package tui

import (
	"albedo/cli/internal/daemon"
	"iter"
	"slices"
	"strings"
	"unicode/utf8"
)

const (
	agentPreviewBytes = 64 << 10
	agentPreviewLines = 120
)

type agentTailSpan struct {
	start, end uint64
	kind       tailKind
}

// agentTail owns its bytes. Absolute offsets let a long line lose its oldest
// bytes without shifting the window or retaining the original stream chunks.
type agentTail struct {
	data    []byte
	lines   [agentPreviewLines]agentTailSpan
	end     uint64
	head    int
	count   int
	open    bool
	omitted bool
}

func (tail *agentTail) dropOldest() {
	tail.lines[tail.head] = agentTailSpan{}
	tail.head = (tail.head + 1) % agentPreviewLines
	tail.count--
	tail.omitted = true
}

func (tail *agentTail) begin(kind tailKind) {
	if tail.count == agentPreviewLines {
		tail.dropOldest()
	}
	index := (tail.head + tail.count) % agentPreviewLines
	tail.lines[index] = agentTailSpan{start: tail.end, end: tail.end, kind: kind}
	tail.count++
	tail.open = true
}

func (tail *agentTail) grow(extra int) {
	start := tail.lines[tail.head].start
	retained := int(tail.end - start)
	required := min(agentPreviewBytes, retained+extra)
	if required <= len(tail.data) {
		return
	}
	data := make([]byte, min(agentPreviewBytes, max(64, required, len(tail.data)*2)))
	if retained > 0 {
		index := int(start % uint64(len(tail.data)))
		copied := copy(data[:retained], tail.data[index:])
		copy(data[copied:retained], tail.data[:retained-copied])
	}
	for offset := range tail.count {
		span := &tail.lines[(tail.head+offset)%agentPreviewLines]
		span.start -= start
		span.end -= start
	}
	tail.end -= start
	tail.data = data
}

func (tail *agentTail) appendText(text string) {
	if len(text) == 0 {
		return
	}
	tail.grow(len(text))
	capacity := uint64(len(tail.data))
	next := tail.end + uint64(len(text))
	if len(text) > len(tail.data) {
		text = text[len(text)-len(tail.data):]
	}
	index := int((next - uint64(len(text))) % capacity)
	copied := copy(tail.data[index:], text)
	copy(tail.data, text[copied:])
	tail.end = next
	tail.lines[(tail.head+tail.count-1)%agentPreviewLines].end = next
	if next <= capacity {
		return
	}
	oldest := next - capacity
	for tail.count > 1 && tail.lines[tail.head].end <= oldest {
		tail.dropOldest()
	}
	first := &tail.lines[tail.head]
	if first.start < oldest {
		first.start = oldest
		for first.start < first.end && !utf8.RuneStart(tail.data[first.start%capacity]) {
			first.start++
		}
		tail.omitted = true
	}
}

func (tail *agentTail) write(text string, kind tailKind) {
	for {
		line, rest, newline := strings.Cut(text, "\n")
		if !tail.open {
			tail.begin(kind)
		}
		tail.appendText(line)
		if !newline {
			return
		}
		tail.open = false
		text = rest
	}
}

func (tail *agentTail) push(line tailLine) {
	tail.open = false
	tail.write(strings.TrimRight(line.text, " "), line.kind)
	tail.open = false
}

func (tail *agentTail) text(span agentTailSpan) string {
	if span.start == span.end {
		return ""
	}
	var text strings.Builder
	text.Grow(int(span.end - span.start))
	start := int(span.start % uint64(len(tail.data)))
	length := int(span.end - span.start)
	first := min(length, len(tail.data)-start)
	text.Write(tail.data[start : start+first])
	text.Write(tail.data[:length-first])
	return text.String()
}

// newest yields owned strings, so callers may retain them after a reset.
func (tail *agentTail) newest(trimNewlines bool) iter.Seq[tailLine] {
	return func(yield func(tailLine) bool) {
		trimming := trimNewlines
		for offset := tail.count - 1; offset >= 0; offset-- {
			span := tail.lines[(tail.head+offset)%agentPreviewLines]
			if trimming && span.start == span.end && offset > 0 {
				continue
			}
			trimming = false
			if !yield(tailLine{kind: span.kind, text: tail.text(span)}) {
				return
			}
		}
	}
}

// setCode replaces the preview window supplied by the daemon.
func (tail *agentTail) setCode(code *daemon.ToolCodePreview) {
	*tail = agentTail{}
	if code != nil {
		tail.write(strings.ReplaceAll(code.Text, "\t", "    "), tailCode)
	}
}

type agentTailCache struct {
	node     *agentNode
	ink      ink
	rows     []string
	revision uint64
	width    int
	height   int
}

// refreshTail runs after updates, never from View. Only the selected node
// needs wrapped rows; animation-only frames reuse the previous result.
func (m *AgentsViewModel) refreshTail() {
	node := m.nodes[m.selected]
	width, height := m.paneWidth()-1, max(0, m.Height)
	cache := &m.tailCache
	if node == nil || width <= 0 || height == 0 {
		*cache = agentTailCache{}
		return
	}
	if cache.node == node && cache.revision == node.revision && cache.width == width && cache.height == height && cache.ink == transcriptInk {
		return
	}
	rows := make([]string, 0, height)
	appendLine := func(line tailLine) bool {
		wrapped := drawTail(line, width, height-len(rows))
		for _, row := range slices.Backward(wrapped) {
			rows = append(rows, row)
		}
		return len(rows) < height
	}
	for line := range node.preview.newest(node.lineKind == tailCode) {
		if line.text == "" && node.lineKind != tailCode {
			continue
		}
		if !appendLine(line) {
			break
		}
	}
	if len(rows) < height {
		for line := range node.tail.newest(false) {
			if !appendLine(line) {
				break
			}
		}
	}
	slices.Reverse(rows)
	*cache = agentTailCache{node: node, rows: rows, ink: transcriptInk, revision: node.revision, width: width, height: height}
}