// Package store keeps the whole challenge in one JSON file on a mounted
// volume. Seventy-five rows for one person does not need a database: the file
// is read into memory at boot, every write goes back out atomically, and a
// mutex serialises the handful of writes a day.
package store

import (
	"encoding/json"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"
)

// DateLayout is the form every date takes, in the URL, in the file, and in the
// map key. Local dates only; there is no time of day anywhere in the model.
const DateLayout = "2006-01-02"

// Settings is what the challenge is, as opposed to how it is deployed. It
// lives in the data file so a target can change from the settings page.
type Settings struct {
	StartDate     string `json:"start_date"` // day 1
	Length        int    `json:"length"`
	ProteinTarget int    `json:"protein_target"` // grams, a floor
	CalorieTarget int    `json:"calorie_target"` // kcal
	CalorieMode   string `json:"calorie_mode"`   // "under" (a ceiling) or "over" (a floor)
	WaterTarget   int    `json:"water_target"`   // fluid ounces, a floor
}

// Defaults are what the setup form is pre-filled with. A gallon is 128 fl oz.
func Defaults() Settings {
	return Settings{
		Length:        75,
		ProteinTarget: 180,
		CalorieTarget: 2200,
		CalorieMode:   "under",
		WaterTarget:   128,
	}
}

func (s Settings) Configured() bool { return s.StartDate != "" }

// Start returns day 1 as a date. It is only valid once Configured.
func (s Settings) Start() time.Time {
	t, _ := time.Parse(DateLayout, s.StartDate)
	return t
}

// End returns the last day of the challenge.
func (s Settings) End() time.Time {
	return s.Start().AddDate(0, 0, s.Length-1)
}

// DayNumber returns the 1-based position of a date in the challenge, or 0 if
// the date falls outside it.
func (s Settings) DayNumber(date string) int {
	t, err := time.Parse(DateLayout, date)
	if err != nil || !s.Configured() {
		return 0
	}
	n := int(t.Sub(s.Start()).Hours()/24) + 1
	if n < 1 || n > s.Length {
		return 0
	}
	return n
}

// Day is one day's log. The three numbers are pointers so that "not logged
// yet" stays distinct from "logged as zero" — a day with no calories entered
// should not read as a perfect calorie day.
type Day struct {
	Date      string    `json:"date"`
	Workout   bool      `json:"workout"`
	Protein   *int      `json:"protein,omitempty"`
	Calories  *int      `json:"calories,omitempty"`
	Water     *int      `json:"water,omitempty"`
	Gratitude [3]string `json:"gratitude"`
	UpdatedAt time.Time `json:"updated_at,omitzero"`
}

// Logged reports whether the day has been touched at all, which is what
// separates an empty future day from a day that was genuinely missed.
func (d Day) Logged() bool {
	if d.Workout || d.Protein != nil || d.Calories != nil || d.Water != nil {
		return true
	}
	for _, g := range d.Gratitude {
		if strings.TrimSpace(g) != "" {
			return true
		}
	}
	return false
}

func (d Day) clone() Day {
	out := d
	out.Protein = clonePtr(d.Protein)
	out.Calories = clonePtr(d.Calories)
	out.Water = clonePtr(d.Water)
	return out
}

func clonePtr(p *int) *int {
	if p == nil {
		return nil
	}
	v := *p
	return &v
}

// Marks is which of the five things a day hit. The five are equal: the card on
// the home page fills a day's tile by how many of them are true.
type Marks struct {
	Workout   bool
	Protein   bool
	Calories  bool
	Water     bool
	Gratitude bool
}

func (m Marks) Score() int {
	n := 0
	for _, ok := range [5]bool{m.Workout, m.Protein, m.Calories, m.Water, m.Gratitude} {
		if ok {
			n++
		}
	}
	return n
}

func (m Marks) Complete() bool { return m.Score() == 5 }

// Marks scores a day against the targets in force.
func (s Settings) Marks(d Day) Marks {
	m := Marks{Workout: d.Workout}

	if d.Protein != nil && *d.Protein >= s.ProteinTarget {
		m.Protein = true
	}
	if d.Calories != nil {
		if s.CalorieMode == "over" {
			m.Calories = *d.Calories >= s.CalorieTarget
		} else {
			m.Calories = *d.Calories <= s.CalorieTarget
		}
	}
	if d.Water != nil && *d.Water >= s.WaterTarget {
		m.Water = true
	}

	m.Gratitude = true
	for _, g := range d.Gratitude {
		if strings.TrimSpace(g) == "" {
			m.Gratitude = false
			break
		}
	}
	return m
}

// data is the on-disk shape. Version is here so a later change to the model
// has something to branch on.
type data struct {
	Version  int             `json:"version"`
	Settings Settings        `json:"settings"`
	Days     map[string]*Day `json:"days"`
}

const currentVersion = 1

// Store owns the file and the in-memory copy of it.
type Store struct {
	path string
	mu   sync.RWMutex
	d    data
}

