/*
   AMU: Custom simple markup language
   Copyright (C) 2021 Arsen Musayelyan

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/

package html

import (
	"bytes"
	"fmt"
	"strings"

	"github.com/alecthomas/chroma"
	"github.com/alecthomas/chroma/formatters/html"
	"github.com/alecthomas/chroma/lexers"
	"github.com/alecthomas/chroma/styles"
	"go.arsenm.dev/amu/ast"
)

// HTMLFormatter formats an AMU AST into HTML source
type HTMLFormatter struct {
	Funcs ast.Funcs
	ast   *ast.AST
	out   *bytes.Buffer
}

// NewFormatter creates a new HTML formatter using the proided AST and functions
func NewFormatter(ast *ast.AST, funcs ast.Funcs) *HTMLFormatter {
	return &HTMLFormatter{ast: ast, Funcs: funcs, out: &bytes.Buffer{}}
}

// formatPara formats a paragraph from the AST into HTML
func (h *HTMLFormatter) formatPara(para *ast.Para, includeTags bool) {
	// If tags are to be included
	if includeTags {
		// Write opening p tag to buffer
		h.out.WriteString("<p>")
	}
	// For every fragment in paragraph
	for _, fragment := range para.Fragments {
		if fragment.Word != nil {
			// Write word to buffer
			h.out.WriteString(*fragment.Word)
		} else if fragment.Whitespace != nil {
			// Write whitespace to buffer
			h.out.WriteString(*fragment.Whitespace)
		} else if fragment.Punct != nil {
			// Write punctuatuon to buffer
			h.out.WriteString(*fragment.Punct)
		} else if fragment.Format != nil {
			// For every format type, write appropriate opening tag to buffer
			for _, ftype := range fragment.Format.Types {
				if ftype == ast.FormatTypeBold {
					h.out.WriteString("<strong>")
				}
				if ftype == ast.FormatTypeItalic {
					h.out.WriteString("<em>")
				}
				if ftype == ast.FormatTypeCode {
					h.out.WriteString("<code>")
				}
				if ftype == ast.FormatTypeStrike {
					h.out.WriteString(`<del>`)
				}
				if ftype == ast.FormatTypeMath {
					h.out.WriteString(`\(`)
				}
			}

			// Write format text to buffer
			h.out.WriteString(fragment.Format.Text)

			// For every format type, write appropriate closing tag to buffer in reverse
			for i := len(fragment.Format.Types) - 1; i >= 0; i-- {
				ftype := fragment.Format.Types[i]
				if ftype == ast.FormatTypeBold {
					h.out.WriteString("</strong>")
				}
				if ftype == ast.FormatTypeItalic {
					h.out.WriteString("</em>")
				}
				if ftype == ast.FormatTypeCode {
					h.out.WriteString("</code>")
				}
				if ftype == ast.FormatTypeStrike {
					h.out.WriteString(`</del>`)
				}
				if ftype == ast.FormatTypeMath {
					h.out.WriteString(`\)`)
				}
			}
		} else if fragment.Func != nil {
			// Attempt to get requested function
			fn, err := h.Funcs.Get(fragment.Func.Name)
			if err != nil {
				// Write error text to function
				h.out.WriteString("Error running function: " + err.Error())
				// Continue to next AST entry
				continue
			}
			// Write output of function to buffer
			h.out.WriteString(fn(fragment.Func.Args))
		} else if fragment.Link != nil {
			// Write link to buffer
			fmt.Fprintf(h.out, `<a href="%s">%s</a>`, fragment.Link.Link, fragment.Link.Text)
		}
	}
	// If tags are to be included
	if includeTags {
		// Write closing p tag to buffer
		h.out.WriteString("</p>")
	}
}

