package api

import (
	"encoding/json"
	"fmt"
	"net/http"
	"strconv"
	"strings"
	"unicode"

	"github.com/restxlsx/restxlsx/internal/auth"
	"github.com/restxlsx/restxlsx/internal/excel"
	"github.com/restxlsx/restxlsx/internal/logger"
)

type token struct {
	kind  tokenKind
	value string
}

type tokenKind int

const (
	tokEOF tokenKind = iota
	tokIdent
	tokString
	tokNumber
	tokStar
	tokComma
	tokLParen
	tokRParen
	tokEq
	tokSemicolon
	tokKeyword
)

type sqlStmt struct {
	kind    string // SELECT, INSERT, UPDATE, DELETE
	table   string
	columns []string
	values  []string
	sets    map[string]string
	whereCol string
	whereVal string
}

type SQLHandler struct {
	engine *excel.Engine
	log    *logger.Logger
}

func NewSQLHandler(engine *excel.Engine, log *logger.Logger) *SQLHandler {
	return &SQLHandler{engine: engine, log: log}
}

func (h *SQLHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	var body struct {
		Query string `json:"query"`
	}
	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
		writeJSON(w, 400, map[string]string{"error": "invalid JSON: " + err.Error()})
		return
	}

	stmt, err := parseSQL(body.Query)
	if err != nil {
		writeJSON(w, 400, map[string]string{"error": "parse error: " + err.Error()})
		return
	}

	role := auth.RoleFromContext(r.Context())
	switch stmt.kind {
	case "SELECT":
	case "INSERT", "UPDATE", "DELETE":
		if !role.CanWrite() {
			writeJSON(w, 403, map[string]string{"error": "forbidden: write access required"})
			return
		}
	default:
		writeJSON(w, 400, map[string]string{"error": "unsupported statement: " + stmt.kind})
		return
	}

	h.engine.Lock()
	result, err := h.execute(stmt)
	h.engine.Unlock()
	if err != nil {
		writeJSON(w, 400, map[string]string{"error": err.Error()})
		return
	}
	writeJSON(w, 200, result)
}

func (h *SQLHandler) execute(stmt sqlStmt) (any, error) {
	table := h.engine.GetTable(stmt.table)
	if table == nil {
		return nil, fmt.Errorf("table %q not found", stmt.table)
	}

	switch stmt.kind {
	case "SELECT":
		return h.executeSelect(table, stmt)
	case "INSERT":
		return h.executeInsert(table, stmt)
	case "UPDATE":
		return h.executeUpdate(table, stmt)
	case "DELETE":
		return h.executeDelete(table, stmt)
	}
	return nil, fmt.Errorf("unsupported: %s", stmt.kind)
}

func (h *SQLHandler) executeSelect(table *excel.Table, stmt sqlStmt) (any, error) {
	var results []map[string]any
	for _, row := range table.Rows {
		if stmt.whereCol != "" {
			if fmt.Sprintf("%v", row[stmt.whereCol]) != stmt.whereVal {
				continue
			}
		}
		if len(stmt.columns) == 1 && stmt.columns[0] == "*" {
			results = append(results, row)
		} else {
			projected := make(map[string]any)
			for _, col := range stmt.columns {
				if v, ok := row[col]; ok {
					projected[col] = v
				}
			}
			results = append(results, projected)
		}
	}
	if stmt.whereCol != "" && len(results) == 1 {
		return results[0], nil
	}
	if results == nil {
		return []map[string]any{}, nil
	}
	return results, nil
}

func (h *SQLHandler) executeInsert(table *excel.Table, stmt sqlStmt) (any, error) {
	if len(stmt.columns) != len(stmt.values) {
		return nil, fmt.Errorf("column count (%d) != value count (%d)", len(stmt.columns), len(stmt.values))
	}
	rec := make(map[string]any)
	for i, col := range stmt.columns {
		rec[col] = parseValue(stmt.values[i])
	}
	idCol := h.engine.IDColumn(table.Name)
	if idCol != "" {
		if _, ok := rec[idCol]; !ok {
			rec[idCol] = len(table.Rows) + 1
		}
	}
	table.Rows = append(table.Rows, rec)
	if err := h.engine.Flush(); err != nil {
		return nil, err
	}
	return rec, nil
}

func (h *SQLHandler) executeUpdate(table *excel.Table, stmt sqlStmt) (any, error) {
	var updated []map[string]any
	for i, row := range table.Rows {
		if stmt.whereCol != "" {
			if fmt.Sprintf("%v", row[stmt.whereCol]) != stmt.whereVal {
				continue
			}
		}
		for k, v := range stmt.sets {
			table.Rows[i][k] = parseValue(v)
		}
		updated = append(updated, table.Rows[i])
	}
	if err := h.engine.Flush(); err != nil {
		return nil, err
	}
	if updated == nil {
		return []map[string]any{}, nil
	}
	return updated, nil
}

func (h *SQLHandler) executeDelete(table *excel.Table, stmt sqlStmt) (any, error) {
	var deleted []map[string]any
	kept := make([]map[string]any, 0, len(table.Rows))
	for _, row := range table.Rows {
		if stmt.whereCol != "" {
			if fmt.Sprintf("%v", row[stmt.whereCol]) == stmt.whereVal {
				deleted = append(deleted, row)
				continue
			}
		} else {
			deleted = append(deleted, row)
			continue
		}
		kept = append(kept, row)
	}
	table.Rows = kept
	if err := h.engine.Flush(); err != nil {
		return nil, err
	}
	return map[string]any{"deleted": len(deleted)}, nil
}

