package database

import (
	"fmt"
	"strings"
	"time"

	"github.com/google/uuid"
)

// ── SQL Dialect Adapter ─────────────────────
//
// Q adapts Postgres-flavoured SQL to the current dialect.
// On Postgres it is a no-op. On SQLite it rewrites:
//   - $1, $2 … $20  →  ?
//   - ::jsonb, ::text  →  removed
//   - NOW()  →  datetime('now')
//   - true / false  →  1 / 0  (bare keywords only, not inside strings)
//   - NULLS LAST  →  removed (SQLite default)
//   - COALESCE(x::text, …)  →  COALESCE(x, …)
//
// Call it at every database.DB.Query / Exec / QueryRow site in handlers.
func Q(query string) string {
	if !IsSQLite() {
		return query
	}
	q := query

	// Replace $N placeholders high-to-low to avoid $1 matching inside $10.
	for i := 20; i >= 1; i-- {
		q = strings.ReplaceAll(q, fmt.Sprintf("$%d", i), "?")
	}

	// Postgres type casts
	q = strings.ReplaceAll(q, "::jsonb", "")
	q = strings.ReplaceAll(q, "::text", "")

	// Time functions
	q = strings.ReplaceAll(q, "NOW()", "datetime('now')")

	// Boolean literals (bare keywords, not inside quotes)
	q = strings.ReplaceAll(q, "= true", "= 1")
	q = strings.ReplaceAll(q, "= false", "= 0")
	q = strings.ReplaceAll(q, "COALESCE(is_private, false)", "COALESCE(is_private, 0)")

	// NULL sort order (SQLite puts NULLs last by default for DESC)
	q = strings.ReplaceAll(q, "NULLS LAST", "")

	// Case-insensitive LIKE (SQLite LIKE is already case-insensitive for ASCII)
	q = strings.ReplaceAll(q, "ILIKE", "LIKE")

	return q
}

// InsertReturningID executes an INSERT … RETURNING id query.
// On Postgres it uses RETURNING directly.
// On SQLite it strips RETURNING, generates a UUID, prepends it to the args,
// adds an "id" column to the INSERT, and executes.
func InsertReturningID(query string, args ...interface{}) (string, error) {
	if !IsSQLite() {
		var id string
		err := DB.QueryRow(query, args...).Scan(&id)
		return id, err
	}

	// Generate ID for SQLite
	id := uuid.New().String()

	// Adapt SQL: strip RETURNING, convert placeholders, add id column+value
	q := Q(query)

	// Remove RETURNING clause
	if idx := strings.Index(strings.ToUpper(q), "RETURNING"); idx >= 0 {
		q = strings.TrimSpace(q[:idx])
	}

	// Inject id column and value into INSERT
	// Pattern: INSERT INTO table (col1, col2, ...) VALUES (?, ?, ...)
	q = injectIDColumn(q)

	// Prepend id to args
	newArgs := make([]interface{}, 0, len(args)+1)
	newArgs = append(newArgs, id)
	newArgs = append(newArgs, args...)

	_, err := DB.Exec(q, newArgs...)
	return id, err
}

// InjectIDForTest adds "id" as the first column and "?" as the first value
// in an INSERT statement. Exported for use in test helpers.
func InjectIDForTest(q string) string {
	return injectIDColumn(q)
}

// injectIDColumn adds "id" as the first column and "?" as the first value
// in an INSERT statement.
func injectIDColumn(q string) string {
	// Find the opening paren of the column list
	upper := strings.ToUpper(q)
	insertIdx := strings.Index(upper, "INSERT INTO")
	if insertIdx < 0 {
		return q
	}

	// Find first ( after INSERT INTO tablename
	firstParen := strings.Index(q[insertIdx:], "(")
	if firstParen < 0 {
		return q
	}
	firstParen += insertIdx

	// Find VALUES (
	valuesIdx := strings.Index(upper, "VALUES")
	if valuesIdx < 0 {
		return q
	}
	valuesParen := strings.Index(q[valuesIdx:], "(")
	if valuesParen < 0 {
		return q
	}
	valuesParen += valuesIdx

	// Insert "id, " after first ( and "?, " after VALUES (
	result := q[:firstParen+1] + "id, " + q[firstParen+1:valuesParen+1] + "?, " + q[valuesParen+1:]
	return result
}

// ── Time Scan Helpers ───────────────────────
//
// SQLite returns timestamps as TEXT strings. These helpers wrap *time.Time
// and sql.NullTime destinations so Scan() works on both dialects.

// ScanTime wraps a *time.Time for use in handler-level Scan() calls.
// On Postgres, time.Time scans natively. On SQLite, parses from string.
type ScanTime struct{ T *time.Time }

func (s *ScanTime) Scan(src interface{}) error {
	if src == nil {
		return nil
	}
	switch v := src.(type) {
	case time.Time:
		*s.T = v
		return nil
	case string:
		for _, f := range compatTimeFormats {
			if p, err := time.Parse(f, v); err == nil {
				*s.T = p
				return nil
			}
		}
		return fmt.Errorf("ScanTime: cannot parse %q", v)
	default:
		return fmt.Errorf("ScanTime: unsupported type %T", src)
	}
}

// ST creates a ScanTime wrapper for use in Scan() argument lists.
func ST(t *time.Time) *ScanTime { return &ScanTime{T: t} }

// ScanNullTime wraps a nullable time destination.
type ScanNullTime struct{ T **time.Time }

func (s *ScanNullTime) Scan(src interface{}) error {
	if src == nil {
		*s.T = nil
		return nil
	}
	var parsed time.Time
	scanner := ST(&parsed)
	if err := scanner.Scan(src); err != nil {
		return err
	}
	*s.T = &parsed
	return nil
}

// SNT creates a ScanNullTime wrapper for use in Scan() argument lists.
func SNT(t **time.Time) *ScanNullTime { return &ScanNullTime{T: t} }

// NullTimeValue extracts a time.Time from sql.NullTime or *time.Time,
// returning the zero value if nil/invalid. Useful in JSON serialization.
func NullTimeValue(t *time.Time) time.Time {
	if t == nil {
		return time.Time{}
	}
	return *t
}

var compatTimeFormats = []string{
	"2006-01-02 15:04:05",
	"2006-01-02T15:04:05Z",
	time.RFC3339,
	"2006-01-02 15:04:05.000000000+00:00",
}

// ── Unique Constraint Detection ─────────────

// IsUniqueViolation checks if an error is a unique constraint violation,
// working on both Postgres and SQLite.
func IsUniqueViolation(err error) bool {
	if err == nil {
		return false
	}
	msg := err.Error()
	return strings.Contains(msg, "duplicate key") || // Postgres
		strings.Contains(msg, "UNIQUE constraint failed") // SQLite
}