#!/usr/bin/env bash
# Pin Mathlib and the Lean toolchain to each other.
#
# Mathlib tags do not exist for every Lean point release, so hardcoding both is how
# image builds break six weeks later. Instead: choose a Mathlib revision, then take
# *its* lean-toolchain as the truth and write both into the Lean project.
#
#   resolve-mathlib.sh <lean-project-dir> [revision]
#
# revision defaults to "auto": the newest Mathlib tag whose toolchain matches the
# toolchain already in the project, else the newest tag, else master.
set -euo pipefail

PROJECT="${1:?usage: resolve-mathlib.sh <lean-project-dir> [revision]}"
REQUESTED="${2:-auto}"
REPO="https://github.com/leanprover-community/mathlib4.git"
RAW="https://raw.githubusercontent.com/leanprover-community/mathlib4"
TOOLCHAIN_FILE="$PROJECT/lean-toolchain"
LAKEFILE="$PROJECT/lakefile.toml"

toolchain_of() {  # toolchain_of <rev> -> prints e.g. leanprover/lean4:v4.33.0
  curl -fsSL --retry 3 --max-time 30 "$RAW/$1/lean-toolchain" 2>/dev/null | tr -d '[:space:]'
}

candidates() {
  git ls-remote --tags --refs "$REPO" 'v*' 2>/dev/null \
    | awk '{print $2}' | sed 's#refs/tags/##' \
    | grep -E '^v[0-9]+\.[0-9]+\.[0-9]+$' \
    | sort -V -r
}

wanted="$(tr -d '[:space:]' < "$TOOLCHAIN_FILE" 2>/dev/null || true)"
rev=""

if [ "$REQUESTED" != "auto" ]; then
  rev="$REQUESTED"
  echo "resolve-mathlib: using requested revision $rev"
else
  echo "resolve-mathlib: looking for a Mathlib tag built on ${wanted:-<unset>}"
  all="$(candidates || true)"
  if [ -n "$wanted" ]; then
    # only the tags sharing a major.minor with what we asked for are plausible
    series="$(printf '%s' "$wanted" | sed -E 's#.*:v([0-9]+\.[0-9]+).*#v\1#')"
    for tag in $(printf '%s\n' "$all" | grep -E "^${series}\." || true); do
      if [ "$(toolchain_of "$tag")" = "$wanted" ]; then
        rev="$tag"
        echo "resolve-mathlib: $tag matches $wanted exactly"
        break
      fi
    done
    if [ -z "$rev" ]; then
      rev="$(printf '%s\n' "$all" | grep -E "^${series}\." | head -1 || true)"
      [ -n "$rev" ] && echo "resolve-mathlib: no exact match; newest in $series series is $rev"
    fi
  fi
  if [ -z "$rev" ]; then
    rev="$(printf '%s\n' "$all" | head -1 || true)"
    echo "resolve-mathlib: falling back to newest tag ${rev:-master}"
  fi
  rev="${rev:-master}"
fi

actual="$(toolchain_of "$rev" || true)"
if [ -z "$actual" ]; then
  echo "resolve-mathlib: could not read the toolchain for $rev; keeping ${wanted:-project default}" >&2
  actual="$wanted"
fi

printf '%s\n' "$actual" > "$TOOLCHAIN_FILE"
# rewrite only the rev line inside the [[require]] block for mathlib
python3 - "$LAKEFILE" "$rev" <<'PY'
import re
import sys

path, rev = sys.argv[1], sys.argv[2]
with open(path, encoding="utf-8") as stream:
    text = stream.read()
text = re.sub(r'(?m)^rev\s*=\s*".*"$', f'rev = "{rev}"', text, count=1)
with open(path, "w", encoding="utf-8") as stream:
    stream.write(text)
PY

echo "resolve-mathlib: mathlib $rev on $actual"