/*
 *	Scope - A simple and minimal metasearch engine
 *	Copyright (C) 2021 Arsen Musayelyan
 *
 *	This program is free software: you can redistribute it and/or modify
 *	it under the terms of the GNU Affero General Public License as published by
 *	the Free Software Foundation, either version 3 of the License, or
 *	(at your option) any later version.
 *
 *	This program is distributed in the hope that it will be useful,
 *	but WITHOUT ANY WARRANTY; without even the implied warranty of
 *	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *	GNU Affero General Public License for more details.
 *
 *	You should have received a copy of the GNU Affero General Public License
 *	along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

package cards

import (
	"fmt"
	"html/template"
	"regexp"
	"strings"
)

const calcExtraHead = `
<!-- Import KaTeX for math rendering -->
<link rel="stylesheet" href="/static/ext/katex.min.css">
<script defer src="/static/ext/katex.min.js"></script>

<!-- Import Nerdamer for equation evaluator -->
<script src="/static/ext/nerdamer.core.js"></script>
<script src="/static/ext/Algebra.js"></script>
<script src="/static/ext/Calculus.js"></script>
<script src="/static/ext/Solve.js"></script>`

const solveRenderScript = `
<div id="calc-content" class="subtitle mx-2 my-0"></div>
<script>
window.onload = () => {
	// Execute input and get output as LaTeX
	latex = nerdamer('%s').latex()
	// Use KaTeX to render output to #calc-content div
	katex.render(latex, document.getElementById('calc-content'))
}
</script>`

func init() {
	// Register calc card
	Register("calc", 0, NewCalcCard)
}

// CalcCard represents a calculation card
type CalcCard struct {
	query      string
	useFunc    bool
	function   string
	args       []string
	expression string
}

// NewCalcCard is a NewCardFunc that creates a new CalcCard
func NewCalcCard(query, _ string) Card {
	return &CalcCard{query: query, useFunc: true}
}

// Matches determines whether a query matches the requirements
// fot CalcCard and determines which function to run with what arguments
func (cc *CalcCard) Matches() bool {
	// If query has solve prefix
	if strings.HasPrefix(cc.query, "solve") {
		// Set function to solve
		cc.function = "solve"

		// Compile regex for specifying veriable to solve for
		forRgx := regexp.MustCompile(`solve (.+) for (.+)`)
		// If query matches regex
		if forRgx.MatchString(cc.query) {
			// Find furst regex match
			matches := forRgx.FindStringSubmatch(cc.query)
			// Append function aeguments. First is equation, second variable
			cc.args = append(cc.args, matches[1], matches[2])
		} else {
			// Append function arguments assuming variable is x
			cc.args = append(cc.args, cc.StripKey(), "x")
		}

		return true
	}

	// If query has integrate prefix
	if strings.HasPrefix(cc.query, "integrate") ||
		strings.HasPrefix(cc.query, "integral of") ||
		strings.HasPrefix(cc.query, "integral") {

		// Set function to integrate
		cc.function = "integrate"
		// Append function arguments
		cc.args = append(cc.args, cc.StripKey())

		return true
	}

	// If query has derivative prefix
	if strings.HasPrefix(cc.query, "diff") ||
		strings.HasPrefix(cc.query, "derive") ||
		strings.HasPrefix(cc.query, "differentiate") ||
		strings.HasPrefix(cc.query, "derivative of") ||
		strings.HasPrefix(cc.query, "derivative") {

		// Set function to diff
		cc.function = "diff"
		// Append function arguments
		cc.args = append(cc.args, cc.StripKey())

		return true
	}

	// If query has calculate prefix
	if strings.HasPrefix(cc.query, "calculate") {
		// This is an expression, so no function needed
		cc.useFunc = false
		// Set expression to query stripped of keys
		cc.expression = cc.StripKey()
		return true
	}

	return false
}

// StripKey removes all key words related to CalcCard
func (cc *CalcCard) StripKey() string {
	// Compile regex for words to be removed
	trimRgx := regexp.MustCompile(`^(.*?)solve|integrate|integral(?: of)?|diff|differentiate|derivative(?: of)?|derive|calculate(.*)$`)
	// Return string with words removed
	return trimRgx.ReplaceAllString(cc.query, "${1}${2}")
}

// Content returns the solveRenderScript with the given input
func (cc *CalcCard) Content() template.HTML {
	var input string
	// If function is being used
	if cc.useFunc {
		// Set input to formatted function
		input = formatFunc(cc.function, cc.args)
	} else {
		// Set input to expression
		input = cc.expression
	}
	// Return script with given input
	return template.HTML(fmt.Sprintf(
		solveRenderScript,
		input,
	))
}

// Footer returns empty string because CalcCard has no footer
func (cc *CalcCard) Footer() template.HTML {
	return ""
}

// Returned always returns true since CalcCard is a frontend
// card and it is thus impossible to determine whether
// the query gets an answer
func (cc *CalcCard) Returned() bool {
	return true
}

// RunQuery returns nil as CalcCard is a frontend card
func (cc *CalcCard) RunQuery() error {
	return nil
}

// Title for CalcCard is "Calculation"
func (cc *CalcCard) Title() string {
	return "Calculation"
}

// Head returns the extra head tags required for CalcCard
func (cc *CalcCard) Head() template.HTML {
	return calcExtraHead
}

func formatFunc(function string, args []string) string {
	// Format as function(arg1,arg2...)
	return function + "(" + strings.Join(args, ",") + ")"
}