"""Environment setup — the decisions, separated from the performing (D-263).

These three ported worst and mattered most to get right. `install-godot`
downloads and unzips a pinned build, `install-rust` drives `rustup`,
`worktree-setup` manipulates git worktrees — none of which can be exercised in
a gate without actually doing it.

So the shape here is deliberate: **every function that decides is pure and
importable, and every function that acts is a thin call through
`core.process.run`.** `godot_plan()` answers "what would be downloaded, and is
it needed" without touching the network; `install_godot()` performs it. The
test of a correct port is whether the decisions can be exercised WITHOUT
performing them — a rewrite that cannot be tested has to be trusted instead,
and trusting an installer is how a working environment becomes an
unreproducible one.
"""

from __future__ import annotations

import os
import platform
import shutil
from dataclasses import dataclass
from pathlib import Path

from tooling.core import config, console, process
from tooling.core.errors import ReachError

DEFAULT_GODOT_VERSION = "4.6"
INSTALL_DIR = Path.home() / "bin"
GODOT_BINARY = INSTALL_DIR / "godot4"

# Godot publishes one archive per platform triple; an unsupported pair is a
# clear failure rather than a download that 404s.
PLATFORMS = {
    ("Linux", "x86_64"): "linux.x86_64",
    ("Linux", "aarch64"): "linux.arm64",
    ("Darwin", "x86_64"): "macos.universal",
    ("Darwin", "arm64"): "macos.universal",
}


@dataclass(frozen=True)
class GodotPlan:
    """What installing Godot would do — decided without doing any of it."""

    wanted: str
    installed: str | None
    platform_tag: str
    url: str
    filename: str

    @property
    def already_current(self) -> bool:
        return self.installed == self.wanted


def godot_plan(wanted: str | None = None) -> GodotPlan:
    """Decide what an install would fetch. Pure apart from reading the binary."""
    wanted = wanted or os.environ.get("GODOT_VERSION", DEFAULT_GODOT_VERSION)
    system, machine = platform.system(), platform.machine()
    tag = PLATFORMS.get((system, machine))
    if tag is None:
        raise ReachError(
            f"unsupported platform: {system} {machine}",
            fix="install Godot manually from https://godotengine.org/download",
        )

    filename = f"Godot_v{wanted}-stable_{tag}.zip"
    return GodotPlan(
        wanted=wanted,
        installed=installed_godot_version(),
        platform_tag=tag,
        filename=filename,
        url=(
            "https://github.com/godotengine/godot/releases/download/"
            f"{wanted}-stable/{filename}"
        ),
    )


def installed_godot_version() -> str | None:
    """The major.minor already on disk, or None. Never raises."""
    if not GODOT_BINARY.is_file() or not os.access(GODOT_BINARY, os.X_OK):
        return None
    result = process.run([str(GODOT_BINARY), "--version"], check=False)
    first = (result.stdout or "").splitlines()
    if not first:
        return None
    return ".".join(first[0].split(".")[:2])


def install_godot(wanted: str | None = None) -> GodotPlan:
    """Perform the install. The decision is `godot_plan`; this is the doing."""
    plan = godot_plan(wanted)
    if plan.already_current:
        console.verdict(f"Godot {plan.wanted} already installed at {GODOT_BINARY}")
        return plan
    if plan.installed:
        console.event(
            f"Godot found but version is {plan.installed}, want {plan.wanted}",
            level="warn",
        )

    INSTALL_DIR.mkdir(parents=True, exist_ok=True)
    import tempfile

    with tempfile.TemporaryDirectory() as tmp:
        archive = Path(tmp) / plan.filename
        console.event(f"downloading Godot {plan.wanted} for {plan.platform_tag}", phase="godot")
        process.run(
            ["curl", "-fSL", "--progress-bar", "-o", str(archive), plan.url],
            capture=False,
            fix=f"check that GODOT_VERSION={plan.wanted} is a real release",
            missing_fix="install curl",
        )
        console.event("extracting", phase="godot")
        process.run(
            ["unzip", "-q", "-o", str(archive), "-d", tmp],
            fix="the archive may be truncated — re-run to download it again",
            missing_fix="install unzip",
        )
        extracted = next(
            (p for p in Path(tmp).iterdir() if p.is_file() and p.name.startswith("Godot")),
            None,
        )
        if extracted is None:
            raise ReachError(
                "the Godot archive contained no binary",
                fix="the download may be corrupt — delete it and re-run",
            )
        shutil.move(str(extracted), GODOT_BINARY)
        GODOT_BINARY.chmod(0o755)

    console.verdict(f"Godot {plan.wanted} installed at {GODOT_BINARY}")
    return plan


def install_rust() -> None:
    """Ensure rustup, clippy and rustfmt are present."""
    if shutil.which("cargo") is None:
        raise ReachError(
            "cargo is not installed",
            fix="install Rust from https://rustup.rs, then re-run — this command "
            "adds the components but does not bootstrap the toolchain",
        )
    for component in ("clippy", "rustfmt"):
        console.event(f"ensuring {component}", phase="rust")
        process.run(
            ["rustup", "component", "add", component],
            check=False,
            missing_fix="install rustup from https://rustup.rs",
        )
    console.verdict("Rust toolchain ready — clippy and rustfmt present")


def worktree_plan(branch: str) -> Path:
    """Where a worktree for `branch` would go. Raises if it cannot be created.

    Both refusals are the original's and both are worth keeping: a worktree
    created from inside a worktree nests confusingly, and silently reusing an
    existing directory is how two branches end up sharing one tree.
    """
    root = config.repo_root()
    if (root / ".git").is_file():
        raise ReachError(
            "this is a worktree, not the main checkout",
            fix="run this from the main checkout — nesting worktrees confuses "
            "both git and the tools that resolve the repo root",
        )
    target = root / ".worktrees" / branch
    if target.exists():
        raise ReachError(
            f"{target} already exists",
            fix=f"reuse it, or remove it first with: git worktree remove {target}",
        )
    return target


def setup_worktree(branch: str, start: str = "HEAD") -> Path:
    """Create a worktree and link the venv into it."""
    target = worktree_plan(branch)
    root = config.repo_root()

    process.run(
        ["git", "worktree", "add", str(target), "-b", branch, start],
        cwd=root,
        fix=f"check that {start} is a valid ref and {branch} is not already a branch",
    )

    venv = root / ".venv"
    if venv.is_dir() and not (target / ".venv").exists():
        (target / ".venv").symlink_to(venv)
        console.event(f"linked .venv -> {venv}")

    console.verdict(
        f"worktree ready: {target}\n"
        f"  pql in this worktree needs --vault {target} (FR-4)\n"
        "  tea runs from the main checkout — its go-git cannot read a linked worktree\n"
        "  reach follows whichever checkout it was installed from; `make reach-repoint` "
        "if you want it to follow this one"
    )
    return target