package mysql

import (
	"context"
	"database/sql"
	"fmt"
	"io"
	"os"
	"sort"
	"strings"

	_ "github.com/go-sql-driver/mysql"

	"git.warky.dev/wdevs/relspecgo/pkg/mariadb"
	"git.warky.dev/wdevs/relspecgo/pkg/models"
	"git.warky.dev/wdevs/relspecgo/pkg/writers"
)

type Writer struct {
	options *writers.WriterOptions
	writer  io.Writer
}

func NewWriter(options *writers.WriterOptions) *Writer { return &Writer{options: options} }
func (w *Writer) WriteDatabase(db *models.Database) error {
	if w.options == nil {
		return fmt.Errorf("writer options are required")
	}
	if conn, ok := w.options.Metadata["connection_string"].(string); ok && conn != "" {
		return w.execute(db, conn)
	}
	release, err := w.openOutput()
	if err != nil {
		return err
	}
	defer release()
	return w.writeDatabaseDDL(db)
}

func (w *Writer) writeDatabaseDDL(db *models.Database) error {
	if _, err := fmt.Fprintf(w.writer, "-- MySQL Database Schema\n-- Database: %s\n-- Generated by RelSpec\n\n", db.Name); err != nil {
		return err
	}
	for _, s := range db.Schemas {
		if err := w.WriteSchema(s); err != nil {
			return err
		}
	}
	return nil
}

// openOutput points w.writer at the configured destination (output file or
// stdout) when none is set, and returns a func that releases it again.
func (w *Writer) openOutput() (func(), error) {
	if w.writer != nil {
		return func() {}, nil
	}
	if w.options != nil && w.options.OutputPath != "" {
		f, err := os.Create(w.options.OutputPath)
		if err != nil {
			return nil, err
		}
		w.writer = f
		return func() {
			f.Close()
			w.writer = nil
		}, nil
	}
	w.writer = os.Stdout
	return func() { w.writer = nil }, nil
}

func (w *Writer) WriteSchema(s *models.Schema) error {
	release, err := w.openOutput()
	if err != nil {
		return err
	}
	defer release()
	for _, t := range s.Tables {
		if err := w.writeTable(s, t); err != nil {
			return err
		}
	}
	return nil
}

func (w *Writer) WriteTable(t *models.Table) error {
	release, err := w.openOutput()
	if err != nil {
		return err
	}
	defer release()
	return w.writeTable(nil, t)
}

func (w *Writer) writeTable(s *models.Schema, t *models.Table) error {
	name := t.Name
	if s != nil {
		name = fmt.Sprintf("%s.%s", quote(s.Name), quote(t.Name))
	} else {
		name = quote(name)
	}
	cols := make([]*models.Column, 0, len(t.Columns))
	for _, c := range t.Columns {
		cols = append(cols, c)
	}
	sort.Slice(cols, func(i, j int) bool {
		if cols[i].Sequence != cols[j].Sequence {
			return cols[i].Sequence < cols[j].Sequence
		}
		return cols[i].Name < cols[j].Name
	})
	defs := []string{}
	pk := []string{}
	for _, c := range cols {
		d := fmt.Sprintf("  %s %s", quote(c.Name), mariadb.ConvertCanonicalToMariaDB(c.Type))
		if c.Length > 0 && strings.EqualFold(c.Type, "string") {
			d = fmt.Sprintf("  %s VARCHAR(%d)", quote(c.Name), c.Length)
		}
		if c.NotNull {
			d += " NOT NULL"
		}
		if c.AutoIncrement {
			d += " AUTO_INCREMENT"
		}
		if c.Default != nil {
			d += fmt.Sprintf(" DEFAULT %s", writers.QuoteDefaultValue(fmt.Sprint(c.Default), c.Type))
		}
		defs = append(defs, d)
		if c.IsPrimaryKey {
			pk = append(pk, quote(c.Name))
		}
	}
	constraintNames := make([]string, 0, len(t.Constraints))
	for name := range t.Constraints {
		constraintNames = append(constraintNames, name)
	}
	sort.Strings(constraintNames)
	for _, name := range constraintNames {
		c := t.Constraints[name]
		if c.Type == models.PrimaryKeyConstraint {
			pk = nil
			for _, n := range c.Columns {
				pk = append(pk, quote(n))
			}
			break
		}
	}
	if len(pk) > 0 {
		defs = append(defs, "  PRIMARY KEY ("+strings.Join(pk, ", ")+")")
	}
	for _, name := range constraintNames {
		c := t.Constraints[name]
		if c.Type == models.UniqueConstraint {
			defs = append(defs, fmt.Sprintf("  CONSTRAINT %s UNIQUE (%s)", quote(c.Name), quoted(c.Columns)))
		}
	}
	sql := fmt.Sprintf("CREATE TABLE IF NOT EXISTS %s (\n%s\n) ENGINE=InnoDB;\n\n", name, strings.Join(defs, ",\n"))
	if _, err := io.WriteString(w.writer, sql); err != nil {
		return err
	}
	return nil
}

func (w *Writer) execute(dbm *models.Database, conn string) error {
	var b strings.Builder
	old := w.writer
	w.writer = &b
	if err := w.writeDatabaseDDL(dbm); err != nil {
		w.writer = old
		return err
	}
	w.writer = old
	db, err := sql.Open("mysql", conn)
	if err != nil {
		return fmt.Errorf("failed to connect: %w", err)
	}
	defer db.Close()
	for _, stmt := range strings.Split(b.String(), ";\n") {
		stmt = stripComments(strings.TrimSpace(stmt))
		if stmt == "" {
			continue
		}
		if _, err := db.ExecContext(context.Background(), stmt); err != nil {
			return fmt.Errorf("failed to execute SQL: %w", err)
		}
	}
	return nil
}

func stripComments(sqlText string) string {
	lines := strings.Split(sqlText, "\n")
	kept := lines[:0]
	for _, line := range lines {
		if !strings.HasPrefix(strings.TrimSpace(line), "--") {
			kept = append(kept, line)
		}
	}
	return strings.TrimSpace(strings.Join(kept, "\n"))
}

func quote(s string) string { return "`" + strings.ReplaceAll(s, "`", "``") + "`" }
func quoted(xs []string) string {
	out := make([]string, len(xs))
	for i, x := range xs {
		out[i] = quote(x)
	}
	return strings.Join(out, ", ")
}