package syntax

import (
	"bytes"
	"sort"
	"strings"

	"git.gophernest.net/azpect/TextEditor/internal/core"
	"git.gophernest.net/azpect/TextEditor/internal/style"
	"github.com/charmbracelet/lipgloss"
	sitter "github.com/tree-sitter/go-tree-sitter"
)

type TreeSitterEngine struct {
	styles   style.Styles
	registry *languageRegistry

	cache map[*core.Buffer]*bufferCache
}

type bufferCache struct {
	built bool
	lines map[int][]lipgloss.Style
	count int

	parser   *sitter.Parser
	tree     *sitter.Tree
	source   []byte
	dirtyAll bool
	dirty    []lineRange

	langID   string
	language *sitter.Language
	query    *sitter.Query
}

type lineRange struct {
	start int
	end   int
}

type captureRange struct {
	startRow uint
	startCol uint
	endRow   uint
	endCol   uint
	name     string
}

// NewTreeSitterEngine: Creates a new tree sitter engine with the styles
// provided attached.
//
// Currently, this engine only support GoLang. But more languages can be
// added with easy.
func NewTreeSitterEngine(styles style.Styles) *TreeSitterEngine {
	return &TreeSitterEngine{
		styles:   styles,
		registry: newLanguageRegistry(),
		cache:    map[*core.Buffer]*bufferCache{},
	}
}

func (e *TreeSitterEngine) PrepareBuffer(buf *core.Buffer) {
	// Cannot prepare a nil buffer
	if buf == nil {
		return
	}

	// Get the buffers cache and return if we are already "built" (ready to render).
	bc := e.getCache(buf)
	if bc.count != buf.LineCount() {
		bc.dirtyAll = true
	}
	if bc.dirtyAll {
		bc.built = false
	}
	if bc.built {
		return
	}

	// If we do no support the buffer, load empty styles into the cache
	lang, ok, err := e.resolveBufferLanguage(buf, bc)
	if err != nil || !ok {
		bc.lines = map[int][]lipgloss.Style{}
		bc.built = true
		return
	}
	_ = lang

	e.buildFullBuffer(buf, bc)
}

func (e *TreeSitterEngine) LineStyleMap(buf *core.Buffer, line int) []lipgloss.Style {
	if buf == nil {
		return nil
	}

	e.PrepareBuffer(buf)
	bc := e.getCache(buf)

	if s, ok := bc.lines[line]; ok {
		return s
	}

	runes := []rune(buf.Line(line))
	out := make([]lipgloss.Style, len(runes))
	for i := range out {
		out[i] = e.styles.LineStyle
	}
	bc.lines[line] = out
	return out
}

func (e *TreeSitterEngine) ApplyEdit(buf *core.Buffer, edit *core.BufferEdit) {
	if buf == nil || edit == nil {
		return
	}

	bc := e.getCache(buf)
	lang, ok, err := e.resolveBufferLanguage(buf, bc)
	if err != nil || !ok {
		bc.built = false
		bc.dirtyAll = true
		return
	}
	_ = lang

	if bc.parser == nil {
		bc.parser = sitter.NewParser()
		bc.parser.SetLanguage(bc.language)
	}

	if bc.tree == nil || len(bc.source) == 0 {
		bc.dirtyAll = true
		return
	}

	bc.tree.Edit(&sitter.InputEdit{
		StartByte:      edit.StartByte,
		OldEndByte:     edit.OldEndByte,
		NewEndByte:     edit.NewEndByte,
		StartPosition:  sitter.NewPoint(edit.StartPoint.Row, edit.StartPoint.Column),
		OldEndPosition: sitter.NewPoint(edit.OldEndPoint.Row, edit.OldEndPoint.Column),
		NewEndPosition: sitter.NewPoint(edit.NewEndPoint.Row, edit.NewEndPoint.Column),
	})

	newSource := buildBufferSource(buf)
	newTree := bc.parser.Parse(newSource, bc.tree)
	if newTree == nil {
		bc.dirtyAll = true
		return
	}

	changed := bc.tree.ChangedRanges(newTree)

	newLineCount := buf.LineCount()
	if newLineCount != bc.count {
		bc.dirtyAll = true
		bc.dirty = nil
	} else {
		startRow := int(edit.StartPoint.Row)
		endRow := int(max(edit.OldEndPoint.Row, edit.NewEndPoint.Row))
		addDirtyRange(bc, startRow, endRow)
		for _, r := range changed {
			addDirtyRange(bc, int(r.StartPoint.Row), int(r.EndPoint.Row))
		}
	}

	bc.source = newSource
	bc.tree.Close()
	bc.tree = newTree
	bc.built = false
}

// TreeSitterEngine.InvalidateBuffer: Deletes the entire buffers cache from the engine. If the
// buffer provided is nil, this function does nothing.
func (e *TreeSitterEngine) InvalidateBuffer(buf *core.Buffer) {
	if buf == nil {
		return
	}
	bc := e.getCache(buf)
	bc.built = false
	bc.dirtyAll = true
	bc.dirty = nil
}

