#!/usr/bin/env bash
# Select and verify a stable Rust toolchain for this source checkout.
# Prints the resolved channel on stdout. Progress/errors go to stderr.
set -Eeuo pipefail

SOURCE_DIR=${1:?usage: ensure-rust-toolchain.sh SOURCE_DIR linux|freebsd}
PLATFORM=${2:?usage: ensure-rust-toolchain.sh SOURCE_DIR linux|freebsd}
[[ "$PLATFORM" == linux || "$PLATFORM" == freebsd ]] || {
    printf 'Unsupported build target: %s\n' "$PLATFORM" >&2
    exit 2
}
[[ -r "$SOURCE_DIR/Cargo.toml" ]] || {
    printf 'Missing Cargo.toml: %s\n' "$SOURCE_DIR" >&2
    exit 1
}

# Rocky Linux 9 builder image supplies Python 3.11 for TOML parsing.
TOML_PYTHON=${TOML_PYTHON:-python3.11}
metadata=$("$TOML_PYTHON" - "$SOURCE_DIR" <<'PY'
import pathlib
import re
import sys
import tomllib

root = pathlib.Path(sys.argv[1])
manifest = tomllib.loads((root / "Cargo.toml").read_text(encoding="utf-8"))
rust_version = manifest.get("package", {}).get("rust-version", "")
if isinstance(rust_version, dict) and rust_version.get("workspace") is True:
    rust_version = manifest.get("workspace", {}).get("package", {}).get("rust-version", "")
if not isinstance(rust_version, str):
    raise SystemExit("Unsupported Cargo.toml rust-version")
if rust_version and not re.fullmatch(r"[0-9]+\.[0-9]+(?:\.[0-9]+)?", rust_version):
    raise SystemExit(f"Unsupported Cargo.toml rust-version: {rust_version}")

pinned = ""
for filename in ("rust-toolchain.toml", "rust-toolchain"):
    path = root / filename
    if not path.exists():
        continue
    if filename.endswith(".toml"):
        pinned = tomllib.loads(path.read_text(encoding="utf-8")).get("toolchain", {}).get("channel", "")
    else:
        value = path.read_text(encoding="utf-8").strip()
        pinned = tomllib.loads(value).get("toolchain", {}).get("channel", "") if value.startswith("[") else value
    break
if pinned and not isinstance(pinned, str):
    raise SystemExit("Invalid rust-toolchain channel")
if pinned and not (pinned == "stable" or re.fullmatch(r"[0-9]+\.[0-9]+(?:\.[0-9]+)?", pinned)):
    raise SystemExit(f"Only stable Rust toolchains are supported: {pinned}")
print(rust_version)
print(pinned)
PY
)
mapfile -t requested <<< "$metadata"
MIN_RUST=${requested[0]:-}
PINNED_TOOLCHAIN=${requested[1]:-}

version_components() {
    local version=$1
    [[ "$version" =~ ^([0-9]+)\.([0-9]+)(\.([0-9]+))?$ ]] || return 1
    V_MAJOR=${BASH_REMATCH[1]}
    V_MINOR=${BASH_REMATCH[2]}
    V_PATCH=${BASH_REMATCH[4]:-0}
}
version_less() {
    local a=$1 b=$2 a_major a_minor a_patch
    version_components "$a" || return 2
    a_major=$V_MAJOR a_minor=$V_MINOR a_patch=$V_PATCH
    version_components "$b" || return 2
    (( 10#$a_major < 10#$V_MAJOR || \
       (10#$a_major == 10#$V_MAJOR && 10#$a_minor < 10#$V_MINOR) || \
       (10#$a_major == 10#$V_MAJOR && 10#$a_minor == 10#$V_MINOR && 10#$a_patch < 10#$V_PATCH) ))
}

if [[ -n "$PINNED_TOOLCHAIN" ]]; then
    channel=$PINNED_TOOLCHAIN
elif [[ "$PLATFORM" == linux ]]; then
    channel=stable
else
    channel=${FREEBSD_RUST_TOOLCHAIN:-1.88.0}
    if [[ "$channel" != stable ]] && [[ -n "$MIN_RUST" ]] && version_less "$channel" "$MIN_RUST"; then
        printf 'FreeBSD base toolchain %s is below project MSRV %s; selecting project MSRV\n' "$channel" "$MIN_RUST" >&2
        channel=$MIN_RUST
    fi
fi
[[ "$channel" == stable || "$channel" =~ ^[0-9]+\.[0-9]+(\.[0-9]+)?$ ]] || {
    printf 'Unsupported Rust toolchain: %s\n' "$channel" >&2
    exit 1
}
if [[ -n "$PINNED_TOOLCHAIN" && -n "$MIN_RUST" && "$channel" != stable ]] && version_less "$channel" "$MIN_RUST"; then
    printf 'Explicit rust-toolchain pin %s is below project MSRV %s; update the source pin\n' "$channel" "$MIN_RUST" >&2
    exit 1
fi

rustc_version() {
    local result
    result=$(rustup run "$channel" rustc --version 2>/dev/null) || return 1
    [[ "$result" =~ ^rustc[[:space:]]+([0-9]+\.[0-9]+\.[0-9]+) ]] || return 1
    printf '%s' "${BASH_REMATCH[1]}"
}

if ! installed=$(rustc_version); then
    printf 'Installing Rust toolchain %s for %s\n' "$channel" "$PLATFORM" >&2
    rustup toolchain install "$channel" --profile minimal >&2
    installed=$(rustc_version) || { printf 'Toolchain %s unavailable after installation\n' "$channel" >&2; exit 1; }
fi

if [[ -n "$MIN_RUST" ]] && version_less "$installed" "$MIN_RUST"; then
    if [[ "$channel" == stable ]]; then
        printf 'Updating stable Rust (%s) to satisfy project MSRV %s\n' "$installed" "$MIN_RUST" >&2
        rustup toolchain install stable --profile minimal >&2
        installed=$(rustc_version) || { printf 'Stable toolchain unavailable after update\n' >&2; exit 1; }
    fi
    if version_less "$installed" "$MIN_RUST"; then
        printf 'Rust %s (%s) does not satisfy project MSRV %s\n' "$installed" "$channel" "$MIN_RUST" >&2
        exit 1
    fi
fi

if [[ "$PLATFORM" == freebsd ]]; then
    target=x86_64-unknown-freebsd
    if ! rustup target list --toolchain "$channel" --installed | grep -Fxq "$target"; then
        printf 'Installing %s target for Rust %s\n' "$target" "$channel" >&2
        rustup target add "$target" --toolchain "$channel" >&2
    fi
    rustup target list --toolchain "$channel" --installed | grep -Fxq "$target" || {
        printf 'FreeBSD target is unavailable for Rust %s\n' "$channel" >&2
        exit 1
    }
fi

printf 'Selected Rust %s (%s) for %s\n' "$installed" "$channel" "$PLATFORM" >&2
printf '%s\n' "$channel"