// Copyright 2017 The Hugo Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Package transform provides template functions for transforming content.
package transform

import (
	"bytes"
	"context"
	"encoding/json"
	"encoding/xml"
	"errors"
	"fmt"
	"html"
	"html/template"
	"io"
	"strings"
	"sync/atomic"

	htmltomarkdown "github.com/JohannesKaufmann/html-to-markdown/v2/converter"
	"github.com/JohannesKaufmann/html-to-markdown/v2/plugin/base"
	"github.com/JohannesKaufmann/html-to-markdown/v2/plugin/commonmark"
	"github.com/JohannesKaufmann/html-to-markdown/v2/plugin/table"

	bp "github.com/gohugoio/hugo/bufferpool"

	"github.com/bep/goportabletext"

	"github.com/gohugoio/hugo/cache/dynacache"
	"github.com/gohugoio/hugo/common/hashing"
	"github.com/gohugoio/hugo/common/hugio"
	"github.com/gohugoio/hugo/internal/warpc"
	"github.com/gohugoio/hugo/markup/converter/hooks"
	"github.com/gohugoio/hugo/markup/highlight"
	"github.com/gohugoio/hugo/markup/highlight/chromalexers"
	"github.com/gohugoio/hugo/resources"
	"github.com/gohugoio/hugo/tpl"
	"github.com/mitchellh/mapstructure"

	"github.com/gohugoio/hugo/deps"
	"github.com/gohugoio/hugo/helpers"
	"github.com/spf13/cast"
)

// New returns a new instance of the transform-namespaced template functions.
func New(deps *deps.Deps) *Namespace {
	if deps.MemCache == nil {
		panic("must provide MemCache")
	}

	return &Namespace{
		deps: deps,
		cacheUnmarshal: dynacache.GetOrCreatePartition[string, *resources.StaleValue[any]](
			deps.MemCache,
			"/tmpl/transform/unmarshal",
			dynacache.OptionsPartition{Weight: 30, ClearWhen: dynacache.ClearOnChange},
		),
		cacheMath: dynacache.GetOrCreatePartition[string, template.HTML](
			deps.MemCache,
			"/tmpl/transform/math",
			dynacache.OptionsPartition{Weight: 30, ClearWhen: dynacache.ClearNever},
		),
	}
}

// Namespace provides template functions for the "transform" namespace.
type Namespace struct {
	cacheUnmarshal *dynacache.Partition[string, *resources.StaleValue[any]]
	cacheMath      *dynacache.Partition[string, template.HTML]

	id   atomic.Uint32
	deps *deps.Deps
}

// Emojify returns a copy of s with all emoji codes replaced with actual emojis.
//
// See http://www.emoji-cheat-sheet.com/
func (ns *Namespace) Emojify(s any) (template.HTML, error) {
	ss, err := cast.ToStringE(s)
	if err != nil {
		return "", err
	}

	return template.HTML(helpers.Emojify([]byte(ss))), nil
}

// Highlight returns a copy of CODE as an HTML string with syntax
// highlighting applied.
//
//	transform.Highlight CODE [LANG] [OPTIONS]
//
// LANG is optional; it can also be set via the type option in OPTIONS, which
// makes this work the same way as HighlightCodeBlock.
func (ns *Namespace) Highlight(s any, args ...any) (template.HTML, error) {
	code, err := cast.ToStringE(s)
	if err != nil {
		return "", err
	}

	var lang string
	var opts any

	switch len(args) {
	case 0:
	case 1:
		// A single argument is either OPTIONS (a map or option string) or LANG.
		if _, ok := args[0].(map[string]any); ok {
			opts = args[0]
		} else {
			var arg string
			if arg, err = cast.ToStringE(args[0]); err != nil {
				return "", err
			}
			if strings.Contains(arg, "=") || strings.Contains(arg, ",") {
				opts = arg
			} else {
				lang = arg
			}
		}
	case 2:
		if lang, err = cast.ToStringE(args[0]); err != nil {
			return "", err
		}
		opts = args[1]
	default:
		return "", errors.New("transform.Highlight: expects at most 3 arguments")
	}

	hl := ns.deps.ContentSpec.Converters.GetHighlighter()
	highlighted, err := hl.Highlight(code, lang, opts)
	if err != nil {
		return "", err
	}
	return template.HTML(highlighted), nil
}