// TreeSitterEngine.InvalidateLines: Deletes lines between start and end (inclusive) from the
// buffers cache. Then marks the cache as "unbuilt." If the buffer provided is nil, this function
// does nothing.
func (e *TreeSitterEngine) InvalidateLines(buf *core.Buffer, startLine, endLine int) {
	if buf == nil {
		return
	}
	bc := e.getCache(buf)
	addDirtyRange(bc, startLine, endLine)
	bc.built = false
}

// TreeSitterEngine.supportsBuffer: Returns whether the buffer can be parsed and highlighted
// by the engine. When false, there should be a fallback.
func (e *TreeSitterEngine) resolveBufferLanguage(buf *core.Buffer, bc *bufferCache) (*resolvedLanguage, bool, error) {
	if e.registry == nil {
		e.registry = newLanguageRegistry()
	}

	resolved, ok, err := e.registry.resolve(buf.Filetype, buf.Filename)
	if err != nil || !ok {
		return nil, ok, err
	}

	if bc.langID != resolved.id {
		bc.langID = resolved.id
		bc.language = resolved.language
		bc.query = resolved.query
		if bc.parser != nil {
			bc.parser.SetLanguage(bc.language)
		}
		bc.dirtyAll = true
		bc.built = false
	}

	return resolved, true, nil
}

// TreeSitterEngine.getCache: Returns the buffers cache. If the cache does not exist, a new one
// is created and applied to the engines cache map.
func (e *TreeSitterEngine) getCache(buf *core.Buffer) *bufferCache {
	if bc, ok := e.cache[buf]; ok {
		return bc
	}
	bc := &bufferCache{lines: map[int][]lipgloss.Style{}}
	e.cache[buf] = bc
	return bc
}

func (e *TreeSitterEngine) buildFullBuffer(buf *core.Buffer, bc *bufferCache) {
	lineCount := buf.LineCount()

	// Load the lines into memory. There is no method for this due to the buffers
	// internal implementation using a gap buffer. So the "Lines" property is of
	// type []*GapBuffer.
	lines := make([]string, lineCount)
	for i := range lineCount {
		lines[i] = buf.Line(i)
	}

	fullRebuild := bc.dirtyAll || len(bc.lines) == 0 || len(bc.dirty) == 0
	if fullRebuild {
		bc.lines = map[int][]lipgloss.Style{}
		for i := range lineCount {
			bc.lines[i] = defaultLineStyles(lines[i], e.styles.LineStyle)
		}
	} else {
		dirty := normalizedDirtyRanges(bc.dirty, lineCount)
		for _, r := range dirty {
			for i := r.start; i <= r.end; i++ {
				bc.lines[i] = defaultLineStyles(lines[i], e.styles.LineStyle)
			}
		}
	}

	source := buildBufferSource(buf)
	useCurrentTree := bc.tree != nil && bytes.Equal(bc.source, source)

	if bc.parser == nil {
		bc.parser = sitter.NewParser()
		bc.parser.SetLanguage(bc.language)
	}

	if !useCurrentTree {
		var baseTree *sitter.Tree
		if bc.tree != nil {
			baseTree = bc.tree
		}

		tree := bc.parser.Parse(source, baseTree)
		if tree == nil {
			bc.built = true
			return
		}

		if bc.tree != nil {
			bc.tree.Close()
		}
		bc.tree = tree
		bc.source = source
	}

	root := bc.tree.RootNode()
	cursor := sitter.NewQueryCursor()
	defer cursor.Close()

	var captures []captureRange

	if fullRebuild {
		iter := cursor.Captures(bc.query, root, source)
		captures = append(captures, collectCaptures(iter, bc.query)...)
	} else {
		dirty := normalizedDirtyRanges(bc.dirty, lineCount)
		for _, r := range dirty {
			queryStart := max(0, r.start-1)
			queryEnd := min(lineCount-1, r.end+1)

			rangeCursor := sitter.NewQueryCursor()
			rangeCursor.SetPointRange(
				sitter.NewPoint(uint(queryStart), 0),
				sitter.NewPoint(uint(queryEnd+1), 0),
			)
			iter := rangeCursor.Captures(bc.query, root, source)
			captures = append(captures, collectCaptures(iter, bc.query)...)
			rangeCursor.Close()
		}
	}

	// Sort the captures in order of their character occurrence in the file
	sort.Slice(captures, func(i, j int) bool {
		if captures[i].startRow == captures[j].startRow {
			if captures[i].startCol == captures[j].startCol {
				if captures[i].endRow == captures[j].endRow {
					return captures[i].endCol > captures[j].endCol
				}
				return captures[i].endRow > captures[j].endRow
			}
			return captures[i].startCol < captures[j].startCol
		}
		return captures[i].startRow < captures[j].startRow
	})

