package web

import (
	"context"
	"net/url"
	"sort"
	"strings"

	"sourcecraft.dev/bigbes/sr-ht-dolt/browse"
	"sourcecraft.dev/bigbes/sr-ht-dolt/core"
)

// milestonePrefix marks labels that name a milestone; the view groups by them.
const milestonePrefix = "milestone:"

// milestonesView groups a beads issue DB by its "milestone:<name>" labels and
// shows per-milestone progress with the issues under each. It shares the beads
// fingerprint, so it appears as a companion tab wherever the Beads view does.
type milestonesView struct{}

func init() { RegisterView(&milestonesView{}) }

func (*milestonesView) Name() string     { return "milestones" }
func (*milestonesView) Label() string    { return "Milestones" }
func (*milestonesView) Template() string { return "milestones.html" }

// Applies mirrors the beads fingerprint so Milestones and Beads pair up. A
// beads DB that happens to use no milestone labels still gets the tab; it just
// renders an empty state.
func (*milestonesView) Applies(tables []browse.TableInfo) bool {
	return (&beadsView{}).Applies(tables)
}

// MilestoneView is the opaque .Data handed to milestones.html.
type MilestoneView struct {
	Milestones []MilestoneDetail
	Unlabeled  int // issues carrying no milestone label
	Total      int // all issues read
}

// MilestoneDetail is one milestone's rollup and the issues under it.
type MilestoneDetail struct {
	Name       string // label with the "milestone:" prefix stripped
	Label      string // full label, for filter links back to the board
	Total      int
	Done       int // closed
	InProgress int
	Open       int // open (or unknown) — the remaining work
	Issues     []BeadCard
}

// Pct is the milestone's completion percentage (0..100) for the progress bar.
func (m MilestoneDetail) Pct() int {
	if m.Total == 0 {
		return 0
	}
	return m.Done * 100 / m.Total
}

// Build reads the issues and their labels, then groups by milestone label. An
// issue with several milestone labels counts under each. Missing labels/statuses
// tables degrade to empty (no milestones), never an error.
func (v *milestonesView) Build(ctx context.Context, sess BrowseSession, _ *core.Repo, ref string, _ url.Values) (any, error) {
	issues, _, err := readRows(ctx, sess, ref, "issues")
	if err != nil {
		return nil, err
	}
	labels, _, _ := readRowsOptional(ctx, sess, ref, "labels")
	statuses, _, _ := readRowsOptional(ctx, sess, ref, "custom_statuses")

	catByStatus := map[string]string{}
	if statuses != nil {
		cols := indexCols(statuses.Columns)
		for _, r := range statuses.Rows {
			if name := cell(cols, r, "name"); name != "" {
				catByStatus[strings.ToLower(name)] = strings.ToLower(cell(cols, r, "category"))
			}
		}
	}

	labelsByIssue := map[string][]string{}
	if labels != nil {
		cols := indexCols(labels.Columns)
		for _, r := range labels.Rows {
			id := cell(cols, r, "issue_id")
			lb := cell(cols, r, "label")
			if id != "" && lb != "" {
				labelsByIssue[id] = append(labelsByIssue[id], lb)
			}
		}
	}

	issueCols := indexCols(issues.Columns)
	byLabel := map[string]*MilestoneDetail{}
	unlabeled := 0
	for _, r := range issues.Rows {
		id := cell(issueCols, r, "id")
		cat := statusCategory(cell(issueCols, r, "status"), catByStatus)
		card := BeadCard{
			ID:       id,
			Title:    cell(issueCols, r, "title"),
			Type:     cell(issueCols, r, "issue_type"),
			Priority: cell(issueCols, r, "priority"),
			Assignee: cell(issueCols, r, "assignee"),
			Category: cat,
		}
		seen := false
		for _, l := range labelsByIssue[id] {
			if !strings.HasPrefix(l, milestonePrefix) {
				continue
			}
			seen = true
			md := byLabel[l]
			if md == nil {
				md = &MilestoneDetail{Name: strings.TrimPrefix(l, milestonePrefix), Label: l}
				byLabel[l] = md
			}
			md.Total++
			switch cat {
			case "closed":
				md.Done++
			case "in_progress":
				md.InProgress++
			default:
				md.Open++
			}
			md.Issues = append(md.Issues, card)
		}
		if !seen {
			unlabeled++
		}
	}

	names := make([]string, 0, len(byLabel))
	for l := range byLabel {
		names = append(names, l)
	}
	sort.Strings(names)
	out := make([]MilestoneDetail, 0, len(names))
	for _, l := range names {
		md := byLabel[l]
		sortMilestoneCards(md.Issues)
		out = append(out, *md)
	}

	return &MilestoneView{Milestones: out, Unlabeled: unlabeled, Total: len(issues.Rows)}, nil
}

// sortMilestoneCards orders a milestone's issues open-work-first (closed sinks to
// the bottom), then by priority, then id — a stable, deterministic order.
func sortMilestoneCards(cards []BeadCard) {
	sort.SliceStable(cards, func(i, j int) bool {
		ci, cj := cards[i].Category == "closed", cards[j].Category == "closed"
		if ci != cj {
			return !ci
		}
		pi, pj := priorityRank(cards[i].Priority), priorityRank(cards[j].Priority)
		if pi != pj {
			return pi < pj
		}
		return cards[i].ID < cards[j].ID
	})
}