// HighlightCodeBlock highlights a code block on the form received in the codeblock render hooks.
func (ns *Namespace) HighlightCodeBlock(ctx hooks.CodeblockContext, opts ...any) (highlight.HighlightResult, error) {
	var optsv any
	if len(opts) > 0 {
		optsv = opts[0]
	}

	hl := ns.deps.ContentSpec.Converters.GetHighlighter()

	return hl.HighlightCodeBlock(ctx, optsv)
}

// CanHighlight returns whether the given code language is supported by the Chroma highlighter.
func (ns *Namespace) CanHighlight(language string) bool {
	return chromalexers.Get(language) != nil
}

// HTMLEscape returns a copy of s with reserved HTML characters escaped.
func (ns *Namespace) HTMLEscape(s any) (string, error) {
	ss, err := cast.ToStringE(s)
	if err != nil {
		return "", err
	}

	return html.EscapeString(ss), nil
}

// HTMLUnescape returns a copy of s with HTML escape requences converted to plain
// text.
func (ns *Namespace) HTMLUnescape(s any) (string, error) {
	ss, err := cast.ToStringE(s)
	if err != nil {
		return "", err
	}

	return html.UnescapeString(ss), nil
}

// XMLEscape returns the given string, removing disallowed characters then
// escaping the result to its XML equivalent.
func (ns *Namespace) XMLEscape(s any) (string, error) {
	ss, err := cast.ToStringE(s)
	if err != nil {
		return "", err
	}

	// https://www.w3.org/TR/xml/#NT-Char
	cleaned := strings.Map(func(r rune) rune {
		if r == 0x9 || r == 0xA || r == 0xD ||
			(r >= 0x20 && r <= 0xD7FF) ||
			(r >= 0xE000 && r <= 0xFFFD) ||
			(r >= 0x10000 && r <= 0x10FFFF) {
			return r
		}
		return -1
	}, ss)

	var buf bytes.Buffer
	err = xml.EscapeText(&buf, []byte(cleaned))
	if err != nil {
		return "", err
	}

	return buf.String(), nil
}

// Markdownify renders s from Markdown to HTML.
func (ns *Namespace) Markdownify(ctx context.Context, s any) (template.HTML, error) {
	home := ns.deps.Site.Home()
	if home == nil {
		panic("home must not be nil")
	}
	ss, err := home.RenderString(ctx, s)
	if err != nil {
		return "", err
	}

	// Strip if this is a short inline type of text.
	bb := ns.deps.ContentSpec.TrimShortHTML([]byte(ss), "markdown")

	return helpers.BytesToHTML(bb), nil
}

// Plainify returns a copy of s with all HTML tags removed.
func (ns *Namespace) Plainify(s any) (template.HTML, error) {
	ss, err := cast.ToStringE(s)
	if err != nil {
		return "", err
	}

	return template.HTML(tpl.StripHTML(ss)), nil
}

// PortableText converts the portable text in v to Markdown.
// We may add more options in the future.
func (ns *Namespace) PortableText(v any) (string, error) {
	buf := bp.GetBuffer()
	defer bp.PutBuffer(buf)
	opts := goportabletext.ToMarkdownOptions{
		Dst: buf,
		Src: v,
	}
	if err := goportabletext.ToMarkdown(opts); err != nil {
		return "", err
	}
	return buf.String(), nil
}

