package main

import (
	"fmt"
	"strings"
	"sync"

	tea "github.com/charmbracelet/bubbletea"
	"github.com/charmbracelet/lipgloss"
	zone "github.com/lrstanley/bubblezone"

	"paperclip-harness/tui/paperclip"
)

// groupOrder is the order of the four status groups on screen 1.
var groupOrder = []string{"Todo", "In progress", "Blocked", "In review", "Done"}

// Row is one task as the screen needs it: the task itself, who has it, and
// what Paperclip says blocks it.
type Row struct {
	Issue   paperclip.Issue
	Group   string
	Who     string
	Blocker *paperclip.BlockerInfo
}

type rowsMsg []Row
type errMsg struct{ err error }

func groupOf(status string) string {
	switch status {
	case "todo", "backlog":
		return "Todo"
	case "in_progress":
		return "In progress"
	case "blocked":
		return "Blocked"
	case "in_review":
		return "In review"
	case "done", "cancelled":
		return "Done"
	}
	return "Todo"
}

// loadRows reads the project's tasks from Paperclip, then asks about each
// task's blockers, because the list endpoint never carries them.
func loadRows(c *paperclip.Client, proj paperclip.Project) ([]Row, error) {
	issues, err := c.Issues()
	if err != nil {
		return nil, err
	}
	mine := make([]paperclip.Issue, 0, len(issues))
	for _, is := range issues {
		if is.ProjectID == proj.ID {
			mine = append(mine, is)
		}
	}

	names := map[string]string{}
	if agents, err := c.Agents(); err == nil {
		for _, a := range agents {
			names[a.ID] = a.Name
		}
	}

	rows := make([]Row, len(mine))
	for i, is := range mine {
		who := "—"
		switch {
		case names[is.AssigneeAgent] != "":
			who = names[is.AssigneeAgent]
		case is.AssigneeAgent != "":
			who = "agent"
		case is.AssigneeUser != "":
			who = "person"
		}
		rows[i] = Row{Issue: is, Group: groupOf(is.Status), Who: who}
	}

	// One request per task. Bounded so a large project does not open a
	// hundred sockets at once.
	var wg sync.WaitGroup
	sem := make(chan struct{}, 6)
	for i := range rows {
		wg.Add(1)
		go func(i int) {
			defer wg.Done()
			sem <- struct{}{}
			defer func() { <-sem }()
			info, err := c.Blockers(rows[i].Issue.ID)
			if err == nil {
				rows[i].Blocker = &info
			}
		}(i)
	}
	wg.Wait()

	order := map[string]int{}
	for i, g := range groupOrder {
		order[g] = i
	}
	// Stable sort by group, then by identifier so the tree does not jump
	// around between refreshes.
	for i := 1; i < len(rows); i++ {
		for j := i; j > 0; j-- {
			a, b := rows[j-1], rows[j]
			if order[a.Group] > order[b.Group] ||
				(order[a.Group] == order[b.Group] && a.Issue.Identifier > b.Issue.Identifier) {
				rows[j-1], rows[j] = rows[j], rows[j-1]
				continue
			}
			break
		}
	}
	return rows, nil
}

type model struct {
	client  *paperclip.Client
	project paperclip.Project
	agent   string
	zones   *zone.Manager

	rows    []Row
	cursor  int
	err     error
	loading bool

	width  int
	height int
}

func newModel(c *paperclip.Client, proj paperclip.Project, agent string) model {
	return model{
		client:  c,
		project: proj,
		agent:   agent,
		// The click-zone manager is created once, here, and the whole view is
		// wrapped and scanned through it. Wrapping parts separately drifts
		// when a pane is resized.
		zones:   zone.New(),
		loading: true,
	}
}

func (m model) Init() tea.Cmd {
	return m.reload()
}

func (m model) reload() tea.Cmd {
	c, proj := m.client, m.project
	return func() tea.Msg {
		rows, err := loadRows(c, proj)
		if err != nil {
			return errMsg{err}
		}
		return rowsMsg(rows)
	}
}

func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
	switch msg := msg.(type) {
	case tea.WindowSizeMsg:
		// Sizes are always taken from the message. Nothing is hardcoded.
		m.width, m.height = msg.Width, msg.Height
		return m, nil

