package command

import (
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"

	"task/internal/ticket"
)

const (
	historyFileName = "history.json"
	// MaxHistory is the maximum number of undo (and redo) entries kept.
	MaxHistory = 20
)

type persistedFile struct {
	Undo []persistedCmd `json:"undo"`
	Redo []persistedCmd `json:"redo"`
}

type persistedCmd struct {
	Type       string            `json:"type"`
	Ticket     *ticket.Ticket    `json:"ticket,omitempty"`
	Snapshot   *ticket.Ticket    `json:"snapshot,omitempty"`
	Before     *ticket.Ticket    `json:"before,omitempty"`
	After      *ticket.Ticket    `json:"after,omitempty"`
	TimeEntry  *ticket.TimeEntry `json:"timeEntry,omitempty"`
	TimeBefore *ticket.TimeEntry `json:"timeBefore,omitempty"`
	TimeAfter  *ticket.TimeEntry `json:"timeAfter,omitempty"`
}

const (
	typeCreate     = "create"
	typeDelete     = "delete"
	typeUpdate     = "update"
	typeAddTime    = "add_time"
	typeRemoveTime = "remove_time"
	typeUpdateTime = "update_time"
)

// HistoryPath returns DataDir/history.json.
func HistoryPath(dataDir string) string {
	return filepath.Join(dataDir, historyFileName)
}

func encodeCmd(cmd Command) (persistedCmd, error) {
	switch c := cmd.(type) {
	case *CreateTicket:
		t := c.Ticket
		if c.created.ID != "" {
			t = c.created
		}
		cp := t
		return persistedCmd{Type: typeCreate, Ticket: &cp}, nil
	case *DeleteTicket:
		cp := c.Snapshot
		return persistedCmd{Type: typeDelete, Snapshot: &cp}, nil
	case *UpdateTicket:
		b, a := c.Before, c.After
		return persistedCmd{Type: typeUpdate, Before: &b, After: &a}, nil
	case *AddTimeEntry:
		e := c.Entry
		if c.created.ID != "" {
			e = c.created
		}
		cp := e
		return persistedCmd{Type: typeAddTime, TimeEntry: &cp}, nil
	case *RemoveTimeEntry:
		cp := c.Snapshot
		return persistedCmd{Type: typeRemoveTime, TimeEntry: &cp}, nil
	case *UpdateTimeEntry:
		b, a := c.Before, c.After
		return persistedCmd{Type: typeUpdateTime, TimeBefore: &b, TimeAfter: &a}, nil
	default:
		return persistedCmd{}, fmt.Errorf("unsupported command type %T", cmd)
	}
}

func decodeCmd(rec persistedCmd, store ticket.Store, timeStore ticket.TimeStore) (Command, error) {
	switch rec.Type {
	case typeCreate:
		if rec.Ticket == nil {
			return nil, fmt.Errorf("create record missing ticket")
		}
		return &CreateTicket{Store: store, Ticket: *rec.Ticket, created: *rec.Ticket}, nil
	case typeDelete:
		if rec.Snapshot == nil {
			return nil, fmt.Errorf("delete record missing snapshot")
		}
		return &DeleteTicket{Store: store, Snapshot: *rec.Snapshot}, nil
	case typeUpdate:
		if rec.Before == nil || rec.After == nil {
			return nil, fmt.Errorf("update record missing before/after")
		}
		return &UpdateTicket{Store: store, Before: *rec.Before, After: *rec.After}, nil
	case typeAddTime:
		if rec.TimeEntry == nil {
			return nil, fmt.Errorf("add_time record missing entry")
		}
		if timeStore == nil {
			return nil, fmt.Errorf("add_time: time store not configured")
		}
		return &AddTimeEntry{Store: timeStore, Entry: *rec.TimeEntry, created: *rec.TimeEntry}, nil
	case typeRemoveTime:
		if rec.TimeEntry == nil {
			return nil, fmt.Errorf("remove_time record missing entry")
		}
		if timeStore == nil {
			return nil, fmt.Errorf("remove_time: time store not configured")
		}
		return &RemoveTimeEntry{Store: timeStore, Snapshot: *rec.TimeEntry}, nil
	case typeUpdateTime:
		if rec.TimeBefore == nil || rec.TimeAfter == nil {
			return nil, fmt.Errorf("update_time record missing before/after")
		}
		if timeStore == nil {
			return nil, fmt.Errorf("update_time: time store not configured")
		}
		return &UpdateTimeEntry{Store: timeStore, Before: *rec.TimeBefore, After: *rec.TimeAfter}, nil
	default:
		return nil, fmt.Errorf("unknown command type %q", rec.Type)
	}
}

func encodeStack(cmds []Command) ([]persistedCmd, error) {
	out := make([]persistedCmd, 0, len(cmds))
	for _, cmd := range cmds {
		rec, err := encodeCmd(cmd)
		if err != nil {
			return nil, err
		}
		out = append(out, rec)
	}
	return out, nil
}

func decodeStack(recs []persistedCmd, store ticket.Store, timeStore ticket.TimeStore) ([]Command, error) {
	out := make([]Command, 0, len(recs))
	for _, rec := range recs {
		cmd, err := decodeCmd(rec, store, timeStore)
		if err != nil {
			return nil, err
		}
		out = append(out, cmd)
	}
	return out, nil
}

func trimStack(cmds []Command, max int) []Command {
	if max <= 0 || len(cmds) <= max {
		return cmds
	}
	return cmds[len(cmds)-max:]
}

func (h *History) persistLocked() error {
	if h.path == "" || h.store == nil {
		return nil
	}
	undo, err := encodeStack(h.undoS)
	if err != nil {
		return err
	}
	redo, err := encodeStack(h.redoS)
	if err != nil {
		return err
	}
	data, err := json.MarshalIndent(persistedFile{Undo: undo, Redo: redo}, "", "  ")
	if err != nil {
		return fmt.Errorf("marshal history: %w", err)
	}
	data = append(data, '\n')

	if err := os.MkdirAll(filepath.Dir(h.path), 0o755); err != nil {
		return fmt.Errorf("create history dir: %w", err)
	}

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

	if _, err := tmp.Write(data); err != nil {
		_ = tmp.Close()
		return fmt.Errorf("write temp history: %w", err)
	}
	if err := tmp.Close(); err != nil {
		return fmt.Errorf("close temp history: %w", err)
	}
	if err := os.Rename(tmpName, h.path); err != nil {
		return fmt.Errorf("rename history: %w", err)
	}
	return nil
}

func loadHistoryFile(path string, store ticket.Store, timeStore ticket.TimeStore) (undo, redo []Command, err error) {
	data, err := os.ReadFile(path)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, nil, nil
		}
		return nil, nil, fmt.Errorf("read history: %w", err)
	}
	if len(data) == 0 {
		return nil, nil, nil
	}
	var file persistedFile
	if err := json.Unmarshal(data, &file); err != nil {
		return nil, nil, fmt.Errorf("parse history: %w", err)
	}
	undo, err = decodeStack(file.Undo, store, timeStore)
	if err != nil {
		return nil, nil, err
	}
	redo, err = decodeStack(file.Redo, store, timeStore)
	if err != nil {
		return nil, nil, err
	}
	return trimStack(undo, MaxHistory), trimStack(redo, MaxHistory), nil
}