package main

import (
	"context"
	"errors"
	"fmt"
	"strings"
	"time"

	tea "github.com/charmbracelet/bubbletea"
	"github.com/charmbracelet/x/ansi"
)

const (
	prEditTitleField = iota
	prEditBaseField
	prEditBodyField
	prEditFieldCount
)

func (m *App) startPREdit() tea.Cmd {
	if reason := m.pullRequestUpdateUnavailable(); reason != "" {
		m.err = errors.New(reason)
		return nil
	}
	m.writeMode = writePREdit
	m.prEditField = prEditBodyField
	m.prEditEditors[prEditTitleField] = newTextEditor(m.details.Title, false)
	m.prEditEditors[prEditBaseField] = newTextEditor(m.details.BaseRef, false)
	m.prEditEditors[prEditBodyField] = newTextEditor(
		normalizeLineEndings(m.details.Body),
		m.editorMode == "vim",
	)
	m.prEditEditors[prEditBodyField].highlightMarkdown = true
	m.prEditOriginal = m.currentPRMetadata()
	m.restorePREditDraft()
	for index := range m.prEditEditors {
		m.prEditEditors[index].hardwareCursor = m.cursorOutput != nil
		m.prEditEditors[index].keys = m.keybindings
	}
	m.prEditBranches = nil
	m.prEditBranchesLoading = false
	m.prEditBranchesError = ""
	m.prEditBranchIndex = 0
	m.scroll = 0
	m.err = m.prEditEditors[m.prEditField].err
	m.prEditEditors[m.prEditField].err = nil
	m.ensurePREditCursorVisible()
	return m.loadPREditBranches()
}

func (m *App) loadPREditBranches() tea.Cmd {
	service, ok := m.service.(GitHubBranchService)
	if !ok {
		m.prEditBranchesError = "configured GitHub service cannot list branches"
		return nil
	}
	m.prEditBranchesLoading = true
	owner, repo := m.details.Owner, m.details.Repository
	return func() tea.Msg {
		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
		defer cancel()
		branches, err := service.ListBranches(ctx, owner, repo)
		return branchesLoadedMsg{owner: owner, repo: repo, branches: branches, err: err}
	}
}

func (m App) pullRequestUpdateUnavailable() string {
	if m.loading {
		return "pull request update unavailable while PR data is refreshing"
	}
	if m.details.FromCache {
		return "pull request update unavailable from an offline cached snapshot"
	}
	if _, ok := m.service.(GitHubPullRequestWriteService); !ok {
		return "configured GitHub service does not support pull request updates"
	}
	if m.details.ID == "" {
		return "pull request details are not loaded"
	}
	if !m.details.Permissions.CanUpdatePR {
		return "GitHub did not grant update permission for this pull request"
	}
	return ""
}

func (m App) updatePREditInput(key tea.KeyMsg) (tea.Model, tea.Cmd) {
	k := m.keybindings.canonicalPREditKey(
		key.String(), m.prEditField, m.writeMode == writePREditConfirm,
	)
	if m.prEditField != prEditBodyField &&
		key.Type != tea.KeyRunes && key.Type != tea.KeySpace {
		switch {
		case keyMatches(key.String(), m.keybindings.Navigation.Up):
			k = "up"
		case keyMatches(key.String(), m.keybindings.Navigation.Down):
			k = "down"
		}
	}
	editorWidth := m.prEditEditorWidth()
	if m.writeMode == writePREditConfirm {
		switch k {
		case "y":
			if reason := m.pullRequestUpdateUnavailable(); reason != "" {
				m.writeMode = writePREdit
				m.err = errors.New(reason)
				m.scroll = 0
				return m, nil
			}
			if m.prEditIsStale() {
				m.writeMode = writePREdit
				m.err = errors.New("pull request metadata changed while editing; cancel and reopen the editor")
				m.scroll = 0
				return m, nil
			}
			m.writeMode = writePREditBusy
			return m, m.submitPREdit()
		case "n", "esc":
			m.writeMode = writePREdit
			m.ensurePREditCursorVisible()
		}
		return m, nil
	}