	case tea.KeyMsg:
		switch msg.String() {
		case "q", "ctrl+c":
			return m, tea.Quit
		case "r":
			m.loading = true
			return m, m.reload()
		case "a":
			// Assign the selected task to one agent. Paperclip wakes that
			// agent as soon as the assignment lands, so this is also the
			// "start work" key.
			if m.cursor < len(m.rows) && m.rows[m.cursor].Issue.AssigneeAgent == "" {
				c, id, agent := m.client, m.rows[m.cursor].Issue.ID, m.agent
				return m, func() tea.Msg {
					if _, err := c.Assign(id, agent); err != nil {
						return errMsg{err}
					}
					rows, err := loadRows(c, m.project)
					if err != nil {
						return errMsg{err}
					}
					return rowsMsg(rows)
				}
			}
			return m, nil
		case "up", "shift+tab":
			if m.cursor > 0 {
				m.cursor--
			}
			return m, nil
		case "down", "tab":
			if m.cursor < len(m.rows)-1 {
				m.cursor++
			}
			return m, nil
		case "home":
			m.cursor = 0
			return m, nil
		case "end":
			if len(m.rows) > 0 {
				m.cursor = len(m.rows) - 1
			}
			return m, nil
		case "esc":
			// A bare Esc stays free for closing a box. Nothing to close yet.
			return m, nil
		}

	case rowsMsg:
		m.rows = msg
		m.loading = false
		m.err = nil
		if m.cursor >= len(m.rows) {
			m.cursor = max(0, len(m.rows)-1)
		}
		return m, nil

	case errMsg:
		m.err = msg.err
		m.loading = false
		return m, nil
	}
	return m, nil
}

var (
	titleStyle    = lipgloss.NewStyle().Bold(true)
	groupStyle    = lipgloss.NewStyle().Bold(true).Foreground(lipgloss.Color("12"))
	selectedStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("0")).Background(lipgloss.Color("12"))
	mutedStyle    = lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
	blockedStyle  = lipgloss.NewStyle().Foreground(lipgloss.Color("9"))
)

// minWidth and minHeight are the smallest box that still shows something
// honest. Below this the program says so instead of drawing a broken tree.
const (
	minWidth  = 56
	minHeight = 12
)

func (m model) View() string {
	if m.width == 0 || m.height == 0 {
		return "loading…"
	}
	if m.width < minWidth || m.height < minHeight {
		return m.zones.Scan(lipgloss.NewStyle().
			Width(m.width).Height(m.height).
			Render(fmt.Sprintf("Window is too small.\nNeed %d×%d, have %d×%d.", minWidth, minHeight, m.width, m.height)))
	}

	var b strings.Builder
	b.WriteString(titleStyle.Render(truncate(m.project.Name+"  ·  task tree", m.width)))
	b.WriteString("\n")

	if m.err != nil {
		b.WriteString(blockedStyle.Render(truncate("error: "+m.err.Error(), m.width)))
		b.WriteString("\n")
	}

	if m.loading && len(m.rows) == 0 {
		b.WriteString(mutedStyle.Render("reading tasks from Paperclip…"))
		b.WriteString("\n")
	}

	lines := 0
	budget := m.height - 3
	for _, g := range groupOrder {
		var group []Row
		for _, r := range m.rows {
			if r.Group == g {
				group = append(group, r)
			}
		}
		if len(group) == 0 {
			continue
		}
		if lines >= budget {
			break
		}
		b.WriteString(groupStyle.Render(fmt.Sprintf("%s  (%d)", strings.ToUpper(g), len(group))))
		b.WriteString("\n")
		lines++
		for _, r := range group {
			if lines >= budget {
				break
			}
			b.WriteString(m.renderRow(r))
			b.WriteString("\n")
			lines++
		}
	}
	if len(m.rows) == 0 && !m.loading && m.err == nil {
		b.WriteString(mutedStyle.Render("no tasks in this project"))
		b.WriteString("\n")
	}

	b.WriteString(mutedStyle.Render(truncate(
		"↑/↓ or Tab/Shift-Tab move · a assign to Builder · r refresh · q quit", m.width)))

	// One scan for the whole view.
	return m.zones.Scan(b.String())
}

func (m model) renderRow(r Row) string {
	i := m.indexOf(r.Issue.ID)
	marker := "  "
	if i == m.cursor {
		marker = "▸ "
	}
	who := r.Who
	if who == "" {
		who = "—"
	}
	line := fmt.Sprintf("%s%-8s %-11s %-10s %s", marker, r.Issue.Identifier, r.Issue.Status, who, r.Issue.Title)
	if r.Blocker != nil && r.Blocker.UnresolvedCount > 0 {
		line += "  [" + strings.Join(r.Blocker.BlockingIdentities, ", ") + "]"
	}
	line = truncate(line, m.width)
	if i == m.cursor {
		return m.zones.Mark("row-"+r.Issue.ID, selectedStyle.Render(line))
	}
	return m.zones.Mark("row-"+r.Issue.ID, line)
}

func (m model) indexOf(id string) int {
	for i, r := range m.rows {
		if r.Issue.ID == id {
			return i
		}
	}
	return -1
}

func truncate(s string, w int) string {
	if w <= 0 {
		return ""
	}
	r := []rune(s)
	if len(r) <= w {
		return s
	}
	if w == 1 {
		return "…"
	}
	return string(r[:w-1]) + "…"
}