package cursor_test

import (
	"bytes"
	"io"
	"testing"

	"git.codemonkeysoftware.net/b/gigaparsec/cursor"
	"github.com/shoenig/test"
	"github.com/shoenig/test/must"
	"pgregory.net/rapid"
)

func Todo(t *testing.T) {
	t.Errorf("TODO")
}

func SliceOfNZero[T any](minLen, maxLen int) *rapid.Generator[[]T] {
	return rapid.Map(rapid.IntRange(minLen, maxLen), func(n int) []T {
		return make([]T, n)
	})
}

func testCursor[C cursor.Cursor[byte]](t *testing.T, makeCursor func([]byte) C) {
	t.Helper()
	t.Run("cursor reads the same position every time", rapid.MakeCheck(func(t *rapid.T) {
		data := rapid.SliceOfN(rapid.Byte(), 1, 100).Draw(t, "data")
		dst := SliceOfNZero[byte](0, len(data)-1).Draw(t, "dst")
		expected := data[:len(dst)]
		c := makeCursor(data)

		_, next, err := c.Read(dst)
		must.NoError(t, err)
		must.SliceEqOp(t, expected, dst)

		next.Read(dst)
		_, _, err = c.Read(dst)
		must.NoError(t, err)
		must.SliceEqOp(t, expected, dst)
	}))
	t.Run("Read returns io.EOF iff it overruns source", rapid.MakeCheck(func(t *rapid.T) {
		data := rapid.SliceOfN(rapid.Byte(), 0, 100).Draw(t, "data")
		dst := SliceOfNZero[byte](0, 200).Draw(t, "dst")
		c := makeCursor(data)

		n, _, err := c.Read(dst)
		t.Logf("n=%d", n)
		must.EqOp(t, min(len(data), len(dst)), int(n))
		if len(dst) > len(data) || c.Pos() == uint64(len(data)) {
			must.ErrorIs(t, err, io.EOF)
		} else {
			must.NoError(t, err)
		}
	}))
	t.Run("next cursor reads next input", rapid.MakeCheck(func(t *rapid.T) {
		const maxLen = 100
		data := rapid.SliceOfN(rapid.Byte(), 1, maxLen).Draw(t, "data")
		skip := rapid.IntRange(0, len(data)-1).Draw(t, "data")
		c := makeCursor(data)

		_, next, err := c.Read(make([]byte, skip))
		must.NoError(t, err)
		must.EqOp(t, skip, int(next.Pos()))
		dst := make([]byte, maxLen)
		n, _, _ := next.Read(dst)
		must.SliceEqOp(t, data[skip:skip+int(n)], dst[:n])
	}))
	t.Run("Read returns an error if n is less than requested", rapid.MakeCheck(func(t *rapid.T) {
		data := rapid.SliceOfN(rapid.Byte(), 0, 100).Draw(t, "data")
		c := makeCursor(data)

		n, _, err := c.Read(make([]byte, len(data)+1))
		test.ErrorIs(t, err, io.EOF)
		test.EqOp(t, len(data), int(n))
	}))
	t.Run("At", Todo)
}

func TestSliceCursor(t *testing.T) {
	testCursor(t, cursor.NewSlice[byte])
}

func TestReaderAtCursor(t *testing.T) {
	testCursor(t, func(b []byte) cursor.ReaderAtCursor {
		return cursor.NewReaderAt(bytes.NewReader(b))
	})
}