	switch k {
	case "ctrl+s":
		if err := m.validatePREdit(); err != nil {
			m.err = err
			m.scroll = 0
			return m, nil
		} else if m.prEditIsStale() {
			m.err = errors.New("pull request metadata changed while editing; cancel and reopen the editor")
			m.scroll = 0
			return m, nil
		} else {
			m.writeMode = writePREditConfirm
			m.err = nil
			return m, nil
		}
	case "tab":
		if m.prEditField != prEditBaseField || !m.completeBranchSuggestion() {
			m.movePREditField(1)
		}
	case "shift+tab":
		m.movePREditField(-1)
	case "ctrl+n":
		if m.prEditField == prEditBaseField {
			m.moveBranchSuggestion(1)
		}
	case "ctrl+p":
		if m.prEditField == prEditBaseField {
			m.moveBranchSuggestion(-1)
		}
	case "ctrl+d", "ctrl+u":
		if m.prEditField == prEditBodyField {
			direction := 1
			if k == "ctrl+u" {
				direction = -1
			}
			delta := direction * max(1, m.dashboardViewportHeight()/2)
			m.prEditEditors[m.prEditField].movePage(delta, editorWidth)
			m.scroll = clamp(m.scroll+delta, 0, m.dashboardMaxScroll())
		}
	case "enter":
		if m.prEditField == prEditBaseField && m.completeBranchSuggestion() {
			break
		}
		if m.prEditField != prEditBodyField {
			m.movePREditField(1)
		} else {
			m.prEditEditors[m.prEditField].handleKeyAtWidth(key, true, editorWidth)
		}
	case "up":
		if m.prEditField != prEditBodyField {
			m.movePREditField(-1)
		} else {
			m.prEditEditors[m.prEditField].handleKeyAtWidth(key, true, editorWidth)
		}
	case "down":
		if m.prEditField != prEditBodyField {
			m.movePREditField(1)
		} else {
			m.prEditEditors[m.prEditField].handleKeyAtWidth(key, true, editorWidth)
		}
	case "esc":
		editor := &m.prEditEditors[m.prEditField]
		if editor.Modal && editor.Mode != textEditorNormal {
			editor.handleKeyAtWidth(key, m.prEditField == prEditBodyField, editorWidth)
		} else {
			m.writeMode = writeNone
			m.clearPREdit()
			m.err = nil
			m.scroll = 0
			return m, nil
		}
	default:
		editor := &m.prEditEditors[m.prEditField]
		before := editor.Text
		editor.handleKeyAtWidth(key, m.prEditField == prEditBodyField, editorWidth)
		if m.prEditField != prEditBodyField {
			editor.Text = normalizeSingleLine(editor.Text)
			editor.Cursor = clamp(editor.Cursor, 0, len([]rune(editor.Text)))
		}
		if m.prEditField == prEditBaseField && editor.Text != before {
			m.prEditBranchIndex = 0
		}
	}
	m.err = nil
	m.ensurePREditCursorVisible()
	return m, m.queuePREditDraft()
}

func (m App) prEditEditorWidth() int {
	return max(1, max(10, m.width-2)-4)
}

func (m App) positionPREditHardwareCursor(scroll, viewportHeight int) {
	if m.cursorOutput == nil {
		return
	}
	editor := m.prEditEditors[m.prEditField]
	if editor.Mode != textEditorInsert {
		return
	}
	_, cursorLine := m.dashboardEditLayout()
	screenRow := cursorLine - scroll
	if screenRow < 0 || screenRow >= viewportHeight {
		return
	}
	_, column := editorCursorVisualPosition(editor, m.prEditEditorWidth())
	// Rows and columns are one-based. Each editor row has a two-cell "│ "
	// context rail before its text.
	m.cursorOutput.SetCursor(true, column+3, screenRow+1)
}

func (m App) submitPREdit() tea.Cmd {
	writer := m.service.(GitHubPullRequestWriteService)
	id := m.details.ID
	update := m.prEditMetadata()
	return func() tea.Msg {
		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
		defer cancel()
		metadata, err := writer.UpdatePullRequest(ctx, id, update)
		return pullRequestUpdatedMsg{metadata: metadata, err: err}
	}
}

