// Copyright 2022 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

package templates

import (
	"bufio"
	"bytes"
	"errors"
	"fmt"
	"io"
	"net/http"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"
	texttemplate "text/template"

	"code.gitea.io/gitea/modules/assetfs"
	"code.gitea.io/gitea/modules/graceful"
	"code.gitea.io/gitea/modules/log"
	"code.gitea.io/gitea/modules/setting"
	"code.gitea.io/gitea/modules/templates/scopedtmpl"
	"code.gitea.io/gitea/modules/util"
)

type TemplateExecutor scopedtmpl.TemplateExecutor

type HTMLRender struct {
	templates atomic.Pointer[scopedtmpl.ScopedTemplate]
}

var (
	htmlRender     *HTMLRender
	htmlRenderOnce sync.Once
)

var ErrTemplateNotInitialized = errors.New("template system is not initialized, check your log for errors")

func (h *HTMLRender) HTML(w io.Writer, status int, name string, data interface{}) error {
	if respWriter, ok := w.(http.ResponseWriter); ok {
		if respWriter.Header().Get("Content-Type") == "" {
			respWriter.Header().Set("Content-Type", "text/html; charset=utf-8")
		}
		respWriter.WriteHeader(status)
	}
	t, err := h.TemplateLookup(name)
	if err != nil {
		return texttemplate.ExecError{Name: name, Err: err}
	}
	return t.Execute(w, data)
}

func (h *HTMLRender) TemplateLookup(name string) (TemplateExecutor, error) {
	tmpls := h.templates.Load()
	if tmpls == nil {
		return nil, ErrTemplateNotInitialized
	}

	return tmpls.Executor(name, NewFuncMap())
}

func (h *HTMLRender) CompileTemplates() error {
	assets := AssetFS()
	extSuffix := ".tmpl"
	tmpls := scopedtmpl.NewScopedTemplate()
	tmpls.Funcs(NewFuncMap())
	files, err := ListWebTemplateAssetNames(assets)
	if err != nil {
		return nil
	}
	for _, file := range files {
		if !strings.HasSuffix(file, extSuffix) {
			continue
		}
		name := strings.TrimSuffix(file, extSuffix)
		tmpl := tmpls.New(filepath.ToSlash(name))
		buf, err := assets.ReadFile(file)
		if err != nil {
			return err
		}
		if _, err = tmpl.Parse(string(buf)); err != nil {
			return err
		}
	}
	tmpls.Freeze()
	h.templates.Store(tmpls)
	return nil
}

// HTMLRenderer init once and returns the globally shared html renderer
func HTMLRenderer() *HTMLRender {
	htmlRenderOnce.Do(initHTMLRenderer)
	return htmlRender
}

func initHTMLRenderer() {
	rendererType := "static"
	if !setting.IsProd {
		rendererType = "auto-reloading"
	}
	log.Debug("Creating %s HTML Renderer", rendererType)

	htmlRender = &HTMLRender{}
	if err := htmlRender.CompileTemplates(); err != nil {
		p := &templateErrorPrettier{assets: AssetFS()}
		wrapFatal(p.handleFuncNotDefinedError(err))
		wrapFatal(p.handleUnexpectedOperandError(err))
		wrapFatal(p.handleExpectedEndError(err))
		wrapFatal(p.handleGenericTemplateError(err))
		log.Fatal("HTMLRenderer CompileTemplates error: %v", err)
	}

	if !setting.IsProd {
		go AssetFS().WatchLocalChanges(graceful.GetManager().ShutdownContext(), func() {
			if err := htmlRender.CompileTemplates(); err != nil {
				log.Error("Template error: %v\n%s", err, log.Stack(2))
			}
		})
	}
}

func wrapFatal(msg string) {
	if msg == "" {
		return
	}
	log.Fatal("Unable to compile templates, %s", msg)
}

type templateErrorPrettier struct {
	assets *assetfs.LayeredFS
}

var reGenericTemplateError = regexp.MustCompile(`^template: (.*):([0-9]+): (.*)`)

func (p *templateErrorPrettier) handleGenericTemplateError(err error) string {
	groups := reGenericTemplateError.FindStringSubmatch(err.Error())
	if len(groups) != 4 {
		return ""
	}
	tmplName, lineStr, message := groups[1], groups[2], groups[3]
	return p.makeDetailedError(message, tmplName, lineStr, -1, "")
}

var reFuncNotDefinedError = regexp.MustCompile(`^template: (.*):([0-9]+): (function "(.*)" not defined)`)

func (p *templateErrorPrettier) handleFuncNotDefinedError(err error) string {
	groups := reFuncNotDefinedError.FindStringSubmatch(err.Error())
	if len(groups) != 5 {
		return ""
	}
	tmplName, lineStr, message, funcName := groups[1], groups[2], groups[3], groups[4]
	funcName, _ = strconv.Unquote(`"` + funcName + `"`)
	return p.makeDetailedError(message, tmplName, lineStr, -1, funcName)
}

