#!/usr/bin/env sh
set -eu

# If first arg is "pre" or "post", treat it as a hook command and shift it out
cmd=""
if [ "${1:-}" = "pre" ] || [ "${1:-}" = "post" ]; then
  cmd="$1"
  shift
fi
file="${1:-CHANGELOG.md}"
tmp="${file}.tmp"

# Define hook functions
pre() {
    prerelease_tags=$(git tag -l | grep -E '^v[0-9]+\.[0-9]+\.[0-9]+-' || true)
    if [ -n "$prerelease_tags" ]; then
        echo "$prerelease_tags" | xargs git tag -d
    fi
}

post() {
    awk '
BEGIN { skip = 0; n_pre = 0; n_section = 0 }

# Enter skip mode for prerelease section headers
/^## \[[^]]*-[^]]+\]/ {
    n_section = 0
    skip = 1
    next
}

# Stable release header: exit skip mode, discard any buffered empty section
/^## \[/ {
    skip = 0
    if (n_section > 0) {
    # An empty section was pending (all items filtered out) - replace it with
    # a single blank separator line before the next release header
    n_section = 0
    n_pre = 0
    print ""
    } else {
    for (i = 0; i < n_pre; i++) print pre[i]
    n_pre = 0
    }
    print
    next
}

skip { next }

# Skip prerelease release-bump commit lines within stable release entries
/^\* \*\*release:\*\* [0-9]+\.[0-9]+\.[0-9]+-/ { next }

# Subsection header: absorb preceding blank lines into the section buffer so
# that they are discarded together if the section turns out to be empty
/^### / {
    n_section = 0
    for (i = 0; i < n_pre; i++) section[i] = pre[i]
    n_section = n_pre
    n_pre = 0
    section[n_section++] = $0
    next
}

# Blank line: buffer inside a pending section, otherwise in the pre-blank pool
/^[[:space:]]*$/ {
    if (n_section > 0) {
    section[n_section++] = $0
    } else {
    pre[n_pre++] = $0
    }
    next
}

# Any other content: flush buffered section header (with its pre-blanks) then print
{
    for (i = 0; i < n_section; i++) print section[i]
    n_section = 0
    for (i = 0; i < n_pre; i++) print pre[i]
    n_pre = 0
    print
}

END {
    for (i = 0; i < n_pre; i++) print pre[i]
}
    ' "$file" > "$tmp"

    mv "$tmp" "$file"
}

# If a hook name was passed as the first argument, call it
if [ -n "${cmd:-}" ]; then
    if [ "$cmd" = "pre" ]; then
        pre
    elif [ "$cmd" = "post" ]; then
        post
    else
        echo "Unknown command: $cmd" >&2
        exit 2
    fi
fi