#!/usr/bin/env bash
# check-migration-backward-compat.sh — pre-deploy gate for canary releases.
#
# Refuses to deploy when the latest migration is NOT backward-compatible
# with the running schema. Backward-compat = the OLD code can still
# read/write against the NEW schema for at least one canary window
# (otherwise canary mode is meaningless ; the old node would crash on
# the first request that touches a removed column).
#
# Heuristic : reject migrations that contain any of these patterns :
#   - DROP COLUMN
#   - DROP TABLE
#   - ALTER COLUMN ... TYPE      (type change is rarely backward-compat)
#   - ADD COLUMN ... NOT NULL    (without DEFAULT — old code can't INSERT)
#   - DROP CONSTRAINT
#   - DROP INDEX UNIQUE          (existing data may already violate)
#
# This is a STATIC check ; some patterns are false-positives (e.g.
# DROP COLUMN of a column that no code reads). When a real migration
# is flagged, the operator either :
#   1. Splits the migration : ship the additive part now, drop in v+1
#      after old-version backends are decommissioned.
#   2. Bypasses with FORCE_MIGRATE=1 + a justification in the commit
#      message of the migration file.
#
# v1.0.9 W5 Day 23.
#
# Usage :
#   bash scripts/check-migration-backward-compat.sh
#
# Required env :
#   MIGRATIONS_DIR  default veza-backend-api/migrations
#   GIT_RANGE       default origin/main..HEAD ; the range to inspect for
#                   newly-added migration files
# Optional env :
#   FORCE_MIGRATE=1 bypass with a logged warning. Use sparingly.
#
# Exit codes :
#   0  — all new migrations are backward-compat (or FORCE_MIGRATE=1)
#   1  — at least one migration carries a forbidden pattern
#   3  — required tool missing / config error
set -euo pipefail

MIGRATIONS_DIR=${MIGRATIONS_DIR:-veza-backend-api/migrations}
GIT_RANGE=${GIT_RANGE:-origin/main..HEAD}
FORCE_MIGRATE=${FORCE_MIGRATE:-0}

log()  { printf '[%s] %s\n' "$(date +%H:%M:%S)" "$*" >&2; }
fail() { log "FAIL: $*"; exit "${2:-1}"; }

require() {
  command -v "$1" >/dev/null 2>&1 || fail "required tool missing: $1" 3
}

require git
require grep
require date

# Patterns that indicate non-backward-compat schema change.
# Heredoc preserves the pipe characters as alternations.
FORBIDDEN_PATTERNS='DROP COLUMN|DROP TABLE|ALTER COLUMN [A-Za-z_]+ TYPE|ADD COLUMN [A-Za-z_]+ [^,;]* NOT NULL[^,;]*(;|$)|DROP CONSTRAINT|DROP INDEX [A-Za-z_]*UNIQUE'

# Identify newly-added migration files in the current range.
new_migrations=$(git diff --name-only --diff-filter=A "$GIT_RANGE" -- "$MIGRATIONS_DIR" 2>/dev/null \
  | grep -E "^${MIGRATIONS_DIR}/[0-9]+_.*\.sql$" || true)

if [ -z "$new_migrations" ]; then
  log "no new migrations in $GIT_RANGE — nothing to check"
  exit 0
fi

log "checking $(echo "$new_migrations" | wc -l) new migration(s) in $GIT_RANGE"
findings=0
for f in $new_migrations; do
  log "  scanning $f"
  # -i case-insensitive ; -E extended regex ; -n line numbers
  matches=$(grep -inE "$FORBIDDEN_PATTERNS" "$f" || true)
  if [ -n "$matches" ]; then
    findings=$((findings + 1))
    log ""
    log "  ⚠ NON-BACKWARD-COMPAT pattern in $f :"
    echo "$matches" | sed 's/^/      /' >&2
    # Special case : ADD COLUMN ... NOT NULL ... DEFAULT <x> is fine.
    # The regex above tries to exclude that but the match-then-filter
    # approach is more reliable than a single regex. Suppress matches
    # that include `DEFAULT` on the same line.
    real=$(echo "$matches" | grep -ivE "DEFAULT" || true)
    if [ -z "$real" ]; then
      log "      ↳ all matches include DEFAULT clause — actually backward-compat"
      findings=$((findings - 1))
    fi
  fi
done

if [ "$findings" -gt 0 ]; then
  log ""
  log "$findings migration(s) flagged as potentially non-backward-compat."
  if [ "$FORCE_MIGRATE" = "1" ]; then
    log "FORCE_MIGRATE=1 set — proceeding anyway."
    exit 0
  fi
  log ""
  log "Options to proceed :"
  log "  1. Split the migration : ship the additive part now, drop the"
  log "     non-compat part in v+1 after old backends are off."
  log "  2. Set FORCE_MIGRATE=1 if you accept the risk + document the"
  log "     justification in the migration's commit message."
  exit 1
fi

log "PASS : all new migrations are backward-compat"
exit 0