// Open reads the data file, or starts an empty one if it does not exist yet.
// A file that exists but does not parse is an error: overwriting it with a
// fresh empty challenge would throw away the log, which is the one thing here
// that cannot be recreated.
func Open(path string) (*Store, error) {
	s := &Store{
		path: path,
		d:    data{Version: currentVersion, Settings: Defaults(), Days: map[string]*Day{}},
	}

	body, err := os.ReadFile(path)
	switch {
	case errors.Is(err, fs.ErrNotExist):
		if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
			return nil, fmt.Errorf("create data directory: %w", err)
		}
		return s, nil
	case err != nil:
		return nil, fmt.Errorf("read %s: %w", path, err)
	}

	if err := json.Unmarshal(body, &s.d); err != nil {
		return nil, fmt.Errorf("parse %s (left untouched; move it aside to start over): %w", path, err)
	}
	if s.d.Days == nil {
		s.d.Days = map[string]*Day{}
	}

	// Keep the copy that was known to parse. If a later write ever produces
	// something unreadable, this is the file to rename back.
	if err := os.WriteFile(path+".bak", body, 0o644); err != nil {
		return nil, fmt.Errorf("write backup: %w", err)
	}
	return s, nil
}

func (s *Store) Settings() Settings {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return s.d.Settings
}

func (s *Store) SaveSettings(next Settings) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.d.Settings = next
	return s.persist()
}

// Day returns the log for a date, or an empty one if nothing is recorded.
func (s *Store) Day(date string) Day {
	s.mu.RLock()
	defer s.mu.RUnlock()
	if d, ok := s.d.Days[date]; ok {
		return d.clone()
	}
	return Day{Date: date}
}

// SaveDay writes one day. A day emptied of everything is deleted rather than
// stored blank, so an accidental visit to a future date leaves no trace.
func (s *Store) SaveDay(d Day) error {
	s.mu.Lock()
	defer s.mu.Unlock()

	if !d.Logged() {
		delete(s.d.Days, d.Date)
		return s.persist()
	}

	d.UpdatedAt = time.Now().UTC()
	stored := d.clone()
	s.d.Days[d.Date] = &stored
	return s.persist()
}

// Days returns count consecutive days starting at from, including the blanks,
// so the caller can lay out the card without checking for gaps.
func (s *Store) Days(from time.Time, count int) []Day {
	s.mu.RLock()
	defer s.mu.RUnlock()

	out := make([]Day, 0, count)
	for i := 0; i < count; i++ {
		date := from.AddDate(0, 0, i).Format(DateLayout)
		if d, ok := s.d.Days[date]; ok {
			out = append(out, d.clone())
			continue
		}
		out = append(out, Day{Date: date})
	}
	return out
}

// Export returns the whole file as it would be written, for the download.
func (s *Store) Export() ([]byte, error) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return json.MarshalIndent(s.d, "", "  ")
}

// Import replaces everything with a previously exported file.
func (s *Store) Import(body []byte) error {
	var next data
	if err := json.Unmarshal(body, &next); err != nil {
		return fmt.Errorf("that file is not a fit export: %w", err)
	}
	if next.Days == nil {
		next.Days = map[string]*Day{}
	}
	for date, d := range next.Days {
		if _, err := time.Parse(DateLayout, date); err != nil {
			return fmt.Errorf("%q is not a date", date)
		}
		d.Date = date
	}

	s.mu.Lock()
	defer s.mu.Unlock()
	next.Version = currentVersion
	s.d = next
	return s.persist()
}

// persist writes the file atomically: a temp file in the same directory, then
// a rename. A crash mid-write therefore leaves the previous file intact rather
// than a half-written one. Callers hold the write lock.
func (s *Store) persist() error {
	body, err := json.MarshalIndent(s.d, "", "  ")
	if err != nil {
		return fmt.Errorf("encode: %w", err)
	}

	dir := filepath.Dir(s.path)
	tmp, err := os.CreateTemp(dir, ".fit-*.json")
	if err != nil {
		return fmt.Errorf("create temp file: %w", err)
	}
	name := tmp.Name()
	defer os.Remove(name) // no-op once the rename has succeeded

	if _, err := tmp.Write(body); err != nil {
		tmp.Close()
		return fmt.Errorf("write temp file: %w", err)
	}
	// Flush to the disk before the rename, so a power cut cannot leave the
	// file renamed into place but empty.
	if err := tmp.Sync(); err != nil {
		tmp.Close()
		return fmt.Errorf("sync temp file: %w", err)
	}
	if err := tmp.Close(); err != nil {
		return fmt.Errorf("close temp file: %w", err)
	}
	if err := os.Chmod(name, 0o644); err != nil {
		return fmt.Errorf("chmod temp file: %w", err)
	}
	if err := os.Rename(name, s.path); err != nil {
		return fmt.Errorf("replace data file: %w", err)
	}

	// Fsync the directory so the rename itself is durable.
	if handle, err := os.Open(dir); err == nil {
		handle.Sync()
		handle.Close()
	}
	return nil
}