package main

import (
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"sort"
	"strings"
)

// spec:planctl-task-cmds/R1.2+R1.3+R2.4+R2.5+R3.1+D§2+D§3
// TaskRecord enriches a TaskLine with the task description text, its parsed
// numeric T-ID, and the same-line traceability tag refs needed by the v2
// subcommands. The underlying TaskLine (File, Line, Indent, Checked) is
// embedded unchanged so v1 consumers are unaffected.
type TaskRecord struct {
	TaskLine              // embedded: File, Line, Indent, Checked
	PlanDir    string    // basename of the plan directory that owns this task
	Text       string    // description stripped of checkbox prefix
	ID         string    // "T" + leading N.M, e.g. "T2.1"; "" if no numeric prefix
	ReqTags    []string  // R-ids from a same-line _Requirements:_ tag
	DesignTags []string  // D§-ids from a same-line _Design:_ tag
}

// spec:planctl-task-cmds/R1.2+D§3
// stripCheckboxPrefix removes the leading `^\s*- \[[ x]\] ` marker from a
// raw checkbox line, returning the task description text. Lines that do not
// match the pattern are returned unchanged.
func stripCheckboxPrefix(line string) string {
	// Match leading whitespace (spaces or tabs), "- [", space or x, "] "
	i := 0
	for i < len(line) && (line[i] == ' ' || line[i] == '\t') {
		i++
	}
	const marker = "- ["
	if !strings.HasPrefix(line[i:], marker) {
		return line
	}
	i += len(marker)
	if i >= len(line) {
		return line
	}
	ch := line[i]
	if ch != ' ' && ch != 'x' {
		return line
	}
	i++
	if i >= len(line) || line[i] != ']' {
		return line
	}
	i++
	if i >= len(line) || line[i] != ' ' {
		return line
	}
	i++
	return line[i:]
}

// spec:planctl-task-cmds/R1.3+R3.1+R3.4+D§3+D§6
// taskIDPattern matches a leading N.M numeric prefix (at least one dot
// segment) followed by whitespace. The captured group is the numeric part
// only; the "T" prefix is added by parseTaskID.
var taskIDPattern = regexp.MustCompile(`^(\d+(?:\.\d+)+)\s`)

// taskIDRefPattern validates a bare T-ID suffix (digits and dots, fully
// anchored). Used by findTaskByID to reject refs like "1.2 extra" that
// would otherwise pass taskIDPattern's unanchored prefix match.
var taskIDRefPattern = regexp.MustCompile(`^\d+(?:\.\d+)+$`)

// spec:planctl-task-cmds/R1.3+R3.1+D§3+D§6
// parseTaskID extracts the leading N.M numeric task ID from task description
// text and returns it as "T<N.M>". Returns "" when the text has no such prefix.
func parseTaskID(text string) string {
	m := taskIDPattern.FindStringSubmatch(text)
	if m == nil {
		return ""
	}
	return "T" + m[1]
}

// spec:planctl-task-cmds/R1.2+R2.4+R2.5+D§2+D§3
// buildTaskRecords constructs []TaskRecord from an Index and the tasks.md
// ScanResult. Tags are associated by line-number equality (D§3). scan must
// not be nil; the result is in the same order as idx.TaskLines.
func buildTaskRecords(idx Index, scan *ScanResult, planDir string) []TaskRecord {
	out := make([]TaskRecord, 0, len(idx.TaskLines))
	dirBase := planDir
	for _, tl := range idx.TaskLines {
		rawLine := ""
		if tl.Line >= 1 && tl.Line <= len(scan.Lines) {
			rawLine = scan.Lines[tl.Line-1]
		}
		text := stripCheckboxPrefix(rawLine)
		id := parseTaskID(text)
		var reqTags, desTags []string
		for _, ref := range idx.TaskTags {
			if ref.Line != tl.Line {
				continue
			}
			switch ref.Kind {
			case KindRequirements:
				reqTags = append(reqTags, ref.ID)
			case KindDesign:
				desTags = append(desTags, ref.ID)
			}
		}
		out = append(out, TaskRecord{
			TaskLine:   tl,
			PlanDir:    dirBase,
			Text:       text,
			ID:         id,
			ReqTags:    reqTags,
			DesignTags: desTags,
		})
	}
	return out
}

// spec:planctl-task-cmds/R3.1+D§3
// buildTaskRecordsFromScan is the lightweight variant used by runComplete's
// pre-write phase. It builds TaskRecords directly from a ScanResult without
// requiring a pre-built Index (avoids loading prd.md / design.md).
func buildTaskRecordsFromScan(scan *ScanResult, planDir string) []TaskRecord {
	taskLines := extractTaskLines(scan)
	tags, _ := extractTaskTags(scan)
	fakeIdx := Index{
		TaskLines:       taskLines,
		TaskTags:        tags,
		PRDRequirements: map[string]Position{},
		DesignSections:  map[string]Position{},
	}
	return buildTaskRecords(fakeIdx, scan, planDir)
}

// spec:planctl-task-cmds/R3.1+R3.4+D§3
// findResult discriminates the three outcomes of findTaskByID.
type findResult int

const (
	findOK        findResult = iota
	findBadFormat            // ref doesn't start with T or suffix isn't N.M
	findNotFound             // valid format, no matching record
)