// ─── SQL Parser ────────────────────────────────────────────────

type lexer struct {
	input string
	pos   int
}

func (l *lexer) peek() byte {
	if l.pos >= len(l.input) {
		return 0
	}
	return l.input[l.pos]
}

func (l *lexer) advance() byte {
	b := l.input[l.pos]
	l.pos++
	return b
}

func (l *lexer) skipWS() {
	for l.pos < len(l.input) && (l.input[l.pos] == ' ' || l.input[l.pos] == '\t' || l.input[l.pos] == '\n') {
		l.pos++
	}
}

var keywords = map[string]bool{
	"select": true, "from": true, "where": true,
	"insert": true, "into": true, "values": true,
	"update": true, "set": true, "delete": true,
}

func lex(input string) ([]token, error) {
	l := &lexer{input: input}
	var toks []token
	for l.pos < len(l.input) {
		l.skipWS()
		if l.pos >= len(l.input) {
			break
		}
		c := l.peek()
		switch {
		case c == ',':
			toks = append(toks, token{tokComma, ","})
			l.advance()
		case c == '(':
			toks = append(toks, token{tokLParen, "("})
			l.advance()
		case c == ')':
			toks = append(toks, token{tokRParen, ")"})
			l.advance()
		case c == ';':
			toks = append(toks, token{tokSemicolon, ";"})
			l.advance()
		case c == '=':
			toks = append(toks, token{tokEq, "="})
			l.advance()
		case c == '*':
			toks = append(toks, token{tokStar, "*"})
			l.advance()
		case c == '\'' || c == '"':
			quote := l.advance()
			var buf strings.Builder
			for l.pos < len(l.input) && l.peek() != quote {
				buf.WriteByte(l.advance())
			}
			if l.pos >= len(l.input) {
				return nil, fmt.Errorf("unterminated string literal")
			}
			l.advance()
			toks = append(toks, token{tokString, buf.String()})
		case c >= '0' && c <= '9' || c == '-':
			var buf strings.Builder
			for l.pos < len(l.input) && (l.peek() >= '0' && l.peek() <= '9' || l.peek() == '.') {
				buf.WriteByte(l.advance())
			}
			toks = append(toks, token{tokNumber, buf.String()})
		case unicode.IsLetter(rune(c)) || c == '_':
			var buf strings.Builder
			for l.pos < len(l.input) && (unicode.IsLetter(rune(l.peek())) || unicode.IsDigit(rune(l.peek())) || l.peek() == '_') {
				buf.WriteByte(l.advance())
			}
			word := buf.String()
			if keywords[strings.ToLower(word)] {
				toks = append(toks, token{tokKeyword, strings.ToUpper(word)})
			} else {
				toks = append(toks, token{tokIdent, word})
			}
		default:
			return nil, fmt.Errorf("unexpected character: %c", c)
		}
	}
	if len(toks) == 0 {
		return nil, fmt.Errorf("empty query")
	}
	toks = append(toks, token{tokEOF, ""})
	return toks, nil
}

func parseSQL(input string) (sqlStmt, error) {
	toks, err := lex(input)
	if err != nil {
		return sqlStmt{}, err
	}
	pos := 0
	next := func() token {
		if pos >= len(toks) {
			return token{tokEOF, ""}
		}
		t := toks[pos]
		pos++
		return t
	}
	peek := func() token {
		if pos >= len(toks) {
			return token{tokEOF, ""}
		}
		return toks[pos]
	}
	expect := func(kind tokenKind, msg string) (token, error) {
		t := next()
		if t.kind != kind {
			return t, fmt.Errorf("%s: expected %d got %q", msg, kind, t.value)
		}
		return t, nil
	}

	first := next()
	if first.kind != tokKeyword {
		return sqlStmt{}, fmt.Errorf("expected keyword, got %q", first.value)
	}

	switch first.value {
	case "SELECT":
		return parseSelect(&pos, toks, next, peek, expect)
	case "INSERT":
		return parseInsert(&pos, toks, next, peek, expect)
	case "UPDATE":
		return parseUpdate(&pos, toks, next, peek, expect)
	case "DELETE":
		return parseDelete(&pos, toks, next, peek, expect)
	default:
		return sqlStmt{}, fmt.Errorf("unsupported statement: %s", first.value)
	}
}

func parseSelect(pos *int, toks []token, next, peek func() token, expect func(tokenKind, string) (token, error)) (sqlStmt, error) {
	stmt := sqlStmt{kind: "SELECT"}

