package sinks

import (
	"context"
	"fmt"
	"strings"
	"time"

	"gitea.maximumdirect.net/ejr/feedkit/event"
)

// PostgresMapFunc maps one event into zero or more table writes.
//
// Returning zero writes means "this event is not mapped for this sink" and is
// treated as a non-error no-op.
type PostgresMapFunc func(ctx context.Context, e event.Event) ([]PostgresWrite, error)

// PostgresSchema describes the downstream-provided relational model and mapper
// for one configured postgres sink.
type PostgresSchema struct {
	Tables   []PostgresTable
	MapEvent PostgresMapFunc
}

type PostgresWrite struct {
	Table  string
	Values map[string]any
}

type PostgresTable struct {
	Name        string
	Columns     []PostgresColumn
	PrimaryKey  []string
	PruneColumn string
	Indexes     []PostgresIndex
}

type PostgresColumn struct {
	Name     string
	Type     string
	Nullable bool
}

type PostgresIndex struct {
	Name    string
	Columns []string
	Unique  bool
}

// PostgresPruner is an optional interface exposed by PostgresSink so downstream
// applications can call retention helpers via type assertion.
type PostgresPruner interface {
	PruneKeepLatest(ctx context.Context, table string, keep int) (int64, error)
	PruneOlderThan(ctx context.Context, table string, cutoff time.Time) (int64, error)
	PruneAllKeepLatest(ctx context.Context, keep int) (map[string]int64, error)
	PruneAllOlderThan(ctx context.Context, cutoff time.Time) (map[string]int64, error)
}

type postgresSchemaCompiled struct {
	tableOrder []string
	tables     map[string]postgresTableCompiled
	mapEvent   PostgresMapFunc
}

type postgresTableCompiled struct {
	name        string
	columns     map[string]PostgresColumn
	columnOrder []string
	primaryKey  []string
	pruneColumn string
	indexes     []PostgresIndex
}

func compilePostgresSchema(schema PostgresSchema) (postgresSchemaCompiled, error) {
	if schema.MapEvent == nil {
		return postgresSchemaCompiled{}, fmt.Errorf("postgres schema: map function is required")
	}
	if len(schema.Tables) == 0 {
		return postgresSchemaCompiled{}, fmt.Errorf("postgres schema: at least one table is required")
	}

	compiled := postgresSchemaCompiled{
		tableOrder: make([]string, 0, len(schema.Tables)),
		tables:     make(map[string]postgresTableCompiled, len(schema.Tables)),
		mapEvent:   schema.MapEvent,
	}

	seenTables := map[string]bool{}
	seenIndexes := map[string]bool{}

	for i, tbl := range schema.Tables {
		tableName := strings.TrimSpace(tbl.Name)
		if tableName == "" {
			return postgresSchemaCompiled{}, fmt.Errorf("postgres schema: tables[%d].name is required", i)
		}
		if seenTables[tableName] {
			return postgresSchemaCompiled{}, fmt.Errorf("postgres schema: duplicate table name %q", tableName)
		}
		seenTables[tableName] = true

		if len(tbl.Columns) == 0 {
			return postgresSchemaCompiled{}, fmt.Errorf("postgres schema: table %q must define at least one column", tableName)
		}

		colOrder := make([]string, 0, len(tbl.Columns))
		colMap := make(map[string]PostgresColumn, len(tbl.Columns))
		for j, col := range tbl.Columns {
			colName := strings.TrimSpace(col.Name)
			if colName == "" {
				return postgresSchemaCompiled{}, fmt.Errorf("postgres schema: table %q columns[%d].name is required", tableName, j)
			}
			if _, exists := colMap[colName]; exists {
				return postgresSchemaCompiled{}, fmt.Errorf("postgres schema: table %q duplicate column %q", tableName, colName)
			}
			if strings.TrimSpace(col.Type) == "" {
				return postgresSchemaCompiled{}, fmt.Errorf("postgres schema: table %q column %q type is required", tableName, colName)
			}
			colOrder = append(colOrder, colName)
			colMap[colName] = PostgresColumn{
				Name:     colName,
				Type:     strings.TrimSpace(col.Type),
				Nullable: col.Nullable,
			}
		}