	// Basically, this code works by rewriting the same range and the last capture wins.
	// This is a great spot for optimization: No need to draw many times, just pick the best one.
	// Or maybe when we sort, if we find ones that are the same, remove the first one, and then
	// we just keep the last one. Then this code can stay the same but will not suffer so many
	// rewrites.
	targetDirty := normalizedDirtyRanges(bc.dirty, lineCount)
	for _, c := range captures {
		sty := style.CaptureStyle(e.styles.LineStyle, c.name)
		for row := c.startRow; row <= c.endRow; row++ {
			if int(row) >= len(lines) {
				break
			}
			if !fullRebuild && !rowInRanges(int(row), targetDirty) {
				continue
			}

			lineBytes := []byte(lines[row])
			startByteCol := uint(0)
			if row == c.startRow {
				startByteCol = c.startCol
			}
			endByteCol := uint(len(lineBytes))
			if row == c.endRow {
				endByteCol = min(c.endCol, uint(len(lineBytes)))
			}

			startRune := byteColToRuneIndex(lineBytes, int(startByteCol))
			endRune := byteColToRuneIndex(lineBytes, int(endByteCol))

			rowStyles := bc.lines[int(row)]
			if startRune < 0 {
				startRune = 0
			}
			if endRune > len(rowStyles) {
				endRune = len(rowStyles)
			}
			if startRune >= endRune {
				continue
			}

			for i := startRune; i < endRune; i++ {
				rowStyles[i] = sty
			}
			bc.lines[int(row)] = rowStyles
		}
	}

	bc.dirtyAll = false
	bc.dirty = nil
	bc.count = lineCount
	bc.built = true
}

func addDirtyRange(bc *bufferCache, start, end int) {
	if bc == nil {
		return
	}
	if end < start {
		start, end = end, start
	}
	if start < 0 {
		start = 0
	}
	if end < 0 {
		end = 0
	}
	bc.dirty = append(bc.dirty, lineRange{start: start, end: end})
	bc.dirty = mergeRanges(bc.dirty)
}

func normalizedDirtyRanges(ranges []lineRange, lineCount int) []lineRange {
	if lineCount <= 0 || len(ranges) == 0 {
		return nil
	}

	clamped := make([]lineRange, 0, len(ranges))
	for _, r := range ranges {
		start := max(0, r.start)
		end := min(lineCount-1, r.end)
		if start > end {
			continue
		}
		clamped = append(clamped, lineRange{start: start, end: end})
	}

	return mergeRanges(clamped)
}

func mergeRanges(ranges []lineRange) []lineRange {
	if len(ranges) == 0 {
		return nil
	}

	sort.Slice(ranges, func(i, j int) bool {
		if ranges[i].start == ranges[j].start {
			return ranges[i].end < ranges[j].end
		}
		return ranges[i].start < ranges[j].start
	})

	merged := make([]lineRange, 0, len(ranges))
	cur := ranges[0]
	for i := 1; i < len(ranges); i++ {
		n := ranges[i]
		if n.start <= cur.end+1 {
			if n.end > cur.end {
				cur.end = n.end
			}
			continue
		}
		merged = append(merged, cur)
		cur = n
	}
	merged = append(merged, cur)
	return merged
}

func rowInRanges(row int, ranges []lineRange) bool {
	for _, r := range ranges {
		if row >= r.start && row <= r.end {
			return true
		}
	}
	return false
}

func defaultLineStyles(line string, base lipgloss.Style) []lipgloss.Style {
	runes := []rune(line)
	row := make([]lipgloss.Style, len(runes))
	for i := range row {
		row[i] = base
	}
	return row
}

func collectCaptures(iter sitter.QueryCaptures, query *sitter.Query) []captureRange {
	if query == nil {
		return nil
	}

	names := query.CaptureNames()
	out := []captureRange{}
	for match, captureIdx := iter.Next(); match != nil; match, captureIdx = iter.Next() {
		capture := match.Captures[captureIdx]
		if int(capture.Index) >= len(names) {
			continue
		}
		name := names[capture.Index]
		if name == "spell" {
			continue
		}

		node := capture.Node
		start := node.StartPosition()
		end := node.EndPosition()
		out = append(out, captureRange{
			startRow: start.Row,
			startCol: start.Column,
			endRow:   end.Row,
			endCol:   end.Column,
			name:     name,
		})
	}

	return out
}

func buildBufferSource(buf *core.Buffer) []byte {
	lineCount := buf.LineCount()
	if lineCount == 0 {
		return []byte{}
	}

	lines := make([]string, lineCount)
	for i := range lineCount {
		lines[i] = buf.Line(i)
	}

	return []byte(strings.Join(lines, "\n"))
}

func byteColToRuneIndex(line []byte, byteCol int) int {
	if byteCol <= 0 {
		return 0
	}
	if byteCol >= len(line) {
		return len([]rune(string(line)))
	}

	prefix := line[:byteCol]
	return len([]rune(string(prefix)))
}