From 406008135ffd60e00b6cf0f1a7f70ccae186d15e Mon Sep 17 00:00:00 2001
From: Andrew Ekstedt <andrew.ekstedt@gmail.com>
Date: Sat, 25 Sep 2021 20:12:26 +0000
Subject: [PATCH] basic merging of <head> <body> <header> <footer>

---
 go.mod                 |   6 +-
 go.sum                 |  23 +++++++
 internal/merge.go      | 142 +++++++++++++++++++++++++++++++++++++++--
 internal/merge_test.go |  41 ++++++++++++
 4 files changed, 207 insertions(+), 5 deletions(-)
 create mode 100644 internal/merge_test.go
diff --git a/go.mod b/go.mod
index 7d0845a..a041318 100644
--- a/go.mod
+++ b/go.mod
@@ -2,4 +2,8 @@ module git.tilde.town/magical/mergehtml
 
 go 1.14
 
-require golang.org/x/net v0.0.0-20200813134508-3edf25e44fcc // indirect
+require (
+	github.com/andreyvit/diff v0.0.0-20170406064948-c7f18ee00883
+	github.com/sergi/go-diff v1.1.0 // indirect
+	golang.org/x/net v0.0.0-20200813134508-3edf25e44fcc
+)
diff --git a/go.sum b/go.sum
index 445d19a..f64bbaf 100644
--- a/go.sum
+++ b/go.sum
@@ -1,3 +1,20 @@
+github.com/andreyvit/diff v0.0.0-20170406064948-c7f18ee00883 h1:bvNMNQO63//z+xNgfBlViaCIJKLlCJ6/fmUseuG0wVQ=
+github.com/andreyvit/diff v0.0.0-20170406064948-c7f18ee00883/go.mod h1:rCTlJbsFo29Kk6CurOXKm700vrz8f0KW0JNfpkRJY/8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/kr/pretty v0.1.0 h1:L/CwN0zerZDmRFUapSPitk6f+Q3+0za1rQkzVuMiMFI=
+github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
+github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
+github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
+github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/sergi/go-diff v1.1.0 h1:we8PVUC3FE2uYfodKH/nBHMSetSfHDR6scGdBi+erh0=
+github.com/sergi/go-diff v1.1.0/go.mod h1:STckp+ISIX8hZLjrqAeVduY0gWCT9IjLuqbuNXdaHfM=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
+github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
@@ -7,3 +24,9 @@ golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5h
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200323222414-85ca7c5b95cd/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 h1:YR8cESwS4TdDjEe65xsg0ogRM/Nc3DYOhEAlW+xobZo=
+gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/yaml.v2 v2.2.4 h1:/eiJrUcujPVeJ3xlSWaiNi3uSVmDGBK1pDHUHAnao1I=
+gopkg.in/yaml.v2 v2.2.4/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
diff --git a/internal/merge.go b/internal/merge.go
index 904a878..e4ae80b 100644
--- a/internal/merge.go
+++ b/internal/merge.go
@@ -1,9 +1,14 @@
 package internal
 
 import (
+	"bytes"
+	"fmt"
 	"io"
+	"log"
+	"strings"
 
 	"golang.org/x/net/html"
+	"golang.org/x/net/html/atom"
 )
 
