/*
Like markdown-it-simplemath, this is a stripped down, simplified version of:
https://github.com/runarberg/markdown-it-math

It differs in that it takes (a subset of) LaTeX as input and relies on KaTeX
for rendering output.
*/

import "katex/dist/katex.min.css";

import katex from "katex";

// Test if potential opening or closing delimieter
// Assumes that there is a "$" at state.src[pos]
function isValidDelim(state, pos) {
    const max = state.posMax;
    const nextChar = pos + 1 <= max ? state.src.charCodeAt(pos + 1) : -1;
    const prevChar = pos > 0 ? state.src.charCodeAt(pos - 1) : -1;

    let can_close = true;
    let can_open = true;

    // Check non-whitespace conditions for opening and closing, and
    // check that closing delimeter isn't followed by a number
    if (
        prevChar === 0x20 /* " " */ ||
        prevChar === 0x09 /* \t */ ||
        (nextChar >= 0x30 /* "0" */ && nextChar <= 0x39) /* "9" */
    ) {
        can_close = false;
    }
    if (nextChar === 0x20 /* " " */ || nextChar === 0x09 /* \t */) {
        can_open = false;
    }

    return {
        can_open: can_open,
        can_close: can_close,
    };
}

function math_inline(state, silent) {
    let match;
    let res;
    let pos;
    let esc_count;

    if (state.src[state.pos] !== "$") {
        return false;
    }

    res = isValidDelim(state, state.pos);
    if (!res.can_open) {
        if (!silent) {
            state.pending += "$";
        }
        state.pos += 1;
        return true;
    }

    // First check for and bypass all properly escaped delimieters
    // This loop will assume that the first leading backtick can not
    // be the first character in state.src, which is known since
    // we have found an opening delimieter already.
    const start = state.pos + 1;
    match = start;
    while ((match = state.src.indexOf("$", match)) !== -1) {
        // Found potential $, look for escapes, pos will point to
        // first non escape when complete
        pos = match - 1;
        while (state.src[pos] === "\\") {
            pos -= 1;
        }

        // Even number of escapes, potential closing delimiter found
        if ((match - pos) % 2 == 1) {
            break;
        }
        match += 1;
    }

    // No closing delimter found.  Consume $ and continue.
    if (match === -1) {
        if (!silent) {
            state.pending += "$";
        }
        state.pos = start;
        return true;
    }

    // Check if we have empty content, ie: $$.  Do not parse.
    if (match - start === 0) {
        if (!silent) {
            state.pending += "$$";
        }
        state.pos = start + 1;
        return true;
    }

    // Check for valid closing delimiter
    res = isValidDelim(state, match);
    if (!res.can_close) {
        if (!silent) {
            state.pending += "$";
        }
        state.pos = start;
        return true;
    }

    if (!silent) {
        const token = state.push("math_inline", "math", 0);
        token.markup = "$";
        token.content = state.src.slice(start, match);
    }

    state.pos = match + 1;
    return true;
}

function math_block(state, start, end, silent) {
    let firstLine;
    let lastLine;
    let next;
    let lastPos;
    let found = false;
    let pos = state.bMarks[start] + state.tShift[start];
    let max = state.eMarks[start];

    if (pos + 2 > max) {
        return false;
    }
    if (state.src.slice(pos, pos + 2) !== "$$") {
        return false;
    }

    pos += 2;
    firstLine = state.src.slice(pos, max);

    if (silent) {
        return true;
    }
    if (firstLine.trim().slice(-2) === "$$") {
        // Single line expression
        firstLine = firstLine.trim().slice(0, -2);
        found = true;
    }

    for (next = start; !found; ) {
        next++;

        if (next >= end) {
            break;
        }

        pos = state.bMarks[next] + state.tShift[next];
        max = state.eMarks[next];

        if (pos < max && state.tShift[next] < state.blkIndent) {
            // non-empty line with negative indent should stop the list:
            break;
        }

        if (state.src.slice(pos, max).trim().slice(-2) === "$$") {
            lastPos = state.src.slice(0, max).lastIndexOf("$$");
            lastLine = state.src.slice(pos, lastPos);
            found = true;
        }
    }

    state.line = next + 1;

    const token = state.push("math_block", "math", 0);
    token.block = true;
    token.content =
        (firstLine && firstLine.trim() ? firstLine + "\n" : "") +
        state.getLines(start + 1, next, state.tShift[start], true) +
        (lastLine && lastLine.trim() ? lastLine : "");
    token.map = [start, state.line];
    token.markup = "$$";
    return true;
}

export default function (md, options) {
    // Default options
    options = options || {};

    // set KaTeX as the renderer for markdown-it-simplemath
    const katexInline = function (latex) {
        options.displayMode = false;
        try {
            return katex.renderToString(latex, options);
        } catch (error) {
            if (options.throwOnError) {
                console.log(error);
            }
            return latex;
        }
    };

    const inlineRenderer = function (tokens, idx) {
        return katexInline(tokens[idx].content);
    };

    const katexBlock = function (latex) {
        options.displayMode = true;
        try {
            return "<p>" + katex.renderToString(latex, options) + "</p>";
        } catch (error) {
            if (options.throwOnError) {
                console.log(error);
            }
            return latex;
        }
    };

    const blockRenderer = function (tokens, idx) {
        return katexBlock(tokens[idx].content) + "\n";
    };

    md.inline.ruler.after("escape", "math_inline", math_inline);
    md.block.ruler.after("blockquote", "math_block", math_block, {
        alt: ["paragraph", "reference", "blockquote", "list"],
    });
    md.renderer.rules.math_inline = inlineRenderer;
    md.renderer.rules.math_block = blockRenderer;
}
