str] = None,
    turn_seconds: Optional[float] = None,
) -> str:
    """Entry point for gateway/run.py: footer text, or "" when disabled / no data.
    Callers append it to the final response themselves, preserving a single
    blank line of separation.

    ``turn_seconds`` is the caller-measured (``time.monotonic()``) run duration;
    ``None`` skips the ``latency`` field.
    """
    cfg = resolve_footer_config(user_config, platform_key)
    if not cfg.get("enabled"):
        return ""
    return format_runtime_footer(
        model=model,
        context_tokens=context_tokens,
        context_length=context_length,
        cwd=cwd,
        turn_seconds=turn_seconds,
        fields=cfg.get("fields") or _DEFAULT_FIELDS,
    )