#!/bin/bash

# Generate a diff of framework files against the upstream version this
# project is based on.  Useful for contributing changes back to diachron.
#
# Usage:
#   ./diff-upstream.sh              # diff against .diachron-version
#   ./diff-upstream.sh <ref>        # diff against a specific ref
#   ./diff-upstream.sh --stat       # show changed files only

set -eu
set -o pipefail
IFS=$'\n\t'

DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"

stat_only=false
ref=""

for arg in "$@"; do
    case "$arg" in
        --stat) stat_only=true ;;
        *)      ref="$arg" ;;
    esac
done

if [ -z "$ref" ]; then
    if [ ! -f "$DIR/.diachron-version" ]; then
        echo "Error: .diachron-version not found and no ref specified." >&2
        echo "Usage: $0 [--stat] [<ref>]" >&2
        exit 1
    fi
    ref=$(cat "$DIR/.diachron-version")
fi

cached_repo="$HOME/.cache/diachron/v1/repositories/diachron.git"

if [ ! -d "$cached_repo" ]; then
    echo "Error: cached repository not found at $cached_repo" >&2
    echo "Run ./update-cached-repository.sh first." >&2
    exit 1
fi

# Update cached repo
"$DIR/update-cached-repository.sh"

# Verify ref exists
if ! git -C "$cached_repo" rev-parse --verify "$ref^{commit}" >/dev/null 2>&1; then
    echo "Error: ref '$ref' not found in cached repository." >&2
    exit 1
fi

# Read file-list
files=()
while IFS= read -r line; do
    [[ "$line" =~ ^[[:space:]]*# ]] && continue
    [[ -z "$line" ]] && continue
    files+=("$line")
done < "$DIR/file-list"

# Check out upstream into a temp directory
tmpdir=$(mktemp -d)
cleanup() { rm -rf "$tmpdir"; }
trap cleanup EXIT

git clone --quiet "$cached_repo" "$tmpdir/upstream"
git -C "$tmpdir/upstream" checkout --quiet "$ref"

# Generate diff
if $stat_only; then
    diff -rq "$tmpdir/upstream" "$DIR" \
        --no-dereference \
        2>/dev/null \
        | grep -v '^\.' \
        || true

    # Simpler: just list files that differ
    for f in "${files[@]}"; do
        # Skip directories
        [ -d "$DIR/$f" ] && continue

        upstream="$tmpdir/upstream/$f"
        local="$DIR/$f"

        if [ ! -f "$upstream" ] && [ -f "$local" ]; then
            echo "added:    $f"
        elif [ -f "$upstream" ] && [ ! -f "$local" ]; then
            echo "removed:  $f"
        elif [ -f "$upstream" ] && [ -f "$local" ]; then
            if ! diff -q "$upstream" "$local" >/dev/null 2>&1; then
                echo "modified: $f"
            fi
        fi
    done
else
    for f in "${files[@]}"; do
        [ -d "$DIR/$f" ] && continue

        upstream="$tmpdir/upstream/$f"
        local="$DIR/$f"

        if [ ! -f "$upstream" ] && [ -f "$local" ]; then
            diff -u /dev/null "$local" \
                --label "a/$f" --label "b/$f" \
                || true
        elif [ -f "$upstream" ] && [ ! -f "$local" ]; then
            diff -u "$upstream" /dev/null \
                --label "a/$f" --label "b/$f" \
                || true
        elif [ -f "$upstream" ] && [ -f "$local" ]; then
            diff -u "$upstream" "$local" \
                --label "a/$f" --label "b/$f" \
                || true
        fi
    done
fi