// Format formats the provided AST into an HTML string
func (h *HTMLFormatter) Format() string {
	// For every entry in AST
	for _, entry := range h.ast.Entries {
		if entry.Heading != nil {
			// Write opening heading tag
			fmt.Fprintf(h.out, "<h%d>", entry.Heading.Level)
			// Format paragraph with heading content without tags
			h.formatPara(entry.Heading.Content, false)
			// Write closing heading tag
			fmt.Fprintf(h.out, "</h%d>", entry.Heading.Level)
		} else if entry.Para != nil {
			// Format paragraph with tags
			h.formatPara(entry.Para, true)
		} else if entry.Image != nil {
			// If image link exists
			if entry.Image.Link != "" {
				// Write opening link tag
				fmt.Fprintf(h.out, `<a href="%s">`, entry.Image.Link)
			}
			// Weite image tag
			fmt.Fprintf(h.out, `<img src="%s" alt="%s">`, entry.Image.Source, entry.Image.Alternate)
			// If image link exists
			if entry.Image.Link != "" {
				// Write closing link tag
				h.out.WriteString("</a>")
			}
		} else if entry.List != nil {
			var openTag, closeTag string
			// Set opening and closing tags depending on list type
			switch entry.List.Type {
			case "unordered":
				openTag = "<ul>"
				closeTag = "</ul>"
			case "ordered":
				openTag = "<ol>"
				closeTag = "</ol>"
			default:
				// Write unknown list type
				h.out.WriteString("unknown list type " + entry.List.Type)
				// Continue to next entry
				continue
			}

			// Create variables for keeping track of list state
			lastLevel := 0
			openLists := 0

			for _, item := range entry.List.Items {
				if item.Level > lastLevel {
					// Get amount of lists to open
					amtOpen := item.Level - lastLevel
					// Increment openLists by amount
					openLists += amtOpen
					// Write opening tag the amount of times required
					h.out.WriteString(strings.Repeat(openTag, amtOpen))
					// Set lastLevel
					lastLevel = item.Level
				} else if item.Level < lastLevel {
					// Get amount of lists to close
					amtClose := lastLevel - item.Level
					// DEcrement openLists by amount
					openLists -= amtClose
					// Write closing tag the amount of times required
					h.out.WriteString(strings.Repeat(closeTag, amtClose))
					// Set lastLevel
					lastLevel = item.Level
				}
				// If content exists
				if len(item.Content) > 0 {
					// Write opening list item tag to output
					h.out.WriteString("<li>")
					// Format content as paragraph
					h.formatPara(item.Content[0], true)
					// Write closing list item tag to output
					h.out.WriteString("</li>")
					// For every line other than the first
					for _, line := range item.Content[1:] {
						// Format content as paragraph
						h.formatPara(line, true)
					}
				}
			}

			// Close all open lists
			h.out.WriteString(strings.Repeat(closeTag, openLists))
		} else if entry.Code != nil {
			// Get lexer for provided language
			lexer := lexers.Get(entry.Code.Language)
			if lexer == nil {
				lexer = lexers.Fallback
			}
			// Coalesce lexer tokens
			lexer = chroma.Coalesce(lexer)
			// Tokenise provided source using lexer
			iterator, err := lexer.Tokenise(nil, entry.Code.Text)
			if err != nil {
				h.out.WriteString("Error tokenising code: " + err.Error())
				continue
			}

			// Create new HTML formatter
			formatter := html.New(
				html.Standalone(false),
				html.WithLineNumbers(true),
				html.LineNumbersInTable(true),
			)

			// If no style
			if entry.Code.Style == "" {
				// Set style to monokai
				entry.Code.Style = "monokai"
			}

			// Get provided style
			chromaStyle := styles.Get(entry.Code.Style)

			// Create buffer
			buf := &bytes.Buffer{}
			// Format source code, writing output to buffer
			err = formatter.Format(buf, chromaStyle, iterator)
			if err != nil {
				h.out.WriteString("Error formatting code: " + err.Error())
				continue
			}

			// Write buffer contents to output
			buf.WriteTo(h.out)
		} else if entry.Break != nil {
			// Write break tag to output
			h.out.WriteString("<br>")
		} else if entry.Hline != nil {
			// Write horizonhal line tag to output
			h.out.WriteString("<hr>")
		}
	}

	// Return contents of output buffer
	return h.out.String()
}