		pk, err := validatePostgresColumnSet(tableName, "primary key", tbl.PrimaryKey, colMap)
		if err != nil {
			return postgresSchemaCompiled{}, err
		}

		pruneCol := strings.TrimSpace(tbl.PruneColumn)
		if pruneCol == "" {
			return postgresSchemaCompiled{}, fmt.Errorf("postgres schema: table %q prune column is required", tableName)
		}
		if _, ok := colMap[pruneCol]; !ok {
			return postgresSchemaCompiled{}, fmt.Errorf("postgres schema: table %q prune column %q not found in columns", tableName, pruneCol)
		}

		indexes := make([]PostgresIndex, 0, len(tbl.Indexes))
		for j, idx := range tbl.Indexes {
			idxName := strings.TrimSpace(idx.Name)
			if idxName == "" {
				return postgresSchemaCompiled{}, fmt.Errorf("postgres schema: table %q indexes[%d].name is required", tableName, j)
			}
			if len(idx.Columns) == 0 {
				return postgresSchemaCompiled{}, fmt.Errorf("postgres schema: table %q index %q must include at least one column", tableName, idxName)
			}
			if seenIndexes[idxName] {
				return postgresSchemaCompiled{}, fmt.Errorf("postgres schema: duplicate index name %q", idxName)
			}
			seenIndexes[idxName] = true

			idxCols, err := validatePostgresColumnSet(tableName, fmt.Sprintf("index %q columns", idxName), idx.Columns, colMap)
			if err != nil {
				return postgresSchemaCompiled{}, err
			}

			indexes = append(indexes, PostgresIndex{
				Name:    idxName,
				Columns: idxCols,
				Unique:  idx.Unique,
			})
		}

		compiled.tableOrder = append(compiled.tableOrder, tableName)
		compiled.tables[tableName] = postgresTableCompiled{
			name:        tableName,
			columns:     colMap,
			columnOrder: colOrder,
			primaryKey:  pk,
			pruneColumn: pruneCol,
			indexes:     indexes,
		}
	}

	return compiled, nil
}

func validatePostgresColumnSet(tableName, label string, cols []string, colMap map[string]PostgresColumn) ([]string, error) {
	if len(cols) == 0 {
		return nil, nil
	}
	out := make([]string, 0, len(cols))
	seen := map[string]bool{}
	for _, c := range cols {
		name := strings.TrimSpace(c)
		if name == "" {
			return nil, fmt.Errorf("postgres schema: table %q %s contains empty column name", tableName, label)
		}
		if seen[name] {
			return nil, fmt.Errorf("postgres schema: table %q %s contains duplicate column %q", tableName, label, name)
		}
		if _, ok := colMap[name]; !ok {
			return nil, fmt.Errorf("postgres schema: table %q %s references unknown column %q", tableName, label, name)
		}
		seen[name] = true
		out = append(out, name)
	}
	return out, nil
}

func (s postgresSchemaCompiled) validateWrite(w PostgresWrite) (postgresTableCompiled, error) {
	tableName := strings.TrimSpace(w.Table)
	if tableName == "" {
		return postgresTableCompiled{}, fmt.Errorf("write table is required")
	}
	t, ok := s.tables[tableName]
	if !ok {
		return postgresTableCompiled{}, fmt.Errorf("table %q is not defined in postgres schema", tableName)
	}

	if len(w.Values) == 0 {
		return postgresTableCompiled{}, fmt.Errorf("write for table %q must include values", tableName)
	}

	for k := range w.Values {
		if _, ok := t.columns[k]; !ok {
			return postgresTableCompiled{}, fmt.Errorf("write for table %q includes unknown column %q", tableName, k)
		}
	}

	if len(w.Values) != len(t.columnOrder) {
		return postgresTableCompiled{}, fmt.Errorf("write for table %q must include all declared columns", tableName)
	}

	for _, col := range t.columnOrder {
		v, ok := w.Values[col]
		if !ok {
			return postgresTableCompiled{}, fmt.Errorf("write for table %q is missing column %q", tableName, col)
		}
		if v == nil {
			if c := t.columns[col]; !c.Nullable {
				return postgresTableCompiled{}, fmt.Errorf("write for table %q has nil value for non-null column %q", tableName, col)
			}
		}
	}

	return t, nil
}