	if peek().kind == tokStar {
		next()
		stmt.columns = []string{"*"}
	} else {
		for {
			t, err := expect(tokIdent, "select column")
			if err != nil {
				return stmt, err
			}
			stmt.columns = append(stmt.columns, t.value)
			if peek().kind != tokComma {
				break
			}
			next()
		}
	}

	if _, err := expect(tokKeyword, "FROM"); err != nil {
		return stmt, err
	}
	t, err := expect(tokIdent, "table name")
	if err != nil {
		return stmt, err
	}
	stmt.table = t.value

	if peek().kind == tokKeyword && strings.ToUpper(peek().value) == "WHERE" {
		next()
		t, err := expect(tokIdent, "where column")
		if err != nil {
			return stmt, err
		}
		stmt.whereCol = t.value
		if _, err := expect(tokEq, "="); err != nil {
			return stmt, err
		}
		v := next()
		if v.kind != tokString && v.kind != tokNumber {
			return stmt, fmt.Errorf("expected value in WHERE, got %q", v.value)
		}
		stmt.whereVal = v.value
	}

	return stmt, nil
}

func parseInsert(pos *int, toks []token, next, peek func() token, expect func(tokenKind, string) (token, error)) (sqlStmt, error) {
	stmt := sqlStmt{kind: "INSERT"}

	if _, err := expect(tokKeyword, "INTO"); err != nil {
		return stmt, err
	}
	t, err := expect(tokIdent, "table name")
	if err != nil {
		return stmt, err
	}
	stmt.table = t.value

	if _, err := expect(tokLParen, "("); err != nil {
		return stmt, err
	}
	for {
		t, err := expect(tokIdent, "column name")
		if err != nil {
			return stmt, err
		}
		stmt.columns = append(stmt.columns, t.value)
		if peek().kind != tokComma {
			break
		}
		next()
	}
	if _, err := expect(tokRParen, ")"); err != nil {
		return stmt, err
	}

	if _, err := expect(tokKeyword, "VALUES"); err != nil {
		return stmt, err
	}
	if _, err := expect(tokLParen, "("); err != nil {
		return stmt, err
	}
	for {
		v := next()
		if v.kind != tokString && v.kind != tokNumber {
			return stmt, fmt.Errorf("expected value, got %q", v.value)
		}
		stmt.values = append(stmt.values, v.value)
		if peek().kind != tokComma {
			break
		}
		next()
	}
	if _, err := expect(tokRParen, ")"); err != nil {
		return stmt, err
	}

	return stmt, nil
}

func parseUpdate(pos *int, toks []token, next, peek func() token, expect func(tokenKind, string) (token, error)) (sqlStmt, error) {
	stmt := sqlStmt{kind: "UPDATE", sets: make(map[string]string)}

	t, err := expect(tokIdent, "table name")
	if err != nil {
		return stmt, err
	}
	stmt.table = t.value

	if _, err := expect(tokKeyword, "SET"); err != nil {
		return stmt, err
	}
	for {
		t, err := expect(tokIdent, "column name")
		if err != nil {
			return stmt, err
		}
		col := t.value
		if _, err := expect(tokEq, "="); err != nil {
			return stmt, err
		}
		v := next()
		if v.kind != tokString && v.kind != tokNumber {
			return stmt, fmt.Errorf("expected value in SET, got %q", v.value)
		}
		stmt.sets[col] = v.value
		if peek().kind != tokComma {
			break
		}
		next()
	}

	if peek().kind == tokKeyword && strings.ToUpper(peek().value) == "WHERE" {
		next()
		t, err := expect(tokIdent, "where column")
		if err != nil {
			return stmt, err
		}
		stmt.whereCol = t.value
		if _, err := expect(tokEq, "="); err != nil {
			return stmt, err
		}
		v := next()
		if v.kind != tokString && v.kind != tokNumber {
			return stmt, fmt.Errorf("expected value in WHERE, got %q", v.value)
		}
		stmt.whereVal = v.value
	}

	return stmt, nil
}

func parseDelete(pos *int, toks []token, next, peek func() token, expect func(tokenKind, string) (token, error)) (sqlStmt, error) {
	stmt := sqlStmt{kind: "DELETE"}

	if _, err := expect(tokKeyword, "FROM"); err != nil {
		return stmt, err
	}
	t, err := expect(tokIdent, "table name")
	if err != nil {
		return stmt, err
	}
	stmt.table = t.value

	if peek().kind == tokKeyword && strings.ToUpper(peek().value) == "WHERE" {
		next()
		t, err := expect(tokIdent, "where column")
		if err != nil {
			return stmt, err
		}
		stmt.whereCol = t.value
		if _, err := expect(tokEq, "="); err != nil {
			return stmt, err
		}
		v := next()
		if v.kind != tokString && v.kind != tokNumber {
			return stmt, fmt.Errorf("expected value in WHERE, got %q", v.value)
		}
		stmt.whereVal = v.value
	}

	return stmt, nil
}

func parseValue(s string) any {
	if i, err := strconv.Atoi(s); err == nil {
		return i
	}
	if f, err := strconv.ParseFloat(s, 64); err == nil {
		return f
	}
	return s
}