func (m App) validatePREdit() error {
	update := m.prEditMetadata()
	if update.Title == "" {
		return errors.New("pull request title cannot be empty")
	}
	if update.BaseRef == "" {
		return errors.New("target branch cannot be empty")
	}
	if len(m.prEditBranches) > 0 {
		found := false
		for _, branch := range m.prEditBranches {
			if branch.Name == update.BaseRef {
				found = true
				break
			}
		}
		if !found {
			return fmt.Errorf("target branch %q is not an available repository branch", update.BaseRef)
		}
	}
	if samePRMetadata(update, m.prEditOriginal) {
		return errors.New("title, target branch, and description are unchanged")
	}
	return nil
}

func (m App) prEditIsStale() bool {
	return !samePRMetadata(m.currentPRMetadata(), m.prEditOriginal)
}

func (m App) currentPRMetadata() PullRequestMetadata {
	return PullRequestMetadata{
		Title: m.details.Title, Body: m.details.Body, BaseRef: m.details.BaseRef,
		Mergeable: m.details.Mergeable, MergeState: m.details.MergeState,
		UpdatedAt: m.details.UpdatedAt,
	}
}

func (m App) prEditMetadata() PullRequestMetadata {
	body := m.prEditEditors[prEditBodyField].Text
	if body == normalizeLineEndings(m.prEditOriginal.Body) {
		// Opening the editor must not turn mixed or CRLF line endings into an
		// apparent edit. Preserve the remote body exactly until its content is
		// actually changed.
		body = m.prEditOriginal.Body
	}
	return PullRequestMetadata{
		Title:   strings.TrimSpace(m.prEditEditors[prEditTitleField].Text),
		Body:    body,
		BaseRef: strings.TrimSpace(m.prEditEditors[prEditBaseField].Text),
	}
}

func samePRMetadata(left, right PullRequestMetadata) bool {
	return left.Title == right.Title && left.Body == right.Body && left.BaseRef == right.BaseRef
}

func (m *App) clearPREdit() {
	m.prEditField = 0
	m.prEditEditors = [3]textEditor{}
	m.prEditOriginal = PullRequestMetadata{}
	m.prEditBranches = nil
	m.prEditBranchesLoading = false
	m.prEditBranchesError = ""
	m.prEditBranchIndex = 0
}

func (m *App) movePREditField(delta int) {
	m.prEditField = (m.prEditField + delta + prEditFieldCount) % prEditFieldCount
}

func textLineStart(value string, cursor int) int {
	runes := []rune(value)
	cursor = clamp(cursor, 0, len(runes))
	for cursor > 0 && runes[cursor-1] != '\n' {
		cursor--
	}
	return cursor
}

func textLineEnd(value string, cursor int) int {
	runes := []rune(value)
	cursor = clamp(cursor, 0, len(runes))
	for cursor < len(runes) && runes[cursor] != '\n' {
		cursor++
	}
	return cursor
}

func moveTextCursorLine(value string, cursor, delta int) int {
	start := textLineStart(value, cursor)
	column := cursor - start
	if delta < 0 {
		if start == 0 {
			return cursor
		}
		previousEnd := start - 1
		previousStart := textLineStart(value, previousEnd)
		return min(previousStart+column, previousEnd)
	}
	end := textLineEnd(value, cursor)
	if end == len([]rune(value)) {
		return cursor
	}
	nextStart := end + 1
	nextEnd := textLineEnd(value, nextStart)
	return min(nextStart+column, nextEnd)
}

func (m App) dashboardEditLines() []string {
	lines, _ := m.dashboardEditLayout()
	return lines
}