// spec:planctl-task-cmds/R3.1+R3.4+D§3
// findTaskByID looks up a TaskRecord by its T-ID ref string (e.g. "T2.1").
// Returns the matched record (or nil), a findResult discriminator, and —
// when findNotFound — a sorted slice of all available non-empty IDs.
func findTaskByID(records []TaskRecord, ref string) (*TaskRecord, findResult, []string) {
	// Normalize to uppercase for case-insensitive matching (R3.1).
	ref = strings.ToUpper(ref)
	// Validate format: must start with "T" and suffix must match N.M pattern.
	if !strings.HasPrefix(ref, "T") {
		return nil, findBadFormat, nil
	}
	suffix := ref[1:]
	if !taskIDRefPattern.MatchString(suffix) {
		return nil, findBadFormat, nil
	}
	for i := range records {
		if records[i].ID == ref {
			return &records[i], findOK, nil
		}
	}
	// Collect available IDs for error message.
	var avail []string
	seen := map[string]bool{}
	for _, r := range records {
		if r.ID != "" && !seen[r.ID] {
			avail = append(avail, r.ID)
			seen[r.ID] = true
		}
	}
	sort.Strings(avail)
	return nil, findNotFound, avail
}

// spec:planctl-task-cmds/R3.2+R3.7+D§3+D§4
// atomicRewriteTaskLine reads path, replaces "- [ ]" with "- [x]" on the
// given 1-indexed lineNum, and writes the result atomically via a temp file
// + rename (D§4). Returns the original and new line text. The function
// validates that the target line contains "- [ ]" before writing.
func atomicRewriteTaskLine(path string, lineNum int) (oldText, newText string, err error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return "", "", fmt.Errorf("planctl: read %s: %w", path, err)
	}
	// Preserve trailing newline presence.
	trailingNewline := len(data) > 0 && data[len(data)-1] == '\n'

	lines := strings.Split(string(data), "\n")
	// Strip the trailing empty element that Split produces for a
	// trailing newline, so we work on content lines only.
	if trailingNewline && len(lines) > 0 && lines[len(lines)-1] == "" {
		lines = lines[:len(lines)-1]
	}

	if lineNum < 1 || lineNum > len(lines) {
		return "", "", fmt.Errorf("planctl: line %d out of range (file has %d lines)", lineNum, len(lines))
	}
	target := lines[lineNum-1]
	if !strings.Contains(target, "- [ ]") {
		return "", "", fmt.Errorf("planctl: line %d does not contain unchecked task marker: %q", lineNum, target)
	}
	changed := strings.Replace(target, "- [ ]", "- [x]", 1)
	lines[lineNum-1] = changed

	joined := strings.Join(lines, "\n")
	if trailingNewline {
		joined += "\n"
	}

	// Preserve original file mode.
	info, err := os.Stat(path)
	if err != nil {
		return "", "", fmt.Errorf("planctl: stat %s: %w", path, err)
	}
	mode := info.Mode()

	tmp, err := os.CreateTemp(filepath.Dir(path), ".planctl-*.tmp")
	if err != nil {
		return "", "", fmt.Errorf("planctl: create temp: %w", err)
	}
	tmpPath := tmp.Name()
	defer func() {
		_ = tmp.Close()
		if err != nil {
			_ = os.Remove(tmpPath)
		}
	}()

	if _, werr := tmp.WriteString(joined); werr != nil {
		err = fmt.Errorf("planctl: write temp: %w", werr)
		return "", "", err
	}
	if cerr := tmp.Close(); cerr != nil {
		err = fmt.Errorf("planctl: close temp: %w", cerr)
		return "", "", err
	}

	if cherr := os.Chmod(tmpPath, mode); cherr != nil {
		err = fmt.Errorf("planctl: chmod temp: %w", cherr)
		return "", "", err
	}
	if rerr := os.Rename(tmpPath, path); rerr != nil {
		err = fmt.Errorf("planctl: rename: %w", rerr)
		return "", "", err
	}
	return target, changed, nil
}

// spec:planctl-task-cmds/R4.5+D§3
// PlanStatus is the overall plan health label from evalPlanStatus.
type PlanStatus string

const (
	StatusLintError     PlanStatus = "lint_error"
	StatusNeedsCloseout PlanStatus = "needs_closeout"
	StatusDone          PlanStatus = "done"
	StatusNotStarted    PlanStatus = "not_started"
	StatusInProgress    PlanStatus = "in_progress"
)

// spec:planctl-task-cmds/R4.5+D§3
// evalPlanStatus derives the PlanStatus for a single plan per the R4.5
// precedence table (first match wins):
//  1. Any SevError diagnostic (excluding missing-closeout-file) → lint_error
//  2. All tasks checked + missing closeout file(s) → needs_closeout
//  3. All tasks checked + closeout present → done
//  4. Zero tasks checked → not_started
//  5. Default → in_progress
//
// CodeMissingCloseoutFile is excluded from the SevError check: per the PRD
// R4.3 example, a needs_closeout plan shows "Lint: PASS (0 errors)" — the
// closeout state is reported separately in the Close line.
func evalPlanStatus(diags []Diagnostic, tasks []TaskRecord, plan *Plan) PlanStatus {
	for _, d := range diags {
		if d.Severity == SevError && d.Code != CodeMissingCloseoutFile {
			return StatusLintError
		}
	}
	if len(tasks) > 0 {
		allChecked := true
		anyChecked := false
		for _, t := range tasks {
			if t.Checked {
				anyChecked = true
			} else {
				allChecked = false
			}
		}
		if allChecked {
			if plan == nil || !plan.CodexLog || !plan.HandoffFound {
				return StatusNeedsCloseout
			}
			return StatusDone
		}
		if !anyChecked {
			return StatusNotStarted
		}
	} else {
		return StatusNotStarted
	}
	return StatusInProgress
}