var reUnexpectedOperandError = regexp.MustCompile(`^template: (.*):([0-9]+): (unexpected "(.*)" in operand)`)

func (p *templateErrorPrettier) handleUnexpectedOperandError(err error) string {
	groups := reUnexpectedOperandError.FindStringSubmatch(err.Error())
	if len(groups) != 5 {
		return ""
	}
	tmplName, lineStr, message, unexpected := groups[1], groups[2], groups[3], groups[4]
	unexpected, _ = strconv.Unquote(`"` + unexpected + `"`)
	return p.makeDetailedError(message, tmplName, lineStr, -1, unexpected)
}

var reExpectedEndError = regexp.MustCompile(`^template: (.*):([0-9]+): (expected end; found (.*))`)

func (p *templateErrorPrettier) handleExpectedEndError(err error) string {
	groups := reExpectedEndError.FindStringSubmatch(err.Error())
	if len(groups) != 5 {
		return ""
	}
	tmplName, lineStr, message, unexpected := groups[1], groups[2], groups[3], groups[4]
	return p.makeDetailedError(message, tmplName, lineStr, -1, unexpected)
}

var (
	reTemplateExecutingError    = regexp.MustCompile(`^template: (.*):([1-9][0-9]*):([1-9][0-9]*): (executing .*)`)
	reTemplateExecutingErrorMsg = regexp.MustCompile(`^executing "(.*)" at <(.*)>: `)
)

func (p *templateErrorPrettier) handleTemplateRenderingError(err error) string {
	if groups := reTemplateExecutingError.FindStringSubmatch(err.Error()); len(groups) > 0 {
		tmplName, lineStr, posStr, msgPart := groups[1], groups[2], groups[3], groups[4]
		target := ""
		if groups = reTemplateExecutingErrorMsg.FindStringSubmatch(msgPart); len(groups) > 0 {
			target = groups[2]
		}
		return p.makeDetailedError(msgPart, tmplName, lineStr, posStr, target)
	} else if execErr, ok := err.(texttemplate.ExecError); ok {
		layerName := p.assets.GetFileLayerName(execErr.Name + ".tmpl")
		return fmt.Sprintf("asset from: %s, %s", layerName, err.Error())
	} else {
		return err.Error()
	}
}

func HandleTemplateRenderingError(err error) string {
	p := &templateErrorPrettier{assets: AssetFS()}
	return p.handleTemplateRenderingError(err)
}

const dashSeparator = "----------------------------------------------------------------------"

func (p *templateErrorPrettier) makeDetailedError(errMsg, tmplName string, lineNum, posNum any, target string) string {
	code, layer, err := p.assets.ReadLayeredFile(tmplName + ".tmpl")
	if err != nil {
		return fmt.Sprintf("template error: %s, and unable to find template file %q", errMsg, tmplName)
	}
	line, err := util.ToInt64(lineNum)
	if err != nil {
		return fmt.Sprintf("template error: %s, unable to parse template %q line number %q", errMsg, tmplName, lineNum)
	}
	pos, err := util.ToInt64(posNum)
	if err != nil {
		return fmt.Sprintf("template error: %s, unable to parse template %q pos number %q", errMsg, tmplName, posNum)
	}
	detail := extractErrorLine(code, int(line), int(pos), target)

	var msg string
	if pos >= 0 {
		msg = fmt.Sprintf("template error: %s:%s:%d:%d : %s", layer, tmplName, line, pos, errMsg)
	} else {
		msg = fmt.Sprintf("template error: %s:%s:%d : %s", layer, tmplName, line, errMsg)
	}
	return msg + "\n" + dashSeparator + "\n" + detail + "\n" + dashSeparator
}

func extractErrorLine(code []byte, lineNum, posNum int, target string) string {
	b := bufio.NewReader(bytes.NewReader(code))
	var line []byte
	var err error
	for i := 0; i < lineNum; i++ {
		if line, err = b.ReadBytes('\n'); err != nil {
			if i == lineNum-1 && errors.Is(err, io.EOF) {
				err = nil
			}
			break
		}
	}
	if err != nil {
		return fmt.Sprintf("unable to find target line %d", lineNum)
	}

	line = bytes.TrimRight(line, "\r\n")
	var indicatorLine []byte
	targetBytes := []byte(target)
	targetLen := len(targetBytes)
	for i := 0; i < len(line); {
		if posNum == -1 && target != "" && bytes.HasPrefix(line[i:], targetBytes) {
			for j := 0; j < targetLen && i < len(line); j++ {
				indicatorLine = append(indicatorLine, '^')
				i++
			}
		} else if i == posNum {
			indicatorLine = append(indicatorLine, '^')
			i++
		} else {
			if line[i] == '\t' {
				indicatorLine = append(indicatorLine, '\t')
			} else {
				indicatorLine = append(indicatorLine, ' ')
			}
			i++
		}
	}
	// if the indicatorLine only contains spaces, trim it together
	return strings.TrimRight(string(line)+"\n"+string(indicatorLine), " \t\r\n")
}