package dashdiffs

import (
	"bytes"
	"html/template"

	diff "github.com/yudai/gojsondiff"
)

// A BasicDiff holds the stateful values that are used when generating a basic
// diff from JSON tokens.
type BasicDiff struct {
	narrow     string
	keysIdent  int
	writing    bool
	LastIndent int
	Block      *BasicBlock
	Change     *BasicChange
	Summary    *BasicSummary
}

// A BasicBlock represents a top-level element in a basic diff.
type BasicBlock struct {
	Title     string
	Old       interface{}
	New       interface{}
	Change    ChangeType
	Changes   []*BasicChange
	Summaries []*BasicSummary
	LineStart int
	LineEnd   int
}

// A BasicChange represents the change from an old to new value. There are many
// BasicChanges in a BasicBlock.
type BasicChange struct {
	Key       string
	Old       interface{}
	New       interface{}
	Change    ChangeType
	LineStart int
	LineEnd   int
}

// A BasicSummary represents the changes within a basic block that're too deep
// or verbose to be represented in the top-level BasicBlock element, or in the
// BasicChange. Instead of showing the values in this case, we simply print
// the key and count how many times the given change was applied to that
// element.
type BasicSummary struct {
	Key       string
	Change    ChangeType
	Count     int
	LineStart int
	LineEnd   int
}

type BasicFormatter struct {
	jsonDiff *JSONFormatter
	tpl      *template.Template
}

func NewBasicFormatter(left interface{}) *BasicFormatter {
	tpl := template.Must(template.New("block").Funcs(tplFuncMap).Parse(tplBlock))
	tpl = template.Must(tpl.New("change").Funcs(tplFuncMap).Parse(tplChange))
	tpl = template.Must(tpl.New("summary").Funcs(tplFuncMap).Parse(tplSummary))

	return &BasicFormatter{
		jsonDiff: NewJSONFormatter(left),
		tpl:      tpl,
	}
}

// Format takes the diff of two JSON documents, and returns the difference
// between them summarized in an HTML document.
func (b *BasicFormatter) Format(d diff.Diff) ([]byte, error) {
	// calling jsonDiff.Format(d) populates the JSON diff's "Lines" value,
	// which we use to compute the basic dif
	_, err := b.jsonDiff.Format(d)
	if err != nil {
		return nil, err
	}

	bd := &BasicDiff{}
	blocks := bd.Basic(b.jsonDiff.Lines)
	buf := &bytes.Buffer{}

	err = b.tpl.ExecuteTemplate(buf, "block", blocks)
	if err != nil {
		return nil, err
	}
	return buf.Bytes(), nil
}

// Basic transforms a slice of JSONLines into a slice of BasicBlocks.
func (b *BasicDiff) Basic(lines []*JSONLine) []*BasicBlock {
	// init an array you can append to for the basic "blocks"
	blocks := make([]*BasicBlock, 0)

	for _, line := range lines {
		// In order to produce distinct "blocks" when rendering the basic diff,
		// we need a way to distinguish between differnt sections of data.
		// To do this, we consider the value(s) of each top-level JSON key to
		// represent a distinct block for Grafana's JSON data structure, so
		// we perform this check to see if we've entered a new "block". If we
		// have, we simply append the existing block to the array of blocks.
		if b.LastIndent == 2 && line.Indent == 1 && line.Change == ChangeNil {
			if b.Block != nil {
				blocks = append(blocks, b.Block)
			}
		}

		// Record the last indent level at each pass in case we need to
		// check for a change in depth inside the JSON data structures.
		b.LastIndent = line.Indent

		// TODO: why special handling for indent 2?
		// Here we
		// If the line's indentation is at level 1, then we know it's a top
		// level key in the JSON document. As mentioned earlier, we treat these
		// specially as they indicate their values belong to distinct blocks.
		//
		// At level 1, we only record single-line changes, ie, the "added",
		// "deleted", "old" or "new" cases, since we know those values aren't
		// arrays or maps. We only handle these cases at level 2 or deeper,
		// since for those we either output a "change" or "summary". This is
		// done for formatting reasons only, so we have logical "blocks" to
		// display.
		if line.Indent == 1 {
			switch line.Change {
			case ChangeNil:
				if line.Change == ChangeNil {
					if line.Key != "" {
						b.Block = &BasicBlock{
							Title:  line.Key,
							Change: line.Change,
						}
					}
				}

			case ChangeAdded, ChangeDeleted:
				blocks = append(blocks, &BasicBlock{
					Title:     line.Key,
					Change:    line.Change,
					New:       line.Val,
					LineStart: line.LineNum,
				})

			case ChangeOld:
				b.Block = &BasicBlock{
					Title:     line.Key,
					Old:       line.Val,
					Change:    line.Change,
					LineStart: line.LineNum,
				}

			case ChangeNew:
				b.Block.New = line.Val
				b.Block.LineEnd = line.LineNum

				// For every "old" change there is a corresponding "new", which
				// is why we wait until we detect the "new" change before
				// appending the change.
				blocks = append(blocks, b.Block)
			default:
				// ok
			}
		}