// ToMath converts a LaTeX string to math in the given format, default MathML.
// This uses KaTeX to render the math, see https://katex.org/.
func (ns *Namespace) ToMath(ctx context.Context, args ...any) (template.HTML, error) {
	if len(args) < 1 {
		return "", errors.New("must provide at least one argument")
	}
	expression, err := cast.ToStringE(args[0])
	if err != nil {
		return "", err
	}

	katexInput := warpc.KatexInput{
		Expression: expression,
		Options: warpc.KatexOptions{
			Output:           "mathml",
			MinRuleThickness: 0.04,
			ErrorColor:       "#cc0000",
			ThrowOnError:     true,
			Strict:           "error",
		},
	}

	if len(args) > 1 {
		if err := mapstructure.WeakDecode(args[1], &katexInput.Options); err != nil {
			return "", err
		}
	}

	switch katexInput.Options.Strict {
	case "error", "ignore", "warn":
		// Valid strict mode, continue
	default:
		return "", fmt.Errorf("invalid strict mode; expected one of error, ignore, or warn; received %s", katexInput.Options.Strict)
	}

	type fileCacheEntry struct {
		Version  string   `json:"version"`
		Output   string   `json:"output"`
		Warnings []string `json:"warnings,omitempty"`
	}

	const fileCacheEntryVersion = "v1" // Increment on incompatible changes.

	s := hashing.HashString(args...)
	key := "tomath/" + fileCacheEntryVersion + "/" + s[:2] + "/" + s[2:]
	fileCache := ns.deps.ResourceSpec.FileCaches.MiscCache()

	v, err := ns.cacheMath.GetOrCreate(key, func(string) (template.HTML, error) {
		_, r, err := fileCache.GetOrCreate(key, func() (io.ReadCloser, error) {
			message := warpc.Message[warpc.KatexInput]{
				Header: warpc.Header{
					Version: 1,
					ID:      ns.id.Add(1),
				},
				Data: katexInput,
			}

			k, err := ns.deps.WasmDispatchers.Katex()
			if err != nil {
				return nil, err
			}
			result, err := k.Execute(ctx, message)
			if err != nil {
				return nil, err
			}

			e := fileCacheEntry{
				Version:  fileCacheEntryVersion,
				Output:   result.Data.Output,
				Warnings: result.Header.Warnings,
			}

			buf := &bytes.Buffer{}
			enc := json.NewEncoder(buf)
			enc.SetEscapeHTML(false)
			if err := enc.Encode(e); err != nil {
				return nil, fmt.Errorf("failed to encode file cache entry: %w", err)
			}
			return hugio.NewReadSeekerNoOpCloserFromBytes(buf.Bytes()), nil
		})
		if err != nil {
			return "", err
		}

		var e fileCacheEntry
		if err := json.NewDecoder(r).Decode(&e); err != nil {
			return "", fmt.Errorf("failed to decode file cache entry: %w", err)
		}

		for _, warning := range e.Warnings {
			ns.deps.Log.Warnf("transform.ToMath: %s", warning)
		}

		return template.HTML(e.Output), err
	})
	if err != nil {
		return "", err
	}

	return v, nil
}

// For internal use.
func (ns *Namespace) Reset() {
	ns.cacheUnmarshal.Clear()
}

// This was added in Hugo v0.151.0 and should be considered experimental for now.
// We need to test this out in the wild for a while before committing to this API,
// and there will eventually be more options here.
func (ns *Namespace) HTMLToMarkdown(ctx context.Context, args ...any) (string, error) {
	if len(args) < 1 {
		return "", errors.New("must provide at least one argument")
	}
	input, err := cast.ToStringE(args[0])
	if err != nil {
		return "", err
	}

	plugins := []htmltomarkdown.Plugin{
		base.NewBasePlugin(),
		commonmark.NewCommonmarkPlugin(),
		table.NewTablePlugin(),
	}

	conv := htmltomarkdown.NewConverter(
		htmltomarkdown.WithPlugins(plugins...),
	)

	markdown, err := conv.ConvertString(input)
	if err != nil {
		return "", err
	}
	return markdown, nil
}
