package basic

import (
	"encoding/json"
	"errors"
	"fmt"
	"math"
)

// Sentinel errors returned by the basic tools. Use errors.Is to test for them.
var (
	// ErrInvalidArgument is returned when a tool is given a missing required
	// argument or an argument of the wrong type.
	ErrInvalidArgument = errors.New("basic: invalid argument")
	// ErrUnsupported is returned when an operation is not in the tool allowlist.
	ErrUnsupported = errors.New("basic: unsupported operation")
	// ErrEvaluation is returned when a calculator expression cannot be parsed or
	// evaluated.
	ErrEvaluation = errors.New("basic: evaluation failed")
)

// asMap asserts args is a nil value or a map[string]any — the shape the
// dispatcher passes when a tool's Parameters declares an object schema.
func asMap(args any) (map[string]any, error) {
	if args == nil {
		return map[string]any{}, nil
	}
	m, ok := args.(map[string]any)
	if !ok {
		return nil, fmt.Errorf("basic: arguments must be an object: %w", ErrInvalidArgument)
	}
	return m, nil
}

// hasKey reports whether m contains key.
func hasKey(m map[string]any, key string) bool {
	_, ok := m[key]
	return ok
}

// reqString returns the string argument under key, erroring when it is absent or
// not a string.
func reqString(m map[string]any, key string) (string, error) {
	v, ok := m[key]
	if !ok {
		return "", fmt.Errorf("basic: missing required argument %q: %w", key, ErrInvalidArgument)
	}
	s, ok := v.(string)
	if !ok {
		return "", fmt.Errorf("basic: argument %q must be a string: %w", key, ErrInvalidArgument)
	}
	return s, nil
}

// optString returns the string argument under key, or def when absent. A present
// non-string is an error.
func optString(m map[string]any, key, def string) (string, error) {
	if !hasKey(m, key) {
		return def, nil
	}
	return reqString(m, key)
}

// reqInt returns the integer argument under key, erroring when it is absent, not
// a number, or not integral.
func reqInt(m map[string]any, key string) (int, error) {
	v, ok := m[key]
	if !ok {
		return 0, fmt.Errorf("basic: missing required argument %q: %w", key, ErrInvalidArgument)
	}
	n, err := asInt(v)
	if err != nil {
		return 0, fmt.Errorf("basic: argument %q: %w", key, err)
	}
	return n, nil
}

// optInt returns the integer argument under key, or def when absent.
func optInt(m map[string]any, key string, def int) (int, error) {
	if !hasKey(m, key) {
		return def, nil
	}
	return reqInt(m, key)
}

// optBool returns the boolean argument under key, or def when absent.
func optBool(m map[string]any, key string, def bool) (bool, error) {
	if !hasKey(m, key) {
		return def, nil
	}
	v, ok := m[key].(bool)
	if !ok {
		return false, fmt.Errorf("basic: argument %q must be a boolean: %w", key, ErrInvalidArgument)
	}
	return v, nil
}

// reqStringMap returns the object argument under key coerced to map[string]string,
// erroring when a value is not a string.
func reqStringMap(m map[string]any, key string) (map[string]string, error) {
	v, ok := m[key]
	if !ok {
		return nil, fmt.Errorf("basic: missing required argument %q: %w", key, ErrInvalidArgument)
	}
	raw, ok := v.(map[string]any)
	if !ok {
		return nil, fmt.Errorf("basic: argument %q must be an object: %w", key, ErrInvalidArgument)
	}
	out := make(map[string]string, len(raw))
	for k, val := range raw {
		s, ok := val.(string)
		if !ok {
			return nil, fmt.Errorf("basic: value %q must be a string: %w", k, ErrInvalidArgument)
		}
		out[k] = s
	}
	return out, nil
}

// strSliceArg returns the array-of-strings argument under key.
func strSliceArg(m map[string]any, key string) ([]string, error) {
	v, ok := m[key]
	if !ok {
		return nil, fmt.Errorf("basic: missing required argument %q: %w", key, ErrInvalidArgument)
	}
	raw, ok := v.([]any)
	if !ok {
		return nil, fmt.Errorf("basic: argument %q must be an array: %w", key, ErrInvalidArgument)
	}
	out := make([]string, len(raw))
	for i, item := range raw {
		s, ok := item.(string)
		if !ok {
			return nil, fmt.Errorf("basic: argument %q item %d must be a string: %w", key, i, ErrInvalidArgument)
		}
		out[i] = s
	}
	return out, nil
}

// strSliceSliceArg returns the array-of-arrays-of-strings argument under key.
func strSliceSliceArg(m map[string]any, key string) ([][]string, error) {
	v, ok := m[key]
	if !ok {
		return nil, fmt.Errorf("basic: missing required argument %q: %w", key, ErrInvalidArgument)
	}
	raw, ok := v.([]any)
	if !ok {
		return nil, fmt.Errorf("basic: argument %q must be an array: %w", key, ErrInvalidArgument)
	}
	out := make([][]string, len(raw))
	for i, item := range raw {
		row, ok := item.([]any)
		if !ok {
			return nil, fmt.Errorf("basic: argument %q item %d must be an array: %w", key, i, ErrInvalidArgument)
		}
		cells := make([]string, len(row))
		for j, c := range row {
			s, ok := c.(string)
			if !ok {
				return nil, fmt.Errorf("basic: argument %q item %d cell %d must be a string: %w", key, i, j, ErrInvalidArgument)
			}
			cells[j] = s
		}
		out[i] = cells
	}
	return out, nil
}

// asInt converts a numeric-typed value (the types the dispatcher decodes JSON
// into) to an int, rejecting non-integral floats.
func asInt(v any) (int, error) {
	switch x := v.(type) {
	case int:
		return x, nil
	case int64:
		return int(x), nil
	case float64:
		if x != math.Trunc(x) || x < math.MinInt64 || x > math.MaxInt64 {
			return 0, fmt.Errorf("must be an integer: %w", ErrInvalidArgument)
		}
		return int(x), nil
	case json.Number:
		n, err := x.Int64()
		if err != nil {
			return 0, fmt.Errorf("must be an integer: %w", ErrInvalidArgument)
		}
		return int(n), nil
	default:
		return 0, fmt.Errorf("must be a number: %w", ErrInvalidArgument)
	}
}