 type Doc struct{}
@@ -14,6 +19,8 @@ type Assets struct {
 	Scripts []Asset
 }
 
+type Asset struct{}
+
 // Merges an HTML document over top of a base template.
 //
 // <head>
@@ -39,12 +46,139 @@ type Assets struct {
 //
 // all scripts and images will be collected and returned in the Assets object
 //
-func Merge(base, doc io.Reader) (merged string, assets *Assets, _ error)
-
-func merge(base, doc *html.Node) (out *html.Node, assets *Assets) {
+func Merge(base, doc io.Reader) (merged string, assets *Assets, _ error) {
+	baseParsed, err := html.Parse(base)
+	if err != nil {
+		return "", nil, fmt.Errorf("couldn't parse base html: %w", err)
+	}
+	docParsed, err := html.Parse(doc)
+	if err != nil {
+		return "", nil, fmt.Errorf("couldn't parse doc: %w", err)
+	}
+	out := merge(baseParsed, docParsed)
+	buf := new(bytes.Buffer)
+	err = html.Render(buf, out)
+	if err != nil {
+		panic(err)
+	}
 	assets = new(Assets)
-	out, err = html.Parse("<!doctype html><html><head></head><body></body></html>")
+	return buf.String(), assets, nil
+}
+
+// merges doc into base. doc and base are modified in the process.
+func merge(base, doc *html.Node) (out *html.Node) {
+	out, err := html.Parse(strings.NewReader("<!doctype html><html><head></head><body></body></html>"))
 	if err != nil {
 		panic("mergehtml: internal error: " + err.Error())
 	}
+
+	// TODO: title
+	html := find(out, atom.Html)
+	if html == nil {
+		log.Panicf("no <html> in %v", out)
+	}
+	head := find(html, atom.Head)
+	reparentChildren(head, find(find(base, atom.Html), atom.Head))
+	reparentChildren(head, find(find(doc, atom.Html), atom.Head))
+
+	body := find(html, atom.Body)
+	if body == nil {
+		log.Panicf("no <body> in %v", html)
+	}
+	baseBody := find(find(base, atom.Html), atom.Body)
+	newBody := find(find(doc, atom.Html), atom.Body)
+
+	reparentChildren(body, baseBody)
+	header := findRec(body, atom.Header)
+	footer := findRec(body, atom.Footer)
+	main := findRec(body, atom.Main)
+
+	if header == nil {
+		header = createElement(atom.Header)
+		body.InsertBefore(header, body.FirstChild)
+	}
+	for {
+		n := findRec(newBody, atom.Header)
+		if n == nil {
+			break
+		}
+		reparentChildren(header, n)
+		n.Parent.RemoveChild(n)
+	}
+
+	if footer == nil {
+		footer = createElement(atom.Header)
+		body.InsertBefore(footer, body.FirstChild)
+	}
+	for {
+		n := findRec(newBody, atom.Footer)
+		if n == nil {
+			break
+		}
+		reparentChildren(footer, n)
+		n.Parent.RemoveChild(n)
+	}
+
+	_ = main // TODO
+
+	return out
+}
+
+func createElement(a atom.Atom) *html.Node {
+	return &html.Node{DataAtom: a, Data: a.String(), Type: html.ElementNode}
+}
+
+// reparentChildren reparents all of src's child nodes to dst.
+func reparentChildren(dst, src *html.Node) {
+	if src == nil {
+		return
+	}
+	for {
+		child := src.FirstChild
+		if child == nil {
+			break
+		}
+		src.RemoveChild(child)
+		dst.AppendChild(child)
+	}
+}
+
+func find(elem *html.Node, tagName atom.Atom) *html.Node {
+	if elem != nil {
+		for n := elem.FirstChild; n != nil; n = n.NextSibling {
+			if n.DataAtom == tagName {
+				return n
+			}
+		}
+	}
+	return nil
+}
+
+// Find the first element named tagName that is a descendent of the given HTML node.
+// Returns nil if no element found.
+func findRec(elem *html.Node, tagName atom.Atom) *html.Node {
+	if elem != nil {
+		for c := elem.FirstChild; c != nil; c = c.NextSibling {
+			if c.Type == html.ElementNode && c.DataAtom == tagName {
+				return c
+			}
+			if d := findRec(c, tagName); d != nil {
+				return d
+			}
+		}
+	}
+	return nil
+}
+
+// clone returns a new node with the same type, data and attributes.
+// The clone has no parent, no siblings and no children.
+func clone(n *html.Node) *html.Node {
+	m := &html.Node{
+		Type:     n.Type,
+		DataAtom: n.DataAtom,
+		Data:     n.Data,
+		Attr:     make([]html.Attribute, len(n.Attr)),
+	}
+	copy(m.Attr, n.Attr)
+	return m
 }
diff --git a/internal/merge_test.go b/internal/merge_test.go
new file mode 100644
index 0000000..408bf6f
--- /dev/null
+++ b/internal/merge_test.go
@@ -0,0 +1,41 @@
+package internal
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/andreyvit/diff"
+)
+
+const baseText = `
+<style>body { background: #ccc; color: black; }</style>
+<header></header>
+<footer></footer>
+`
+
+const pageText = `
+<title>This is a title</title>
+<style>p { color: red; }</style>
+<header><h1>Title</h1></header>
+<p>Body text
+`
+
+const mergeText = `<!DOCTYPE html><html><head><style>body { background: #ccc; color: black; }</style>
+<title>This is a title</title>
+<style>p { color: red; }</style>
+</head><body><header><h1>Title</h1></header>
+<footer></footer>
+</body></html>`
+
+func TestMerge(t *testing.T) {
+	got, _, err := Merge(strings.NewReader(baseText), strings.NewReader(pageText))
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	if got != mergeText {
+		//fmt.Println(got)
+		//t.Errorf("merge mismatch (-want, +got):\n%s", cmp.Diff(mergeText, got))
+		t.Errorf("merge mismatch (-want, +got):\n%s", diff.LineDiff(mergeText, got))
+	}
+}
