package tui

import (
	"strings"
	"unicode"
	"unicode/utf8"

	"github.com/charmbracelet/glamour"
	"github.com/charmbracelet/glamour/ansi"
	glamstyles "github.com/charmbracelet/glamour/styles"
)

const minMarkdownWidth = 20

func renderMarkdown(content string, width int, th theme) string {
	width = max(minMarkdownWidth, width)
	renderer, err := glamour.NewTermRenderer(
		glamour.WithStyles(markdownStyle(th)),
		glamour.WithWordWrap(width),
	)
	if err != nil {
		return content
	}

	rendered, err := renderer.Render(content)
	if err != nil {
		return content
	}
	return trimRenderedMarkdown(rendered)
}

func markdownStyle(th theme) ansi.StyleConfig {
	cfg := glamstyles.LightStyleConfig
	if th.Mode == ThemeDark {
		cfg = glamstyles.DarkStyleConfig
	}
	clearMarkdownBackgrounds(&cfg)

	zero := uint(0)
	cfg.Document.Margin = &zero
	cfg.Document.BlockPrefix = ""
	cfg.Document.BlockSuffix = ""
	cfg.Document.Color = stringPtr(th.Text)

	cfg.Heading.Color = stringPtr(th.Assistant)
	cfg.H1.Prefix = ""
	cfg.H1.Suffix = ""
	cfg.H1.Color = stringPtr(th.Assistant)
	cfg.H1.BackgroundColor = nil
	cfg.H1.Bold = boolPtr(true)

	cfg.BlockQuote.Color = stringPtr(th.Muted)
	cfg.Link.Color = stringPtr(th.User)
	cfg.LinkText.Color = stringPtr(th.User)

	cfg.Code.Color = stringPtr(th.Tool)
	cfg.Code.BackgroundColor = nil
	cfg.CodeBlock.Color = stringPtr(th.Text)
	cfg.CodeBlock.BackgroundColor = nil
	cfg.CodeBlock.Margin = &zero

	return cfg
}

func clearMarkdownBackgrounds(cfg *ansi.StyleConfig) {
	cfg.Document.BackgroundColor = nil
	cfg.BlockQuote.BackgroundColor = nil
	cfg.Paragraph.BackgroundColor = nil
	cfg.Heading.BackgroundColor = nil
	cfg.H1.BackgroundColor = nil
	cfg.H2.BackgroundColor = nil
	cfg.H3.BackgroundColor = nil
	cfg.H4.BackgroundColor = nil
	cfg.H5.BackgroundColor = nil
	cfg.H6.BackgroundColor = nil
	cfg.Text.BackgroundColor = nil
	cfg.Strikethrough.BackgroundColor = nil
	cfg.Emph.BackgroundColor = nil
	cfg.Strong.BackgroundColor = nil
	cfg.HorizontalRule.BackgroundColor = nil
	cfg.Item.BackgroundColor = nil
	cfg.Enumeration.BackgroundColor = nil
	cfg.Task.BackgroundColor = nil
	cfg.Link.BackgroundColor = nil
	cfg.LinkText.BackgroundColor = nil
	cfg.Image.BackgroundColor = nil
	cfg.ImageText.BackgroundColor = nil
	cfg.Code.BackgroundColor = nil
	cfg.CodeBlock.BackgroundColor = nil
	cfg.Table.BackgroundColor = nil
	cfg.DefinitionList.BackgroundColor = nil
	cfg.DefinitionTerm.BackgroundColor = nil
	cfg.DefinitionDescription.BackgroundColor = nil
	cfg.HTMLBlock.BackgroundColor = nil
	cfg.HTMLSpan.BackgroundColor = nil
}

func trimRenderedMarkdown(value string) string {
	lines := strings.Split(strings.TrimRight(value, "\n"), "\n")
	for i, line := range lines {
		lines[i] = trimStyledTrailingSpaces(line)
	}
	return strings.Join(lines, "\n")
}

func trimStyledTrailingSpaces(line string) string {
	cut := 0
	seenNonSpace := false
	seenWhitespaceAfterLastNonSpace := false
	for i := 0; i < len(line); {
		if end, ok := ansiSequenceEnd(line, i); ok {
			if seenNonSpace && !seenWhitespaceAfterLastNonSpace {
				cut = end
			}
			i = end
			continue
		}

		r, size := utf8.DecodeRuneInString(line[i:])
		if r == utf8.RuneError && size == 0 {
			break
		}
		end := i + size
		if unicode.IsSpace(r) {
			if seenNonSpace {
				seenWhitespaceAfterLastNonSpace = true
			}
		} else {
			seenNonSpace = true
			seenWhitespaceAfterLastNonSpace = false
			cut = end
		}
		i = end
	}
	if cut == 0 {
		return ""
	}
	return line[:cut]
}

func ansiSequenceEnd(value string, start int) (int, bool) {
	if start+2 >= len(value) || value[start] != '\x1b' || value[start+1] != '[' {
		return 0, false
	}
	for i := start + 2; i < len(value); i++ {
		if value[i] >= 0x40 && value[i] <= 0x7e {
			return i + 1, true
		}
	}
	return 0, false
}
func stringPtr(value string) *string {
	return &value
}

func boolPtr(value bool) *bool {
	return &value
}