#!/bin/sh

start_time=$(date +%s)
domain="https://btxx.org"
timestamp_file="timestamps.tsv"

# Check the operating system and set aliases
case $(uname -s) in
    OpenBSD)
        alias sed=gsed
        alias date=gdate
        alias rsync=openrsync
        ;;
    Darwin)
        alias sed=gsed
        alias date=gdate
        ;;
esac

set -eu
MARKDOWN=lowdown
IFS=$'\t'

# Precompute values used in multiple places
header_title=$(sed -n '/^# /{s/# //p; q}' index.md)
git_user_name=$(git config user.name)
first_commit_date=$(git log --pretty='format:%ai' . | cut -d ' ' -f1 | tail -1)
now=$(date +%FT%TZ)
now_rss=$(date -u +"%a, %d %b %Y %H:%M:%S %z")

# Update the timestamp for a markdown file
update_timestamp() {
    local filename=$1
    local timestamp=$(date -r "$filename" +%s)
    # Remove old timestamp and add new
    awk -v file="$filename" -v ts="$timestamp" '$1 != file {print $0}' "$timestamp_file" > "${timestamp_file}.tmp"
    echo "$filename $timestamp" >> "${timestamp_file}.tmp"
    mv "${timestamp_file}.tmp" "$timestamp_file"
}

# Check if the markdown file needs rebuilding
needs_rebuilding() {
    local filename=$1
    local last_mod=$(date -r "$filename" +%s)
    local last_build=$(awk -v file="$filename" '$1 == file {print $2}' "$timestamp_file")

    if [ "$last_mod" -gt "${last_build:-0}" ]; then
        return 0  # needs rebuilding
    else
        return 1  # does not need rebuilding
    fi
}

# Define write_page function
write_page() {
    local filename=$1
    local title=$2
    local category=$3  # Category determines if it's a post or a page

    if needs_rebuilding "$filename"; then
        local directory
        if [ "$category" = "posts" ]; then
            directory="build/posts/$(basename "$filename" .md)"
        else
            directory="build/$(basename "$filename" .md)"
        fi
        mkdir -p "$directory"
        local target="${directory}/index.html"
        local created=$(head -3 "$filename" | tail -1)

        {
            sed "s|{{TITLE}}|$title|" header.html
            $MARKDOWN "$filename"
            cat footer.html
        } > "$target"
        update_timestamp "$filename"
        
        echo "Rebuilt: $filename"
    fi
}

# Create tab separated file with filename, title
index_tsv() {
    for f in "$1"/*.md; do
        title=$(sed -n '/^# /{s/# //p; q}' "$f")
        printf '%s\t%s\n' "$f" "${title:="No Title"}"
    done
}

# Generate index.html
index_html() {
    sed "s/{{TITLE}}/$header_title/" header.html
    $MARKDOWN index.md
    echo "<div>"

    while read -r f title; do
        link="${f%.md}/"
        created=$(head -3 "$f" | tail -1)
        echo "<span>$created &middot; <a href=\"$link\">$title</a></span><br>"
    done < "$1" | sort -r

    echo "</div>"
    cat footer.html
}

# Generate atom.xml
atom_xml() {
    echo "<?xml version=\"1.0\" encoding=\"utf-8\"?>
<feed xmlns=\"http://www.w3.org/2005/Atom\">
    <title>$header_title</title>
    <link href=\"$domain/atom.xml\" rel=\"self\" />
    <updated>$now</updated>
    <author>
        <name>$git_user_name</name>
    </author>
    <id>$domain,$first_commit_date:default-atom-feed</id>"

    while read -r f title; do
        content=$($MARKDOWN "$f" | sed 's/&/\&amp;/g; s/</\&lt;/g; s/>/\&gt;/g; s/"/\&quot;/g; s/'"'"'/\&#39;/g')
        post_link="${f%.md}"
        basic_date=$(head -3 "$f" | tail -1)
        published_date=$(date -d "$basic_date" -u +%Y-%m-%dT10:%M:%SZ)
        echo "    <entry>
        <title>$title</title>
        <content type=\"html\">$content</content>
        <link href=\"$domain/$post_link\"/>
        <id>$domain/$post_link</id>
        <updated>$published_date</updated>
        <published>$published_date</published>
    </entry>"
    done < "$1"
    echo '</feed>'
}

# Generate RSS
rss_xml() {
    uri=$(sed -rn '/rss.xml/ s/.*href="([^"]*)".*/\1/ p' header.html)
    first_commit_date=$(git log --pretty='format:%ai' . | cut -d ' ' -f1 | tail -1)

    cat <<EOF
<?xml version="1.0" encoding="utf-8"?>
<rss version="2.0">
    <channel>
        <title>$(sed -n '/^# /{s/# //p; q}' index.md)</title>
        <link>$domain/rss.xml</link>
        <description>Feed description here</description>
        <lastBuildDate>$(date -u +"%a, %d %b %Y %H:%M:%S %z")</lastBuildDate>
        <pubDate>$(date -u +"%a, %d %b %Y %H:%M:%S %z")</pubDate>
        <generator>Custom RSS Generator</generator>
        <ttl>1800</ttl>
EOF

    while read -r f title created; do
        content=$($MARKDOWN "$f" | sed 's/&/\&amp;/g; s/</\&lt;/g; s/>/\&gt;/g; s/"/\&quot;/g; s/'"'"'/\&#39;/g')
        post_link=$(echo "$f" | sed -E 's|posts/(.*).md|\1|')
        basic_date=$(echo $(head -3 "$f" | tail -1))
        published_date=$(date -d "$basic_date" -u +"%a, %d %b %Y %H:%M:%S %z")

        cat <<EOF
        <item>
            <title>$title</title>
            <description>$content</description>
            <link>$domain/$post_link</link>
            <guid isPermaLink="false">$domain/$post_link</guid>
            <pubDate>$published_date</pubDate>
        </item>
EOF
    done < "$1"

    echo '</channel>'
    echo '</rss>'
}

# Initialize timestamps for all Markdown files if not already done
initialize_timestamps() {
    if [ ! -f "$timestamp_file" ] || [ ! -s "$timestamp_file" ]; then
        echo "Initializing timestamps..."
        for f in index.md posts/*.md pages/*.md; do
            update_timestamp "$f"
        done
        echo "Timestamps initialized for all Markdown files."
    fi
}

# Main operations
mkdir -p build/posts build/pages
initialize_timestamps

index_tsv posts > build/posts.tsv
index_tsv pages > build/pages.tsv

while read -r f title; do
    write_page "$f" "$title" "posts"
done < build/posts.tsv

while read -r f title; do
    write_page "$f" "$title" "pages"
done < build/pages.tsv

if needs_rebuilding "index.md"; then
    index_html build/posts.tsv > build/index.html
    echo "Rebuilt index.html due to changes in index.md"
    update_timestamp "index.md"
fi

atom_xml build/posts.tsv > build/atom.xml
rss_xml build/posts.tsv > build/rss.xml

end_time=$(date +%s)
elapsed_time=$((end_time - start_time))
echo "Total time: ${elapsed_time}s"