#!/usr/bin/env bash
# check-links.sh — Verify all external URLs in content/*.md are reachable.
#
# Extracts https?:// URLs from content/*.md, sends a HEAD request (fallback to GET),
# and reports 404s / connection errors. Known bot-blockers (403 responses from
# hhs.gov, jamanetwork.com etc.) are treated as OK.
#
# Exit codes:
#   0 — all links OK or only bot-blocked
#   1 — one or more broken links found
#   2 — usage error
#
# Usage:
#   scripts/check-links.sh              # check all content files
#   scripts/check-links.sh --fast       # stop at first failure
#   scripts/check-links.sh --verbose    # show every URL being checked
#   scripts/check-links.sh path/to.md   # check a specific file

set -euo pipefail

SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
PROJECT_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"

FAST=0
VERBOSE=0
FILES=()

for arg in "$@"; do
    case "$arg" in
        --fast) FAST=1 ;;
        --verbose|-v) VERBOSE=1 ;;
        --help|-h)
            sed -n '2,18p' "$0" | sed 's/^# \{0,1\}//'
            exit 0 ;;
        -*) echo "Unknown option: $arg" >&2; exit 2 ;;
        *)  FILES+=("$arg") ;;
    esac
done

# Default: all .md files under content/
if [ "${#FILES[@]}" -eq 0 ]; then
    mapfile -t FILES < <(find "$PROJECT_ROOT/content" -type f -name '*.md')
fi

# Domains known to return 403 for automated requests but are valid sources.
# Keep this list short — anything that doesn't load in a browser should fail.
ALLOW_403='^(www\.)?(hhs\.gov|jamanetwork\.com|commission\.europa\.eu|digital-strategy\.ec\.europa\.eu|pubmed\.ncbi\.nlm\.nih\.gov|who\.int|oecd\.org|unesco\.org|unicef\.org|amnesty\.org|linkedin\.com|sciencedirect\.com|nature\.com|tandfonline\.com|springer\.com|wiley\.com|bmj\.com|nytimes\.com|ft\.com|wsj\.com|spiegel\.de|zeit\.de|lemonde\.fr|lefigaro\.fr|cnn\.com|worldhappiness\.report|danish-presidency\.consilium\.europa\.eu|consilium\.europa\.eu|europarl\.europa\.eu|ec\.europa\.eu)$'

# Extract URLs from markdown. Strip trailing punctuation/brackets.
extract_urls() {
    local file="$1"
    grep -Eo 'https?://[A-Za-z0-9._~:/?#@!$&+,;=%-]+' "$file" \
        | sed -E 's/[,.;:!?)\]]+$//' \
        | sort -u
}

# Returns status code (HTTP number or "000" if fetch failed)
check_url() {
    local url="$1"
    local status
    status=$(curl -sS -o /dev/null -w "%{http_code}" \
        --max-time 10 \
        --connect-timeout 5 \
        --retry 1 \
        --user-agent "Mozilla/5.0 (compatible; IFK-LinkChecker/1.0; +https://internetforkids.org)" \
        -I -L "$url" 2>/dev/null || echo "000")
    # Many servers reject HEAD → retry with GET
    if [ "$status" = "000" ] || [ "$status" = "405" ] || [ "$status" = "403" ]; then
        status=$(curl -sS -o /dev/null -w "%{http_code}" \
            --max-time 10 \
            --connect-timeout 5 \
            --retry 1 \
            --user-agent "Mozilla/5.0 (compatible; IFK-LinkChecker/1.0; +https://internetforkids.org)" \
            -L "$url" 2>/dev/null || echo "000")
    fi
    echo "$status"
}

# Classify status code as OK / bot-blocked / broken
classify() {
    local status="$1" url="$2"
    case "$status" in
        2[0-9][0-9]|3[0-9][0-9]) echo "ok" ;;
        403)
            local host
            host=$(echo "$url" | awk -F/ '{print $3}')
            if [[ "$host" =~ $ALLOW_403 ]]; then
                echo "ok-blocked"
            else
                echo "broken"
            fi ;;
        404|410|5[0-9][0-9]|000) echo "broken" ;;
        *) echo "broken" ;;
    esac
}

# Collect URL → files mapping
declare -A URL_FILES=()
for file in "${FILES[@]}"; do
    while IFS= read -r url; do
        [ -z "$url" ] && continue
        rel="${file#$PROJECT_ROOT/}"
        if [ -z "${URL_FILES[$url]+x}" ]; then
            URL_FILES[$url]="$rel"
        else
            URL_FILES[$url]="${URL_FILES[$url]}, $rel"
        fi
    done < <(extract_urls "$file")
done

TOTAL=${#URL_FILES[@]}
echo "Checking $TOTAL unique external URLs across ${#FILES[@]} files..."

if [ "$TOTAL" -eq 0 ]; then
    echo "No external URLs found."
    exit 0
fi

BROKEN=0
OK=0
BLOCKED=0

for url in "${!URL_FILES[@]}"; do
    status=$(check_url "$url")
    result=$(classify "$status" "$url")

    case "$result" in
        ok)
            OK=$((OK + 1))
            [ "$VERBOSE" -eq 1 ] && printf "  OK   %s %s\n" "$status" "$url"
            ;;
        ok-blocked)
            BLOCKED=$((BLOCKED + 1))
            [ "$VERBOSE" -eq 1 ] && printf "  403* %s (bot-blocked, allowlisted)\n" "$url"
            ;;
        broken)
            BROKEN=$((BROKEN + 1))
            printf "  FAIL %s %s\n       in: %s\n" "$status" "$url" "${URL_FILES[$url]}"
            if [ "$FAST" -eq 1 ]; then
                echo ""
                echo "Aborting early (--fast). $BROKEN broken, $OK ok, $BLOCKED allowlisted."
                exit 1
            fi
            ;;
    esac
done

echo ""
echo "Summary: $OK OK, $BLOCKED allowlisted (403), $BROKEN broken"

if [ "$BROKEN" -gt 0 ]; then
    exit 1
fi