		// Here is where we handle changes for all types, appending each change
		// to the current block based on the value.
		//
		// Values which only occupy a single line in JSON (like a string or
		// int, for example) are treated as "Basic Changes" that we append to
		// the current block as soon as they're detected.
		//
		// Values which occupy multiple lines (either slices or maps) are
		// treated as "Basic Summaries". When we detect the "ChangeNil" type,
		// we know we've encountered one of these types, so we record the
		// starting position as well the type of the change, and stop
		// performing comparisons until we find the end of that change. Upon
		// finding the change, we append it to the current block, and begin
		// performing comparisons again.
		if line.Indent > 1 {
			// Ensure a single line change
			if line.Key != "" && line.Val != nil && !b.writing {
				switch line.Change {
				case ChangeAdded, ChangeDeleted:

					b.Block.Changes = append(b.Block.Changes, &BasicChange{
						Key:       line.Key,
						Change:    line.Change,
						New:       line.Val,
						LineStart: line.LineNum,
					})

				case ChangeOld:
					b.Change = &BasicChange{
						Key:       line.Key,
						Change:    line.Change,
						Old:       line.Val,
						LineStart: line.LineNum,
					}

				case ChangeNew:
					b.Change.New = line.Val
					b.Change.LineEnd = line.LineNum
					b.Block.Changes = append(b.Block.Changes, b.Change)

				default:
					//ok
				}

			} else {
				if line.Change != ChangeUnchanged {
					if line.Key != "" {
						b.narrow = line.Key
						b.keysIdent = line.Indent
					}

					if line.Change != ChangeNil {
						if !b.writing {
							b.writing = true
							key := b.Block.Title

							if b.narrow != "" {
								key = b.narrow
								if b.keysIdent > line.Indent {
									key = b.Block.Title
								}
							}

							b.Summary = &BasicSummary{
								Key:       key,
								Change:    line.Change,
								LineStart: line.LineNum,
							}
						}
					}
				} else {
					if b.writing {
						b.writing = false
						b.Summary.LineEnd = line.LineNum
						b.Block.Summaries = append(b.Block.Summaries, b.Summary)
					}
				}
			}
		}
	}

	return blocks
}

// encStateMap is used in the template helper
var (
	encStateMap = map[ChangeType]string{
		ChangeAdded:   "added",
		ChangeDeleted: "deleted",
		ChangeOld:     "changed",
		ChangeNew:     "changed",
	}

	// tplFuncMap is the function map for each template
	tplFuncMap = template.FuncMap{
		"getChange": func(c ChangeType) string {
			state, ok := encStateMap[c]
			if !ok {
				return "changed"
			}
			return state
		},
	}
)

var (
	// tplBlock is the whole thing
	tplBlock = `{{ define "block" -}}
{{ range . }}
<div class="diff-group">
	<div class="diff-block">
		<h2 class="diff-block-title">
			<i class="diff-circle diff-circle-{{ getChange .Change }} fa fa-circle"></i>
			<strong class="diff-title">{{ .Title }}</strong> {{ getChange .Change }}
		</h2>


		<!-- Overview -->
		{{ if .Old }}
			<div class="diff-label">{{ .Old }}</div>
			<i class="diff-arrow fa fa-long-arrow-right"></i>
		{{ end }}
		{{ if .New }}
				<div class="diff-label">{{ .New }}</div>
		{{ end }}

		{{ if .LineStart }}
			<diff-link-json
				line-link="{{ .LineStart }}"
				line-display="{{ .LineStart }}{{ if .LineEnd }} - {{ .LineEnd }}{{ end }}"
				switch-view="ctrl.getDiff('html')"
			/>
		{{ end }}

	</div>

	<!-- Basic Changes -->
	{{ range .Changes }}
		<ul class="diff-change-container">
		{{ template "change" . }}
		</ul>
	{{ end }}

	<!-- Basic Summary -->
	{{ range .Summaries }}
		{{ template "summary" . }}
	{{ end }}

</div>
{{ end }}
{{ end }}`

	// tplChange is the template for changes
	tplChange = `{{ define "change" -}}
<li class="diff-change-group">
	<span class="bullet-position-container">
		<div class="diff-change-item diff-change-title">{{ getChange .Change }} {{ .Key }}</div>

		<div class="diff-change-item">
			{{ if .Old }}
				<div class="diff-label">{{ .Old }}</div>
				<i class="diff-arrow fa fa-long-arrow-right"></i>
			{{ end }}
			{{ if .New }}
					<div class="diff-label">{{ .New }}</div>
			{{ end }}
		</div>

		{{ if .LineStart }}
			<diff-link-json
				line-link="{{ .LineStart }}"
				line-display="{{ .LineStart }}{{ if .LineEnd }} - {{ .LineEnd }}{{ end }}"
				switch-view="ctrl.getDiff('json')"
			/>
		{{ end }}
	</span>
</li>
{{ end }}`

	// tplSummary is for basis summaries
	tplSummary = `{{ define "summary" -}}
<div class="diff-group-name">
	<i class="diff-circle diff-circle-{{ getChange .Change }} fa fa-circle-o diff-list-circle"></i>

	{{ if .Count }}
		<strong>{{ .Count }}</strong>
	{{ end }}

	{{ if .Key }}
		<strong class="diff-summary-key">{{ .Key }}</strong>
		{{ getChange .Change }}
	{{ end }}

	{{ if .LineStart }}
		<diff-link-json
			line-link="{{ .LineStart }}"
			line-display="{{ .LineStart }}{{ if .LineEnd }} - {{ .LineEnd }}{{ end }}"
			switch-view="ctrl.getDiff('json')"
		/>
	{{ end }}
</div>
{{ end }}`
)