import std.exception;
import std.experimental.logger;
import std.file;
import std.process;
import std.stdio;

import dyaml;
import vibe.vibe;


/**
 * Exception thrown when a page has syntax errors e.g.
 */
class ArticleParseException : Exception {
	mixin basicExceptionCtors;
}


/**
 * Represents a page on the blog. Every other page, including blog articles,
 * projects and so on derrive from this class.
 */
class Page {
    /**
     * Internal name of the article. Usually the file name.
     */
	protected string m_name;

	/**
	 * Slug either manually assigned or generated based on file name.
	 * Only used in the url.
	 */
	protected string m_slug;
	protected string m_title;
	protected string m_content;
	protected string m_contentSource;

	/**
     * Option for the markdown parser: the amount of levels the header found in the markdown should
	 * be shifted. For example, 0 means H1 -> H1, 1 means H1 -> H2, 2 means H1 -> H3 and so on.
	 */
	protected int m_headerShift = 1;

	private bool hasCalledSuper = false;

	/**
	 * Creates a page from a file. This will read from the file and parse it.
	 */
	this(string file) {
		this.m_name = file;
        this.m_contentSource = readText(file);
		// Find the seperator and split the string in two
        const long seperatorIndex = indexOf(m_contentSource, "---\n");
        enforce!ArticleParseException(seperatorIndex >= 0);
        string header = m_contentSource[0..seperatorIndex];
        
	    Node node = Loader.fromString(header).load();
        loadHeader(node);
		assert(hasCalledSuper);
        
		this.m_content = Page.parseMarkdown(m_contentSource[seperatorIndex + 4..$], 
				this.m_headerShift);
	}


	/**
	 * Parse metadata from the header. Subclasses should override this method,
	 * to parse their own metadata and call super.
	 * Params: 
	 *     headerNode = the YAML node to parse the header metadata from.
	 */
	@safe
	protected void loadHeader(Node headerNode){
		if (headerNode.containsKey("title")) {
            this.m_title = headerNode["title"].as!string;
        } else {
            warningf("%s does not contain a title", this.m_name);
        }
        if (headerNode.containsKey("slug")) {
            this.m_slug = headerNode["slug"].as!string;
        } else {
            this.m_slug = this.m_title;
            infof("%s does not have a slug. Using %s", this.m_name, this.m_slug);
        }
		hasCalledSuper = true;
	}

	/**
	 * Starts pandoc to convert MarkDown to HTML
	 * Params:
	 *     source = The MarkDown source as a string (not a path!)
	 *     shiftHeader = (Optional) The amount a header needs to be shifted. If for example, it 
	 *                   is set to 1, first level headings within MarkDown become second level
	 *                   headers within HTML.
	 */
	public static string parseMarkdown(string source, int shiftHeader = 0) {
		string[] args = ["pandoc", 
				"-f", "markdown", 
				"-t", "html"];

		if (shiftHeader != 0) args ~= "--shift-heading-level-by=" ~ to!string(shiftHeader);

		ProcessPipes pandoc = pipeProcess(args);
		pandoc.stdin.write(source);
		pandoc.stdin.writeln();
		pandoc.stdin.flush();
		pandoc.stdin.close();
		string result;
		string line;
		while ((line = pandoc.stdout.readln()) !is null) {
			result ~= line;
		}
		return result;
	}

    @property string name() { return m_name; }
    @property string title() { return m_title; }
    @property string slug() { return m_slug; }
	@property string content() { return m_content; }
	@property string contentSource() { return m_contentSource; }
}