func (m App) dashboardEditLayout() ([]string, int) {
	width := max(10, m.width-2)
	cursorLine := 0
	lines := []string{
		titleStyle.Render(fmt.Sprintf("%s #%d", m.details.RepoWithOwner, m.details.Number)) +
			"  " + warnStyle.Render("EDITING"),
		"",
		titleStyle.Render("Edit pull request"),
		dimStyle.Render("Raw Markdown is preserved in the description."),
	}
	if m.err != nil {
		errorWidth := max(1, width-2)
		wrapped := ansi.Hardwrap(ansi.Wordwrap(m.err.Error(), errorWidth, ""), errorWidth, false)
		lines = append(lines, "")
		for _, line := range strings.Split(wrapped, "\n") {
			lines = append(lines, badStyle.Render(line))
		}
	}
	appendField := func(label string, field int) {
		lines = append(lines, "")
		start := len(lines)
		lines = append(lines, m.prEditFieldLines(label, field, width)...)
		if m.prEditField == field {
			cursorLine = start + 1 + editorCursorVisualLine(m.prEditEditors[field], max(1, width-4))
		}
	}
	appendField("title", prEditTitleField)
	appendField("target branch", prEditBaseField)
	appendField("description", prEditBodyField)
	return lines, cursorLine
}

func (m App) prEditFieldLines(label string, field, width int) []string {
	active := m.prEditField == field
	editor := m.prEditEditors[field]
	prefix := "  "
	if active {
		prefix = "▶ "
	}
	mode := editor.modeLabel()
	if mode != "" {
		label += " [" + mode + "]"
	}
	labelLine := dimStyle.Render(prefix + label)
	if active {
		labelLine = titleStyle.Render(prefix + label)
	}
	textWidth := max(1, width-4)
	rendered := renderTextEditor(editor, textWidth, active)
	lines := []string{labelLine}
	for _, line := range rendered {
		if line.active {
			// Style the rail and text as one row. Nesting the cursor or rail
			// style inside a background style emits resets that can erase the
			// remainder of wrapped terminal rows.
			lines = append(lines, editorLineStyle.Render("│ "+line.text))
			continue
		}
		lines = append(lines, dimStyle.Render("│ ")+line.text)
	}
	if active && field == prEditBaseField {
		lines = append(lines, m.branchCompletionLines(max(1, width-2))...)
	}
	return lines
}

func (m *App) ensurePREditCursorVisible() {
	if m.writeMode != writePREdit {
		return
	}
	lines, cursorLine := m.dashboardEditLayout()
	height := m.dashboardViewportHeight()
	if m.prEditField == prEditTitleField && cursorLine < height {
		// The title is the first editable field. Returning to it should also
		// restore the dashboard/editor heading instead of pinning the title's
		// text row to the top and clipping its label.
		m.scroll = 0
	} else if contextTop := max(0, cursorLine-2); contextTop < m.scroll {
		// Keep the active field label and its rail visible above the cursor.
		m.scroll = contextTop
	} else if cursorLine >= m.scroll+height {
		m.scroll = cursorLine - height + 1
	}
	m.scroll = clamp(m.scroll, 0, max(0, len(lines)-height))
}

func (m App) prEditConfirmationLines(width int) []string {
	update := m.prEditMetadata()
	lines := []string{titleStyle.Render("Update this pull request?"), ""}
	if update.Title != m.prEditOriginal.Title {
		lines = append(lines,
			dimStyle.Render("title"),
			ansi.Truncate(m.prEditOriginal.Title, width, "…"),
			"→ "+ansi.Truncate(update.Title, max(1, width-2), "…"),
			"",
		)
	}
	if update.BaseRef != m.prEditOriginal.BaseRef {
		lines = append(lines,
			dimStyle.Render("target branch"),
			m.prEditOriginal.BaseRef+" → "+update.BaseRef,
			"",
		)
	}
	if update.Body != m.prEditOriginal.Body {
		lines = append(lines, fmt.Sprintf(
			"description changed  •  %d → %d characters",
			len([]rune(m.prEditOriginal.Body)), len([]rune(update.Body)),
		), "")
	}
	lines = append(lines, warnStyle.Render(fmt.Sprintf(
		"%s submit  •  %s continue editing",
		primaryKeyLabel(m.keybindings.General.Confirm),
		primaryCombinedKeyLabel(m.keybindings.General.Reject, m.keybindings.Input.Cancel),
	)))
	return lines
}