//Calendar implementation for the HTWK Leipzig timetable. Evaluation and display of the individual dates in iCal format.
//Copyright (C) 2024 HTWKalender support@htwkalender.de

//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 v1

import (
	"golang.org/x/net/html"
	"log/slog"
	"strings"
)

// Find the first <table> element in the HTML document
func findFirstTable(node *html.Node) *html.Node {
	if node.Type == html.ElementNode && node.Data == "table" {
		return node
	}
	// Traverse child nodes recursively
	for child := node.FirstChild; child != nil; child = child.NextSibling {
		found := findFirstTable(child)
		if found != nil {
			return found
		}
	}
	return nil
}

// Find the first <span> element with the specified class attribute value
func findFirstSpanWithClass(node *html.Node, classValue string) *html.Node {

	if node == nil {
		return nil
	}

	// Check if the current node is a <span> element with the specified class attribute value
	if node.Type == html.ElementNode && node.Data == "span" {
		if hasClassAttribute(node, classValue) {
			return node
		}
	}

	// Traverse child nodes recursively
	for child := node.FirstChild; child != nil; child = child.NextSibling {
		found := findFirstSpanWithClass(child, classValue)
		if found != nil {
			return found
		}
	}
	return nil
}

// Check if the specified element has the specified class attribute value
func hasClassAttribute(node *html.Node, classValue string) bool {
	for _, attr := range node.Attr {
		if attr.Key == "class" && strings.Contains(attr.Val, classValue) {
			return true
		}
	}
	return false
}

type dayTable struct {
	day   string
	table []*html.Node
}

// Get Tables with days
func getEventTables(node *html.Node, dayLabels []string) map[string][]*html.Node {
	// Create a map to store the tables with the corresponding day from the dayLabels
	dayTablesMap := make(map[string][]*html.Node)

	tables := findTables(node)

	// Ensure we have the same number of tables as day labels
	if len(tables) != len(dayLabels) {
		// Handle the case where the number of tables doesn't match the dayLabels (log error or return early)
		slog.Error("Number of tables does not match number of day labels")
		return dayTablesMap // Returning empty map
	}

	// Iterate over dayLabels and their corresponding tables
	for i, day := range dayLabels {
		rows := findTableRows(tables[i])

		// check that rows exist and skip the header
		if len(rows) > 1 {
			rows = rows[1:] // Skip header row
			// Add the event rows to the map entry for this day
			dayTablesMap[day] = rows
		}
	}

	// Remove days that have no events (empty slices)
	for day, eventTable := range dayTablesMap {
		if len(eventTable) == 0 {
			delete(dayTablesMap, day)
		}
	}

	return dayTablesMap
}

// Get Tables with days
func getAllDayLabels(node *html.Node) []string {
	paragraphs := findParagraphs(node)
	var dayArray []string

	for _, p := range paragraphs {
		label := getDayLabel(p)
		if label != "" {
			dayArray = append(dayArray, label)
		}
	}
	return dayArray
}

// Find all <p> elements in the HTML document
func findParagraphs(node *html.Node) []*html.Node {
	var paragraphs []*html.Node

	if node.Type == html.ElementNode && node.Data == "p" {
		paragraphs = append(paragraphs, node)
	}

	for child := node.FirstChild; child != nil; child = child.NextSibling {
		paragraphs = append(paragraphs, findParagraphs(child)...)
	}

	return paragraphs
}

// Find all <tr> elements in <tbody>, excluding the first one
func findTableRows(node *html.Node) []*html.Node {
	var tableRows []*html.Node

	if node.Type == html.ElementNode && node.Data == "tbody" {
		child := node.FirstChild
		for child != nil {
			if child.Type == html.ElementNode && child.Data == "tr" {
				tableRows = append(tableRows, child)
			}
			child = child.NextSibling
		}
	}

	// Traverse child nodes recursively
	for child := node.FirstChild; child != nil; child = child.NextSibling {
		var tableRowElement = findTableRows(child)
		if tableRowElement != nil {
			tableRows = append(tableRows, tableRowElement...)
		}
	}

	// check if tableRows is nil
	if tableRows == nil {
		return []*html.Node{}
	} else {
		return tableRows
	}
}

// Find all <p> elements in the HTML document
func findTables(node *html.Node) []*html.Node {
	var tables []*html.Node

	if node.Type == html.ElementNode && node.Data == "table" {
		tables = append(tables, node)
	}

	for child := node.FirstChild; child != nil; child = child.NextSibling {
		tables = append(tables, findDayTables(child)...)
	}

	return tables
}

// Find all <p> elements in the HTML document
func findDayTables(node *html.Node) []*html.Node {
	var tables []*html.Node

	for child := node.FirstChild; child != nil; child = child.NextSibling {
		tables = append(tables, findDayTables(child)...)
	}

	if node.Type == html.ElementNode && node.Data == "table" && hasClassAttribute(node, "spreadsheet") {
		tables = append(tables, node)
	}

	return tables
}

// Get the text content of the specified node and its descendants
func getDayLabel(node *html.Node) string {

	child := node.FirstChild
	if child != nil {
		if child.Type == html.ElementNode && child.Data == "span" {
			if child.FirstChild != nil {
				return child.FirstChild.Data
			}
		}
	}
	return ""
}

// Find all <td> elements in the current <tr>
func findTableData(node *html.Node) []*html.Node {
	var tableData []*html.Node

	if node.Type == html.ElementNode && node.Data == "tr" {
		child := node.FirstChild
		for child != nil {
			if child.Type == html.ElementNode && child.Data == "td" {
				tableData = append(tableData, child)
			}
			child = child.NextSibling
		}
	}
	return tableData
}

// Get the text content of the specified node and its descendants
func getTextContent(node *html.Node) string {
	var textContent string

	if node.Type == html.TextNode {
		textContent = node.Data
	}

	for child := node.FirstChild; child != nil; child = child.NextSibling {
		textContent += getTextContent(child)
	}

	return textContent
}